NATL INST. OF STAND & TECH

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NBS SPECIAL PUBLICATION 640

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

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Innovation for

Maintenance

Technology

Improvements

MFPG

33rd Meeting
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

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the Institute for Computer Sciences and Technology.

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'Headquarters and Laboratories at Gaithersburg, M D, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
NATlOIfAI. BUREAU pr STANDARDS. UBHARY

MFPG 9EC 1 1li^2

Innovation for Maintenance

Technology Improvements

Mechanical Failures Prevention Group,

held at the National Bureau of Standards,

Gaithersburg, MD, April 21-23, 1981

Edited by:

T. Robert Shives

William A. Willard

Center for Materials Science

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

These proceedings were sponsored jointly by NBS and the:

Naval Air Systenns Connmand

U.S. Department of the Navy

Washington, DC 20360

Office of Naval Research

U.S. Department of the Navy

Arlington, VA 22217

National Aeronautics and Space Administration

Goddard Space Flight Center

Greenbelt, MD 20771

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1982
Library of Congress Catalog Card Number: 82-600598

National Bureau of Standards Special Publication 640

Nat. Bur. Stand. (U.S.), Spec. Publ. 640, 518 pages (Oct. 1982)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1982

For Sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Price $11 00 (Add 25 percent for other than U.S. mailing.)

/
FOREWORD

The 33rd meeting of the Mechanical Failures Prevention Group was held

April 21-23, 1981, at the National Bureau of Standards in Gai thersburg,

Maryland. The symposium was under the general coordination of the MFPG

Technical Committee on flaterials Durability Evaluation with A. Ruff

of the National Bureau of Standards as Chairman. The program was organized under the chairmanship of A. J. Koury of the Naval Air Systems

Command with technical support from M. J. Devine of General Technology,

D. V. Minuti of the Naval Air Development Center, and M. B. Peterson

of Wear Sciences, Inc. Publicity was handled by M. J. Devine.

The organizers, the session chairmen, and especially the speakers, are

to be commended for an excellent program.

Appreciation is expressed to William A. Willard, formerly of the National Bureau of Standards Fracture and Deformation Division and currently

with the Naval Surface Weapons Center, for his assistance in editing,

organizing and preparing these proceedings. Where possible, the papers

in the proceedings are presented as submitted by the authors as camera

ready copy. Some editorial changes and retyping were required.

Gratitude is expressed to Marian L. Slusser of the NBS Center for

Materials Science for handling financial matters, to Annette Shives

for typing, and to Jo Ann Lorden and Greta Pignone of the NBS Public

Information Division for the meeting and hotel arrangements.

This proceedings is the first MFPG publication to go to press since NBS

assumed the role as major MFPG sponsor in 1972 without the guidance of

Harry C. Burnett. Mr. Burnett, former executive secretary and long

time supporter of MFPG activities, died in September of 1981. He is

missed by his many friends in MFPG and at NBS. His enthusiasm and

genteel manner were an inspiration to all of us.

T. ROBERT SHIVES

Executive Secretary, MFPG

Center for Materials Science

National Bureau of Standards

III
TABLE OF CONTENTS

Page

FOREWORD III

SESSION I: MAINTENANCE TECHNOLOGY AND MAINTENANCE CONCEPTS

1. Maintenance Technology Concept. A. J. Koury 3

2. Innovation for Maintenance Technology Improvements. 17

Harry Rolka

3. An Overview of Maintenance Information Systems 27

Functions. Victor S. Middlebrook and George

D. S. Andrews

4. Failure Mechanism and Cause Analysis of Structures: 45

A Paradigm for the Analysis of Failures or Potential

Failures. L. E. Sloter, W. R. Shawver and

D. J. White

5. Mechanical Systems Integrity Management. 61

Robert L. Kincaid and William S. Kincaid

5. Field Monitoring of NC-Machines - A System Approach. 71 K-E. Johansson

7. A Maintenance Plan for A Batch Chemical Plant. 86

G. N. D. Seddon and A. Kelly

SESSION II: TECHNOLOGY IMPROVEMENTS FOR POWER PLANT APPLICATIONS

1. Improved Engine Maintenance through Automated 115

Vibration Diagnostic Systems. Richard A. Rio

2. Innovations in Epicyclic Gear System Design for 130

Increased Service Life. D. E. Pauze

3. Effect of Antimony Thioantimonate in Greases on 150

Abrasive Wear. J. P. King, Yayesh Asmerom, and

M. J. Devine

4. Silicone Brake Fluid: The Answer to Reduced 162

Maintenance and Longer Lifel G. W. Holbrook

IV
5. The Requirement of Lubrication Systems in 170

Maintenance Programs and New Developments to

Enable More Precise Control. C. Trainer and

D. R. Rokos

6. Conceptual Proposal for Self-Lubricating High 187

Carbon Piston Ring Steel. Philip 0. Badger

7. Thermal Deposition Systems for Improved 194

Maintenance. Vincent J. Lanza

SESSION III: MAINTENANCE ANALYSIS SYSTEMS

1. Simulation of Track Maintenance Costs. 199

Richard L. Smith and Allan I. Krauter

2. Automatic Test System for Reliability Assessment 216

of Guided Missile Re-Entry Vehicles. Walter D. Downing, Jr., John P. Pruett and Bryan D. Winn

3. Reduction of Test Equipment Proliferation with 222

Third Generation ATE. S. Perra (Abstract only)

4. The Development of Automated Test Procedures for 223

Complex Electro-Mechanical Systems. R. E. Hartwell

5. Advanced Attack Helicopter AH-64 Fault Detection/ 235

Location System. H. E. Pohlenz

SESSION IV: IMPROVED MAINTENANCE PROCESSES

1. Service Life of Bearings Can Be Increased with 257

"Proper Maintenance". R. A. Guyer

2. The Application of Nylon Powder Coating to 275

Vehicular Components. H. T. Lootens

3. Alternative Antistatic Packaging Materials for 290

Precision Bearings. Marianne K. Bernett and

Harold Ravner

4. A Thermal Prediction Technique for Extending 295

In-Service Life of Roller Bearing Assemblies.

B. R. Reason and V. A. Schwarz

5. The Influence of Filtration on Rolling Element 326

Bearing Life. R. Bhachu, R. Sayles and

P. B. Macpherson

V
6. Improved Instrument Bearing Lubrication. 348

N. Rebuck and L. Stallings

7. Advanced Structures Maintenance Technology. 364

Nikolaos Caravasos

8. Design Guidelines for Avionic Corrosion Prevention 379

and Control. Albert F. Carrato, George E. DeLong

and Irv S. Shaffer

9. Use & Experience of Advance Composites Reinforced 400

with Kevlar in Aircraft. Paul R. Langston

SESSION V: INNOVATIVE MAINTENANCE DIAGNOSTICS AND

MAINTENANCE INDICATORS

1. The Role of Neutron Radiography in a Maintenance 417

Environment. Joseph John

2. CREGTM Eddy Current NDE: A Cost Effective Approach 454

to Failure Prevention. S. Sarian (Abstract only)

3. Design and Development of a Colorimetric Field Test 455

Kit for Iron Wear Metal Determination. W. J. Hillan

W. D. Ross and K. L. Eisentraut

»

4. Ferrography Standardization. Peter B. Senholzi 466

5. A Continuous Corrosive Monitoring Device for the 476

Marine Environments. V. Agarwala

6. Improving Maintenance Manpower Utilization. 495

Warren W. Lee

APPENDIX

List of Registrants for the 33rd MFPG Meeting 507

MFPG Publications 514

VI
ABSTRACT

These proceedings consist of a group of 34 submitted entries (32 papers

and 2 abstracts) from the 33rd meeting of the Mechanical Failures

Prevention Group which was held at the National Bureau of Standards,

Gaithersburg, Maryland, April 21-23, 1981. The subject of the symposium

was maintenance technology improvement through innovation. Areas of

special emphasis included maintenance concepts, maintenance analysis

systems, improved maintenance processes, innovative maintenance

diagnostics and maintenance indicators, and technology improvements

for power plant applications.

Key words: fault detection/location system; lubrication; maintenance;

maintenance management; maintenance technology; manpower utilization;

reliability assessment.

UNITS ANO SYMBOLS

Customary U. S. units and symbols appear in some of the papers in these

proceedings. The participants in the 33rd meeting of the Mechanical

Failures Prevention Group have used the established units and symbols

commonly employed in their professional fields. However, as an aid

to the reader in increasing familiarity with the usage of the metric

system of units (SI), the following references are given:

NBS Special Publication, SP330, 1981 Edition, "The International System

of Units."

ISO International Standard 1000 (1973 Edition), "SI Units and Recommendations for Use of Their Multiples."

IEEE Standard Metric Practice (Institute of Electrical and Electronics

Engineers, Inc., Standard 268-1979).

Disci aimer:

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are neces- saily the best available for the purpose. Views expressed by the

various authors are their own and do not necessarily represent those

of the National Bureau of Standards.

VII

Ij

' SESSION I

MAINTENANCE TECHNOLOGY AND

MAINTENANCE CONCEPTS

chairman: a. w. ruff

national bureau of standards

MAINTENANCE TECHNOLOGY CONCEPT

A. J. Koury

Naval Air Systems Command

Washington, D. C. 20361

An examination of the scale of mechanical and structural failure

can be readily estimated from the list of very recent equipment

malfunctions receiving national attention shown on Figure 1. The first concerns a nuclear-power plant closed due to reactor and cooling system

failure during October 1980. Not including equipment replacement cost,

an expenditure of $800,000/day was incurred for a period exceeding

ninety days! The second covers a major recall in automobile history

due to the failure of two bolts over 6 million autos are involved!

Consider several additional failures representing national concern (A)

Flow control equipment identified as cause of failure at Three Mile

Island Nuclear Power Plant — estimated cost $1 billion (B) Improper

valve component installation resulting in the total loss of a chemical

processing plant in Newark, Delaware (C) Motor failure in a steel mill

finishing plant — in this instance a rapid repair costing $400,000 —

avoided a loss estimated at 30 million dollars. (D) Steel Reinforcing

rods in concrete and bridge systems have been severely damaged from

salt used to prevent highway icing, cost estimates for failures

represents millions of dollars expended.

Every major industry, utility and government service involved with

equipment operation has described failures of major cost and

consequences. These failures also have a direct and significant impact

on productivity.

Improvement in failure avoidance and problem solution is a mandatory

national requirement. Innovative approaches based on technology

clearly focused on safety, durability, reliability and operating

economy, of a wide range of machinery and equipment can yield effective

solutions

.

Mechanical and structural failure prevention is critically

dependent on a number of important disciplines listed in Figure 2.

Requirements include 1) identification and assessment of the failure

process, such processes include wear, corrosion, fatigue and fracture

representing the more common modes, 2) the operational environment such

as vibration, shock, humidity, temperature, salt, sand and

contamination can accelerate severe damage, 3) materials and material

processing including composition, heat treatment, surface coatings and

surface finishing can be key determinants of service life, 4) assembly,

transport and preservation involves training, manuals and publications,

handling equipment, and protective materials required for effectiveness,

5) human performance covering knowledge, skill , experience and motivation

3
are vital elements.

Prior to describing the "Maintenance Technology Concept" and the

factors involved with successfully linking research and development

with failure prevention, a review of current programs for conducting

equipment and plant maintenance will be reviewed.

PREVENTIVE MAINTENANCE

In the early days of industrial development and through much of its

history, there has been primarily one approach to maintenance;

Preventive Maintenance. There are still many adherents today with

obvious justification. It only costs $4 to grease a bearing but $400

to replace it. While the bearing is being replaced several million

dollars of production may be lost. In preventive maintenance those

actions are taken which are necessary to forestall equipment

deterioration. Where preventive maintenance is practiced, technology

efforts have been mainly directed to improving two areas: management

techniques and for improved tools and equipment which shorten the

maintenance task times.

Maintenance management has gone from a random scheduling of tasks

to a highly organized, minutely scheduled work system with accurate

cost accounting and accountability. Computer systems analyse the work

load and organize it efficently. CRT terminals have replaced

maintenance manuals and provide rapid information acquisition. Some of

the maintenance tasks taken over by computers are listed in Figure 3.

Another important development in preventive maintenance is

simplified inspection and repair. "In situ" repairs are listed in

Figure 4. These include leaks, under-water repair techniques,

rebuilding of worn surfaces, repair of FOD damage to turbine blades,

repair of composite structures, restoring surfaces which have been

damaged by corrosion or erosion, crack repair, and machinery

alignment. Analysis has shown that one of the most costly elements of

the maintenance process is not the repair but the disassembly, removal

and reassembly. Thus, the development of components such as bearings

and seals which can be removed without extensive disassembly are particularly valuable.

The realization that many inspections are invalid and frequently

unnecessary and often redundant, has led many organizations to abandon

preventive maintenance as too costly. Secondly, it has been realized

that maintenance actions often are the causes for systems to

malfunction; that is, errors are committed during maintenance. Thus,

other alternatives were investigated.

ON CONDITION MAINTENANCE

In "on condition" maintenance, actions are taken when inspections

4
or the operating characteristics of the equipment indicate that

maintenance is required. Many of us use this approach to automobile

maintenance. The literature reports successful use in a wide range of

applications such as aircraft, appliances, and plant equipment.

Once success was achieved with certain applications, there was the

natural inclination to expand the concept to other more critical ones.

For critical applications it was necessary to get an early, positive

indication of failure so that maintenance could be accomplished before

failure actually occurred. This led to the concept of condition

monitoring in which instruments and warning devices replaced the eyes

and ears of maintenance and operating personnel. This more sophisticated approach to "on condition" maintenance is described in

the following section.

CONDITION MONITORING

During the past 10 years a vast amount of work has been undertaken

to develop and improve condition monitoring capabilities. The main

thrust of the work has been to develop sensors and appropriate hardware

to give some sort of a malfunction warning to the operator.

The concept of condition monitoring is not new. Temperature

sensors, oil pressure indicators, fire lights, wear detectors, flow

indicators, fluid level gages and power level sensors have always been

used to give an indication of the condition of at least one component

of a system. What was new was the idea that eventually all sensors would be connected to a single "black box" which would not only warn

the operator of a problem but would tell him what was wrong and what to

do about it.

The literature shows that condition mointoring has been applied to

the types of machinery listed on Figure 5 with various degrees of success. This equipment includes gas turbine engines, diesel engines,

turbomachinery , automobiles, trucks, tanks, buses, ships, transmissons

,

computers, construction machinery, space craft, nuclear power plants,

and hydraulic systems. The major systems which have been used are listed on Figure 6. In the first approach critical sensors are specifically selected for each malfunction or component. This might be

only a thermocouple or it would be a complete system. For example, the

literature describes bearing monitors, structural fatigue monitors,

corrosion detectors, wear indicators, misalignment, and a variety of

other gages. The difficulty with the critical sensor approach is that

in many systems a large number of sensors are required. Approaches

were sought for a single technique which would detect a large number of

different types of malfunctions. Another approach receiving the most

attention has been vibration analysis. In this approach each

malfunction produces a characteristic signal which can be recognized

and interpreted by the analyser. Oil analysis measures the composition

of wear particles in the oils to isolate facility components. Gas path

5
and exhaust analysis monitor the combustion process while IR analysis

monitors "hot spots".

Although great strides are being made it is impossible to monitor

everything. Monitoring has been most effective in systems of reduced

complexity not requiring a multiplicity of sensors.

MODULARIZATION

Modularization is the design approach to maintenance. Essentially

a machine is designed with easily replaceable modules. If service

problems develop, the modules are interchangeable and replaced while

the faulty module is repaired. Although this concept has been used

successfully in consumer appliances and electronic equipment for many

years, its use in complex machinery is just beginning. For example, a gas turbine engine is built in four modules viz. power turbine, hot

section, cold section, and accessory section. The power turbine module

consists of the turbine case, the turbine rotor assembly, the turbine

drive shaft and the exhaust frame. The hot section includes the

combustion liner, the turbine stator and rotor assemblies. The cold

section has the output shaft, the front frame, the main frame, the

compressor rotor and stator and the diffuser casing. The accessory

section contains the various accessories. The main advantage is of course that the whole engine is not down while one part is being

repaired. There are, however, disadvantages. The principal

disadvantage is that maintenance personnel often take the path of least

resistance and remove modules for trivial reasons. It is not uncommon

to find a large increase in the "no defect" removals when this approach

is used. What is needed is test equipment so that the need for module

removement can be accurately determined. Performance records become of

limited value since interchangeability can lead to loss of identity.

However, the benefits gained in availability usually outweigh the

disadvantages. This approach will probably find increased useage as demands for quick response maintainability increase.

RELIABILITY-CENTERED MAINTENANCE

Reliability-centered maintenance (RCM) is a technique for

developing scheduled maintenance programs for aircraft, although the

technique is equally applicable to other equipment. It was developed

by United Airlines in 1965 and has since been adopted in principle by a large number of other airlines. The significant difference between

this program and others is each maintenance task is directly related to

component failure modes and their consequences. The process begins

with the identification of all failure significant components. The

functions of these components are then defined and possible failure

modes are selected based upon component functions. Consequences of

failure are identified as safety, availability, cost or failure

producing. With this information, decision diagrams are then used to

identify scheduled maintenance tasks. Four scheduled maintenance tasks

6
can be assigned:

On-condition inspection

Scheduled rework

Scheduled discard

Failure inspections

These tasks are then grouped into a specific maintenance program for a specific piece of equipment.

This approach basically selects from an all-encompassing preventive

maintenance program (which inspects and repairs all components with

equal vigor) those tasks which have a direct effect on maintenance

objectives. Where RCM has been used maintenance costs have been

reduced significantly. More extensive benefits of this program will be

realized when the data base and information is expanded on service

failure modes.

ANALYTICAL MAINTENANCE PROGRAMS

With preventive maintenance programs the main flow of work is from

the manufacturer, through manuals, to maintenance personnel who

effectively schedule and undertake the necessary tasks. With an analytical maintenance program there are strong inputs from maintenance

as to what is done, when it is done, and how it is done. The basis for

this program is a complete understanding of maintenance objectives and

effective measurements of current maintenance operations. Such

information is now available with computerized maintenance operations

which make available records of all maintenance operations. The Navy

3M system is typical. All maintenance actions are recorded in a computer and can be recalled for review. This is illustrated in Figure

7 where the man hours associated with certain malfunctions are recorded. The malfunctions and the WUC's are pre-selected and the

computer sums the maintenance man hours for each part and each

malfunction. The value of such data is obvious. Components requiring

excessive man hours can be investigated for specific details so that

corrective measures can be taken in maintenance. For example, in

Figure 8 leaking actuators are summarized. Failure analysis shows that

the problem in all cases is actuator rod wear due to dirt trapped in

the exclusion seal. A variety of maintenance approaches are available

to reduce this sort of problem. These data identify component problem

areas; however, additional data yields other kinds of information such

as squadron differences, budget data, cost effectiveness, future design

modifications, and research directions.

7
FAILURE CONTROL

With an effective analytical maintenance program equipment users

are able to practice what might be called failure control, a positive

approach to reducing maintenance costs. This can only be achieved by

obtaining a complete understanding of service failures and then

applying the appropriate technology to reduce these failures. There is

extensive literature on the subject of component failures and ways that

these failures can be avoided I This technology is often not considered

in design because the designer is unaware of the potential of certain

kinds of failure. Once these failures are observed in maintenance,

appropriate changes can be instituted. Experience shows that most

failures originate because of one of the conditions listed on Figure

9. Much more research is necessary to develop components more

tolerable to these conditions and make failure control information

available to designers and maintenance personnel so that an effective

information linkage is established.

MAINTENANCE TECHNOLOGY CONCEPT

The Maintenance Technology Concept is a scientific approach to

failure prevention and maintenance improvements. It stresses the

continual application of demonstrated technology and recognizes a multi-disciplinary requirement shown on Figure 10 and involves

structures, materials, tribology, corrosion, preservations, fracture

mechanics, diagnostics, life predictions, repair processes, quality

assurance and the life cycle phases of machinery. Failure prevention

and effective maintenance based on this concept emphasizes:

- Research and development clearly focused

on maintenance objectives.

Performance information data base retrievable for design and management decisions.

- Implementation of new technology for

performance upgrading and durability.

In-situ structural monitoring.

- Non destructive inspections.

Assessment of failure process - standardized classification and description.

- Assessment of repair process including

repair verification.

The comprehensive plan for the Maintenance Technology Concept includes

requirements for:

8
- Training

Publications

- Personnel

Engineering

Support

A systems approach is inherent in this concept and an imaginative

management linking technology advances with manufacturing, processing

and maintenance operations as well as information data bases is needed

on a sustained basis. The Maintenance Technology Concept involves the

following three essential phases:

PHASE I - MAINTENANCE TECHNOLOGY INFORMATION BASE

(1) Review information/data from maintenance documents,

(2) On-site surveys for various levels of maintenance to

inspect machinery, structure and equipment; discuss and

examine maintenance procedures to detennine current

practice and techniques.

(3) Compilation and analysis comparing maintenance

requirements and maintenance capabilities.

(4) Determine condition of machinery/equipment /structure and causes of degradation.

(5) Assessment covering optimum materials, processes,

treatment, repair and inspection procedures.

PHASE II - MATERIAL/PROCESSES FOR EFFECTIVE MAINTENANCE

(1) Define optimum procedures for detection and

interpretation of the degree of material degradation.

(2) Determine from data generated under Phase I latest

applicable technology for increasing equipment

performance and service life.

(3) Define optimum materials and processes for treatment and

repair for application at the various levels of

maintenance

.

(4) Initiate verification procedures.

(5) Conduct on-site demonstrations of improved procedures.

9
PHASE III - TECHNICAL REQUIREMENTS FOR MAINTENANCE IMPROVEMENTS

(1) Revise maintenance publications, e.g., manuals and

rework specifications.

(2) Define or recommend design/material changes where

required

.

(3) Recommend R&D starts covering technology voids.

In this approach, the earliest exploitation of new technology will be

emphasized, viz:

(a) Identification of improved materials and processes

for various levels of maintenance.

(b) Implement/accelerate use of the improved technology

in new production and manufacturing processes.

(c) Utilization of innovations in technology on a continual basis for maintenance improvements.

SUMMARY

Significant technical advances are the critical elements of this new approach to maintenance. Technology can be the vital element of

the maintenance plan resulting from a policy emphasizing increased

durability and equipment availability with effective cost control.

Examples of maintenance technology available to support this policy

are

1. Use of computer systems to optimize data storage, retrieval,

dissemination as well as maintenance scheduling, record and

analyse service problems, and control inventories.

2. Application of maintenance models to weigh complex

alternatives

.

3. Apply condition monitoring instrumentation for early warning

of impending failures or malfunctions.

4. Introduce rapid inspection and repair techniques.

5. Require failure resistant designs.

6. Use improved maintenance materials and processes.

The ultimate goal of maintenance technology is to achieve a specified period of trouble-free operation followed by an all-inclusive

maintenance period. With the new and emerging technology we are now

10
approaching that goal. The major conclusion is that the widest

possible benefit to industry and government can be achieved from a national program exploiting the maintenance technology concept.

11
MECHANICAL/STRUCTURAL FAILURE

RECENT EXAMPLES

NUCLEAR-POWER PLANT MALFUNCTION

EXPENDITURE: $800,000/day

AUTOMOBILE BOLT FAILURES

RECALL: 6 MILLION PLUS AUTOS

TMI - FLOW CONTROL FAILURE

LOSS: 1 BILLION PLUS DOLLARS

CHEMICAL PROCESS VALVE FAILURE

RESULT: LOSS OF CHEMICAL PLANT

STEEL MILL FINISHING PLANT - MOTOR FAILURE

EXPENDITURE: $400,000 RAPID REPAIR TO

AVOID A $30 MILLION LOSS

HIGHWAY/BRIDGE SYSTEM REINFORCEMENT FAILURE

COST: MULTI-MILLION DOLLARS

Figure 1

MAINTENANCE TECHNOLOGY DISCIPLINES

• STRUCTURES

• MATERIALS

• TRIBOLOGY

• CORROSION

• PRESERVATION

• FRACTURE MECHANICS

• DIAGNOSTICS

• NONDESTRUCTIVE INSPECTION

• REPAIR PROCESS

• LIFE PREDICTION

• QUALITY ASSURANCE

Figure 2

12
COMPUTER USES IN MAINTENANCE

• MATERIALS INVENTORY AND ORDERING

• SCHEDULING MAINTENANCE AND INSPECTIONS

• REPORTING MAINTENANCE HISTORY

• COST ANALYSIS AND CONTROL

• ISSUING WORK ORDERS

• CRITICAL PATH NETWORK ANALYSIS

Figure 3

"INSITU REPAIRS"

• LEAKS

• UNDERWATER REPAIR TECHNIQUES

• WEAR

• TURBINE BLADES

• COMPOSITE STRUCTURES

• CORROSION AND EROSION DAMAGE

• CRACK REPAIR

• ALIGNMENT

• COMPONENT REPLACEMENT

Figure 4

CONDITION MONITORED EQUIPMENT

• GAS TURBINE ENGINE

• DIESEL ENGINES

• TURBOMACHINERY

• AUTOMOBILES

• TRUCKS

• TANKS

• BUSES

• SHIPS

• TRANSMISSIONS

• COMPUTERS

• CONSTRUCTION MACHINERY

• SPACE CRAFT

• NUCLEAR POWER PLANTS

• HYDRAULIC SYSTEMS

Figure 5

13
CONDITION MONITORING APPROACHES

• CRITICAL SENSORS

• VIBRATION

• OIL ANALYSIS

• GAS PATH ANALYSIS

• EXHAUST ANALYSIS

• IR ANALYSIS

Figure 6

A6 AIRCRAFT STRUCTURE

330 /A/C 1 YEAR OPERATION

MALFUNCTIONS (Manhours)

lmprop«r Work Unll Coda Idenlltlcatlon Hour! Incldenctt CorKKlad Crictad Loking Sluck Worn Loot* Lubfhcallon 1121500 Wing Skin 12,778 1752 1 1 ,429 331 170 534 0 127 B 0 1113000 Misc Access Doors/Panels 11,122 2295 5,723 3,206 1,057 143 41 299 316 10 1113100 Forward Engine Access Door 9,491 1659 4,846 3,505 533 8 237 147 91 10 1113800 Access Panel 7,775 1646 4,080 2,071 762 72 6 290 162 16 1432100 Flaperon Actuator 5,724 139 2 19 2 5,622 60 10 7 4 1481400 Slat Assembly 4,895 533 3,559 595 346 7 54 183 4 3 1121200 Wing Outer Panel 4,591 296 2,880 159 783 591 0 103 1 0 1121100 Wing Inner Panel 4,558 378 3,991 27 87 434 2 0 0 3 1411200 Flaperon Skin 4,124 442 3,170 45 37 0 40 3 0 0 1118300 Boarding Ladder Assembly 3,972 879 2,331 774 501 6 27 283 19 6 1442100 Rudder Actuator 3,919 99 9 92 0 2,289 42 79 23 0 1452100 Stabilizer Actuator 3,496 83 16 62 0 2,272 1 20 0 0 1131200 Vert Stabilizer Skin 3,275 495 3,024 110 55 0 0 12 14 0 1116100 Ext Equipment Platform 2,494 538 1,127 872 180 15 43 123 79 4 1121400 Wing Leading Edge 2,578 407 1,778 79 60 70 2 244 21 0 1113500 Aft Engine Access Door 2,457 420 1,975 317 74 0 IB 35 22 1 1113600 Tall Pipe Access Door 2,383 369 1,819 368 60 12 0 106 7 0 1311100 MLG Shock Strut 2,385 313 1,114 36 465 492 122 10 2 116 1311000 MLG Mechanical Components 2,365 291 1,144 217 77 47 162 99 12 578 1321100 NLG Shock Strut 2,559 167 1,464 9 3 897 4 16 4 147 1451100 Hor Stabilizer Cable 2,453 46 4 1,979 0 120 0 349 6 0

Figure 7

14
A6 ATTACK AIRCRAFT

LEAKING MALFUNCTIONS

330 AIRCRAFT 1 year operation

O & I Component Incidents Manhours

Flaperon actuator 138 5622

Rudder actuator 79 2289

Stabilizer actuator 71 2272

MLG sequence valve 82 1321

MLG hydraulic lines 104 1215

NLG shock strut 52 897

NLG Retract cylinder 34 753

Wing structure 55 711

Wing outer panel 63 591

Wing skin 39 534

MLG retract actuator 64 500

MLG shock strut 26 492

TOTAL 807 17,197

Figure 8

CONDITIONS RESPONSIBLE FOR FAILURES

• ENVIRONMENT

• CONTAMINATION

• MISALIGNMENT AND POSITIONING

• EXCESSIVE LOADS OR TEMPERATURES

• VIBRATION

• MATERIAL DEGRADATION

• INADEQUATE LUBRICATION

• SHOCK LOADS

• DAMAGE

Figure 9

15
FOCUS

MAINTENANCE TECHNOLOGY CONCEPT

SCIENTIFIC APPROACH STRESSING TECHNOLOGY

INNOVATION FOCUSED ON IMPROVEMENTS FOR SAFETY,

RELIABILITY, DURABILITY & OPERATING ECONOMY.

MANAGEMENT INITIATIVES LINKING TECHNOLOGY

ADVANCES WITH MANUFACTURING, PROCESSING, AND

MAINTENANCE AS WELL AS INFORMATION SYSTEMS

ON A SUSTAINED BASIS.

Figure 10

16
IMNCVATION FCR MAINTENANCE TEGHNCLC GY IMPRCVEMENT3

Harry Rolka

Dow Corning Corporation

Midland, Michigan ^£6^0

Abstract: The high cost and complexity of today's industrial operation makes it imperative that maintenance technology be put to work. In 1980 American industry spent in

the range of 2^6 billion dollars in maintenance costs for

plant facilities and equipment. These estimates do not take

into consideration the cost of lost sales caused by production downtime and poor product quality. The need and opportunity for skilled, results oriented maintenance administrators has never been better nor more important. The address

will focus on the more critical maintenance problems facing

industry; their impact and some innovative productivity

practices and concepts that hold great promise for the

future

.

Key words: Maintenance; maintenance costs; maintenance

technology; technology centers; technology innovation.

It is essential, I believe, that we occasionally step back

from our daily job activities and take stock. '-Ve should

reassess our goals, priorities, and performance, in light

of present and future needs. When we do, these needs becom.e

better defined, and meeting them means "taking on a

challenge" rather than sim.ply "dealing with a problem."

We have an opportunity during these next three days to

engage in this kind of reassessment, thanks to this joint

Symposium sponsored by the Tlechanical Failures Prevention

Group of the National Bureau of Standards, and the Naval Air

Systems Gom.mand. Although my background is prim.arily with

chem.ical processing, associates from other fields assure me

that our maintenance operations are far more similar than

dissimilar. So with this in mind, I'm pleased to be here

to share v/ith you my experiences and ideas for meeting some

of industry's more critical maintenance challenges.

First, an understanding of what is meant by "maintenance

technology" -- and its economic significance -- is in order.

This will provide the basis from which to discuss innovative

productivity practices and concepts that hold great promise

for the future.

17
Broa.dly speakir.g, /Je'bRter defines "technology" as "the

systerriatic treatment of an art; an applied science or a technical method of achieving a practical purpose." A good

example is Thomas Edison's development of the electric light

'bulb after 50 1 000 experiments.

I will define " maintenanc

c

technology" as "the systeraatic

and scientific approach to preserving a plant's physical

facilities and equipment in optimum working order." And,

to do this often requires the dogged persistence of Edison - who remarked to his flustered colleagues, "Well, at least

we now know of 50,000 things that will not work." Faced

with today's complex and costly industrial operations, maintenance technology must be vigorously developed and applied.

19?0 to maintain plant facilities and equipment. (This

does not include the cost of lost sales resulting from

production downtime and poor product quality.) The statistical com.parisons shown in figure 1 illustrate the economic

impact of miaintenance costs.

After looking at this, you might say, "Great, miaintenance

operations is big business, but it's still not getting all

the funds it needs That's probably true. But, we could

make that money go a lot farther. Industrial consultants

tell us that 30% -- about 75 billion dollars -- is wasted

through poor managem.ent. A list of the causes of this

waste are shown in figure 2.

It's important to note, that these same experts put the

blame for this situation squarely on top management. This

is because top management does not understand maintenance

operations. For this reason I propose to you that the

greatest single challenge facing maintenance managers today

is closing the credibility gap between themselves and

corporate executives. Effective maintenance managers will

leave the tenuous safety of their "trenches and pillboxes"

and take on all competitors vying for executive management

support and limited cash resources. These battles will be

won by using the same weapon the competitors use: knowing

and selling the "bottom line" financial advantages, payback,

and productivity improvements of your proposals. Maintenance administrators must speak in the financial terms

executives understand -- cost analysis, economic evaluation,

and cost/benefit comparisons. The successful manager needs

to have a "fighter pilot mentality" of knowing the mission,

the competition, and tenaciously pursuing the objective,

i-^e should keep in. mind that the requirements for a good

miaintenance operation are the same as for any other

business operation. A brief list of important maintenance

requirements is shown in figure 3'

U.S. companies spent

18
The maintenance i^icture is changing as more companies come

to the realization that maintenance is the single largest

controllable cost in the plant. In these companies

effective maintenance administrators are finding top

manae:ement support. Hew and innovative productivity practices and concepts are "being implemented. Some of these

improvements are worth mentioning.

I ?-';aintenanc e Technology Centers (figure 4)

Typical Charter

Proad Representation

Annual Reviews v/ith Executive Management

II Capitalization Improvement

Buying Current Technology

Increasing Utilization of Industrial Robots

Computerization of Operations

III Latest Instrumentation Training and Manpower Trends

Traditional Instrumentation is Changing

Technical Specialists for:

- Process Computers

- Cn-Stream-Analyzers

- Electronic Controls

IV Fifth and Sixth Shift Operations

Humanization of the Shift iVorker (figures 5i 6)

V Team Action Circles (Quality Circles)

VI Exotic Materials of Construction

VII Non-Destructive Testing

Vibration Analysis

Ultrasonic Testing

Fiber Optic Inspection Equipment

Thermovision Equipment

VIII Multi-skill Craftsmen

. Electrical/instrument Combinations

i'.'echanical Craftsmen

19
Recent studies by the Brookings Institute on labor productivity estimates that implementation of technological

innovation provides 44-;^ of this nation's productivity

improvem.ent . So I will close with the same statement I started with -- the high cost and complexity of today's

industrial operations makes it imperative that we put

maintenance technology to work. Let's renew our commitment

as maintenance professionals to assure this happens.

1980 COST CCKPARISCNS

* INDUSTRIES' KAINTEIIANCE COSTS 246 BILLION DOLLARS

* AP/ERICAN'S TOTAL TAX BILL - — 750 BILLION DOLLARS

FEDERAL - 520 BILL. DOLLARS

LOCAL & STATE - 230 BILL. DOLLARS

INDUSTRIES' TKEFT LOSSES 40 BILLION DOLLARS

INDUSTRIES' ABSENTEEISM COSTS 20 BILLION DOLLARS

10 BILLION DOLLARS ATTRIBUTED TO

POOR ATTITUDE AND LACK OF

JOB COr/lMITrSNT

GM'S ANNUAL ABSENTEEISM COST IS

1 BILL. DOLLARS

RAILROAD ^MAINTENANCE COST 11.3 BILLION DOLLARS

THREE KILE ISLAND ESTItlATED REPAIR AND

REFURBISHING BILL 1 BILLION DOLLARS

(PLUS EIGHT YEARS)

Fi gure 1

20
CAUSES OF miNTENANGE WASTES

^ LACK OF I\^ir:AaEmiT COST CONTROL.

LACK OF GOOD EQUIPMENT REPAIR RECORDS AND LITTLE

ENGINEERING ANALYSIS OF EQUIPMENT FAILURES.

* POOR OPERATOR TRAINING RESULTING IN IMPROPER EQUIPMENT

OPERATION.

^ ^aSMANAGEtlENT OF SPARE PARTS INVENTORIES AND MAINTENANCE

SUPPLIES

.

^^ INEFFICIENT PLANNING AND SCHEDULING.

* LACK OF PREVENTIVE MAINTENANCE PROGRAMS.

^ LACK OF EFFECTIVE USE OF NON-DESTRUCTIVE TESTING AND

DIAGNOSTIC EQUIPMENT.

^ NO INCENTIVES TO ENCOURAGE BRIGHT SUPERVISORS AND

ENGINEERS TO GST INTO MAINTENANCE.

LACK OF COORDINATION BETWEEN PRODUCTION AND MAINTENANCE.

Figure 2

21
IMPORTANT MAINTENANCE REQUIREMENTS

I DSVELCP A GOOD ORGANIZATION AND INSTALL THE MOST

EFFECTIVE MANAGERS AND SUPERVISORS YOU CAN FIND.

. CENTRALIZED, DECENTRALIZED AND MATRIX ORGANIZATIONS

ALL WORK IF MANAGED PROPERLY.

II DEVELOP SEVERAL HISTORIC MiAINTENANCE INDICES THAT

'

MEASURE YOUR TEAM'S PERFORMANCE. TYPICAL INDICES

. P^AINTENANCE COST PER UNIT OF OUTPUT

. EQUIVALENT MANPOWER PER UNIT OF OUTPUT

. EQUIPMENT DOWNTIME OR UTILIZATION RIEASUREMENTS

. 0VERTIMJ2 RECORDS

. ABSENTEEISM RECORDS

. CAPITALIZATION OF EXPENSE WORKERS

. WORK SAMPLING

III IMPLEMENT AN EFFECTIVE MANAGEf/IENT BY OBJECTIVES

PROGRAM (mo) WITH QUARTERLY REVIEWS. GAIN CCMiLiITRIENT

.

ASSIGN ACCOUNTABILITY.

IV CONTROL COSTS AND PEOPLE RESOURCES

V REWARD GOOD PERFORMERS

VI RETRAIN POOR PERFORIVIERS

Figure 3

22
CHARTER

MAINTENANCE TECHNOLOGY CENTER

PRIORITY I DEVELOP MAINTENANCE TECHNOLOGY, PRIORITIZE AND

ASSIGN MULTI PLANT OR CRITICAL MAINTENANCE

PROBLEMS TO SKILL SPECIALISTS OR THE SKILL CENTER

TASK FORCE FOR SOLUTION. COORDINATE IMPLEMENTATION

OF CORRECTIONS WITH APPROPRIATE CONSIDERATION FOR

SAFETY AND COSTS. ELIMINATE DUPLICATION OF EFFORT.

PRIORI TY I I OPERATE AS A CLEARING HOUSE FOR MAINTENANCE

TECHNOLOGY AND INFORMATION.

A. MAINTAIN TECHNICAL LIBRARY OF RECORDS

AND REPORTS.

B. MAINTAIN AND DISTRIBUTE UPDATED LIST OF

TECHNOLOGY BOARD MEMBERSHIP AND SKILL

SPECI AL I STS

.

C. COMMUNICATE MAINTENANCE TECHNOLOGY.

PRIORI TY III ASSIST PLANTS IN IMPROVING MAINTENANCE PROGRAMS

PRIORITY IV DEVELOP INDICES TO MEASURE PLANT AND CORPORATE

MAINTENANCE COST EFFECTIVENESS, PRODUCTIVITY

AND EQUIPMENT ON LINE TIME.

PRIORITY V IMPROVE CAPITAL UTILIZATION AND PRODUCTIVITY

BY MAXIMIZING ON-LINE-TIME WHILE OPTIMIZING

BOTH MAINTENANCE COST AND INITIAL CAPITAL.

Figure 4

23
40 HRS/WEEK

Mm Te 1 r { U f AL nUUrib

\

** N N N N H N 48

2 N L L L L L 48

3 L L M m M 40

4 M M 32

5 D 0 D D D

mm 40

N =^ L = LATE SHIFT

M= MORr^lfr^jGSH^FT

D = DAYSHIFT

208

= 4f.6 HRS/WEEK

SHIFT I SHIFT 2

SHIFT 3

SHIFT 4

SHIFT 5

OFF-HOURS DURING WEEK

24

56

56

OFF-HOURS VVEEKEf^D

89

54.5

+ 10.5 EXTRA FREE DAYS/YEiAR

Figure 5

24
SALARY IMPROVEMENTS

HIGHER SHIFT ALLOWANCES

SHORTER WORKING WEEK

MORE TIME-OFF

FEWER NIGHTS WORKED

MORE WEEK-ENPS AT HOME

GREATER JOB SATISFACTION

DEFINITE FUTURE JOB GROWTH

PROPER TRAINING

MORE RESPONSIBILITY

TECHNICIAN SKILLS

Figure 5

25
PRIMARY CONTRIBUTORS

TO

IMPROVED PRODUCTIVITY*

TECHNOLOGICAL

INNOVATION

TANGIBLE

CAPITAL

16;^

ECONOMIES

OF SCALE

"LABOR" PRODUCTIVITY; RATIO OF MEASURABLE OUTPUT TO INPUT.

SOURCE: BROOKINGS INSTITUTE STUDY 1979

Figure 7

26
AN OVERVIEW OF MAINTENANCE INFORMATION SYSTEMS FUNCTIONS

Abstract: Aircraft Maintenance costs are escalating rapidly

on practically every front. Maintenance information systems

are one of the few areas where costs have remained relatively stable in recent years because computer hardware costs

have continued to decrease. This has enabled the development of more cost-effective applications to control costs

and manage aircraft maintenance. In this paper a framework

of primary maintenance information systems functions is outlined. The list is all-inclusive and covers those functions

which interface directly with the aircraft, the powerplant/

component/support shops and the management and financial

areas. Over fifty different functions are reviewed in some

detail to present each potential user with a list he should

consider in developing comprehensive maintenance systems.

Implementation steps are also discussed and conclusions

drawn.

Key words: Aircraft Maintenance Functions; Maintenance

Information Systems Functions; Management and Financial

Functions; Master Planning; Material and Logistics Functions; Personnel/Component/Support Shop Functions; PowerPlant/Component/Support Shop Functions.

Maintenance Information Systems Functions Overview

It is helpful to have a framework in which to review the

Maintenance Information Systems functions. There are a number of approaches to accomplish this. Regardless of which

approach is selected there will be individual functions

which do not conveniently fit the framework. The framework

outline depicted in figure 2 appears to be workable.

The functions are analyzed with respect to their relationship to the aircraft, working away from the aircraft to

overall maintenance management costs. The first group of

functions to be reviewed are those which interface directly

with aircraft maintenance.

Victor S. Middlebrook and George D.

Transportation Systems Consult

P.O. Box 230 * 5 Sanford S

Huntington Station, New York

S. Andrews

ing Corp.

treet

1 1746

27
AN OVERVIEW OF MAINTENANCE INFORMATION SYSTEMS FUNCTIONS

ABSTRACT

MAINTENANCE COSTS - RISING RAPIDLY:

- LABOR

- MATERIAL

- FACILITIES

MAINTENANCE INFORMATION SYSTEMS COSTS - STABLE

- PROGRAMMING UP MODESTLY BUT

- HARDWARE CONTINUES TO COME DOWN

NET RESULT - INCREASED USE OF MAINTENANCE

INFORMATION SYSTEMS (MIS)

THIS PAPER PROVIDES A SHOPPING LIST OF

OVER FIFTY MIS FUNCTIONS TO CONSIDER

CAVEATS: EACH FUNCTION MUST BE:

- COST EFFECTIVE

- INTEGRATED

- USER INVOLVED

1

Figure 1

28
MAINTENANCE INFORMATION SYSTEMS FUNCTIONS OVERVIEW

AIRCRAFT MAINTENANCE

I

POWERPLANT/COMPONENT SUPPORT

I

MATERIAL

1 1i

PERSONNEL/FACILITY

I LJLJl

OVERALL MANAGEMENT/COSTS

Figure 2

DIRECT

AIRCRAFT

SUPPORT

INDIRECT

AIRCRAFT

SUPPORT

RESOURCE

MANAGEMENT

EMPHASIS ON

COST-CONTROL

AND

PRODUCTIVITY

29
The next set of functions pertain to the powerplant/

component/support areas which include all of the shop activities that support an aircraft. This is an area where improved information systems can often reduce costly aircraft

delays

.

The next group are the material functions which is the next

lower support step. If not properly organized, these functions can be a large contributor to delays. The volume of

the material processed requires efficient information pro- cessing support.

Next are the personnel and facility functions. Personnel is

an area, in the decade of the eighties, which will require

much more control because of accelerating labor rates. Facility management is just starting to be developed.

Finally, overall maintenance management/costs ties it all

together and produces the maintenance organization's bottom

line

.

Aircraft Direct Maintenance Functions (1 of 2)

A/C Configuration Tracking . Keeps track, for each aircraft, of

the powerplant, maintenance units, components, assemblies, and parts

presently "hanging on the A/C", by serial number.

A/C Status . Provides the status of pilot reports (pireps), delays,

deferrals, previous maintenance actions, etc.

A/C Time . Keeps track of time-on-ai rcraft in terms of hours, cycles,

calendar time, opportunity hours, etc., as appropriate.

A/C Time-When-Due Record Keeping . Compares times on components

against allowable times and creates a scheduled maintenance list.

A/C History . Allows maintenance analyst to review any selected

tail number, or system, for its maintenance history.

A/C Service Forecasting . Based on reliability history and seasonal A/C requirements, provides a service forecast for a 2 month to

2 year period.

A/C Service Scheduling . Refinement of forecasting function

covering 2 days to a 2 month period of time and includes material and

personnel requirements.

30
AIRCRAFT DIRECT MAINTENANCE FUNCTIONS (1 OF 2)

DIRECT

AIRCRAFT

MAINTENANCE

I

POWERPLANT/

COMPONENT/

SUPPORT SHOPS

I

MATERIAL

AND

LOGISTICS

PERSONNEL

FACILITY

I

MANAGEMENT

AND

FINANCIAL

PILOT

REPORTS

ROTABLE

CHANGES

HOURS,

CYCLES,

TIME

/ A/C \

/ SERVICE \ P[ SCHED. I ^2-60 DAYS/

STATUS

PLANNING

CONTROL

Figure 3

31
Aircraft Direct Maintenance Functions (2 of 2)

A/C Routing . A real-time operations center function with the ability to

redirect aircraft based on maintenance and operational implications.

Work Card Control . A combination of manual and computer work card man- agement (work card index is computerized).

Work Package Generation . Creates a work package for a specific service

based on time-when-due, work cards required, modifications planned,

servicing required, etc.

Specific Service Work Status . Provides the ability to control heavy

services (C & D), integrate inspection generated work, and provide work

status

.

Modification Control . Provides for control by aircraft and by modification. Allows planning of modifications to be accomplished during a servi ce

.

A/C Reliability . Sums up reliability, by aircraft, for monthly fleet

reporting.

Warranty Control . Allows the determination of warranty status and

provides information for supplier material cost guarantee programs.

Powerpl ant/Component/Support Shop Functions

Powerplant Forecasting . Provides a 2 month to 2 year forecast of

powerpl ant needs based on A/C requirements.

Component Forecasting . Similar to powerplant forecasting function.

Workshop Forecasting . Provides a 2 month to 2 year forecast of component requirements, by workshop, based on A/C schedule changes and

reliability forecasts.

Powerplant Scheduling . Provides scheduling functions for powerpl ants

covering a 2 to 60 day period indicating required powerpl ants, maintenance units, components, assemblies, and parts based on reliability and

A/C schedules.

Component Scheduling . Comparable to powerplant scheduling above, for

components

.

Workshop Scheduling . Prioritizes workshop schedules for components

based on the most critical aircraft needs so that components shops are working on what is most required.

32
AIRCRAFT DIRECT MAINTENANCE FUNCTIONS (2 OF 2)

MTCE.

TASKS

J

WORK

CARD

CTL.

SVCE

R0MNTS

WORK . PACK. • GEN.

A/C

SVCE.

STATUS

ACCEPTED

MODS SCHED.

^

MODS

•* MODI-

• FICATION-

\ CONTROL*

WARRANTY \

CONTROL •

REAL

TIME

INPUTS

> • A/C • ROUTING ;

SCHED. &

UNSCHED.

RQMNTS.

WARRANTY

COVERAGE

STATUS

PLANNING

CONTROL

Figure 4

33
Work Order Generation . Generates on-line work packages that provide

complete service instructions.

Support/Service Shop Load Control . Anticipates the magnitude of the

load on various machine types, or areas, based on A/C requirements.

Powerplant Tracking/Status . Provides configuration control for powerplants on the A/C comparable and integrated with A/C configuration.

Component Tracking/Status . Comparable to powerplant tracking/status

above for components.

Note that there are functions comparable to those in the aircraft area

for modifications, warranty and reliability functions.

Material and Logistics Functions (1 of 2)

Parts Identification . This function provides the ability for senior

production personnel to identify required components and expendables by

part number. A key function is to provide alternate interchangeable

part numbers

.

Parts Requisition . Companion function to parts identification which

allows production personnel to automatically order parts.

Expendables Inventory Status . Provides status function for expendable

items by measure rather than by item.

Expendables Consumption (History) . Pxecords the issue rate and in turn

provides consumption data for planning and purchasing.

Parts Requirements Forecasting . Similar to other forecasting functions

covering 2 months to a 2 year period and pertaining primarily to

expendabl es

.

Overstock Control . Recognizes overstock situations and provides the

basis for surplus sales activities.

Understock Control . Recognizes stockouts and provides the basis for

supply level management.

Warranty Management . Provides warranty management control for defective

items which are still within the warranty period and guaranteed by the

vendor.

34
POWERPLANT/COHPONENT/SUPPORT SHOP FUNCTIONS

AIRCRAFT

FORECAST

I

/ \

I POWERPLANT,

I FORECAST./"

AIRCRAFT

^SCHEDULE

SCHEDULED

AND

UNSCHEDULED

REMOVALS

t COMPONENT \ \ FORECAST.

••loading/

STATUS

PLANNING

CONTROL

Figure 5

35
MATERIAL AND LOGISTICS FUNCTIONS (1 OF 2)

OVERSTOCK

CONTROL •

expendable*,

'pnsumption

Hhistory/

: UNDERSTOCK;

•.CONTROL /

AIRCRAFT/

POWERPLANT/

COMPONENT

REQUIREMENTS

/ PARTS

[ ROMNTS I .FORECAST.'

STATUS

PLANNING

CONTROL

; WARRAflTY'.

management:

Figure 6

36
Material and Logistics Functions (2 of 2)

Vendor Control . Keeps track of vendor performance and other critical

information required to support purchasing functions.

Purchasing/Ordering . Provides for automatic ordering and generation of

purchase orders for certain categories of material. May also have override features to enhance control.

Receiving/Inspection . Provides a convenient method of logging-in re- ceived inventory, recording irregularities/short-shipments, beginning

status and proof-of-recei pt for invoice payment.

Customs Control . Manipulates the shipping and receiving data pertaining

to rotables and expendables material so that it is suitable for customs

inspection/control

Shi pping Control - Provides shipping data (method, rates, etc.) and

tracking information to line stations/vendors.

Line Station Functions . Consideration should be given to real-time

tracking of rotables and expendables material issued to line stations.

Material Accounting . Supports accounting functions by listing appropriate inventory as capital items (rotables) and expense items (expendables). Supports perpetual inventory audit.

Spares Provisioning . Provides formula approaches for developing initial

support requirements.

Personnel Functions

Personnel Skill Requirements . Provides a forecast of labor requirements

based upon aircraft and shop forecasted workloads and historical labor

task performance.

Current Personnel Status . Indicates scope of present labor force and near- term availabilities. Can be compared with requirements above.

Labor Reporting . Collects labor statistics by job, during a shift rotation. Produces various management reports concerning productivity,

human behavior and overtime status.

Labor Analysis . Analyzes labor expenditures against standards and

provides labor productivity information.

Job Costing . Produces total maintenance manpower costs by job function.

37
MATERIAL AND LOGISTICS FUNCTIONS (2 OF 2)

REQUIREMENTS

VENDOR

I CONTROL ;

•ACCOUNTING'

STATUS

PLANNING

CONTROL

Figure 7

38
PERSONNEL FUNCTIONS

MAINTENANCE

TASKS

TERSONNEU

SKILL

REQUIR.. CAPABILITIES

DATA

CURRENT

PERSONNEL

STATUS

TASK

ACCOMP.

DATA

LABOR

REPORTING]

STANDARDS

1

STATUS

PLANNING

CONTROL

; LABOR

• ANALYSIS JOB

DATA

; JOB :

*. COSTING

.*

Figure 8

39
Facility Functions

Facility Status . Provides the location, condition, and assignment of high cost items (payloaders, stands, etc.) which

are usually in short supply.

Facility Planning/Scheduling . Provides support for service

scheduling and permits a "reservation" function.

Ground Support Equipment . An extensive function in its own

right which contains the status, planning and control components described previously.

Container Tracking . Another form of facility for those involved in cargo activities which also has status, planning,

and control functions.

Management and Financial Functions

Material Costs Analysis . Collects rotables anr expendables

material costs by A/C type, by service, and by part number,

for cost comparisons.

Personnel Costs Analysis . Collects personnel costs by

skill, by A/C type, by service, for cost analysis and comparisons . Facility/Overhead Costs Analysis . Collects facility costs

and provides an analytical figure for monthly cost analysis

and overhead costs as a basis for allocating overheads.

Maintenance Costs Analysis . Analyzes total costs based on

labor and material costs by A/C type, A/C tail number, service, ATA chapter, etc. Supports third party billing procedures .

40
FACILITY FUNCTIONS

ISSUES AND RETURNS

STATUS

PLANNING

CONTROL

Figure 9

41
MANAGEMENT AND FINANCIAL FUNCTIONS

; MATER I AL*-

: COSTS ; ANALYSIS/

/personnel*-

: costs • \analysis /

.•FACILITY/.

: OVERHEAD *.

: COSTS : •ANALYSIS.*

J"

STATUS

MTCE.

• COSTS

ANALYSIS

PLANNING

• CONTROL

Figure 10

42
Implementation Steps and Summary

This paper has presented over fifty different maintenance

information system functions in six major categories. Each

of these functions can be cost effective under the proper

circumstances. It is extremely important to appreciate the

scope of capabilities in order to select those that are required in your organization.

Fisure 11 lists six implementation steps. Master planning

is extremely important to prevent major revisions to systems

every few years. Each and every effort should start with a feasibility study so that management knows what it is in

for. The last step is one we don't spend enough time with

and that is system critique. Does the system/module do the

job it was designed for and can/should we make it perform

better?

Maintenance Information Systems are not a panacea. However,

more extensive use of MIS in the maintenance world does offer the opportunity of holding maintenance costs stable in

an inflating environment. Effective use of MIS also offers

cost efficiency that may not be achievable any other way.

43
IHPLEHENTATION STEPS AND SUMMARY

MAINTENANCE INFORMATION

SYSTEM FUNCTIONS

HIERARCHY

• DIRECT AIRCRAFT MAINTENANCE FUNCTIONS

• POWERPLANT/COMPONENT/SUPPORT SHOP FUNCTIONS

• MATERIAL AND LOGISTICS FUNCTIONS

• PERSONNEL FUNCTIONS

• FACILITY FUNCTIONS

• MANAGEMENT AND FINANCIAL FUNCTIONS

IMPLEMENTATION

STEPS

• MASTER PLAN

• FEASIBILITY STUDY

• ANALYSIS AND DESIGN

• PROGRAMMING AND TEST

• I MPLEMENTAT I ON/OPERAT I ON

• SYSTEM CRITIQUE

THE PROMISE

OF MIS

• HOLD MAINTENANCE COSTS RELATIVELY STABLE

• IMPROVE THE ORGANIZATIONS EFFICIENCY

• PROVIDE MANAGEMENT AND COST CONTROLS

Figure 11

44
FAILURE MECHANISM AND CAUSE ANALYSIS OF STRUCTURES: A PARADIGM FOR

THE ANALYSIS OF FAILURES OR POTENTIAL FAILURES

L. E. Sloter

Vouqht Corporation

P.O. Box 226144

Dallas, Texas 75266

W. R. Shawver

Vouqht Corporation

P.O. Box 225907

Dallas, Texas 75265

D. J. White

Vouqht Corporation

P.O. Box 225907

Dallas, Texas 75265

A novel heuristic failure analysis procedure that incorporates multidisciplinary considerations within a constructive framework to aid in

the analysis of actual enqineerinq failures or the failure potential

of structures is described and discussed. The Failure Mechanism and

Cause Analysis (FMCA) procedure disassembles a failure process into

its component parts such that the overall process may be analyzed more

easily. From such a breakdown the sources or causes of an actual

failure may be more effectively determined or the most probable potential failure processes identified. Once an overall failure process,

either actual or potential, has been defined and understood, remedial

or preventive action may be taken more effectively. Such action may

include redesiqn, stricter quality control, a maintenance task, or a combination of these thinqs.

Key Words: Enqineerinq failure mode; failure; failure analysis; Fail- ure Modes and Effects Analysis; maintenance (inspection) interval

1.0 INTRODUCTION

The failure analysis procedure reported herein was developed durinq

the execution of a proqram that had been desiqned to create a methodoloqy for the determination of structural maintenance intervals for

U.S. Navy aircraft on the basis of calculated safety-of-f 1 iqht risk

criteria. In particular, the overall methodoloqy had been required to

realistically address the complete process of structural deqradation

45
and to provide a quantitative rationale for structural maintenance intervals based on a statistical analysis of failure mechanisms, failure

rates, and inspection capabilities.

1.1 METHODOLOGY OVERVIEW

The method, in order to be as comprehensive as possible, models the

entire process that an aircraft item would see in its lifetime, that

is from desian throuqh manufacturing to flight operations and inspections. The method allows for the use of the latest state-of-the-art

analytical techniques where possible and proposes new or modified

techniques where necessary. The basic methodology for determining

maintenance intervals is illustrated in flowchart form in Figure 1.

It consists of two major analytical sections that are effected after

those critical items requirinq analysis are identified. These sec- tions are briefly the followinq:

(1) Damaae Identification - Analyze potential failure processes

for each item, payinq particular attention to corrosion and crack,

especially f atique-crack, initiation.

(2) Damaqe Rate Analysis - Conduct probabilistic damaqe rate

analyses for both corrosion and fatique usinq appropriate load spectra

and environments. Two calculational sections are applied followinq

the kinetic analysis as follows:

(a) Assess Risk - Predict failure probabilities from the

joint probability density function of critical crack sizes and predicted crack qrowth.

(b) Schedule Maintenance - Determine maintenance intervals

considerinq non-destructive inspection capabilities and safety

(risk). Recalculate failure probabilites in liqht of the scheduled

maintenance and repair and redetermine intervals if necessary.

The methodoloqy thus consists of two primary analytical activites - the Failure Mechanism and Cause Analysis (FMCA) and the Damaqe Rate

Analysis (DRA). The former technique is a loqical framework developed

in order to provide a definitive procedure for analyzinq the failure

potential of items and a means for reportinq the results of such an analysis. It should be considered as a definitive means whereby an analyst may perform an analysis of the potential failure process to

which an item may be susceptible, divide that process into analyzable

components, and convey the analytical results for purposes of decision

makinq or further kinetic analysis. The kinetic analysis developed

for this purpose is the Damaqe Rate Analysis procedure incorporated in

the overall structural maintenance methodoloqy. The details of the

DRA as well as an example of the overall implementation of the structural maintenance methodoloqy have been reported, by Shawver, et

al^. The present discussion is limited to the failure analysis procedure (FMCA) developed for the methodoloqy.

46
METHODOLOGY PROCESS

DAMAGE IDENTIFICATION

IDENTIFY CRACK

MECHANISMS, CAUSES

DAMAGE RATE ANALYSIS

ESTABLISH CRACK

INITIATIONS

CALCULATE CRACK

GROWTH, DISTRIBUTION

REPA

REPl

IR OR

.ACE

; I

DETECTED

CRACKS

CALCULATE PROBABILITY

OF FAILURE

UNDETECTED

CRACKS

GO-2423-2

FIGURE 1: STRUCTURAL MAINTENANCE INTERVAL METHODOLOGY-SCHEMATIC PROCESS

OVERVIEW. 1

2.0 FAILURE MECHANISM AND CAUSE ANALYSIS

2.1 BACKGROUND

Failure Mechanism and Cause Analysis (FMCA) is a logical framework developed to assist the designer, failure analyst, maintenance engineer,

or other interested party in the evaluation of the potential failures

inherent in a product design and the paths by which failure could oc- cur or in the evaluation of the possible causes of a particular failure under analysis.

2.2 ORIGIN

Failure Mechanism and Cause Analysis has its origins in the general

technigues of Preliminary Hazards Analysis^; Failure Mode and Effect

Analysis^'"^ »^ ; Failure Modes, Effects, and Criticality Analy5-152,3,4. Decision Tree Analysis^; and Maintenance Plan Analysis'*^ as well as the aeneral engineering disciplines of failure

47
analysis and risk analysis. Although the FMCA technique is derived

from these other areas and bears a strong resemblance to them in

parts, its purpose, uses, and procedures are sufficiently distinct

that it is uniquely named and should be considered to be a unique and

individual analysis technique.

2.3 FMCA AND FMEA

The principal difference between the Failure Mechanism and Cause Analysis (FMCA) and the classical Failure Mode and Effect Analysis (FMEA)

is that the latter mainly examines functional failure modes while the

former examines essentially engineering failure modes (Figure 2). It

cannot be emphasized too stronaly that functional and engineering

failure modes are distinctly different, albeit related things. FMEA's

usually begin with the functional failure mode and examine its effect

on system operation. FMCA's begin with the engineering failure mode

responsible for the functional failure and examine the failure mechanisms and sources which had led to or caused the occurrence of the engineerina failure mode for purposes of preventing the failure from re- curring. The FMCA may also begin with the failure mechanisms and sources and examine the potential for the occurrence of an engineering

failure mode for purposes of designing or maintaining against the oc- currence of the failure. In either case, actual engineering failure

mode or potential engineering failure mode, the FMCA may also consider

the failure effect or effects of the identified failure. In summary,

then, the FMCA is an engineering analysis. The FMEA, on the other

hand, is principally a systems approach to failure and failure effect. Generally, beginning with a functional failure mode, the FMEA

examines the effect of that failure on system reliability or effectiveness for the purpose of minimizing the consequences of failure

through fail-safe design, redundant design, or failure tolerant design. The FMEA and its more general progenitor, the Preliminary

Hazards Analysis, are principally systems analysis and design techniques, not engineering failure analysis tools.

3.0 FAILURE MECHANISM AND CAUSE ANALYSIS METHODS

3.1 PURPOSE

Failure analysis encompasses a variety of systematic and logical

methods and procedures which may be applied to failures which have oc- curred in testing or in service or which potentially may occur. A

hypothetical failure analysis may also be performed by a designer or other person to discern potential weaknesses or failure possibilities

in a design. Most often, however, failure analyses are undertaken

following an actual failure, although the failure may have occurred in

testina and not in actual service.

48
FIGURE 2: FAILURE MECHANISM AND CAUSE ANALYSIS AND FAILURE MODES AND

EFFECTS ANALYSIS CONTRASTED.

3.2 GOALS

In aenoral, it is aood practice to explicitly state the purpose or

goal of the analysis initially so that misunderstandinqs are avoided

and the proper analyst for the specific job is chosen. The goals of a failure analyst or the purposes of an individual failure analysis are

not always the same or even compatible. Some failure analyses are conducted in order to determine a fix which will prevent a similar

failure from occurring. Such a fix may be a design change, material

substitution or modification, a change in environment, or some other

alteration. Other failure analyses are performed in order to determine the cause of failure or the most basic action, event, mechanism,

or source without which there would have been no failure. Analogous

to this goal may be an interest on the part of the failure analyst to

understand the fundamentals of a failure process. Finally, a failure

analysis may be conducted primarily for the purpose of assessing re- sponsibility or blame for a failure. This responsibility may be laid

upon the designer, the manufacturer, the repairer, the user, some other party, or any combination of these persons. In order to assess

blame in such an analysis, cause must usually be determined such that

some party, the responsible party, had control of or could have prevented the cause. Often these failure analysis goals lead to incompatibility among the opinions and conclusions of the analysts.

49
3.3 THE ANALYST

In addition to variability in analysis goals, various persons may be

assigned the task of performing a failure analysis. The analyst may

be an inspector or repairman who discoveres an unusual circumstance

and performs a brief failure analysis to determine if the occurrence

should be reported, more closely inspected, repaired, or ignored. A

maintenance enaineer may often act as failure analyst in order to determine if a maintenance task may be effective in preventing or postponing failure. On occasion, failures of sufficient importance or magnitude will occasion the services of professional failure ana- lysts. Such persons will often be mechanical or structural engineers,

materials engineers, specific product engineers, other engineering

specialists, or teams of such individuals. In any given instance of

failure, a decision must be made at the beginning with respect to the

necessary level of the analysis and the personnel required. Such a decision will set the goals of the analysis and generally the depth to

which it will be conducted. Of course, during the analysis process,

the analysis may be expanded or limited in order to efficiently meet

changing goals or react to additional information.

In general, it should be noted that failure analyses are usually con- ducted under the auspices of someone other than the failure analyst

himself. This responsible authority will generally decide that an analysis will be performed, who will perform it, and what the level or depth of the analysis will be. This authority should become sufficiently familiar with the failure, the techniques of failure analysis,

and the potential causes of failure so that he can effectively make

the necessary decisions.

3.4 TECHNIQUES

The specific experimental and analytical techniques employed in failure analysis are potentially and virtually all the experimental techniques employed in engineering and science in the broadest sense. The

language of failure analysis includes terms from most engineering disciplines as well as terms specific to itself. For these reasons, no brief discussion can effectively document or cover the "fields" of

failure and failure analysis. These areas, therefore, must be broken

up into concisely explicable parts.

The followino sections present a discussion of a logical technique

which can aid the failure analyst in the examination of a failure by

presenting him with a framework wherein failure potentialities may be

discerned or placed. Furthermore, this framework or Failure Mechanisms and Cause Analysis may aid the designer in detecting specific,

potential failure processes in items. In this respect the FMCA is

complementary to a Failure Mode and Effect Analysis which may also be

specified in the design stage of an item. Finally, the FMCA is used

to disassemble a failure process into analyzable parts such that Dam50
aqe Rate Analysis may be applied in order to predict failure or define

the risk of failure with time.

3.5 FMCA METHODOLOGY

The path which leads to failure is often a very twisted and non-direct

one made up of unlikely events, unconsidered driving forces, and interactive occurrences. When only the cause of failure is to be determined, then it is only necessary to examine the specific chain of

events which could lead to an individual failure. When a failure is

to be more fully analyzed, however, these individual events must be

sorted and defined for individual analysis and interactions must be

considered. Such an analysis may be termed a "Potential Failure

Analysis" and is outlined as follows usinq the Failure Mechanism and

Cause Analysis terminology (also See Figure 3):

FMCA: POTENTIAL FAILURE ANALYSIS OUTLINE

I. Identify and carefully describe the item to be analyzed.

A. Describe the function of the item.

B. Describe the physical characteristics of the item.

II. Identify and describe the intended environment in which the item

is to be used and the time or time related parameter associated with

the environment.

A. Include.

1. Physical environment.

2. Mechanical environment.

3. Chemical environment.

4. Functional environment.

B. Evaluate the probability of changes or additions to the use environment and possible environmental interactions with other items.

III. Identify and list the potential primary engineering failure

modes to which the items may be susceptible.

A. Examples.

1. A structural item may be susceptible to fracture.

2. A rotating item may be susceptible to seizure and

fracture.

51
3. A semiconductor device may be susceptible to fracture

(of leads or case) and to thermal failure.

B. Estimate the level of severity of each engineering failure

mode.

IV. Identify and list the driving forces to which the item is subjected in its environment.

V. Identify and list the failure mechanisms and sub-mechanisms

which could lead to a given engineering failure mode in the use en- vironment under the identified driving forces.

A. Determine the probable failure mechanisms and

sub-mechanisms.

VI. List the failure sources and sub-sources which could lead to the

probable failure mechanisms or to the engineering failure mode.

A. Determine the probable failure sources and sub-sources.

VII. Determine the most probable cause(s) of failure for each engineering failure mode.

VIII. Estimate the overall probability of each engineering failure

mode.

IX. Determine if secondary engineering failure modes are possible

and if their severity requires further analysis.

A. If such analysis is required, repeat steps III through VIII

for the secondary engineering failure modes.

X. Determine the necessary actions required to prevent those engineering failure modes which are intolerable.

In the performance of the above failure analysis scheme, the construction of a failure tree may be of use. Such a construction also may be

of use in presenting in a graphical format the results of a potential

failure analysis. The failure tree itself is a graphical construction, similar to a decision tree^*^ that illustrates failure mechanisms, sub-mechanisms, sources, sub-sources, and their relationship to one another. Driving forces may be shown below failure mechanisms and

sub-mechanisms and other notations may be contained on the tree. Although the discussion of the analysis methods contained herein begins

or ends with an identified engineering failure mode not a failure effect, the logical completion of a potential failure analysis will often reouire consideration of failure effects. Nevertheless, in this

regard, it often may be preferable to consider the functional failure

mode which corresponds to an engineering failure mode and perform a

52
FUNCTIONAL CHARACTERISTICS"

FUNCTIONAL

SOURCESSOURCESIDENTIFY AND DESCRIBE THE

ITEM

IDENTIFY AND DESCRIBE THE

USE ENVIRONMENT

IDENTIFY AND

LIST THE POTENTIAL ENG. FAILURE MODES V

ESTIMATE

THE PROBABILITIES

PHYSICAL

'CHARACTERISTICS

.PHYSICAL

-MECHANICAL

^CHEMICAL

MECHANISMS

.DRIVING

FORCES

-MECHANISMS

DRIVING

FORCES

LEVEL

>

SPECIFICITYSEVERITYMATERIALv

DESIGN'

1 DETERMINE

THE PROBABLE

FAILURE PROCESS (ES)

ESTIMATE THE PROBABILITY

OF THE ENG. FAILURE f10D£(S)

ESTIMATE THE PROBABI LITY

OF THE FUNCT, FAILURE nODE(S)

MAKE RECOMMENDATIONS

FOR MODIFICATION

• CAUSE

•MAINTENANCE

MANUFACTURE

FIGURE 3: FMCA POTENTIAL FAILURE ANALYSIS OUTLINE.

Failure Mode and Effect Analysis in order to determine the failure effect. It will often prove necessary and difficult to analyze the re- lationship of enaineerina failure modes and a failure effect in order

to determine the level of each engineering failure mode or potential

enqineerina failure mode. When functional failure modes and effects

are most important to the analysis, then the suggested analysis technique would be Failure Mode and Effect Analysis. Also see Fiqure 4.

In addition to the performance of a potential failure analysis, the

FMCA methodology is amenable to the performance of a failure analysis

of an item that has actually failed in service. It may aid the

analyst in logically and systematically disassembling the failure

53
c

u

3

C

3 ^

U. CO 3- u.

JCu

O LU

U. CO

CO ~

O ro o

LL Lu br54
process into its most probable parts. When only the cause of failure

is to be determined, then it is only necessary to examine the specific

chain of events which led to an individual failure. When a failure is

to be more fully analyzed, however, these individual events must be

sorted and defined for individual analysis and interactions must be

considered. The following, then, is an outline of a failure analysis

within the overall framework of Failure Mechanism and Cause Analysis

(also see Figure 5):

FMCA: FAILURE ANALYSIS OUTLINE

I. Examine the overall failure.

A. Examine the failed item.

B. Examine the history of the failed item.

C. Determine the designed and actual environment of item use.

II. Identify the engineering failure mode(s).

A. Examples.

1. Fracture.

2. Seizure.

3. Elastic failure.

4. Plastic failure.

5. Thermal failure.

III. Identify the potential failure mechanisms, sub-mechanisms, and

driving forces which could lead to the identified engineering failure

mode(s)

.

A. Estimate the probability of each failure mechanism and submechanism.

B. Identify the probable failure mechanisms and driving forces.

IV. Identify the potential failure sources and sub-sources.

A. Estimate the probability of each failure source and

sub-source.

B. Identifv the probable failure sources and sub-sources.

55
V. Determine the severity of the enqineerinq failure mode(s).

VI. Determine the most probable mechanisms, sub-mechanisms, sources,

and sub-sources, as well as the most probable drivinq forces which

could lead to the identified enqineerinq failure mode(s).

A. From the above information determine the most probable

failure process(es).

VII. Estimate the probability of the enqineerinq failure mode(s) and

the functional failure mode.

VIII. Determine the level of the enqineerinq failure mode(s).

A. Primary failures.

B. Secondary failures.

IX. Determine the cause(s) of failure.

A. Primary failures will have mechanisms or sources as causes. Sub-mechanisms and sub-sources may, of course, also be causes.

B. Secondary failures will have a primary failure as a cause.

X. Determine if the enaineerinq failure modes are qeneric or specific.

A. Examples.

1. Primary fatique failures are usually qeneric.

2. A seizure caused by a unique instance in which lubrication was not performed is a specific failure.

3. A seizure caused by the failure of a specified lubricant is a qeneric failure.

4. The plastic failure of a link caused by a wheels-up

landinq is a specific failure.

XI. If the analysis calls for it, assess various methods for preventinq the same or similar enqineerinq failure modes in the future.

A. Often secondary failures will require no action, since they

may be prevented by prevent inq the primary failure. Of course, a more reliable system may result if a modification is made to independently

prevent a secondary failure.

B. The above often also may apply to specific failures.

56
C. Modifications which may be made to prevent failures include

modifications in:

1. Desiqn,

2. Material,

3. Maintenance, and

4. Manufacture.

D. Recommendations for failure prevention should be accom- plished by sufficient analysis and justification to show the efficacy

of the proposed change.

A partial failure tree constructed to illustrate the technique for the

structural failure of aircraft by fracture is illustrated in an addendum. This failure tree is not intended to he rigorously complete or definitive, but rather to be sufficiently detailed and inclusive so that the requisite parts of the failure tree are illustrated. In addition, the tree has been constructed such that it may be used as an example both overall for other failure trees and in detail for structural fatigue fractures. An attempt has been made to be as technically correct and precise as is possible in the construction of a general failure tree.

4.0 SUMMARY

The performance of failure analysis - either of items that have failed

in service or for the purpose of determining the ways an item could

fail in service - is an intearal part of both product performance and

safety analysis as well as product design and redesign. Although each

product and each product failure are unique, there are many facets of

commonality respectively among them. In particular, the inductive or deductive sequence of a failure analysis or poential failure analysis

is not greatly product or event specific. Many considerations, such

as usage environment and careful item description including secondary

functions, should be included in any failure analysis of a product.

Finally, due to the fact that failure analyses are performed by multidisciplinary means, it is extremely important that precise language be

used to describe failure or potential failure and to convey the information and conclusions obtained during the analysis. This may require

an almost forensic attention to the semantic details of a failure ana- lysis report.

The procedures presented herein are intended to aid in the conducting

and reporting of a failure analysis and have been devised to achieve

the above analytical requirements. In addition, the FMCA methodology

57
is intended to be an integral part of a larger methodology that ex- amines the kinetics of identified failure processes such that an estimate may be made of failure probabilities for purposes of lifetime

estimation or maintenance scheduling.

5.0 ACKNOWLEDGEMENT

The Maintenance Intervals for Aircraft Structures Methodology development was conducted by Vought Corporation for the Naval Air Systems

Command, Washington, DC under CMES Task LTV-79-12. The program con- tract monitor was Mr. George Donovan, Naval Air Systems Command, Maintenance Policy and Engineering Division, Aircraft Structures and

Equipment Branch, AIR 4114.

EXAMINE THE OVERALL

FAILURE

SOURCES

SOURCESIDENTIFY

THE ENG. FAILURE MODE V

ESTIMATE THE PROBABILITIES

DETERMINE

THE PROBABLE

FAILURE PROCESS(ES)

.MECHANISMS

DRIVING

' FORCES

-MECHANISMS

DRIVING

' FORCES

CAUSE MATERIAL.

DESIGN'

7

DETERMINE THE PROBABILITY OF THE ENG. FAILURE MODE(S)

7

DETERMINE THE PROBABILITY OF THE FUNCT. FAILURE MODE

7

MAKE RECOMMENDATIONS

FOR MODIFICATION

-MAINTENANCE

'MANUFACTURE

FIGURE 5: FMCA FAILURE ANALYSIS OUTLINE.

58
6.0 REFERENCES

1. Shawver, W. R., L. E. Sloter, J. T. Stracener, and D. J. White,

"Determination of Aircraft Structural Inspection Intervals," 1981

Proc. Ann. Reliability and Maintainability Symp., 1981, pp. 452-458.

2. Lambert, H. E., "Systems Safety Analysis and Fault Tree Analysis," Lawrence Livermore Laboratory, 1973, UCID-16238.

3. "Procedures for performing a Failure Mode and Effect Analysis

for Shipboard Equipment", MIL-STD-1629(SHIPS)

.

4. "Fault/Failure Analysis Procedure", ARP 926A; SAE Aerospace Recommended Practice, Society of Automotive Engineers, Inc., 1971.

5. "Maintenance Plan Analysis for Aircraft and Ground Support

Equipment," MIL-STD-2080(AS)

.

6. "Analytical Maintenance Program Guide for the Application of Reliability Centered Maintenance for Naval Aircraft," NAVAIR-00-25-400,

Naval Air Systems Command.

ADDENDUM: FAILURE MECHANISM AND CAUSE ANALYSIS-FAILURE TREE

KEY

P Analytical Aspects of Failure Mechanisms

1. Deterministic

2. Probabilistic

3. Potentially either deterministic or probabilistic

Q Analytical Aspects of Failure Sources

1. Deterministic

2. Probabilistic

3. Potentially either deterministic or probabilistic

I Locations at which Inspection May Alter or Arrest Path or Process

D Locations at which Design May Have a Beneficial Effect

1. Structural design

2. Material selection or design

M Location at which Fabrication May Have an Effect (Fabrication

Refers to Assembly and any Reassembly)

R Locations at which Maintenance May have a Beneficial Effect

59
FAILURE MECHANISM AND CAUSE ANALYSIS; FAILURE TREE - STRUCTURAL FAILURE

FMCA

PAE D

P.3,D.LD.2AR

CORROSinN- FATI6UE CRACK GROWTH

STATIC LOADS

EXISTING CRACK-LIKE FLAW - CI

CORROSION - FATIGUE CRACK

INITIATION - Dl

CHEMISTRY

CYCLIC

LOADS

GUST

LOADS

MANEUVER

LOADS

VIBRO- ACOUSTICAL

LOADS

THERMAL

CYCLING

LOADS

LANDING

LOADS

CATAPULT

LOADS

60
MECHANICAL SYSTEMS INTEGRITY MANAGEMENT

Robert L. Kincaid

Spectron Caribe, Inc.

Caparra Heights, Puerto Rico 00921

William S. Kincaid

Spectron Caribe, Inc.

Caparra Heights, Puerto Rico 00921

Abstract: As mechanical systems have become more sophisticated and dependence upon them more absolute, increasingly

complex problems have been generated for both maintenance

and management. Maintenance of these systems no longer can

be treated as an isolated technical activity, but must be a

vital, integral part of the entire industrial management

function. Modern analytical techniques are available for

determining mechanical and lubricant integrity. When this

information is organized and systematized into a program

for the management of maintenance, it can provide constantly

updated information as to required maintenance action as

well as benchmarks against which to measure the effectiveness of maintenance operations, establish trends and evaluations for projections to the future, and provide an almost

unlimited source of management information as related to

the mechanical systems monitored.

Key words: Atomic emission spectroscopy; cost-effective;

data processing; infrared spectrophotometry; integrated

reporting system; maintenance management; mechanical and

lubricant integrity; MIR (multiple internal reflectance)

;

on-condition maintenance; oscillation viscometry.

We live in an age of technology explosion. Our society is

dependent upon mechanization: the mechanization of industry, transportation, construction, power generation,

agriculture, natural resource extraction and processing,

and national defense.

The increasing sophistication of mechanical systems has

been accompanied by an increase in the complexity of problems faced in maintenance management. Each piece of equipment today represents a greater part of total productive

capacity than ever before. As a consequence, repair and

61
down-time costs have soared. These costs are further magnified by the shortage of adequately trained mechanics and

technicians, the time and distance involved in obtaining

repair parts, and in many cases the problem of securing

foreign exchange for purchase of parts and service.

Industry can no longer afford outdated maintenance programs.

Today's problems are forcing the management of maintenance

into its proper perspective. Maintenance cannot be treated

as an isolated technical activity, but must become a vital,

integral part of the entire industrial management function.

The responsibility of management is to promote the greatest

efficiency of operations possible, and a maintenance program

must therefore be judged according to the following criteria : For maintenance efficiency, it must reduce breakdowns and unnecessary repairs.

For operations efficiency, it must improve the

availability and reliability of production

equipment

For fiscal efficiency, it must reduce expenditures and provide cost effectiveness.

As a discipline, maintenance management has lagged far

behind the pace of modern industrial technology, and a major reason for this has been the lack of timely and

appropriate information with which to manage. When exact

knowledge of mechanical condition is available, neither

time, money nor effort need be expended in unnecessary

maintenance activity, and these assets can be concentrated

exclusively where the need exists. This is the fundamental

concept of on-condition maintenance.

Since 1961, the efforts of SPECTRON CARIBE, INC. have

focused on the development of programs to bridge the gap

between current technology and maintenance management. We

refer to these programs as Mechanical Systems Integrity

Management. They are based on continuous monitoring of

equipment condition and generate the information needed for

effective on-condition maintenance.

The mechanical integrity of a lubricated system is both

reflected in and influenced by its lubricant. Monitoring

a lubricant can therefore reveal a system's condition.

Spectron has applied advanced analytical techniques to

accomplish this.

62
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A system's moving components are comprised of different

metals and alloys, which are deposited as submicroscopic

wear particles in the oil circulating around them. Abnormal

wear conditions result in abnormal concentrations of these

metals, which, through atomic emission spectroscopy, can be

detected and measured far enough in advance of component

failure that corrective action can be taken.

Infrared spectrophotometry, another modern and highly

effective analytical technique, determines the chemical

composition and contamination level of a used oil by direct

comparison with the new oil. This qualitative/quantitative

analysis of the differences allows a lubricant to remain in

use until it is no longer in "like-new" condition.

Common problems revealed by these analyses are: contamination of lubricants with dirt, fuel, water, and entrained

gases; degradation through nitration, additive depletion,

and oxidation-polymerization; and abnormal equipment wear.

Conventional maintenance scheduling is based strictly on

accumulated operating time. As manufacturers have no control over the conditions to which their equipment is subjected, their service interval recommendations tend to be

very conservative. This unavoidably results in overmaintenance. In contrast, a monitoring program is able to

distinguish between equipment which genuinely requires

attention and that which does not, and allows equipment

and lubricants to safely remain in operation until a need

for service is identified. The potential savings resulting

from on-condition maintenance are enormous. The average

extension of useful lubricant life is generally sufficient

in itself to make a complete monitoring program cost-effective.

The full benefit of a monitoring program can only be

realized when the information it generates, is properly

organized and applied. Spectron offers an integrated

reporting system which provides a client information at

three levels: individual unit reports communicate problems

and corrective action to shop personnel; sample batch

reports summarize results for maintenance supervisors and

focus administrative attention; monthly reports evaluate

aggregate equipment condition and trends for management.

Individual unit reports combine analytical results and

history to indicate mechanical conditions. Specific maintenance recommendations are furnished where problems are

detected, and the equipment is classified as being either

66
HONITORINC PROGRAM SRVINCS

>0ix ZBesE soex ^eex seek bmx pobx eem 9»x

NET INTtSVBL EXTENStOM

PRRnHETERS FOR DADE CO. HTA CORCH ENCINES(I

OIL CHANGE COST= *40

ORIGINfiL OIL CHRNGE INTERVfiL= 6000 MIL€S

CHfiRGE PER OIL SflMPLE= »12

SAMPLING INTERVAL= 6000 MILES

This plot projects the annual savings possible through

extension of service intervals. In the case shown, it can be seen that an extension of only 40% makes the

program cost-effective. Projected yearly savings are displayed on these curves as a function of net service

interval extension. Each curve represents the savings

associated with a particular rate of equipment usage.

67
critical (in need of immediate attention) , borderline

(highlighted for closer scrutiny or minor corrective

action) , or normal.

Batch reports summarize the results of each batch of

samples. As well, they provide the maintenance manager

with an update of equipment status, required maintenance

action, and equipment due for sampling.

Monthly evaluations provide a management-oriented overview

of equipment condition and program control, emphasizing

trends and identifying problem areas.

The information generated by Mechanical Systems Integrity

Management can serve as a basis for a wide variety of

special studies as well, such as comparative evaluations

of equipment, lubricants, components, and maintenance and

operational procedures.

The storage of all data on discs makes it available for special studies, comparisons and statistics.

68
The central processing unit is composed of a IHewlett- Pacltard 9825 minicomputer with perpheral disc drives and printer. All reports are generated by this unit with the exception of the graphics in the Monthly Evaluation Report which are generated by a Hewlett-Packard 9845

Modern analytical tools and data processing can provide the

information vital to successful maintenance management. Bymonitoring equipment condition, problems are detected before they develop, and the role of maintenance becomes pre- ventive rather than remedial . Disassembly repairs shrink

to a small fraction of total maintenance effort, being replaced by minor action to correct abnormalities before they

can cause mechanical damage. To put this in perspective,

Spectron's experience is that while as many as 20% of all

samples analyzed reveal abnormalities requiring minor

corrective action, less than 1% of all monitored components

require disassembly inspections and repair. On-condition

maintenance, through Mechanical Systems Integrity Management, makes the best possible use of available resources.

And thus, the modern technology explosion comes full-circle.

It has created new and sophisticated problems for industrial

management, and yet has also provided the means not only of

resolving those very problems, but of establishing a sound

basis for technology management.

69
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70
FIELD ?..XKTT(.Kir:G CF KC-IvIA CHINES - A oYSTSM APPRCACii

X-E Johansson

Linkoping Institute of Technology

I TP, 3-581 83 Linkoping, Sweden

Abstract: In Sweden unmanned factories have become a

reality. Condition monitoring (CK) of HC-machines becomes a

vital concern in this type of factory and it is important

that the monitoring system be integrated into the normal

maintenance system of a factory. This paper addresses the

following points:

• ^Vhich machine components need CK

• .'Jhich system should be used for Ch

• Design of alarm systems both for a single machine

and for an entire factory

The investigations which have been carried out show that

each machine is unique with regard to its specific alarm

limits, set-points, etc. The measurements used in condition

monitoring are not necessarily absolute since interest is

focused on the changes that occur over a life span, iiv'hen monitoring an entire factory one should avoid building the

system around one centralized master computer since each

machine must be accessible to separate monitoring independent of a central computer.

Key words: Administrative system for maintenance; automatic

condition monitoring; condition monitoring module; microcomputer .

GSMEHAL AECUT THE ?.':AINT£NAITCE FUNCTION

How Twaintenance Work is Done Today in the Mechanical Industry

In most mechanical industries the major emphasis has been

on corrective maintenance rather than preventive maintenance. It is only during the last three or four years that

preventive maintenance has noticeably increased.

Data processing systems, which are used by many companies,

are only used for following the costs of the maintenance

departm^ent. In Sweden the cost for industrial equipment

maintenance is about 50/^ of the yearly new investment volume.

71
Administrative systems for maintenance with rond lists and

different follow-up systems are increasing in use. There is

no special way to organize the maintenance department which

is found to be the best solution. Both centralized and

decentralized maintenance and a mixture of both are used

with varying degrees of success.

Different Faults and Their Distribution

The predominant failure mode is wear, but there can be many

other reasons such as: operator mistake, wrong voltage

from the line, etc. C ne can classify the faults into

different groups along with the repair time and time for

trouble shooting (table 1).

Table 1

Type of system Trouble shooting time Ftepair time

El.

faults

Electronic

Electrical

Yech. Hydraulic

faults r/.'echanical

90%

60/o

10%

10fo

30;/.

90%

From table 1, it can be seen that mechanical faults take

much more time to repair, but are easier to locate than the

electrical faults.

A typical machine in the mechanical industry is an NG-Lathe

and if we are looking at the frequency distribution of the

length of the failure we will have the following figure.

CO

LU

oc

5-

I OF THE FAILUR. = 385=100%

1

-Trl-r- 1 1 1 r till' \ f\ 1 10 15

LENGTH OF THE FAILURES (h)

Fig. 1. Frequency distribution of the length of failures for

a NC- Lathe

72
The total time for repair is almost the same for mechanical

and electrical faults, hut elsctrical faults predorninate.

In fig. 1, almost all faults with a length of more than 5

hours are mechanical faults.

Administrative System for Maintenance

In many plants administrative systems are used to get a

"better follov/-up of maintenance costs. If the maintenance

people need to have a better follov/-up system they must have

their own "maintenance computer." It is true that the cost

is a very imjporta.nt parameter, but there are many other

imiportant parameters such as ?.'.TTR ( P.-ean Time To Repair) and

TI^F (Mean Time '^etween Failure).

u'lJhen the company is going to buy new equipment it is of

great importance for the maintenance people to be able to

influence the selection. This influence can easily be

applied if they have the right statistics from the administrative system.

REQUIRSMEIIT :3PECIFICATICK FCR Ci.; CF A r:C-i.!AGKI

The following demands should be met by a systemi which

performs GIV of a HC-machine:

The Gi."-system should be based on a real time method.

The system must have high reliability.

The system m^ust be able to give early warning of incipient

failure, thus permitting service action to be taken when

no production is planned.

When a breakdown has occurred, the system should be able

to rapidly identify and locate the failure.

The alarms must be graded into different levels depending

on the nature of the breakdown. iA/hen an alarmi is urgent

the machine must be stopped by the system.

The alarms should be easily recognized by the operator as

well as by the maintenance personnel.

The CM-system should be set up in such a manner that it is

possible to connect it to a master-computer.

In addition to the above points which apply to a single

machine the following additional demands in CI" of a group of

machines m;ust be met :

73
Alarms should be displayed at the machine as well as at a

central maintenance department.

Every separate G?.I-Eystera monitoring a particular machine

must function independently of the others.

The central system for collecting data should not influence

the separate Cr.l-systems

The error m.essages which- are obtained must "be stored in

the system so that a malfunction can be corrected when

maintenance personnel are available.

CJEIIERAL DESGRlPTICrf OF THE [/lAINTENANCE SYSTEM

IVHSRS A FGCRCCCr\TI^UTER IS USED

The total maintenance system consists of two parts:

a) Automatic Condition Ivlonitoring System (AGIvS)

b) Administrative system.

Fost of the v;ork in this project has been part a), but later

on, part b) v;ill be more thoroughly analyzed. The maintenance department is often one of many sub-departments in the

total organization with communications in all directions.

Tn order to build up an effective maintenance system one

m.ust put the maintenance department in the center and build

the system up from this point.

Reasons to Introduce AGMS

a) Reduce dov/ntime for the machines.

b) Key/ machines are getting more complex; therefore they

must have better monitoring.

c) Production will be unmanned, especially in the night;

therefore there is a need for better condition monitoring.

d) ;/ith an effective AGIvU the maintenance work will be more

preventive than corrective - this means a more continuous

working load.

e) To influence the nachine manufacturers to design their

machines for proper accesss for the installation of suitable transducers.

f) Give better data to the production-planning department.

g) The total machine service life will increase.

74
How to Build up an ACLlo?

To be at'le to handle all problems in this area it was

necessary to divide the system into different levels as

shown in figure 2. VJith an AGIS one can stop at level 1 and

2 if one only wants to monitor a single ma.chine. The

systems which are used today are using only one coiriputer to

monitor all the m.achines; this means that level 2 is missing

in these systems.

Level 2 is very important because:

a) If the maintenance computer has a failure, all machines

are unattended if their computer has the direct monitoring

of the inachines . b) If only one machine is monitored v/ith kClIB, it would be

too expensive to use a maintenance computer as shown in

figure 3"

A condition A'onitoring I.lodule (Cl.-module) for a NG-Lathe is

shown in figure k.

The following measurements may be of interest:

a) By measuring the current to the feed driver the following

ca.n be noticed:

1) Lubrication is finished.

2) The slide goes too slow, possibly because a chip

maybe between the slide and the sliding plane.

3) The condition of the motor.

b) r^Tain voltage - this is very important to know before

looking for faults.

c) Numbers of movem,ents in the Z- and X-slide. By indicating

the number of movements one will have a value of the wear

on the slides. (This is verified by Tekn. lie L-E Tlelson,

KTH, 3tockholm).

Kow a total maintenance system can be applied in a normal

industry can be seen in figure 2.

The integration between an AGRC3 and an administrative system

for maintenance can be seen in figure 5-

75
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76
LEVEL 1

LEVEL 5

TRANSDUCES + WARNING DEVICE

CM-MODULE

MICROCOMPUTER OR CM-UNIT

A*

MAINTENANCE-COMPUTER

(minicomputer ALFA LSl)

DATABANK

BIG-COMPUTER

MONITORING

DIRECT ON

RESPECTIVELY

MACHINE

CENTRAL

V MAINTENANCE

/ DEPARTMENT

COMMUNICATION

y WITH OTHER UNITS

J

INSIDE THE COMPANY

Fig. 3 Different levels in the maintenance system

77
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78
Administrative system - function

FAULT OCCUR OR

IS PREDICTED

CAtL FOR KAIN- TENANCE-WOR

a) cm-system

gives a signal

b) OPERATOR MAKES

A TELEPHONE ORDER

C) WRITTEN

ORDER

EV. MORE COMP- LETE ORDE!^

ORDERRECEPTION

PREPARATION

PLANNING

WORK IS DONE

DATA WHICH ARE SEND

TO A CENTRAL COMPUTER SYSTEM

MAINTENANCE

COMPUTER

FUNDAMENTAL DATA ARE LOA- | DED INTO THE COMPUTER I SYSTEM: CODEMR, ACCOUNT, DELIVERY TIME

THE PREPARATION MAN WORKS I WITH i STORAGEREG. ADDITIONALhMACHINEREG. DATA ARE I INDIVIDUALREG. LOADED INT* THE SYSTEM!

SUDDE BREAK NLY

JDOWNS

RONDLIST

STORAGE

MACHINEREG,

NORMAL

WORK

THE JOBS

ARE LISTED

OUT DIRECT

IF THEY CAN

BE DONE WITHIN X HOUR

BIG MAINTENANCE WORK

PRE VET I VE ' MAINTENANCE

FOREMEN IN EACH DEPT, TAKE THESE PREPARED

WORKS EVERY MORNING

ALL WORKS

ARE STORED

IN THE COM PUTER SYS- TEM WHICH

WILL GIVE

DOWNTly;E, RESOURCES

ORDER FOR SPARE PARTS

ALL REGISTRATION IS DONE IN REEL TIME

FOR EX. MTRL, DOWNTIME, SPARE PARTS |

ECONOMIC

-SALARY PURCHASE

Fig. 5. Administrative maintenance system

79
Automatic Condition Konitoring System a Specification

The automatic condition monitoring system includes all

functions from transducers located on the different machines

to the data processing which is done in the maintenance

computer. The different levels which will occur in the

total system are shown in figures 2 and 3«

Level 1

On each machine the monitoring is done with analog and

div^ital transducers which are placed on different parts of

the machine.

A warning unit must also be placed on each machine and the

warning unit must give some sort of signal when any fault

occurs. This alarm signal will give information about where

the fault has occurred so that the machine operator can take

corrective measures. The warning unit must also be supplied

with som.e form of equipment from which can be read the downtime and the reason for the break-down. These data will be

used by both the production and the maintenance departments.

Level 2

Condition monitoring module

From figure 2 it, can be seen that the CK-module can be any

of three different configurations:

1. Cr'-computer (microcomputer).

2. GIv'-module is already built into the machine computer.

3. Cn-unit.

The Civi-module alone must do the monitoring of its respective

machine even if the maintenance-computer should have a break

down

Continuous condition monitoring specifies that the following

functions must be in the CK-module.

data-logging of measurement test results from different

transducers, digital and analog.

comparison of actual measurement test results toward a

given limit value where both an upper and a lower lim.it

can exist.

calculation of complex values from different measurement

test results, i.e., median value.

80
calculation of temp, derivative.

control of visual alarm when malfunction has occurred,

possibility of reading actual value for each analog signalpossibility, from outside via maintenance-computer, to be

able to control the GTvl-module, so that one can control a

certain parameter and transform this measuremient test

result to the maintenance-computer for further treatment.

possibility to use AND and OR functions.

Level 3

Maintenance- computer

One function of the minicomputer which is placed in the

maintenance department is to v/ork as a data-concentrator in

the automatic condition-monitoring system so that the

maintenance staff has the different machines under control

at all times

.

V/hen there is an alarm that some fault has occurred on a

machine, this will be recorded both on a typewriter and on

a viewing screen, both of which are connected to the minicomputer.

The alarm which is received from the m.inicomputer normally

includes enough information so that there is no need for

more trouble shooting - preparation of the repair work can

start immediately. iVhen the work is finished acknowledgement must be entered into the respective machine *s alarm

unit so that the downtime will be registered.

From figure 5 it can be seen how the administrative system

for maintenance works - it can also be seen how the GMsystemx is connected at point a) and supplies data to the

administrative system.

To make the preparation of maintenance work easier, the

administrative system specifies that the planning personnel

have access to the spare parts store, machine - and individual register, in real time. These data can be stored in

different ways

.

a) Centrally stored in the companies' databank-.

b) Locally stored on a disc storage in the maintenance

department

.

81
The machine register means, for example, a complete machine

tool; on the other hand, the individual register includes

the different parts, such as, for example, an electrical

motor of a certain manufacturer.

Level ^ Databank

All data which are not needed for calculations in real time

are stored in a central databank. The data which are stored

here are as per the following:

data from all machines

data from, machine details

all spare parts are registered

Machine reg. - - Individual reg.

.3pare part reg.

Level 5

Communication v/ith other units in the company

From the maintenance department one needs ccmmuni cations

v/ith other units in the company and this can be done via the

company's main computer. Other units in the company sometimes need data from the maintenance departm.ent, for example:

a) Dovmtime - production department

b) Repair times - economics department

c) Reliability - department for buying new m.achines

DESGRTPTICI: OF TH2 MICRCCOrffUTSR USED IK CM FOR A ^!C-LATHE

The system is built around the microcomputer Intel 8080 and

the configuration is presented in figure 6 below.

o

Transducers NC-Lathe <+-S-cuc

1—

1

ij-dator

MY-15

Minicomputer

Alpha LSI

Measure Digital Fig. 6. System

signals signals configuration

82
The signals from the transducers on the NC-Lathe are of two

kinds

:

a) analog signals

b) on/off signals

The transducer signals are often obscured by noise such as:

thyristor con-rollers on the KC-Lathe (high frequency),

line frequency (50 Kz)

.

contact-bounces

.

different ground potential in the NC-Lathe 's and the microcomputer's grounding system.

The analog signals are electrical voltages with differing

levels from 1 mV - 30 V DC

.

The computer only accepts digital signals of the type TTL in

word length of eight bytes.

To be able to handle the signals in the microcomputer the

signals must be transformed through the interface, and it

must fulfil the following demands.

eliminate high frequency noise and noise from the line,

eliminate contact-bounces.

separate the NG-Lathe's and the microcomputer's grounding

system.

give suitable signal level for transformation,

give eight bytes TTL- data out.

The interface for AKALC3 signals is solved by using a

differential amplifier, analog multiplexer and A/D converter

as can be seen in figure ?•

The address is given from r.iy-15 by a plug-in-card . This

card also calls "and transforms data to a main computer (TTLsignals )

.

The interface for the CN/CFF SIGNALS is solved by using

optocouplers and the interface is shown in figure 8.

83
Analog channel nr

differential

ampl if ier

Fig. 7. Interface analog signals

Analog multiplexer

IN

1

2

16

analog

MUX

OUT

Address from MY-15

Figure 8.

84
+24 V o

o

i ^

to the

computer

O

transducer

on the NCLathe

transient

protection

filter backvoltage

protection

optocouple

Fig. 9. Interface on/off signals

^h e optoc o ux^ler gives ;;i;alvanic isolation l:etween the two

/rrounding systemG {?J4- V resp 5^^)' ground potential

differences of hundreds of volts can be allowed.

The filter takes away the contact-hounces hut gives at the

same time a pulse with growing flank. For this reason a Schmitt trigger rrust be used on the 5-volt side to give the

TTL-logic a strong enough pulse.

The signal levels fro'^; both analog and digital transducers

vary frorn 2 tt.V - 220 V and therefore one must have special

circuits to get suitable levels to the microcomputer.

The different parameters which are controlled are presented

in figure ^.

"[3y introducing an automatic condition monitoring system in

the shop, the maintenance of the equipm.ent will be much,

m^ore effective and the downtime will decrease. To be

prepared for unmanned production in the future it is of

great importance that the monitoring of the production

equipment be fully automated. Zuoh a system is presented

in this paper and it is shown how the monitoring system is

integrated to an administrative system for maintenance.

ummary

85
A MAINTENANCE PLAN FOR A BATCH CHEMICAL PLANT

G. N. D. Seddon and A. Kelly

University of Manchester

Manchester M139PL, United Kingdom

Abstract: Many maintenance departments find themselves in

one of two situations: either they are "fire-fighting", or

they are over maintaining.

This paper presents a method of establishing a maintenance

plan to overcome this problem. A dynamic model of the

maintenance/production system is proposed as a background

against which a systematic method for establishing a maintenance plan is developed. The method proposed uses a "top

down" approach to analyse the maintenance requirements of a

plant. Once determined, the requirements are synthesized

into a maintenance plan. An example of the method as

applied to a batch chemical plant is then given.

Key words: Preventive maintenance plan; maintenance effectiveness; cost effectiveness; programmed inspections.

INTRODUCTION

If a maintenance manager is to establish the best maintenance strategy for his company, he must follow the same

rules as for any other industrial management problem. He

needs to understand the maintenance characteristics of the

plant, the relationship between maintenance and production

and what the function of the maintenance department really

is. In other words, he needs to be familiar with his sphere

of responsibility, to accept that the maintenance production

system is dynamic and to understand how such a system works.

From this the maintenance objective can be defined and then,

and only then, can the maintenance plan, organization and

control be established. This paper is concerned with the

maintenance plan. An attempt will be made to lay down a

systematic method of establishing such a plan for a large

continuously operating process plant.

86
THE production/maintenance SYSTEM - A DYNAMIC MODEL

In simple terras the maintenance plan is concerned with

matching the best combination of maintenance procedures

(Figure 1) to the particular spectrum of plant items

(Figure 2). In order to do this, and also to look in detail

at some of the basic ideas of maintenance management, a

dynamic model of a typical maintenance-production system

will be examined. The function of a plant is to manufacture

a product for some given period thus providing a planned

output. This output will depend upon the sales demand and

its long term total can be forecast, even though there may

be short term fluctuations, as with a power station for

example. Thus, the long term production plan will determine

the working pattern and availability requirements of the

plant (e.g., 2 shifts/day, 6 days/week, 48 weeks/year at an

average availability level of, say, 90%) . Obviously this

could change in the short term. The plant or some part of

it may be in one of the following states (Figure 3)»

A - in production and only running maintenance can be

carried out;

B - not wanted for production (e.g., during night shift, or

during feedstock shortage) and available for maintenance

without production loss. This is the available-formaintenance "window" where "stopwork" will not incur

production loss;

C - taken out of production for scheduled (preventive and

corrective) maintenance. Major stopwork can be carried

out but there is production loss;

D - failed unexpectedly and undergoing corrective maintenance under breakdown conditions. Production is being

lost and maintenance is difficult to plan;

E - failed, but due to shortage of maintenance resources, is

•waiting for maintenance'. This is the worst state of

all.

The plant availability is, therefore,

T A + B M.T.B.F.

A = or or

T, +T A+B+C+D+E M.T.B.F. + M.T.F.M down up

which is one measure of the effectiveness of the maintenance

department. Caution is needed when using this definition of

availability since:

a) it is often difficult to cost unavailability,

b) the cause of failure may not be due to maintenance,

c) the definition assumes only two levels of performance.

87
THE MAINTENANCE FUNCTION AND OBJECTIVE

It can be considered that the function of maintenance

(Figure 3) is to use resources (men, spares and tools) to

replace, repair, adjust or modify the parts of a plant to

enable it to operate at a specified availability and perfornh

ance, in a specified manner over a specified time. Maintenance then affects company profitability through its influence on availability, i.e., plant output; through the cost

of the maintenance resources used; and through its influence

on the life of the plant. Although this is clear, it is

still difficult to generalize about the maintenance objective. However, what can be stated is that the objective

should be closely linked to the production plan (Figure ^)

In short, the maintenance objective is to provide production with the required long and short term plant availability

needed to meet the planned production at minimum cost.

THE MAINTENANCE PLAN

In simple terms the maintenance plan can be considered as

being concerned with directing the maintenance resources in

the best way (Figure 3) in order to achieve the planned output (1). Broadly speaking, the options are: to carry out

the maintenance before plant failure (some combination of

procedure 1 to 3i Figure 1); to allow the plant to fail and

then carry out corrective maintenance (procedure ^) ; to

eliminate the cause of maintenance (procedure 5)' The

initial choice is between procedures 1-4, whilst procedure

5 becomes important as plant operating experience is accumulated. It is becoming increasingly advantageous, because of

the high cost of unavailability, to direct resources towards

carrying out planned maintenance in states A, B, or C and,

where possible, to use condition-based maintenance (CBM)

procedures in A and/or B in order to schedule the resultant

maintenance in either B and/or C. This can only be effective if there is close liaison between maintenance and

production to establish the scheduling of B and the best

time for C. The minor failures, not causing plant (or unit)

failure (known jobs), can be handled in a similar way.

Carrying out maintenance in this fashion has a number of

advantages since the maintenance resources can be planned

and scheduled, a high resource utilization can be achieved;

it is easier to achieve the required plant availability;

the effect of unavailability can often be minimized; plant

is mostly prevented from deteriorating beyond the "resource

elbow" (2) which makes for better plant condition and a

longer useful life. Conversely, if the strategy is to

operate the plant to failure, its condition will rapidly

88
degenerate beyond the resource elbow (1). This will lead to

a difficult planning problem, high unavailability, failures

often at the worst time, poor plant condition and a short

useful life. Obviously, a strategy based on some form of

Planned Maintenance would appear to be essential. In

practice, the difficulty is to determine the best plan for a

particular plant, taking into consideration the everchanging nature of the production situation, the consequent

priorities and limitations of maintenance resources. It is

worthwhile repeating that the maintenance plan must be based

on the real situation and be designed to respond to the

dynamics of production demand. In addition, the organization of the production and maintenance departments must be

such that the importance of adhering to the maintenance plan

is appreciated by both, and the communication between them

must be sufficiently good to enable an effective and, where

necessary, flexible maintenance schedule to be operated.

A SYSTEMATIC METHOD FOR ESTABLISHING A MAINTENANCE PLAN

It will be instructive at this point to outline a systematic

method of matching maintenance procedures to plant items.

Step (i) Establishing critical plant units and maintenance

windows. Determine the nature of the plant process

(continuous batch, etc.). Classify the plant into units

and construct a process flow diagram to include inter-stage

storage. Carry out a simple 'consequences of failure'

analysis. Determine the production plan and therefore its

pattern of operation and expected unit availabilities. From

such information determine (a) the critical plant units,

perhaps even ranking them according to the cost and consequences of failure, (b) the schedule of maintenance windows

for the plant and units, including consideration of the

possibility of random production stops.

Step (ii) Classify the plant into its constituent items.

This will be a complete classification in the case of

critical units, and a partial classification in the case of

non-critical units.

Step (iii) Determine and rank the effective procedures.

Establish the effective procedures for each item and determine the best of these from cost and safety factors. In

general the procedures for the simple items will be reasonably certain and mostly running maintenance. However, this

will not necessarily be so in the case of the complex items

and the best approach is often to identify if possible a

simple method of condition checking. Such a procedure

should establish the following:

89
I tern Searing

Timing

R or S

Periodicity

Time and labour

Initial maintenance action

R or S

Periodicity

Time and labour

Secondary action

C.B.M. Shock Pulse Check

R

M

15 min. 1 fitter

Replace bearing

S

Approx . 2 years

3 hrs. 1 fitter

None

Step (iv) Establish a schedule for the identified stopwork.

This schedule will obviously depend on whether the plant is

a series continuous, parallel batch, or a fleet system.

Fleet or parallel systems differ from series continuous ones

in that the units are independent of each other and a degree

of spare capacity is usual. Consequently, the maintenance

is usually all stopwork and scheduled at unit level, without

production loss, into daily, weekly, monthly, etc., inspection and service schedules. Since the series continuous

plant is the most difficult to schedule, it will be considered in more detail.

Rank the stopwork in order of increasing periodicity; for

the same periodicity rank in order of decreasing repair time,

e.g.

EXPECTED

ITEM ACTION PERIODICITY STOP TIME BEST PROCEDURE

A Replace M 5 hr Visual Ih^ectiDn

B Replace M 2 hr Shock pulse

C Repair M 1 hr Time-based

D Replace 2M 5 hr Time-based

E Replace 4m 1 hr Shock pulse

This stopwork can now be compared with the schedule of

maintenance windows. If the stopwork is less than the time

available for maintenance (State B, Figure 3)» then consider

a plan based on this schedule. Obviously, the periodicities

can be rationalized to make the best use of time and

resources. If the stopwork exceeds the time available for

maintenance, or indeed if there are no maintenance windows,

then consider a plan based on an agreed production stoppage

(State C, Figure 3) » the initial periodicity of such a

schedule being based on the lowest periodicity item (see

above table) . Where possible CBM should be used to determine

the best time for such a stoppage and the extent of the

subsequent opportunity maintenance. What must also be

90
considered is the fact that plant failures will still occur,

in spite of the preventive effort. The failures will be of

two types, those affecting plant output and those that might

do so in the future. In the first case such plant failures

can "be taken advantage of via opportunity maintenance, if

CBIV! is used to monitor the condition of critical items. In

the second case, a list of "Known Jobs" should be kept and

dealt with during the next convenient scheduled stop. Again,

the resources necessary to carry out this work can now be

organized

.

Step (v) Establish a schedule for running maintenance. In

this case the work is largely independent of production and

can be scheduled to make the best use of resources. This

will normally result in inspection and lubrication routines.

Step (vi) Corrective maintenance. Instead of the above plan,

the plant could be operated to failure, in conjunction with

opportunity maintenance. However, in most cases, especially

if unavailability cost is high, this is a very expensive

policy and can only be justified if the failures are unpredictable and their onset undetectable.

In spite of preventive maintenance there must still be some

failures. These have to be planned for in terms of spares,

methods, documentation and decision guidelines. Such planning should be reserved for critical plant units.

A MAINTENANCS PLAN FOR A SECTION OF A GHEr/IIGAL PLANT

Introduction

A chemical plant producing organic chemicals is taken as an

illustrative example. An outline of the plant is shown in

Figure 5' The plant manufactures a wide range of similar

organic chemicals. Some of the products are soluble in

water and some are insoluble; the plant is divided into two

sections to accommodate this. The products are made and

isolated in the reaction streams, they are adjusted for

quality and then dried, leaving the plant in powdered form.

The insoluble products require extra processing stages

(particle size reduction and clarifying) and there is a

facility for packaging them as liquids. The reaction

streams operate in batch mode, and one stream is not readily

interchangeable with another, each being adapted to a

selection of the range of products. The streams used for

finishing the products are interchangeable, they operate in

a semi-continuous mode. It can be appreciated that with a

plant of this complexity, production scheduling can play as

great a part as effective maintenance in achieving a high

91
utilization. In addition to the main product flows, the

plant is supported by a full range of chemical and engineering services. Commonly used primary chemicals and

intermediates are held in "bulk and can be transferred to

appropriate parts of the plant. Salt is pneumatically

conveyed to the reaction streams and flake ice is transferred in a similar manner. The reaction streams are

computer controlled and the rest of the plant is remotely

controlled so the plant can be operated by a small staff.

This example will concentrate on a typical reaction stream

as shown schematically in Figure 6. Reaction Unit 1 (RUl)

is charged with one component. A second component is added

and Reaction lA takes place. The contents of RUl are then

transferred to RU2 where Reaction IB takes place. Meanwhile,

a third component has been prepared in the Preparation Unit

and has then been transferred to RU3. Reaction 2 takes

place when the contents of RU2 are added to RU3. RU3 now

contains the product either in solution or suspension. The

product is isolated and filtered through the Filter Press

Units 1 and 2. The filter cake is washed and then discharged

into the Disperser Unit. The disperser takes advantage of

the thixotropic properties of the filter cake and beats it

into a liquid with a high speed agitator. The product is

discharged from the disperser into an intermediate storage

tank

The outline description of operations illustrates their

sequential nature. It will be appreciated that the various

stages of the reaction process take different lengths of

time, and that these times vary from product to product. It

will also be appreciated that various washing out procedures

are required between batches. Thus, certain units can

become bottleneck units during the production of particular

products and non-bottleneck units are then less heavily

utilized. However, because of the variability from one

product to another, it is very difficult to predict whether

a certain unit will be in use at a particular time, except

in the very short term.

Description of Units

A brief description of the units and their major items and

principal maintenance follows.

Preparation Unit

Mild steel rubber-lined vessel (1500 gal); The rubber is

subject to deterioration and to damage, requiring periodic

inspection and repair, with replacement after 10 years.

92
Agitation system; 2-speed AC motor; lA/orm reduction gearbox;

Mild steel rubber-lined paddle agitator

Level instrumentation (dp cell): Replacement or calibration

only possible when vessel empty

Temperature instrumentation: Thermocouple in tantalum clad

pocket

Steam injection posts:

Pumping system (transfer and re-circulation): 2-speed AC

motor; Mono pump; Pump protection instrumentation (pressure

switches and logic)

Weigh vessel system: Mild steel rubber-lined vessel (300

gal); Weighing mechanism; Weigh scale instrumentation

Pipework: Mild steel rubber-lined; GRP/PVC lined; Valves

and fittings

Reaction Unit 1

Mild steel glass-lined with welded jacket (1500 gal):

Pressure vessel inspection necessary (jacket classed as

steam receiver)

Agitation system: AC motor; Worm reduction gearbox;

Agitator oland - requires periodic lubrication and adjustment;

Agitator {stainless steel anchor)

Temperature dip pipe:

Weigh vessel (as for PU)

Powder hopper:

Powder feeder: Variable speed drive - hydraulic

Coolant re-circulation system: AC motor; Pump (centrifugal)

Pipework: Mild steel glass-lined, stainless steel, G.R.P.;

Valves and fittings

Reaction Unit 2

As RUl

93
Reaction Unit 3

Mild steel rubber-lined vessel in ring sections (10,000 gal):

Rubber subject to deterioration and damage

Agitation system: DC variable speed motor; Worm reduction

gearbox; Kild steel rubber-lined paddle agitator

Level instrumentation (dp cell):

Temperature instrumentation: Thermocouple in tantalum clad

pocket

Steam injection posts:

Weigh vessel: As for PU

Pumping system 1 (re-circulation and filter press feed):

DC variable speed motor; Mono pump; Pump protection instrumentation

Pumping system 2 (filter press feed): As for pumping

system 1

,pH Instrumentation: pH probe

Pipework: Mild steel rubber-lined, GRP/PVC lined; Valves

and fittings

Filtration Unit 1

Semi-automatic recessed plate filter press: Press closing

system; Motor; Gears; Closing screw

Plate separating system: Motor; Gearbox; Mechanism

Filtrate washing system: GRP vessel (300 gal); AC motor;

Centrifugal pump

Flow instrumentation:

Pressure instrumentation:

Pipework: GRP/PVC lined; Valves and fittings; Gross wash

valves replaced every 3 years

Rubber belt conveyor: AC motor; Gearbox

94
Disperser Unit

Stainless steel vessel:

Agitation system: AC motor; Butterfly agitator - accelerated seal wear due to abrasive product

Discharge pump: AC motor; Centrifugal pump

Pipework: GRP/PVC lined; Valves and fittings

Existing maintenance policy

The existing maintenance policy is to perform essential

lubrication on a running basis, and to shutdown the entire

stream for approximately 5 days each year. This enables

internal inspection of the vessels, replacement of certain

valves on rotation, and overhaul of pumps if necessary. The

shutdown is also used for rehabilitation work, and for the

implementation of modification work. It may be extended to

allow for the replacement of vessels or vessel sections.

Systematic Method

Step (i) The plant is operated in batch mode on a continuous

basis. Because of product variations it should be assumed

that the plant is "occupied" continuously, although individual units may be unoccupied at times during the operation

of the plant. The plant has already been classified into

units for the purposes of description. The consequences of

failure of a particular item are dependent upon the stage of

the process. However, since most failures are discovered

when an item is required, it can be assumed that most

failures will cause a delay to the process. The cost of the

delay is the opportunity cost of the quantity of product

that could have been made during the delay, i.e., the contribution from the sale of that quantity of product. Under

these circumstances all units except the filtration units

are critical since failure of one filtration unit will

reduce the capacity of the stream to 5^°/° • Moreover, there

is no schedule of maintenance windows, although it may be

possible to find windows of several hours duration on

certain units only at short notice. This latter observation

has important implications for the scheduling of non-urgent

breakdown repairs and certain preventive stopwork; close

co-operation between production and maintenance departments

is required.

Step (ii) An example of a detailed classification is given

in Figure 7

95
step (iii) A simple example of the approach to be taken is

given by rolling element bearings in, say, a centrifugal

pump fitted with a mechanical seal. Under certain circumstances failure of the bearings can lead to failure of the

mechanical seal and even to damaging the impeller. The

options are:

a) operate to failure,

b) fixed-time replacement (every 24 months),

c) condition-based replacement based on a monitoring scheme,

e.g., subjective judgement (look, listen, feel), objective

measurement (vibration level, shock pulse value, kurtosis

value), (3-monthly inspection).

The selection of c) would be preferred, not only for

preventing bearing failures, but also because it provides a

useful peg on which to hang general condition or housekeeping checks. Thus, a complete instruction for the item

would be

I tern

Timing

R or 3

Periodicity

Time and labour

Initial Maintenance Action

R or S

Periodicity

Time and labour

Secondary action

Centrifugal pump

CBM : SPM/Kurtosis + visual

(seal, housekeeping)

R

3 months

10 mins. 1 inspector

Replace pump

3

Approximately 24 months

2 hrs. 1 fitter

Recondition pumps

A more complex example is given by the rubber-lined reaction

vessel. The item itself is simple enough, it consists of

four components; cover, top section, bottom section and base.

The rubber lining on the sections and base is subject to

permeation by chemicals over a period of time. The rubber

can also be damaged accidentally. Once the rubber has been

penetrated, rapid corrosion of the parent metal takes place.

Further deterioration of the surface of the rubber could

lead to particles of rubber contaminating the product. The

present practice is to carry out an internal visual/tactile

inspection. As a result of this inspection, rubber repairs

may be necessary. The range of procedures to be considered

can be summarized as:

a) operate to failure,

b) fixed-time internal inspection.

96
c) fixed-time external inspection (e.g., through manhole),

d) fixed-time electro-chemical measurements,

e) continuous electro-chemical monitoring,

f) product sampling for contamination (at levels below

current acceptable level).

Although d) and e) are attractive GBM procedures, only

lining failure in terms of penetration is detectable and no

indication of the surface condition of the lining is given,

f ) would appear to be an appropriate CBK procedure for this

failure mode. However, the deterioration of the rubber is

thought to be due to the effect of specific chemicals which

could bring about sudden changes in condition. Thus, the

frequency of measurements would have to be high in order to

give a failure prediction with an acceptable level of

confidence. Procedure c) would be suitable if the surface

could be assessed visually remotely, e.g., by use of closed

circuit television, etc. Procedure a) is unacceptable on

grounds of safety, let alone other costly consequences of

failure. Therefore, until a more suitable alternative is

developed, the existing procedure of fixed-time internal

inspections is all that remains. Replacement of vessel

sections will take place according to condition. This can

be detailed as follows:

I tern

Timing

R or S

Periodicity

Time and labour

Initial Maintenance Action

R or 3

Periodicity

Time and labour

Further maintenance actions

Reaction vessel - rubber lining

Fixed time

S

12 months

2 fitters for 2 days - 1

inspector for half a day

Repair in situ

S

24 months

48 hours elapsed time - 2

rubber men for 8 hours

1. Remove and replace vessel

section

k fitters for 4o hours - ^ heavy gang for l6 hours

2. Strip rubber and reline

sections - contractors

Step (iv) Due to the nature of the plant (i.e., parallel

batch streams) the step (iv) of the general approach outlined in section 5 has to be modified.

a. List the stopwork as shown in Table 1 and separate the

stopwork which can be carried out in the maintenance windows

and that which requires the stream to be taken out of production.

97
I

I

b. Establish a schedule for carrying out the 'maintenance

window stopwork' . Since this work does not require the

shutting down of a stream the schedule can be for the whole

of the plant. The schedule is established from Table 2 and

written in the form of a Bar Chart or as schedule on a

computer; the objective being to achieve a high labour

utilization. In this particular case the schedule is

completely condition-based and only the timing of the

actions are scheduled. The resulting work is reported (the

maintenance action) and carried out in the window (or some

subsequent window) as corrective maintenance.

The execution of this schedule requires close liaison

between production and maintenance supervisors.

c. Establish a schedule for the stopwork that requires the

stream to be taken out of production (see Table 3)

The schedule can be established by ranking the stopwork by

periodicity and time for each stream and proceeding as for

the previous example. Since there are 6 streams the stops

for each stream should be scheduled on a Bar Chart so as not

to coincide and where possible to incorporate known jobs and

window maintenance. The main aid in this case is to

minimize the cost of production loss.

In this example it was found that although the inspection of

the rubber lining of the vessel necessitated a scheduled

production stop, very few of the other preventive maintenance activities actually lined up with this new window.

Thus, the successful implementation of the programme would

rely on close communication between the maintenance and

production departments in order to carry out preventive

maintenance activities during windows in production. This

implies that much of the stopwork can be scheduled only in

the short term.

The importance of Step (iii) cannot be emphasized too

strongly. If, for example, a more remote type of vessel

inspection were possible, the whole of the stopwork programme

could be re-organized. Obviously, this is the long-term

plan for the plant which can be modified in the light of

unexpected failures or production stoppages. It will be

appreciated that the success of the stopwork schedule and,

therefore, of the plan, relies heavily upon condition

monitoring.

Step (v) From the above schedule the running maintenance can

be extracted, added to the remaining running maintenance

(e.g., lubrication), divided into trades and scheduled into

98
routines and services. Such work is independent of the

state of the plant.

Step (vi) From the point of view of corrective maintenance,

it is important to identify those items that in spite of

monitoring might still fail unexpectedly, and cause serious

disruption to production.

SUMMARY

Firstly, it is important to point out that the example was

considerably simplified to illustrate a number of important

principles. However, this accepted, the question that must

now be answered is whether the alternative plan is an

improvement over the existing plan - in other words, is it

cheaper in terms of the combined effort of unavailability

and the cost of resources. Although it is difficult to

quantify the improvement, it will be obvious that some

improvement should indeed result. The difficulty comes

from the uncertainty in forecasting the level of emergency

maintenance that will result from the new plan. However,

since the plan is based on CBM methods, even if more

emergency work than that forecast occurs, it should be

easier to minimize its effect on the production output. The

authors cannot emphasize enough the considerable advantage

for the planning of maintenance work that stems from knowledge about the condition of plant. It is hoped that the new

plan will result in a movement from situation (a) in Figure

8 to situation (b).

REFERENCES

1. KELLY, A. July 1980. Terotechnica Vol 1. No. 4 . "A

review of the maintenance management problem".

2. LEADBEATER, A. A. C.E.G.B. Internal Report . "Station

Planning - The stability problem"

.

3. SEDDON, G.N.D. University of Manchester . Ph.D. notes.

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PLANT performing the overall function

UNITS performing mojor plant functions

(e.g. a compressor in a petrochemical plant)

ITEMS permanent (e.g. the main shell of

a chemical reactor)

replaceable complex {e.g. a gearbox)

replaceable simple (e.g. a brake pad assembly)

COMPONENTS the individual parts of a plants possibly

very few In simple replaceable,

hundreds in complex replaceable items.

FIGURE 2. PLANT HIERARCHY.

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FIGURE 4. THE MAINTENANCE OBJECTIVE.

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112
SESSION II

TECHNOLOGY INPROVEMENTS FOR POWER

PLANT APPLICATIONS

CHAIRMAN: K. LUDEMA

UNIVERSITY OF MICHIGAN

IMPROVED ENGINE MAINTENANCE

THROUGH AUTOMATED VIBRATION DIAGNOSTIC SYSTEMS

Richard A. Rio

Mechanical Technology Incorporated

968 Alb any- Shaker Road

Latham, New York 12110

The rapidly increasing cost of maintenance, the demand for increased

equipment utilization, fuel costs, and the difficulty of correctly

diagnosing internal mechanical problems in fully assembled jet engines,

have stressed the need for more effective engine test equipment. This

paper describes the successful application of a component (module)

high-speed balancing technique developed for the U. S. Army for use at

the Corpus Christi Army Depot and an Automated Vibration Diagnostic

System (AVID) for the U. S. Air Force's engine overhaul center at

Tinker Air Force Base, Oklahoma. The AVID concept to automate troubleshooting procedures for fully assembled rebuilt engines is addressed.

This system extracts high-frequency vibration data from existing standard instrumentation, thereby providing meaningful mechanical information. A growing appreciation on the part of engine overhaul personnel

of the power of automated test equipment has enabled these key features

to be combined to reduce operating expenses at engine rebuild facilities.

Key words: Balancing; diagnostics; faults; monitoring; jet engines;

overhaul; productivity; vibration.

Significant concern has been expressed in recent years about the relatively high and growing levels of maintenance costs required to keep

many kinds of key equipment operational. The aircraft gas turbine

engine has been no exception to this trend. Aircraft gas turbine engines have compiled remarkable endurance and safety records over the

years, especially given the sophistication of their designs and the

rotor speed involved. These records have been and are being earned

through expensive and painstaking overhaul practices, applied at regular intervals of operating time. While the costs of this approach have

been substantial, the consequences of failure have always far outweighed

them. While safety of flight cannot be compromised, future improvements

in maintenance engineering can and must be realized to keep the costs of

safe oiieration from becoming prohibitive.

This paper presents two vibration diagnostic techniques which have been

developed for the latest jet engine overhaul techniques being developed

by the military. These maintenance procedures take advantage of the

115
latest modular jet engine design concepts.

There are two tiers of maintenance decisions. In the first tier, repair

decisions will be performed by the end users at the base installations.

Engine components or modules will be returned to the depot for repair

and/or refurbishment based upon modifications observed by the user or based upon the established time and cycle limit of that particular

module in service. The second tier involves removal of entire engines

which are then returned for depot level maintenance. Therefore, both

complete engines and discrete engine modules will be cycled through the

maintenance facilities.

It will be necessary to have a vibration acceptance test which will cer- tify that repaired engines and modules are acceptable for fleet use. As presented here, a high-speed balancing system will identify potential

problems before the module is shipped to the field. For entire engines

which require a complete test cell acceptance procedure, an Automated

Vibration Diagnostic System (AVID) has been developed which will identify internal mechanical faults using the standard engine vibration sensors.

High Speed Balancing

Rotor balancing is the process of applying a single set of correction

weights simultaneously in two or more planes on a rotating shaft to

achieve low vibration levels at each measurement location along the

shaft, and at a special number of shaft speeds. In its simplest form,

this process involves two planes, two sensors, and a single, relatively

low speed. In its most complex form, as many as eight or ten balancing

planes may be involved, together with an equal number of sensors. As

nany as six or eight balancing speeds may be required.

When a rotating body remains rigid (i.e., no elastic axis bending, over

its entire operating speed range), the simplest, tvjo-plane, low-speed

approach can be fully satisfactory. It is this fact which has permitted

the governing relationships to be "programmed" in electronic packages

as parts of commercially offered balancing machines. What causes difficulty in many cases is the fact that the commercial balancing machine

fails to simulate adequately the design operating condition of the com- ponent .

The balancing of advanced rotating systems is becoming increasingly difficult with design trends toward lighter, more flexible components which

turn at higher speeds. The operating speeds of many systems now being

designed are often beyond the first critical. The reason this situation

causes concern is that the modes of vibration at the critical speeds

often involve significant bending of the system's elastic axis. Since

these deformation properties are speed dependent, low-speed two-plane

balancing has only limited effectiveness. In fact, such balancing can often make vibration levels worse at the bending critical speeds.

Unfortunately, present-day manufacturing procedures, in spite

116
of their high-precision nature, leave some distributed residual unbalance in each rotating component. The result is a considerable trialand-error effort to find a satisfactory balance at the trim-balance

stage, and increased efforts toward tighter tolerances and more stringent assembly procedures; all of which can be very costly. As rotors

become longer and more flexible, and as lighter weight rotor systems are developed, balancing requirements and methodology must adjust to accom- modate them. Problems introduced by disassembly and reassembly are also

significant; especially in a gas turbine engine having several disk and

blade assemblies, bearings, and a cantilevered turbine.

A procedure for performing rotor balancing in two or more planes, so as

to achieve low vibration levels at each of a number of measurement locations and at each of a number of speeds, has been developed. The procedure is conceptually quite simple, and has been designed for operation

by technician-level personnel. It may merely be used to supplement the

capabilities of a commercially offered balancing machine; or, in its

most complete form, it offers the option of replacing a series of twoplane balancing steps by a single multiplane-multispeed balancing of the

rotor in its final installation.

In their maintenance philosophy, the military has identified a number of

potential advantages in high-speed balancing gas turbine modules.

Cost Savings . It is often extremely complex, time consuming and expensive to high-speed balance an engine while it is installed in a test

cell. Quality high-speed balancing of components will often reduce or completely eliminate the need for assembled engine balancing and reduce

the rejection rate; thereby saving teardown, reassembly and retest cost.

Improved Rotor Life . If the engine component is flexible (i.e. , approaches or traverses bending critical speeds within its operating

speed range) , high-speed balancing offers unique advantages because of

the inability of traditional low-speed balancing to reduce shaft vibrations at these speeds.

Component Diagnostics . Operating component parts at high speeds before

assembly to the engine allows a significant degree of component diagnostics (i.e., shift in parts, misalignment, faulty bearings, etc). This,

therefore, occurs before the added cost and complexity of installing a complete engine for test and trim balancing.

Accessibility to Problem Component . It is often impractical or impossible to access rotors inside an assembled engine. Accessibility to

prescribed balance planes is also often limited because of the "trapped

rotor" design of many gas turbine engines. Component "stack up" also

makes access to interior shaft components impractical in the assembled

engine, but practical in a high-speed balancing module.

Seating of Sub-Component Parts . Operating a component before assembly

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Into the engine allows subcomponent parts (i.e., turbine blades, snap

fits, etc.), by the action of centrifugal force, to seat in the position

in which they will run in an engine. This is especially important in

shafts with a high degree of sensitivity to changes in unbalance. Such

"run in" of component parts cannot be achieved by only low-speed operation.

Application to United States Army Jet Engines

A system developed for the United States Army permits high-speed balancing of assembled power turbine shafts for both T53 and T55 helicopter

engines. Based on an extensive background study, it was determined

that one of the power turbines (T53) traverses a bending critical speed

well below its normal operating speed in the engine. The other power

turbine (T55) traverses a rigid body critical speed and approaches its

first bending critical speed at its normal operating speed.

In their present configuration, neither of these engines have the capability to trim balance the power turbine shaft in the test cell. Each

vibration-related reject in the test cell requires engine removal and

tear down for subcomponent balancing. The engine must then be rebuilt,

reinstalled, and rerun in the test cell. The prototype high-speed

balancing system allows both T53 and T55 power turbine shafts to be run

and high-speed balanced as an assembly before installation into the

engine.

Figure 1 shows the major mechanical components of the balancing system.

Drive power is provided by a variable-speed electric motor. Speed is

increased through a gearbox with output shaft speeds equaling engine

operating speeds for the power turbine shaft. The shaft is operated in

a vacuum chamber to both reduce the windage (and therefore the amount of

drive power required), and to provide for operator safety.

A control console with dedicated minicomputer and CRT terminal is located in a separate control room. An auxiliary control panel mounted on

the test stand provides for local low-speed operation and control.

In order to duplicate the dynamic characteristics of the engine installation, engine bearings support structures are used to mount the shaft for

balancing. Displacement probes are used to measure shaft deflection.

Vibration data are routed to the minicomputer for automatic data acquisition and balancing weight calculation.

Automated Vibration Diagnostics

In several cases, operators of gas turbine engines have begun to adopt

the practice of "on-condition" maintenance costs. In the process of

this change, the increased emphasis that must be placed on diagnostic

systems and procedures has become apparent. These procedures are re- quired to obtain data to determine the presence of a problem, identify

trends, and locate the specific faulty component within a fully assembled engine.

119
Figures 2 and 3 show typical results for high-speed balancing T53 and

T55 power turbines using the prototype high-speed balancing system.

Significant technological advances have occurred in recent years in

small low-cost minicomputers, digital data processing and filtering, and

new methods for using high-frequency vibrations as information carriers.

These advances are expected to be of great utility for new monitoring

and diagnostic procedures.

The first level of analysis is a comparison of the output signal levels

of instrumentation with predetermined limits, such as bearing vibration.

The comparison is accomplished by analyzing a number of past readings

and permits an initial classification of the machine's condition, such

as whether the equipment is operating within safe limits, or whether a large percentage change has occurred in any measured parameter since the

last measurement. Presenting this data as a function of time can indicate wear, growing unbalance or component degradation.

Once a signal has been found to be out of bounds, a detailed analysis of

the Signal and related parameters is initiated. High-speed detailed

sampling provides a full-frequency component analysis of vibration.

Oil pressure and temperature, and other key static signals are sampled

concurrently. This information, together with the operator's understanding of the machinery, will often permit the operator to make a reasonably accurate determination of the probable cause of the observed

variance. Typical actions the operator may wish to have the system

undertake at this point may include: providing an advisory to circumstances or operating levels; increasing the frequency at which the re- view of the machine occurs; trending and analyzing measured machine

responses for representative past operating history; calculating fullfrequency component composition of time-varying signals to identify

specific contributing frequencies and amplitudes; and comparing frequency components with stored tables of potential forcing frequencies,

such as one-per-rev, gear mesh, etc. The structure of the diagnostic

system's logic often permits the maintenance engineering staff to

tailor the system to their particular needs.

Analytical and experimental information about the machine may be stored

within the system. For example, design data about blading, bearing

design, coupling characteristics, critical speeds, and sometimes even analytical equations may be provided. With such information, automated

diagnosis is possible. When a machine is overhauled or undergoes maintenance, the details of any observations can be entered into the data

base, and the system can categorize experienced changes in behavior

with actual physical parameters. Theoretical considerations may be re- inforced through operating experience and successful maintenance actions.

As time elapses, the data base assembled through these interactions permits more accurate diagnostic logic to be prepared. The important con120
121

cept in the logic is that the system learns from proven experience and

can formally document machine problem histories. Predictive maintenance recommendations are also available. Machinery operating costs can be minimized by providing cost-based logic for accomplishing specific

maintenance on only those modules requiring checking. The symptomfault logic may be asked to identify preventive actions and replacement

parts as part of the overhaul process.

Application to United States Air Force Jet Engines

The technologies discussed abcve^ have been successfully combined to

provide an Automated Vibration Diagnosis System (AVID) for United States

Air Force jet engines. The system was installed in four engine test

cells at one of the main United States Air Force engine overhaul centers,

Oklahoma City Air Logistics Center (OC-ALC) . Operation of the equipment by Air Force personnel has demonstrated the practical application

of combining minicomputer technology with gas turbine engineering ex- pertise to provide the Air Force with a system which provides fuel savings, increased engine production capacity, and greatly reduced vibration rejection rates.

Overhaul Procedures . Overhaul procedures require that rotating components undergo both static and dynamic balancing during the overhaul

process. Engine parts are first weighed and balanced as individual

parts, then balanced as assemblies (i.e., compressors and turbines)

prior to final assembly. Following final assembly, engines undergo an acceptance test during which critical performance and operating parameters are determined.

During the acceptance test, engines frequently experience vibrations

which exceed allowable technical order limits. Depending upon the

amplitude, frequency, and location of the vibrations, an engine may be

trim balanced while it is on test. If trim balancing is not possible

(e.g., vibration not synchronous with rotor vibration, or indicated trim

weight too large) , then the engine is returned to the final assembly

area for corrective rework. Former engine technical order procedures

required that three trial trim balance weights be installed separately

and the engine operated after insertion of each weight. Data resulting

from each run was used to calculate the amount and location of a final

balance weight. Approximately eight hours were required to trim balance an engine using this procedure. One major objective of the diagnostic system was to reduce the exszessive amount of time required to

trim balance the engines.

Engines on which trim balancing was not permissible were returned to the

final assembly area with only minimal vibration data available to direct

engine rework. Information provided was highly subjective and dependent

on test cell operator experience. As a result, rework which was performed on an engine often did not correct the problem, causing the en- gine to be rejected several times due to excessive vibration levels.

Repetitive rework to correct vibration problems results in additional

123
costs, much of which could be avoided if accurate repair action recom- mendations were another major objective of the diagnostic system.

Engine rework and test costs are expected to continue to increase as a result of upward trends in manpower and material costs. In addition,

the complexity of the new generation of turbofan engines is also re- sulting in increased maintenance time and costs. These factors, coupled with the requirement for rapid turnaround of er^gines undergoing over- haul (due to reduced engine inventories) required that a diagnostic

system be available to reduce the time required to trim balance, test

and provide accurate diagnostic information to direct engine rework.

Automated Engine Trim Balancing Benefits

The TF30 engine was selected for the pilot system demonstration because it is designed for trim balancing and was considered by the Air

Force to be a typical engine in its maintenance requirements and vibration characteristics. The engine vibration signals used during acceptance testing were derived from the three standard military velocity

sensors normally installed on the engine during test. Before filtering

within the vibration amplifier, the signals are routed, along with the

speed measurements, to the computer room (see Figure 4).

The TF30 engine AVID System (see Figure 5) consists of six assemblies;

the central balancing system, four digital signal processors, and a CRT

terminal and hardcopy unit. All of these assemblies are located in a central computer room adjacent to the four test cell control rooms. Each of the digital signal processors is dedicated to monitoring speed

and engine vibration signals from one test cell. All the digital

signal processors are connected to the central balancing and diagnostic

system. The CRT terminal and hardcopy unit are connected to the central

balancing system or the digital signal processors. During acceptance

testing, the trim balancing system is activated if the engine vibration exceeds the technical order limit. Vibration data ia automatically acquired and processed to provide a spectral analysis of the overall signals of the engine's vibration sensors.

The size and location of the required trim balance weight are calculated by the system based on the engine's vibration characteristics. The

unique aspect of the trim balancing portion of the AVID system is that

trial weight runs are not needed. Engine sensitivity data, also known

as influence coefficients, are stored within the minicomputer system.

These data are then recalled and processed with the dynamic response

of the engine on test to calculate the proper correction weights.

During a verification test period, ten TF30 engines were trim balanced.

Trim balancing was successful in all cases. The engines were trim balanced using the influence coefficient method and the engine vibrations , were reduced to a level below the technical order specifications. Engines are now routinely trim balanced by Air Force maintenance personnel

The average time to trim balance has been reduced to 1 hour and 20

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126
minutes, compared to the original 8 hours. Test cell time per engine

was thus reduced by about 80% for the trim balancing operation, with

attendant savings in fuel usage and increases in engine production

rates.

Automated Engine Condition Diagnosis Benefits

The key principles of the vibrations diagnostic system operation are based on engineering experience in machinery dynamics. This experience

has shown that dynamic observation, particularly of rotor and casing

vibrations, is an excellent method to identify existing or impending

problems. The complex raw signal data can be processed to provide re- liable information that permits the evaluation and pinpointing of the

problem source. These diagnostic elements have been combined into

systems for making accurate decisions once suitable levels of vibrational characteristics have been defined. The AVID system minimizes

the decisions required of the operator and offers rapid identification

of problems. The system samples the outputs of the standard existing

engine vibration sensors in a logical sequential manner to arrive at a decision as to the condition of the engine under test.

The engine condition diagnosis system acquires both synchronous and non

synchronous vibration signatures from engines in all four test cells.

The system conducts an analysis of each engine's vibration response and

produces a hardcopy printout indicating the cause for high vibration,

numerically ranked from highest to lowest severity. The TF30

engine Sjmip torn-Fault Matrix, based upon existing data and upon preprogrammed engineering knowledge of the engine, identifies the engine

faults. Malfunctions are identified in the order of severity. This

unique system feature makes use of general symptom-fault relationships

for gas turbines, with specific experience probabilities for the TF30

engine. The diagnostic printouts indicate those faults which should be

corrected. These data provide guidelines to the maintenance staff and

help establish rework priorities.

Vibration diagnostics were performed on ten TF30 engines during a verification test period. To document the accuracy of the predicted engine

faults, maintenance action worksheets accompanied the engines that were

rejected for vibration-related malfunctions. Successful correlation be

tween the AVID System's diagnostic summaries and the actual maintenance

required by the engines has provided verification of the TF30 vibration

diagnostics. The verification test included TF30-P7, TF30-P9, and

TF30-P100 engines. The diagnostic system proved nearly 90% accurate

(20 out of 23 cases)

.

In addition, the system maintains an archive of engine data:

• Stored signatures of rejected analysis

• Stored signatures of average engines

Overall vibration

127
- Ni and N2 components versus speed

Spectral plots

- Six-month sampling (continuously updated)

• Engine serial numbers tracked for short term

- Repeat rejects identified

- Engine corrective maintenance history compiled

• Six-month interval of good engine data

- Overall vibration

Retrieval data on earlier rejects

Automated Engine Performance Diagnosis Benefits

In addition to vibration-related engine rejections, a significant portion of post-overhaul rejections are caused by gas-path performance

problems such as low thrust, high exhaust gas temperature and high

specific fuel consumption. A methodology is being developed (Ref . 1)

to increase the acceptance rate of overhauled J75-P-17 turbojet engines.

To avoid engine modification, a minimum number of additional sensors were installed to diagnose faulty components from the performance signature. A computer simulation was also developed to identify the faults

and to calculate the beneficial effects of easily installed changes or replacements of components. Gas-path performance diagnosis is planned

for implementation on the installed AVID system. Static channels such

as those for pressure and temperature will be incorporated into the

S3miptoin- fault logic to expand the system capability.

Summary and Conclusions

Automated systems for balancing and diagnosing engine faults has been

designed, developed, and successfully demonstrated in production jet

engine overhaul facilities.

Quality high-speed balancing of components will often reduce or completely eliminate the need for assembled engine balancing and reduce the

reject rate, thereby saving teardown, reassembly, and retest costs.

Stored engine sensitivity data can be used to calculate single-shot

balance weights which, when installed, bring the engine vibration down

to acceptable levels. This process has eliminated the need for trial

weights and average trim balance time has been reduced from between 7 and 8 hours to 1 hour and 20 minutes through the use of this system.

An automated diagnostic system which uses only vibration data from

standard sensors has successfully predicted faults within the engine.

During a verification of the system's diagnostic capability, nine

engines were torn down and inspected with 90% accuracy of predicted

engine faults.

Based upon fuel savings, increased engine production capacity, and re- duced vibration reject rate, the installed trim balancing and diagnos128
tic system is projected to yield a multimillion dollar cost savings in

its first year of operation.

Air Force maintenance personnel are routinely operating the trim balanc

ing and diagnostic system without additional skilled personnel during

normal engine acceptance testing.

The AVID System can be expanded to include gas-path performance

diagnostics, and with field-level communication and data processing,

should provide a practical method of engine health accountability

during the entire life of the engine.

Reference

1. Lazalier, F. R. , Reynolds, E.G., Jr., Jacox, J.O., "A Gas-Path

Performance Diagnostic System to Reduce J75-P-17 Engine Overhaul Costs.

ASME, 1978, Paper No. 78-GT-116.

129
INNOVATIONS IN EPICYCLIC GEAR SYSTEM DESIGN

FOR INCREASED SERVICE LIFE

D. E. Pauze

US Army Aviation Research and Development Command

Propulsion Laboratory

Lewis Research Center

Cleveland, Ohio 44135

Abstract: Current epicyclic gear systems in helicopter drive trains

are designed for a non-catastrophic failure mode: surface fatigue.

The sun and ring gears are loaded on one side of the gear teeth only,

so that otherwise perfectly good gears are retired from service. With

design innovations, the epicyclic gears can be made with fore and aft

symmetry to perform double duty.

Key words: Bearing life; bearings; epicyclic system; gear train;

planet bearings; planetary gears.

When aviation was in its infancy, the propulsion system for aircraft

consisted of a propeller driven by a reciprocating engine. The thrust

requirements were low because the aircraft was small and low-speed.

The small propeller could be direct drive at engine speed without ex- ceeding the propeller's limit in tip speed. As aviation technology

advanced, the aircraft grew in size and speed, and the propeller became larger to provide the higher thrust required, its RPM reduced to

maintain tip speed. Meanwhile, engine RPM was increased to improve

the specific weight (lb/hp) and specific fuel consumption (lb per

hr/hp) . At that time, propeller speed decreaser gear was introduced,

and was made integral with the engine.

With the advent of the aircraft gas turbine, the need for propellers

and their speed decreaser gear dramatically changed. The pure-jet

airplane (fixed-wing aircraft powered by a turbojet engine) required

no propeller whatsoever, while the prop-jet airplane (fixed-wing aircraft powered by a turboprop engine) continued to use a propeller and

speed decreaser gear. Since the pure jets far outnumbered the propjets, the number of speed decreaser gears flying in the world would

have been significantly reduced except for another change.

The third type of aircraft gas turbine, the turboshaft engine, provided a significant improvement in specific weight which equated to a jump from less than one to more than three horsepower per pound of

engine weight. This breakthrough made the helicopter practical. The

130
slack in the use of speed decreaser gears created by the pure jet was

picked up by the helicopter, so that the speed decreaser gear is still

important in aircraft applications.

Figure 1 shows a typical helicopter arrangement of drive train with

twin engines. This is a composite of several installations. The

power turbine in the turboshaft engine is a free turbine which feeds

power through a right-angle drive gearbox into a transmission. The

outputs from the transmission are: the main rotor, airframe accessory

drives, and tail rotor. The tail rotor drive includes an intermediate

gearbox and a tail rotor gearbox.

The gear arrangement in this typical helicopter drive train is shown

in schematic form in Figure 2. The epicyclic gear system is the final

reduction in the main rotor drive, and the axes of these gears are vertical or near vertical. Shown here is a large helicopter. There

is an earlier small helicopter which incorporates a two-stage planetary reduction driven by a single engine.

Figure 3 shows the drive system schematic of an existing tandem rotor

helicopter. This one uses a two-stage epicyclic gear system in the

final reduction of each rotor. Figure 4 shows the drive system schematic of a turboprop engine. Again, the epicyclic gear system is the

final reduction of the speed decreaser gear. In this case, the firststage reduction provides an offset so that the propeller is offset

from the engine centerline. This offset provides a cleaner inlet to

the engine.

The reciprocating engine and the gas turbine for aircraft share a com- mon trait in their speed decreaser gear. They both use the epicyclic

gear system, but there the similarity ends. The reciprocating engine

is essentially a low-speed (RPM) machine, while the gas turbine is

high-speed. The difference in reduction ratio is significant, and is

manifested in the evolution of the epicyclic gear arrangement as shown

in Table I.

Referring to Table I, consider the 1950 and 1980 meshing frequencies

of the sun gear relative to the planet idler. Their actual disparity

in operation is greater than the calculated 3.0 vs. 6.5 or 2:1. The

sharing of the load among the planet idlers was and is dependent on

the manufacturing error in tooth-to-tooth spacing. In 1950, that error was in the neighborhood of 0.0005 inch; in 1980, 0.0002 inch.

Translated into terms of load sharing, in 1950 one could expect approximately 1/3 of the total number of planets to share the load at

any given moment. In 1980, that fraction is slightly more than doubled. Adjusting the relative meshing frequencies for load sharing,

the 1950 figure becomes approximately unity, and the 1980 figure becomes approximately 4.5. Their actual (adjusted) disparity becomes

1.0 vs. 4.5 or 4:1. Therein lies the concern for the sun gear in

today's helicopter. It is using up its surface fatigue life at many

131
times the rate of its mating gears.

Figure 5 shows graphically the

gear arrangements in the speed

explanation lies in the nature

Aircraft

Type

Vintage year

Speed Decreaser Gear (SDG)

Rating, Approximate

Supplied by

Driven by

Engine

Type

Power to Weight Ratio

Input Shaft to SDG

Input Shaft Speed

large difference between the epicyclic

decreaser gears, then and now. The

of the prime movers:

Airplane

1950

3500 Hp

Engine Mfr

One Engine

Rec iprocating

1:1

Crankshaft

Low

Helicopter

1980

3500 Hp

Airframe Mfr

Two Engines

GoS Turbine

4:1

Power Turbine

High

Naturally, the epicyclic gear system did not make this large change in one jump. Figure 6 shows some selected interim arrangements. The

1960 helicopter was powered by a single engine, the 1970 helicopter by

two engines. The evolution of aircraft epicyclic gear systems shows a distinct trend of higher reduction ratios, which is a direct result of

the evolution of turboshaft engines. The engine trend is to smaller,

higher-speed engines. This is in keeping with the square-cube law.

Recall the horsepower per pound of engine weight previously mentioned.

Horsepower is a function of mass flow (W^) in the engine which is directly proportional to the inlet cross-sectional area (L^) . Weight is

a function of volume (l3). The natural corollary is the trend to

smaller engines and multi-engine installations. The latter provided

another benefit for helicopters: one engine inoperative (OEI) capability.

Since a discussion of epicyclic gear systems would be incomplete without turboprops. Figure 7 touches on this application. The 3-planet

epicyclic gear system is probably beyond the practical limit, the sun gear being very small. The planetary reduction ratio of 1 + R/S = 13

is attractive, but the relative meshing frequency of n.P/S = 16.5 is

not. All of the epicyclic arrangements shown in Figures 5 through 7 have full-depth teeth with minimum clearances between planets. These

are high-density gear sets, much favored by gear designers.

Figure 8 is a graphic representation of the trends in planetary re- duction ratios and sun gear meshing frequencies. These are diverging

curves, with the latter rising more rapidly than the former, A star

arrangement would displace the lower curve by one unit, but the slope

would be the same.

Figure 9 describes the two families of epicyclic gear systems: planetary and star arrangements. Their names have their origin in astron132
omy; planets orbit about the sun, and the stars are fixed relative to

the sun. Both arrangements have been used in aircraft applications,

but the planetary system is by far the more popular. The reason is

obvious: the gear designer obtains an additional unit of reduction

ratio with the same size star arrangement. The epicyclic gear systems

are also attractive for other reasons. Their high reduction ratios

fit well with high-speed aircraft gas turbines. Their multiple load

path provides a compact, high-density gear set which is lightweight

and of low volume.

The design constraints in epicyclic gear systems for aircraft applications are formidable. The system is designed for a non-catastrophic

failure mode: surface fatigue. The accent is on weight and volume.

Cost and the "ilities" ( produc ib il ity , af fordability , availability,

reliability, maintainability, vulnerability, and survivability) are important considerations, too. However, the designer's first hurdle

is weight and cost. To avoid the unpleasant prospect of a good engine

dragging an inoperative engine, an over-running clutch is provided in

the drive system. The helicopter is essentially a constant-speed

machine while the turboprop is variable speed. For reverse thrust,

the propeller goes into reverse pitch, with the engine driving as in

forward thrust.

What are the pacing items in epicyclic gear system life? The sun gear

has the shortest gear life, and the planet bearing has the shortest

bearing life. The planet gears and ring gears follow in that order.

As previously mentioned, the gear mode of failure is surface fatigue

of the gear teeth. The planet bearing mode of failure is surface

fatigue of the inner race.

For a better understanding of epicyclic gear systems, let us consider

the applications of load and those features which will "respond to

treatment." The sun gear has many more applications of load than its

mating gears by the ratio of n.P/S. It drives on one side of the gear

teeth only - recall the over-running clutch. The planet bearing "sees"

double the useful, transmitted load, a condition which is inherent in an idler bearing. The inner race is fixed in the carrier, with the

outer race rotating. (In many cases, the outer race is integral with

the idler gear.) Being fixed, the bearing inner race is loaded on one half of the circumference only. The planet gear teeth are subjected

to reverse bending, a condition also inherent in an idler gear. In

addition, the unit (contact compressive) stress is higher with the sun than with the ring gear. Like the sun gear, the ring gear teeth are loaded on one side only.

In the area of gear life, there is not 100% agreement among the helicopter manufacturers. One claims his gears have infinite life, that

his gears are replaced only when abused. Another calculates surface

fatigue life in accordance with AGMA Standards, ostensibly to replace

133
the gears when their calculated life is used up. All reconimend stocking spares. A frequent mode of failure is reported to be scoring,

which is due to overtemperature and/or overtorque, oil interruption,

or loss of lubricant. Current practice calls for replacing "failed"

gears with new ones, so that otherwise perfectly good gears are re- tired from service.

Any criticism, however constructive, should be followed by a suggestion of a better way. The change proposed herein would provide for

double duty of the epicyclic gears and planet bearings. The change

would provide fore and aft symmetry in the affected parts for rever- sibility in service. Some of the parts affected already have that

capability. A limited survey of the field disclosed the following:

Currently in Use

Item

Fore & Aft

Symmetry

Part Reversed

In Service

Sun Gear No No

Planet Gear Yes No

Planet Bearing Some Some

Ring Gear Some ?

The sun gear would require special treatment in the helicopter application. The main rotor shaft is inside the sun gear to provide the

maximum possible bearing span for the main rotor bearings. These

bearings straddle the sun gear and collector gear (bevel gear driven

by both engines of a twin-engine helicopter). Therefore, Figure 10

shows the sun shaftgear with an external spline which provides the

maximum gear ID.

The turboprop sun gear and some large sun gears in helicopters could

accommodate an internal spline which has the advantage of minimizing

the additional length needed to accept the fore-and-aft locking device

between the separable sun gear and shaft. Figure 11 shows an internal-external snap ring. This arrangement is akin to a piston ring.

The difference is that the "cylinder" has an internal groove into

which the snap ring expands during assembly. The sun gear incorporates four radial holes equally spaced at the snap ring groove for

disassembly

.

Figure 12 shows a ring gear for a 2-stage planetary gear set in an existing helicopter. The manufacturer achieved low cost by providing

identical epicyclics in both stages, thereby opening up the possibility of a reversible gear for double duty. There would be no in- crease in cost, in this case, but an increase in weight.

Figure 13 identifies the assembly/disassembly tools required for the

reversible sun gear which uses the internal-external snap ring. There

is no need to show the assembly tool. It is a piston ring compressor

134
which is commercially available. The disassembly tool is a ring with

four radial screws, equally spaced. These screws would be positioned

over the radial holes in the sun gear which are located at the internal snap-ring groove. They (the screws) would be turned in sequentially to press the snap ring out of internal groove preparatory to

disengagement of the sun gear from its shaft. The latter operation

would be accomplished in an arbor press.

The change proposed herein is not 100% gain; it is a tradeoff. For a small increase in weight and flyaway cost, save in the cost of spares.

Of course, this change would have to begin v/ith design and be implemented in the field. However, the helicopter manufacturer's primary

concern in the area of cost is to be competitive in flyaway cost;

there is no incentive to increase flyaway cost now with the prospect

of recovering that cost in spares sometime in the future. Therefore,

a double-duty epicyclic system would probably have to begin with the

Government specs accompanying the RFP/RFQ for new helicopter systems.

Here again, the Government is inhibited by af fordability , the cost of

acquisition.

There is another consideration, the intangible benefits to the user.

If and when the U.S. Army's helicopters are used in war, the lessons

of the last high-intensity conflict can be expected to be re-learned,

that there are never enough spares on hand. Whatever the intensity of

the conflict, there will be combat damage; there will be loss of lubricant and/or loss of lube pressure. The double-duty epicyclic system could enhance the availability of helicopters by reducing the

incidence of AOCP (aircraft out of commission for parts) on account of

slight but otherwise disabling damage to one side of gear teeth and/or

to one-half the circumference of a planet bearing inner race.

135
EVOLUTION OF EPICYCLIC GEAR SYSTEMS

AIRCRAFT APPLICATIONS

ENGINE EPICYCLIC GEAR SYSTEM

TYPE IOC

DECADE

R

S S

RECIPROCATING 1950 1.3 20 3.0

TURBOSHAFT 1960 2.1 8 4.4

TURBOS HAFT 1970 2.8 6 5.4

TURBOSHAFT 1980 3.6 5 6.5

TURBOPROP 1960 5.4 4 8.6

MESHING FREQUENCY OF THE SUN GEAR RELATIVE TO PLANET IDLER:

fj pWHERE 7} = NUMBER OF PLANET IDLERS

T P = NUMBER OF TEETH IN PLANET IDLER

R = NUMBER OF TEETH IN RING GEAR

S = NUMBER OF TEETH IN SUN GEAR

TABLE 1.

136
HELICOPTER PROPULSION ENGINES

AND DRIVE TRAIN

FIGURE 1.

137
DRIVE SYSTEM SCHEMATIC

SINGLE-ROTOR HELICOPTER

MAIN ROTOR

ENGINE

li(

EPICYCLIC GEAR SYSTEM

TAIL

ROTOR

ENGINE

FIGURE 2

138
GO

CO

OO

L±J I—

Q-Oo

I—o< 1 ^

>- \^ — <

Q_ LU >-

Lu

O cyo t l>

UJ

UIM, LU LU q:

IDO

u_

139
DRIVE SYSTEM SCHEMATIC

TURBOPROP

I

^^--EPICYCLIC GEAR

SYSTEM

FIGURE 4.

140
EPICYCLIC GEAR ARRANGEMENTS - THEN AND NOW

AIRCRAFT APPLICATIONS

FIGURE 5.

141
INTERIM EPICYCLIC GEAR ARRANGEMENTS

TURBOSHAFT ENGINES

n = 8

1960

HELICOPTER

n = 6

1970

HELICOPTER

FIGURE 6.

142
I EPICYCLIC GEAR ARRANGEMENTS

TURBOPROP ENGINES

FIGURE 7,

143
EFFECT OF REDUCTION RATIO ON SUN GEAR LIFE

EPICYCLIC GEAR SYSTEMS

10

8

RECIPS TURBOSHAFTS

2-

0

MESHING FREQUENCY RATIO

S UN/ PLANET

n=20 8

PLANETARY REDUCTION RATIO

INPUT/OUTPUT

4

1950 I960 1970 1980 1990

DECADE OF INITIAL OPERATIONAL CAPABILITY (IOC)

FIGURE 8.

144
TWO FAMILIES OF EPICYCLIC GEAR SYSTEMS

STAR ARRANGEMENT

REDUCTION: R/S

ROTATION, OUTPUT

VS. INPUT- OPPOSITE

n/

RING GEAR

OUTPUT

L

/

STAR

IDLERS

SUN

INPUT

'

i

Lr

T

CARRIER

FIXED

PLANETARY ARRANGEMENT

REDUCTION = 1 + R/S

ROTATION, OUTPUT

VS. INPUT = SAME

RING GEAR

FIXED

7/////A

PLANET CARRIER

OUTPUT

- PLANET

IDLERS

SUN

INPUT

\777777?

FIGURE 9.

145
DOUBLE-DUTY SUN GEAR

HELICOPTER

CURRENT: SHAFTGEAR

SINGLE DUTY

PROPOSED: REVERSIBLE GEAR

DOUBLE DUTY

FIGURE 10.

146
DOUBLE-DUTY SUN GEAR

TURBOPROP

CURRENT: SHAFTGEAR

SINGLE DUTY

PROPOSED: REVERSIBLE GEAR

DOUBLE DUTY

ffn

/-INTERNAL-EXTERNAL

^ SNAP RING

FIGURE 11,

147
DOUBLE-DUTY RING GEAR

HELICOPTER

CURRENT: ASYMMETRICAL GEAR

SINGLE DUTY

n

I

PROPOSED: REVERSIBLE GEAR

DOUBLE DUTY

FIGURE IZ

148
ASSEMBLY/DISASSEMBLY TOOLS

INTERNAL-EXTERNAL SNAP RING

REVERSIBLE SUN GEAR

PISTON

RING

COMPRESSOR

(COMMERCIALLY

AVAILABLE)

DISASSEMBLY

TOOL

FIGURE 13.

ASSEMBLY

TOOL

149
EFFECT OF ANTIMONY THIOANTIMONATE IN GREASES

ON ABRASIVE WEAR

J. P. King

Pennwalt Corporation

King of Prussia, PA 19406

Yayesh Asmerom

Pennwalt Corporation

King of Prussia, PA 19406

M. J. Devine

General Technology

Havertown, PA 190 86

Abstract: There is a crucial need for effective lubricant

additives that are capable of preventing damage that may

occur due to contamination of lubricating systems by abrasive particles. This is an essential requirement for

lubricants used in equipment and military vehicles that are

operated in sandy environments. The effect of antimony

thioantimonate (SbSbS^) in three base greases —MIL-G-10924,

MIL-G-24139, and MIL-G-81322 —was investigated. The presence of SbSbS4 in these greases provided considerable improvements in weld point, load wear index, and wear prevention properties with two different alloys. Moreover,

impressive wear resistance properties were imparted by low

concentrations of SbSbS4 in these greases deliberately contaminated with hard abrasive particles. The combination of

outstanding EP and antiwear characteristics and anti-abrasion properties of antimony thioantimonate makes this

material an attractive candidate as a grease additive. Extensive field testing of greases containing this material

is recommended.

Key words: Solid lubricant additive; antimony thioantimonate; abrasive wear; extreme pressure and antiwear properties; greases.

INTRODUCTION

Abrasive wear is well recognized as the primary cause of

surface damage for military vehicles and equipment as well

as industrial machinery.! This form of wear is encountered

when foreign materials, e.g., sand, grit or other hard

150
particles become entrained in the lubricant. Sources of

such hard particles include airborne contaminants entering

the system during equipment assembly or repair, finely

divided wear products from system components, fine debris

resulting from oxidation or corrosion, and operation in

sandy environments. Accordingly, a critical property of a

lubricant material or additive is its ability to prevent or

minimize component wear in the presence of hard abrasive

particles

.

Antimony thioantimonate (SbSbS4), when incorporated into a

number of selected greases as a solid additive at low concentration, imparts outstanding extreme pressure properties

on both chrome tool and stainless steels. 2 An initial

evaluation of SbSbS4 in several military greases was conducted with the objective of selecting one or more of these

greases to be formulated with SbSbS4 for field evaluation

involving sandy environment. To investigate additive response in the presence of abrasives, a grit material having

precise composition and known particle size was incorporated into those greases with and without the presence of

SbSbS4. The extreme pressure and antiwear characteristics

of these greases with and without SbSbS4 and M0S2 as additives were determined and compared.

PREPARATION OF ANTIMONY THIOANTIMONATE (SbSbS4)

Antimony thioantimonate was prepared by the procedures as

previously described. ^ a large supply of this material was

synthesized in preparation for the coming field evaluation.

GREASES

Three fully fomulated greases meeting the following military specifications were used as base materials:

MIL-G-10924 - Grease, Automotive and Artillery (GAA)

MIL-G-24139 - Grease, Multipurpose Quiet Service

MIL-G-81322 - Grease, Aircraft General Purpose Wide

Temperature Range

GRIT MATERIAL

The grit material used in abrasive study was supplied by

the A/C Division of General Motors Corporation, Flint,

Michigan. It has an average particle size of 60-80 y and

the following composition:

151
TEST METHODS

Falex Machine

Si02 68%

Fe203 5%

AI2O3 16%

CaO 3%

MgO 1%

Na20 5%

Ignition Loss 2-3%

The abrasive wear study was carried out on a Falex machine

using AISI-C-3135 steel pins (Rb87-91) and AISI-C-1137 Vblocks (R^20-24) . The testing speed, temperature, and load

were 290 rpm, 77°F, and 100 lbs, respectively. The following procedures were employed.

1. Test specimens (pin and V-blocks) were cleaned with

xylene followed by acetone and then air dried.

2. Test pin was inserted in pinholder.

3. Grooves of V-blocks were filled with grease sample and

struck flush.

4. V-blocks were set in their sockets.

5. Jaw loading assembly was mounted on lever arms.

6. Jaw load was brought to a gauge load of 100 lbs (manual

turning of ratchet wheel)

.

7. Drive motor was started and test run to 30 seconds, or

to failure if prior to 30 seconds. Failure was indicated by rupture of pin or rapid torque increases above

40 in-lb and excessive noise.

8. Test pin was cleaned with xylene and acetone before

making visual observation.

Four-Ball Testers

The extreme pressure and antiwear properties of the greases

were determined on Shell Four-Ball EP and Wear Testers.

These testers consist of steel spherical specimens sliding

against each other. Weld points and load wear indices were

determined in a series of runs (10 sec, 1800 rpm at 77°F)

conducted at various loads, and scar diameters were measured after each run in accordance with ASTM-D-2596. Wear

152
prevention characteristics were determined by measuring

scar diameters of test specimens after each run at specified rpm, load, temperature and duration (ASTM-D-2266 )

Two alloys—chrome tool steel AISI-C-52100 and stainless

steel AISI-440C—were used.

RESULTS AND DISCUSSION

Abrasive Wear Study

Abrasive wear tests were conducted with the Falex machine

for the three base greases (MIL-G-10924 , MIL-G-24139, and

MIL-G-81392) , the three base greases with 5% M0S2/ the

three base greases with 5% SbSbS4, and same modified

greases containing abrasive particles. The results for the

abrasive wear resistance imparted by 5% concentration of

SbSbS4 in MIL-G-10924 and MIL-G-24139 greases are presented

in Figure 1. It can be observed that severe wear and surface damage occur with either MIL-G-10924 or MIL-G-24139

(both containing 5% grit) ; however, SbSbS4 virtually eliminates such wear and surface damage. Wear effects were

also noted with MIL-G-81322 in the presence of abrasive

particles, although the base grease is originally formulated to provide some degree of protection from surface

damage in sliding contact. The presence of SbSbS4 further

improved the antiwear properties of this grease. The presence of M0S2 in all the three base greases also provides

some degree of surface protection; however, by visual observation the results are not as evident in all cases as

those obtained with SbSbS4.

Extreme Pressure and Antiwear Properties

As indicated earlier, all three base greases studied had

been fully formulated at the source in order to meet the

military specifications, i.e., they contained additives.

Our primary interest was to improve abrasive wear resistance of these greases by incorporation of SbSbS4; however,

the extreme pressure and antiwear properties were also obtained in order to determine whether these performance

properties were further improved by the presence of SbSbS4.

We found that the weld points and load wear indices of MILG-10924 could be considerably improved by the presence of

1 to 5% SbSbS4. At 5% concentration of M0S2 no increase in

weld point of this grease was observed; however, its load

wear index was somewhat higher than the base grease. Indeed, the EP properties of the base grease containing 1%

SbSbS4 were found to be superior to those of the same base

grease containing 5% M0S2. The antiwear characteristics of

153
the base grease containing 1-5% SbSbS4 showed slight improvement over its base grease. The experimental data are

recorded in Table I. A graphical comparison of the data

obtained on these greases is presented in Figure 2.

The weld point and load wear index of MIL-G-24139 containing 1% SbSbS4 were significantly higher than those of the

base grease. The weld point and load wear index of the

base grease containing 5% M0S2 were lower than that of the

same base grease containing 1% SbSbS4. The wear prevention

characteristics of samples of the base grease containing 1%

SbSbS4 and 5% M0S2/ respectively, were comparable and were

a dramatic improvement over the base grease on both chrome

tool and stainless steels. The experimental data are recorded in Table II and a graphical presentation is shown in

Figure 3.

Because of insufficient supply of MIL-G-81322 grease available to us at this time, load wear indices were not determined. The weld points of MIL-G-81322 containing 1 and 3%

SbSbS4 showed 25 and 100% improvements over the base grease,

respectively. With 5% M0S2 a weld point increase of 56%

was observed. The base grease, as originally formulated,

showed good wear prevention characteristics on chrome tool

steel. No significant improvement of wear prevention characteristics on both chrome tool and stainless steels was

achieved by incorporation of M0S2 or SbSbS4 into the base

grease. The results are listed in Table III.

CONCLUSIONS

1. The abrasive wear resistance of both MIL-G-10924 and

MIL-G-24139 greases was dramatically improved by incorporation of low concentrations of SbSbS4.

2. The extreme pressure and antiwear properties of three

base greases—MIL-G-10924, MIL-G-24139, and MIL-G-81322 —were greatly enhanced by using SbSbS4 as a solid

additive. At a lower concentration this additive outperformed M0S2 in all cases.

3. Antimony thioantimonate showed good response to both

chrome tool steel AISI-C-52100 and stainless steel

AISI-440C in all three base greases investigated.

4. If the presence of SbSbS4 in these three base greases

does not adversely affect other properties such as

water washing out, rust prevention, drop point, etc.

(investigation of some of these properties is planned)

,

the use of SbSbS4 as a solid additive in these greases

154
should be highly beneficial.

5. These results with SbSbS4 as extreme pressure and antiwear agent indicate potential for significant impact

covering major improvements for lubricating greases,

especially the current MIL-G-10924 (GAA) improvements

being pursued by the U. S. Army Mobility Equipment

Research and Development Command (DRDME-GL) , Fort Belvoir, Va.

ACKNOWLEDGMENT

This work was supported by the Office of Naval Research.

The guidance and encouragement provided by Commander Harold

P. Martin is greatly appreciated.

REFERENCES

1. T. S. Eyre, "The Mechanism of Wear", Tribology International, 11 (2), 91-104 (1978).

2. J. P. King and Yayesh Asmerom, paper presented as an

American Society of Lubrication Engineers Paper at the

ASME/ASLE Lubrication Conference in San Francisco,

Calif., Aug. 18-21, 1980 (ASLE Preprint No. 80-LC-7A2)

.

155
Table I. Weld Points ^ Load Wear Indices ^ and Wear

Scar Diameters of MIL-G-10924 Grease

Containing Additives

Grease Composition Weld Point/

kg

LWIWear Scar'

Diameter

,

mm

MIL-G-10924 Grease (GAA)

" + 1% SbSbS^

" +5% SbSbS^

" +5% MoS^

160

250

315

160

29.3 0.62

39.4 0.59

56.7 0.59

38.4 0.57

1. ASTM-D-2596 - AISI

2. ASTM-D-2266 - 1200

hour on AISI 52100

52100 Steel

rpm, 40 kg, 167°F for one

steel

156
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158
Figure 1. Effect of SbSbS4 on Abrasive Wear

The outstanding wear resistance properties imparted by SbSbS^ to

greases containing grit particles (primarily Si02 60-80 u) are illustrated by these Falex pins

a = grease MIL-G-24139 with 5% grit

b = " " " " and 5% SbSbS^

a' = " MIL-G-10924 " " b' = " " " " and 5% SbSbS4

159
3.0

2.0

1.5

1.0

0.5

0.4

0.3

0.2

u

(U

u

o

1.

2.

3.

4.

MIL-G-10924 (GAA)

GAA + 5% M0S2

GAA + 1% SbSbS^

GAA + 5% SbSbS,

I I 20 30 40 50 100

Load, kg

200 300 400 500

Figure 2. Wear Scar Diameter vs. Load; AISI-C-52100 Steel

Balls; 25''C, 1800 rpm, 10s

160
1. AMI (MIL-G-24139)

2. AMI + 5% M0S2

3. AMI + 1% SbSbS,

_J I I I I

i » 20 30 50 100 200 300 400

Load, kg

Figure 3. Wear Scar Diameter vs. Load; AISI-C-52100 Steel

Balls; 25''C, 1800 rpm, 10s

161
SILICONE BRAKE FLUID: THE ANSWER TO REDUCED

MAINTENANCE AND LONGER LIFE!

G. W. Holbrook

Associate Consultant

Dow Corning Corporation

2200 W. Salzburg Road

Midland, MI 48640

Abstract: One of the most costly maintenance items in a

motor vehicle is the hydraulic braking system. Studies by

the Department of Transportation indicate that on an average

the hydraulic braking components are replaced at least twice

during the life of a vehicle at a cost of $700 to $1000.

A thirteen-year development and testing program involving

the U.S. Army, the Department of Transportation, and the

silicone industry has resulted in the development of silicone-based brake fluids. Extensive testing has demonstrated

the superior performance of these fluids which give promise

of providing a hydraulic system which will need no maintenance for the life of the vehicle, exclusive of friction

materials

.

Key words: Long life; reduced maintenance; silicone brake

fluid; U.S. Army.

A common goal of design engineers, maintenance engineers,

and equipment users is to reduce maintenance while increasing durability and reliability. These goals are often incompatible without expensive and sometimes impractical engineering changes.

Although often not recognized, one of the most costly items

in vehicle maintenance is the hydraulic braking system.

Studies by the Department of Transportation indicate that on

an average the master cylinder and wheel cylinders are replaced at least twice during the life of a vehicle. [1] In

a fleet operation the average interval to the first master

cylinder replacement is 15.8 months or 35,000 miles and 17.2

months or 38,900 miles to the first wheel cylinder replacement. [2]

Typical fleet practice is to perform a brake overhaul every

25,000 to 30,000 miles. Any hydraulic components which show

162
signs of leakage are replaced. At this second maintenance

interval all components are automatically replaced, an operation estimated by one fleet manager to cost $350.00

Curiously, preventive maintenance programs sometimes obscure

the real cost of brake system maintenance since emphasis is

placed on reliability and elimination of unscheduled down

time. Fleet managers take pride in the fact that they have

no problems with hydraulic braking systems. Further discussion often reveals that the lack of operational problems are

the result of a rigorous maintenance schedule. In one case,

examination of a vehicle record card selected at random

showed that nearly $1000 had been spent on maintenance of a

seven-year-old vehicle I

In 1967 the Mobility Equipment Research and Development Command recognized the need to reduce maintenance and to increase reliability and life of braking systems on military

vehicles

.

Primary emphasis was placed on an improved brake fluid rather than hardware since major engineering changes in the

braking system were considered impractical, and was brought

about because of a need to use three brake fluids an operational fluid for use in most theaters, an Arctic fluid for

low temperature use, and a preservative fluid, installed

whenever a vehicle was put into storage.

The logistics of maintaining three fluids in the supply system, the cost of repetitive fluid changes, and the general

inadequacy of the operational fluid pointed clearly to the

need for a single fluid, suitable for all three types of

service

.

An earlier unsuccessful evaluation of silicate esters and a

successful program to develop a silicone fluid for use in

rotary shock absorbers led the U.S. Army to initiate a joint

development program with the silicone industry. [3]

The rationale for selecting a silicone-based brake fluid is

brought into focus by a 1969 SAE publication entitled, "What

the Brake Engineer Wants From Brake Fluid. "[4]

In that paper the ideal fluid was described as:

having a high boiling point, preferable over 4 00°F which

is unaffected by any atmospheric condition.

having the lowest possible viscosity at -40°F.

163
being chemically inert, thermally stable, noncorrosive

,

and having no effect on paint.

being compatible with every type of automotive brake

fluid and brake hardware on the market.

These criteria demonstrate an uncanny fit with the properties of polydimethylsiloxanes , popularly referred to as silicones. These materials:

have a high boiling point, typically 700°F in the viscosity ranges suitable for use in a braking system.

- —do not attract moisture and thus will maintain their high

boiling points.

have the flattest viscosity temperature slope of any

known polymeric material.

possess outstanding thermal, chemical, and mechanical

stability

.

are noncorrosive and do not attack paint.

An intensive development program over the next six years

produced fluids which appeared to meet all criteria for a

single, all weather fluid.

In March, 1973 a program was initiated by the Army to evaluate the performance of silicone brake fluids in military

vehicles operating in a variety of climatic conditions . [5]

The fluids were field tested for two years in direct comparison with conventional fluids at the Tropic Test Center

(Panama Canal Zone) , Yuma Proving Ground (Arizona) , and the

Arctic Test Center (Fort Greeley, Alaska)

.

The performance of the silicone fluids was reported to be

"significantly better than that of conventional fluids."

The differences were especially striking in the Canal Zone

where all conventional fluid-filled vehicles failed within

one year because of corrosion, with water contents reaching

15.7%. In contrast, the silicone-filled systems were in

excellent condition.

In Yuma, water contents reached a surprisingly high 8.4%,

and caused severe corrosion, although all vehicles completed

the two-year test. The condition of the silicone-f illed

braking systems was judged to be excellent.

164
1974 MUSTANG fI

Fi gure 1

.

165
In Alaska the test was conducted for only one year, primarily to document low temperature performance. Even after one

year corrosion was noted in the polyglycol-filled vehicles.

As a result of these field test results a recommendation was

made that all military vehicles be converted to silicone

brake fluid.

The two-year field test, although impressive, did not truly

demonstrate the increased life and reduced maintenance afforded by use of a silicone brake fluid.

Our test fleet has spanned ten years and includes over 300

vehicles from all domestic and most foreign manufacturers.

Examination of components has documented that silicone brake

fluids will provide maintenance-free operation, exclusive of

friction materials, for the life of the vehicle.

One of our test cars was recently examined after seven years

and 123,650 miles. Water content of the fluid was 200 parts

per million. All components were found to be in new condition, with no evidence of bore wear, seal chipping or corrosion, as shown in Figure 1.

In 1977 the National Highway Traffic Safety Administration

funded a contract to determine technical feasibility, expected economic impact and required lead times for a ruling

which would require a long life warranty for hydraulic braking systems.

The contract report [6] concluded, "The survey task uncovered

a body of testing data related to the use of silicone base

brake fluids. Evidence appears to be sufficient to support serious consideration of their use in candidate long

life braking systems."

Included in the recommendations were a number of engineering

changes which would have increased vehicle costs by $12.50

per vehicle and which in the opinion of this author would be

unnecessary. The incremental cost of OEM installation of

silicone brake fluid is estimated to be $1.50 to $2.00 per

vehicle

.

Savings to the consumer, including the engineering changes

recommended by the contractor were estimated to be

$460,000,000 per year. Elimination of these engineering

changes would result in savings of over $500,000,000 per

year

.

Legitimate questions have been raised concerning the risks

166
of substituting a fluid having substantially different chemical and physical properties into a braking system designed

for polyglycol/polyglycol ether-based brake fluids.

These concerns included seal compatibility, the consequences

of the inevitable mixing of the two fluids and the effect of

water entry into a totally water intolerant fluid.

It has been demonstrated [7] that the base polydimethylsiloxanes, which shrink brake system elastomers, will function

adequately in a braking system. However, government, military, industry, and SAE standards require controlled swell

and a high degree of seal compatibility.

Elastomeric compositions used in braking systems are designed around the properties of conventional brake fluids.

The task of formulating a silicone fluid to give controlled

response with four dissimilar elastomers having widely different responses to plasticizers proved to be formidable,

and was primarily responsible for the long developmental

phase of the program.

As a result of the intense concern over seal compatibility,

current silicone brake fluids are not only compatible with

brake system elastomers but have been shown to be superior

to conventional brake fluids.

In the most definitive study to date [8] "1200 immersion

tests were carried out at temperatures ranging from 0°F to

248 °F with fourteen different elastomers and five different

brake fluids. It was found that silicone brake fluids performed as well as/or better than conventional fluids. Extended periods of exposure did not reveal any deficiencies."

Deficiencies were revealed in conventional fluids when tested outside the narrow ranges specified in current standards,

as follows:

SBR - Shrinkage at ambient temperature.

EP - Shrinkage at 0°F.

Neoprene - Excessive swell at elevated temperatures.

Federal Motor Vehicle Safety Standard 116 and MIL B 46176

contain provisions designed to ensure compatibility of silicone fluids with conventional fluids. Although immiscible,

the fluids are compatible and mixtures perform well in a

braking system.

One vehicle in our test fleet operated for seven years and

93,000 miles on a mixture of 70% silicone and 30% conven167
tional fluid. Examination revealed a small amount of

sludge in the polyglycol layer and some surface staining.

However, there was no evidence of pitting, corrosion scale,

or seal damage.

This vehicle was placed back in service using all the original components, this time using pure silicone brake fluid,

and has now passed the ten-year mark and has accumulated

170,000 miles.

As a result of the extreme hygroscopicity of conventional

fluids, water in a braking system has become an accepted

fact of life to brake engineers. As a result, the concept

of a totally water intolerant fluid was difficult to accept.

Extensive laboratory testing, plus well over four million

miles accumulated by our test fleet, has demonstrated that

water does not enter a silicone-f illed system.

As manufactured, our silicone brake fluids typically contain

300 parts per million water. Humidif ication as specified in

FMVSS 116 gives approximately 350 parts per million.

Ten vehicles were examined for water content after service

use ranging from two to six years and mileage ranging from

6000 to 60,000. Water contents averaged 27 0 ppm.

The effect of direct addition to the master cylinder has

also been addressed. Stroking data at high and low temperatures, submitted to the SAE Motor Vehicle Brake Fluid Subcommittee ,[ 9 ] showed that water added to a silicone-f illed

system remained localized in the master cylinder and had

little or no effect on performance; in a glycol-filled system the water migrated rapidly through the system, causing

vapor lock at elevated temperatures and sluggish to inoperative brakes at lower temperatures.

Given the high levels of water typically present in a glycol

filled system and the rapid migration of additional water

through the system, these studies indicate that direct entry

of water via the master cylinder would have a more deleterious effect with "water tolerant" polyglycols than with nonwater tolerant silicones.

Summary

The seemingly incompatible goals of reducing or eliminating

brake system maintenance while increasing durability, reliability and service life are clearly attainable and cost effective by use of silicone brake fluids.

168
This is best demonstrated by the title of MIL B 46176,

issued in March, 1974:

"Brake Fluid, Silicone, Automotive, All Weather, Operational

and Preservative."

Bibliography

1. "Maintainability and Repairability of Vehicles in Use,"

DOT HS 800-512, June 1971.

2. "Optimized Brake Inspection," NHTSA DOT HS 6-0183, December 1971.

3. "One Third of a Century of Army Interest in Automotive

Hydraulic Brake Fluids," C. B. Jordan, U.S. Army Aberdeen

Proving Ground, SAE Publication 760294, February 1976.

4. "What the Brake Engineer Wants from Brake Fluid," R. H.

Hellman, SAE Publication 690222, February 1969.

5. "Silicone Brake Fluids: Two Year Field Test," J. Conley,

et al. Report 2164 AD-AO26180, U.S. Army Mobility Equipment Research and Development Command, January 1976.

6. "Long Life Hydraulic Brake System," Ziskind, et al , DOT

HS-805 068, May 1979.

7 . Communication to the SAE Motor Vehicle Brake Fluid Subcommittee, A. Torkleson, General Electric Corporation,

October 1974.

8. "Compatibility of Silicone Based Brake Fluids With Elastomeric Components of Army Vehicles and Weapons Systems ,

C. B. Jordan, Aberdeen Proving Grounds, Test Activity Report APG-MT-5351, February 1980.

9. General Electric Technical Information Series Reports,

75 CM-S-100 and 75 CM-S-101, J. C. Frewin and G. R.

Browning.

169
THE REQUIREMENT OF LUBRICATION SYSTEMS

IN MAINTENANCE PROGRAMS AND NEW

DEVELOPMENTS TO El'^ABLE MORE

PRECISE CONTROL

C. Trainer

Interlude Systems, Ltd.

Plymouth , r]n gl and.

D. R. Rokos

Interlutie, Inc.

Bensenville, Illinois 60106

A prime part of any maintenance program is the prevention of

damage to moving parts, positive accurately controlled lubrication

is essential to avoid costly breakdowns and to extend life of plant in

its operational environment.

In simple terms effective lubrication is achieved vihen. a film of

lubricant is maintained between two surfaces in relative motion, this

is generally termed as a Hydro-dynamic condition.

To maintain this condition lubrication systems are designed to

supply quantities of lubricant either cyclically or continuously, the

fomer more generally used enabling simplicity of machine design, this

in turn creates problems of system design vjhere outputs of lubricant

injectors must be accurate and the timing of injection critical.

In recent developments it is possible to supply lubrication

systems with inbuilt diagnostic controls Vi^iich monitor all functional

aspects including the actual passage of lubricant as it is discharged

from the injector into the bearing. This latter development has been

made using latest technology and removes maintenance engineers'

anxiety and concern in being sure that lubricant has reached the

moving parts and has not been dispensed via broken tail feed tubes

or that a particular system injector has not operated.

The purpose of this paper is to examine the concept of

lubrication in its use and to highlight developments \A^ich lead to

more precise control and ensuring protection of costly moving parts

which in turn leads to higher productivity.

170
FUNCTION OF LUBRICATION

To reduce friction or resistance to motion.

DEFINITION OF FRICTION

Eriction is defined as 'that force v^ich acts between two bodies at

their surfaces of contact so as to resist their sliding upon each other'

TYPES OF FRICTION

1. Solid Friction :- two ccmponents in contact and relative

motion. To sustain this motion great effort is required

and heat generated.

2. Rolliiig Friction :- one conponent rolling on the other.

Here at first glance there would appear to be no friction

at all, other than the resistance of the atmosphere.

However, we find that there is no perfect rolling action,

seme sliding or solid friction is always present.

3. Fluid Friction :- two ccmponents in relative motion

prevented from making contact by a film of fluid lubricant.

Here the friction depends on the fluid lubricants' ability

to slide within itself. The effort required here to sustain

movement and the heat generated is minimal. This is

generally termed 'Hydro-dynamic' lubrication.

HYDRO-DYNAMIC LUBRICATION

Hydro-dynamic lubrication is achieved vihen a complex number of

considerations v\^ich include type of oil, loads movement, amounts of

lubricant to be supplied etc., are combined together to give the

effect of a wedge of lubricant separating the asperities of solid

bodies v\^ile in relative motion.

Let us consider a journal bearing through' its cycle of rest and work:-

a) When the journal is at rest practically all the lubricant

has been squeezed from the load area.

b) When rotation starts, with the clearance space filled with

oil, the journal will tend to ride up the bearing surface

and in so doing will entrain some lubricant vHnich will pass

between the journal and bearing surface. A wedge of oil

is developed which will support the journal whilst it

proceeds to rotate (see Diagram 1.).

This is the easiest example to show and understand. The principle

remains the same for linear and oscillating bearings, with the wedge

being assisted by lubricant 'ways' and the surface texture of the

171
FORMATION OF FULL FLUID

FILM IN A JOURNAL BEARING

172
moving bodies.

Hydro-dynamic lubrication is a most effective method of minimising

wear and surface damage.

FLUID LUBRICANTS (OIL AND GREASE)

,

Oil Offers advantages over grease since oil feeds more readily into

the loaded contact area of a bearing. There is no known limit to the

speed \4iich can be attained with the correct amount of oil lubrication

provided that the oil is delivered in correct quantities, at correct

intervals, and is fluid enough to reach and support the moving parts.

Under certain conditions the plastic nature of a soap-thickened oil

is prefered to the fluidity of a lubricating oil. Such a mixture of

oil and soap constitutes a grease, the resultant lubricant is capable

of forming a plastic lubricating film. Generally speaking greases are reconmended v\*iere:-

a) mechanical design would result in excessive oil leakage.

b) in industries vdiere excessive oil leakage might result

in contamination of the finished product.

c) on slow moving parts v\^ich would have long intervals between

re-lubrication

.

DEFINITION OF OIL AND GREASE

1) Oil is a true 'Newtonian liquid' v\^ich means that the

molecules of v^^ich the oil comprises slide over each other

at a rate directly proportional to the force tending to

make them slide.

2) Grease is defined by the American Society for testing and

materials (ASTME designation D-288) as follows.

'A solid to semi-fluid product of dispersion of a thickening

agent in a liquid lubricant. Other ingredients imparting

special properties may be included •

By definition grease is merely a lubricating oil plus a thickening

agent.

Oil is therefore better suited to attaining efficient lubrication

between moving bodies than grease.

173
OBJECTIVES OF PROGRAMiyED LUBRICATION

The Four Rights :-

Resulting in:-

1) Right type in.

2) Right amount at.

3) Right place at.

4) Right time.

a) Safety of personnel.

b) Uninterupted production.

c) Extended machinery life.

d) Good housekeeping.

e) Lower operational costs.

CENTRALISED LUBRICATION SYSTEMS

Centralised lubrication systems fall into two main headings

1. Total loss systans - v^ere lubricant is supplied in small

quantities at pre-determined Intervals, worked by the

bearings and lost in the process.

2. Recirculating systems - where lubricant is supplied in

flood quantities continuously to bearings, the lubricant

that is not used is captured ^d returned to a sunp or reservoir and re-cycled.

It is quite canmon to find both types of system on the same machine.

Total loss supplying lubricant to slides, exposed bearings, or anywhere that design limitations make it irrpracticable to capture

and re-cycle excess oil.

Recirculation systems in gear-boxes or enclosed housings v\*iere excess lubricant can be easily contained.

The two types of systems are subject material, each worthy of it's own paper. This paper will concern itself with the total loss system

which is in daily use on virtually every moving mechanism.

174
TOTAL LOSS CENTRALISED LUBRICATION SYSTEMS

These systems can be divided into two main categories :-

1. Single line resistance systems.

2. Positive Displacement systems.

1. Single Line Resistance Systems

General description:- a prime mover forces a pre-determined volume

of oil, under pressure, into the distribution system. Oil is

apportioned to each bearing based upon its individual requirement by

means of resistance fittings or fixed orifice flow control units.

The interval between shots of lubricant is controlled in various ways,

but the two most comnon are:-

i) build-up and discharge of a spring loaded accumulator.

ii) through an electronic timer switching a motorised gear

pump on and off.

The electronic timer offers the most scope in setting parameters,

and modem controls combine: a motorised gear pump in a reservoir,

electronic timer with capacity to monitor low-level and pressure

failure, incorporating inter-face facility to m/c panel, all housed

in one unit.

A typical system layout is shown below:-

To Pressun Stultch

PRESSURC

SlUITCH

Po«t r i'jpply

To Control ContrB

Intarfacd

to n/z

1

-I

I

I

LINE FILTER

TYPICAL ii BEARINnCJ

DO

CONTROL CENTRE

^ LI D o o o

FLOU/ UNITS

175
SYSTEM ANALYSIS

a) Suitable for oil only.

b) Manual or autcmatic.

c) Out-put pressure from prime mover 40 - 100 p.s.i. normally.

d) Monitoring available on basic system

i. broken line (i.e. pressure loss)

ii. filter blockage

iii. main line blockage

iv. low level

e) Installation relatively simple. Flow units compact and can be

fitted direct into bearing housing

f) Low pressure system with small orifices. Flow units can be

prone to blockage (not monitored by basic system)

.

g) Adding or subtracting lubrication points to a system can cause

the system to go out of balance.

h) Blocked flow units should never be drilled-out to clear, as this

changes the flow characteristic, but should be re-placed by a new unit.

i) In general, if a resistance system has been in service for

sometime and a flow unit blocks-off , it is better to replace all

flow units as their condition is usually related.

2. Positive DisjxLacement Systems

These systems can be sub-divided yet again into:-

i) single line simple positive displacement injectors systems.

ii) single line series of progressive positive displacenent

systems

.

iii) dual line positive displacement systems.

These three variations represent the more caramon positive displacement

systems in use today.

i) Single Line Simple Positive Displacanent Injector

General description: the method of controlling the amount of

lubricant supplied per cycle is through positive displacement

injectors, v^Aiich can be likened to single acting hydraulic piston

176
puirps. The best way to show how they work is in diagramatic fom:-

(a R

l\ Vi

o m

At rest Delivery of lubricarrt Transfer of kjbrcant

a) At rest: prime-mover is at rest. No oil is being pushed around

the system.

b) Delivery: prime-mover is switched on and oil is pushed into the

main line, building up the pressure. At a pre-determined pressure

the cup-seal on the inlet to the P.D.U. is pushed forward against

the central tube, sealing the tube. As the pressure continues to

rise the outer lip of the cup-seal collapses and allows lubricant

to pass. The lubricant goes through the spider, supporting the

central tube and onto the back face of the piston, pushing the

piston forward displacing the lubricant in front of the piston,

forcing it out of the injector, through a hole in the side of the

tube and finally into the bearing. When the piston reaches its

•stop' no more lubricant is delivered to that bearing during this

cycle. By varying the stroke of the piston the amount of

lubricant delivered is increased or reduced.

When all the pistons in the injectors of a system have moved

forward, the delivery of lubricant to that system for that cycle

is complete, and although the prime-mover will still be operating

its output being by-passed to the reservoir, no more lubricant

is delivered to any of the bearings and eventually the prime-mover

is switched off.

c) Transfer of lubricant: v\*ien the prime-mover is switched off, a pressure residual relief valve opens in the main line and reduces

177
the pressure back to atmospheric, the excess lubricant being

returned to the reservoir.

This fall in main line pressure allows the cup-seal to expand

back to its normal state, sealing-off the inlet of the injector and

acting as a non-return valve.

The spring is now dcminant and pushes the piston back, but the

lubricant behind the piston cannot travel past the cup-seal. The

cup-seal is thus lifted back off the central tube, allowing the

lubricant to travel down the tube, transfering from the back of

the piston to the front, as the piston moves. Note:- The piston is moving on a shaft so the displacement of

lubricant on both sides of the piston is equal, making it

inpossible to draw lubricant back from the bearing.

d) At rest: as a) awaiting the start of the next cycle, vAien the

prime-mover is switched on.

The principle outlined in a) to d) is common to this type of system

although the technique may change fran manufacturer to manufacturer.

The interval between cycles for this system is usually controlled by

a motorised gear pump operated by a timer. As with the Resistance

System the modem controller is of the ccmbined type, i.e. motorised

gear pump, electronic timer etc.

A typical system layout is shown below:-

To Prtsiur* Snitch

PICSSURE

SWITCH

Poiuo r r

" Supply T"

Interface

to m/c

1 1

I

I

I

LINF FILTER

CONTROL CENTRE

To Control Contr*

TYPICAL

aEf.RING Q

IINJECTOR An

o

178
SYSTEM ANALYSIS

a) suitable for oil or in seme cases semi-fluid grease up to

Index '0'.

b) manual or automatic.

c) out-put pressure from prime-mover normally around 300 p.s.i.

d) monitoring available on basic system

e) installation relatively simple. Positive displacement units are

coirpact and can be fitted direct into bearing housing.

f) injector design makes a blockage or piston seizure a rarity, but

should one occur the basic system does not monitor.

g) adding or subtracting lubrication points to a system is no

problem.

h) positive displacement gives specific amounts of lubricant,

delivered to bearings from .03cc per cycle upward. Amounts vary

with manufacturer.

i) performance unaffected by back pressures.

j) failure of one lubrication point does not prevent others receiving

the correct amount of lubricant.

k) a flexible system, widely used on medium to high production plant

lubricated by oil or semi-fluid grease.

ii) Single Line Series or Progressive System

General d«bscription : the method of controlling the amount of

lubricant supplied per cycle is a combination of prime-mover output

and spool-valve movement.

The operation of the spool-valves is best observed in diagramatic

form (see overleaf) :-

i)

ii)

iii)

iv)

broken line anyv\^ere in circuit,

filter blockage,

main line blockage.

low level.

179
Fig.._ 1 shows the pressure path,

i.e. dark shaded areas, as the

first spool begins to move across,

The light shaded area shows the

path of the lubricant out of

exit point 1.

Fig. 2 shows the new pressure path,

i.e. dark shaded areas vAien spool

one has moved across and now spool

two is forced to move. When spool

two has crossed spool three will be

pressured.

The light shaded area shows the

exit path for point 2.

Fig. 3 shows the pressure path,

i.e. dark shaded area ^en spool

three has moved across. Fran this

it can be seen that the pressure

is now back on spool one but this

time pushing the spool back and

delivering lubricant out of exit 4 as indicated by light shaded area. Thus the cycle continues pushing

spools two and three back and then

starting all over again (see Fig.l)

180
The three element block described (i.e. three spools) is the smallest

block that can operate within the series principle. Larger element

blocks (i.e. 4, 5, 6 etc.) operate in exactly the same way i.e. spool

1 then 2 then 3 etc . , until the end one is reached and the vAiole block

of spools starts to move back in sequence, spool 1, then 2, then 3 etc.

It may be noted at this point that if pressure is maintained on the

inlet line the block will cycle over and over again. When the block

has corpleted one cycle the prime-mover has to be switched off

immediately or the block will begin to cycle again.

The interval between cycles for this system is usually controlled by

a timer operating a single or double acting air or hydraulic piston

pump with adjustable stroke. Motorised punps can be used but are

not as easily controlled.

The timer normally has capacity to monitor for lubricant level and

end of cycle switching, incorporating an inter-face to the m/c giving

shut-down facilities.

A typical layout is shown below:

TIITER c 1

RESERVOIR

flIR LINE J\

o—SOLENOID

VALUE

AIR PUIYIP

OHO

o-O

oaErJO OF CYCLE

SU/ITCH -O

-OO

-O

A03USTABLE

STROKE

oo—

1

—

o

o— —

o

o— —

-o

-o

-o

TVPICAL BEARINGS

SERIES BLOCK

181
SYSTEM ANALYSIS

a) suitable for oil or grease up to Index 2.

b) manual or automatic.

c) output pressure from prime-mover up to 2000 p.s.i.

d) monitoring available on basic system.

i) blockage anyv\^ere in the circuit,

ii) main line broken,

iii) low level.

e) installation is complex. Blocks are bulky because the positive

displacement spools are part of the block.

f) the spools are match-ground with bores, this means small particles

of contaminent either in the lubricant or in the pipe cause the

spools to bind. This is monitored by the basic system as a blockage. Broken pipes fron block to block or block to bearing

point cannot be monitored by basic system.

g) adding or subtracting points on a system is corrparatively ccmplex.

h) positive displacement gives specific amounts of lubricant delivered

to bearings.

i) failure of one spool to deliver lubricant stops all other spools

operating.

j) series systems are probably the only practical, cost effective

means of applying measured amounts of grease to the lubrication

points on small and medium machines. However, for oil systems the

corrplexity of installation and lack of layout flexibility may outweigh any advantages over other Positive Displacement types.

iii) Dual Line Positive Displacement Systems

General description: the method of supplying lubricant is by movement

of spool valves operating main pistons. Each spool and piston operates

independent of the others in the system. This is achieved by

connecting the P.D. units in parallel and supplying pressure to one side of the spools via the first main line, v/hen all the main pistons

have moved their full travel a reversor valve, operated by pressure in

the main line, changes the out-put of the prime-mover to the second

main line and relieves the pressure in the first main line, allowing

the spools to be pushed back by the pressure in the second main line.

The main pistons travel back. As the pressure builds up in the second

main line the reversor operates again and the cycle begins again.

182
A typical valve arrangement is shown in diagram form below:-

INDICATOR

MAIN

PISTON

SPOOL

VALVE

Fig. A) Lubricant frcm main line 1 pushes

down the spool valve. Main piston is forced

downwards delivering lubricant below piston

through outlet 'B' to bearing.

Fig. B) Main line 1 depressurised. Main

line 2 pressurised lifting the spool valve.

Lubricant above main piston is delivered

through outlet 'A* to bearing.

The interval between cycles for this system is controlled by a timer

switching a prime-mover. The main line reversor is usually automatic,

and the timer switches off the prime-mover when the second line

pressurises

.

A typical system layout is shown overleaf :-

183
VENT LINE

REUERSER UALVE

lYIAIN PRESSURE LINE

SECONDARY LINE typical

6

BEARING typical o

SYSTEM ANALYSIS

a) suitable for oil or grease.

b) manual or autanatic.

c) out-put pressure from pump up to 5000 p.s.i.

d) monitoring available on basic system.

i) broken main line,

ii) main line blocked,

iii) low level.

e) installation complex. Two main lines instead of one and blocks are large.

f ) system operates with spools again prone to seizure. Not monitored

by basic system.

g) adding and subtracting points to a system no problem.

h) positive displacement gives specific amounts of lubricant

delivered to bearing.

i) failure of one spool or main piston to operate does not prevent

other points from being lubricated.

j) these systems are capable of applying grease to widely separated

lubrication points on very large machines. Main application in

steel industry and similar large equipment users.

184
LUBRICATION SYSTEM DIAGNOSTICS

All the systems we have IcxDked at have their applications v\^ere they

can be used to their best effect, but each system has disadvantages

that cannot be overcome by layout or system design. These

disadvantages are inherent faults that makes the system prone to

failure, resulting in a starvation of lubricant to one or more bearing

points.

As we have seen, some systems will monitor broken lines, others will

monitor a blockage, but there is no basic system that will fully

monitor the passage of oil to the bearing.

It is possible to add micro-switches, mechanically operated by

plungers attached to individual P.D. units. It is possible to add

pressure controlled micro-switches to each secondary line frcm the

series block to the bearing, all in an effort to monitor that

lubricant has entered the bearing, and all of these methods adds more

ccmplication, more moving parts to go wrong. In the end they are just

not reliable.

The answer to the problem has been found using modern micro-electronic

technology.

GENERAL DESCRIPTiqsi

A transducer assembly has been designed for fitting into the bearing

lubrication entry point. The transducer has no moving parts. It

signals to a console that lubricant has flowed past it into the

bearing during a lubrication cycle.

When the console receives a signal frcm one of the transducers in a system the console records that as a good point. At the end of a lubrication cycle any points monitored by the transducers that have

not past lubricant are shown on a numbered read-out. The maintenance

engineer reads the number of the lubrication point or points v\^ich

has failed. That number corresponds to a reference on a lubrication

circuit layout and the engineer is pointed quickly and accurately to

the heart of the problem. Cutting maintenance and down-time to a minimal, but the main advantage is that the lubricant starvation has

became obvious before it has become costly.

ANALYSIS

a) the system is called LUBESCAN.

b) it can be fitted to any of the lubrication systems previously

discussed.

c) the system indicates that lubricant has passed into the bearing.

Should lubricant not flow past a transducer for any reason, e.g.

blockage, broken line, pump failure etc., then the system will

185
indicate the bearing or group of bearings not supplied with lubricant.

d) transducers do not have to be fitted to every lubrication point on

a system. If required, only selected points may be monitored.

e) installation is simple and transducer assemblies are contact.

f) LUBESCAN can be retro-fitted to existing lubrication systems.

Cable Socket Oil Flow

Transducer assembly Lubescan- console

IN CONCLUSION

This short appreciation of industrial practices, the importance of

correct lubrication and the comments on the most widely used systems

will, we hope, give you a better understanding of this topic.

Everyone knows moving parts require lubricating to keep them working

properly, but how many people fully realise the iirprovements in overall

performance v^^ich can be achieved by lubricating bearing areas correctly. This is an area v^ere the preventitive maintenance engineer

has a tremendous influence. An area of vital innportance to plant

engineers v\^o are responsible for achieving agreed levels of production.

A major part of our activity is advising designers and users of

machinery on the best way to lubricate their products or plant. This

is a function we feel particularly well qualified to perfom since we

have available a wide range of lubrication equipment.

If you need any assistance on specific applications we shall be

delighted to place our considerable technical resources at your

disposal.

186
CONCEPTUAL PROPOSAL POR SELF-LUBRICATING

HIGH CARBON PISTON RING STEEL

Philip 0. Badger

P. 0. Box 54, V/ashburn Branch

Waterloo, lov/a 507O6

Abstract: Molybdenum disulfide bonding to high carbon interstitial alloys utilized in the manufacture of piston

rings is performed at an intermediate stage of the steel

making process when voids existing between surface asperities are pronounced. Subsequent steps in the traditional

steel making process impregnate the lubricant into the

outer periphery of the cross-section by mechanical pressures. The alloy produced maintains the same physical properties such as yield strength and Rc hardness specified for

piston ring stock but exhibits a sustaining self-lubricating characteristic of a bearing material.

Key words: Carbide precipitation; decarburization zones;

implantment by mechanical inclusion; macro-molecular clustering; molybdenum disulphide imbedment.

It has been demonstrated in applicable dry solid lubrication investigations that molybdenum disulfide (M0S2) has

proven to be a versatile lubricant. Inherent basal cleavage intrinsically occurring within its atomic structure

causes low lamellar shear strength. This property contributes to superior anti-friction and lubricity properties.

In prior work by the author in motor spring applications an

inorganic bonded film containing M0S2 was utilized to improve dynamic torque levels. This property has proved extremely useful in various MT fuze designs related to ordnance applications. Horological mechanisms of the classical design using escapement assemblies have in certain

instances been operated 500^ longer than those not using

the coating before rewinding was required. These increased

performance levels were a product of reduction in the kinetic coefficient of friction between the spring leaves

during the unwinding process; from fully wound to fully extended. Also associated with these torque measurements, in

the dynamic state especially, was a dramatic reduction in

stick-slip phenomena historically associated with mainspring application technology.

187
Pursuant to this prior activity, a proprietary technique

was developed for application of the bonded film containing

M0S2 to various substrates that has proven to be extremely

cost effective. It is applied in a "coil to coil" operation at reasonably rapid rates. Adhesion properties of the

film to the substrate has in all cases proved outstanding.

The process also has demonstrated an ability to apply a

uniform thickness to the surfaces of the substrate (as

ultra thin as ,00015" or as much as .0005" depending on

thickness desired) irrespective of cross-sectional area or

quantity. Due to this process, it is possible to apply a

bonded film containing M0S2 to metallic substrates of varying elemental composition at an intermediate stage of processing.

It should be noted that conventional application of bonded

films of various dry film lubricants have traditionally

been applied by spraying or dipping methods and subsequent

drying and/or baking. These methods have precluded a procedure for applying lubricants at the intermediate stage of

processing, as suggested herein. Most commercially utilized bonding agents react slowly. The bonding agent used

in the "coil to coil" procedure reacts very rapidly permitting a recoiling operation immediately after the solvent is

flash evaporated.

Certain piston ring materials now being used in internal

combustion engines are fabricated from alloy variations of

high carbon steel. Some of these materials are furnished

to piston ring manufacturers by steel suppliers in flat

strip cross-sections; for example, ,024" x ,105", These

materials are produced by a combination of cold working and

tempering in order to achieve suitable strength and hardness parameters for application in the piston assembly.

In the process, breakdown sizes of larger diameters than

the finished size in terms of cross-sectional areas are

produced from larger diameter hot rolled stock. To relieve

the stock from dislocation of its crystal lattice at these

various breakdown sizes an annealins: operation is done at

the metals "recrystallization temperature" which relieves

residual stress and restores the alloy to its original

state. This condition then permits further cold working,

A by-product of the annealing process not frequently discussed is a phenomenon called "carbide precipitation". The

formation of the precipitates in interstitial alloys generally speaking is a process best described as macro-molecular clustering which causes asperities in the surface

finish. At the termination of the anneal inp^ cycle cooling

period the voids caused by precipitation are more pro188
nouQced than they are when the finished surface is reduced

to final size. Also occurring during the annealing process is the discharge of carbon monoxide (Co) and carbon

dioxide (CO2) creating decarburization zones. Typically

these zones in highly interstitial alloys such as the one

being discussed is between •001" and «002". To control

this phenomenon, many producers have started using vacuum

melting procedures and other control measures during the

annealin-7 cycle. (Dr. John Smith (1))

The proposal being made herewith entails incorporating an

intermediate process subsequent to annealing, and before

reducing to final size and tempering. This process would

lubricate the substrate in a "coil to coil" operation with

a solid lubricant as discussed previously. At this stage

of processing, the lubricant would then be imbedded in the

micro-voids or surface imperfections that result from carbide precipitation and decarburization. It has shown that

by sandblasting or phosphating various alloys preparatory

to being treated with M0S2 bearing lubricants, "micro reservoirs" form in their surfaces that are used for storage

areas for the lubricant and "suggest that this is essentially what is occurring in the case of optimum surface

finish." (M. J. Devine et al (2))

It has been shown that the formation of the transferred

film appears to be primarily a mechanical process with

three distinct processes: (a) direct imbedding of the

solid into a softer surface, (b) deposition of the solid

into surface depressions generated in the substrate during

sliding by the abrasive action of the solid itself, (c) deposition of the solid into the surface depressions characteristic of the original surface finish and surface hardness of the substrate. (J. K. Lancaster (5,^))

Since the surface hardness of the steel substrate will be

less after annealing than it will after final drawing and

tempering, the MoSg can be applied most effectively at this

time. Then during final drawing, the extreme pressures

developed will imbed the M0S2 into the surface of the steel.

Also, the anisotropic properties of M0S2 permit the material to partially penetrate the bottom of the reservoir

voids more so than would be possible when applying the lubricant to a substrate with a high superficial hardness.

V/hen the resulting substrate is in a "prelubricated condition" and is then reduced 60-70^ in cross-sectional area,

plastic deformation or dislocation occurs in the grain

structure of the alloy. An essentially spheroidal grain

structure characteristic of the annealed condition of the

189
substrate will be changed to a hjrper-extended or elongated

grain structure. M0S2 molecules existent on the surface of

the steel will ease the frictional pressures when the material passes through the wire drawing dies and will shear

along the basal plane. Inherent to this process, however,

would be the implantation by mechanical inclusion of the

solid lubricant into the surface depressions (surface imperfections) characteristic of the post-treated surface of

the substrate.

It is noteworthy to consider that the alloy is essentially

unchanged from an elemental composition point of view. As

a result, work hardening properties, hardness characteristics and yield strengths are the same. However, due to

trace amounts of M0S2 implanted and included on the outer

periphery of the cross-section, improved bearing properties

favorable for reduced friction and increased wear performance would exist.

The alloy produced would have desirable "bearing properties" but the essential properties necessary for piston

ring applications would be uncompromised.

Radial wear characteristics of piston rings have been compensated for in some mechanical designs by utilizing a

material with "spring" properties, that exert an outward

force on the cylinder wall due to inherent elasticity of

the material. This design acknowledges the fact that wear

will take place. From a cross-sectional standpoint, the

lubricant would not only be present on the wear surface

which is the smallest of the keystone surfaces employed,

but also homogeneously present on the surface fit into the

piston grooves which is the larger surface. When exhaustion of the lubricant occurs in the outer periphery of the

ring, it would be replaced by that present in the adjoining

micro-radial cross-section. Plate (1) illustrates the

cross-sectional lubricant implantment in the ring and shows

how supplemental lubricity can be anticipated.

This alloy would then be able, for the life of the ring, to

supplement normal lubrication between the piston ring and

cylinder wall that is mainly hydrodynamic . Piston rings

treated in this manner would be able to perform more efficiently some of the required functions demanded from traditional bearing materials. They are as follows:

1. Withstand high loads at appropriate operating temperatures.

2. Operate for short periods of time with only boundary

lubrication.

190
Mechanical drawing of this plate are efforts of Julia Fish,

Senior, Mayo High School, Rochester, Minnesota,

PIATE ONE

PISTON ASSEMBLY

PISTON

I

When the implanted M0S2 is exhausted on surface one (1) it

will be replaced by implanted M0S2 on surfaces two (2)

nearest the cylinder wall.

191
5» Redistribute local high loads.

4. Improve wear characteristics of the mating surface due

to inherent anti-friction properties.

Practical benefits such an alloy would yield are beyond the

scope of this proposal. However, the alloy would tend to

reduce wear of the cylinder wall in an internal combustion

engine at top and bottom dead center of the piston assembly,

in the areas of the cylinder wall where oil films are unable to accumulate in sufficient film thickness due to the

reciprocating action of the piston assembly. Also, the

pistons and rings have zero velocity at dead centers so

that the hydrodynamic requirement of relative velocity between opposing surfaces is not met and lubrication must

rely upon the squeeze-film effect in these areas. (E. R.

Braithwaite et al (5)) Parallel studies by numerous others

confirm this finding since cylinder wall wear in life cycle

testing is greatest in the precise areas opposite these two

piston operating positions. The proposed alloy would provide beneficial supplemental lubricity because of the implanted solid lubricant. Thus increased wear performance

is reasonably anticipated.

A residual benefit worth considering would be the reduction

of initial scoring of the cylinder wall during break-in by

the mating ring. This would be due to a smoother surface

on the ring and also due to initial dry lubrication previously determined to be a positive benefit to general engine performance.

A proj'ect to produce this alloy to determine beneficial effects with respect to friction and wear is proposed. Engineering disciplines including these which consider the

metallurgical properties of the alloy need to be employed

in order to establish the extent to which the alloy will

make positive improvements in the operation of the piston

and cylinder of the internal combustion engine.

The exact nature of the research will depend on the type

and amount of information desired by the funding agency.

Pursuant to this goal officials at the Department of Transportation employed by The Bureau of Basic Automotive Research have been contacted.

The author wishes to acknowledge the assistance provided by

Dr. Arthur Akers, Professor of Engineering Mechanics and

Dr. Paul W. Barcus, Assistant Dean, both of the College of

192
Engineering, Iowa State University of Science and Technology, Ames, Iowa in the preparation of this paper.

1. Dr. John Smith, U. S. Department of Transportation, Private Commimication.

2. M. J. Devine, E. E. Lamson and J. H. Bowen,

The Lubrication of Ball Bearings With Solid

Films, ASME Paper No. 61-LUBS-11, 1961.

3. J. K. Lancaster, Anisotropy in the Mechanical Properties of Lamellar Solids, Wear, 9

(1966) 169-188.

4. J. K. Lancaster, The Influence of Substrate

Hardness on the Formation and Endurance of

Molybdenxim Disulphide Films, Wear, 10 (196?)

103-117.

5. E. R. Braithwaite and A. B. Greene, A Critical Analysis of the Performance of Molybdenum

Compounds in Motor Vehicles, Wear, 46 (1978)

405-432.

193
THERML DEPOSITION 3Y3T2US FOR I^TROVSD ?/AiriTEKAr;Gii

Vincent J. Lanza

Government I-larketing Kanager

f.:ETGO, Inc.

iestbury, !;ew York 11590

Abstract: The military has a continuing need to improve the

service life of its equipment. The Navy with its ships and

shipboard equipment exposed to marine environment, as well

as erosion and wear, has an everlasting requirement to keep

its equipment in readiness. The Navy builds its ships to

have a thirty (30) to forty (^0) year service life. The

latest designs of these ships are the DD963 Sprunce Glass

Destroyer and the Frigate Glass Ships. This paper will

attempt to describe the applications implemented aboard

ships of this class dealing with corrosion, erosion and

wear. We will also attempt to describe the equipment, along

with the application, and their respective economical advantages. The Navy being one of the forerunners using this

process, is by no means the only one. The Army has implemented applications in its new gas turbine used in the XMl

Tank. In attempting to stress the use of the flame spray

process, guidance is recommended. The new industry and

program to be discussed in this paper will be the diesel

rebuilt market and the applications already implemented by

the original equipment manufacturer.

Key words: Thermal deposition systems; plasma coatings;

aluminum non-skid coating; corrosion control; thermospray

process; erosion; wear; flame spray process.

The function of the r/IETGC Government Marketing Department is

to develop the use of the thermal spraying process within

the military and to act as liaison between military agencies

and the C.E.K. (Original Equipment Ivlanufacturers ) . Agencies

are encouraged to consult with each other directly based on

technical results and facts.

The programs and applications in process, to date, include

the gas turbine engine for the XIQ Tank. This engine is

being manufactured by Avco Lycoming and has seventeen (1?)

separate applications designed into it. These applications,

produced by computerized equipment designed and built by

R'lETGO, provide protection from wear, erosion and corrosion

and are thus increasing engine life and efficiency.

194
The Army is using the process in both R&D facilities such

as ARRADCCM, Watertown Arsenal and Fort Monmouth, as well as

at Depot level. The depots are reviewing the process to

extend the life of equipment already in line such as rvl60 gun

mounts, road arms and many others.

The Air Force, on the other hand, is also a very strong

proponent of the process. The ALC , Kelly AFB, Tinker AFB,

Wright-Patterson AFB, Plill AFB as well as Warner Robins, are

all very active users. The jet engines turned out by these

ALC's each have thermospray or plasma coatings applied per

specifications developed by the manufacturer. Hov/ever,

military personnel with IV^STCO assistance have developed

applications beyond the scope of the C.E.M. with great

success. These approved applications have resulted in cost

savings to the Air Force in both funds and engine turn

around time.

The Navy has used the process at the NARF's (Naval Air

Rework Facilities) in the same manner as the Air Force.

They have extended the process use to ships and shipboard

applications. GCiYil'-IAVSURFPAC has made it Navy policy to use

the aluminum wire thermospray process on all valves to

eliminate corrosion. This process is being extended to all

applications above the waterline. This program is being

implemented at Ingalls Shipyard on the Sprunce Class

Destroyers and the Frigate Class.

The Navy, with ?1ETCC, developed an aluminum arc sprayed nonskid coating that was first used on the USS Truett with

great success. Since then, it was applied to several other

ships including the USS Hewitt and USS Fox, with equal

success. The aluminum non-skid coating has outlasted the

conventional non-skid coating and provides corrosion

protection as well.

The coating, when applied to the helo deck, has eliminated a

serious problem with the tie downs. These items, generally

made of stainless steel mounted to a 606IT6 helo deck,

caused exfoliation and a costly repair. The coating has

eliminated this problem on all decks sprayed at this time.

The Navy is extending the process to cover machine repair

components and has issued a series of specifications to

cover the aforementioned applications. The most recent is

r.lil-Std-1687 , which covers procedure operator certification,

as well as materials. Others are as listed:

195
1) Corrosion Control for Shipboard Launch and Recovery

Systems (NAVSEA and N.A.E.C.)

2) Navy Policy - Flame Spray Valves (CCM^AVSURFPAC)

3) Job Performance Aid for Applying Wire Sprayed

Aluminum

4) DD963 Corrosion Control Manual

5) Equipment Specification Available:

Mil-M-3800, VJire Systems

Mil-P-80l4l, ThermoSpray Systems

Mil-P-80109, Plasma Spray Systems

6) Materials Specification Available:

Mil-W- 6712, Wire

Mil-P- 833^8, Powders

Mil-Std-1687, Process and Materials

The propulsion unit used in the Navy's latest destroyers is

the LM2500. This unit is manufactured by General Electric

and contains eighty-one (81) applications in the compressor

section at 1100 degrees F and seventy-five (75) applications

in the turbine section. r/ETCO has worked very closely with

General Electric to provide the proper material and process

for each of these applications.

The development of a new series of one-step materials has

given METCC the opportunity to penetrate the diesel engine

market. METCC has contacted all of the major diesel engine

manufacturers to demonstrate the process in major problem

areas. Areas being reviewed are the engine blocks, turbo

chargers, water pump engine components and automatic transmissions. It was demonstrated that by applying METCO

one-step stainless steel to the saddle and thrust faces of a

diesel engine block, that a $3,000 block can be restored at

a cost of $200.00. METCC has documented all of its applications on diesel engines and is providing this documentation

to the Navy and other agencies to repair or authorize the

repair of its diesel engines.

It was estimated, based on the first quarter of FY' 81, that

the Government will spend $930 million annually on rebuilt

or replacement parts. Out of this, $190 million worth of

used parts are suitable for repair by the therm.ospray

process. This would generate an estimated cost saving of

$160 million annually.

Conclusion: The thermospray process can increase equipment

readiness through increased utilization of the estimated

$3.6 million in equipm.ent already purchased. What is

required is additional official support and serious investigation of future applications. I/ETCO is willing to offer

its support to any and all agencies to further the controlled

use of these processes.

196
SESSION III

MAINTENANCE ANALYSIS SYSTEMS

CHAIRMAN: D. V. MINUTI

NAVAL AIR DEVELOPMENT CENTER

SIMULATION OF TRACK MAINTENANCE COSTS

Richard L. Smith

Allan I. Krauter

Shaker Research Corporation

Northway 10 Executive Park

Ballston Lake, NY 12019

The Simulation Cost Model (SCM) provides economic evaluations for maintenance of systems, components, or assemblies. The application of this

technique for costing maintenance operations of track and its component

structures is described. Examples are provided which illustrate the use of maintenance action diagrams. These diagrams graphically represent the system being modeled.

The SCM procedure allows separate maintenance cost entries to be associated with definable track substructures such as rail, cross ties, or ballast. In this manner separate tabulations of maintenance expenditures can be obtained from the computerized technique. The SCM also

allows time-dependent cost estimating and produces costs by year for:

class of track, component or substructure repaired, type of maintenance

operations, labor, material, equipment, delays, scrap, fines, etc.

The track SCM computer program is tailored specifically for track maintenance cost analysis, but user flexibility is built in and any maintenance operation which can be depicted through use of a "maintenance

action" diagram can be analyzed.

Key words: Computer simulation; life cycle costs; maintenance, track;

simulation cost model; track maintenance planning; track standards.

INTRODUCTION

The actual total cost of maintaining a segment of railroad track is ex- tremely difficult to ascertain. At the point of manufacture, a length

of rail, a tie, or a ton of ballast has, at a given instant, a fixed

determinable cost. However, materials of repair are only a fraction of

overall maintenance expenses. Costs of inspection, delivery, installation, and resulting delays must also be considered.

The task of costing any proposed maintenance practice or policy modification is complicated by:

• the fact that there are almost as many maintenance practices as there are railroads to perform them;

• the constant replacement of system materials;

199
• the unplanned nature of some maintenance operations; and

• the ever-changing demands of business which can alter the physical

loading of the track structures themselves.

These problems have prompted several attempts in recent years to improve

the techniques for estimating task maintenance costs. Several of these

were reviewed recently at a workshop [1]* on the subject of track maintenance. Table 1 is a summary of techniques being used today for evaluating track maintenance costs of performance. The simulation cost

model (SCM) , the last entry in the table, differs from the more typical

techniques in that it provides a

• graphic representation of the system being simulated through use

of a maintenance action diagram;

• evaluation of proposed alternate maintenance action policies or procedures;

• listing of all annual track maintenance costs including those for

several different subcategories; and

• time simulations to predict future maintenance operations and

associated costs.

Simulation cost modeling is described in detail in [2-4].

DEFINING TRACK MAINTENANCE FOR A SIMULATION

Track maintenance costs can be defined as the annual direct charges for

the upkeep of track property and equipment. Track property includes

rail, cross ties, ballast, and associated hardware fastenings. Equipment refers to those pieces of machinery used for inspecting, installing, and keeping the track in satisfactory operating condition. Although some maintenance operations are performed by every railroad,

there are many different ways to perform typical major tasks of track

repair. Each railroad has its own maintenance policy which has usually

been derived from many years of experience.

In applying the SCM method for determining track maintenance costs it was desired that:

• the technique be applicable to a variety of railroads' maintenance of way operations;

• the procedure allow for cost comparison of alternate maintenance

operations-, either actual or potential.

The approach taken centers around a general computerized simulation

procedure which can handle any user-defined maintenance system. The

program uses a standard fourth order integration technique to simulate

future maintenance actions. This integration technique can handle

*Numbers in brackets denote references.

200
costs and maintenance operations which are time varying, nonlinear, or interdependent. A Weibull distribution is used to describe the rate at

which the components become defective. Figure 1 shows conceptually how

the time integration process operates in the SCM.

Costs which the model can consider include:

• labor cost to inspect an arbitrary number of track components

• labor cost for an arbitrary number of track components

• equipment cost to inspect an arbitrary number of track components

• material costs of new component-s installed

• cost of track inspection labor and processes

• supervisory labor in monitoring subcontracted maintenance

• fines accrued for deficiencies in track safety

• delays of trains caused by the • maintenance repair crews

• slow order delays from insufficient maintenance

• return costs from scrapping components of system

• subcontracted maintenance of the components

• delivery costs of transporting new (renewed) components

• travel and living associated with repairs

• cost of heavy equipment needed to perform repairs

• cost of fueling or powering certain pieces of equipment

• accident costs resulting from maintenance deficiencies

• costs of converting jointed rail to welded rail

• track idling costs

Simulation cost modeling can address questions of:

• How much does it cost to maintain track?

• What are the cost breakdowns within the maintenance system by

structural component (e.g., rail, cross ties, or ballast)?

• Where in the maintenance system are the most costly procedures?

• What savings in annual maintenance can be expected if modeled

operations are altered?

• What will be future maintenance costs if the system work volume

or operations are changed?

Maintenance costs are available for output at any time point in the

simulation process. This "snap-shot" of maintenance repair costs and

system rates of repair can be used to compare with past or present

accounting records of the railroad system being modeled.

SIMULATION TECHNIQUE

The Simulation Cost Modeling technique consists of a graphic diagram of

the track maintenance system being modeled, the associated data, and

the FORTRAN computer program. The maintenance action diagram is a qualitative representation which is constructed by the user and describes the maintenance actions (inspection and repair) and their re- lationships to one another. The data set is the quantitative repre201
sentation of the action diagram. Linking these is the computer program. The program quantifies the modeled actions shown in the diagram,

implements the associated data set, and provides a selected set of cost

outputs.

Maintenance Action Diagrams

The SCM representation of the maintenance system takes the form of a pictorial action diagram which 'describes how the railroad maintains its

track. The maintenance action diagram is analagous to a diagram of a water pipe network. Water systems can be represented by drawings which

show the various connecting or branching points as well as their distribution pattern. In a similar fashion the cost model maintenance action

diagram displays the system being represented. The user represents

pictorially the way in which a railroad (or the industry as a whole)

maintains its track. The maintenance actions occur on paths (lines with

arrowheads) which are linked together. The paths indicate the order in

which these actions are carried out and the order in which the computer

carries out its cost computations. The simulation cost modeling procedure calculates the cost for each individual maintenance action represented and thus the total cost to maintain the track system under con- sideration .

A simple example of a maintenance action diagram is shown in Figure 2.

The figure contains shaded blocks in which track exists in a conceptual

sense. Track leaves the in-use block because of track inspections which

occur on path 1. Track which fails this inspection is separated from

the remainder of the track at node (s) and is sent for maintenance.

This track is either maintained (via path 5) or is slow-ordered (deferred maintenance - path 4). The separation point is node (s) . Repair

operations occur in the maintenance repair block, after which the track

returns to use.

It can be seen that the maintenance action diagram simply identifies the

maintenance system. Paths (uncircled numbers) represent actions in the

system whereas nodes (circled numbers) represent decision points. At

the decision points, the components are separated for the two outgoing

paths, -each having or leading to different maintenance actions. Further

descriptions of concepts involved in a maintenance action diagram are given in Figures 3 and 4.

Typical maintenance action diagrams for track normally contain:

• The "in use" or "in service" portion of the track system;

• The inspection-of-track loop;

• The removal or scrapping of defective system components;

• The act of maintaining the defective track found from a single

inspection process; and

• The supplying or bringing of new components to replace those being

scrapped from the system.

202
A more typical maintenance action diagram for track is shown in Figure

5.

Because the diagram treats many components simultaneously, and because

of the shorthand notations used, the diagram is at once convenient and

misleading. It is convenient in that the overall system may be viewed

at a glance, and if the notation is understood, can give an impression

of the complexity of its structure. It is misleading in that many of

the details of the system cannot be shown explicitly in the display, and

may lead the viewer to believe that the model is too simple.

The maintenance action diagram can be as simple or as complex as necessary to suit the requirements of the problem. An example is a remote

rework shop where components are sent for repair. If the repair rates

and costs are known the details of the maintenance work in the facility

might be disregarded and the applied costs be attached only to the

maintenance actions as one lump sum or cost per component repaired.

Similarly, major maintenance actions might be simulated initially and

then updated in more detail at a later time when more information is

obtained and/or desired.

Data for Model

Whereas the maintenance system is defined qualitatively by the maintenance action diagram, the system is described quantitatively by the

data and by functions associated with the paths. The data consist

typically of costs and of rates at which the maintenance system oper--

ates. For complex problems these data can be voluminous; consequently,

the computer program was developed to

1. Provide the user with an annotated description of the data coded;

2. Allow the user to update the data quickly as new (or more reliable) information about the system becomes available; and

3. Let the user add (delete) associations between data elements

without restructuring the whole body of data already established.

The computerized cost data are treated in the analysis under separate

categories. These categories are, in general, expandable by the user,

The subcategories used in the model discussed include maintenance ex- penses by:

• Maintenance Action Diagram Path Number

• Major Repair Block Operation (usually a collection of paths)

• Track Structural Component

• FRA Track Classification

• User Identified Cost Descriptor Codes

Sources for costs can be obtained from many different places. Such sources include

203
• Standard accounting records

• Policy definitions

• Business practices

• Accident records

• Component failure histories

• Standard maintenance practices

• Safety compliance standards

• Published reports

Functions for Data Modification During Simulations

The majority of cost models developed to date lack a method of evaluating the cost effects of certain parametric alternatives. The cost advantages (or disadvantages) in terms of track maintenance expenditure

caused by higher traffic densities, changes in Federal Safety Standards,

or an alternate component design, are" not usually handled in the traditional cost modeling procedures. The present model addresses these

potential variations in the operating system through user-defined

functions.

If a cost or rate of track repair has a known dependence which can be

written in terms of parameters in the SCM or of time, then use can be

made of several preprogrammed families of functions which will carry

out the definable dependencies during the simulation. Seven types of

functions are presently incorporated in the track SCM including linear,

power, and exponential. These can be "turned-on" through the use of

various data codes. An example of turning on the Weibull function and

3 other functions is shown in Table 2.

Track Simulation Cost Results

Results from the SCM are obtained for discrete times as required by the user. At each such time, these results, for each path in the track

model, consist of:

1. Simulation maintenance action diagram path number.

2. Track component (i.e., rail, tie, ballast, etc.)

3. FRA track class (1-6).

4. Major repair block or type (such as rail laying, surfacing, etc.

For example purposes, 20 separate types were identified.).

5. Cost code (the present example includes the following codes):

a. material costs

b. equipment costs

c. fines

d. delays

e. scrap return costs

f. contracted costs

204
g. delivery costs

h. travel and living

i. six levels of labor

An example of this output is shown in Table 3.

Simulation results are composed of a set of discrete time outputs as produced from the SCM by the Runge-Kutta integration procedure. An ex- ample of such simulation results is shown in Figure 6. These results

are for a hypothetical Alpha Railroad having the maintenance system

described by the maintenance action diagram of Figure 2. The railroad

has 1,000 miles of track whose distribution among the FRA track classes

is fairly typical of the rail freight industry. The figure shows the

annual and total cumulative expenditure for maintenance on the track of

this railroad for a period of 5 years. The base case results shown are

for a track characteristic life of 32 years. The modified case results

are for a reduction in this characteristic life to 24 years. It can be

seen that the increased costs over the 5 year period due to the decreased rail life are substantial. It can also be seen that the cost in- crease is greatest at the start of the simulation and becomes progressively smaller toward the end of the_ 5 year period. The nature of this

transient behavior can be significant in the consideration of the track

and other maintenance systems and the determination of such transients

is an important characteristic of the SCM technique. The output costing

shown would be typical of the higher wear rates of rail resulting from

either more traffic or higher loaded rail cars.

REFERENCES

1. Track Maintenance Planning Workshop, Pennsylvania State University,

June 1980.

2. Krauter, A.I., and Smith, R.L., "A Methodology for Evaluating the

Maintenance of High Speed Passenger Train Trucks", Final Report Contract No. DOT-TSC-1308, Report No. FRA/ORD-78/73 , Dec. 1978.

3. Smith, R.L., Krauter, A.I., and Betor, J., "User's Manual for the

Maintainability Methodology for High Speed Passenger Train Trucks",

Final Report Contract DOT-TSC-1619 , April 1980.

4. Smith, R.L., Krauter, A.I., and Betor, J., "User's Guide for a Computerized Track Simulation Cost Methodology", Final Report Contract

No. •DOT-TSC-1594, September 1980.

205
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207
TRACK HAIHTEHANCE COST

RUN HUNBER

DATE PLACE SIHULATIOH TINE:

I BASE HOD 3

! THU, AUG 14 1980

I SHAKER RESEARCH CORP

0 00

POPULATION

IN USE CLASS COMPONENT

QUAL I r

V

700 .00 30 .00

t 00 00

130 .00

0 10000

0 10000

0 10000

0 10000 NODE PATN CLASS conpoONEHT

OUAL 1 r

Y

PATH FLOWS

rtlLES/YEAR nAINTENANCE

DOLLARS

1 t 1 1 0 100000 700 00 2 10000

1 1 1 2 0 100000 50 00 15000

1 1 2 1 0 laoooo 100 00 30000

1 1 2 2 0 100000 ISO 00 45000

2 2 1 1 0 000000 630 00 0 IS 1 1 1 000000 70 00 0

2 1 2 0 000000 43 00 0

2 18 1 2 1 000000 3 00 0

2 2 2 1 0 000000 90 00 0

2 IB 2 1 1 000000 10 00 0

2 2 2 2 0 000000 133 00 0 2 IB 2 2 1 000000 13 00 0

3 17 1 1

11 u u u u u u QO nnuu 24000

3 17 1 2 1 000000 1 00 3000

J 17 2 1 1 000000 1 00 3000

) 1 1 000000 78 00 Q

4 3 1 2 1 000000 6 00 0

2 1 1 000000 1 1 00 0

2 2 1 000000 13 00 0

1 1 1 000000 70 00 0

1 1 1 000000 8 00 200000

I 2 1 000000 5 00 0

1 2 1 000000 1 00 25000

2 1 1 000000 10 00 0 2 1 1 000000 I 00 23000

2 2 1 000000 13 00 0

1 1 0 000000 70 00 1260000

1 1 0 sooooo 140 00 1099700

1 2 0 000000 5 00 430000

1 2 0 sooooo 1 0 00 70000

2 1 0 000000 10 00 430000

2 1 0 300000 20 00 276000

2 2 0 000000 15 00 1290000

2 2 0 300000 30 00 30994

1 1 0 U£6«7 84 OG 3

1 1 1 000000 36 00 0

1 2 0 t(4(«7 6 00 0

1 2 1 000000 4 00 n

2 1 0 1C6667 12 00 0

2 1 I 000000 8 00 0

2 2 0 062500 16 00 0

2 2 1 000000 1 4 00 0

1

1

1 1 0 000040 70 00 0 10 1 1 1 000000 1 4 00 -1 39972

1

1

1 2 0 000040 3 00 0 10 1 2 1 000000 1 00 -9998

1

1

2 1 0 000040 1 0 GO 0 10 2 1 1 000000 2 00 -19996

11 2 2 0 04000S 13 63 0 10 2 2 1 000000 0 37 -3749

12 1 1 0 102396 78 00 0 12 1 2 0 Utoi94 6 00 0 12 2 I 0 090942 1 1 00 0 12 2 2 0 040003 1 5 63 0 TOTAL 1 5312979

Table 3 Example of SCM Output at

a Discrete Time Point

208
TRACK MAINTEHhMCE COST SUMMARY

RUN NUMBER

DATE

PLACE

SIMULATION TIME

BASE MOD 2

THU/ AUG 14 1980

SHAKER RESEARCH CORP

2 . 00

COST

CODE

MA IHTEMAHCE

COST

31

32

33

34

35

36

37

38

39

40

4 1 42

43

44

ANNUAL TOTAL

1 2881

0

34963

0

39933

-82700

13 162

6993

13986

0

13986

13 986

34576

406825

6993

99091

42

76

00

1 8

33

1 5

1 7

42

00

42

42

45

09

1 7 3 1

CLASS M A INTENANCE

COST

12

ANNUAL TOTAL

1972324 34

1 0 18589 ,97

2990914 31

COMPONENTMA INTENANCE

COST

12

ANNUAL TOTAL

2083623 .55

907290 .76

299091 4 .31

REPAIR

BLOCK

BLOCK

COST

2220938 . 07

Table 3 (Continued)

209
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--r^.^.^ .a. . .<^r- SCHEMATIC DIAGRAM TRACK IN USE number

0001

PERIODIC

INSPECTIONS

®' 17 PROPOSED

MAINTENANCE

4 TO MAINTAIN

PATH

DEFERRED

MAINTENANCE

-(z>

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MANUFACTURER

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BLOCK

RENEW

SHOPS

10

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®

INDICATES NODE BY (N) NUMBER IN CIRCLE

12 '4)

SMALL NUMBERS (n) ARE PATH NUMBERS

Figure 2 Simplified Maintenance Action

Diagram of Track

211
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t-^>»HH tin.

Figure 5 Typical Maintenance Action

Diagram for Track

214
7

Figure 6 System Maintenance Costs From

Example Simulation Run

28

1 1 1 I 0 1 2 3 4 5

TIME (Years)

215
AUTOMATIC TEST SYSTEM FOR RELIABILITY

ASSESSMENT OF GUIDED MISSILE RE-ENTRY VEHICLES

Walter D. Downing, Jr.

Southwest Research Institute

P.O. Drawer 28510, Div. 14

San Antonio, Texas 78284

John P. Pruett

U.S. Air Force

SA-ALC/MMETS

Kelly AFB, Texas 78241

Bryan D. Winn

Southwest Research Institute

P.O. Drawer 28510, Div. 14

San Antonio, Texas 78284

Abstract: A computer-automated test system (ATS) to perform a system

level test of guided missile re-entry vehicles (RV) for reliability

assessment is being developed for use at Kelly AFB. The ATS is intended

to replace the original test complex control system which has been in

operation since 1968. During the test, the ATS will control flight

environment equipment, deliver discrete signals to the RV and monitor

output signals from the RV. Data acquired during the test is used for

reliability scoring. This paper gives a brief description of the

performance requirements and design solutions being implemented in the

new ATS. Emphasis will be given to those areas in which major changes

will be made in both hardware and software to take advantage of the

experience gained over the several years of testing, as well as those

required to provide additional testing capability. The final portion

of the paper describes how the data acquired during the test is used in

reliability assessment.

Key words: Automatic test system; computer -automated; re-entry

vehicles; reliability assessment.

Guided missile re-entry vehicles are subject to mission failures because

of the unique requirements under which they operate. An RV incorporates

a very extensive set of mechanical and electrical interlocks in order

to prevent accidental detonation of the warhead, yet it also must

operate with an extremely high degree of reliability. It is by design,

a "one-shot" device, stored under silo environments for long periods of

time, and must function properly the first time from launch to target.

A single component failure could result in a complete mission failure.

216
Component failures may occur because of the severe altitude and

acceleration environments to which an RV is subjected during flight.

The chances of component failure are increased by the long periods of

silo storage, during which the arming and fuzing components are

inactive.

Early in the history of the guided missile weapon system it was realized that there was no program in being for determining the

reliability of the re-entry system. As a result of the above situation,

Hq USAF directed that Air Force Logistics Command (AFLC) develop an approach for assessing the operational reliability of re-entry systems

throughout their operational life. Due to San Antonio Logistics

Center's (SA-ALC) assigned responsibility for logistics management and

support of weapons, the Directorate of Special Weapons (DSW) was tasked

with development of a reliability assessment effort. A feasibility

study of alternate approaches was conducted and submitted to Hq AFLC

and Hq USAF. Concurrence with the study was received and resulted in

issuance of a "Plan for the Assessment of the Reliability of Air Force

Arming and Fuzing Systems and Re-entry Vehicles in the Operational

Inventory" in September, 1962.

The plan was first implemented on the MK3 re-entry vehicle in 1962.

Since no test capability was then available at SA-ALC, this effort was conducted under contract with the development contractor. The original

feasibility study proposed establishment of an independent USAF testing

capability for all re-entry vehicles. Therefore, concurrent with the

contractual evaluation of MK3, a separate study of test equipment for

all the then operational USAF re-entry vehicles was placed on contract

with a major supplier of automated test equipment. The contractual

effort culminated with the delivery and installation of equipment giving

SA-ALC a full range of testing capability.

The current contract with Southwest Research Institute is to develop a prototype automatic test system to update the test complex for the MK12

re-entry vehicle. The existing test complex consists of seven (7)

functionally related components: the computer system, an automatic test

set, two (2) centrifuge systems, a programmable pressure generator, an instrumentation recording system and several support systems. Many of

these components are old, obsolete and becoming an increasing

maintenance problem. The main task of the current contract is to

replace the components of the test complex which are obsolete with

updated equipment. To accomplish this goal, the existing computer

system and automatic test set will be replaced with a new test console

and the existing centrifuge controllers will be replaced with new

control consoles. In both instances, the new equipment is being

designed to interface with the remaining test complex equipment with a minimum amount of rewiring. In addition to the replacement of major

components of the test complex, the current contract requires modification of some of the support systems and the instrumentation recording

system to provide improved test capability.

217
The new test console will provide the functions required to target the

RV, sequence the test and control the instrumentation recording system,

under the control of the functional test program. The console is

composed of a Digital Equipment Corporation (DEC) PDP-11/ 23 microcomputer system with ROM based application software, I/O interface circuitry and an operator's control and display panel. The test console

will utilize power FET's to deliver high energy activation pulses to

the RV and opto-couplers on inputs to provide isolation protection from

transients in the centrifuge arm wiring or the slip ring interface. A

major drawback to the existing test complex is the lack of indication

of the progress of the test program. The new test console will provide

visual indication of the test status, under program control, and the

occurrence of important signals, captured on a visual annunciator

system. A video tape recording system is being provided to record

events versus time so that in the event of a failure, the video tape

may be played back and analyzed for error assessment. The test console

includes an uninterruptible power supply.

The functional test program is divided into states which are related to

the different stages of the test. The program requires operator

intervention in the form of a pushbutton entry initiated interrupt

before proceeding to the next state. Interrupts are selectively

enabled by the program in order to prevent erroneous entry into a state

at the wrong time. Status lights prompt the operator as to when an

entry is required. Numerical entries for targeting function settings are made via thumbwheel switches on the test console. All operator

interaction is provided by the test program without the need for a system terminal

.

Since hardware failures such as component failure, interconnection

failure and power failure could cause catastrophic errors, the test

program includes certain safety and tolerance checks. In the event of

test equipment failure the program sets itself in a hold state, alerts

the operator and awaits instructions to continue or abort the test.

The options also include the capability to run a portion of the test

again. These provisions were added because previous testing experience

indicates that if at all possible, a test should be allowed to continue

to completion and to gather as much data as possible.

The most difficult problem in developing the test program software was

in providing for fault tolerance. Reference was made in earlier paragraphs to using ROM based software and reduction of operator error,

both of which reduce the possibility of program error. In addition to

these provisions, the test program also tries to reduce faults resulting from improper branching. To accomplish this the program tries to

limit any branching in any critical areas of the test. When branching

is required, the program performs an additional check to insure the

execution of the proper code. A combination of software and hardware

flags are used to provide the additional checks. After major branches,

the program contains an allowable time for operator intervention. All

218
waiting loops contain multiple exit conditions, including a time-delayed

interrupt which is generated by a programmable clock module.

The centrifuge control consoles provide the functions for a programmed

run of the selected centrifuge from a table of g versus time values

entered by the operator. The centrifuge control console is also composed of a PDP-11/23 microcomputer with ROM based application software,

I/O interface circuitry and an operator's control and display panel.

The system will utilize multiple EPROM boards to contain g versus time

tables for routine flight profiles. Each profile is addressed at the same 2K word "window" of memory, via standard DEC control registers.

The operator also has the option of writing a new table directly into

RAM from the system console, after which the table may be executed,

saved on EPROM or punched on paper tape. The centrifuge control consoles provide complete manual backup. Centrifuge speed, as indicated

by a shaft encoder, will be measured by an F/V converter in the analog

control loop and by a programmable counter module in the computer

system. The control program will make a frequency measurement at high

speeds, but will convert to a period measurement at low speeds.

The centrifuge control program is somewhat different from that of the

test set. Like the test program, the control program is divided into

states, but in this case the states represent different modes of operation. The different modes are: profile building, manual operation and

automatic operation. The profile building mode is used to enter the g

versus time tables. The manual mode only provides display support for

operator information. The automatic mode is a program controlled run using the values of a g versus time table as setpoints for the flight

profile.

Hardware generated interrupts are used in the control consoles to insure

safe operation of the centrifuge. A crystal controlled clock generates

interrupts at .5 msec (for setpoint calculation), 1 msec (for speed

measurement) , 10 msec (for test console support update) and 500 msec

(for display update) . Runaway checks will be performed by the program

which limit the measured speed to 110% of the setpoint. Loss of line

power generates an interrupt which will put the control program into a waiting state after the centrifuge has coasted to a stop.

Fault tolerance provisions in the control programs do not include extensive branch checking due to the absence of significant branches in

critical areas of operation. Software checks are provided to insure

accurate profile execution. The control program also provides emergency

stopping capability.

Support systems being updated during the current contract include the

simulation system, the radar test system and mechanical accelerometer

test system. The simulation system is being updated to incorporate a resettable on-board simulator constructed from actual RV components.

This is an improvement over the present method of simulation by

219
generating the simulated RV signals external to the centrifuge arm

wiring. The radar test system is being updated to incorporate remote

programming from the test console. In the present complex all components of the radar test system are on the centrifuge arm, and data is

being lost during some runs. The mechanical accelerometer test system

is being updated to provide recaging capability. The mechanical

accelerometer should be recaged after testing before the RV is removed

from the test complex in order to prevent the mechanical movement in

the device from slamming into the stops.

The testing of RV systems for reliability assessment presents unique

problems in data acquisition, i.e., the data is available for recording

only once and in some cases comes and goes in microseconds. Therefore,

instrumentation of demonstrated reliability and accuracy is chosen.

Signals are prioritized into levels of importance, i.e., signals

affecting overall system performance have the highest priority of

measurement, with component data being secondary. For system level

tests, it has been found that a good mix of digital and analog instrumentation should be used. The updated test complex will utilize the

following instrumentation:

Analog

CRT Visicorder (2 ea.) - 50 channels

Tape Recorder - 14 channels

Oscilloscopes (2 ea.) - 4 channels

Digital:

Minicomputer based - 32 channels

data acquisition system

with A/D converter and

digital voltmeter

Reliability assessment is accomplished by selecting a representative

sample of the population, testing the sample and finally through

statistical analysis making an inference about the total population.

The validity of the process is dependent on the integrity of the

sampling since all statistical theory is based on a random selection

from the population. Stated simply, in making a random selection every

member of the population must have an equal opportunity of being

selected

.

Statistical theory determines the number of samples required for reliability assessment. Normally the larger number of samples available the

more confident the resulting assessment. Initially, this test program

required a large sample size dictated by use of classical statistical

methodology and one-time use of test data. The expense involved in this

approach led to development by SA-ALC of the current Bayesian statistical technique and aggregation of test data. These measures permitted a

220
reduction in sample size to 24 samples per year. This sampling level,

if no failures occur, will permit an assessment of 90% reliability at

90% confidence. Combination of successive annual test quantities support higher numerical estimates.

221
REDUCTION OF TEST EQUIPMENT PROLIFERATION

WITH THIRD GENERATION ATE

S. Perra

RCA Corporation

Burlington, MA 01803

Abstract

Conventional ATE systems use discrete test instruments to measure each

parameter. Third generation ATE exploits the full computational

capabilities of the system computer to evaluate test parameters by

applying such techniques as Fast-Fourier transformers, digital filtering, statistical analysis, list sorting, and least-squares curve

fitting. Hardware-associated errors such as those introduced by lead

length, gain and offset, and A- to D- converter non-linearity are corrected automatically by calibration software routine on a sample-bysample basis.

Similarly, the system also has the capability which allows the user to

create complex stimulus waveforms using the computer. Thus, any number

of waveform types (classical, complex or arbitrary waveforms) can be

generated by computer algorithms.

This basic stimulus ans measurements capability forms a third generation

core system, which when augmented with special front-ends, such as hydraulic/pneumatic, electro-optical and motion, provides an optimum

solution to meeting avionics testing requirements.

The result is less peculiar test stations with less measurement and

stimulus hardware, and thus more reliability, less calibration, and more flexibility to meet future needs.

222
THE DEVELOPMENT OF AUTOMATED TEST PROCEDURES

FOR COMPLEX ELECTRO-MECHANICAL SYSTEMS

R.E. Hartwell

RCA, Government Systems Division

Automated Systems

P.O. Box 588, Burlington, Massachusetts 01803

Abstract: Systems which are partly mechanical and have significant

electrical controls, drives and testing/monitor points are well suited

to automatic testing. The use of a microprocessor controlled test system permits improved test strategy, with sophisticated measurement processing, rapid test step execution, and program controlled interactive

messages to the mechanic. This paper discusses design methods and techniques which lead to improved tests. The turret stabilization and fire

control system of a modern combat vehicle are used in an example of au- tomated test development for complex, interactive, electro-mechanical

systems. Quantitative and qualitative techniques are presented, as used in developing test strategies for that vehicle, and for evaluating

the effectiveness of the test programs and their validation in actual

fault isolation exercises.

Key words: Automated test equipment; fault isolation diagnostics;

functional subsystem; line replaceable units; malfunction; microprocessor controlled test set; symptom; test strategy.

BACKGROUND

The Ml Tank and the Infantry/Cavalry carrier Fighting Vehicle System

both have a mixture of sophisticated weapons control and conventional

automotive electrical systems. A microprocessor controlled automatic

test system has been developed for on-vehicle testing and fault isolation diagnostics. The testing techniques developed on this Simplified

Test Equipment Ml/FVS (STE-Ml/FVS) project are presented in this paper.

Military mechanics are the end users of the STE-Ml/FVS, and they are

not skilled in the interpretation of electrical schematics, nor are . they expected to perform complex technical evaluations. The test set

must provide comprehensive instructions to the mechanics, make measurements at electrical test point interfaces, and sequence test steps to

achieve effective and comprehensive testing.

223
MISSION

The test programs encoded in the test set must be able to achieve testing for the majority of the electrical and electronic subsystems on the

vehicle. The mechanic, with the test set, must be able to determine GO or NO GO conditions for each testable subsystem, and when the NO GO

condition is detected, fault isolation to the "Line Replaceable Unit"

(LRU) is necessary. In the Army, this is the Organizational Level of

Maintenance, conducted by teams of mechanics stationed at the company

and battalion level of armored and infantry units.

OBJECTIVES

The design of both the test set hardware and its encoded test programs

must achieve certain elementary requirements for field user acceptance.

It is strongly desired to encourage the use of effective and reliable

maintenance procedures, to avoid "best guess" replacement techniques.

The guessing game has been costly to the military for vehicles of com- parative simplicity. With sophisticated weapons and fire control systems, a disciplined maintenance approach is essential.

Another objective is to reduce the incidence of disconnecting vehicle

harnesses in the process of testing. The use of built-in test connectors is of great value in this respect. Ml and the FVS vehicles have

several multi-pin test connectors, through which electrical measurements

are made in the initial steps of all diagnostic investigations. Vehicle harnesses are not disconnected until tracing faulty signal paths

in the final stages of fault isolation.

A further very important objective is to reduce the need for printed

charts and instructions; that is to reduce the reliance on written

technical manuals. An automated test set cannot eliminate the need for

these manuals, especially the need for pictures and graphics. Well co- ordinated planning of both test set and manuals is needed to achieve an effective diagnostic capability.

TWO VIEWPOINTS OF THE VEHICLE AS A SYSTEM

There are two distinct ways of viewing the vehicle as a system, and this

has led to confusion and complications in the design of diagnostic test

procedures for these vehicles. In the first instance, the vehicle is seen as a network of physical boxes (LRUs) connected by cable harnesses,

as shown in Figure 1. This is the perception of the vehicle to its man- ufacturer and to the provisioner of spare parts; it is the image of the

vehicle portrayed in the mechanical drawings package. Unfortunately,

this hardware module viewpoint is greatly at variance with the image of

the vehicle as perceived by the crew.

224
IFV Turret Components

TURRET CONTROL GUN TOv/ ROTOR

SV/lTCH

BACK-UF

BATTERY

MOTION

DETECT CKl

1

1

1 VEHICLE

BATTCRY

Fi gure 1

.

225
To the users, the vehicle consists of functional subsystems which perform a number of missions. The aiming of weapons, the firing of weapons, the stabilization of weapon platforms, and the provision of safety, comfort, and support are crew related functions. The crew is intimately concerned with the normal or abnormal operation of the functions.

Failures in the vehicle hardware are eventually perceived as the loss

of one or more normal vehicle functions. Failure conditions can, in

fact, be described at three levels of abstraction; hardware fault,

malfunction condition, and symptom description. The failure itself is

imbedded in the hardware module or cable at the instant of physical

breakdown. The crew eventually experiences the failure as a loss of

normal performance, or the malfunction condition. The crew perceives

and then reports the situation, which gives rise to the symptom description. Figure 2 shows a relationship between these levels of fault

perception.

STATEMENT OF OBJECTIVES FOR EFFECTIVE TESTING

Recognizing that the crew senses the physical failure condition as the

loss of a vehicle function, the test procedures should, in some way,

relate to functional aspects of the vehicle. As any garage mechanic

can tell you, the vehicle user's description of symptoms is usually

crude, incomplete, and inaccurate. Test procedures must therefore es- tablish, by measurement and observation, what type of malfunctions are

present.

This leads to the conclusion that test procedures should be provided

for each and every functional subsystem of the vehicle. With such subsystem partitioning, there will be at least one test procedure to check

out any suspected or known malfunctioning condition. That test will

confirm that performance is defective, or else the test will find a "NO

FAULTS FOUND" condition. The ability to run the proper test to find

and isolate the fault is simply a matter of selecting the applicable

subsystem in which the malfunction has occurred.

WEAKNESSES IN "CONVENTIONAL" TEST STRATEGY

Test procedures have too often been based on the intuitive diagnostic

approach which appeals so much to design engineers. The technique is

to observe what works and what doesn't, eliminate whole areas of concern based on these symptoms, and make further measurements and observations to branch to successively narrower portions of the circuits

which are involved. The first problem with this technique, for adaptation to a computer programmed test set, is that careful and accurate

interpretation of symptoms is necessary. The second problem is that

system schematics and detailed system operation must be understood by

the troubleshooter . Many military technical manuals base their troubleshooting section on large lists of symptoms with corresponding test

procedures to be run. Close scrutiny of the symptom lists always

shows ambiguity. The test procedures may be correct for the intended

226
LRU

LRU

LRU

CREW-RELATED

VEHICLE

FUNCTIONS

o GUN MOTION

O TURRET MOTION

O WEAPON FIRING

o IVEAPON SELECTION

O SAFETY INTERLOCKS

o ETC

FAULT OCCURS IN^

AN UNKNOWN

LRU^

2 J MALFUNCTION IS CAUSED

IN A VEHICLE FUNCTIONCREW

MALFUNCTION IS OBSERVED

BY CREW DURING VEHICLE

OPERATION

\

0CONDITION IS REPORTED

A

BY

THE CREW AS A STATED SYMPTOM

SYMPTOM

FIGURE 2. PERCEPTION OF MALFUNCTION LEADS TO

STATEMENT OF A SYMPTOM

227
meaning of the symptom, but the test procedure may be very wrong for

other conditions which can and will be misinterpreted relative to the

symptom as stated.

Other pitfalls must also be noted in the traditional symptom oriented

approach. There is often a disregard for prerequisite test conditions.

The procedures presume that related or supporting functions are healthy

and this can be a fatal error to the diagnostic logic. For example, a presumed gun firing malfunction may be caused by a safety interlock

failure. If the interlocks are not checked in the test, there is no hope of reaching the proper diagnostic conclusion. Another serious

problem occurs if the test procedure does not have a "NO FAULTS FOUND"

exit, and many symptom-oriented test procedures always fault some LRU.

Sooner or later some mechanic will run that test procedure even though

that symptom is not present, and a healthy LRU will be condemned as faulty.

IMPROVED TEST STRATEGY

Test procedures encoded in microprocessor code in the STE-Ml/FVS have

taken advantage of computer age technology, to produce more effective

diagnostics. Because the test set is fast in execution of the tests,

and because it can store large quantities of instruction and procedures, there is freedom in the development of concept, strategy, and

scope of these tests. The following design concepts have evolved as

the most effective and successful approaches to diagnostic testing:

(1) For test procedure development, the vehicle should be partitioned into functional subsystems. Each subsystem should cover a function which is clearly perceived by the crew as essential to the operation of the vehicle and its various missions. Such subsystem oriented tests can therefore be called

upon whenever a suspected problem exists in the operation of

that function on the vehicle. As a consequence, the same test

can be run as a partial check on vehicle "readiness", since if

there are faults in the subsystem, the test should detect them.

(2) The first step in each test must be to establish uniform and

consistent initial conditions. No assumptions can be made

that other supporting functions are fault free. Checks of

power supply sources, and verification of interlock functions,

are among the necessary initial conditions checks. Comprehensive and uniform checks on initial conditions assure that the

test procedure will arrive at the same test conclusions no matter how many times the test is run.

(3) Measurements are first restricted to test signals at the vehicle's test connectors, without breaking into vehicle cable

harnesses. As long as no malfunctioning conditions are substantiated, vehicle harnesses should be left intact. When the

measurements and observations firmly establish a malfunction228
ing condition, vehicle harnesses may have to be broken so as

to make measurements at these intersections for final resolution of the fault source. The STE-Ml/FVS has adapters and "T"

connections to permit measurements at harness intersections.

DESIGN TOOLS

A number of tools which have proved beneficial in the development of

tests and test strategies are presented at this point. Figure 1 previously showed the network of boxes and harnesses in the Fighting Vehicle System Turret. The list of LRUs and cables is readily available

from the vehicle manufacturer, but the synthesis of functional subsystems for the same vehicle are not as readily established. Troubleshooting sections of the vehicle technical manuals tend to be organized

in a hybrid relationship, based on functions of the vehicle, and failure-symptom lists. One means to establish functional subsystems is to

develop a functional zone chart, as in Figure 3. Here the functions

and their overlapping relationships are presented. Some refinement is

needed before the chart becomes truly representative of the inter-related functions. Only when the intricate overlap of functions is truly

understood, can the logical development of test strategies begin.

Once the subsystems have been established, a test procedure will be developed for each subsystem. A subsystem/LRU Matrix can then be formed,

as in Figure 4. In one form of this Matrix, an "X" at the intersection

of a subsystem and an LRU means that the LRU can have a fault which

leads to malfunction in that subsystem. In further refinement of the

Matrix, numbers may appear at each intersection, to indicate the number

of fault conditions which the LRU can contribute to cause a malfunction

of the subsystem.

The final design tool in the development of the diagnostic test is the

test flow chart. In the STE-Ml/FVS project, it was found necessary and

effective to produce "Top Level" flow charts which completely trace each

test through its "GO CHAIN", listing each message to the mechanic and

each measurement made by the test set in the process. The "NO GO" paths

at each measurement decision branch are simply indicated by listing the

possible LRUs which could cause that NO GO condition at that point in

the test. The strategy of each test is quite well represented with

this level of floW chart, and can be reviewed and revised before full

detailed flow chart expansion is attempted.

Detailed flow charts eventually show each and every message and measurement step for the entire test procedure. Such flow charts are the basis for test coding, and serve to document the content of the test.

They are essential reference documents during on-vehicle validation of

the test procedures. Although space does not permit a detailed description of the flow chart techniques adapted for STE-Ml/FVS, I will note

that a rigorous set of standards has been established, which results in

flow charts which clearly define the essential steps in these proce229
POWER/CONTROL

GUN

25 MM GUN

AMMO SELECT

FEEDER

LOW AMMO

INTERLOCKS

WEAPON

SELECT

7.62 MM GUN

1

TRIGGER

CIRCUITS

SMOKE! GRENADES

TURRET DRIVE

DRIVE POWER

STAB

TRAVERSE

GUN ELEVATION

TOW DRIVES

HANDSTATIONS

n

fan"

TOW

FIGURE 3. FUNCTIONAL ZONES OF INTER-DEPENDENCE

FVS TURRET SUBSYSTEMS

230
FVS SUSSYSTtMS

TURfi ET (G EnERAl) TURRET OR IV c

REF PWP INTR WEAF TOW SMK GUM TOW TCW

DES LRU 01 ST LOCK SEL TRG S GUN CTL ORO FAN TRA V EL L^T EL STiE

zai TOB 1 X X X 1 X 1 X 1 X 1 X X X X 1 X X 1 X ! ZiZ AZ: X ! 1 1 X X 1 X ! 2i3 TCE 1 X X 1 1 X 1 X X X ! X X 1 X ! ki<* UC5 X 1 X 1 X ) X ! X . 1 . X I 2fi5 TW8 X • ! X 1 1 I X 1 X 1 2A6 Asr 1 X X ! X ! X 1 ! ! 1 2i7 SLR 1 X ! X 1 ! 1 1 X 1 I X 1 2 AS CPI X 1 1 1 ! X i ! 1 2A9 GPI X • 1 1 I X ! 1

' ' 1 2A10 FNV • 1 1 1 X ! 1 1 2A14 MG5 1 X 1 ] ! 2 A 1 5 GJN 1 X 1 ! 1 '

' ' 2 A 2 0 MGL 1 X

I

!

; !! ! 2 A 2 1 A •> L ! X 2A22 MEL 1 X j 2A 2 3 APS ! X 1 i ! , j j 2A 24 H t S 1 X 1 1 1 j

. ,

j 2A27 R r A ! X !

1 1 X 1 1 ! j 2 A29 GRL X ! ,

.

1 ,j 2 A30 TS S X ! j 1 1

1 .

1 j

.

2 A31 UGL I 1 ! X 1 1 1 2 A32 S GL .

1 ! X ! 1 1 2A33 GRS 1 X t 1 ! 2 A34 T RR X 1 2A36 Axe 1 X t 2A37 AX8 1 X ! 2A100 ISU X X 1 1 X 1 X 1 ! X ! 2A1C1 CGE X 1 ! 2A103 LNn X 1 1 2A104 PWC X X 1 1 X ! X t 1 X ! 2 A 2 0 C ECA X 1 X 1 X X 1 1 X ! X ! X 1 X 1 X ! 2A201 T CA X 1 X X ! 2A202 GEO X 1 X ! ! X ! 2 A203 TEO X 1 X ! X 1 X ! 2A204 TLM X 1 1 X I 2A205 GHS X X 1 XIX! X 1 2A206 CHS X X ! X 1 X 1 X ! 2A207 TGY X 1 1 X I 2A208 GGY X 1 X ! ! 2A209 HGY X 1 X 1

(CONTINUED NEXT PAGE)

Figure 4. LRU/Subsystem Matrix

231
TURRET (G eneral) TU R R ET DRIVE

REF PWR INT S .J £ A ? TOW SMK oUN TOh TCW

CES LRU 01 ST LCCK SEL TRGR GUN CTL GRO FAN TRA V EL LFT EL STAB

2wl CiSLE X ' ' Z'tiZ " X X X t 2W3 " X XI IX X X X 1 .

j ] X 1 2W4 " X X XI IX 1 X X X X i X 1 2^15 " X X t 1 X 1 X X 1 X 1 X 1 2W6 " X 1 X 1 X X 1 1 X t 2 W 7

" X 2^9 "

1 1 X X 2 W 1 0

"

i 1 X X 2 W 1 2 "

1 t X

2 W 1 4

" X

2 W 1 5 " X 2 W 1 0 1 "

1 I X 1 X 1 X 1 1 X 1 2 U 1 0 2 " 1 X 1 X 1 1 X 1 2W103 " X 1 1 X 1 2W104 "

1 X 1 1 X 1 2'«301 "

X X ! 1 X 1 X 1 X 1 X X 1 2W30 2

" X X 1 X 1 X 1 X 1 X 1 2W303 " X 1 X 1 2 w 3 0 4

" X ! t X 1 2 '« 3 0 5 " X 1 X 1 X 1 2 W 3 0 6 " 1 X 1 X 2W307 " X 1 X 1 X 1 2 w 3 0 8 " 1 X ! X 1 X 1 X I X 1 X 1 2W309 " 1 X ! X 1 HULL CABLE

1 W 1 3 " 1 X 1 1 1 7 " 1 X 1 1 H 1 3 " I X 1 1 u 1 9 " 1 X 1

Figure 4. LRU/Subsystem Matrix

Each "X" shows that the LRU (listed at the left) can create one or more failure conditions in the Subsystem (listed along the top).

232
dures, in terms of the verbatim messages displayed to the mechanic, the

test point measurements executed, and the measurement tolerances used

in each decision branch.

IMPROVED TEST STRATEGY USING AUTOMATED TEST EQUIPMENT

By combining improved test strategy along with microprocessor technology, diagnostic test procedures have been improved in a number of ways:

0 More measurements can be made in shorter testing time.

0 Tests are more comprehensive (cover more failure modes).

0 Tests are more reliable (conducted from uniform and established initial conditions, they always reach the same consistent

results)

.

0 Vehicle harnesses are not needlessly disconnected in testing.

0 Test set use is encouraged, guessing is discouraged.

POSTSCRIPTS

A number of design factors and program constraints were recognized during the development of STE-Ml and STE-Ml/FVS and some of these are enu- merated here:

(1) Comprehensive test coverage requires a great amount of procedures to be coded and validated. Formal means to document

such procedures and validate these tests as needed.

(2) Software validation aids must be built into the tests. While

checking the procedures on-vehicle, the validation team must

be able to track the test set and monitor measurement results

at each step in the test.

(3) Vehicle use for test program validation is a valuable and scarce resource. Plan for the most efficient possible use of

on-vehicle time.

(4) Plan for changes to the test programs (software) during the

initial fielding of the vehicle. Changes to the software due

to testing considerations as well as to vehicle changes are bound to be needed.

(.5) Because a large portion of the test procedures are involved

with messages to the mechanic, an appreciable portion of the

software changes will, in fact, be "human factors" considerations. A message which is sometimes misunderstood causes test

unreliability, as much so as improper test limits.

233
CONCLUSION

By partitioning the vehicle into a few fundamental subsystems, diagnostic test procedures have been established which prove effective and efficient. There are a limited number of test procedures available, cor- responding to functional subsystems with which the vehicle user is intimately concerned and aware. Because the test set is fully programmed

under computer control, the large number of measurement and message

steps in each procedure can be rapidly executed.

234
ADVANCED ATTACK HELICOPTER AH-64

FAULT DETECTION/LOCATION SYSTEM

H. E. Pohlenz

Manager, Maintainability Section - Systems Engineering Department

Hughes Helicopters, Incorporated

Culver City, California 90230

Abstract: Army and Hughes Helicopters Advanced Attack Helicopter

(AH-64) Program Management have stressed the importance of an effective

Fault Detection and Location System (FD/LS) throughout the AH-64 design

process. The FD/LS program objectives were to avoid flights with failed

safety and mission critical hardware, reduce maintainability downtime

and prevent removal and replacement of good hardware. The design

approach was to make extensive use of existing AH-64 equipment with

Built-in Test Equipment (BITE) added, and to emphasize reliability and

maintainability techniques, analyses and tradeoff processes from the

earliest stages of the design effort. The resulting AH-64 FD/LS is an optimum mix of hardware (conventional caution and warning devices

coupled with microprocessor controlled multiplexing system for data

handling and display), Man-in-the-Loop systems operations, and technical

procedures and maintenance manuals. Both AH-64 FD/LS test and analysis

results indicate that systems objectives and requirements have been met

or exceeded.

Key Words: Fault Detection/Location System; Failure Modes and Effects

Critical ity Analysis (FMECA); Reliability Centered Maintenance (RCM);

Caution, Warning and Advisory Panels; Multiplex (MUX) System; Fire

Control Computer; On-Condition Monitor; Condition Monitoring; Built-in

Test Equipment (BITE); and. Skill Performance Aids (SPA)

INTRODUCTION

The U.S. Army's Advanced Attack Helicopter, the Hughes AH-64, is the

first Army Attack Helicopter to be developed specifically for the day/

night/adverse weather anti-armor mission. The AH-64 is a tandem seat,

two place, twin engine helicopter with a four bladed main rotor system

having a 48.0 foot diameter. Equipped with completely integrated aircraft and weapons systems, the AH-64 will acquire and destroy hostile

targets at maximum standoff ranges.

The primary point target weapon of the Advanced Attack Helicopter is the

HELLFIRE anti-tank missile, with area suppression fire provided by 30 mm

cannon and 2.75 FFAR^rocket subsystems. The Target Acquisition Designator Sight (TADS) and Pilots Night Vision Sensor (PNVS) provide the day/

night/adverse weather target acquisition/designation and Nap of Earth

235
flight ability which enables the AH-64 to effectively launch its attack

armaments from stand-off ranges. The excellent performance characteristics of the AH-64 are highlighted by its demonstrated airspeed of

204 knots, g loads ranging from -0.5 to +3.5 g's, and sideward and rear- ward flight speeds of 45 knots. Designed for a fifteen year service

life, this helicopter will contribute greatly to the Army's ability to

fight outnumbered — and win!

Recently, there have been numerous articles and reports addressing the

problems associated with high complex and sophisticated weapon systems

that exceeded their performance requirements but became operating and

maintenance nightmares when they were fielded. While the statistics

vary from study to study the basic problems reported were similar in

nature: (1) Excessive maintenance downtime; (2) Excessive removal and

replacement of good hardware; and (3) Equipment design too complex for

available maintenance skill levels. To preclude these problems on the

Advanced Attack Helicopter, both Hughes and the Army have stressed reliability and maintainability requirements as basic drivers throughout the

design effort.

This emphasis on reducing reliability and maintainability problems from

those experienced on earlier weapon systems brought about many specific

design features in the AH-64: transmission and engine removal without

removing the rotor head; low-vibration rotor system; integral work

platforms; excellent access to electronic, visionics and avionics equipments; and an innovative Fault Detection/Location System (FD/LS). This

paper will cover the AH-64 FD/LS. The FD/LS objectives, requirements,

development techniques and problems, equipment design and operating procedures, and the role of the "Man-in-the-Loop will all be addressed.

The primary objectives of the AH-64 Fault Detection and Location System

were to: (1) Avoid flying the aircraft with failed mission essential or flight critical hardware; (2) Minimize maintenance down time; and

(3) Prevent the removal and replacement of good hardware. Other related

objectives were for the FD/LS system itself to be cost-effective, easy

to operate and easy to maintain.

The overall AH-64 Fault Detection/Location System is defined by the

Government as an optimum mix of Built-in Test Equipment (BITE), onboard

diagnostic equipment, ground test equipment, automatic test equipment,

technical manuals, diagnostic procedures, and other design techniques.

A thorough analyses of AH-64 mission requirements and systems hardware,

in light of FD/LS objectives to ensure that FD/LS equipment, personnel

and procedures were indeed optimized , was the major challenge of this

systems development effort.

RELIABILITY AND MAINTAINABILITY ANALYSES

As noted above, both Hughes Helicopters and the Army have placed special

emphasis on reliability and maintainability requirements throughout the

Advanced Attack Helicopter design process. While there were numerous

236
techniques and procedures involved in the AH-64 Reliability and

Maintainability Programs, the primary elements involved in the FD/LS

development effort were Reliability FMECA data and Maintainability

Engineering Analyses conducted in accordance with Reliability Centered

Maintenance principles.

Reliability Failure Modes, Effects, and Critical ity Analysis (FMECA)

reports were prepared on the total AH-64 system, major assemblies, AVUM

Replaceable Units, and significant Replaceable Modules. Mission and

system reliability failure modes were analyzed to the level necessary to

meet the overall mission and system reliability requirements. The FMECA

for each level of analysis identified the hardware, its quantity and

function, all identifiable failure modes, the frequency of each failure

mode and the effect of the failure mode on the subsystem and system.

Failure rates and K-factors for nonstandard parts were obtained from

MIL-HDKBK-217A, the GIDEP (FARADA) handbook, or from vendor data for

state-of-the-art devices that have not been published in MIL-M-38510,

General Specification for Microci rcui ts.

Maintainability Engineering analysis of the FMECA data was conducted in

the development of the AH-64 Maintenance Plan. This analysis involved

the application of the principles of Reliability Centered Maintenance

(RCM), using the Army's DARCOM-P 750-16 Pamphlet, Appendix C as a guide.

RCM provides a logic process that results in the segregation of maintenance requirements into:

(1) On-condition category : scheduled inspections or tests to

measure deterioration of an item, with the item either remaining in service or corrective maintenance being performed.

(2) Hardtime category : scheduled removal tasks based on predetermined fixed intervals of age or usage.

(3) Condition monitoring category : unscheduled tasks on components which are allowed to fail or components where impending

failure can be detected by crew through routine monitoring

during normal operations.

In a sharp departure from the traditional approaches, RCM forces maintenance attention more on the actual condition of the equipment and less

on mandatory inspections and hard time removals. The driving force in

the development of maintenance planning for the Advanced Attack Helicopter was to reduce the scheduled maintenance burden and operating and

support cost incurred by the system while maintaining the necessary

readiness rate.

RCM logic was applied to each replaceable unit in the system, addressing

each individual failure mode. The RCM logic presented in DARCOM-P

750-16, Appendix C, is structured into block diagrams which logically

addresses such factors as mission/flight critical ity, rate of and

detectibility of degradation of the item, cost impact associated with

237
scheduled and unscheduled maintenance, and criteria for categorizing

the maintenance task. The criteria upon which this logic process is

based is that: (1) Scheduled maintenance tasks should be performed on non-critical components only when such scheduled tasks reduce the life

cycle cost of the system; and (2) scheduled maintenance tasks should be

performed on critical components only when such tasks will prevent

deterioration in reliability and/or safety to unacceptable levels, or when such tasks reduce life cycle costs.

There were no hard-time limits established on AH-64 components as a result of this analysis process. All scheduled inspections and tests

on the AH-64 were categorized into on-condition limits, which are included in Phased-Maintenance procedures. Some components were

included in both the condition monitoring category and the on-condition

category, while the remaining components were categorized for condition

monitoring only.

As described in DARCOM-P 750-16, Appendix C, condition monitoring is the

process where the operator or crew detects either impending or experienced failures through routine monitoring of equipment operation and

use. Impending failures are those detectable either directly through

the human senses (vibration, heat, noise, etc.), or indirectly, through

design features such as Built-in Test Equipment (BITE) and sensors/

transducers (warning lights, gauges, etc.) before they occur. The

experienced failures are those that are detected by the operator or crew when or after they occur.

It should be emphasized that these reliability and maintainability

analysis processes were structured to generate design changes when that

action was indicated by analysis results. In addition, these analyses were iterative in nature and were reapplied as measured values became

available to replace predicted values, and as design changes were implemented. This ensured that reliability and maintainability requirements

were part of the earliest stages of design and that they were reinforced

throughout all stages of the Advanced Attack Helicopter design process.

Further, reliability and maintainability performance data was recorded

and analyzed throughout an extensive flight test program to ensure that

the AH-64 complied with rigorous and specific reliability and maintainability requirements.

FAULT DETECTION/LOCATION SYSTEM REQUIREMENTS

The general design requirements for this system were negotiated by

Hughes and the Army during the competitive phase of the Advanced Attack

Helicopter program. The general requirements for the FD/LS include the

capability to: (1) provide on-aircraft inflight "GO/NO-GO" status of

mission essential subsystems; (2) detect failures of flight critical

subsystems; (3) fault isolate electrical and electronic failures to the

Aviation Unit Maintenance (AVUM) replaceable unit; and, (4) provide

electrical and electronic fault isolation within removed replaceable

238
units. Additionally, FD/LS must be fail-safe so that its failure will

not degrade the performance of monitored components.

In designing the AH-64 FD/LS Hughes Helicopter established specific

requirements regarding the percentage of failures to be detected and

located by FD/LS and the percentage of "false alarms" allowed. The

on-aircraft fault location requirement specified that EACH AVUM electrical and electronic replaceable unit must provide for at least 95 percent

of its failures, weighted by failure rate, to be indicated by the FD/LS

system, with no more than 2 percent erroneous indications.

This requirement to isolate at least 95 percent of the failures in

" each " replaceable unit resulted in several difficult problems. The

basic problem in specifying the requirement for "each" unit stems from

the wide range in reliability (MTBF) between the 137 replaceable units

monitored by FD/LS. The data presented in Figure 1 shows that 47 of

these replaceable units (35 percent of all units) have an MTBF greater

than 20,000 hours. At a war time flying rate of 1320 hours per year the

aircraft would accumulate a total of 19,800 flying hours during its

15 year service life. It can be seen from Figure 1, which was developed

from the reliability FMECA reports, that it is predicted that some replaceable units will not fail within two or more lifetimes of the aircraft. (Figure 2 presents a distribution of this data showing the percentage of detectable failures within aircraft lifetimes based on a wartime flying rate of 1320 hours per year. Figure 3 shows the same type of distribution based on a peacetime flying rate of 360 hours per

year.) In the case of some highly reliable mission essential or flight

critical hardware, such as the Flight Control Position Sensors

(100,000 hours MTBF) it is effective from a flight safety point of view

to detect and locate more than 95 percent of their total failures. In

other instances, involving less critical hardware, it may not be cost

effective to meet this requirement. Conversely, it is also true that

on some of the less reliable units 95 percent of the failures may be

too low — conventional troubleshooting for 5 percent of the failures

in the range of 95 to 100 percent on one unit with low reliability may

result in more maintenance downtime than such troubleshooting would

entail for say 50 percent of the failures on a unit with high

reliability.

An alternate approach to determine the type and quantity of failures to

be detected and located would be to establish an overall requirement

for the total system. Although the distributions in Figures 2 and 3

indicate that 95 percent may be unnecessarily high for the AH-64, a requirement that "the Fault Detection/Location System shall detect and

locate at least 95 percent of all the failures occurring in an electrical and electronic replaceable units specified in the weapon system,

with no more than 2 percent erroneous indications" could be implemented

to satisfy FD/LS design objectives on an effective and efficient basis.,

using the reliability and maintainability analysis and tradeoff process

described earlier.

239
LRU % OF

MTBF QUANTITY TOTAL LRU'S

300 - 5000 41 30

5001 - 10,000 22 16

10,001 - 15,000 13 g

1 5,001 - 20,000 14 10

20,001 - 25,000 9 7

25,000 - 30,000 7 5

30,001 -35,000 2 2

35,001 - 50,000 6 4

50,001 - 1 00,000 15 11 > 100,000 8 6

137

Figure 1: MTBF Distribution by Number of LRUs

0 25 50 75 100 0 25 50 75 100 % DETECTABLE FAILUREf % DETECTABLE FAILURES

Figure 2: % Detectable Failures by Figure 3: % Detectable Failures by

A/C Lifetime (1320 hours per year) A/C Lifetime (360 hours per year)

240
FAULT DETECTION/LOCATION SYSTEM DESIGN

Notwithstanding the foregoing, Hughes Helicopters has been very successful during the Full Scale Engineering Development Phase of the AH-64

Program in meeting both the objectives and requirements of the FD/LS.

The current FD/LS design will detect and locate at least 95 percent of

all the failures expected to occur on each of 104 replaceable units.

Further, the current design will detect and locate over 91 percent of

all the failures expected to occur on all the replaceable units included

in the FD/LS system. Follow-on design improvements have already been

developed to ensure that the production aircraft FD/LS has sufficient

test provisions so that at least 95 percent of all failures within each

replaceable unit result in a failure indication.

The overall AH-64 FD/LS is an optimum mix of design features such as Caution and Warning Lights, computer-oriented BITE, Ground Test Equipment and Automatic Test Equipment coupled with Man-in-the-Loop, Technical Manuals and Diagnostic Procedures.

Caution and Warning System

A major portion of the overall AH-64 FD/LS is included in the Caution

and Warning System. The caution and warning system provides visual

indications of systems status and visual and aural indications of actual

and impending failures critical to aircraft mission or flight safety.

Various devices, such as chip detectors, pressure sensors, temperature

sensors and valve or switch position indicators are included in equipment designs throughout the aircraft and are interconnected with caution

and warning equipment installed in the crew stations.

Master Caution and Warning Panels and Caution, Warning and Advisory

Panels (Figures 4 and 5) are installed in both the pilot and copilot/

gunner stations. The two Master Caution and Warning Panels, one located

on the top center of the pilot's instrument panel and the other on the

top right side of the copilot/gunner's instrument panel, provide the

initial indications of impending failure, actual failures, or dangerous

conditions. The MASTER CAUTION display on these Master Caution and

Warning Panels is pushbutton operated. Initially, the MASTER CAUTION

will flash (5 ±1 hertz rate) when a Caution, Warning and Advisory Panel

segment simultaneously starts flashing (2 ±1 hertz rate). Pressing the

MASTER CAUTION display will cause it to extinguish and will convert the

flashing fault segment to steady on. It will remain on until the fault

or condition is corrected. When the PRESS TO TEST button on the Master

Caution and Warning Panel is pressed, all Caution, Warning and Advisory

lights in the crewstation are illuminated. When any of the remaining

warning lights on the Master Caution and Warning Panel are lit, immediate attention is required by the crew members in accordance with operating instructions. An aural tone (700 to 1000 hertz continuous sweep)

is incorporated with the LOW RPM ROTOR, ENG 1 OUT and ENG 2 OUT segments

241

I

243
on the Master Caution and Warning Panels. The MANUAL STAB segment on both Caution, Warning and Advisory panels incorporate a steady 1000 Hz

aural tone.

Other caution, warning and advisory indicators are located with associated subsystem panels installed in the crew stations. In addition, there

are appropriate gauges, indicators and instruments in the pilot and

copilot/gunner instrument panel which serve as system status and

caution/warning advisors.

FD/LS on Multiplex System

This portion of the overall AH-64 FD/LS is included as part of the

Multiplex (MUX) and Fire Control Computer, (FCC) subsystems. The AH-64

Multiplex system is a general purpose information transfer system that

performs the function of command and control of avionic and mission

equipment functions, and provides for FD/LS signal routing and processing. Conforming to MIL-STD-1 553B , the AH-64 Multiplex system makes this

the first helicopter to incorporate a multiplex data bus system for subsystem interface and data handling.

The FD/LS operation of this system provides CONTINUOUS in-flight monitoring of electrical/electronic mission essential and flight critical

systems for "GO/NO-GO" status, with in-flight/on the ground ON-DEMAND

monitoring by the copilot/gunner or ground maintenace personnel. The

FD/LS detects and locates failed AVUM electrical/electronic replaceable

units, with equipment status annotated on the Caution and Warning panels

or displayed on the TADS Heads Out Display (HOD) and Heads Down Display

(HDD). This FD/LS capability is provided through operation of the

Multiplex (MUX) data bus software programs in the Fire Control Computer,

a Data Entry Keyboard, Symbol Generator, Caution and Warning Panels,

TADS Displays, and the fault sensor or BITE of the subsystems being

monitored. Figure 6 shows the AH-64 Multiplex system distribution

throughout the aircraft, highlighting widely separated redundant data

buses and bus controllers (p-rimary residing in the FCC; backup residing

in the copilot compartment Remote Terminal Unit Backup Bus Controller

BBC) for improved reliability and survivability. An overview of the

FD/LS functions of this equipment is summarized below:

Data Bus Operati on. The AH-64 MUX data buses consist of low-loss

twisted, shielded, 24 gauge. Teflon insulated wire pairs, terminated at

each end for impedance matching. The data bus operates asynchronously

in a command/response mode, with data transfer occurring in either

direction, but only one direction at a time (half duplex). All connections to the data bus system use a Data Link Terminal Unit (DLTU) which

provides short-circuit isolation, impedance matching, and line termination. Sole control of data transfer on the bus resides with the bus

244
245
controller (FCC primary; BBC secondary) which initiates all data (both

analog and digital) transmissions. Time Division Multiplexing (TDM)

allows transmission of signals to more than one unit over one data bus

line by staggering the time sequence of the signal. Data bus main frame

time is a nominal 20 milliseconds (50 times per second) while functions

not requiring this high of an update rate are processed at lower rates

of 25 times per second, 12-1/2 times per second, 6-1/4 times per second,

or 3-1/8 times per second.

Fire Control Computer (FCC) . The FCC is the primary computer for FD/LS

functions, with logic processing capabilities sufficient to perform

sequencing, interlock priorities and interrupts, and other control

functions involving the discrete, analog, and digital signals associated

with the AH-64 MUX system. The FCC contains software programs for data

entry, continuous monitoring routine, end-to-end test routine, and

individual test routines to provide the required control flexibility.

As indicated earlier, the FCC interfaces with the systems under test as well as other FD/LS components through the MUX system. The FCC meets

the fail-safe operational requirements of MIL-STD-1553B, and performs

continuous self-test functions to determine failures and accomplish

transfers to redundant components, circuits, or modes of operation.

Multiplex Remote Terminal Units (MRTU) . The MRTUs provide interface

between the MUX system and the aircraft systems being monitored. There

are three standard aircraft MRTUs used in the AH-64 data bus system.

The remote terminal units input and output a standard assortment of

bilevels, ac and dc analog, serial digital, and synchro input/output

signals to the aircraft systems. These remote terminal units contain

redundant data bus interfaces, and they contain sufficient built-in

circuitry to detect 95 percent of all faults within each MRTU.

Back-up Bus Controller (BBC) . The BBC is a computer within an MRTU

located in the copilot/gunner's station. The BBC automatically assumes

control of the FD/LS if the FCC fails, or if a manual switch located

in the copilot/gunner's Fire Control Panel is placed in an override

position. The BBC contains the capability to perform the FD/LS con- tinuous monitoring routine and the associated display routines.

Data Entry Keyboard . The Data Entry Keyboard is located in the copilot/

gunner's station and provides the means for the copilot/gunner or maintenance personnel to enter FD/LS test modes and to acknowledge actions

taken. When a manual switch in the keyboard circuit is so positioned,

the data entry keyboard provides itself with continuous internal self

testing.

Symbol Generator . The AH-64 Symbol Generator takes information from the

interfacing subsystems equipment and generates the necessary character

symbology information. This information provides FD/LS status data

visually displayed on TADS Heads Out and Heads Down Display Units. The

Symbology Generator also contains a BITE self-test capability.

246
Target Acquisition and Designation Sight (TADS) Displays . The TADS

provides three displays capable of presenting FD/LS messages: Heads Out

Display (HOD), Heads Down Display, and the Alphanumeric Display (AND).

The displayed messages announce test progress, required operator action

items, and status information. As indicated above, the messages to be

displayed on the HOD and HDD are generated by the Symbol Generator. The

messages to be displayed on the AND are generated and commanded by the

FCC.

FD/LS BITE . There are two categories of FD/LS BITE included in this

system: (1) Equipment that has a microprocessor (computer) as part of

its BITE; and (2) Equipment without a microprocessor. With equipment

that has a microprocessor controlling BITE, the self-test is initiated

by a signal sent from the bus controller via the MUX bus to the microprocessor. The microprocessor then runs the BITE and sends the resulting test data, via the MUX bus, back to the bus controller. Each bit, or bit pattern in this test data, corresponds to either the GO/NO GO

status of the equipment as a whole, or individual functions, or AVUM

replaceable units. Appropriate FD/LS software then checks for and

displays any failures. With equipment that does not have a microprocessor to run the BITE, the parameters of the equipment are transmitted to

the bus controller, in COMMAND/RESPONSE mode, over the MUX bus. The

data (equipment parameters) is then evaluated by FD/LS software in the

bus controller to detect any abnormalities in the operation of the

equipment. If a significant abnormality (failure) is detected, the

software will isolate the problem to the appropriate AVUM replaceable

unit, and announce it to the crew.

As previously indicated, the FD/LS functions integrated with the MUX bus are designed to handle continuous monitoring of mission essential and

flight critical equipment and keyboard initiated equipment monitoring.

Figure 7 is presented to show an overview of these FD/LS interactive

system devices.

With the continuous monitoring FD/LS capability most equipment will run

a continuous self-check at a functional level without assessing detailed

parameters. These equipments generally check critical components or functions such as a processor, power supply or critical timing. If any

of these components or functions show an abnormality (failure), an appropriate signal is sent to the computer controlling the data bus.

This data transmission will then result in the Caution and Warning Panel

announcing the failure; or the copilot/gunner getting a failure indication on one of the TADS displays. If the crew then requires additional

information about the type of failure or what capability has been lost,

the copilot/gunner will initiate the appropriate FD/LS test for that

equipment through the Data Entry Keyboard Panel. The following mission

essential or flight critical equipment is under continuous FD/LS

monitoring:

t POINT TARGET

• AREA WEAPON

247
248
• AERIAL ROCKET

• EXTERNAL STORES

• TADS/PNVS

• DIGITAL AUTOMATIC STABILIZATION EQUIPMENT (DASE)

• ELECTRONIC ATTITUDE DISPLAY INDICATOR (EADI)

• DATA ENTRY KEYBOARD

0 AIR DATA SYSTEM

• HEADING ATTITUDE REFERENCE SYSTEM (HARS)

• INTEGRATED HELMET AND DISPLAY SIGHT SYSTEM (IHADSS)

• MULTIPLEX

• SYMBOL GENERATOR

When a FD/LS test is initiated via the keyboard, the code for the

requested test is preceded by either a "G" (for copilot/gunner) or an

"M" (for maintenance personnel). The major difference in these data

entries is reflected in the displays. When a test code is preceded by

a "G" and a failure has occurred in monitored equipment, the display

will indicate system status, such as EADI NO-GO. When a test code is

preceded by an "M" and a failure has occurred in monitored equipment,

the display will indicate an AVUM replaceable unit status, such as EADI Display Unit NO-GO Pilot Comp. (Figure 8 lists the systems/

equipment monitored by keyboard initiated test and the Keyboard Entry

Codes.

)

As stated earlier, the aircrew and maintenance personnel, as well as the

Technical Manuals and Diagnostic Procedures, are also part of the AH-64

FD/LS. When faults or failures can be effectively detected and located

by human observation, then FD/LS design features are not added to the

related equipment design. An example of this FD/LS Man-in-the-Loop

capability would be the communications equipment.

In other Man-in-the-Loop actions, the flight crew or ground maintenance

personnel must make observations and/or perform operations during FD/LS

on-demand test operations and acknowledge observation results or actions

through the Data Entry Keyboard. The FD/LS program will then execute the

next step or sequence of steps in the test and display the results, and

display additional actions or inquiries of the Man-in-the-Loop. For

example, when the in-flight continuous monitoring procedure indicates a failure in the DASE by Displaying "DASE NO GO", the ground maintenance

personnel would operate the FD/LS and interface with the systems as

Man-in-the-Loop FD/LS

follows:

MAN-IN-LOOP: II MDASE II

FD/LS DISPLAY: ENGAGE ROTOR BRAKE"

MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: II CENTER ALL CONTROLS AND ENGAGE FORCE TRIM. II

249
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MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: "CHECK FOR FREE CYCLIC, PEDAL AND COLLECTIVE

MOVEMENT."

MAN-IN-LOOP: PERFORM CHECK AND RESPOND "YES" or "NO" VIA KEYBOARD

FD/LS DISPLAY (IF NO): "CAN NOT RUN DASE FD/LS. PERFORM

CORRECTIVE ACTION."

FD/LS DISPLAY (IF YES): "ENGAGE PITCH AND ROLL SWS ON DASE PANEL.

MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: "IS BUC ON? C & W LIGHT ON AND SAS AND BUC FAIL

C & W LIGHT OFF?"

MAN-IN-LOOP: PERFORM CHECK AND RESPOND "YES" OR "NO" VIA KEYBOARD

FD/LS DISPLAY: "ENGAGE ALL DASE PANEL SWS. CYCLE BUCS S/T SW TO

PLT CPG. CENTER POS."

MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: "PLT TOGGEL FORCE TRIM SW TO OFF, ON, MOM REL.

PRESS DASE RELEASE SW."

MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: "ARE SAS AND BUC FAIL C & W LIGHTS ON, BUC ON

C & W LIGHTS OFF?"

MAN-IN-LOOP: PERFORM CHECK AND RESPOND "YES" OR "NO"

FD/LS DISPLAY: "ENGAGE ALL ASE PANEL SWS. CPG PULL BUCS LVDT SEL

TRIGGER. PRESS TRIM & ASE RELEASE SWS."

MAN-IN-LOOP: PERFORM TASKS AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: "IS TURN RATE INDICATOR ON EADI APPROX HALF SCALE

ON RIGHT?"

MAN-IN-LOOP: PERFORM CHECK AND RESPOND "YES" OR "NO" VIA KEYBOARD

FD/LS DISPLAY: "ENGAGE PITCH SAS SW."

MAN-IN-LOOP: PERFORM TASK AND ACKNOWLEDGE VIA KEYBOARD

FD/LS DISPLAY: PERFORMS CHECK OF ALL REPLACEABLE UNITS AND

DISPLAYS ALL FAILED UNITS IN DASE

251
It should also be noted that the Maintenance Procedures and Manuals

developed for the AH-64 are in compliance with the content and format

requirements of Skill Performance Aids (SPA) Figure 9. These SPA

manuals, coupled with the FD/LS design features described earlier ensure

that the FD/LS can be operated and maintained with maintenance skill

levels currently available in the field.

AVIM and Depot Automatic Test Equipment

Another important segment of the overall AH-64 FD/LS is the Automatic

Test Equipment (ATE) for AVIM and depot level testing of all avionics,

electronics and visionics equipment. The AH-64 ATE was developed by RCA

Automated Systems, with extensive "team support" provided by Hughes

Helicopters and the Army and the other aerospace companies involved in

the Advanced Attack Helicopter Program as Associate Contractors and Subcontractors. This team effort provided extensive information reflecting

the combined points of view of the user, the weapon systems integrator

and the designer and manufacturer of the equipments to be tested.

The requirements developed for the ATE segment of the FD/LS included

testing capability so that at least 98 percent of all failures weighted

by failure rate could be detected and located to the repairable module

fault, with no more than 2 percent erroneous indications. Further

requirements specified: (1) That failure isolation of the replaceable

units must be accomplished without disassembly of the unit or removal

of covers; (2) That substitution of known good replaceable modules, or probing as a means of fault isolation is not allowed; and, (3) That

calibration or adjustment of the replaceable units would not be required

when they were installed in the next higher assemblies.

RCA, in conjunction with Hughes Helicopters and the other AH-64 team

members, developed FMECA's, Optimum Repair Level Analyses (ORLS's), and

related data, along with new design approaches based on "lessons

learned" from earlier ATE development programs, to ensure that the AH-64

ATE complied with system requirements. The resulting AH-64 ATE is a third generation system using its computer to generate stimulus signals

and to perform diagnostics and fault location, as well as to control the

testing procedure. The system eliminates racks of special test devices,

simplifies test procedures, and provides the flexibility necessary to

support the diverse subsystem equipment of the AH-64 helicopter.

SUMMARY

The primary objectives of the AH-64 FD/LS were to: (1) Avoid flying the

aircraft with failed mission essential or flight critical hardware;

(2) Minimize maintenance downtime; and (3) Prevent the removal and

replacement of good hardware. Each of these objectives represent major

problem areas experienced in earlier programs involving complex high

performance weapons systems, and it was recognized that an effective

252
253
Fault Detection and Location System would significantly reduce these

problems. The need for good reliability and maintainability features as inherent design characteristics was stressed during the earliest stages

of the AH-64 design process, as was the need for ongoing testing to ensure compliance with these requirements. Emphasis was also placed on the need to base maintenance actions on the actual condition of the

hardware rather than on calendar time or flying hours. Finally,

requirements were established to ensure that the FD/LS equipment itself was simple to operate and maintain, and the need for an optimum mix of

FD/LS hardware, technical procedures and Man-in-the-Loop operations was established and enforced.

The resulting AH-64 FD/LS design includes conventional on-board sensors

and detectors interconnected with aural and visual caution and warning

devices; a computer controlled multiplexing system using existing aircraft electronics and visionics equipment in conjunction with BITE for

continuous and on-demand systems monitoring; and SPA, technical and

maintenance manuals for simple, highly illustrated FD/LS operating and

diagnostic procedures.

The six AH-64 helicopters manufactured to date have accumulated approximately 4000 flight hours and 1000 ground hours, making this aircraft one of the most thoroughly tested developmental aircraft programs in aviation

history. However, the final assessment of the AH-64 FD/LS effectiveness

must wait until the production aircraft is fully fielded. But developmental testing to date, including on the ground FD/LS operation by Army

Maintenance personnel, clearly indicates that the AH-64 FD/LS system

is an "Innovation for Maintenance Technology Improvement."

254
SESSION IV

IMPROVED MAINTENANCE PROCESSES

chairman: GEORGE KITCHEN

BELL TELEPHONE LABORATORIES, INC.

SERVICE LIFE OF BEARINGS CAN BE

INCREASED WITH "PROPER MAINTENANCE"

R. A. Guyer, Jr.

SKF Industries, Inc.

11-00 First Avenue

King of Prussia, Pennsylvania 19406

Abstract: Many times a bearing sees only 10 to 20 percent

of its calculated life due to such life shortening factors

as: poor shaft and housing fits; improper installation;

inadequate lubrication; dirt and water intrusion. When a bearing failure occurs it is of primary importance to be

able to determine what caused the failure in order to prevent future failures.

On many occasions a bearing will be replaced without checking the shaft and housing fits and the condition of the

failed bearing and as a result still another bearing will

fail because the inherent deficiency in the previous

installation was not properly diagnosed.

Key words: Corrosion; dirt; dirt and water intrusion; fine

cracks; fine roughening of the surface; glazed surface;

inadequate lubrication; life adjustment factor; minimum

viscosity; misalignment; moisture; operating temperature;

poor shaft and housing fits; smearing; spalling.

When a bearing has to be replaced the shaft diameter and

housing bore should be checked for size according to the

specifications. There should be no nicks or gouges on the

shaft, shaft shoulder, housing bore and housing shoulder.

The failed bearing should be inspected for turning on the

shaft or in the housing. An examination of the raceways

will determine how the bearing was running.

In order to determine what is an improper installation one

has to be able to "READ" what is the normal wear pattern of

a properly mounted bearing. Figures 1 to 4 show the normal

load zones on a properly mounted radial ball bearing. The

same load zones are visible on both tapered roller and

spherical roller bearings however, they are somewhat more

difficult to see.

257
Figure 1 shows the normal load zones with inner ring rotation. Notice the load zone on the inner ring is a full

360 degrees and centrally located, whereas the load zone on

the outer ring is 150 degrees and centrally located.

Figure 2 shows the normal load zones with outer ring rotation. The load zone on the outer ring is a full 360

degrees and centrally located whereas the load zone on the

inner ring is 150 degrees and centrally located.

Figure 3 shows the normal load zones with an axial load.

Both inner ring and outer ring have a full 360 degree load

zone on the side of the groove away from the land.

Combined thrust and radial load will produce load zones as shown in Figure 4. With combined load, the load zone on

the inner ring is slightly off center and the length on the

outer is greater than that produced by radial load, but not

necessarily 360 degrees.

If the axial load is excessive, the load zone can actually

override the lands as is shown in Figure 5. This is an

abnormal load zone.

Misalignment of the housing relative to the shaft will produce abnormal load zones as seen in Figure 6. When the

shaft is misaligned relative to the housing, the load zones

are shown in Figure 7.

When improper fits and/or too small an internal radial

clearance is used, a bearing can become internally preloaded and the load zones are shown in Figure 8.

Distorted or out-of-round housing bores can radially pinch

an outer ring. Figure 9 illustrates the load zones found

in a bearing when the housing bore was initially out-ofround or became out-of-round by bolting the housing to a concave or convex surface. The outer ring will show two or

more load zones depending on the type of distortion.

By properly being able to identify and rectify the abnormal

load zones as shown in Figures 5 through 9 repeating

similar bearing failures can be eliminated.

Another common bearing failure is "Inadequate Lubrication".

Simply put, "Inadequate Lubrication" means that the oil ifoil lubricated, or the oil in the grease if grease lubricated is not of sufficient viscosity to separate the rolling elements from the raceways.

258
The first stage in "Inadequate Lubrication" is a fine

roughening of the surface as seen in Figure 10. The next

step is fine cracks shown in Figure 11. Finally, spalling

commences as shown in Figure 12 and then more advanced

spalling as shown in Figure 13.

Sometimes "Inadequate Lubrication" initially manifests itself as a highly glazed or glossy surface which as damage

progresses takes on a frosty appearance and eventually

spalls. The highly glazed surface is seen on the roller in

Figure 14.

Another form of surface damage due to "Inadequate Lubrication" is called smearing. It appears when two surfaces

slide and the lubricant cannot prevent adhesion of the surfaces. This can be seen in Figure 15.

In order to obtain the proper viscosity of the lubricant it

is only necessary to know the mean diameter of the bearing

[(O.D. + I.D.)-f-2] and the speed in RPM. From Figure 16

the minimum viscosity at the "OPERATING TEMPERATURE" can be

easily obtained.

The life adjustment factor (a23) can be obtained from

Figure 17. There are two bands shown in Figure 17; one is

for vacuum melted steels and one is for standard bearing

steels. The type of bearing and the viscosity ratio v/vi

determines the life adjustment factor Ca23) • The upper

boundary in each band is for ball and cylindrical roller

bearings and the lower boundary is for spherical and tapered

roller bearings.

Examples of how to use these graphs are given below:

EXAMPLE I An SKF 6209 ball bearing is required to operate under a radial load of 395 pounds at a speed of 2000 rpm. What

the adjusted rating life? Lubrication is by static oil

having a viscosity of 35 mm2/s (165 SUS) at the bearing

operating temperature.

IS

From the catalog, the basic load rating (C) is 5700 pounds

The basic rating life is:

Lio = 106 = 3000 x 10^ revolutions or

3000x10^

60x2000

= 25,000 hrs.

259
The minimum lubricant viscosity is obtained from Figure

16. The pitch diameter of bearing 6209 is taken as the

mean between the bore and O.D. and is equal to 65 mm. At

the speed of 2000 rpm, the minimum required viscosity is

13 mm^/s (70 SUS) . The viscosity ratio is therefore:

v/vi = 35/13 = 2.7.

The reliability factor ai for 901 reliability is 1.0. The

lubricant and material factor a23 is obtained from Figure

17 and is found to be 3 for SKF standard steels.

The adjusted rating life is:

LlOa = ^23 (Lio) = 3 x 25,000 hrs . = 75,000 hrs

.

EXAMPLE II

An SKF 22328 CJ spherical roller radial bearing is

required to operate under a radial load of 32,300 pounds

at a speed of 500 rpm. What is the adjusted rating life?

Lubrication is by static oil having a viscosity of

35 mm2/s (165 SUS) at the bearing operating temperature.

From the catalog, the basic load rating (C) is 220,000

pounds. The basic rating life is:

Lio = ^^52'500-^ "3 ^ = ^ revolutions or

600x106

60x500 = 20,000 hrs.

The minimum lubricant viscosity is obtained from Figure

16. The pitch diameter of bearing 22328 is taken as the

mean between the bore and O.D. and is equal to 220 mm.

At the speed of 500 rpm, the minimum required viscosity is

16 mm2/s (80 SUS). The viscosity ratio is therefore:

v/vi = 35/16 = 2.2.

The reliability factor a^ for 90% reliability is 1.0. The

lubricant and material factor a23 is obtained from Figure

17 and is found to be 1.7 for SKF standard steels.

The adjusted rating life is:

LlOa " ^23 CLio) = 1.7 x 20,000 hrs. = 34,000 hrs.

The effect of dirt and abrasive in the bearing during operation will result in a gross change in bearing internal

geometry. Figure 18 shows this condition.

260
s When moisture or actual water enters a bearing it mixes

with the lubricant and forms an acid which results in either

static corrosion when the bearing is not turning, Figure 19,

or with an overall corrosive attack on the bearing parts as shown in Figure 20.

SUMMARY

In order to achieve the calculated catalog life of a bearing for a given load, the bearing should have: (1) correct

shaft and housing fits; (2) proper installation; (3) adequate lubrication; (4) free of dirt and water intrusion.

It is even possible to obtain more than the calculated

catalog life by increasing the viscosity of the oil if oil

lubricated, or the oil in the grease if grease lubricated

in accordance with the examples previously shown. By

increasing the present service life of a bearing, production will be increased resulting in a more profitable operation.

In order to help SKF's customers obtain considerably

greater service life out of their bearings, SKF in 1980

introduced paid three-day "Bearing Maintenance Seminars"

that are held at Corporate Headquarters in King of Prussia,

Pennsylvania. Five seminars were held in 1980 and six are

scheduled for 1981. Each seminar is limited to 30 persons.

The seminar highlights are shown below:

PROGRAM HIGHLIGHTS

1. Rolling Bearing Basics —Covers the fundamentals of rolling bearing technology: bearing components, loads, nomenclature, lubrication and an overview of why bearings

fail.

2. Shaft and Housings —Measuring Procedures—Poor fitting

practice can ruin an otherwise good bearing application

in a short period of time.

3. Bearing Mounting and Dismounting Procedures —Proper

mounting and dismounting procedures prevent premature

bearing failure. Life shortening subjects covered are:

careless handling, neglected and improper maintenance,

and lubrication related failures.

4. Bearing Lubrication—Lubrication functions and principles as related to the importance of proper maintenance

procedures are covered. How Heat Affects Bearings

261
The higher the temperature, the more critical it

becomes to select the right lubricant for an application. Learn why the wrong lubricant significantly reduces bearing life.

5. Bearing vibration and noise measurement.

6. Seals for bearings.

7. Interpretation of bearing failures to prevent additional failures and review of individual bearing

problems

.

8. "Hands-on" demonstrations for mounting and dismounting

bearings

.

9. Tour of SKF Technology Services.

262
With a rotating inner ring, and a constant load direction, normal wear patterns look like this.

FIGURE 1

Here is a normal wearl pattern where the outer ring rotates relative to a load of constant direction, or where

the inner ring rotates and the load also rotates in phase

with the shaft

FIGURE 2

263
These drawings show the load zone and patterns in a deep-groove ball bearing under normal axial load

FIGURE 3

FIGURE 4

264
Excessive Thrust

This IS an example'of the load path when axial loads are excessive This is the one condition where the load paths follow the full circumference of both rings.

FIGURE 5

When an outer nng in a deep-groove ball bearing

IS nnisaligned relative to the shaft, you II see nonparallel wear patterns such as this.

FIGURE 6

265
When an inner ring is nnisaligned relative to the housing, a pattern like this will appear.

FIGURE 7

Too tight an interference fit can internally preload

a bearing by squeezing the rolling elements between

the rings, and that shows in a pattern like this

FIGURE 8

266
Distorted or out-of-round housing bores can

radially pinch an outer ring, resulting in a wear

pattern such as you see here.

FIGURE 9

The first indication of trouble is usually a fine roughening or waviness on the surface.

FIGURE 10

267
Later, fine cracks will develop.

FIGURE 11

Then spelling appears.

FIGURE 12

268
And finally, spalling occurs over the entire surface.

FIGURE 13

FIGURE 14

269
Smearing is another result of inadequate lubrication, as two surfaces adhere, and metal from one

surface is actually welded to the other. FIGURE 15

270
10 20 50 100 200 500 1000

Minimum Required Lubricant Viscosity (bearing bore * bearing O D ) - 2

I', i required lubricant viscosity for adequate

lubrication at ttie operating temperature

FIGURE 16

271
023 10

t

05

02

0 ! 0 05 0 tI I I I

i®i©

I

I

I I J_L

02 05

SKf VOQuum-Meltscr

StondOKl

StoeH

1111

?0

Fottgge Life Adjustment Foctof Ojjtof leortng

Mcjietids ondLubrtcotton

V lubricant viscosity in oppliccJtion

-- reoMred lubncont viscosity from Figure 16

FIGURE 17.

272
Abrasives can result in fast wear of both the rollers or balls and the rings, dramatically shown in this photograph.

FIGURE 18

FIGURE 19

273
Moisture h the lubricant can cause rusting on a

roller end -or on the roller surface if it is inactive.

FIGURE 2 0

274
THE APPLICATION OF NYLON POWDER COATING

TO VEHICULAR COMPONENTS

H. T. Lootens

US Army Materiel Systems Analysis Activity

Aberdeen Proving Ground, MD 21005

Abstract: Rust causes serious damage to vehicles, especially in a saltair environment. Also, leakage or spillage of battery acid causes significant corrosion of battery-related components. Another type of cor- rosion occurs inside fuel filler sleeves of diesel-fueled vehicles.

This corrosion deposit (lead carbonate), formed by the interaction of

the fuel, moisture and the lead coating on the sleeve, can cause major

problems in the vehicle fuel injection system. Approximately 1500 ve- hicular parts were coated with Nylon 11 to evaluate its effectiveness

in the prevention of rust and corrosion. These parts included battery

boxes, trays and frames, as well as fuel sleeves and frames. The characteristics and properties of Nylon 11 are summarized, the coating facilities and procedures are described and recommendations are presented.

Key words: Battery-acid corrosion; metal coating; polymer coating; rust

prevention; vehicular rust.

INTRODUCTION

Rust causes widespread and serious damage to vehicles. This is particularly true when the vehicles are used around salt water because here the

atmosphere is extremely corrosive. Mild rust damage to the bodies and

frames of vehicles requires that the affected area be repainted. In severe cases, the vehicle may be declared not economically repairable,

and the purchase of a replacement may be necessary.

In addition to environmentally-induced rust damage, vehicles suffer from

corrosion caused by the leakage or spillage of battery acid. This type

of damage is common on battery boxes, frames, trays, and associated

hardware. As in the case of rust damage, corroded parts require

either repeated painting or replacement.

Another type of corrosion, normally seen inside the fuel filler sleeves

of diesel vehicles, is caused by the interaction of diesel fuel, air

(moisture), and the lead coating on the filler sleeve. A white, pasty

deposit (lead carbonate) forms on the inside of the sleeve and the un- derside of the filler cap. Unless this deposit is cleaned off, it

275
will get into the fuel tank and can create major problems in the fuel

injection system of the vehicle.

One of the most effective methods of preventing rust and corrosion damage is to protect the metal surfaces with a coating of Nylon 11. The

coating is applied in powdered form by electrostatic deposition and is

fused to the metal surface with heat. Coatings of this type have been

used industrially for a number of years, and have proven to be extremel,

resistant to rust and corrosion.

The Field Equipment & Technology Division, US Army Materiel Systems

Analysis Activity (AMSAA) recently completed a project to evaluate the

effectiveness of Nylon 11 on Army vehicular components. Working

jointly with the US Army Ordnance & Chemical Center & School (OCCS),

approximately 1500 vehicular parts were coated at the OCCS from Decembe

1977 through February 1978. The coated parts included battery boxes,

trays, frames, brackets, braces, and holddown bolts; fuel sleeves and

sleeve frames; and miscellaneous OCCS training aids.

This paper presents a summary of the properties and uses of Nylon 11,

describes the AMSAA-OCCS powder coating facility and procedures, identi

fies the parts that were coated, and recommends future action.

BACKGROUND

In early 1977, personnel from the Naval Air Development Center (NADC),

Warminster, PA presented a briefing at AMSAA in which they described

the Nylon 11 powder coating technique. They had been using this type

of coating on a variety of naval aircraft and ship components since

1970 in order to reduce rust and corrosion and to improve wearability.

In October 1977, representatives from AMSAA visited NADC to observe

their powder coating facility and learn more about the technique.

NADC personnel indicated that they had assisted the US Marine Corps

in setting up a small powder coating facility at Camp LeJeune, North

Carolina approximately twelve months earlier. The AMSAA-OCCS coating

project was discussed, and NADC personnel stated they would support

such a program with their technical guidance and equipment.

In November 1977, AMSAA personnel visited Camp LeJeune (2d Marine Division, Force Troops and HQ, Camp LeJeune) to see their coating operation

The Marines were coating small numbers of battery frames, fuel sleeves,

and sleeve frames. NADC had loaned them powder coating equipment and

provided on-side technical instruction on the application of Nylon 11

coatings.

Following the visit to Camp LaJeune, AMSAA decided to proceed jointly

with the OCCS in a powder coating project. The objective of this proj276
ect was to obtain a data base on the effectiveness of Nylon 11 when

applied to components of Army vehicles.

CHARACTERISTICS AND PROPERTIES OF NYLON 11 POWDER COATINGS

Nylon 11 is a thermoplastic polymer produced from a vegetable source,

rather than a petroleum source. It was introduced on the market a little more than twenty years ago, and offers the following advantages

when applied to a metal surface:

(a) Excellent corrosion resistance.

(b) Improved abrasion resistance and wearability.

(c) High impact resistance.

(d) Good fungus and stain resistance.

(e) Good outdoor weathering properties.

(f) Good electrical properties.

(g) Good resistance to toxic agents and ease in decontamination,

compared to alkyd paint.

The use of the powder coating technique to protect metal surfaces has

several advantages over other coating methods and materials. The first

and probably most significant advantage, especially from an ecological

standpoint, is the elimination of the use of solvents in the coating

process. The absence of solvents provides a virtually pollution-free

atmosphere. Other safety standards are also improved because the fire

hazard in the work area is substantially reduced. The second advantage

that results from the use of powder coating technology is its ability

to form a protective resin coating that cannot be applied in any other manner without difficulty, primarily because of the poor solubility of

the resins in most solvents. Thus, many coating properties can be

obtained that were not previously available. The third advantage of

powder coating is that almost none of the powder is wasted. The over- sprayed powder is easily collected and reused.

One method used for coating metals with Nylon 11 powder is the Electrostatic Process. In this process, the powder is passed through a nozzle

carrying a high electrical potential (20-60 KV). The powder particles

become charged and are attracted to the metal part, which is at zero

potential. The thickness of the coating is a function of the static

attractabi 1 ity of the charged particles and the mechanical packing of

the dry powder. Since Nylon 11 is a thermoplastic, it is only necessary

to melt the adhered powder in an oven to fuse the coating to the metal

277
surface. Fusion temperatures range from 400 to 450°F.

Most metal parts can be coated with Nylon 11 provided they can withstand the fusion temperature without undergoing a physical change or a dimensional distortion. All parts to be coated must be thoroughly

cleaned to remove oil, grease, paint, rust, and corrosion. A primer

coat is often used to improve the adherence of the Nylon 11 powder and

to provide additional protection for the metal in the event the coating

becomes scratched or chipped.

Table 1 is a summary of the properties of the Nylon 11 powder used for

this project.

Table 1. Properties of Nylon 11 Powder

for Electrostatic Deposition

Nomenclature

Grade

Manufacturers code

Standard colors

Custom colors

Particle size

Fusion temperature

Film thickness

Melting point

Dielectric Strength at 68°F, 65% RH

3 mil coating

8 mil coating

Spray gun voltage

Spray gun distance

Coverage

Fine Powder ES

Functional

RDP-15

Black, White, Grey,

Beige, Light Green,

Dark Green

Red, Light Blue

0-80 microns

430-450°

F

2 mils (minimum)

7 mils (maximum)

360-365°F

4.62 KV

9.93 KV

20-60 KV

8-12 inches

160 sq ft per mil per

lb

278
ORGANIZING THE COATING FACILITY

AMSAA arranged with the Mobility Department (OCCS) to coat selected

components from the vehicles used as training aids in the department.

Since both AMSAA and the OCCS are located at APG, the logistical and

management problems of working with their vehicles would be minimized.

The components to be coated were battery boxes and related hardware,

fuel filler tubes, and fuel filler tube frames (these latter tv/o items are referred to in this report as fuel sleeves and sleeve frames). The

sandblasting and degreasing of the parts was performed by personnel of

the Materiel Testing Directorate (MTD), US Army Test and Evaluation

Command, Aberdeen Proving Ground, Maryland.

NADC loaned AMSAA an oven, a coating control console and a powder spray

gun. Under contract, they provided a second control console and gun.

Nylon 11 powder and primer and many other expendable supplies. They

also presented an initial briefing on the coating process to AMSAA-OCCS

personnel at Aberdeen Proving Ground, and furnished a two-man team to

give on-site technical assistance for a one-week period at the beginning

of the project.

In order to fuse the coating on the larger parts, AMSAA requested that

the Metal Surfaces Department (OCCS) build a large oven. This oven (Figure 1) was approximately 4-feet square with an inner wall of 16-

gauge steel and an outer wall of 1/8-inch steel. It is insulated between the walls with 2 inches of fiberglass, and is heated with four

electric stove elements. The elements are connected in pairs and each

pair is thermostatically controlled with a separate set of oven controls

taken from a household stove. It achieves a temperature of 500°F

within ten minutes and maintains the desired setting within 5°F.

A training shop area in the Mobility Department was chosen to set up

the coating facility. A compressed air supply (100 psi) was available

in the shop, and the Facilities Engineering Directorate at Aberdeen

Proving Ground installed two 30-ampere electrical outlets to power the

large oven. The NADC oven was wired directly into the circuit breaker

panel

.

DESCRIPTION OF THE COATING PROCEDURE

Initial Marking of Parts

The parts to be coated were removed from the vehicles and marked so they

could be returned to the vehicle from which they were taken. This is

particularly important when parts are being collected concurrently from

a number of vehicles belonging to different local units. It avoids

confusion (and arguments) later if all parts are marked at the time of

279
Figure 1. Large oven built at Aberdeen Proving Ground.

pickup. Metal dog tags are ideal for this purpose. They can be stamped

with the vehicle number and then wired to the part. At the conclusion

of the coating process, the tag will still be legible and can be used

to assure that each part gets reinstalled on the proper vehicle.

Sandblasting

The parts were sandblasted to remove all paint, grease, dirt, etc. To

sandblast a large number of parts in a relatively short time (particularly large parts such as battery boxes and frames), required the use

of machine shop, heavy-duty sandblasting facilities.

Various types of sandblasting machines were used, including Hydro-Finish

(Vapor Hone), tumble blasters, rotary blasters and hand-held hose type

blasters.

Degreasing

After sandblasting, the parts were degreased to remove the blasting

residue and any dirt that accumulated because of handling. Small parts,

such as fuel sleeves, sleeve frames, and battery holddown rods, were

280
degreased in an approved, portable solvent tank, using xylene (or equivalent) as the solvent, with a final wash in a tank of denatured alcohol.

Adequate ventilation must be provided when using these solvents.

To degrease large parts such as battery boxes or frames in a portable

tank is not practical. To do this job efficiently requires a vapor

degreaser. The solvent used i-n this type of degreaser is trichloroethylene heated to 250° F. The parts are put into a metal basket and lowered

into the solvent fumes for a few minutes. When removed from the basket,

the parts dry almost instantly and are completely free of grease and

dirt.

After degreasing, parts should be handled with cotton work gloves

throughout the rest of the coating process to avoid contamination of

the metal surface.

Priming

Before coating, the parts were primed with a zinc phosphate primer. As

mentioned earlier, the primer improves the adherence of the coating and

provides additional protection for the metal in case the coating is

broken. The primer was applied with a special apparatus consisting of

a small CO2 gas can, a primer bottle, and a trigger- type spray head.

When the gas can was exhausted, it was easily replaced with a new can. Figure 2 shows the primer being applied to a fuel sleeve. Care must

be exercised to avoid putting on too much primer. The optimum is a 0.3 mil thick coat, with no runs or sags. It is also important to

allow primed parts to dry completely (5-10 minutes at 72° F) before

applying polymer powder.

Coating (Electrostatic Method)

For coating, the parts must be electrically grounded. This was accom- plished by suspending them with wire from a metal rod in the powder

booth. The rod was grounded to the coating control console, and the

entire inside of the booth was metal -lined and grounded to an earth

ground. The nylon powder is positively charged as it leaves the spray

gun, and is attracted to the grounded part. The thickness of the

powder coating can be varied from 2-7 mils, and is a function of the

potential difference between the part and the powder particles. Generally, best results are obtained with a 4-5 mil thick coating. This

can be achieved consistently with proper adjustment of the control

console and an experienced operator.

The booth has a 12-inch circular fan in the lower part of the rear wall

that draws air through the front of the booth. This air flow pulls the

powder into the booth and keeps it from collecting on the operator's

hands and arms. The fan also pulls the oversprayed powder down through

281
Figure 2. Priming a fuel sleeve.

a funnel-shaped opening in the bottom of the booth, where it is collected and reused. A filter inside the booth prevents powder from being

exhausted into the work area. This arrangement insures almost no loss of powder, which is one of the advantages of the powder coating

technique. Figure 3 shows the nylon powder being sprayed on a 5-ton

truck battery box.

The flow of powder and the charge on the particles is controlled by the

control console. The unit used was the INTERRAD/GEMA Model 710 and con- sists of a powder hopper, a control module, a lightweight manual spray

gun, and the necessary hoses and cables. The control module output is

12 volts AC or less, since the high-voltage power supply is built-in

to the spray gun; therefore, there is no high voltage cable from the

module to the gun. Four electrodes charge the powder particles inside

the gun barrel from 0-70 KV (variable). The control module has controls

for high voltage, compressed air, and powder flow rate. The spray gun

operates at 80-100 psi (3-5 cfm), and is equipped with an adjustable

automatic safety shutoff to limit output current. The powder spray

pattern can be easily adjusted, while spraying, by changing the position

of the deflector extending from the gun nozzle.

282
Figure 3. Applying nylon powder to a truck battery box.

The parts being powdered must be solidly grounded so that the powder

will adhere properly. To accomplish this, the metal rod in the booth

and all connections between it and the parts are blown clean with a low pressure air hose before beginning to spray the powder. Once the

parts have been coated, they must not be touched or the powder will come off. If this does occur accidentally, the part should be returned

to the booth and the marred area repowdered.

Fusion of the Coating

After coating, the parts were suspended in an oven at a temperature of

425°F for approximately fifteen minutes. This fusion time will vary depending on the thickness (mass) of the part (thicker parts require a longer time to achieve fusion temperature). When the powdered surface

of the part appears shiny and wet, it is ready to be removed from the

oven and allowed to cool. It is important not to leave parts in the

oven too long or cure them at too high a temperature, because excessive

heat will cause the coating to begin to run off. Also, care must be

exercised when heating fuel sleeves, since excessive heat will cause

the solder around the filter screen to melt and drip out.

283
Care must be exercised when removing heated parts from the oven. Small

parts can easily be handled with pliers. The 5-ton truck battery boxes,

however, weigh 28 pounds, and are much too heavy and unwieldy to handle

with pliers. For this reason, two special tools were fabricated to move

the boxes from the powder booth to the oven and to remove them from the

oven. The battery box is suspended by its handles from a T-hook, and a forked rod engages the vertical section of the hook to lift the box.

IDENTIFICATION OF THE COATED PARTS

Table 2 shows the types of parts coated and the number of each. In general, the battery boxes, battery box frames, battery holddown frames,

battery trays, battery brackets, and transmission stands were heat-cured

in the large oven because of their size. The fuel sleeves and sleeve

frames, chains and slides, and the smaller battery frames and holddowns were processed in the NADC oven.

Table 2. Summary of Parts Coated

Item Quantity

Battery Box 133

Battery Box Frame 16

Battery Hold-Down Bolt 736

Battery Hold-Down Frame 280

Battery Tray 55

Battery Bracket 11

Battery Brace 11

Fuel Sleeve 179

Fuel Sleeve Frame 48

Chain and Slide 32

Transmission Stand 6

TOTAL 1507

284
Table 3 indicates the number of coated parts from each vehicle. The

ratio between battery bolts and frames is not consistent because some

of the frames had missing bolts. This created some confusion when the

finished parts were being returned to the local units, and serves to

emphasize the fact that all parts must be positively marked when removed

from the vehicles.

Figure 4 shows a variety of finished parts. Figure 5 is a severly cor- roded battery tray and a new tray from an M151A2 vehicle. Figure 6

shows a coated and uncoated 5-ton truck battery box. The damaged

parts in these two photographs dramatically illustrate the effects of

battery acid corrosion. Many deteriorated parts similar to these

were coated during this project, to minimize further corrosion damage.

To powder coat the parts described in this paper the materials shown in

Table 4 were required.

Table 4. Bulk Supplies Used

Item Quantity

Nylon 11 Powder, Dark Green 5151 100 lbs

Functional Grade, Type RDP-15

Rilsan Corporation

Glen Rock, New Jersey

RILPRIM Primer, Type 104A & 104B 5 gals

Rilsan Corporation (each type)

Glen Rock, New Jersey

Methyl Ethyl Ketone (MEK) 2 gals

Xylene 55 gals

Alcohol, Denatured 20 gals

REQUIREMENTS FOR A LARGE-SCALE COATING FACILITY

A large-scale powder coating operation can be conducted in any suitable,

indoor area where sufficient electrical capacity, a compressed air supply and adequate ventilation are available.

The sandblasting and vapor degreasing facilities are absolutely essential in order to coat many, large parts in a relatively short time.

These parts, particularly 5-ton battery boxes and battery box frames

require the use of heavy-duty sandblasting equipment, and they cannot

be degreased conveniently without a vapor degreaser. This type of

285
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O rH

286
Figure 4. Typical coated parts.
Figure 6. A coated and an uncoated truck battery box.

equipment is normally found in large machine shops or foundries. Any

local military unit desiring to use the powder coating technique should

make sure that such facilities are available very early in the project.

The other critical item is an oven large enough to accommodate whatever

parts are being coated, and capable of achieving a temperature of

450°F. There are, however, numerous ovens commercially available for

rent, so the problem of oven availability is probably easier to solve

than the problem of locating sandblasting and degreasing facilities.

ADDITIONAL COATING EFFORTS

In order to obtain additional field data on the rust and corrosion re- sistance of Nylon 11 coating in a salt water atmosphere, AMSAA assisted

the 2d Marine Division/Force Troops/Marine Corps Base, Camp LeJeune,

North Carolina in setting up a large-scale facility for coating vehicle

components, similar to the program described in this paper. The AMSAAOCCS coating team provided technical advice, equipment, and supplies to

help them convert their current coating facility to a large-scale operation. This project was completed in June 1978.

288
SUMMARY

The feasibility of the use of Nylon 11 powder coating as a rust and

corrosion preventative has been demonstrated in the laboratory and in numerous industrial applications. The AMSAA-OCCS powder coating project

will provide the Army with field data on the value of this coating for

tactical vehicle components under a variety of environmental and use conditions.

A test performed by the Army Chemical Systems Laboratory in 1978 showed

that Nylon 11 coating resists toxic agent sorption far better than the

alkyd enamel currently used on Army vehicles. The nylon coating does

not resisttoxic agents as well as polyurethane paint, however. Of

course, the spray application of any urethane coating requires that

strict safety procedures be observed. For this reason, polyurethane

paint has not been approved for use by tactical field units as yet.

If the long-term wear characteristics of this coating prove acceptable,

we would recommend the Army-wide use of such a coating for selected ve- hicle parts. The most cost effective and practical way to implement an Army-wide program would be to coat the parts at the time of manufacture,

rather than later. If parts were coated when new, it would avoid the

expense of sandblasting and degreasing. This, coupled with the savings

realized by eliminating the final finishing process, would make Nylon

II powder coating competitive with current methods of protecting metal

surfaces.

289
ALTERNATIVE ANTISTATIC PACKAGING MATERIALS FOR PRECISION BEARINGS

Marianne K. Bemett and Harold Ravner

Naval Research Laboratory

Washington, DC 20375

Abstract: Precision instrument bearings currently are packaged in

polyetheylene or nylon films containing minor amounts of antistatic

agents. A previous NRL study shewed that the presently used surfaceseeking antistatic agents adversely affect the contacting bearing raetal

surface and/or bearing lubricant. To ameliorate these problems, the

following alternatives were investigated: 1) chemically characterized

antistatic agents either incoiporated into or topically applied to the

polymer films; 2) alternate packaging materials. Effects of ejroosure

of these alternatives to pure lubricants, lubricated steel surfaces,

and clean steel surfaces were examined. The results provided information on possibly deleterious transfer of the antistatic agent to any

contacting surface affecting lubricant properties and surface

wettability.

Key words: Antistatic agents; precision instrument bearings; bearing

packaging materials; antistat-lubricant interaction; antistat-bearing

steel interaction; lubricant displacement; bearing steel wettability.

To minimize exposure to atmosphere-borne particulate contamination

during transport or storage, precision instrument bearings are often

packaged in ultraclean polymer (nylon or polyethylene) containers.

Since electrostatic charges tend to accumulate during normal handling,

polymeric films are now conmercially available with incorporated antistatic agents (antistats) . However, these currently losed long chain,

surface-seeking surfactants (1) in contact with lubricated miniature

bearings can migrate from the polymer surface to the lubricant and

ultimately to the bearing surface (2), adversely affecting the

operational characteristics of the bearings, particularly with regard

to torque changes and wear due to lack of lubricant.

The present investigation examines the interactions of several alternate

chemically characterized species of antistats as well as a multilaminate antistat-containing polymer film with instrument lubricants

and bearing metal surfaces. All materials used, their chemical

identities, and convenient abbreviated codes are listed in Table I.

29(1)
Table 1

Coirponent

Lubricant

Lubricant

Lubricant

Antistatic Agent

(Internal)

Antistatic Agent

(Internal)

Antistatic Agent

(Internal)

Antistatic Agent

(Topical)

Polymer

Polymer

Polymer

Antistatic System Conponents

Identification

Synthetic Hydrocarbon,

base stock

Synthetic Hydrocarbon,

formulated

PolyolesterHDiester

,

formulated

Polyethylene glycol monolaurate

Laurie diethanol amide

N-N-bis (2-hydroxyethyl)

alkyl amine

AHq'I 4 arannonium chloride

Polyethylene

Nylon

Multilaminate

Code

SHC-B

SHC-F

m-20

PEG

LDA

BHA

AAC

PE

NY

ML

Depending on their molecular function, antistatic agents may be either

incorporated into polymer packaging as internal additives, or applied

topically. In this study PEG, LDA and BHA were investigated as incorporated polymer components (5% by weic^t) and AAC (0.26% by weight)

as a topical coating (3) , vdiich was painted onto the surfaces of either

PE or NY films and air-dried. Vfe also examined a ooitmercial staticshielding bag (4) , fashioned from a multilaminate sheet consisting of

three electrically distinct layers: a conductive nickel outer layer

(40% light transmission) , a polyester central layer, and an inner layer

of PE containing the antistat (5) identified as PEG (6)

.

The specific interactions studied included: 1) migration of the agent

into the lubricant and its subsequent solution; 2) chemical or physical

change of the lubricant; 3) displacement of the lubricant from the

bearing surface by the agent; and 4) adsorption of the agent on the

bearing surface preventing respreading or rewetting by the liibricant.

All pure antistatic agents deposited as drops on the surface of thin

films of the lubricants surface-chemically displaced (7) the latter

from steel substrates. Regardless of the specific interactions involved.
a universal effect on the substrate was the appearance of a "dry" area

adjacent to or surrounded by retracted liquid. The failure of the

displaced liquid to respread over it, as well as the nonspreading of a

freshly placed drop of the pure lubricant, attested to the intractable

nonwettability of the "dry" surface. Effects of the antistats on the

lubricants ranged fron soltibility of the antistat in the lubricant with

concomitant change in the properties of the latter, to complete

immiscibility

.

Minor amounts of the antistats incorporated into, or topically applied

to the polymer material had various effects on lubricant and substrate

during extended contact with the lubricated steel surface. After

removal of the antistat-containing polymer, cotposition of the

lubricants remaining on the steel si±>strates were determined by FTIR.

Each FTIR spectrum was compared with those of the respective pure

lubricant and pure antistat: as an exairple, subtraction of the spectrum

of pure SHC-B (Figure lb) from that of the liquid remaining on the

surface after SHC-B had been in contact with PE + PEG (Figure la)

resulted in the spectrum in Figure Ic, v^ose prcxninent features

corresponded to those of PEG (Figure Id) . This established transfer

of the additive into the lubricant. Hovever, under adsorption/

desorption equilibrium conditions, the low concentration of PEG in the

lubricants was insufficient to displace the lubricants from the steel

surface. Other antistats, such as BHA, not only thickened the lubricant,

but were sufficiently surface-active to migrate through it, strongly

adsorb onto the substrate, and displace the liquid.

Extended contact of antistat-containing polymer with the unlubricated

steel surface resulted in antistat transfer to the surface, as observed

visually after separation of surface and polymer film. To ascertain

v^ether the affected steel surfaces were wettable by either lubricant

or antistat, contact angles (0) of each liquid were measured on the

"dry" portion of the surfaces. The most wettable surface was from

contact with ML, the low 9 being evidence that the surface was

virtually free of organic adsorbants.

The various displacement mechanisms showed that lubricant-insoli±>le

antistats are not suitable if they either strongly adsorb on the solid

substrate to form an oleophobic film or chemically interact with the

lubricant. Topically applied agents, especially those v^ose chemical

structure contain corrosive or hydrolysis-pronoting ions, appear to be

unsuitable for long-term protection of delicate instrument bearings.

Of the antistat polymer combinations studied, ML had the least deleterious effects on steel substrates and/or lubricants. Although, after

prolonged contact, traces of the agent were detected in the lubricant

by FTIR analysis, no adverse reactions, i.e., nonwettability of substrate

or physical changes of lubricant, was observed. The problems of static

build-up, its dissipation, and the precautions necessary with antistatic plastic use have been widely discussed (8,9). Multilayer

292
laminated containers, as exenplified by ML, may overcome many of these

problems (5) . However, two general problems remain v^ich this study

has not addressed: 1) the tendency of packaging material (with or without antistatic additives) to slough off in contact with solid surfaces

(9) causing major problems in critical applications, e.g., instrument

bearings, etc. and 2) the long-term effects of the antistats on such

important lubricant properties as stability, deposit formation, and

antiwear activity.

4000 3600 3200 2800 2400 2000 1600 1200 800 400 WAVENUMBERS

4000 3600 3200 2800 2400 2000 1600 1200 800 400 WAVENUMBERS

Figure 1; Antistatic Agent Transfer from Antistat-Containing Polymer

Film to Li±>ricant After 5 Months Contact as Monitored by FTIR Spectra.

a) Liquid Remaining on Substrate After Contact of SHC-B with PE + PEG;

b) Pure SHC-B; c) Component Remaining After Subtraction of Fig. lb fron

Fig. la; d) Pure PEG

293
References

1. Johnson, K. , Antistatic Corrpositions for Textiles and Plastics , Noyes Data Corp., Park Ridge, N.J. (1976) pp. 236-267.

2. Kinzig, B.J. and Ravner, H. , "Probleins Encomtered with Antistatic

Packaging for Miniature Bearings", LiiDric. Eng. 36, (4) pp. 219-

225 (1980). —

3. Halperin, S.A. , "Static Control Using Topical Antistatics",

presented at Electrical Overstress/Electrostatic Discharge

Synposium, Denver, Colorado (1979)

.

4. Yenni, D.M. and Himtsman, J.R. , "The Deficiencies in Military

Specification MIL-B-81705: Considerations and a Sinnple Model for

Static Protection", presented at Electrical Overstress/Electrostatic Discharge Synposium, Denver, Colorado (1979).

5. Huntsman, J.R. and Yenni, D.M. , "Coping with Static Electricity.

Part VII: A New Technology in Transparent Static Protective Bags",

Evaluation Eng. 17, (4) p. 48 (1978).

6. Baker, T.E. and Recesso, J., "Review of Antistatic Packaging

Materials", presented at the Fifth Inertial Guidance Conmunity

Containination Control Seminar, El Segundo, CA (1979) .

7. Bemett, M.K. and Zisman, W.A. , "Surface Chemical Displacement of

Organic Liquids from Solid Surfaces", J. Phys. Chem. 70 , pp. 1064-1075 (1966).

8. Anderson, D.C., "Electrostatic Damage Prevention: An Overall View",

presented to Amer. Def. Prep. Assoc. (November 1978)

.

9. Woods, W.R. , "Precautions to be Considered in Using Antistatic

Plastics", JPL, NASA NAS7-100 (1975).

294
A THERMAL PREDICTION TECHNIQUE FOR

EXTENDING IN-SERVICE LIFE OF ROLLER

BEARING ASSEMBLIES

B. R. Reason

Cranfield Institute of Technology

Cranfield, Bedford MK43 OAL, England

V. A. Schwarz

Escola Federal de Engenharia de Itajuba

Itajuba, M.G., Brazil

Abstract: A programme is described involving the measurement of spacial

temperatures in a rolling contact bearing assembly. A technique of

thermal analysis, amenable to computer programming, is presented and

the results from this compared with the experimental findings. The

paper concludes with a discussion on the temperature correlation obtained and the thermal factors influencing premature bearing failure.

Key words: Bearing failure; bearing reliability; condition monitoring;

roller bearings; thermal analysis.

I. INTRODUCTION

Premature failure of rolling contact bearings arising from temperature

effects is a common phenomenon. In a given design situation when

parameters such as applied load, operating speed, lubricant characteristics and bearing and housing geometries are specified it is obviously of great importance if the designer is in a position to predict

the spacial temperature distribution at specific points within the

unit. Furthermore, for units which are already in service the ability

to predict local operating temperatures gives the bearing user an assessment both of the likelihood of thermal failure hazard and the

capability, from the thermal standpoint, of anticipating the ramifications arising from any planned increase of duty specification.

Previous attempts at a tractable solution of the theoretical problem

had been gravely hampered by an inadequate knowledge of the spacial

division of the generated heat between the component parts of the

bearing assembly, together with the heat 'take-up' of the lubricant

itself. Additionally, though to a lesser degree of importance, a paucity of information on the choice of suitable heat-transfer coefficients existed.

295
To circumvent these problems and to provide a firm foundation for an analytical approach it was decided to build a fully instrumented test

rig to provide an experimental yardstick against which the veracity of

any theoretical approach might to tested and a viable programme ultimately produced.

In the field of condition monitoring, should a programme exist from

which temperatures can be predicted at specific points from one single

temperature measurement (such as oil bath temperature) then the

question of premature thermal failure could clearly, be greatly mitigated. In short, the direct result of employing such a system would be

better overall bearing reliability and an extended service life.

It is the aim of the present paper to present such a system from both

the practical and theoretical standpoints and to invoke the user/

designer's confidence by demonstrating the degree of correlation which

has been obtained between the two.

2. EXPERIMENTAL STUDY

2.1 Object

The experimental work herein described was carried out on a specially

instrumented rolling contact bearing test rig which gave the following

measurement capabilities.

(a) Bearing load (radial and axial).

(b) Test shaft rotational speed.

(c) Bearing friction power losses.

(d) Spacial temperature distributions within bearing components,

shaft, housings and at specific points in the bedplate/foundations.

2.2 Rolling Contact Bearing Test Rig

The test rig configuation consists essentially of a drive test shaft

which may, optionally, carry three or four rolling contact roller

bearings of various types, mounted in selected housing configurations.

Fig. 1 shows the general arrangement and indicates two typical bearing

options on the central section.

Power is supplied to the rig from a 3H.P., 50 cycle three-phase

electric motor via a hydraulic variator unit. This allowed stepless

speed variation from 0 to 1400 r.p.m. at the variator output shaft.

Intermediate between the test module and variator, a slave pillow block

unit carries a flexible coupling at its input drive to the test shaft

and a pulley and flat belt drive at its other end to a second pulley

at the variator output. This system allows a speed step-up to a

296
maximum of 5600 r.p.m. at the test shaft and circumvents the problem

of belt drive forces acting on the test bearings.

To eliminate transmitted bedplate vibrations the test module and drive

system are separately mounted on mild steel, surface-ground gauge

plates of 40mm thickness, these being grouted and bolted to a large

concrete foundation block. The system has been found in other test rig

designs to provide maximum drive energy dissipation, thus minimising

extraneous vibration effects on the test module proper. The foundation block itself is mounted on rubber pressure mats to dampen ground

vibration from outside sources.

2.3 Test Rig Evolution

The test module evolved in three distinct stages concomitant with

testing requirements.

Stage 1 is delineated in fig. 1 as the area above the shaft centre line.

Two identical taper-roller bearings, mounted back-to-back on the test

shaft, are contained within a cylindrical sleeve. The latter rests on

a hydrostatic bearing (9)*, which applies radial load to the system.

Reaction to the applied load is provided by two identical plain roller

bearings, the forward one being mounted in a conventional mount (3)

whilst the rear bearing is carried in an inverted hydrostatic system

(5). The loading block of this (4) carries a circumferential pool,

a constant film thickness being maintained between it and the bearing

mounting ring by the external oil pressure to the system. The test

module is symmetrical about the centre-line of the hydrostatic system

(9).

Stage 2 (the area below the shaft centre-line in Fig 1) shows the

taper-roller bearing arrangement replaced by a single double-row

spherical roller bearing. Aluminum cooling fins (8) were also shrinkfitted to the test shaft at this stage to investigate free and forcedconvection cooling modes.

Stage 3 saw the original plain roller bearings (2) of stage 1 replaced

by two identical spherical roller bearings, mounted in the original

housings and fitted to the shaft by special adaptor sleeves.

3. TEST RIG INSTRUMENTATION

The primary objective of the experimental testing was to monitor

parameters of bearing friction torque and spacial temperature distribution throughout the bearing test module for a wide spectrum of

*Numbers in this Section refer to Fig. 1.

297
speed, load and lubricant viscosity combinations. This was achieved via

the following systems:

3.1 Speed System

Input speed to the test shaft is monitored by an inductive proximity

transducer triggered by a sixty-tooth wheel integral with the test

shaft. The transducer output signal is initially amplified and then

fed to a calibrated meter giving an analogue display reading directly

in r.p.m. The meter can be switched to a spectrum of speed ranges in

additon to 'monitor mode' function, indicating the percentage error drift with time from any initially selected speed. Warning-light

indicators are activated if a required speed tolerance is exceeded.

3.2 Bearing Torque System

As already described, hydrostatic lifts operate at (5) and (9) metalto metal contact being therefore avoided. Thus operating torques within the bearing systems mounted at these points would be transmitted to

the outer mounting ring at (5) and the bearing sleeve at (9). These

torques may be monitored at both points by employing twin radial tubes

extending from the ring/sleeve to load-cells (7), thereby producing a push-pull reactive system to the applied torques.

The load-cells are high-sensitivity units designed, developed and con- structed within the laboratory. They consist, in essence of a cruciform member of Beryllium Copper carrying a "Wheatstone" strain-gauge

bridge, the assembly being mounted in a brass housing, threaded to

allow vertical adjustment.

Output from the cells is amplified by high-stability D.C. differential

amplifiers before being tansmitted to the recording system. The cells were specifically calibrated for both torque measuring systems. Temperature variations were accounted for during calibration.

3.3 Bearing Loads

(a) Radial Loading

Infintely variable radial loading is applied to the bearing system by means of the hydrostatic oil lift located at (9). The lift is a fourpocket system applying its load directly to the bearings mounted in

the central cylindrical sleeve.

The applied load is reacted by the fixed front bearing-housing (3)

bolted to the bedplate and, after being transmitted through the inverted hydrostatic system (5), is again reacted out via the twin

loading pillars (6). A D.C. activated "Wheatstone" bridge of strain

298
gauges mounted on each pillar measures the radial load on the rear bearing. The pillars were separately calibrated in a "Denison"

tensile-test machine before final assembly in the test rig. Thus

radial loads can be continuously monitored throughout the test.

(b) Axial Loading

Axial preload is applied to the twin taper roller bearing system via

a finely threaded nut on the test shaft, the load being measured by a proving ring mounted in-situ with the assembly. The ring carries a "Wheatstone" bridge of strain gauges and was separately calibrated

before final mounting. Since the inner ring of the outmost bearing

is an interference fit with the test shaft, pressurised oil injection

is employed to eliminate friction between these componenets when

applying axial loading.

3.4 Temperature Measurement

For purposes of assessing the spacial temperature distribution throughout the bearing unit and its housing an array of Chromel/Constantan

thermocouples is used each couple being located at a specific modal

point (see Fig. 2).

High hardness bearing surfaces were drilled by spark-machining for

thermocouple placement.

Thermocouple and transducer output signals are transmitted to a 'Fluke' 2200B' sixty-channel data- logger for capture and signal con- ditioning. The makers specified an accuracy of ± 0.1 °C between

0-100°C. This was confirmed on laboratory calibration.

In programming the instrument a total of fifty channels was assigned

for temperature recording, the remaining ten receiving pre-ampl ified

signals from the load and torque transducers; solid state D.C. differential amplifier being utilised for this purpose. Thermal drift

on these units is< ±2yv/°C.

Thermocouples for non-rotating nodal points are connected directly

to the data logger. Rotating component signals are passed through

high-quality silver/silver-graphite slip rings, the rings being aircooled to negate thermal drift. Maximum peak-to-peak noise on these

units is < 20yA/mA at 10,000 r.p.m. Since output signals are in the

micro-amp range, slip ring noise was not a problem.

To circumvent resistivity errors at junctions, gold-plated contacts were employed throughout the system. 'Seebeck' effects were alleviated

by mounting rotating junctions on a junction disc integral with the

shaft and rotating in ambient air. Temperature calibrations were made

299
to negate spurious temperature effects at metal connection points.

In studying the thermal equilibrium situation within the test module

particular attention was directed to interfacial heat transfer, thermocouples being concentrated at specific points at either side of the

interfaces (See Fig 2).

Cage temperature capture is effected by the use of trailing thermocouples on the rotating cage. All thermocouples were manufactured in

the laboratory from 0.005 ins wire, junctions being formed by electrical

arc welding.

Chromel/Constantan was used in preference to Copper/Constantan since

certain additives in mineral oil had been found to react with copper over extended periods of time. Since it was envisaged that long term

testing would be carried out on the rig the precaution was considered

necessary to avoid long-term drift effects.

The data logger was programmable for various thermocouple combinations

and included an electric cold junction. Cyclic nodal scanning was a further feature of the unit.

4. TEST LUBRICANTS, ROLLER BEARINGS AND COOLING FINS.

4.1 Lubricants

Mineral oil is used as the lubricant in the vast majority of bath lubricated rolling-contact bearing situations. SAE 20W, 30 and 50 oils, were selected to produce a reasonably wide range of viscosities during

the tests.

Viscosity- temperature measurements were carried out on the lubricants

to establish data for the theoretical part of the programme. A high

accuracy "Tamson" viscometer bath carrying certified reference tubes was employed.

4.2 Bearings

The basic bearing used in the test reported herein is a plain Cylindrical Roller bearing, type MRJ. 1-3/4.

Bearing dimensions are as follows:

Bore 44.45 mm (1.750 ins). Outer Diameter 107.95 mm (4.250 ins). Radial

Clearance 0.0127 mm (0.0005 ins). Width 26.9875 mm (1.0625 ins). The

flange configuration is as shown in Fig 2, the cage, of machined brass,

riding on the inner ring.

300
4.3 Cooling Fins

To study free and forced convection modes aluminum fins were employed

during later testing. These were shrink-fitted to the shaft to

encourage effective heat transfer at the joint interface.

5. TESTING PROCEDURE.

5.1 General Testing

Progressive "running-in" of the bearing was achieved through a gradually increasing duty cycle of speed and load. Thermal equilibrium

generally manifested itself after some five hours of running.

Loads were initially fixed, the speed being varied in steps of 500

r.p.m. from 500 to 5000 r.p.m. Speed increments generally took

approximately one hour to stabilise after initial "warm-up" running of

the rig.

5.2 Specific Testing (with Convective Shaft Cooling)

To study in some detail the influence of heat transfer directly from

the surface of the test shaft, cooling fins as outlined under 4.3 were

employed:

(a) Fins With Air Jet: Compressed air was blown tangentially onto

the rotating fins in the direction of the rotation, readings of

temperature and torque being taken on attaining thermal stability.

Bearing duty was the same as in the initial part of the programme.

(b) Fins Without Air Jet: As (a) but without employing compressed

air impingement.

6. RESULTS

6.1 Experimental and Theoretical Correlation

Fig. 2 shows typically measured temperatures for the front bearing

unit. Predicted theoretical values given by the computer programme

at relevant nodal points are included to indicate the correlation with

the experimental results. The degree of agreement is noteworthy.

6.2 Effect of speed on Torque and Nodal Temperatures

Fig. 3 indicates, as a typical case, the general trend of torque and

nodal temperatures with varying speed. The particular example is

taken at a constant radial load of 2000 N using an SAE 30 oil.

301
6.3 Effect of Forced Air Convection

Fig. 4 illustrates directly results obtained with and without air

jet cooling. Both temperature and flow rate of the jet air stream

could be measured. The particular example is for an ambient air

stream of 586 1/min continuously applied. The radial load was 8 KN

the lubricant being an SAE 30 oil.

A general discussion of all the results obtained appears in the

Section (9) "Discussion of Results".

6.4 'Heat Generation' and 'Heat Dissipation'

Fig. 5 shows both 'Heat Generation' and 'Heat Dissipation' curves plotted against temperature for two mineral oils, an SAE 50 and an SAE 30. Torque is also plotted on the ordinate.

The 'Heat Generation' curves might, on initial inspection, appear

contradictory in that as the heat generation falls, the temperature

increases. In the context of their interpretation a temporal element

should be envisaged. At the initial stage of a test the temperature

is low and the corresponding oil viscosity therefore high. As testing

proceeds the temperature increases, decreasing the oil viscosity and

consequently the heat generated.

7. THEORETICAL PREDICTION OF SPACIAL TEMPERATURES AND HEAT GENERATION

7.1 Modes of Heat Transfer Employed

In studying the thermal equilibrium of the bearing assembly and its

surroundings the three basic modes of heat- transfer were employed,

namely conduction, convection and radiation. These may be separately

considered as follows:

(I) Conduction

(a) Solid

For radial conduction within the bearing rings and shaft the modified

standard Fourier expression was employed viz:

27rk W(^i""^o)

(1) 1-0

302
This expression was modified by Wong (1)* as follows for conduction

from the inner circular surface of the bearing housing to its horizontal

and vertical planar surfaces viz:

Log( J

The thermal conductivity 'k' used in the above expression is a function

both of the material and its temperature level. The latter variation is

of second-order importance and was therefore neglected.

(b) Interfacial (Thermal Contact Resistance)

Conduction through a joint or surface interface in intimate contact is

inhibited both by the limited area of the true contact and surface

contamination at the interface.

These, in combination, act as a thermal resistance to heat transmission.

The heat transfer may be expressed as

:

Qs

= H^A (gti-^ta) (3)

where 'H ' is known as the "Thermal Contact Conductance" (the inverse

of the Thermal Resistance).

In bearing assemblies thermal contact resistance is manifest at the

following surfaces:

(a) Shaft/Inner Ring

(b) Outer Ring/Housing

(c) Housing/Machine Base

The subject is treated in some depth in the following references:

(2), (3), (4)

(II) Convection

Newton's law of cooling describes convective heat flow: viz:

'h ' the "heat transfer coefficient," sometimes called the "film coefficient", is a complex function dependent on the geometry and temperature

of the heated surfaces and the temperature flow characteristics and

physical properties (viscosity, thermal conductivity and density) of

the convecting fluid.

*Numbers in the text from this point refer to references.

303
Few analytical expressions exist for the heat transfer coefficients,

empirical equations, obtained by combining experimental results with

dimensional analysis, being employed. Thus the coefficients often

appear as relationships between dimensionless number groups such as Nusselt (N ), Reynolds (R ), Grashof (G ) and Prandtl (P ) depending

on whether free or forced convection pertains. For free convection

= f (G^,P^) and for forced

In the present analysis the following expressions for 'h ', given by

Fujii and Imura (5) and simplified by the authors, were employed.

For horizontal plates and cylinders facing upward:

h = 1-398

c

and for similar vertical situations

(5)

h^ = 1-452

c

t -t.

S <x (6)

No completely reliable expressions for heat transfer coefficients

between bearing components and lubricant could be found by the authors,

although expressions are given by Bjordlund and Kays (6) and Gazley

(7) pertaining to concentric cylinders. The existence of the rollers

and cage between the bearing rings, however, tends to negate any

analogy.

An expression used by Harris pertaining to heat flow across a flat

plate, although of limited accuracy, was finally used in the present

analysis, viz:

h^ = 0.332 ^Rg^ P^ (7)

Characteristic terms in the previous equation were obtained as suggested by Harris (8).

The following expressions for additional heat transfer coefficients

were employed additionally in the present analysis.

(a) For a rotating cylinder in air (after Dropkin and Carmi (9))

h D = M = r R 0.7

k % (8)

304
= 0-076 for 8000 <Re <15000

= 0-073 for Re >15000

(b) For a rotating disc in air (after Oehlbeck and Erian (10))

where the coefficient 'C. * is mainly dependent on the geometry of the

system.

(Ill) Radiation

Heat transfer by radiation between a small enclosed structure and a large surface may be expressed by a modified form of the Stefan/

Bol tzmann law viz

Values of the emmissivity 'e' between 0-6 and 0-8 are given by Jakob

and Hawkins (11 )

7.2 Heat Generation

Generated heat in rolling contact bearings is dependent on several

factors. Chiefly, these are rotational speed and lubricant viscosity

and to a lesser extent, applied load and bearing geometry. Loading

effects, however, become much more important if the bearings are preloaded.

Specificaly, the heat generated is a function of the bearing speed and

torque. The latter however may be considered as the summation of the

viscous friction torque and the load dependent torque MiThe following empirical equations were produced by Palmgren (12) for

these torques, ie

(9)

Q = aeAi(Ti^-T2^) (10)

K = f« {^r)r^ X 10

0 0 m

-1

N.m. (11)

fi.F^. X Dm

N.m. (12)

305
7.3 Distribution of Generated Heat

Based on results produced by Garnell (13), Astridge and Smith (14)

and work of the authors, the following distribution of generated heat was incorporated into the present programme.

(a) Roller Contacts at the Outer Raceway 30-40%

(b) Roller Contacts at the Inner Raceway 30-40%

(c) Roller Contacts in the Cage Pockets 8-12%

(d) Cage Contacts at the Land Riding Ring 8-12%

(e) Viscous Churning of Lubricant 8-12%

(f) Roller Guide Flange Contacts 0»l-0-8%

7.4 Temperature Prediction Technique

The so called "Heat Balance Method" was employed as the foundation to

the programme. The method which is used where spacial temperature

distributions are required in structures, is given in several textbooks on advanced heat transfer, a good description being that given by

Welty (15).

Basically the method involves the thermal equilibrium between a given

point or 'node' and its surrounding nodes and is achieved by equating

the total heat influx and efflux to and from the node (including any

thermal energy generated at the mode).

An initial step involves the spacial selection of nodes throughout

the structure, the accuracy of the analysis being dependent on both

the number of nodes and their position. Fig 2 shows the nodes selected

in the front bearing assembly together with the measured and predicted nodal temperatures under the particular conditions of the test.

As a second step the "Heat Balance Method" is applied to each node, all

modes of heat transfer being considered. For a bearing assembly these

may be typically delineated as follows:

(a) Convective heat transfer from outer surface of the housing to the

environment.

(b) Radiation of heat from the outer housing surface to the surroundings.

(c) Conductive heat transfer from the housing base to the foundations.

(d) Conductive heat transfer from the bearing outer ring to the housing.

(e) Conductive heat transfer from the bearing inner ring to the shaft.

(f) Axial heat transfer by conduction along the shaft including

extraneous heat inputs outside the bearing system proper.

(g) Convective heat transfer from the rotating shaft/fins to a sur- rounding fluid.

306
(h) Convective heat transfer from the bearing components to sur- rounding fluid/fluids inside the housing.

(i) Heat generation produced between surfaces in relative motion ie

roller contacts with bearing raceways, ring shoulders and cage pockets;

cage contract with ring lips; together with heat generation from viscous churning.

As an illustration of the method consider Fig. 2 as a typical bearing

system with the following arbitary selection of nodal points:

Node 1 - Air surrounding housing - temperature 'ti'

Node 2 - Outer surface of the housing - temperature 't2'

Node 3 - Inner surface of the housing - temperature 't^'

Node 4 - Bottom surface of the housing - temperature 'ti+'

Applying the "Heat Balance Method" to Node '2' gives:

Q3-2 - -Q2-1 = 0 (13)

(For convenience it is assumed that the heat influx to Node 2 is

positive)

'Q'3-2 and 'Q'2_tt illustrate conductive heat transfer from Node '3' to

Node '2', and Node '2' to Node '4' respectively, whilst 'Q'2-1 illustrates convective and radiative heat transfer from Node '2' to Node '1'.

Equations (2), (4), and (5) and (10) when simplified and applied to

these nodes yield

Q3-2 = Ci(t3-t2) (14)

Q2-4 = C2(t2-tJ (15)

Q2-I = C3(t2-ti)^'^^+ C4((t2+273.15)''-(ti+273.15)'') ^^^^

Substituting equations (14), (15) and (16) into equation (13) gives:

Ci(t3-ti)-C2(t2-tJ-C3(t2-ti)^*^^C4((ta+273.15)^(ti+273.15)^ = 0(17)

This final equation (17) is therefore the result of applying the "Heat

Balance Method" to Node 2 for the specified conditions and illustrates

a typical nodal equation.

It is obvious from the foregoing that similar equations will pertain

for each nodal point giving a system of non-linear equations to be

solved whose number is governed by the number of nodes selected.

307
The third and final step of the process is to obtain a simultaneous

solution to the set of non-linear equations erected, which will then

represent the predicted nodal temperatures. This was accomplished by use of the computer programme briefly described hereunder.

8. THE COMPUTER PROGRAMME.

8.1 Programme Capability

At its present stage of development the computer programme has the

following capability.

(a) Prediction of spacial temperature distribution at twenty nodes;

these including bearing raceways, rollers, cage, housing, shaft and

lubricant bath temperatures.

(b) Calculation of lubricant viscosity at the operating temperature

of the oil bath.

(c) Reactive bearing torque and total heat generated.

8.2 Programme Description

The computer programme was derived from a "Fortran" subroutine given

by Powell (16). The package consists of hybrid solution method com- bining the "Newton Raphson" method and the so-called "Method of

Steepest Descent". The former provides for the linearisation of the

non-linear equations whilst the latter ensures a smooth and rapid con- vergence. Writing equation (17) in the form RC(1 ) then the remaining

heat balance equations may be written RC(2), RC(3) RC(N).

The method of solution is iterative and requires an initally guessed

input for the nodal temperatures. The computer routine then calculates

the residuals RC(I), these approaching zero as iteration proceeds.

On reaching a specified convergence criterion, programme iteration

ceases, the computed solutions being then obtained as a final printout.

A monitor sub-routine programme is incorporated in the package which

displays current nodal temperatures and residuals in print-out format,

thereby enabling the convergence rate of the master programme to be

studied. This optimises computer time utilisation and checks out any

programme errors as iteration proceeds.

9. DISCUSSION OF RESULTS

9.1 Theoretically Predicted Results

Fig. 5 shows the relationship between the total generated heat (including any external input) and the total heat dissipated through heat

transfer, plotted against the mean operating temperature for the two

308
test oils, an SAE 30 and an SAE 50. A corresponding ordinate for the

friction torque has also been included. The condition is for a fixed

load of 2000 N at an operating speed of 4000 r.p.m.

Points of interception of the 'Heat Generation' and 'Heat Dissipation' curves give thermal equilibrium and indicate both the relevant temperature and friction torque for this condition.

It is immediately obvious that the choice of the thinner oil would

result, as is to be expected, in a lower operating temperature and

reduced power loss in the bearing unit and shows the advantage of the use of a thinner oil. Values of oil film thickness computed from

Elasto-Hydrodynamic theory showed an insignificant difference between

the two oils. It is to be appreciated that a lower operating temperature infers increased oil change periods. Fig. 5 shows the importance of an accurate prediction of heat dissipation rate from the unit.

If an underestimation of heat dissipation rate is made, there is an apparent anomaly in that the predicted temperature is greater than theexperimental , whilst the corresponding friction torque is less .

This anomaly is readily explained, however, on the basis of the high

non-linearity between bearing temperature and lubricant viscosity.

If the heat dissipation is underestimated in the programme, the predicted bearing temperature will obviously be higher, giving a lower

operating viscosity. Since the friction torque equation used in the

programme itself contains a viscosity term, the result will be a lower

predicted friction torque than that measured experimentally.

Apparently this anomaly was experienced by Schwartz (17), the experimental and theoretical findings reported in his paper giving a similar

contradiction in the two parameters.

The effect was demonstrated, somewhat dramatically for the authors,

during early development work on the programme. In normal running,

after thermal equilibrium is reached, an appreciable amount of heat is

conducted out of the bearing from the housing base to the bedplate.

This was initially underestimated in the earlier programmes the re- sultant temperatures being, in certain cases, almost 50% higher than

those experimentally measured, whilst the calculated torques from the

programme were unexpectedly less than those measured on test.

The anomaly was finally resolved when thermocouples were placed at

the base of the housing. These gave a true picture of the extent of

the conduction heat transfer. It is to be inferred, therefore, in

the light of this, that close attention to foundation conduction is

highly relevant when assaying thermal problems in bolted down bearing

housings.

309
A further important aspect, found when the programme had finally produced close correlation with the experimentally measured temperatures,

was that roller temperatures predicted by the programme were some 15%-20% higher than those predicted at the inner ring. Since roller

temperatures were not experimentally measured in the test rig, current

literature was investigated with a view to producing some substantiation

of this result. Confirmation was found in experimental results obtained by Norlander and Stackling (18) who measured element temperatures

some 18% higher than inner ring temperatures with deep-groove ball

bearings under similar operating conditions. It is possible that, in

addition to viscous shear in the pocket oil film, the elements experience some rubbing against the cage from centrifugal force on the clear- ance side of the bearing rings, though it is appreciated that this

effect depends on cage geometry and operating clearance. The fact that

roller skidding had been measured in this area in previous rig trials

lends some credence to this possibility.

9.2 Experimental Inferences

The effect of the housing shape and heat dissipation potential is

illustrated in the asymmetrical experimental temperature distribution

about the horizontal centre line in Fig. 2.

This could not be attributed to the direction of the load line since

the same effect had been noted by the authors who, in earlier work on the rig, applied loads up to 22500 N, in the opposite direction, on the same bearing unit, using a hydraulic cylinder. The oil bath itself,

clearly, does not transfer heat from the outer ring since its own temperature, as shown in Fig. 2, approximates to that of the outer

ring in this area.

In the light of what has already been discussed on the influence of

conductive heat transfer through the bearing housing base it is to be

concluded that this is the controlling factor; the base conductive heat

transfer outweighing surface convective heat transfer to produce the

asymmetrical temperature profile. This was confirmed on measuring

temperatures on the inverted hydrostatic bearing at the rear of the ring,

the same asymmetry being produced in the ring irrespective of oil flow

between the hydrostatic bearing surfaces. This conclusion is reinforced

on observing the significant temperature gradients in the lower part

of the housing (Fig. 2.). Calculations based on these values showed

that some 45% of the total heat generated is dissipated in this way.

Similar calculations showed a further 28% of generated heat dissipated

through the rotating shaft/fin assembly.

310
10. CONCLUSIONS

10.1 General Programme Utilisation

It has been demonstrated that a viable computer programme based on analytical heat transfer techniques may be constructed which is capable

of predicting spacial temperature distributions in rolling contact

bearing assemblies and that the predicted results yield close correlation with experimentally meas-ured values.

From the standpoint of the industrial user/designer the programme

capability can be utilised in several ways:

(a) Optimum lubricant selection, commensurate with the bearing duty,

may be obtained at the design stage to ensure minimum power loss.

(b) For a lubricant already specified the designer can quantify any

critical thermal situation from a knowledge of both the spacial distribution of temperature and the prediction of any localised temperature. This is of particular importance when temperature effects

induce dimensional changes.

(c) Since different bearing geometries may be catered for in the

programme, the designer can study the effect of differing housing con- figurations on spacial temperature distribution and heat dissipation.

Foundation effects can also be catered for.

(d) For bearing assemblies already in operation the industrial user

can assess potential energy saving through lubricant viscosity changes,

together with the effects of extended oil change periods when bearing

temperatures have been lowered.

10.2 Specific Design Considerations

If thermal analysis indicates that bearing cooling is necessary,

particular attention should be paid to which components should be

specifically cooled.

External cooling of the housing will, in general, reduce dimensions

between inner and outer rings if the shaft temperature itself is not

appreciably affected. The resulting reduction in element clearances

may produce an increase in power loss tending to invoke a thermal

spiral. In extreme cases this may produce bearing seizure.

Since it has been shown that a significant percentage of heat is

conducted through the housing base to the foundations, excessive conI duction in this area may produce similar effects to those outlined

j above. Conversely any condition increasing insulation at the joint

face will tend to retard these effects.

311
Good surface contact at the interface is important. Variations in

surface flatness may produce large variations in local contact resistance with a concomitant variation in conductive heat transfer.

Thermal distortions arising from this effect may be passed to the

bearing with a consequent reduction in its useful life.

Shaft cooling will undoubtedly increase radial clearances between

rollers and rings of plain roller bearings. However, in pre-loaded

assemblies axial contraction of the shaft may increase the pre-load,

dependent on the mounting arrangement, particularly in taper-roller

bearings with "indirect" mounting. Such a situation may incur high

local temperatures between rollers and guide flanges. Overcooling of

a shaft can, additionally, initiate inner ring creep or even slippage.

It is seen from the foregoing that variations of temperature within a bearing assembly are capable of producing exceedingly complex effects

and this highlights the importance, to the designer, of having a thermal

analysis programme capable of predicting local temperatures.

Such a programme, it may be inferred, not only mitigates any proppensity towards premature mechanical failure initiated from thermal sources but, from the standpoint of basic design and subsequent inservice duty, provides a further step towards an optimum level of

total energy conservation.

The economic implications of such an approach, particularly in the longterm aspect, are deemed worthy of consideration.

ACKNOWLEDGEMENTS

This work was accomplished as part of a programme at the Cranfield

Institute of Technology. One of the authors was sponsored by Escola

Federal de Engenharia de Itajuba, and by CAPES, Brasil.

REFERENCES

1. H. Y. Wong, "Heat Transfer for Engineers," Ed. Longman Inc.,

New York, 1977. 18-22.

2. M. J. Edmonds, et al ., "The Prediction and Measurement of Thermal

Contact Resistance," Wear, 50 (1978), Ed. Elsevier Sequoia S.A.,

Lausane, Netherlands, 299-319.

3. A. W. Brunot and F. F. Buckland, "Thermal Contact Resistance of

Laminated and Machined Joints," Trans. ASME, April 1949, 253-257.

4. N. D. Weills and E. A. Ryder, "Thermal Resistance Measurements of

Joints Formed Between Stationary Metal Surfaces," Trans. ASME, 1949,

259-267.

312
5. T. Fujii and H. Imura, "National Convection Heat Transfer From a Plate With Arbitrary Inclination," Int. J. Heat & Mass Transfer,

Vol. 15, 1972, 755-767.

6. I. S. Bjorklund and W. M. Kays, "Heat Transfer Between Concentric

Rotating Cylinders," Trans. ASME, Journal of Heat Transfer, August 1959,

175-186.

7. C. Gazley, "Heat Transfer Characteristics of the Rotational and

Axial Flow Between Concentric Cylinders," Trans. ASME, Vol. 80, 1958,

79-90.

8. T. A. Harris, "Rolling Bearing Analysis," Ed. John Wiley and Sons,

Inc., New York, 1966, 452-474.

9. D. Dropkin and A. Carmi , "Natural Convection Heat Transfer From a Horizontal Cylinder Rotating in Air," Trans. ASME, May 1957, 741-749.

10. D. L. Oehlbeck and F. F. Erian, "Heat Transfer From Axisymmetric

Sources at the Surface of a Rotating Disc," Int. J. Heat & Mass Transfer, Vol. 22, 1979, 601-610.

11. M. Jakob and G. A. Hawkins, "Elements of Heat Transfer," Ed. John

Wiley and Sons, 1957.

12. A. Palmgren, "Ball and Roller Bearing Engineering," 3rd. ed., S. H. Burbank and Co. Inc., Philadelphia, 1959.

13. P. Garnell, "Further Investigations of the Mechanics of Roller

Bearings," Proc. Inst. Mech. Engrs., Vol. 181, pt. 1, No. 16, 1966-67,

339-348.

14. D. G. Astridge and C. F. Smith, "Heat Generation in High-Speed

Cylindrical Roller Bearings," Elastohydrodynamic Lubrication 1972,

Inst. Mech. Engrs., London, 83-94.

15. J. R. Welty, "Engineering Heat Transfer," Ed. John Wiley and Sons,

New York, 1974, 38-65.

16. M. J. D. Powell, "A FORTRAN Subroutine For Solving Systems of Nonlinear Algebraic Equations," From 'Numerical Methods For Non-Linear

Algebraic Equations,' by P. Rabinowitz, Ed. Gordon and Breach, 1970,

115-161

.

17. J. I. Schwartz, "Friction-Induced Heating in Axially Loaded Ball

Bearings," Trans. ASME, J. of Lubrication Technology, Jan. 1970, 105-112.

18. G. Norlander and H. Stackling, "A New Way to Measure Temperature,"

Ball Bearing Journal 172, 1972, SKF, 1-6.

313
NOTATION.

a

A

Al,2

b

^1234

D

Dmm

f

fo,i

Fr

"c

k

I<1,2

L

M

M2

Length of larger side of a rectangular section

Area of a surface normal to heat flow

Area of surface 1 , 2

Length of smaller side of rectangular section

Constants in the "Heat balance equations"

Constants in the equations for the heat transfer

coefficients

Diameter of shaft

D D. Mean diameter of bearing D =-^-4

-

m

- Outer diameter of bearing

- Inner diameter of bearing

- Geometrical factor f = ^

- Friction torque coefficients, given by bearing

manufacturers

- Radial load

- Heat transfer coefficient

- Minimum oil film thickness

- Thermal contact conductance

- Subscript referring to Node i and j

- Thermal conductivity solid or fluid

- Constants

- Length of heat transfer path

- Total bearing torque

- Viscous friction torque

(m)

(m")

(m)

(m)

(m)

(m)

(m)

(N)

{W/m^°C)

(vim)

{W/m^°C)

(W/m°C)

(m)

(N.m)

(N.m)

314
Ml - Load dependent torque (N.m)

n - Shaft rotational speed (r.p.m.)

N - Number of temperature Nodes

h X h D Nu - Nusselt Number Nu = — ' —

Q - Heat flowing from a surface to a fluid (W)

Qg - External heat input to bearing assembly (W)

Q. . - Heat conducted from surface 'i' to surface 'j' (W)

^Gen

" ^^^^ generated in the bearing (W)

- Heat flowing through contacting surfaces (W)

R - Radium of housing bore (m)

RC(1) - Residuals, in computer programme I = 1,2 N

R^

e

- Reynolds number R

e

= —V

,

' R

e

= —V

R. - Inner radius of bearing ring (m)

R^ - Outer radius of bearing ring (m)

t. . - Temperature Node 'i' and Node 'j' (°C)

tg - Surface temperature (°C)

t

s 1-2 - Temperature of surfaces 1 and 2 (°C)

t^ ^ - Fluid temperature and air temperature (°C)

T ,a

T. . - Absolute temperatures of surfaces 'i' and 'j' (k)

V - Linear velocity (m/s)

0) - Angular velocity (rd/s)

X - Characteristic dimension of a heat transfer path (m)

e.g. width, length or height of a surface or diameter of a cylinder

315
e - Effective "emissivity" between surface 'i' and 'j'

—8 a - Stefan/Bol tzmann constant = 5«76 x 10' W/m^ K**

V - Kinematic viscosity of a fluid (mm^/s)

316
317
00o IT)

q» CO

00

(O (O

61-9 60-8 LLER

RO

66-0 63-5 99-3 63-7 66-6 IT) 00

ob o in CO

»-z

UJ

00<o

fSI do - -* ^ e O CL cn I- UJ 2 8 < ^ o

I/) CM ^ <o— _j

UJ

O

Q. _l X <

UJ o

cr

OLO . . cr _..«=><

cr

Q ^ UJ

CD < LU 00 S ,Qr _J _i t/) oo

Z5

00

q:

I-Q

UJ

(r

CCUJ

Q.

UJ

CMo

u.

318
o

80

70

60-

50-

AO

ill o:z>

!<

ffi 30

Q.

Z

UJ

^- 20

10

INNER RACEWAY

SHAFT OUTER SURFACE

OPERATING TORQUE

RADIAL LOAD • 2000 N

LUBRICANT : SAE 30

1000 2000 3000

SHAFT SPEED (r.p.m.)

UJa H02g

0-1

uooo

FIG. 3 TEMPERATURE AND TORQUE VARIATION WITH SPEED

319
RADIAL UDAO 8 kN

LUBRICANT : SAE 30

nNS(WITH AIR JET) • INNER RACE

T OUTER RACE

FINS ONLY

O INNER RACE

V OUTER RACE

1000 2000

SHAFT SPEED Ir.p.m.)

3000

FIG. THE EFFECT OF AIR COOLING ON BEARING TEMPERATURE

BEARING RMJ 1^"

320
MEAN OPERATING TEMPERATURE CC ) (BEARING RINGS)

FIG. 5. THERMAL BALANCE : BEARING RMJ 1V

SPEED: AOOO R.RM. LOAD-- 2000N

321


324
325
THE INFLUENCE OF FILTRATION ON ROLLING ELEMENT BEARING LIFE

R. Bhachu and R. Sayles

Imperial College

London, SW7 2BT, England

P. B. Macpherson

Westland Helicopters Limited

Yeovil, England

Abstract: Using a gear machine to generate debris, which had been

verified by Ferrographic analysis as being representative of that found

in helicopter gearboxes, contaminated oil was passed through filters

of different sizes before being fed into a parallel roller bearing

fatigue machine. In-line particle counting monitored the debris

content of the oil which was based on a helicopter type of lubricant.

Filter sizes ranged between 1 and 40 ym absolute ratings and submi cronic extraction was achieved by using electro-magnetic filtration.

Bearing fatigue tests were run, under constant operating conditions,

for all filter ratings and Wei bull lines were drawn based on a minimum

sample size of 10 failures. From these a relationship between filter

rating and fatigue life was established. The experimental program is

described and results discussed.

Key words: Filtration; gearboxes; helicopter transmission; pitting;

rolling element bearings; rolling fatigue; spalling.

Introduction : Observations carried out during the last 20 years provide

strong evidence to suggest that indentations formed by the rolling-in

of debris were responsible for many of the early rolling element bearing failures experienced in helicopter gearboxes. During this period

effective steps were taken to improve the cleanliness of bearing steels

and this resulted in greatly increased rolling fatigue lives. It

seemed reasonable to suppose that a debris indentation could impair

fatigue properties just as much as a non-metallic inclusion yet, until

recent years, such obviously damaging defects have been ignored.

It was not until the work described in (1) was published that active

interest was directed towards the influence of filtration on bearing

lives. A more comprehensive study (2) confirmed the importance of

filtration. The present authors considered that the morphology of the

indentations to be of such importance that they elected to study the

effect of real debris, as opposed to artificial as used in (1) and (2), on rolling fatigue lives.

326
Current practice is to fit either 40 or 25 ym filters to helicopter

main gearboxes. Sufficient evidence was available to suggest that 3 ym

filtration would improve bearing performance to such an extent that

little purpose would be served in extending the proposed study to finer

levels of filtration. On the other hand, the oil film generated

between opposing asperities in a typical EHD contact is about0.012ym

and so, for complete protection, the aim could well be to incorporate

sub-mi cronic filtration.

From practical considerations, 3 ym absolute rating cartridge type

filters could be fitted retrospectively with a minimum of work, even

using existing filter housings. Sub-mi cronic filtration would involve

the regular polishing of the lubricating oil as is sometimes the

practice with hydraulic systems. Centrifugal type filters, being

limited by size and speed if fitted to a helicopter gearbox, would

remove particles down to the equivalent of 2 ym size but care would

have to be exercised in the design to prevent mechanical damage to the

long chain molecules present in the oil. Centrifugal filters could

only be considered for new gearbox designs but what could be a strong

point in their favour would be water and air extraction. The water

content in synthetic oils tends to be surprisingly high (3) and the

prevention of fretting demands a minimum amount of air in circulation

(4).

The main objective of the experimental work described in this paper was

to determine a practical filtration target for immediate application

that could reasonably be expected to lead to extensions in 'Times

between overhaul' (TBO's). It was also the intention to collect data

for use in a subsequent theoretical exercise to be aimed at minimising

the amount of debris generated within a damaging size range. It was hoped that a satisfactory explanation of the bi-modal situation, which

is so often present in Wei bull line presentations, along with the

variation in Weibull line slopes for different operating conditions,

could be established. The theoretical studies are now in hand and in

the present paper the experimental programme and results obtained are described and discussed.

Apparatus : The philosophy behind the design of apparatus used was,

basically, that representative helicopter type debris be continuously

generated so that by filtering and monitoring the oil, known con- taminant distributions were present when it was fed into a parallel

roller bearing fatigue machine. Bearing lives were to be measured in

terms of absolute filter ratings, and 3 values which are more informative, while all other variables were maintained constant. In order

to minimise unprogrammed stoppages it was decided to generate debris

in gear pairs by running with a helicopter type oil specially

formulated to have a lower load carrying capacity than normal. This

was preferable to operating a gear machine at high torques over

protracted periods when, inevitably, much time would be expended in

maintaining the machine.

327
As it was intended to retain the gear machine for general laboratory

use much consideration was given to choice of gear specimens. They

had to be of EN39B or similar type of steel, carburized and hardened

to approximately 750 VPN after grinding. They also had to be

essentially of helicopter form, so a suitable pair was designed. On

reflection this appeared to be a retrograde step because, once again,

we should find ourselves using unique test equipment with the con- sequent difficulty of correlating results with those from other

laboratories. The NASA test gears did not differ overmuch from our

own design so, with their agreement, their design was adopted.

It is essential that torque can be altered in a gear machine while

running. Extensive experience with disc machines clearly shows that

results obtained by stopping a machine to alter the torque should be

treated with caution. It is the normal practice in the laboratories

with which the author's are associated, to use an epi cyclic system

for applying torque. In the present case funds would not permit the

use of an epi cyclic so, again, help was sought from NASA who agreed

to the use of their hydraulically loaded blade torquing design which

is basically similar to the well established system used in marine

work. Thus, essentially, the gear machine designed was similar to that

which NASA has established over the years although it differs in layout and detai 1

.

Fig. 1 shows the layout of the equipment but omits the bearing fatigue

machine which is of conventional design. Contaminated oil is fed

through a previously calibrated filter into the bearing machine. Inline particle counting is provided for continuous monitoring from

positions down and upstream of the filter. Problems associated with

air bubbles had been anticipated but by using a funnel shaped settling

tank all air was liberated and no bubbles were, in fact, observed in

the HIAC system. The magnetic filter to be seen to the left in Fig.l was used for sub-mi cronic particle extraction and for the rapid polishing of the oil when required. The cartridge type filters were of

absolute ratings 40, 25, 8, 2 and 1 ym. The test oil circuit is shown

in Fig. 2.

An accelerometer, centrally located between the two test bearings,

successfully registered the onset of spalling and the machine was automatically shut down on reaching a pre-determined vibration amplitude.

All previous attempts to monitor line contact failures with an accelerometer had proved unsuccessful so it was with considerable

surprise that the system worked well in this instance. It just so happened that the accelerometer had been sited immediately over the

loading bearing yoke and, fortuitously, this was acting as a mechanical

amplifier. Repositioning the accelerometer rendered it useless so throughout the testing both test bearings had to be removed and

examined to determine which one had failed.

Appendices 1,2 and 3 describe the test bearings, gear steel and

328
bearing steel respectively.

Fil ter Ratings : AC Fine Test Dust (ACFTD) is universally used as a fluid contaminant for determining the effectiveness of a filter because

it has a known particle size distribution. However, these dust

particles bear little resemblance to those generated in a gearbox and

thus filter ratings are a standard only and do not necessarily relate

directly to practical situations. It has to be emphasised that a filter rated at 2 ym will not prevent the passage of all particles

sized 2 and above.

Every filter has a characteristic curve of efficiency in terms of

particle size as illustrated in Fig. 3, where the efficiency n for

each particle of radius a is defined as,

n_(a)

n (a) = = 1 n.(a)

n-(a) = number of particles of size a per unit vol. captured by the

field

n-j(a) = number of particles at filter inlet

ng(a) = number of particles at filter exit

Fig. 3 also shows how absolute filter performance relates to the real one.

In many respects the 3 ratio, developed by Fitch and his colleagues (6)

and (7) as a filter model to define its performance, is more informative

than the absolute rating.

n^(a > a^)

This is the ratio of the number of particles per unit volume of size

greater than at the inlet to the number at the exit. Thus the

higher the 3 value the better the filtration. This ratio led to the

3]0 model (8). 3 curves are established for the filters by plotting

on special semi-log paper and then each curve is soecified bv its 3io

value, i.e. the 3 values for 10 ym particles. It is to be noted that

3(a(-) can also be determined from the particle frequency distribution

function.

It is obviously convenient to use a single parameter to define

performance but the Authors are by no means convinced that the 3 ratio,

based on ACFTD calibrations fulfils this function any better than a c.£. a. (RA) value describes the topography of a surface. It seems clear that in both cases the single parameter is useful when comparing

'Like with Like', but its usefulness is not so clear in other cases.

n (a)

329
Parameters such as collector size, porosity, material, flow rate,

viscosity, length, particle concentration etc. must all influence

filter performance. The Authors have found the use of discriminant

functions useful in determining the relative importance of groups of

variables and are currently applying such techniques as part of a detailed theoretical study into many aspects relating to filtration

and the damaging influence of debris. For this reason absolute

ratings are used in the present paper and reference to 3 values is

reserved for a future occasion. Meanwhile it is to be noted that the

375 rating, i.e. the particle size at which 3 = 75, is very close to

the absolute rating. Thus an absolute rating of 40 ym closely

approximates to 340 ^75.

Resul ts : Unless otherwise stated, tests were run under the following

conditions:

Bearing speed 5,000 r.p.m.

Applied load 2,957 N (665 lbs f)

Max. contact stress between rollers and inner race, 2.82 GPa (408,900

lbs/in2

Bulk oil temperature 70°C (158 F)

Calculated central oil film thickness, 0.576 ym (22.68 y ins)

Mean calculated A ratio, 1.52

Catalogue life of bearing under these conditions 13 hours

Tests were terminated on detection of a pit measuring 0.4 to 0.6 mm

diameter.

S/N Curve : Initially tests were run with a 3 ym filter at 3 stress

levels to establish a rudimentary S/N curve from which to select an appropriate bearing load for use in the experimental programme. The curve was subsequently refined, so that it could be used for reference

purposes, and is shown in Fig. 4 based on B^^ lives.

Rolling Fatigue Lives : Tests were run under standard conditions to

determine the fatigue lives for the various levels of filtration, viz.

1,3,8,25 and 40 ym absolute ratings. Sample size was such as to give

a minimum of 10 failures for each series of tests and Wei bull lines were drawn for all results. These lines are shown in Fig. 5 and B-jQ

and B50 lives for the series are plotted against filter rating in

Fig. 6. The results are tabulated in Table 1 and include confidence

1 imi ts

.

Oil Film Thickness : The influence of the oil film thickness being

generated was investigated by reducing the bulk oil temperature to 30°C.

The increased viscosity raised the oil film thicknesses to 0.987 ym and

resulted in longer life as can be seen from Table 1.

Changing Filtration Level during Test : Tests were run at 30°C oil

temperature with 40 ym filtration for 30 minutes before switching to

^30
3 ym filtration at which level the bearings were run to failure. As

will be seen from Table 1 the lives are substantially the same as if

the test had been run with 40 ym filtration.

Post Test Examinations

^' Metallurgical : Preliminary examination of all rolling surfaces

was made under low magnification (x 25) when general features were noted and nature of the failures tentatively identified. Debris

indentations were revealed over all the surfaces along with occasional

transverse cracks. Microhardness measurements were made across the

rolling tracks and Nital-etch examination for possible grinding burns.

The most interesting looking failures were selected for detailed

examination when metal lographic sections were prepared through failure

sites to study the microstructure and to obtain further information on the failure mechanism. Fatigue failure profiles were studied by

progressively grinding back and polishing across the running path.

The following failure modes were identified and classified as follows:

Transverse cracks across running path

Incipient failure at a transverse crack

Straight sided or circular pit at transverse crack

Incipient failure not associated with a transverse crack

Fatigue pit not associated with transverse crack

Fatigue pit at indentation

Extensive surface break-up near an indentation or crack

The distribution of failure classification in terms of contamination

level was studied, but no overall pattern was discernible. A summary

of main observations is as follows:

1) Generally, transverse cracks were found for all levels of

filtration.

2) The presence of failures both with and without transverse crack

association, under all levels of filtration, demonstrated that

the failure mechanism was independent of filtration level.

3) Many of the failures were associated with debris indentations

and surface scratches.

4) Metallographic examination in the rolling direction revealed that

the transverse surface cracks penetrated perpendicularly to the

surface to depths of between 0.20 and 0.75 mm.

5) Secondary cracking branching off the primary cracks was frequently observed at depths below the surface of 0.08 to

0.10 mm.

A typical example of a debris indentation initiation site crack is

shown in Fig. 7. The average size of pit formed was between 0.4 to

331
0.6 mm diameter and 0.05 to 0.10 mm deep.

2. Surface Topography : Talysurf recordings were taken of track and

roller surfaces from both damaged and undamaged areas. From these the

geometry of the indentations was determined. Composite roughness

values and \ ratios are set out in Table 2.

3. Roundness : 'Talyround' measurements were made of a virgin bearing

inner race along with those from all suspended, i.e. unfailed, bearings.

The recordings are shown in Fig. 8.

Discussion : While it is not suggested that all helicopter bearing

failures result from the rolling-in of debris, the experimental results

clearly imply that better performance would result from the introduction

of finer filtration. It will be seen from the 90% confidence limits

quoted that a large difference in filter rating is required before

statistical significance can be placed on the results. The results

also suggest that the fitting of fine filters to a gearbox is likely to

prove of little value unless extreme care is taken to ensure that all

damaging debris is removed from the gearbox prior to its initial run in

a test stand. Likewise, steps must be taken to prevent the entry of

contaminants into the gearbox from test stand parts such as oil coolers.

The apparent relationship of filter rating and Weibull line slope is

interesting and confirms the trend noted in (9 and 2). At first sight

the slope relationship would appear to be similar to that experienced

at different loadings in bearing fatigue tests. Normally, as in the

case of rotating bending, at high loads the scatter is much smaller and

this can be related to cycles required for crack development and crack

propagation. A detailed study is being made of the Weibull line slopes.

As is usual in rolling fatigue work the Weibull lines tend to display

bi -modal situations. This will result from the summing of two or more failure mechanism distributions. There appears to be a connection

between filter rating and the incidence of the bi-modal situation and

this becomes more obvious as the state of filtration is improved. By

considering the Equivalent Stress concept{which is discussed later and

recorded in Table 3), it could, perhaps, be expected that the position

would tend to be analogous to Reverse Bending experience. This is not,

however, the case because in bending work the bi-modal situation tends

to arise in the mid stress region, i.e. as a result of summing the two

distributions that are so apparent at high and low stress levels.

To derive a feel for the benefits that could be expected to result

from improved filtration in terms of load carrying capacity, resort

was made to a concept of 'Equivalent Stress to Failure'. This is

simply the stress, taken from the S/N curve, required to produce a failure with a 3 ym filter for corresponding B^q lives for different

332
1

filter ratings. The results, as tabulated in Table 3, indicate that

contact stress limits could be doubled to achieve the same life by

changing from 40 to 3 ym filtration. This is, of course, no more than

a guide but should further testing confirm that such improvements are feasible then much importance will be attached to this aspect. In

general terms it is not difficult to extend fatigue lives, corresponding to just below the stress endurance level, by large amounts whereas

it is extremely difficult to achieve any really worthwhile increase in

load carrying capacity.

The relationship between filter ratings and B50 fatigue lives is shown

in Fig. 9. Between the 3 and 40 ym filter levels L = 77.33y"0-^8>

where y represents filter rating. Replotting the results as in Fig. 10

clearly shows the improvement in performance that can be achieved by

fitting filters finer than 40 ym. It is apparent that for really

worthwhile benefits the filtration level should be improved to at

least 10 ym.

One of the most interesting features of the post test examinations

was in the 'Talyround' recordings. With 40 ym filtration the outof-roundness was greater than in the virgin bearing. A gradual

improvement was observed with finer filtration down to the 8 ym rating

and then a marked improvement between 8 and 3 ym at which point there

was virtually no out-of-roundness. Below the 3 ym level the trace was similar to that of the virgin bearing. It would seem that

particles smaller than 3 ym were too small to have any effect and

merely passed through the contacts. Over 3 ym size produced a lapping

action which in the case of 3 ym filtration improved the roundness of

the race. This result tends to confirm suspicions that the size range

of damaging debris is relatively small. Above a limiting size the

particles will not enter the contact and below a lower limit will pass

straight through. The prevention of the generation of damaging size

debris through control of surface finish is currently being sought by

the Authors. The Talyround results tend to substantiate the main

findings that, under the conditions of the testing, there would be

little point in filtering finer than a 3 ym rating.

As could reasonably be predicted for a given particle size or, more correctly, a given filter rating, the thicker the oil film generated

within the contact the less the damage, but only so long as one is

dealing with debris of a damaging size which, in turn, will relate

to the oil film thickness. An increase in oil film thickness from

0.576 to 0.987 ym brought about an increase in fatigue life of some 40% for the 3 ym rating whereas it was only 10% with a 25 ym filter.

It would appear that an equivalent to the well established X ratio

is relevant to relate debris size to surface roughness. This aspect is now being considered but, as in the case of X , it is necessary to

replace the 'Composite Roughness' with something more meaningful and

to establish a relationship between particle size as recorded and its

deformed thickness.

333
No metallurgical reason could be found to account for those very early

failures which tended to reduce Biq lives quite markedly. In general

it was found that the depth of the primary cracks exceeded that of the

estimated maximum shear stress by a considerable margin. However

secondary cracking did arise at depths between 0.08 and 0.10 mm and

these dimensions do correspond with the depth of maximum shear stress.

As usual, subsequent propagation was in the rolling direction and

parallel to the surface, to lead to breakout of the crack and flake

dis lodgement to form a fatigue pit.

The influence of filter size on the rate of generation of particles

greater than 2.5 ym is shown in Fig. 11. Presumably some of the larger

particles will break up into smaller ones and this will be a function

of running time.

Conclusions : The experimental work described in this paper supports

the evidence becoming available from helicopter trials, and other

relevant experience, that the replacing of 40 or 25 ym filters by

units rated at 3 ym absolute is to be recommended for helicopter gearbox installations. Such action should lead to improved reliability,

longer periods between overhaul, cheaper overhauls and consequent

reductions in ownership costs. Times between oil changes, where

relevant, should be substantially increased. These improvements in

performance can, however, only be realised if the gearbox

manufacturers ensure that primary damage has not already been initiated

before the gearbox is installed in a helicopter.

It could, possibly, be found in future work that filtration down to submicronic levels is worthwhile. If so, then regular polishing of the

oil at pre-determined intervals would be indicated. Such could,

however, possibly result in the situation of producing an ultra clean

oil that would not lubricate as a direct result of contaminant

extraction. The role played by contaminants in lubrication is

currently being investigated.

No matter how fine the filtration it is not going to prevent freshly

generated debris from entering contacts. It is, accordingly, necessary

to take steps to ensure that, as far as is practicable, the debris

being generated is of a non-damaging size. Results obtained from the

experimental programme described in this paper suggest that an approach

along these lines is a realistic one because the damaging size range

is relatively narrow.

In conclusion, it can fairly be stated that one of the most encouraging

features of this work is the generally growing realisation that debris

indentations are just as damaging as non-metallic inclusions and that

fine filtration is essential just as in the use of clean steels in

bearing and gear manufacture.

334
Acknowledgements : Reference should be made to the unusually large

degree of co-operation that has been extended to the Authors during

the course of running the filtration programme. Assistance from the

following organisations is gratefully acknowledged; NASA (Lewis),

Mobil Oil Company, R.H.P. Bearings and Pall Filters.

The Authors thank the U.S. Office of Naval Research and the U.K.

Ministry of Defence for having funded the project and, along with

Westland Helicopters Limited, permission to publish.

335
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336
Specimen

Composite

Roughness

(micron)

Calculated

Film Thickness

(micron)

X

Virgin Bearing 0.38 0.576 1 .52

40 micron 0.41 0.576 1 .41

25 micron 0.36 0.576 1 .60

8 micron 0.32 0.576 1 .80

3 micron 0.26 0.576 2.22

1 micron 0.22 0.576 2.62

Magnetic 0.20 0.576 2.88

Table 2

Filter

(micron)

Experimental

^50 ""i^^

(stress cycles)

Equivalent Stress

GPa (Ib/in^)

40 2.076 X 10^ 6.30 (913,827)

25 3.001 X 10^ 5.32 (771,938)

8 5.849 X 10^ 3.92 (568.690)

3 12.021 X 10^ 2.82 (408,900)

1 12.430 X 10^ 2.78 (402,684)

magnetic 12.480 X 10^ 2.77 (401.944)

Table 3

337
APPENDIX I

Bearing Material Properties and Test Parameters

Material: High carbon chromium EN31 steel (AlSl 52100)

Compressive strength: l.SSGPa (0.2 x lO^lb/in^)

Elastic Modulus: 207GPA (30 x 10^ Ib/in^)

Poisson's Ratio: 0.3

Hardness: 750 VHN (MIN.)

Surface Roughness: 0.3 ym (12y in ) Inner/outer race Surface Roughness: 0.05 ym (2y in) Rollers

Reduced Elastic Modulus: 357GPa (51.8 x 10^ Ib/in^)

Specific Conductivity: 50.4 W/mk

~6

Coefficient of Linear Expansion: 15 x 10 /K

Bore Diameter: 25 mm (0.9843 in)

Test Speed: 5000 revs/mi

n

Lubricant: Modified Mobil Jet II Operating Temperature: 70°C (158°F) and 30°C (86°F)

Axial load: 0

Radial Load: 2957N (6651bf)

Min. Lubricant Film Thickness: 0.5767 ym (22.70y in)

Max. Hertz's Contact Stress: 2.82GPa (408,900 p.s.i.)

Contact Size: 0.293 mm x 3.708 mm (0.01152 in x 0.146 in)

Max. Depth to Max. Shear Stress: 0.095 mm (0.00374 in)

338
APPENDIX II

Chemical Composition of EN39B steel.

Type: 4% Nickel Chromium Molybdenum

Gear Material by Percent Weight

Element

c Pfo Si Ni Cr Mo

Weight % 0.12 0.25 0.10 3.90 1.00 0.15 p

0.18 0.50 0.35 4.30 1.40 0.30 s

APPENDIX III

Heat Treatment Process for EN39B Steel

Step Process Temperature Time

K (°F) (hrs)

1 Carburize 1172 (1650) 8

2 Air Cool to Room Temperature

3 Copper-plate All Over

4 Reheat 922 (1200) 2.5

5 Air Cool to Room Temperature

6 Austen ize 1117 (1550) 2.5

7 Oil Quench

8 Sub-zero Cool 189 (-120) 3.5

9 Double Temperature 450 (350) 2 each

10 Finish Grind

11 Stress Relieve 450 (350) 2

N.B. All test gears were case-hardened and carburized as per above

process to a nominal depth of 0.762 nm (0.030 inches)

0.040 ) = 0.050

Max,

339
References

1. Dalai, H. and Senholzi, P. "Characteristics of Wear Particles

Generated During Failure Progression of Rolling Bearings".

Trans. ASLE, Vol. 20 (3), (1976), P. 233.

2. Loewenthal, S.H. and Moyer, P.W. "Filtration Effects on Ball

Bearing Life and Condition in a Contaminated Lubricant".

Jour. Lub. Tech. Trans. ASME, Vol. 101(2) (1979), P. 171.

3. Spikes, H.A. and Macpherson, P.B. "Water Content of Helicopter

Gear Oils". International Power Transmissions and Gearing Conf.

San Francisco, Aug. 1980, 80-C2/DET-12

.

4. Newley, R.A. , Spikes, H.A. and Macpherson, P.B. "Oxidation Wear

in Lubricated Contact". Jour. Lub. Tech. Trans. ASME, Vol. 102,

(1980), P. 539.

5. Coy, J.J., Townsend, D.P., Zaretsky, E.V. "Dynamic Capacity and

Surface Fatigue Life for Spur and Helical Gears". NASA

Technical Memorandum, NASA TMX-71743.

6. Fitch, E.C. "The Multiples Filter Test - Now a Viable Tool".

BFPR Program, 8, Oklahoma State University, 1974.

7. Bensch, L.E. , Fitch, E.C. and Tessman, R.K. "Contamination

Control for the Fluid Power Industry". Pacific Scientific Co.,

1978.

8. Fitch, E.C. "Controlling Contaminant Wear Through Filtration".

Wear (34,4) 1975.

9. Tallian, T.E. "Prediction of Rolling Contact Fatigue in

Contaminated Lubricants". Trans. ASME Papers Nos. 75-Lub-37 and

38.

340
FIG, 1 Layout of Equipment,

0

PRESSURE

GAUGE

WEAR DEBRIS BEARING

GENERATOR TEST RIG

r 1 f-UGN£TIC- FILTER

PIG. 2

Diagram of Test Oil Circuit,

HEAT- EXCHANGER

MAIN OIL TANK

341
PIG. 4 Preliminary S - N Cvirve.

342
STRESS CYCLES I Log NilO I Fig. 5(a) Weibull Distribution of Fatigue

Results Under 40 micron Filtration.

H - n -

3 »h

J I

I I I I

STRESS CYCLCS I lot KilO I Fig. 5(c) Weibull Distribution of latigue Results Under 8 micron Filtration.

STRESS CYCLES I Log NilO I

Fig. 5(e). Weibull Distribution of Fatigue

Results Under 1 micron Filtration.

STRESS CYCLES I Log N.IO I Fig. 5(b) Weibull Distribution of Fatigue Results Under 25 micron [iltration.

J 1 I I I

STRESS CYCLES I Fig. 5(d) Weibull Distribution of Fatigue

Results Under 3 micron Filtration.

} ^StTB40 K

STRESS CYCLES I log M.io'l Fig. 5(f) Weibull Distribution of Fatigue Results Under Magnetic Filtration.

343
95

90

80

70

60

50

i.0

30

20

I I I I I 1

FIG. 6

2 3 4 5 6 7 8 910 20 STRESS CYCLES ( Log NxlO^I Showing B10 and B50 Lives.

PIG. 7 Crack Propagation from an Indentation with

40 Micron Filtration (>i500).

344
I

PIG, 8(c) 25 Micron Filtration, jiG, 8(d) 8 Micron Filtration,

345
346
8 12 16 20 24

OPERATING TIME I Hours I

11 Rate of Particle Generatlon#

28 32 36

CYLINDRICAL ROLLER BEARING RHP - NIOOS

No. of Rollers Roller Length Roller Diameter

Diametral Clearance

Pitch Diameter

PIG. 12

14

5.563inm (0.219 in) 5.563mm (0.219 in) O.OSlnm (0.0012 in) 36.043nin (1.419 in)

Test Bearing*

11. 959 mm

347
IMPROVED INSTRUr/lENT BEARING LUBRICATICT!

n. Rebuck and L. otallings

Ilaval Air Development Center

v'\larminster , Pennsylvania 1P97^

Abstract: This paper will present the results of laboratory

tests on three viscosity ^^rades of synthetic hydrocarbon

oils for the purpose of providing proposed specification

requirements to cover these oils for military instrument

bearing applications.

Synthetic hydrocarbon oils (fabricated from L Olifins) have

become increasingly more popular in the last dacade. The

initial widespread use of one such type fluid was as a base

oil in a grease covered by Military Specification ?/.IL-G-

°1322 which was originally developed for use in aircraft

wheel bearings. This was followed by the use of a lov/er

viscosity grade oil as an aircraft hydraulic fluid covered

by r/ilitary Specification rv^IL-Ji-832.^2 . Today both the

grease and the hydraulic fluid are high volunrie items in

the I'avy Supply System. The grease is currently being used

in a wide variety of military weapons systems applications

including instrument bearings.

Interest in these fluids has also expanded to the industrial

and commercial markets. Formulated fluids are available as

multi-purpose gear lubricants, automotive engine oils, gas

turbine lubricants, and high temperature bearing lubricants.

Some of the major attributes of the oils include: (1) their

hi^h viscosity index, (2) their good thermal stability,

(3) receptiveness of common additives and inhibitors,

their low tem.perature fluidity and (5) their com.patibi lity

with other lubricants and materials. Still another

attractive feature is the outlook for their long term availability, an aspect which is of considerable interest to the

instrument bearing community.

T-'ey words: Aircraft hydraulic fluid; aircraft wheel bearing

grease; instrument bearing lubrication; low temperature

fluidity; synthetic hydrocarbon oils.

348
3Aa^'3R( UND

Instrurrient and instrument "bearin.g lubrication is a demanding; and specialized field in terms of requirements.

Unfortunately, it has a very low lubricant market volume,

thus making it difficult for the lubricant supplier to

.iustify .eivin.p; it a ,<T;reat deal of attention, ab a result

most of the lubricants used in the past for instrument

bearing applications were designed for other uses, which

often did not require the same quality control or the

special properties that are often required in these applications . Also, modifications or further developments of these

lubricants were made without much if any concern for the

requirement of the small volume applications.

An example of such a situation existed back in the 1960s at

which time a mineral oil, desi/^nated Teresso V 7?., was

being used for lubricating spin axis ;3yro bearings. The

V 78 oil was designed primarily for power ^eneratini^ equipment used in the electrical industry. When the m.anufactuier

modified the process for making this oil, the military

decided to develop a replacement oil desif^ned specifically

for use in spin axis bearings. This Air Force sponsored

development program resulted in a product designated KG 80.

A ^"111 tary Specification i'''IL-I.— -3176 was written to cover

this product. Actually, a series of different viscosity

oi].s was produced under this program. With well defined

processing steps using generally available mineral oil

stocks, a primary objective of the Air Force program was to

provide for a multi-sources capability of the finished

product. Hov/ever, obviously due to the low volume requirements, the original producer of the KG 30 lubricants,

Kendall Refining Co. i remains today as the only qualified

supplier of this oil.

In the mid 1970s, r'endall indicated the possibility that

they might discontinue the manufacture of the KG cO oils,

due to the small volume of the oils being requested.

Although the producer v/as persuaded to continue supplying

this oil, the military and industry became alarmed at the

prospects of its discontinuance and began looking for

potential replacements.

Since the synthetic hydrocarbon oils have many properties

which are similar to those of the best petroleum oils it

appeared that they were a logical choice for consideration

in this area of application. Also, these oils were

becoming more readily available in a variety of viscosity

349
f^rades and at competitive prices. fore suppliers v/ere

i ntroducin.'?: them into their product lines.

7.ever3.1 years a<=r,o the ' Corporation made available three

viscosity =:rades (hif^h, low and medium) of the synthetic

hydrocarbon fluids formulated specially for instrument

bearinf? applications. These oils were formulated with the

same antiwear additive, i.e. tricresyl phosphate, as is

contained in the KG ^0 oils. Although the specific

oxidation inhibitor for these oils is not specified, it

appears to be similar to or the same hindered bis-phenol

that is required in the KG 80 oil by the :v;lL-L-33176

Specification.

At the request of the I\'aval Air Systems Command, laboratory

evaluations were initiated on these oils at the Naval Air

Development Center, with the objective of comparing their

properties to those of the KG 80 oils and establishing

proposed specification requirements.

TZZT3 AND R?.3ULTS

In order to develop data, not only suitable for comparison

with KG ^0 but also showing the differences among the yiTB

C ils themselves, all the laboratory chemical and physical

tests for each of the oils were conducted under the same

conditions. The results of the tests on the highest

viscosity prrade (similar to KG 80) r"PB Gil, designated

T'C HQ, are compared with those on the KG 80 oil and a^inst

requirements of Specification ;/JL-L-83176. The results of

the low and medium viscosity grade oils designated KG 16

and 'T 7 5 respectively are com,pared with those of a synthetic ester instrument oil KB 20B and against requirements of iaL-L-818^6 Specification to which~the ¥3 20B oil

is qualified.

PHYSICAL PRGFEBTTZS

Standard viscosity determinations were made on each of the

oils at the norm^al 210° and 100°? temperatures. Additional

viscosity tests were conducted on the Ki 18, lf.0 75 and

]'• ':: 20"^ oils at -ko'^ and-65°F. The viscosity index for each

oil was calculated. These results are shown in Tables I

a nd 1 1

.

Pour points and Plash points were also determined on each

of the oils using standard ASTK procedures with results

shown in Tables I and II as well.

350
A superior viscosity-temperature relationship and pour

point is noted for the 119 over that of the 80, while

the KG SO has an advanta=:e with its hi^^her flash point.

The MO 18 and ¥B 20B oils have very similar viscosities.

The IT 18 has a slight advanta^^e at -65°F even though the

MB 20B has a considerable edge in the calculated viscosity

index. IfiB 20p also has a slightly higher flash point. The

V.Q 75 has the advanta^'^e at the higher temperature while

having a somewhat disadvantage at the lower temperatures.

OXI DA TI ON-C OR R OS T C M

Cxidation-corrosion tests were conducted on each of the

oils with the exception of the KB 20B . Results are shown

in Tables III and IV. A modified I^'ethod 530^; of Federal

Test Fethod Standard 791 was used to test the oils. The

metals used were those called out by KIL-L-8l"^J-6 except for

the aluminum which was used in place of a mild carbon steel.

The test time and temperature were also those required by

r'"IL-L-."l 8^-1-6 which is significantly greater than that called

out by the ifII-L-83176 specification.

There is a significant difference between the >( 119 and

the KG 80 oil in the of change in viscosity with the

TG 80 shov/ing considerable increase in viscosity. A similar

situation exists with acid number indicating a great

advantage in oxidation resistance for the I'/C 119.

Although no tests were conducted on the MB 20P it has

obvious advantages over the "C 19 and ¥S. 75 based on the

r.'IL-L-8l8^6 requirements.

TPIIN YIW STABILITY AND VOLATILITY

Typical instrument bearing applications require extremely

minute quantities of lubricant so that high bearing

surface area to lubricant volume ratios exist for the

entire life or maintenance cycle of the bearing. Thin film

properties can be quite different from those of the bulk

properties of a lubricant.

In the thin film stability test required by rt'IL-L-818'^6 , a 0.35 gram sample of the test oil is placed in a stainless

steel planchet (5 cm. diameter and 1 cm. deep). The

planchets containing the lubricants are then held in a

thermostated , gravity convection oven maintained at 350 1

for Sj- hours. The weight loss and final appearance of

the oil is noted.

351
The results of the thin f\lm stability and "bulk evaporation

tests are shov/n in Tables V and V7 . Tt appears that '^O has an advanta'-':^e over [.(, 119 for the

volatility portion of this test alt;iou.^,h ;.'C 119 has a

sli.^ht ed,r:e in flow.

Axrain the 'T' ?0H shows excellent resistance to chaa^e as

indicated ty its free flowing abilit-y ever; after having

lost '^(A of its weight due to evaporation. It should he

noted that the t e.-operature control was not held to the

requirements of r/JL-I-^'lP^c-, althou'ih relative comparisons

of the results are valid since the tests were all conducted

at the sare tin'^e.

PCUH-?.ALL WEAR

'^our hall v;ear tests are most frequently conducted usinp;

standard 5?iOC steel ball specimens. It should be noted,

hov/ever, that the majority of instruTent bearings today

are fabricated from ^I'-iOC stainless steel. Also, stainless

steel is rruch more difficult to lubricate under boundary

conditions than is the 5-100 steel. Tour-ball wear tests

were therefore conducted usin?j both 52100 and 4A'0C

specimens. Test conditions and results of tests are shown

in Tables VJ J and VJ n

.

These results indicate slightly bettor boundary lubrication

for 52100 steel with the Kl PO v/hile the opposite is true

for ^-i^i-OC stainless steel.

A somewhat different effect is shown with the ester

luhricant. ?'he s^nqthetic hydrocarbon oils Sxhow definite

advantages under all conditions except under the high load

for the '''J-^OG specimens.

R-^ ".earing - Lubricant Life

Teariiig-lubricant operating life tests were conducted on all

but the TX 75 sam,ple. The tests were run in accordance

with A,"/!:'." Method 1)3"? 37 except that bearings having porous

phenolic retainers were used in rjlace of the ribbon type

retainers. The bearings were lubricated by the manufacturer

using the vacuum impregnation technique. Test conditions

and results are shown in Tables IX and X.

The failure criteria for these bearing tests is a torque

increase of 5 times the running torque taken one hour after

reaching test tem.perature . The test temperature is

normally stabilized after one hour of running.

352
The results of the bearin.f^ tests shov/n here do not

indicate bearin;^ lubrication superiority, of one type of

lubricant over another, in all or even the majority of

instrument bearing applications.

They do hovvever show the need for further investigation and

testin-;^ in the instrurr.ent bearing applications field.

Cf, i CLU nC

The svnthetic hyirocarbon oils as represented by those

tested in this prc^rann were shown to have excellent

properties when compared with both the "] .'.'O super-refined

petroleum oil and the highly effective IVIB 20P. ester

instrument oil. Another advantage for these oils is the

outlook for their apparent long tei:'mi availability based on

the increased demand from industrial and com.riercial markets.

353
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361
Sunoco R-4 Bearing Lubricant Life

of

MPB MO 119 and Kendall KG

Comparison

80

Results (Hrs)

Test Conditions MO 119 KG 80

Speed - 12000 RPM

Load - 1/2 lb. Radial 40.4 18.0

- 5 lb. Axial 100.0 20.0

Temp - 300OF 86.0 20.0

Bearing: MPB 100.0 20.0

SR4MCHH7 74.8 9.6

Retainer - Phenolic*

Avg 80.2 17.5

Test Cycle: 20 Hrs Running

4 Hrs Shutdown

* Vacuum Impregnated by MPB

TABLE IX

362
I

Sunoco R-4 Bearing - Lubricant Life Comparison

of

MPB M018 and Grignard MB 20B

Results (Hrs)

Test Conditions MO 18 MB 20B

Speed - 12000 RPM

Load - 1/2 lb Radial

5 lb Axial

Temp - 250OF

Bearing: MPB

SR4MCHH7

Retainer - Phenolic* Avg

Test Cycle: 20 Hrs Running

4 Hrs Shutdovm

* Vacuum Impregnated by MPB

TABLE X

140.0

57.5

150.5

60.0

190.2

119.6

9.6

12.0

16.2

6.5

13.3

11.5

363
ADVANCED STRUCTURES MAINTENANCE TECHNOLOGY

Nikolaos (Nick) Caravasos

Advanced Composites Technology

Boeing Vertol Company

Philadelphia, Pennsylvania 19142

Abstract: The use of composites in aircraft structures

has been increasingly evident in the last decade as the

drive for lower cost, lighter weight, more reliable aircraft structure has intensified. Composite structural

systems are meeting these challenges and their use is

being accepted and is expected to expand in the future.

New hybrid constructions where materials such as graphite are integrally fabricated with fiberglass or Kevlar

designs to control stiffness and provide fail safety

while maintaining high strength to weight ratio will

require unique repair and quality control methods.

This paper (a) summarizes the state-of-the-art in structural repair and maintenance of advanced composite structures, (b) identifies technological gaps, and (c) outlines a development and test program to fill in these

technological gaps

.

Key words: Composite materials; Maintenance; Repairability; Sandwich structure; Laminate

structure. Testing

List of Abbreviations

FRB - Fiberglass Rotor Blade

Gl/Ep - Fiberglass/Epoxy

Gr/Ep - Graphite/Epoxy

Gr/Kev/Ep - Graphite-Kevlar/Epoxy

HFT - Honeycomb Fiber Truss

Kev/Ep - Kevlar/Epoxy

RT - Room Temperature

Ti - Titanium

RH - Relative Humidity

364
Introduction: Boeing Vertol Company engineers and manufacturing personnel have been engaged in advancing the

state-of-the-art in composite structures applications

since the first helicopter fiberglass fuselage section was

fabricated in 1956. Repair of composite structures has

been a primary consideration on fiberglass rotor blades

for the CH-46 and CH-47 helicopters. Figures 1 and 2. It

included step-by-step repair procedures, validation of

repairs through testing and inspection as well as formulating training programs for field repair.

Composite structures will constantly be subjected to the

same 'real world' heavy handed use, enemy threat levels

and inexperienced personnel as the systems they will replace. As such, they will become damaged in a multitude

of ways ranging from ballistic impact damage, to abuse by

operating personnel , to environmental effects

Repair of composite structures is, therefore, of primary

importance, as it has been on the CH-46 and CH-47 fiberglass rotor blades. Although repairs of airframe structures will generally be less critical than rotor blades,

rapid repairs in a field or "on aircraft" environment

along with simplification of repair procedures and equipment must be emphasized.

A number of repair problems have been solved in the current uses of composites; however, numerous problems are

still unresolved. As new hybrid materials are used more

and more in structural applications, a great need arises

not only in designing such structures to meet the design

requirements, but also in maintaining them in the field.

Field repair adaptability on the aircraft using aircraft

power sources will provide greater aircraft utilization,

and less maintenance man-hour expenditure and less facilities cost.

Repair techniques for composites, although different from

standard metal repair methods, can be readily mastered by

basic or intermediate skill level personnel. Training requirements are not extensive or complicated. Experience

has shown that once maintenance personnel have learned the

fundamentals of (1) proper preparation of the repair area,

(2) cleanliness and (3) strict adherence to handling and

mixing of adhesives, repair of composites is a relatively

easy task for the average mechanic.

The typical resource requirements that are necessary for

performing repairs are

365
366
o Materials

o Support equipment

o Repair procedures

o Personnel skills

o Inspection

Typical materials currently in use are as follows:

Solvents, e.g., acetone or aliphatic naptha

Adhesives, e.g., EC2216, EA9309.3, EA9628

Resin, e.g., EPON 828/DTA

Sealant, e.g., Proseal 890

Fabrics, e.g., teflon/Dacron-S-1854, teflon/

fiberglass, fiberglass cloth #181 & #1500,

peel ply, scrim cloth, cured crossply

Fillers, e.g. urethane foam 2-lb/cu. ft.

density, non-metallic honeycomb core, etc.

Coatings, e.g., primer, antistatic coating,

lacquer

Typical examples of repairs were developed for both the

CH-46 and CH-47 fiberglass rotor blade repair programs and

are schematically depicted on Figures 3 through 5. Stepby-step procedures provide the mechanic with didactic examples for performing repairs such as, full core, partial

core, and skin repairs. Core repairs can also be performed using foam as a plug instead of the nomex honeycomb

core as shown on Figure 6. Foam can effectively be substituted only in small core repairs because of the loss in

structural integrity. Adaptability of such repair techniques was recently demonstrated on a Boeing 757 airplane

(SSO^F cure) wing panel section fabricated from Kevlar

skins with HFT honeycomb core. Several RT repairs were

performed including a transitioned core and skin repair,

a core replacement with 2 -pound density foam and a skin

replacement using fiberglass skin instead of Kevlar skin.

These repairs are shown on Figures 7 and 8

.

Inspection also plays an important part in maintaining

composite structures. This is due to the fact that damage

to the exterior surface of composites can cause localized

internal failure which is not readily detectable unless a

thorough inspection is made. Therefore, whenever cracks,

dents, tears, punctures, etc., are discovered during routine scheduled inspections, a detailed follow-up inspection must be made in order to assess the damage and make

proper repairs. In addition to visual inspection, other

nondestructive test techniques may be required such as

coin-tapping and ultrasonic testing with portable equipment.

367

• C48094

Figure 7. 757 Wing Panel Repairs in Progress

C48115

Figure 8. 757 Wing Panel Completed Repairs

369
Problematic Observation: Due to recent implementation of

composites for structural applications, limited data are

available regarding advanced composite structures to adequately define repair problems both in the laminate and

sandwich form. From the information that is available

several broad observations can be drawn. First, the major

causes of failure in honeycomb sandwich designs were coreto-skin delamination caused by either faulty lay up, cleaning and cure techniques, or inadequate design with materials frequently affected by environmental conditions such

as moisture and temperature. Second, the failure of composite laminates was also due to inadequate detail designs, materials, and environmental protection systems.

In the case of honeycomb core, ingress of water into the

core cells nearest to the panel edge, or in areas of panel

cut outs and fasteners where capillary action and barometric pressure and altitude changes induce cell-to-cell

moisture migration, leads eventually to skin/core delamination failures. Complete cell boundary encapsulation in

the adhesive matrix is required to eliminate or minimize

cell-to-cell moisture migration.

Repair techniques of advanced composite airframe structures have been studied more extensively by the commercial

fixed-wing industry because of their relatively wider use

of such structures. In the rotary wing area, repair of

advanced composites has largely been limited to rotor

blades and secondary structures. Advanced composite concepts, under contract or independent research and development, are now being applied to primary fuselage applications in helicopters. Most of the work up to now has

been conceptual but firm designs are now being implemented. As advanced composites assume an increasingly

more important role in structural applications, repair

techniques of such structures will be developed and substantiated against the same operational criteria limits as

their metallic counterparts. These limits encompass extreme climactic and environmental conditions, i.e., temperatures ranging from -65°F to 160°F, prolonged high

relative humidity, and exposure to fluids such as oil,

salt water, fuel, and maintenance solvents.

The repair concepts for advanced composite structures will

have to satisfy the above limits as related to strength,

stiffness, and functional performance. The limited work

thus far completed points to several technological gaps

.

Materials such as graphite/epoxy , Kevlar/epoxy , Kevlargraphite/epoxy used in sandwich panels and laminated plate

specimens have been tested at various operational conditions. Skin patches were composed of similar thickness

370
materials with fiber orientation matching the skin fibers.

Two layers of fabric were used to replace each layer of

unidirectional tape. Representative results as shown on

Figures 9 and 10 reveal that all room temperature curing

systems tend to lose strength at temperature (i.e. > 180 **F)

which is why they haven't been used for loaded primary

structure. The prepreg patch applied at 350°F in an autoclave retained its strength throughout the range of temperature testing. Conditioned RT repair specimens (conditioned usually for 30 days at 140*'F/100% RH) performed

equally as well at -65 °F and at RT as the nonconditioned

specimens while similarly experiencing loss of strength

at 180 °F. It appears from this set of data that the high

temperature exposure of RT cured patches produces reduced

strength and therefore, this consideration must be given

to repairs of highly loaded structures. Additionally,

the critical temperature for serviceability of RT cured

patches is further reduced by exposure to a combination

of hot and humid environmental conditions. The loss of

strength characteristic at high temperatures does not

prevent the effective use of RT repairs as evidenced by

the excellent results demonstrated in the FRB program.

However the repair criteria (depth, extent, etc.) must

recognize the effect, especially for highly loaded

structures

.

110 r

SANDWICH FLEXURE TEST nnta cowpmow

NORMAL ROOM TEMPERATURE DRY

120

RErAW COMOmONt o KEVLAR/EPOXr ZSO'F AUTOCLAVE

A KEVLAR CLOTH ROOM TEMPERATURE

CURE

40 -

to -

SANDWKN FLEXURE TEST

EXPOSED COHOmON

NORMAL ROOM HMPERATURE ORT

REPARI CONOmONI o KEVLAR/EPOXY tSO'F AUTOCLAVE

A KEVLAR CLOTH ROOM TEMPERATURE CURE

-OS 0 70 TEMPERATURE ("F) KEVLAR/Epoxy

ISO J

-OB 0 70 1SS TEMPERATURE ('F) KEVLAR - Graphite/Epoxy

Figure 9. 250°F Cure Specimens

371
372
Technological gaps: A summary of tests compiled from published data is shown in Table 1. One can see from this

long list of available data that all tests were performed

on either sandwich or laminate specimens which constitute

aircraft skins. Very little or no work at all has been

performed on frame sections or structural fitting applications. Additionally, other areas of interest where

little or no work at all has been performed are;

A - Sandwich Panels

1) Primary Structure Construction

a) Use of HFT core

b) Use of foam instead of core

c) Use of adhesive bonding

2 ) Repair components

a) precure skin patches

b) HFT core

c) Nomex core

d) Polyurethane foam

3 ) Testing

a) high temperature exposure/testing

b) high humidity exposure

B - Laminates

1 ) Primary Structure Construction

a ) Kev/Ep

b ) Gr/Kev/Ep

c) adhesive bonding

2 ) Repair Concepts

a ) Kev/Ep

b ) Gr/Ep

3) Testing

a) Prior exposure

b ) High/Low temperature tests

After thoroughly examining the data, a specimen matrix was

constructed. Table 2 representing typical specimens of advanced composite materials for aircraft application. The

asterisk (*) areas signify that sufficient test data are

available to conclusively determine damage/repair limitations. The existing data, although thorough, are limited

only to laminate and sandwich coupons. The difficulty

arises in that no frame sections nor structural fittings

have been tested. These are common structural aircraft

applications which would require more complex repair techniques.

It is evident that further development is required to

broaden and/or improve the repair limits of advanced composites, especially in high temperature/high humidity environments. Room temperature cure repairs when subjected

to high temperatures produced strength results that were

373
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* o * o o o * o o o o o o o o o o

saivd3U aod Aiiavwiad aasn 3a niM

saivd3a aod Aiiavwiad Q3sn 3a tiim

X- 0 * o

O 0 o o o o

saivd3a aod Aiiavwiad aasn 3a niM o * o O * 0 c o o o o o

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375
generally lower than 100 percent of baseline strength. A

number of tests under this condition showed as much as 50

per cent loss of strength.

Approach to solution: Further testing is recommended in

several areas, such as, (1) cold bonding repairs - sandwich

panels of glass and Kevlar and hybrids varying temperature

and test conditions to evaluate other repair materials/

adhesives, (2) hot bonding repairs - panels with varying

temperature and test conditions to evaluate repair materials/ adhesives, (3) core repairs - to determine correct

foam density and flexure tests for core replacement, (4)

structural fittings - fabricated from sandwich/laminate

and laminate/laminate both attached with mechanical fasteners, and (5) frames - from several materials.

A typical preliminary test plan outline is offered for

conducting the necessary laboratory investigations:

a) fabrication of representative structural elements

b) structural integrity tests to determine baseline strength

c) simulate damage

d) application of damage assessment techniques

e) repair

f) retest

Specifically:

a) Fabrication - A sufficient number of specimens

should be fabricated to represent the spectrum

of various types of structural specimens.

b) Structural Integrity Tests - Specimens representative of skins, frames, longerons and structural fittings should be tested to determine

their undamaged structural capabilities at

various environmental conditions

.

c) Simulated Damage

(1) damage from the structural integrity tests

(2) simulated operational damage, normal "wear

and tear", environmental damage

(3) simulated and/or actual ballistic damage

376
d) Damage Assessment - Damage assessment techniques

should be applied to evaluate the severity of

the damage and to permit preparation of inspection manuals.

e) Repair - each specimen, if repairable, should be

repaired. The procedure should be documented

for each type of. specimen.

f ) Retest - The specimens should be retested as per

b) above to determine the quality and integrity

of the repair.

g) Documentation - satisfactory repair methods

should be documented, suitable for operational

repair manuals.

Summary: Structural repair methods, materials, and techniques have been developed for field level repairs using

cold bond (room temperature) cures. These room temperature cures, although demonstrated to be adequate in normal

temperature and humidity environments, lost as much as 50

percent of their baseline strength when tested at elevated

temperatures and high humidity conditions . Secondary

structure and rotor blade fairing repairs using room temperature cures are acceptable for the allowed (lightly

loaded) repair areas. High temperatures weakened the bonding adhesive in the repaired area resulting in premature

shearing of both laminate and sandwich panels. The 350°F

autoclave repair method proved to be the most effective at

high temperature conditions

.

Hybrid constructions of materials such as graphite reinforced fiberglass or Kevlar designs to control stiffness

while providing high strength to weight ratio will require

unique repair and quality control methods. Aircraft structural areas such as frames and mechanically fastened joints

require development to define repair methods and procedures. The approach presented is one way, and by no means

the only way, of advancing the state-of-the-art in advanced composite repairs both to broaden the existing base as

well as to begin exploring new aircraft concepts and applications as the use of hybrid materials widens.

377
REFERENCES

1. Horton, Ray, "Investigation of Repair Procedures for

Graphite-Epoxy Structure" presented at the Naval Air

Systems Command Workshop on Shipboard Repair of Composite Structure and Material, Salt Lake City, Utah

9-11 September 1980.

2. Caravasos, Nikolaos, "CH-46 Fiberglass Rotor Blade

Repair Program" presented at the American Helicopter

Society, Mideast Region, National Specialists' Meeting on Rotor System Design, Philadelphia, PA. , 22-24

October 1980.

3. Technical Manual NAVAIR 01-250HDA-2-4. 5 "Fiberglass

Rotor Blade" Naval Air Systems Command, Washington,

DC, 15 September 1979.

4. Caravasos, N. , and Donnelly, J. P. "CH-47 Fiberglass Rotor Blade Repair Criteria Development and

Validation Program" Boeing Vertol Report Number

D210-11728-1 and -2, February 1981.

5. Tuttle, M. M. , "Design Properties for Graphite-Kevlar

Advanced Hybrid Composite 767 Engine Cowl" Boeing

Document Number D314T103.

378
DESIGN GUIDELINES FOR AVIONIC

CORROSION PREVENTION AND CONTROL

Albert F. Carrato

George E. DeLong

Resource Management Systems

1250 Sixth Avenue, Suite 300

San Diego, California 92101

Irv S. Shaffer

Naval Air Development Center

Warminster, Pennsylvania 18974

Abstract: There is evidence that moisture intrusion currently is the

largest single cause of Navy avionic (airborne electronic) equipment

becoming non-operational while installed in carrier aircraft. The basis

of this failure mode includes not only the general severity of the naval

marine environment, but particularly the intrusiveness of the chlorideion laden moisture that permeates the interior of the aircraft — including entering equipment housings, connectors and almost all areas generally considered to be "protected." Equipment designed for optimum

electrical performance during the time it is operating can be particularly vulnerable to corrosion during the other 95% of the time when it

is in a static, non-operating condition. Fundamental to the continuing

nature of the design characteristics that permit such equipment deterioration is the lack of feedback information on fleet failure modes to

the original equipment designer. Seldom is the original design engineer

appraised of the design- induced problems he had created several years

previously. Understandably, therefore, he incorporates the same design

characteristics in his following assignments.

Key words: Avionic component design; avionic corrosion damage; corro- sion damage; equipment design failures; marine environmental factors;

moisture intrusion in avionic equipment.

1. INTRODUCTION

Avionic equipment comprises the very heart of the remarkable sophisticated capabilities designed into the current U.S. Navy combat aircraft.

Consistently, however, the reliability of such avionic equipment, when

deployed in fleet service, is significantly below that predicted during the design and contractual demonstration phases. Military Specifications, Military Standards and Military Handbooks describe the design

characteristics of various components that are to be used in new avionic

379
equipment. There are laboratory tests designed to demonstrate the capability of the assembled equipment to meet prescribed requirements relative to shock, vibration, salt spray, temperature electromagnetic interference and other characteristics that can be quantified and objectively

measured. These design and test requirements, however, have not been

adequate to preclude the recurring and ever-increasingly costly failures

when avionic equipment is operated and maintained in the U.S. Navy's

fleet environment.

There is evidence that the major unforeseen avionic equipment failure

mode in this fleet environment is corrosion. While the "real world"

fleet environmental factors are difficult-to-impossible to duplicate in

the laboratory, it is possible to minimize avionic equipment susceptibility through enlightened design once the factors are recognized and

understood. There are many design decisions to be made in the development of new avionic equipment that are not constrained by Military

Specifications. An understanding of the characteristics of the fleet

environment which, heretofore, has not been known by the design engineer, can permit consideration of such degrading factors and provide the

basis for enhanced life-cycle reliability.

The fundamental source of corrosion problems in avionic equipment is due

to moisture and fluid intrusion throughout naval aircraft, especially

those operating in the harsh marine environment aboard aircraft carriers

and low- freeboard destroyers. The moisture and fluid intrusion, coupled

with widely varying conditions involving temperature and pressure cycling, humidity, dust and dirt, industrial pollutants in the atmosphere,

salt air, and stack (combustion) gases, are environmental conditions

that have not been adequately recognized in avionic system and equipment

design.

The degree of corrosion damage caused by moisture and fluid intrusion is

compounded by five "real world" factors. The first factor is the prolific use of galvanic couples in circuitry, interfacing wire harnesses,

equipment enclosures, ground and bonding junctions, and hardware mounting. The second factor is that airframe environmental integrity is an assumption rather than a fact. Recent studies by the Navy, on-site

investigations at the user level, and quantitative maintenance data show

a significant number of avionic systems and equipment failures are a direct result of moisture and fluid intrusion caused by poor environmental integrity of the airframe. The third factor is equipment environmental integrity. Equipment enclosures are not designed to withstand

the lack of airframe environmental integrity and the results are disastrous to the contained circuitry. The fourth factor is the lack of

consideration for the impact of the operational and maintenance environment on equipment design. Avionic systems and equipment are designed

for optimum performance during in-flight conditions with little con- sideration for the fact that most equipment spends 95% of the time in a static, non-operating condition. It is during the ground maintenance

time that the installed avionic system experiences a major impact from

380
moisture and fluid intrusion and, subsequently, corrosion damage. Any

maintenance man can attest to the problems encountered during the maintenance cycle, but design engineers do not recognize the existance and

the impact of these conditions during the design phase. The last, and

probably the most important, factor is the lack of feedback information

on failure modes to an equipment design engineer. Even when an engineer

previously has designed similar equipment he is seldom aware of the

failure modes experienced by his earlier equipment when deployed in the

fleet environment. In most cases corrective action is performed by

other activities, or a different group within the original contractor's

organization. Since the original design engineer is not appraised of

the design- induced problems, years later he perpetuates a faulty design.

When an original designer cannot get viable feedback on his own design,

what chance is there to get useful data on design weaknesses in similar

equipment, but designed by other contractors?

2. GALVANIC COUPLES

The design of modern avionic systems and equipment includes a wide proliferation of metals not normally considered for use in airframe structures. Some of the rarer metals are found in the discrete circuit com- ponents such as those used in the manufacture and assembly of miniature

and microminiature, integrated, and hybrid circuits. Gold is traditionally considered the best coating for corrosion resistance and solderability and silver is commonly used as a protective coating where conductivity is a requirement. Magnesium is used in applications requiring

low weight-to-strength ratios. The more common metals, such as iron,

steel, aluminum, copper, etc., are, of course, the mainstays in avionic

equipment designs. The following is a brief list of the metals and

their uses in avionic equipment:

a. Gold is common in electrical connector pins, edge connectors,

leaf- type relays, miniature coaxial connectors, printed circuit board

runs, semi-conductor leads, and microminiature and hybrid circuits.

b. Silver is commonly used as a protective coating on relay contacts,

waveguides, wire, high frequency cavities, tank circuits, RF shields and

RF gaskets.

c. Magnesium alloys find high use for antenna dishes and lightweight

structures such as hardware, chassis, supports and frames.

d. Iron and steel (ferrous alloys) are used as component leads, magnetic shields, transformers, brackets, racks and general hardware.

e. Aluminum and aluminum alloys are widely used as equipment housings, chassis, mounting racks, supports, frames and electrical connector

shells

f. Copper and copper-based alloys are generally used as the base

metal in edge connectors, contacts, springs, leads, connectors, printed

381
circuit boards and wire.

g. Cadmium is used to coat ferrous hardware, such as bolts, washers,

screws and electrical connectors that come in contact with other metals.

h. Nickel and tin-plating are used for protective coatings and for

compatibility purposes. Tin is widely used in solder and tin-plating is common in RF shields, filters, small enclosures and automatic switching

devices

.

These metals, common and exotic, combine to form literally thoiasands of

galvanic couples, or cells, within a complex avionic environment. It is

obvious that the potential for galvanic corrosion is an inherent design

characteristic. Exposing these galvanic couples to the assumed "normal"

environment wherein there is seldom a significant amount of electrolyte

(chloride-ion laden moisture) present would not cause a major problem,

but when the unpredicted element of moisture and fluid intrusion enters,

created by maintenance and/ or flight requirements and poor airframe

environmental integrity, the results are disastrous. A good example is

the use of gold plating. When an excessively thin (porous) layer of

gold plating is placed directly on a ferrous substrate, in the presence

of an electrolyte, corrosion always is the result!

3. AIRFRAME ENVIRONMENTAL INTEGRITY

Given the high use of dissimilar metals in the design of avionic equipment, an assumption by the avionic design engineer — based upon an interpretation of a Military Standard that the airframe environmental

integrity will continuously protect the avionic equipment — is critical

to the reliability and maintainability of avionic equipment design.

Unfortunately, however, on high speed carrier aircraft and helicopters

there is no such thing as a watertight airframe. The high degree of

flexure of the airframe precludes effective sealing of equipment bay

doors, access panels, doors, steps, canopies, windows, vents, ducts,

static pressure sensors, and other fuselage openings. The "form-inplace" seals and gaskets have not been designed that will withstand this

in-flight flexure. In the case of helicopters, there has never been an airframe built (to date) that does not have water intrusion as a primary

problem in the fleet environment. Naval aircraft are generally susceptible to moisture and fluid intrusion originating from the following

sources

a. Rainstorms

b. Water washdown systems

c. Hand washing evolutions

d. Salt water inundation

e. Environmental control systems

f. Hydraulic, fuel, engine oil, anti-icing, and coolant line leaks

g. Condensation from cyclic temperature and pressure variation

h. Low- level over-water flight

382
i. Emergency firefighting materials

j. Solvents, detergents, strippers and other cleaning materials.

The avionic system in a modern aircraft is not a series of isolated

"black boxes" sealed against the environment. There are many components,

relays, terminal boards, circuit breaker panels, switches, antennas,

lights and other hardware that make up a complete avionic system. A

sophisticated aircraft contains miles of electrical wire, extensive co- axial cables, hard lines, waveguides, and hundreds of electrical connectors. That same aircraft contains hydraulic lines, oil lines, fuel

lines, cooling air ducts, flight control linkages, and control rods.

When water penetrates the airframe these lines and cables become "moisture and fluid conduits" that carry the insidious electrolyte directly

to the avionic equipment and components. A simple hydraulic line can direct water many feet through the airframe and deposit the water on equipment and components that are assumed to be in a protected area of

the airframe. A wire bundle can carry moisture or water directly into

the back of an electrical connector, through the connector and into the

avionic equipment housing. Just as moisture and fluid intrusion and

moisture conduits are inherent in aircraft design, there is another

problem of water-traps. Moisture, water and fluids pool in water-traps

or "bathtub" areas and are especially damaging to avionic equipment installed in these areas. The bilge area of the airframe is particularly

susceptible to this condition, and it is in this area where cable runs,

wire bundles, coaxial cables, lights and antennas are installed. It is

almost impossible to seal the equipment and components in this area against moisture and fluid intrusion because of requirements for maintenance access. Thus, it is these components that are exposed to the

"bathtub" areas where corrosion is particularly evident. Even though

the bilge is a rather obvious problem area, there are other areas of

concern, such as structural stringers, ribs, bulkheads, shelving, etc.

4. EQUIPMENT ENVIRONMENTAL INTEGRITY

Avionic equipment must be designed with consideration for the presence

of moisture and fluids. The environmental integrity of the equipment

enclosure must be evaluated in relation to the ultimate installation in

the airframe with consideration for cooling air, weight, space, etc.

Long ago pressurized equipment was identified as too heavy, but it is

the only equipment design that has displayed the ability to withstand

the marine environment. Recent investigations of U.S. Navy front-line

aircraft show the following equipment design deficiencies are common:

a. Equipment lids that contain holes for cooling air. These holes

become sources for moisture intrusion.

b. Screws and hardware that are installed in dimpled or countersunk

areas on top of equipment lids. These areas become water-traps and sources for moisture intrusion.

383
c. Drain holes installed in the bottom of avionic equipment housings.

These drain holes become a problem when the equipment stands in watertrap or bathtub areas. There are also cases where equipment later is

mounted in some other type of airframe with the drain holes now facing

up, creating an obvious problem.

d. The use of foam material in the lids of equipment that reverts as a result of a combination of temperature, pressure and moisture intrusion.

e. The use of foam in the lid of equipment designed to hold down circuit cards where the top of the circuit card contains electrical "test

points." This practice becomes a problem when the foam acts as a sponge, holding moisture which results in corrosion across the "test

points," and creates short circuit conditions.

f. The use of wire-wrap "mother" boards mounted in the bottom of avionic equipment containing drain holes. When moisture is present the

result is corrosion on the wire-wrap "mother" board. This creates a problem in that it is essentially impossible to clean or remove corro- sion from wire wrap.

g. Equipment designs where one element in the equipment requires

barometric pressure, yet the whole equipment is exposed to the ambient

environment

.

h. Electrical connectors mounted vertically, vice horizontally, on equipment housings.

i. The use of direct-air cooling systems where air is channeled directly onto active electronic components and circuit cards. This is a high source of direct water intrusion, especially where salt-laden ram

air is channeled from outside the aircraft for emergency cooling purposes .

j. The use of conductive gaskets impregnated with silver, gold or graphite as lid and enclosure environmental seals. These gaskets create

gross galvanic corrosion when they are in contact with the aluminum

enclosure surfaces.

The steps taken to solve the problems of poor equipment and airframe

environmental integrity could be considered comical, were it not for the

immensity of the problem. Modern aircraft now have curtains installed

in airframe and cockpit areas designed to shunt water around equipment

and control boxes. Drip pans and drain lines are installed to catch

water that would otherwise inundate equipment. RTV (Room Temperature

Vulcanizing) sealants, which are highly susceptible to hydraulic fluid

and coolant fluid, are being used to seal electrical connector back

shells and equipment housings against moisture. Last, but not least, numerous drain holes are being placed in airframe structures, radomes.

384
antenna housings, etc., in order to drain water. Unfortunately, they

become sources of moisture entry during water washdowns, splashing from

wet runways, etc.

This paints a grim picture for the design engineer, but, unfortunately,

there is still more to consider.

5. OPERATIONAL AND MAINTENANCE ENVIRONMENT

The operational and maintenance environment has a number of characteristics which should be recognized in the design of avionic equipment.

Military Specifications (and other design specifications and standards)

imposed on the avionic design engineer dictate that avionic equipment

perform at its optimum during in-flight conditions. The problem with

this premise is that avionic equipment spends approximately 95% of the

time in a static, non-operating condition. Most U.S. Navy front-line

combat aircraft average between one-to-two hours per day in flight and

the remainder of the time in maintenance or a static condition. In some

cases an aircraft may be non-operational for many weeks while awaiting

parts. During these periods the aircraft may be "unbuttoned" to facilitate maintenance; canopies, radomes, equipment bays, doors, etc., opened

and avionic equipment removed. This results in electrical connectors,

wire bundles, equipment racks, control boxes, circuit breaker panels,

relays, antennas, and the multitude of other avionic components in the

aircraft being exposed to salt air, moisture, stack and industrial gases, dirt, dust, and other environmental factors that cause corrosion

damage in the equipment. This is a "real world" condition that constitutes the vast majority of the operational and maintenance environment.

It is not adequately recognized by design specification, testing re- quirements or avionic system and equipment design engineers.

The following are some examples of the operational and maintenance en- vironment that require consideration by the design engineer:

a. During fresh water washdown the high pressure water washdown system deluges the aircraft with tremendous amounts of water, from all

directions, in a very short period of time. Clamshell doors on helicopters and equipment bay doors on fixed wing aircraft leak like sieves

when gaskets become worn or damaged. Exhaust fan inlet and ram air

cooling ducts, vapor exhaust ports, cockpit canopies, even the simple

molded step (helicopters) that are designed without a self-sealing

mechanism, become entry areas for water intrusion. The external bulkhead electrical connectors, external wire and cable runs, antennas,

control linkages and other such areas where the shell of the fuselage is

penetrated are potential points for water intrusion.

b. Rainstorms create a similar water intrusion problem and, as stated

previously, the flexure of the airframe essentially ensures water intrusion around access panels and doors. Of course, water intrusion is

especially severe to avionic equipment and components mounted external

385
to the airframe, such as: electronic countermeasure pods, photographic

pods, refueling stores, bomb and missile racks, lights, antennas, and

wheel well areas

.

c. Environmental control systems add another facet to the overall

problem of moisture and fluid intrusion in the maintenance environment.

During flight (a relatively small part of the life of the equipment),

the avionic equipment is protected by the dry conditioned air provided

by the environmental control system. This is not the case during the

time the equipment spends on the flight-line or flight deck, however.

Here the equipment is exposed for a much longer period of time to a com- pletely different and harsher environment. In those instances where

environmental cooling is required for ground operation and ground cooling units are available, the environmental cooling system may, in fact,

induce moisture by the introduction of cool air directly into the warm

humid area of the avionic equipment, thus causing condensation.

d. Leaks in hydraulic lines, fuel lines, coolant lines and oil lines

are other common sources of fluid intrusion in avionic equipment. Each

of these fluids has the potential for adverse reaction with various or- ganic materials in the aircraft. Some fluids may, for example, attack

the adhesion of protective organic finishes, soften potting compounds, cause undue seal and gasket swelling, or attack wire and coaxial cable

insulation. Damage to these organic materials generally results in

increased susceptibility to corrosion.

e. The storage and transportation of avionic equipment between supply

facilities, work spaces and the flight-line or flight deck is continually suspect. Depending on the locality, the equipment can be exposed

to very harsh environmental conditions . It is not uncommon to find so- phisticated avionic equipment temporarily stored behind the "island" on

a carrier flight deck where it is exposed to salt air, stack gases, etc.

On carriers and "LAMPS" destroyers, avionic equipment is stored on the

hanger deck where it is constantly exposed to moisture laden salt air.

Occasionally, equipment on the hanger deck is exposed to sloshing water

that can occur during operations in rainstorms, high winds and high

seas

.

f. Maintenance publications intended to support specific equipment

seldom recognize the potential corrosion problem, and essentially never

call out the proper use of the best anti-corrosion materials. The "flyto-failure" maintenance philosophy applied to most avionic equipment

limits maintenance as a practical means to compensate for inadequate

corrosion resistant design.

6. EFFECTS OF CORROSION ON AVIONIC COMPONENTS

Corrosion attack on the various elements that make up the total avionic

systems costs millions of dollars worth of maintenance manhours and re- placement parts, plus a reduction of aircraft system availability.

386
Table 1 summarizes the effects of corrosion on avionic components. The

following discussion is intended to highlight the specific design problems that cause corrosion damage in present day avionic systems, equipments and components

.

Automatic direction finder, doppler and numerous blade antennas are usually mounted in bilge areas. Water becomes entrapped in the bilges

by stringers causing water "pools" to form around antenna coax leads.

This entrapped water penetrates through to the antenna base/ fuselage

skin interface and sets up a corrosive condition with the antenna gasket, antenna housing and aircraft skin. Fiber gaskets act as sponges,

holding moisture between the antenna and skin. Much worse, though, are the conductive gaskets impregnated with graphite, silver or copper.

These gaskets, placed between bare aluminum skin and the aluminxam antenna to enhance conductivity, create a galvanic corrosion condition that

not only precludes the enhanced conductivity, but causes the antenna to

require frequent replacement. Antenna electrical connectors and coaxial

connectors in the bilge areas are corrosion prone because of the continual presence of entrapped water. In addition, access to interior con- nections of many blade and flush-mounted belly antennas for the purpose

of inspection or corrosion control is not feasible. Radomes in the

lower fuselage or nose section are a major problem. The inadequate use of sealants, poor gasket design and drain holes allow the intrusion of

the corrosive environment. Where metal-to-metal contact is present,

especially if a bimetallic condition exists, the contacting parts are highly corrosion-prone. Mounting hardware, including screws, nuts,

bolts, etc., on antennas in radomes and on the lower fuselage is an example of this problem.

Considering the large number of electrical connectors in a modern avionic system, the connector corrosion problems are "mind-boggling."

Since fluid intrusion frequently allows moisture to be present in a con- nector, it is evident the state-of-the-art electrical connectors are not

really "environmentally sealed." The following electrical and coaxial

connector corrosion problems are considered commonplace in naval aircraft :

a. Electrical connectors that are externally mounted in the air

stream are degraded by erosion of the external protective coatings with

subsequent corrosion of the base metal.

b. Electrical and coaxial connectors mounted horizontally are susceptible to water intrusion through the rear section when attaching cables

do not contain a "drip loop."

c. Bayonet-type electrical and coaxial connectors mounted vertically

are susceptible to degradation due to fluid entrapment around the base

of the connector from standing water and/or hydraulic fluid.

d. Externally mounted electrical connectors hidden by fairing covers

387
Table 1, Effects of Corrosion on Avionic Components

COMPONENT FAILURE MODE

ANTENNA SYSTEMS

CHASSIS, HOUSINGS, COVERS,

AND MOUNTING FRAMES

SHOCK MOUNTS AND SUPPORTS

CONTROL BOX MECHANICAL AND

ELECTRICAL TUNING LINKAGE

WATER TRAPS

RELAYS AND SWITCHES

PLUGS, CONNECTORS, JACKS

AND RECEPTACLES

MULT I -PIN CABLE CONNECTORS

POWER CABLES

DISPLAY LAMPS AND WING

LIGHTS

WAVEGUIDES

RADAR PLUMBING JOINTS

PRINTED CIRCUITS AND

MICROMINIATURE CIRCUITS

BATTERIES

BUS BARS

COAXIAL LINES

Shorts or changes in circuit constants

and structural deterioration.

Contamination, pitting, loss of finish

and structural deterioration.

Deterioration/ loss of shock effectiveness . Intermittent operation and faulty frequency selection.

Structural deterioration.

Mechanical failure, shorts, intermittent

operation and reduced system reliability.

Shorts, increased resistance, intermittent operation and reduced system reliability.

Shorts, increased resistance, intermittent operation and water seal deterioration.

Disintegration of insulation and wire/

connector deterioration.

Intermittent operation, mechanical and

electrical failures.

Loss of moisture integrity, pitting, loss

of efficiency and structural deterioration.

Failure of gaskets, pitting and power

loss

.

Shorts, increased resistance, component

and system failures.

High resistance and failure of terminals,

and structural deterioration of mounting.

Structural and electrical failures.

Impedance fluctuations, loss of signal

and structural deterioration of connectors .

388
are prone to extensive corrosion damage because they are not visible for

routine inspection and, therefore, timely corrective action.

e. Vertically mounted external electrical connectors on the upper

fuselage transmission area of helicopters are susceptible to water en- trapment at the base and rear of the connectors.

f. Supposedly environmentally sealed connectors on the engine, transmission, constant speed drive and hydraulic compartments are subject to

damage of the environmental seal by hydraulic fluid, fuel and cleaning

solutions. Numerous connectors in these areas are potted to eliminate

this problem.

g. High density environmental electrical connectors are subject to

seal damage and loss of integrity when maintenance personnel replace

pins with pin insertion and removal tools.

Although definitive maintenance failure documentation has not been

available in the Navy Maintenance Data Collection System (MDCS) to support this allegation, it appears that a consensus of avionic maintenance

engineers and technicians are beginning to support the thesis that a large percentage of in-flight avionic discrepancies are attributable to

moisture in electrical connectors. Over the past 20 years a high rate

of anomalies, such as the "no-defect" and "phantom gripe," have occurred

in the complex avionic systems or equipment. These anomalies ultimately

have become an accepted "norm" in the troubleshooting and maintenance of

the equipment. It is a common experience to find that the "in-flight

reported" discrepancies disappear when the electrical connectors are parted and then remated during troubleshooting. Since nothing is actually seen when the connector is parted, a "no-defect" is entered in the

maintenance documentation. In reality, there was a discrepancy (defect)

caused by moisture, cleanable film, or a small amount of corrosion that was displaced during the parting and remating of the electrical connector. Although this anomaly has long been related to wire bundle electrical connectors and antenna coaxial connectors, it has recently been

identified as a major problem on circuit card "edge connectors" within

avionic equipment. A recent study of a sophisticated radar system

(installed in a U.S. Navy fighter aircraft) indicates that approximately

50% of all in-flight discrepancies associated with the radar equipment

are directly related to moisture and corrosion deposits on the circuit

card edge connectors. In such cases the maintenance technician reseats

the circuit card edge connectors prior to bench testing the specific

equipment in question. This action eliminates over one-half of the

reported discrepancies, as verified by the bench test. Unfortunately,

neither the identification of the true problem, nor a preventive action

to preclude reoccurrence, takes place in such a situation.

Wire bundles and coaxial cables are another problem area that can be

categorized. As previously mentioned, a wire bundle or a coaxial cable,

depending on location, can become a conduit for fluid in the airframe.

389
In addition, the wire bundles and coaxial cables are prone to a rather

unique environmental problem — certain wire coatings are hygroscopic.

It is recognized that once a wire jacket "breaks down" due to moisture,

it is susceptible to a rapid deterioration. Older helicopters show a high degree of corrosion in wire bundles behind the nose clamshell

doors. This problem is usually evidenced by the wire run turning green

under the protective coating. An associated problem is the possibility

that the wire jacket may deteriorate in the presence of the aircraft

cleaning compounds. Investigations have shown that certain types of

wire jackets are susceptible to major deterioration due to the alkalinity (high pH) of the detergents normally used to clean the aircraft.

This problem is particularly prevalent in wing fold, wheel well and

other areas exposed during aircraft cleaning evolutions. Understandably, this problem can become highly critical wherever water intrusion

occurs. It takes little imagination to envision the consequences should

a high pH solution remain in contact with an internal wire bundle for

any period of time. The following are additional corrosion problems

associated with wire bundles and coaxial cables:

a. Braided fiber wrapping for abrasion resistance on coaxial cables

acts as a wick to lead water and other fluids into associated connectors .

b. Environmental seals on electrical connectors are damaged by loads

imposed during flexing of wire bundles, permitting water intrusion past

the damaged seals.

c. The wire bundles in external stores pylons are exposed to engine

cleaning compounds, particularly on helicopters. These compounds saturate the wiring and connectors, thus damaging the integrity of the protective coatings.

d. The wire bundles and electrical connectors in the vicinity of the

engine exhaust gases are prone to accelerated corrosion damage due to

heat and additional elements such as sulfur that are contained in the

exhaust gas.

e. On helicopters, the cargo hook controller and rotor blade wire

bundles, with their associated electrical connectors, are in a highly

corrosive environment.

Cockpit and cabin areas exposed to moisture intrusion through open cano- pies, cabin doors and windows. Most control boxes are susceptible to

corrosion damage internally, especially those exposed to direct water

impingement. In addition, the back of instrument panels are normally

hidden from view. The numerous bimetallic couples and difficulty of inspection result in considerable corrosion damage. In the case of helicopters, the emergency ram air cooling ducts create an additional corro- sion problem on the back of instrument panels. All aircraft consoles

use dissimilar metals fasteners, screws and nut blocks to secure instru390
merits, thus creating galvanic couples.

Circuit breakers, relay racks and terminal boards also are prone to cor- rosion due to the dissimilar metals construction and exposure to moisture intrusion. Circuit breaker panels mounted in the overhead of helicopters are especially susceptible to water intrusion. Water enters

through skin seams, windscreen edges and through upper fuselage skin

penetrations for actuators, cables, etc. The water migrates onto the

back of the circuit breaker panels via cable conduits and initiates the

corrosion process with little chance of visual detection until it is too

late.

Radar waveguides, couples and joints are susceptible to corrosion damage

due to moisture intrusion and dissimilar metals couples. As previously

discussed, the waveguide is a natural fluid conduit. When water runs along a waveguide it causes corrosive attack at the waveguide couples

and joints, and without good preventive measures, may enter the waveguide flange causing serious degradation of the signal. The pressurized

waveguide appears to be the best design to preclude these problems be- cause a pressurization loss is an immediate warning of loss of integri-^

ty.

Avionic equipment shock mounts, racks and associated hardware are normally constructed of dissimilar metals and are relatively inaccessible for

inspection and timely corrosion control. Associated with this problem

is the grounding strap, which normally is used to bond the rack, shock

mount, or an actual piece of equipment electrically to the airframe.

The washers, screws and grounding straps usually create a dissimilar

metals or galvanic couple. The slightest amount of corrosion at any

point of mating (where dissimilar metals come in contact) can cause electromagnetic interference (EMI) . This problem is especially critical

in the more sophisticated avionic systems found in modern aircraft.

Lighting system failures due to corrosion run high during shipboard

operations where the light and its associated plug are susceptible to

the harsh salt-air environment. The slightest moisture intrusion cre- ates a corrosion product between the bayonet-type bulb base and socket,

creating a loss of electrical contact (or ground) . This problem is prevalent in all external light systems, such as wing lights, formation

lights, approach lights, etc.

7. DESIGN FEEDBACK ENHANCEMENT

From the standpoint of the avionic design engineer, there is a real

problem of determining what features of his new design might be a source of corrosion problems. Obviously, designing equipment to the present

available Military Specifications and testing based on laboratory situations vice the "real world" environment discussed here are not adequate

to ensure the newly designed equipment will be capable of existing in

the environment in which it must function.

391
Feedback appears to be the missing link. A program intended to produce

design guidelines relative to the marine environment for the avionic

design engineer presently is being conducted by Naval Material Command

and Naval Air Systems Command. This program is sponsored by Mr. A. J.

Koury (NAVAIR Code 4114C) and has shown that the avionic design industry, as a whole, is lacking feedback data on the failure modes that are occurring in the fleet environment. This factor appears to be the loophole in the present information system for the design engineers attempting to produce equipment without reliability and maintainability problems associated with corrosion.

Presently there are two sources of feedback information available to the

design engineer. One is quantitative and the other is qualitative. The

quantitative source is the maintenance failure data available through

the various U.S. Navy maintenance data collection systems, such as:

a. Maintenance Data Collection System (MDCS)

b. Computerized Unsatisfactory Report Engineering System (CURES)

c. Analytical Maintenance Program Analysis System (AMPAS)

d. Depot Maintenance Data Collection System (DMDCS)

e. Navy Safety Center failure data

These data sources provide valuable feedback of a general nature, but

also can provide definitive information if the user has a good understanding of how the data is formulated by the avionic maintenance technician. Tables 2, 3 and 4 are samples of MDCS data on three types of

aircraft: a front-line fighter aircraft, an advanced ASW aircraft, and

a sophisticated attack aircraft. Each table was constructed from MDCS

data covering a period from November 1979 through October 1980. In all cases the "documented corrosion repair manhours" are those manhours ex- pended by the avionic maintenance technician in repair or correction of

a corrosion related discrepancy on the specific avionic system. The

malfunctions analyzed were: corrosion, wet, weather, contamination

(moisture and fluid), dirty, and delamination.

Table 2. Fighter Aircraft Documented Annual

Avionic Corrosion Manhours

System

Power Supply/Wiring

Lighting

Documented Corrosion

Repair Manhours

3,558

636

Instruments 1,830

Flight Reference

Flight Controls

680

558

Corranuni cat ions 611

Interphone 224

392
Table 2. Fighter Aircraft Documented Annual

Avionic Corrosion Manhours (Cont)

System

IFF

CNI Package

Radio Navigation

Radar Navigation

Bombing Navigation

Weapons Control

ECM

Documented Corrosion

Repair Manhours

250

190

547

176

125

8,081

833

TOTAL 18,299

Table 3. ASW Aircraft Documented Annual

Avionic Corrosion Manhours

System

Power Supply/Wiring

Lighting

Instruments

Flight Reference

Flight Controls

Communications

Interphone

IFF

CNI Package

Radio Navigation

Radar Navigation

Bombing Navigation

Weapons Control

ECM

Documented Corrosion

Repair Manhours

4,301

586

594

349

811

491

1,033

279

44

333

742

4,004

114

592

TOTAL 14,273

393
Table 4. Attack Aircraft Documented Annual

Avionic Corrosion Manhours

Documented Corrosion

System Repair Manhours

Power Supply/Wiring 10,116

Lighting 2,657

Instruments 2,332

Flight Reference 357

Flight Controls 352

C ommun i c at i ons 1,465

Interphone 1,143

IFF 761

CNI Package 1,029

Radio Navigation 520

Bombing Navigation 3,091

Weapons Control 2,716

ECM 4,953

TOTAL 31,492

Table 5 shows a summary of the documented avionic corrosion on the same three aircraft and includes the cost of the maintenance manhours. This

table includes the "documented support action manhours" which are those

manhours expended in cleaning and preservation of the avionic systems.

Most design and maintenance engineers responsible for avionic equipment

in modern naval aircraft tend to consider the failure data provided by

the fleet maintenance technician to be somewhat less than definitive.

Interestingly, in all three aircraft shown in Tables 2, 3 and 4, the

aircraft power supply and wiring are high manhour consumers in relation

to the other systems. This problem has consistently plagued the avionic

maintenance technician and is obviously reported. Every new aircraft

delivered to the U.S. Navy continues to exhibit high manhours expended

in wiring, connectors and power supply system. One wonders why? From a morale standpoint, if nothing else, the maintenance man who continuously

generates the maintenance data would like to see some evidence that someone is using the data as a guide to problems requiring solutions.

It should be noted that the "documented support action manhours" exceeds

the "documented corrosion repair manhours" in all three sample aircraft.

This is a direct indication that the avionic maintenance technician is

spending a good deal of maintenance time battling the corrosive effects

of the environment. It is obvious that the MDCS data bears out the fact

that avionic corrosion does exist. It goes without saying that $3,000,

394
000 in annual manhour cost is not a small problem, but what good is this

kind of data to the avionic design engineer?

Table 5. Documented Annual Avionic Corrosion Summary

Ai rcraf

t

Type

fT. A "\/f^T* V C J. Ciy U O C Number

of

Aircraft

Corrosion

Renai t

Manhours

Support

A r1" i OP

Manhours

Total

Corrosion

Manhours

Annual

Cost

Fighter 194 18,299 21,642 39,941 $ 665,000

ASW 124 14,273 30,359 44,632 744,000

Attack 259 31,492 64,026 95,518 1,591,000

Totals 577 64,064 116,027 180,091 $3,000,000

The design engineer must consider two points in his new design:

a. Is the new system or equipment similar to a previous design by the

engineer or his company?

b. Is the new system or equipment similar to any previous design

presently used in fleet aircraft built by another company?

In the case where designs of avionic equipment that are similar to

equipment previously designed by the engineer (or another engineering

group in his company) the problem of acquiring the failure data on the

previous design would appear to be relatively simple. Unfortunately,

this seldom seems to be the case. Usually, the original designer of individual avionic equipment is a subcontractor to the prime contractor of

an aircraft, or avionic system for an aircraft. The "feedback" loop for

failure data relative to corrosion in avionic equipment appears to be

relatively limited from the prime-to-subcontractor on previous system

designs unless the original design is a complete failure and requires a redesign or retrofit. But even with the breakdown in the "feedback"

loop, the quantitative maintenance failure data is available and the

design engineer, or his company, can acquire the data to show previous

failure modes in similar designs. In the second case where a design

concept is "new" to the design engineer, there is little or no formal

"feedback" loop for failure data from the prime-to-subcontractor.

Still, the quantitative maintenance data exists if like equipment is in

use in the fleet.

This brings up the second source of maintenance data — the qualitative

source. The fleet avionic maintenance technician is the primary source of qualitative maintenance failure data. He is the individual who originally documents the maintenance failure data available in the various

data collection systems. The avionic maintenance technician inherently

395
is left "out-in-the-cold" when a new avionic system is on the drawing

board, however, this intrepid individual is a fountain of knowledge,

because, like any consumer in today's world, he is the ultimate user of

the avionic equipment and knows, better than anyone, the shortcomings of

the supposedly "state-of-the-art" equipment he deals with every day.

When the design engineer proposes to carry out a design similar to a previous design, or opts to use a new design, it is important that consideration be given to both the quantitative and the qualitative data

source. The steps in accumulating the quantitative data are available

through numerous U.S. Navy organizations, the prime contractor, commercial maintenance engineering consultants, etc. The qualitative source

is only available through direct liaison with the fleet avionic maintenance technician. The maintenance technician not only has the background in the problems and failure modes in similar fleet equipment, but

he is also able to expand upon the maintenance failure data he normally

provides during the maintenance function.

An example of the input provided by the maintenance technician is highlighted by a program sponsored by Mr. A. J. Koury of Naval Air Systems

Command to study "the effects of corrosion on aircraft external lights."

This study required interviews with the fleet avionic maintenance technicians to determine why maintenance failure data did not reflect significant corrosion in aircraft external light systems. The study was conducted using the same fighter and ASW aircraft listed in Tables 2 and

3, plus the addition of a front-line helicopter. Initially, the MDCS

maintenance failure data was reviewed in an effort to identify all cor- rosion related malfunctions involving external lights. The next step

was interviews with the maintenance technicians in two squadrons for

each of the subject aircraft.

These interviews brought to light some rather interesting facts. First,

the maintenance technicians (over 25 interviewed) stated, to a man, that

only one-third of the corrosion malfunctions in aircraft external lights were documented. Second, they advised that a large number of documented

failures reported were not identified as corrosion failures, but were,

in fact, corrosion related. Instantly, the documented corrosion problem

more than tripled. The point is that the fleet avionic maintenance

technician was invaluable in more accurately quantifying the available

maintenance failure data and, with his input, the problem of corrosion

in external light systems took on a different perspective.

Table 6 shows results of the study, with emphasis on maintenance man- hours and annual cost of those manhours, for the purpose of demonstrating the cost of corrosion failures in U.S. Navy aircraft. The "total

maintenance manhours" are the documented manhours expended on all external light malfunctions (including corrosion) . The "corrosion repair

manhours" are the documented manhours which include all malfunctions

identified by the avionic maintenance technician. The "percent corro- sion" relates the percent of total maintenance manhours that were

396
corrosion related. The "documented corrosion annual cost" is based on "corrosion repair manhours" times the cost of $16.66/mmh. The "estimated corrosion annual cost" is based on three times the "documented corro- sion annual cost" figures, which resulted from the fact that all maintenance technicians interviewed indicated that 66% (two-thirds) of the

problem went unreported in the MDCS system.

Table 6. Results of External Lights Corrosion Study

Aircraft

Type

Total

Maintenance

Manhours

Corrosion

Repair

Manhours

Percent

Corrosion

Documented

Corrosion

Annual Cost

Estimated

Corrosion

Annual Cost

Fighter 18,960 7,281 38.4 $121,000 $363,000

Helo 3,400 2,026 59.6 34,000 102,000

ASW 7,169 3,004 41.9 50,000 150,000

Totals 29,529 12,311 41.7 $205,000 $615,000

Table 7 represents the results of the same study, but now includes the

corrosion manhours and annual cost of "internal and external light systems" in the subject aircraft. The interviews with the maintenance

technicians indicated that the same deficiencies in maintenance failure

data existed in the internal light systems as was shown in external

light systems. Again, 66% (two-thirds) of the problem was not documented in the MDCS system. The figures now begin to indicate that the maintenance failure data has many hidden statements that only the avionic

maintenance technician can quantify. Any assumption that the maintenance failure data is useless to maintenance or design engineers is,

obviously, erroneous in terms of identification of the "real world"

problems. The figures in Table 7 show approximately $1,000,000 expended

annually in the maintenance manhours on corrosion related problems in

"internal and external light systems." An extrapolation of the internal

and external light systems in all U.S. Navy aircraft indicates that over

$5,800,000 is expended in maintenance manhours on light systems alone.

Table 7. Estimated Cost of Internal/External Light Corrosion

Aircraft

Type

Total

Maintenance

Manhours

Corrosion

Repair

Manhours

Total

Corrosion

Annual Cost

Estimated

Corrosion

Annual Cost

Fighter 25,712 10,284 $171,000 $ 514,000

Helo 8,520 3,408 57,000 170,000

ASW 15,812 6,325 105,000 316,000

Totals 50,044 20,017 $333,000 $1,000,000

All Navy

Aircraft 294,364 118,000 $1,960,000 $5,800,000

397
i

Is there a documented and quantifiable corrosion problem in avionic

systems and equipment? The answer is evident by comparing the "documented MDCS avionic corrosion manhours and cost" with the "light system cor- rosion manhours and cost." Table 8 demonstrates this relationship for

the fighter and ASW aircraft. In Table 8, the "MDCS documented avionic

corrosion" annual maintenance manhours and cost figures from Table 5 are used for the fighter and ASW aircraft. The "light system corrosion"

annual maintenance manhours and cost figures from Table 7 are used for

comparison. It is obvious that the "light system corrosion" data is a good percentage of the total "MDCS" data that represents all avionic

systems on the subject aircraft. There are 12 to 14 avionic systems in

an average aircraft and light systems are but one of those avionic systems .

Table 8. Estimated Annual Cost of Avionic Corrosion

Aircraft

Type

Fighter

ASW

Totals

MDCS Documented

Avionic Corrosion

MMH COST

39,941 $ 665,000

44,632 744,000

85,573 $1,409,000

Light System

Corrosion

MMH COST

30,852 $514,000

18,975 316,000

49,827 $830,000

Estimated Annual

Avionic Corrosion

wm COST

308,000 $5,000,000

189,000 5,000,000

497,000 $8,000,000

Assume for this discussion that the light systems represent approximately 10% of the total avionic corrosion problem. Based on this premise,

it is evident, with simple extrapolation, that the fighter aircraft has

an avionic corrosion problem that approaches $5,000,000 annually and the

ASW aircraft is approximately $3,000,000 annually. Impressive? Imagine

what aircraft power supplies and wiring are costing. It is this

kind of feedback that is required by the design engineer; without it he

is not recognizing a problem that is costing millions in maintenance

manhours and avionic equipment failures caused by the lack of recognition of a "real world" problem. With the significance of a problem,

defined by the MDCS data, the design engineer must now investigate the

WHY of that problem, including acquisition of qualitative data as previously described. From this he can design the new equipment knowing

he is not perpetuating a known weakness.

8. CONCLUSIONS

The environment in which avionic equipment exists is not presently

recognized by the avionic design engineer. The Military Specifications

and accepted standards for the testing of avionic equipment do not duplicate, nor even recognize in some cases, the "real world" environment.

The prolific use of dissimilar metals and the lack of airframe and avionic equipment integrity against fluid intrusion have created a major

cause of avionic equipment failures. These conditions are compounded by

moisture conduits in the airframe and the effects of the operational

and maintenance environment. This results in corrosion that may be the

398
primary single source of failures in avionic equipment and systems.

Granted, some of the problems discussed could possibly be alleviated

through the use of preventive maintenance techniques on the part of the

avionic maintenance technician. The problem is that preventive maintenance has continuing costs in money and manhours. A recently completed

study of "antenna system corrosion," sponsored by Mr. A, J. Koury of

Naval Air Systems Command, shows that this problem consumes nearly $2,

000,000 in manhours annually on front-line combat aircraft!

The operational and maintenance environment is an element of the "real

world" that requires understanding by the avionic system and equipment

engineer. Since avionic equipment is most subject to corrosion during

the 95% of the time it is in the static, non-operating condition, it

stands that this "worst case condition" is what the avionic design engineer should be working toward in preventing corrosion in new and retrofit equipment design.

In the past the avionic maintenance engineers and design engineers have

stated that no data, or hard facts, exist to justify changes to standard

design techniques. In light of the data collected and partially represented in this dissertation, this is no longer valid. The MDCS and

other available maintenance failure data proves unequivocably that an avionic corrosion problem does exist. The design engineer must become

aware of the quantitative and qualitative data sources available to him.

It is imperative that the design engineer meet the maintenance technician and understand his environment, plus the effects it has on the

latest equipment entering into design.

It is the authors' hopes that this discussion will prompt a serious look

at the problems highlighted in the text. The fact is that the present

equipment designs put responsibility for the control of avionic corro- sion on the maintenance technician at this time. It appears that avionic systems and equipment could be designed with appropriate consideration for the environment in which it must exist — then the problem is

solved for good!

399
USE & EXPERIENCE OF ADVANCE COMPOSITES

REINFORCED WITH KEVLAR® IN AIRCRAFT

Paul R. Langston

E. I. du Pont de Nemours & Co., Inc.

Wilmington, Delaware, U.S.A., 19899

Kevlar® has experienced rapid growth due to its use in a wide variety of industries and applications. From its use

on the ground in tires, to satellites in space and to

cables on the ocean floor, scientists continue to expand

its use.

Kevlar® was introduced in 1972 with a total capacity of

100,000 Ibs./yr.; in 1978 we had expanded into a plant

capacity of 15,000,000 Ibs./yr. and now a new construction

is in progress for a plant to produce 45,000,000 Ibs./yr.

which will be on line in early 1982.

The purpose of this presentation is to update you on the

wide use of Kevlar® in industry, with emphasis on the use

of Kevlar® in aircraft and aerospace.

Kevlar® is sold in three different forms. Each is developed for a particular application. (Fig. 1)

KE¥LAR mmm fibefis

KEVLAR*

litoSititlctI RuMarOocMto

KEVLAR* 29 ^ noMsanclCiMes

Btflistlct

CoMMi Fabrics

KEVLAR* 49 — ftolnffofoad Pliitlcs

Puttruslon

Figure 1

400
Kevlar® can be described technically as being 4 3 percent

lighter than fiberglass, with a density of 1.44 g./cc. for

Kevlar® versus 2.55 g./cc. for fiberglass.

Twice as strong as E-glass and 16 times as strong as aluminum on a specific tensile strength basis, the highest

specific tensile strength of any commercially available

fiber. Specific tensile modulus is 3x that of fiberglass

and approaches that of HT graphite.

SPECIFIC TENSILE STRENGTH AND SPECIFIC* TENSILE MODULUS OF REINFORCING FIBERS

•TENSILE STRENGTH OR MODULUS OIVIOED BY DENSITY

10* .:m10 15 —I

1

; 1

KEVLAR ® 29 KEVLAR ® 49

Ararrna Aiam<n

RESIN IMPRESNATEO STRANDS

(•ITM 025491

-I 25

20

S -GLASS

OTHER ORGANICS • "E"-GLASS

HT GRAPHITE

BORON

HM GRAPHITH-

• STEEL

• ALUMINUM

J I

-I 5

2 3 4 5 6 SPECIFIC TENSILE MODULUS, 10* In

Figure 2

Kevlar® 49 displays excellent stability over a wide range

of temperatures for prolonged periods. The data shown are

based on a resin impregnated fiber. A composite reinforced

with fabric of Kevlar® 49 would be expected to behave similarly.

Even at a temperature as low as -320°F (-196°C) Kevlar® 49

shows essentially no embrittlement or strength loss.

Kevlar® 49 also has excellent dimensional stability with a

slightly negative coefficient of thermal expansion (-1.1 x 10-6/°F or -2 X 106/°C)

.

401
THE EFFECT OF ELEVATED TEMPERATURE ON THE TENSILE STRENGTH

OF ROVING STRANDS OF KEVLAR® 49 ARAMID / EPOXY

EXPOSED AT TEMi^RATURE SHOWN. TESTED AT ROOM TEMPERATURE. PREPARED AND TESTED PER ASTM 02343

TIMC OF EXPOSUMC Figure 3

The major difference between Kevlar®

Kevlar® 49 is modulus. (12MM vs. 18

and Kevlar® 29 versus

m psi/in2) .

The aerospace industry with its sensitivity to weight was

one of the first to recognize the merits of the specific

tensile strength of Kevlar®. Pictured is the Trident

Missile. All three stages of this missile are filament

wound composites motor cases of Kevlar®. Engineers were

able to effect about 800 lbs. of weight savings replacing

S glass with Kevlar®.

Pictured is the filament wound motor cases that are used in

the Trident Missiles. This same configuration and missile

casement construction will be used for the new MX Missile.

(Fig. 4).

402
Figure 4

Shown is. the middle stage of the Trident. (Fig. 5).

Pershing missile shown has two motor cases reinforced with

Kevlar®. (Fig. 6).

Figure 5 Figure 5

403
Coming from the missile development are pressure bottles

reinforced with Kevlar® 40. Pictured are two round cylinders that came from the space lab and a cylindrical bottle

which is used on the Boeing 747 for inflating their escape

slides. The round bottles are being evaluated for possible

use as pressure water bottles and waste containing bottles

on commercial aircraft. (Fig. 7)

Figure 7

In aircraft and helicopter the key programs are the:

Boeing 767

DeHavilland • s Dash-7

Lockheed's L-1011

Sikorsky "Sprit S-76"

Aircraft manufacturers are making significant use of Kevlar®

both on the exterior and interior of aircraft to reduce

weight. Increase in fuel prices since the OPEC oil crunch

has resulted in fuel price increases from $0.13 in the early

404
1970 's to over $1.10 today. This has resulted in the fuel

cost rising from 18% of direct operating cost to approximately 55% of DOC on commercial jet carriers. An estimated

fuel cost to fly one pound of weight on a commercial aircraft for a year is $360.

Lockheed engineered use of 2,500 lb. composites of Kevlar®

on their L-1011-500 in the early 1970 's, resulting in a weight savings of over 800 lbs. NASA evaluations seven years

later are showing these parts to be performing satisfactorily.

Recent committal to composites by Boeing containing Kevlar®

for the 767 has resulted in 1,000 lbs. of weight savings.

The de Havilland Aircraft Co. were able to save 200 lbs. of

weight by using Kevlar® to replace fiberglass on their

DASH-7, a much smaller commuter aircraft.

The use of light. weight , aramid fiber reinforced plastics in

the 50-passenger DASH-7 is extensive, including the complete

cabin interior and floors of Kevlar® 4 9 epoxy/Nomex® honeycomb sandwich construction. Externally, Kevlar® is used in

the nose avionics compartment, the leading edge of the flaps

and various aerodynamic fairings, many with complex double

curvatures

.

Fi gure 8

405
Over 50% of the exposed surface of the S-76 consists of advance composites reinforced with Kevlar® 49, representing in

total, 138 internal and 25 external components, for a weight

saving of 30% versus conventional structures.

Kevlar® has found a wide range of use in the interior and

exterior use of commercial aircraft. In the interior,

Kevlar® is basically used for all the fiber reinforced

plastics.

Shown is the interior of the Concord produced by British

Aerospace, where Kevlar® was used extensively in the sidewalls, overhead storage and ceiling panels, bulkheads, etc.

(Fig. 9^

Figure ^

The first radar dome reinforced with Kevlar® was on the

Cessna Citation I. The Citation 3, now in production, uses

Kevlar® in the various fairings plus motor nacelles in addition to the radar dome.

The passenger seat for Cessna's 402 passenger aircraft is

reinforced with Kevlar®. This seat weighs 13 1/2 lbs. versus

the lightest weight metal tube seat which weighed 32 lbs.

(Fig. 10)

406
Enviro-Porni

Seating.

Figure 10

In aircraft motor nacelles, Kevlar® is experiencing fast

growth

Shown is a Rohr Industry motor nacelle made with Kevlar®

for the Boeing 727. The weight saved on this nacelle is

between 40 & 45% lighter than the metal it is replacing.

(Fig. 11)

Figure 11

407
Pictured is the Douglas DC-9-80 motor nacelle of Kevlar®,

opened. (Fig. 12)

Figure 12

Helicopters are very weight sensitive because of the way

the weight has to be lifted. For this reason, a pound of

weight saved on a helicopter probably has the highest value

of any of the aircraft. In one particular contract, the

supplier is paying $800 per pound for weight saved. Normally, we estimate a lb. of weight saved on a helicopter

being worth around $300/lb.

The Black Hawk helicopter is being produced by Sikorsky for

the U.S. Army. Kevlar® is used in various fairings and

doors on this helicopter; the dog house or the area around

the engine is a typical application.

After the development of the Black Hawk, Sikorsky used

their technology to develop the S-76 commercial helicopter.

This is a 10-passenger helicopter. Here Kevlar® was used

to save 30% in the frame weight. (Fig. 13)

408
Figure 13

Boeing are developing a commercial Chinook helicopter for

servicing the North Sea oil platforms. This helicopter will

probably be constructed with more pounds of advanced composites than any helicopter flying. They use Kevlar® and

Nomex® honeycomb in the fuel cells on both sides of the

aircraft. These fuel cells are supported by a beam made of

Kevlar® with graphite caps. The floor of the helicopter is

made from tapes of Kevlar® and supported with beams of

Kevlar®. The motor cowlings and front section of the helicopter are slated to be Kevlar® solid laminates. (Fig. 14)

Figure 14

409
This is a summary of Boeing's & MBB's evaluation of

possible use of Kevlar® for replacement of fiberglass and

aluminum on their BOE-105 helicopter. This study was made

about 5 years ago and use of Kevlar® has been implemented.

They have been able to save more than the. 11% weight first

estimated. MBB have a contract for over 400 of these helicopters for the German army. (Fig. 15)

Shown is a Hughes AAH-6 4A, close ground support army helicopter. Much more Kevlar® has now been adopted for this

helicopter than shown. (Fig. 15)

nmt ui «tvt '^i-n covto

Figure 15

Figure 16

HUGHES HELICOPTERS/TELEDYNE RYAN AAH AIRFRAME STRUCTURES

410
This is a prototype rotor blade for the AAH 6 4 helicopter/

by Hughes, that is made using Kevlar® fiber for reinforcement. It is a good bit lighter than a similar one of

fiberglass. This blade is presently going through inflight evaluation. (Fig. 17)

Bell Helicopter are putting on 40 existing Bell-206 helicopters, 3 major parts for NASA durability evaluation.

(Fig. 18)

411
Applebay produced the first sailplane with its laminates

predominately reinforced with Kevlar®. The Zuni II is

^^70 lbs. lighter than the same sailplane in fiberglass.

Kevlar® is being developed for escape slides for commercial

aircraft. Its potential advantages are weight savings plus

improved resistance to radiant heat. It does not stretch

when it is inflated, making it easy to put back into the

pack. ( Fig. T<j)

Figure 19

Pictured is a cargo container of Kevlar® 49 developed for

Pan Am. Kevlar® offers a 10-20% weight reduction and hopefully a big increase in damage tolerance. We presently

have 22 of these containers flying around the world. The

containers are marked so that if any damage occurs, they

call in the damage to Central Control. To date, we have

had no reports of damage after 18 months. (Fig. 20)

In addition to the motor cowling use of Kevlar®, we feel

that Kevlar®, in felt form, can help reduce noise. Also,

the containment rings, which are presently titanium, can

be replaced with fabrics of Kevlar®, offering 30-50% weight

savings. The major engine manufacturers presently have

Kevlar® under evaluation for containment rings.

412
Figure 29

There are various and sundry applications in space where

Kevlar® is being used. It has been used for structural

parts for the satellite and antennas that are being used

by many broadcasting companies. We see the future for

Kevlar® being widely used in aerospace applications.

We have various studies and articles that are available to

you to help in any evaluation of Kevlar® you may be contemplating. Please let us know how we can help you I

413

SESSION V

INNOVATIVE MAINTENANCE DIAGNOSTICS AND

MAINTENANCE INDICATORS

CHAIRMAN: M. B. PETERSON

WEAR SCIENCES, INC.

I

THE ROLE OF NEUTRON RADIOGRAPHY IN A

MAINTENANCE ENVIRONMENT

Joseph 3ohn

IRT Corporation

P.O. Box 80817

San Diego, CA 92138

ABSTRACT

Neutron radiography is similar to x-ray inspection in that both depend upon use

of radiation that penetrates some materials and is absorbed by others to provide a contrast image of conditions not readily available for visual inspection. But an

important difference is the type of materials that absorb each of the two kinds

of radiation. X-rays are absorbed by dense materials, such as metals, whereas

neutrons readily penetrate metals but are absorbed by materials containing

hydrogen.

The neutron radiography technique has been successfully applied to a number of

inspection situations. These include the inspection of explosives, advanced

composites, adhesively bonded structures and a number of aircraft engine

components. With the availability of Californium -252, it has become feasible to

construct mobile neutron radiography systems suitable for field use. Such

systems have been used for in situ inspection of flight line aircraft, particularly

to locate and measure hidden corrosion.

Key words: Composite inspection; corrosion detection; cost savings;

NDE; neutron radiography; preventive maintenance.

1. INTRODUCTION

Neutron radiography is a nondestructive inspection technique that is similar in

principle to x-ray, in that a penetrating radiation (neutrons) is used to obtain a

visual image of the internal form of an object. The transmitted neutron beam is detected and permanently recorded on a suitable imaging system (usually film).

The recorded image represents a shadow of the object with the lower density on

the image corresponding to portions of the object that are more effective in

attenuating the direct neutron beam.

417
Although neutron radiographic and x-ray techniques are similar in principle, they

actually complement each other. This is because . the relative absorption

characteristics of most elements are essentially reversed; thermal neutrons are

highly attenuated by light elements. Thus with neutron radiography, nondestructive inspection can be made of light elements or certain defects encased in or behind heavy elements. It can detect imperfections in thick samples through

which x-rays cannot penetrate, or in samples containing hydrogeneous matter or contaminants whose neutron absorbing and scattering properties differ significantly from the base material.

The mass absorption coefficients of naturally occurring elements for neutrons

and x-rays are displayed in Figure 1. When plotted as a function of atomic

number, the mass absorption coefficient for x-rays is a smoothly varying

function increasing with atomic number. On the other hand, the corresponding

values for neutrons fluctuate from element to element, and on the average

decrease with increasing atomic number. Hence, in general, the lightest

elements (particularly hydrogen) are the most opaque and the heavier elements

are the least opaque to thermal nuetrons. This characteristic is the opposite of

the attenuation properties of x-rays in which the heavy elements, such as lead, are the most opaque and the light elements are quite transparent. Hence, by

complementing x-ray inspection the neutron radiographic technique extends the

capability of radiography to a much broader spectrum of applications.

The majority of neutron radiography is performed with neutrons having an energy

of 0.3 eV or less. The neutrons are in thermal equilibrium with the surrounding

material so that there is no net transfer of kinetic energy between the neutrons

and the surrounding medium. The average energy of thermal neutrons is usually

taken to be 0.025 eV. Thermal neutrons are more widely used because of their

higher probability of interaction with most materials. This makes them easier to

detect and gives the best contrast between the elements of interest and the

surrounding medium.

In the past, the availability of suitable neutron sources has limited the growth

and application of neutron radiography. Nuclear reactors and large accelerators

which are commonly used are expensive to acquire, troublesome to maintain, and

lack portability. However, the availability of the man-made isotope Californium -252, a copious emitter of neutrons, and small accelerators has made it feasible to construct neutron radiographic systems, which because of their lower

cost and portability, promise to significantly expand the use of neutron radiography for nondestructive inpsection.

418
2. IMAGE SYSTEMS FOR NEUTRON RADIOGRAPHY

The purpose of the system is to photographically detect neutrons. Unlike x-rays,

neutrons do not interact with normal photographic films; therefore, a converter

screen must be used with a conventional x-ray film to produce a permanent

image. The role of the converter screen is to change the neutron image to alpha,

beta, or gamma radiation which is detectable by a wide range of x-ray films.

Two different methods of exposure may be utilized in neutron radiography,

depending on the type of converter used. Some of the metal converters and all of the scintillators emit their radiation promptly upon capturing a neutron.

These converters are used in the direct-exposure method, with the converter

screen and film exposed to the neutron beam together. The transfer method

exposes only the converter screen to the neutron beam. Upon capturing the

neutron, the metal screen becomes radioactive and emits a delayed radiation in a time period that is characteristic of the specific isotope produced in the metal

screen. The delayed radiation is used to activate the film. The transfer method

is useful when the object is radioactive, the neutron beam is contaminated with

gamma rays, or the very best contrast is desirable.

Converters fall into two general classes: metal screens that emit low-energy

gammas or x-rays often accompanied with electrons, and scintillators that are loaded with ^Li or ^^B that captures the neutron and emits an alpha particle,

which in turn excites the scintillator material (ZnS) into emitting visible light.

As one would expect, metal converters use standard x-ray film and scintillators use light-sensitive film.

The most common converter screen used in neutron radiography is gadolinium.

Gadolinium screens can only be used in the direct-exposure method as it emits

soft gamma rays and 70-keV electrons promptly upon capturing neutrons. Using a thin Gd converter about 0.001 -inch-thick, very high-resolution radiographs are

possible. Resolutions of less than 0.0005 inch have been achieved using Gd

converters in neutron beams having low angular divergence.

X-ray films having a range of speeds from 100 to 1600 (GAF Ref) are routinely

used with the converter screens mentioned above. Resolution of cracks or opaque inclusions with one-mil dimensions are possible with GAF 100 or EK SR

film when good radiation geometry is present.

Combinations of scintillator material and photographic film have been produced

to obtain increased speed by Gavaert, Polaroid, and 3M Company. Resolution

suffers, but some interesting applications are possible.

As more sensitive imaging systems become available, fewer total neutrons are

required to produce the desired image. However, a quantum limit exists that is determined by the statistical accuracy necessary to define an object over a given

419
area. This limit is approximately 10^ n/cm2. Fewer neutrons than this per unit area will produce a fuzzy image no matter how sensitive the converter screen.

Other imaging techniques have been tried or are being developed. The tracketch method uses cellulose nitrate screens to detect hydrogen atoms that have

been scattered by the neutron beam. Neutron television systems are being

studied using a scintillator material. Multiwire spark counters, similar to those

used in high-energy particle experiments, are also being developed for neutron

radiography.

3. NEUTRON RADIOGRAPHY CAMERA

The basic function of a neutron radiographic camera is to achieve as large a thermal neutron flux as possible at the object and imaging system with a minimum of gamma rays. In addition, the thermal neutron flux must arrive at

the imaging plane in a beam to produce a sharp, clear picture of the object.

252cf is a compromise on the ideal neutron source for neutron radiography. It is true that 252cf several of the attributes of an ideal source. It is a very

intense source (essentially a point source) with relatively few gamma rays.

Unfortunately, the neutron energy distribution is similar to a fission spectrum

with an average neutron energy of slightly over 2 MeV. Consequently, to do

thermal neutron radiography, it is necessary to reduce the average energy of the

neutron spectrum. The moderation of the neutron energy distribution is accomplished by placing the 252cf source in a material that has a high density of

hydrogen. Hydrogen has the unique ability of moderating the neutron energy in

the fewest number of scattering collisions and thus in the smallest volume.

Now that we are forced to use a neutron source with a finite volume to generate

thermal neutrons, we must define an aperture through which the neutron beam

must go to get to the imaging plane. To do this effectively, a hole is introduced

into the moderator region that extends into the middle of the material next to

the source. This is the region with the highest thermal-neutron flux density.

The aperture looks at the imaging plane through a divergent collimator. The

collimator is made divergent to maximize the neutron flux over as wide an area

as possible. The function of the collimator is to capture (with a minimum of

gamma activity) all neutrons that might possibly scatter into the imaging plane.

The image plane is the location of the object. The film must be placed as close as possible to the object to produce clear, high-resolution radiographs. The

geometric unsharpness of a radiograph is inversely proportional to the L/D ratio,

where L is the distance from the aperture of dimension D to the imaging plane.

It is usually convenient to have a variable L/D ratio by allowing for a variable L

and/or D.

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The bulk of a neutron camera consists of biological shielding. The cheapest

shielding material for a neutron source is water. Unfortunately, water can be

inconvenient in that it has a tendency to leak and provides poor gamma-ray

shielding. We use a solid material that contains a large amount of water and can

also be mixed with other neutron capturing material to reduce the amount of

secondary gamma rays that are produced. This material is called waterextended polyester (WEP). It is an efficient neutron and gamma shield when

mixed with material containing boron.

In principle, a neutron camera with proper shielding can be operated in the same

room with personnel. However, for safety reasons, it is best to have controlled access to the camera area. A shutter and interlock system can be provided that

essentially eliminates the remotest possibility of a radiation accident. The

access door and the shutter automatically closes. Loss of power will also cause

the shutter to close. Additional safety features include a flashing light when the

shutter is open, a radiation monitor with a threshold setting, a shut-off from the

cells, and a console key lock.

3.1 PORTABLE NEUTRON-RADIOGRAPHY SYSTEM

A standard neutron-radiography system using 252cf weighs far too much to

enable its use as a convenient portable source to inspect an aircraft or an

aircraft component without first removing it from the aircraft. Fortunately,

most of the weight resides in the biological neutron and gamma-ray shielding

necessary if personnel are to be in close proximity to the radiography system.

The camera itself consists only of the source, moderator, and thermal-neutron

collimator, and weighs approximately one tenth of a standard fixed system.

Hence, a portable system, consisting essentially of only the camera components,

has been shown to be feasible [l] if the need for personnel to be in close

proximity during exposure is eliminated.

Such a portable camera, improvised for aircraft maintenance inspection, is shown in Figure 2. This system is shown readied to inspect the wing tank of an E-2 aircraft [2]. Although this system has not been specifically designed for

mobile operation, its performance in this less-than-optimum configuration helps

to demonstrate the feasibility of a portable neutron-radiography system (see

Ref 3 for additional discussion). The camera and the biological shield are constructed as separate entities, with the source residing in the shield except

during actual exposure. The portable neutron-radiographic camera is located on

top of the aircraft wing, with the beam aimed downward. The cylindrical

biological shield is located on the right-hand portion of this figure. The two

subsystems are connected by a polyethylene hose through which the source is transferred between the camera and the shield by a flexible cable.

The process of making an individual exposure consists of positioning the film

cassettes on the lower surface of the wing under the camera. The exposure is initiated by transferring the 252cf source from the storage container by means

of a crank-driven cable. The cable arrangement allows the operator to stand

some 25 feet away from the camera during source transfer, as shown in Figure 2.

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When the crank is driven forward, the flexible cable with a nnagnetic tip moves

from the neutron camera through the polyethylene hose, which guides the cable

into the source storage container. The magnetic tip of the cable is driven down

against the source, and with contact a magnetic latch is established. The crank

mechanism is then reversed, withdrawing the cable, with the source magnetically

attached, from the storage container back through the polyetheylene tube into

the camera body. This operation requires about four seconds. The exposure is terminated by reversing this process, thereby transferring the source from the

camera into the source container.

Using 5.8 mg of ^^^Ci, it was possible to inspect 6-1/2 square feet of the lower

skin of the E-2 aircraft integral fuel tank in a single exposure, lasting

approximately 2-\lk hours. The radiographic geometry allowed the resolution of

most spherical clusters of corrosion with a diameter of 0.010 inch, which was

considered adequate.

To comply with radiation safety regulations, an exclusion area having a radius of

approximately RO feet is necessary. The total radiation dose at the perimeter

of this area if 2 mrem/hr during exposure. When necessary, partial radiation

shields consisting of borated paraffin positioned between the camera and

maintenance personnel can reduce the exclusion area to permit access to other

portions of the aircraft during an exposure.

A series of programs - 12) have been carried out to evaluate applications of

neutron radiography to solve a number of inspection problems. A selected set of

examples are described in the following section.

SELECTED APPLICATIONS

METAL JACKETED EXPLOSIVES

Neutron radiography is quite effective for inspecting metal-jacketed explosive

devices to observe density variations, voids, and foreign materials. This

application provides excellent examples of the ability of neutrons to effectively

image light materials within heavy ones. Examination of the same components

with x-rays only reveals the metallic claddings. Aircraft depend on propellantactivated devices and linear-shaped charges for emergency escape systems; here

fast and reliable performance is demanded. Figure 3 shows three neutron

radiographs taken with varying L/D ratios of small explosive train devices with

known defects, such as missing end tips. These pictures establish that although

radiographs wth an L/D of I'fO obtain the best resolution, an L/D of 11 provided

radiographs with adequate resolution to discern many defects. This reduction of

L/D from \kO to 11 is accompanied by a reduction in the exposure time by a factor of about 100.

422
I

Figure shows three shielded mild detonating cords with known gaps of 2, 5, and

12 mils; these cords are sealed in stainless-steel cases. Neutron radiographs

taken with the 252cf camera successfully detected all of these gaps. Here

again, it should be noted that x-ray inspection images only the stainless-steel

casings and provides no information on defects in the explosive.

A number of pyrotechnic devices are used in the F-111 aircraft system. These

are widely used in emergency escape mechanisms. One such device, consisting

of the end fittings and a line charge enclosed in a metallic sheath, is shown in

Figure 5; this is a photograph of the device. The radiograph shown in Figure 6

clearly images the explosive charge, since the metallic sheath is transparent to

neutrons. In this particular case, the pyrotechnic device is in good condition and

is devoid of any defects.

*.2 ADVANCED COMPOSITE MATERIALS

The development and widespread use of advanced composites in aircraft structures calls for a parallel effort in the development of new NDI techniques for

inspecting these components. Conventional NDI techniques, developed primarily

for metallic components, will become of limited use as components fabricated

from these advanced composites begin to replace the all-metal ones. Neutron

radiography is capable of inspecting these composites, an example of which is shown in Figure 7. This is a single layer of tungsten-boron fibers in an aluminum

matrix. The filaments consist of 0.5-mil tungsten core coated with boron to

make '^-mil fibers. This neutron radiograph is able to see single filaments for

detailed inspection. Cracks and other defects are easily observed.

*.3 INSPECTION OF ADHESIVE BONDED STRUCTURE

Neutron radiography is quite effective in detecting common defects in adhesive

bonded honeycomb structure. Since neutron radiography highlights the organic

adhesive material instead of the metallic core seen by x-rays, it is possible to

detect variations in adhesive density which can lead to inadequate bonding. This

is illustrated in Figure 8. Shown here is a neutron radiograph of a test panel

approximately 12 inches long, 7 inches wide, and 5/8-inch thick. The end panels are approximately 1/16 inch thick. The honeycomb structure visible in this

radiograph shows the distribution of the organic adhesive around the metallic

honeycomb core. This radiograph clearly shows four circular areas where no

adhesive was applied to one of the end panels. Careful examination reveals that

the edges of two of these circles are better defined than those of the other two,

implying that two of these voids are on one side of the panel, while the other

pair is on the opposite side. Since neutron radiography images the adhesive,

rather than the metallic core, it is speculated that a technique involving neutron

radiography may be possible to detect defective bonds resulting from the failure

of the adhesive to wet the honeycomb.

423
A second example for inspecting adhesive bonded aircraft structure is seen in the case of the F-111 aircraft. The vertical stabilizer of the F-111 aircraft consists

of phenolic honeycomb bonded to aluminum skin. The leading edge of the

vertical stabilizer is an aluminum strip shaped in the form of an arrowhead. The

adhesive bond lines between the aluminum arrowhead and the aluminum skin

have been suspected of being deficient, leading to the existence of minute

leakage path ("worm holes") connecting the honeycomb cells to the outside

environment. It is surmised that water accumulation in the honeycomb cells

results from these leakage paths. During supersonic flights, considerable heat is produced in the region of the leading edge, causing the water to boil and

resulting in the rupture of the skin and loss of portions of the vertical stabilizer

in flight.

A neutron radiographic examination of an F-111 sample was performed and the

resulting radiograph is displayed in Figure 9. This radiograph clearly shows the

adhesive bond line between the arrowhead and the aluminum skin. A careful

examination of the radiograph reveals adhesive deficiencies, and a number of

possible paths linking the honeycomb cells to the outside environment can be

identified. In addition, this radiograph reveals great nonuniformity in the

application of the adhesive in this region.

Several models of helicopters are equipped with main rotor blade systems that are bonded by adhesives. Failures of these bondings have been attributed to

insufficient amounts of adhesive in the bond area, voids or air bubbles in the

adhesive, improper preparation of the bond surface, corrosion of the surfaces

under the adhesives, or a variety of other possible causes. Such defects are known to result in catastrophic failures, particularly when the disbonding occurs

in the closure of a C-shaped spar of the main rotor blade system.

The feasibility of using the neutron radiographic technique to detect these

disbonds has been established through a program [s] conducted at IRT Corporation. Selected test blades were subjected to the standard neutron radiography

procedure. The neutron beam from the camera was directed toward the sample

at an angle so that the adhesive region on one side of the C-spar, between the

spar and the spar closure, was clearly imaged on the film. The orientation of the

blade was such that the adhesive region on the opposite side of the C-spar did

not interfere with imaging of the adhesive bond close to the film. These

radiographs showed areas of nonuniform adhesive distribution, but were naturally

unable to detect disbonded areas that were properly bonded prior to use. A suitable enhacing agent was then used to wet the area near the spar closure.

The orientation of the blade was such as to encourage the penetrant to seep into areas where any disbonding occurs. After a short period of time the excess penetrant was removed, and the sample was subjected to a second inspection.

The penetrant, a good absorber of neutrons, helped highlight the disbonded or unbonded area.

424
Figure 10 shows a composite of two neutron radiographs obtained with a blade.

At the top is a standard radiograph clearly showing the honeycomb structure in

the trailing portion of the blade. The bond line is the region between the two

parallel lines below the honeycomb. The lower radiograph was taken after

treatment with the penetrant. The disbonded portion of the spar closure area

allows the penetrant to enter the space between the spar and the closure tip,

highlighting the area of disbond. The extent of disbond is clearly identified.

A second type of defect in helicopter blade detected by neutron radiography is illustrated in Figure 11. The bond line, in this case, appears uneven and

discontinuous, indicating the location where fretting corrosion has occurred.

When two metal surfaces are allowed to rub against each other due to

insufficient amount of adhesive, fretting often results which leads to the

initation of cracks followed by catastrophic failure.

After completion of the neutron radiographic inspection, these blades were

disassembled and subjected to visual inspection. The disbonds detected by this

destructive inspection process correlated exactly with the defects identified by

neutron radiography.

INSPECTION OF AIRCRAFT ENGINE COMPONENTS

Turbine engine blades and vanes for high-temperature applications are generally

cooled by internal passages formed by investment casting processes. Air is supplied at the base of the blade, which flows through the passageways cooling

the blade and exits through a series of holes. Cooling is aided by the use of pins

and fins within the blade, which increase the surface area to improve the heat

transfer efficiency.

A ceramic core is used to form the cooling passages when the blade is cast, and

after casting this core is chemically leached out. The high operating temperatures necessary to achieve higher engine efficiency demand that all the ceramic

core be removed. Any amount of residual core remaining in the blade can cause

the cooling passages to be blocked, which will reduce durability and can lead to

blade failure. The amount of residual core remaining which could cause serious

damage is below the resolution limits of x-radiography.

Figure 12 shows an x-radiograph of a set of TF-41 turbine blades on the left and

the corresponding neutron radiograph on the right. The x-radiograph is able to

detect the large amount of residual core which is blocking almost the entire

cooling passage. This residual core is seen with much greater contrast in the

neutron radiograph. As the amount of core is reduced, x-radiography is unable

to detect it, but it is still clearly imaged in the corresponding neutron

radiograph.

Turbine blades, fuel manifolds, and oil lines in aircraft engines are often clogged

by coke deposits. The high temperatures at which these components operate cause the hydrocarbons in the fuel and oil to dissociate depositing carbon on

425
their surfaces. Figure 13 is a composite of three neutron radiographs showing

sections of oil lines of a CF-6 aircraft engine. Coke deposits are visible on the

inner surfaces of these tubes. A large piece of coke, dislodged from the tube

wall, is seen resting near the shoulder of the 'J'-shaped tube.

The TF-30 engine used on high-performance military aircraft has been known to

fail due to fatigue cracking of compressor and turbine blades. An example is shown in Figure 1^ which contains a neutron radiograph of the tip of a compressor blade. The cracks are clearly imaged in the radiograph. The

enhancing used in this case assists in defining the orientation of the cracks [I'f].

^.5 DETECTION OF CORROSION IN AIRCRAFT STRUCTURE

Corrosion within the cross sections of aircraft structures can affect the

structural integrity, resulting in damages that range from fuel leakage to

catastrophic failures. The timely detection of corrosion is essential if corrective measures are to be taken to arrest corrosion and avoid subsequent expensive

rework.

The primary technique at present for identifying corrosion is visual detection of

external manifestations of corrosion, such as appearance of blisters or the

swelling of skin blanket. This technique completely fails when the corrosion is at

the interface between two structural members, or is concealed behind a heavy

coating of sealant.

1f.5.1 Wing Tank Corrosion

The wing fuel tanks of aircraft have been known to be susceptible to in-service

corrosion and subsequent damage. This has been attributed to moisture seepage

under the sealant and between the skin and ribs, spar flanges, and fasteners.

Corrosion damage identified by de-skinning, or cutting out skin portions so corroded that fuel leaked through, has not shown a pattern related to either

flight hours or months in service. Visual inspection through available access

panels covers only a small fraction of the area, making the identification of

wings requiring priority rework and definition of safe damage limits unreliable.

The extreme effectiveness of the neutron radiographic technique to identify

corrosion is illustrated by two examples in the following subsections.

^.5.1.1 Wing Tank Corrosion in a Commercial DC-9 Aircraft.

Several instances of exfoliation corrosion in the outboard flange of station

Xcw = 58.500 lower tee cap in DC-9 aircraft have been reported. Exfoliation

corrosion is attributed to fuel contamination or water or both, allowing corrosion

to originate between the stringer and the tee cap. Exfoliation corrosion in the

tee cap has been reported on aircraft having as few as 10,000 flight hours.

426
The recommended inspection procedure called for visual inspection, followed by

the addition of a radio-opaque oil and subsequent x-ray inspection. The special

oil mixture is forced into the area between the stringer and the tee cap using a vacuum method prior to x-ray inspection. The results obtained with x-rays are

unsatisfactory. Since the stringer is nearly two inches thick, x-rays merely

display the outline of the stringer and fail to reveal corrosion (see Figure 10 in

Ref

Under a program sponsored by Douglas Aircraft Company, a series of radiographs

has been taken simulating in situ inspection of a DC-9 aircraft. A set of

stringers, received from Douglas Aircraft Company, was inspected using the

portable neutron-radiography system, and the resulting neutron radiograph is shown in Figure 15. It displays the outline of the thick portion of the stringer,

the tee cap, and the bolts attaching the stringer to the tee cap. In addition, the

radiograph clearly reveals the extent of corrosion through the thick stringer, and

presents no difficulty in interpreting the results. A composite photograph

showing two views of the tee cap surface is given in Figure 16. Tee caps marked

13 and I'f correspond to the radiograph displayed in Figure 15. It is clear that

the surface has been subjected to a major corrosion attack. It should be noted

that Figure 16 displays only the corrosion visible on the surface, whereas the

radiograph in Figure 15 images both surface and subsurface corrosion, and hence

the apparent disparity in the extent of corrosion seen in these two figures.

The main factor in favor of the neutron radiographic technique is that it does not

require visual inspection, the application of radio-opaque oil, or intrusion of the

oil into a corroded area for detection. Also, it does not require removal of the

barrel nut or evacuation of the barrel nut hole. It could also locate corrosion

between the wing skin and the tee cap if it exists.

^^.5.1.2 Corrosion in C-130 Aircraft Wing

The C-130 Hercules aircraft has all-metal wings, with two-spar stressed-skin

structure, with integrally stiffened, tapered, machined skin panels. Several

instances of extensive surface and intergranular corrosion have led to fuel leaks

in this aircraft. This problem is particularly difficult to identify when the

corrosion is located within the lap joint.

This wing-tank problem is illustrated in Figure 17. This is a photograph of a

portion of the lower wing-tank structure of a C-130 aircraft. It clearly shows

the origin of the corrosion attack. An inspection of the upper surface of the skin

does not provide any indication of the severity of corrosion damage. Figure 18

shows two neutron radiographs of this sample. The radiograph on the right half

of this figure is a standard neutron radiograph. It shows the corroded region to

originate at the locations identified in Figure 17, and the intergranular corrosion

to extend to one rivet hole. This could clearly cause a fuel leak, although the

rivet itself may appear to be in good condition. When a small quantity of

enhancing fluid is used, the corrosion feature is considerably enhanced, as shown

in the neutron radiograph on the left half of Figure 18. This radiograph indicates

427
that the intergranular corrosion has enveloped several rivet holes, clearly

explaining the cause of the fuel leak.

^.5.1.3 Stress Corrosion in A-7 Nose Landing Gear.

In the course of a program [6] sponsored by the Navy, a number of A-7 nose

landing gear struts were screened using the neutron radiographic technique. This

investigation was carried out to detect corrosion on the inner surface of the

trunnion, at the interface between the aluminum housing and the bronze bushing.

Disassembly of the gear for this inspection without damaging the component is very difficult. Over 52 landing gears were inspected, and nearly half of them

were found to have been subjected to corrosion attack to some degree.

One of the most critical specimens examined during this study was an A-7 strut

with a stress-corrosion defect. The defect appeared as a hairline crack in the

trunnion region, barely detectable by visual inspection, even after the location

was detected by an eddy current probe. However, the eddy current technique

was unable to provide any additional information regarding the extent or shape

of the stress-corrosion crack.

This strut was subjected to neutron radiographic inspection, and the resulting

neutron radiograph is shown in Figure 19. The stress-corrosion crack is seen to

originate at a point on the inner surface of the trunnion bore and extend almost

to the outer surface, clearly showing the extent, shape, and nature of the crack.

This appears to be the first experimental work in which a stress-corrosion crack

has been imaged by neutron radiography.

The sample was then sectioned; a photograph of the sectioned trunnion area is shown in Figure 10. The extent of the stress-corrosion crack is clearly visible,

and the correlation with neutron radiography is excellent.

'^.^.l.'^ Quantiative Determination of Corrosion

In order to take full advantage of this nondestructive inspection technique, it is desirable not only to identify the location of the corrosion, but also determine . the extent of the corrosion damage. Hence, a program has been conducted to

evaluate the potential of using the neutron radiographic technique as a quantitative tool to measure the depth of corrosion so that selective rework of the

aircraft can be carried out. This work is reported in detail in References 9

and 13.

The results of the investigation show that an experimental relationship can be

formulated which will quantitatively determine the corrosion depth from the

film density measured from a neutron radiograph. This is graphically represented in Figure 21, showing the data obtained from a corroded torque-box panel

of an F-'^ aircraft. The deviation of the photographic density at a corroded point

from the corresponding value at the undamaged portions (plotted along the

ordinate) is shown to be proportional to the depth of corrosion (plotted along the

428
abscissa). Such linear relationships have been shown to exist for a variety of

aluminum alloys used in the structure of aircraft that have operated in different

environments.

This study has further established that the thickness of corrosion products and

the thickness of aluminum remaining can be determined with a precision of two

to three percent. This ability to precisely determine the amount of structural

material remaining (particularly the aircraft skin in the case of integral fuel

tanks) enables rework decisions to be based on actual structural conditions.

5. COMPARISON TO OTHER INSPECTION TECHNIQUES

In order to compare the corrosion detection capability of the neutron radiographic technique with those of other inspection techniques, a careful experiment was carried out on a flight-line aircraft. For this investigation, a

particular E-2 aircraft was selected as a test vehicle due to its past history of

in-service corrosion susceptibility. The lower skin of the wing tank was first

surveyed with neutron radiography. The wing was later subjected to x-ray

examination, ultrasonic scan, visual inspection after the upper skin of the wing

tank was removed, and a second visual inspection after the sealant and paint was

removed from the inner surface of the tank. The major conclusions of this study

are:

1. The neutron radiographic technique, unlike x-ray and ultrasonic

techniques, detects corrosion by the presence of corrosion products.

Hence, this technique identified the actual condition of the skin, and

therefore the interpretation requires no knowledge of its prior

maintenance or rework history.

2. Neutron radiography permits inspection of 95 percent of the lower

internal skin area. It can detect corrosion hidden under sealant,

behind ribs, spars, spar flanges, and fasteners. On the other hand,

x-ray, ultrasonic, and visual inspection techniques are severely

restricted by the internal structure of the wing, as well as the uneven

nature of the skin. Only 80 to 85 percent of the surface can be

covered by a combination of these three conventional techniques.

3. Of the ^19 regions of corrosion identified by neutron radiography, 28^^ were confirmed by ultrasonic inspection and a total of 309 were

confirmed by a combination of all three conventional techniques.

Most of the uncorrelated areas are accounted for by the limitations

of the conventional techniques resulting from inaccessibility or from

interfering structure. Only five discrepancies were attributable to

poor interpretation of neutron radiographs.

429
6. COST EVALUATION

The E-2 aircraft inspection also provides a means of evaluating the cost savings

to be achieved with neutron radiography. A complete inspection of the wing

tank, as it is carried out now, calls for the deskinning of the upper wing surface,

followed by the removal of the sealant and paint by chemical stripping or shell

blasting. With the wing tank fully open from the top, visual access is now

available to the entire exposed portion of the upper surface of the lower wing

skin. However, even this elaborate and time-consuming operation does not

provide a means of inspecting the region between the skin and ribs where

corrosion is very likely to occur. Only complete disassembly of the wing

structure can provide any sure way to conduct visual inspection of the entire

wing tank for corrosion detection.

It is estimated that approximately 5,000 manhours are expended in reworking the

integral fuel cell areas of a single E-2 aircraft for corrosion. This consists of

deskinning, removal of paint and sealant, cleaning, visual inspection for corrosion, chemical conversion coating, application of new sealant, painting, resl^inning, and checkout. The actual inspection portion of this procedure takes

manhours.

The experience gained with the E-2 aircraft shows that a team of two can carry

out the neutron radiographic inspection, including setup, film developing, and

interpretation. Allowing 16 manhours for initial preparation, and an equal

amount for shutdown operations, the entire neutron radiographic inspection of

the lower skin of the E-2 aircraft can be accomplished with an expenditure of

152 manhours. This is a substantial savings over the manhours estimated to

perform the inspection using the currently recommended practice. In addition,

by eliminating the need for deskinning, paint removal, and reskinning required

for visual inspection, it appears that the cost of acquiring and operating a neutron radiography system can be repaid in a short time, even if its use is restricted to the E-2 aircraft.

7. CONCLUSION

These studies have helped to establish that neutron radiography as a nondestructive inspection tool has a definite role to play in a number of inspection

situations. Its capability complements those of other inspection techniques

currently in use. The ability of neutron radiography to identify surface and

intergranular corrosion, and to detect them quantitatively, is unique. The

feasibility of performing neutron radiographic inspection in a maintenance

environment is now clearly established.

430
8. ACKNOWLEDGMENTS

A large number of persons have contributed to making this program possible, and

any attempt to name them would only result in an incomplete list. The author

would like to acknowledge their assistance. Special mention should be made of

the assistance received from Naval Air Systems Command, Air Force Logistics

Command, and Army Aviation Systems Command.

REFERENCES

[l] John, Joseph, "Mobile Neutron Radiography System for Aircraft Inspection," Text of paper presented at Air Transport Association of America

Nondestructive Testing Subcommittee Meeting, Houston, Texas,

Sept. 11-13, 1973, IRT Corporation Technical Report RT-TB-151.

[2] Larsen, J. E., Baltgalvis, J., Patricelli, F., Gallardo, M., John, Joseph,

"Evaluation of a Portable Neutron Radiographic System for the Detection

of Hidden Corrosion in the Wing Fuel Tank of the E-2C Aircraft," IRT

Corporation Technical Report INTEL-RT 6082-001, February 25, 1975.

{3] John, Joseph, Rundquist, D. E., Sharp, R., "Application of NeutronRadiography Techniques for Nondestructive Detection of Corrosion in

Naval Aircraft and Aircraft Components," IRT Corporation Technical

Report INTEL-RT 60'^'^-002, March 15, 197^.

[jt] John, Joseph, Orphan, V. J., Rundquist, D. E., Sharp, R., "Feasibility Study

of Applying Neutron Radiography for Improved Maintenance Inspection of

Naval Aircraft and Aircraft Components," IRT Corporation Technical

Report INTEL-RT 60^^^-001, November 1, 1973.

[5] Rundquist, D. E., Sharp, R., John, Joseph, "Feasibility Evaluation of Real

Time Imaging for Neutron Radiographic Inspection of Naval Aircraft,"

IRT Corporation Technical Report INTEL-RT 6072-001, August 1, 197^^.

[s] Larsen, J. E., Rundquist, D. E., Baltgalvis, J., John, Joseph, "Investigation

of Neutron Radiography Techniques for Corrosion Inspection of A-7 Nose

Landing Gear," IRT Corporation Technical Report INTEL-RT 6071-001,

August 16, 197^^.

[7] Larsen, J. E., Parks, R., Baltgalvis, J., John, Joseph, "Investigation of

Neutron Radiographic Techniques for Maintenance Inspection of Air Force

Aircraft," IRT Corporation Technical Report INTEL-RT 6081-001,

March 3, 1975.

431
Patricelli, F., Larsen, J. E., Baltgalvis, J., Parks, R., John, Joseph,

"Californium -252 Based Neutron Radiography for the Detection of Disbonds in the Spar Closure Area of 5W Series Helicopter Blades," IRT

Corporation Technical Report INTEL-RT 6085-001, February 28, 1975.

Patricelli, F., Larsen, J. E., Baltgalvis, 3., John, Joseph, "Experimental

Evaluation of Neutron Radiography for Quantitative Determination of

Corrosion in Aircraft Structure," IRT Corporation Technical Report

INTEL-RT 6093-001, January 28, 1976.

John, Joseph, "Californium-Based Neutron Radiography for Corrosion

Detection in Aircraft," Practical Applications of Neutron Radiography

and Gauging, Edited by Harold Berger, Published by American Society for

Testing and Materials, January 1976, pages 168-180.

John, Joseph, Larsen, J. E., Patricelli, F., Harper, H., Baltgalvis, J., Devine, M. J., and Koury, A. J., "Neutron Radiography for Maintenance

Inspection of Military and Civilian Aircraft," Proceedings of International

Symposium on Californium-252 Utilization, Fontenay-aux-Roses, France,

April 26-28, 1976.

Harper, H., Baltgalvis, J., Weber, Hans, Young, J. C, and John, Joseph,

"Evaluation of Californium-252-Based Neutron Radiography and Photon

Scattering Techniques for the Inspection of Hot Isostatically Pressed

Components of T-700 Aircraft Engine," AVSCOM Report No. TR76-2'f,

August 1976.

Harper, H., Baltgalvis, J., Weber, Hans, and John, Joseph, "Quantitative

Determination of Corrosion Using Neutron Radiography," IRT Corporation

Technical Report INTEL-RT 6119-001, July 30, 1976.

Harper, H., John, Joseph, "Preliminary Feasibility Evaluation of Neutron

Radiography for Detecting Cracks in Titanium Compressor Blades from

TF-30 Aircraft Engines," IRT Corporation Technical Report IRT

615^^-001, October 7, 1976.

432
0.1

0.01

1

1

Gd

•

-

-

COMPARISON OF NEUTRON AND X-RAY MASS ABSORPTION

COEFFICIENTS FOR ALL THE ELEMENTS

• THERMAL NEUTRONS (25''C) — MONOENERGETIC X-RAYS (125 keV)

[SOURCE: BNL 325, EDITION III, 1973]

( orooralion

Smn OlsBO. C»)iforni» 9213B

• B

Sm

•

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Eli • H Cd

•

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In

Ir

• Hg

N

- Be

• •

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CI•

p

Co

•

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Ti •,Fe

•• Cu.

Kr

•

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•Ag

•

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•

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• Tb

•

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, Au

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Yb

•Mg

* •

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•

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•

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Te

iSn .

' Ce

Ta. .

Tl•Pb

•bi

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• U

0 10 20 30 40 50 60 7q so go 100 ATOMIC NUMBER, Z

Figure 1. Comparison of x-ray and n-ray mass absorption coefficients

433
Figure 2. Portable neutron radiography camera positioned to radiograph

lower skin of aircraft fuel tank. The camera is mounted on top of the wing, with the neutron beam aimed downward. The

Cali fornium-252 source normally resides in the biological

shield shown on the right-hand side of the photograph. The

operator initiates an exposure by moving the source from the

cask into the camera through a flexible hose using a remotely

operated cable-driven mechanism.

434

111
•••fit

II.'

L/O » AO

11.

* 1

} -m

1 % 1 m

i 1 m

•:>

1 m

• I m i « »

*

i

« mm

Figure 3. Prints of neutron radiographs of explosive train devices having known

defects (such as missing end tips) taken with L/D ratio (resolution) of

1*0, typical of reactor-based radiography, and L/D ratios of *0 and 11,

more typical of Cf-252-based neutron radiography.

435

Figure 5. Photograph of pyrotechnic device used in the F-111 adrcraft

437
Figure 6. Neutron radiograph of pyrotechnic device. The explosive material

is clearly imaged through the metallic sheath.

438
Figure 7. Enlarged print of neutron radiograph of tungsten-boron composite

material consisting of 0.3-mil tungsten and 4-mil boron in aluminum

matrix.

439
Figure 8. Neutron radiograph of an adhesively bonded test panel approximately

12 inches long, 7 inches wide, and 5/8 inch thick. The four circular areas seen in this figure are regions where no adhesive was applied to

one of the end panels. The two circles with clearly defined edges are on the side of the panel close to the film, and the other two are on

the opposite side of the panel. The honeycomb structure visible in

this radiograph results from the adhesive around the metallic core

rather than the core itself.

i

|;

I,

I'

440
Neutron radiograph of a portion of the leading edge of the vertical

stabilizer of an F-111 aircraft. The adhesive bond line between the

aluminum arrowhead and the aluminum skin shows adhesive deficiencies providing possible leakage paths between the honeycomb cells

and the outside environment. One such '"worm hole" is labeled.

441
Figure 10. A composite of two neutron radiographs of a portion of a 540

helicopter blade system. The one at the left is a standard

neutron radiograph showing the bond line between the C-spar

and the spar closure clip, as well as the honeycomb. The

one at the right shows the result after treatment with an enhancing agent. The penetration of the enhancing agent

into the disbonded area helps clearly identify the extent

of the disbond.

442
FigMre 11. Neutron radiograph of a helicopter blade with fretting corrosion.

The uneven nature of the bond line results from metal-to-metal

contact due to inadequate quantities of adhesive.

443
Figure 12. Comparison of x-radiograph and neutron radiograph for

inspecting turbine blades for residual ceramic core. The

set at the bottom is x-rays, and the one at the top was obtained with neutrons.

444
Figure 13. Neutron radiograph of portions of oil lines in aircraft engine

showing coke dep>osits on the inner walls. A large piece of coke

dislodged from the tube wall, is seen resting near the shoulder of

the J-shaped tube.

445
i

Figure 1*^. Neutron radiograph showing cracks at the tip of compressor blade of a TF-30 engine. The enhancing agent used in this case assists in

defining the depth cind orientation of the cracks.

446
FigMre 13. Neutron radiograph of a portion of the DC-9 wing tank showing

the outline of the stringer, tee cap, and a set of bolts. The cor- roded area is visible through the stringer approximately two

inches thick.

447
Figure 16. Photograph showing two views of the tee-cap surface from the DC-9

wing tank. Tee caps identified as 13 and 1^ correspond to radiographs

displayed in Figure 15.

448
Figure 17. Photograph of a portion of the lower wing skin structure of a C-130 aircraft, showing the origin of the corrosion attack. The

extent of corrosion is not clear from such visual inspection.

449
Figure 18. Neutron radiograph of C-130 wing structure. The neutron

radiograph at the top is obtained in the usual way, and the

one at the bottom with the use of a penetrant. The intergranular corrosion is seen to extend beyond the rivet holes,

clearly explaining the cause of fuel leak from these holes.

450
Figure 19. Neutron radiograph of an A-7 nose landing gear strut showing the

extent, shape, and nature of stress-corrosion crack. This crack was

barely visible, even ctfter its location was confirmed by the eddy

current technique.

451
Figure 20. Photograph of the sectioned trunnion area showing the extent and

shap>e of stress-corrosion crack

452
I

FigMre 21. Graph of film density difference versus pit depth

for corroded pits located on torque box panels

(with AA film)

453
CREG^'' EDDY CURRENT NDE: A COST EFFECTIVE

APPROACH TO FAILURE PREVENTION

S. Sarian

Reluxtrol, Inc.

S. San Francisco, CA 49080

Abstract

State-of-the-art NDE practice for quality assurance and failure prevention relies basically on magnetic parti cl e/penetrant, ultrasonic, and

conventional eddy current techniques. Of these techniques, eddy current

is the most attractive because it is versatile and can be applied to a wide spectrum of NDE problems - defect detection and sizing, coating

thickness measurement, determination of heat treat/metallurgical con- dition such as hardness profile, dimensional measurement, to name a few - and it is especially amenable to rapid testing and screening of

metal parts under production line conditions. In spite of its attractiveness, eddy current has not found widespread use because it suffers

from edge effect which greatly reduces the effectiveness of the inspection in the vicinity of geometric tight spots, as well as lack of

sensitivity, especially in the inspection of low conductivity titanium

and nickel base alloys, and ferro-magnetic alloys because of problems

with high background noise. Therefore, improvements in eddy current

inspection performance are necessary to assure reliable micro-examination of materials and to avoid confusing the inspection because of

false signals arising from material artifacts not conducive to the

mechanical integrity - especially in production and maintenance

environments

.

There are three complimentary areas where improvements in early

detection, identification, and sizing of metal distress can be made:

(1) in the sensing element, (2) in the eddy current test instrumentation, and (3) in the signal data processing. It has been Reluxtrol 's experience that the first of these areas is subject to greatest

improvement in inspection performance.^ In this paper we describe the

high-sensitivity, high resolution CRE6 focused field eddy current sensors and ancillary electronics to accomplish inspection of a wide

variety of test parts under production line and field maintenance

conditions

.

454
DESIGN AND DEVELOPMENT OF A COLORIMETRIC FIELD

TEST KIT FOR IRON WEAR METAL DETERMINATION

W. J. Hillan and W. D. Ross

Monsanto Research Corporation

Dayton, OH 45407

K. J. Eisentraut

Materials Laboratory

Wright-Patterson AFB, OH 45433

Abstract: A rapid, flight-line kit for the analysis of iron

wear metal (a major wear indicator) in jet engine lubricants

has been developed by Monsanto Research Corporation in

conjunction with the U.S. Air Force. The Colorimetric Iron

Kit (CIK) was developed to reduce the analytical lag time

caused by sending all lubricating oil samples to an Air

Force Oil Analysis Program (AF-OAP) laboratory. The CIK

is portable, compact, light weight (25 pounds) , and can be

operated by nontechnical personnel.

The kit utilizes a colorimetric method which employs a solvent extraction-chelation procedure. Reagents required

for the procedure are sealed in plastic tubes and along with

all disposable items are packaged in analysis packets which

are contained in the Colorimetric Iron Kit. The colored

solution resulting from the analysis procedure is quantitated with a spectrophotometer.

A Hach DR/2 spectrophotometer has been modified to meet the

specific requirements of the CIK. The required wavelength

is preset and the meter scale reads directly in parts-permillion iron. Designed to analyze concentrations between

0 and 50 ppm iron, the kit contains all required components

in a 23.5 x 10 x 8.5 inch carrying case.

Six kits and 1,500 analysis packets were successfully field

tested by the Air Force in the United States. Currently

six kits and 2,000 analysis packets are being tested by the

U.S. Air Force in Europe.

Key words: Colorimetric iron kit; iron; jet engine oil;

portable; rapid; wear-metal analysis.

455
The U.S. Air Force currently uses the Air Force Oil Analysis

Program (AF-OAP) to analyze its used jet engine lubricating

oils to detect abnormal engine wear. There are approximately 120 AF-OAP laboratories located throughout the Air

Force which employ atomic absorption or atomic emission

methods to analyze the used oil samples. The principal

thrust of the AF-OAP program is to prevent engine failure

by predicting engine wear from the results of the wearmetal analyses.

However, there are several drawbacks to this procedure.

Every sample tested at an AF-OAP laboratory receives

detailed, multielement analysis. The AF-OAP labs are

generally located away from the flight-line and since

there is not a lab at every operational base, the samples,

in some instances, must be sent off-site for wear-metal

analysis. More specifically, European maneuvers often

demand remote site aircraft operations which require oil

samples to be flown to an AF-OAP lab for analysis. As a

result of these facts, a lag time is created between the

time the sample is removed from the aircraft and the time

the corrective action dictated by the AF-OAP lab results

can be implemented. In some cases this lag time may be too

long and corrective action may be too late to prevent engine

failure

.

Therefore, the Air Force requires a rapid, on-the-spot test

for a major wear-metal. The test should also be simple,

inexpensive, portable, and able to be done at the flightline or remote sites by maintenance personnel. The test

would be a supplement to the current oil analysis program

and would be used in specific cases where AF-OAP labs were

not readily available or instantaneous results were required.

We have developed the Colorimetric Iron Kit (CIK) to fill

this Air Force need. The kit utilizes a colorimetric

procedure we developed to determine the iron content of

used oil samples. The procedure is based on the concept

of analysis by solvent extraction-chelation (SEC) . This

concept generally involves four common steps performed in

varying order for different methods:

(1) Extraction of all iron into an immiscible layer,

(2) Conversion of iron to an appropriate oxidation

state

,

(3) Chelation with a colorimetric indicator, and

(4) Determination of color intensity.

456
The SEC method was modified and improved many times during

the course of the research. The reagents and procedure

described below are the result of these improvements and

the procedure is the one employed in the CIK.

Reagents

(1) HaSOu solution - 7.6 mL concentrated E^SOn + 63.6 mL

iron-free deionized H2O + 28.8 mL ethanol.

(2) Isoamyl alcohol - reagent grade.

(3) Buffer solution - 50 g sodium acetate dissolved in

iron-free deionized water by diluting to 100 mL.

(4) Reducer solution - 40 g hydroxylamine hydrochloride

dissolved in iron-free deionized water by diluting

to 100 mL.

(5) Indicator solution (0.019M) - 0.1 g bathophenanthrolinedisulfonic acid in 10 mL iron-free deionized water.

Procedure

Step 1. To 1 mL of 3N H2SO4 solution and 2 mL of isoamyl

alcohol in a 1-oz French square bottle, add 1 mL

of used oil. Shake for 2 min on a vortex mixer.

Step 2. Add 1 mL of the buffer solution and 0.5 mL of

reducer solution. Shake for 1 min.

Step 3. Add 0.5 mL of 0.019M indicator solution. Shake

well for 1 min and allow the phases to separate.

Step 4. Add 21 mL of iron-free deionized water and test

on a Hach DR/2 spectrophotometer at 5 30 nm.

The red coloration of the lower aqueous layer is indicative

of the iron concentration.

Many reagent packaging systems were investigated and the

system shown in Figure 1 was selected for use in the CIK.

The system shown in Figure 1 is packaged in a 5-in. x 5-in.

Zip-Lip® polyethylene bag. All one-time-use items are

contained in this bag and can be returned to the bag after

use for disposal. The reagents are sealed in polyethylene

tubes. The bag contains the following items, numbered to

correspond to the numbers in Figure 1:

457
Zip- Lip® iMg

Figure 1. Reagent packaging system for the

Colorimetric Iron Kit (CIK)

.

(1) One 1-oz French square bottle containing 1 mL

H2SO4 solution and 2 mL isoamyl alcohol.

(2) Pipette tip for the oil pipette.

(3) Plastic cap (with hole in top) and cap liner

(with hole to fit reagent tubes)

.

(4) Tube containing 1 mL of buffer solution.

(5) Tube containing 0.5 mL of reducer solution.

(6) Tube containing 0.5 mL of indicator solution.

(7) and (8) Two tubes, each containing 10.5 mL

of deionized water.

The 1-oz French square bottle was chosen to serve as both

the reaction vessel and test cell because it is inexpensive, and it fits the specimen chamber of the Hach DR/2

spectrophotometer used for the field test kits.

The Hach DR/2 spectrophotometer was chosen to be used in

the CIK because it fits our needs better than other commercially available instruments. That is, it is relatively low in cost, has its own large carrying case, and

458
can operate on either 115-V alternating current or on battery

power (self-contained) . The square specimen chamber that

allows us to use the 1-oz French square bottles is also an

important feature.

Figure 2 shows the Colorimetric Iron Kit. The following

modifications were made to the spectrophotometer to meet

the specific requirements of the CIK:

(1) The variable interference light filter was fixed

at 530 nm.

(2) The variable zero adjust and light adjust knobs

were replaced by locking screwdriver-driven

adjust knobs.

(3) The removable scale card on the meter was replaced

by a permanent card that reads directly in parts

per million (ppm) iron.

(4) A plastic cover was placed over the wavelength

thumbwheel to protect the interference filter

from spills.

In addition, a timer which controls the vortex mixer was

permanently wired into the spectrophotometer, and the vortex

mixer was plugged into the timer. Therefore, only one

power supply cord is required to operate the spectrophotometer, timer, and mixer. A holder for the screwdriver and

stainless steel scissors was fitted into the large compartment on the spectrophotometer face. The screwdriver is

used to adjust the zero adjust and light adjust knobs, and

the stainless steel scissors are used to cut the tips off

of the reagent tubes. The timer is fastened to the righthand compartment of the carrying case, and the vortex

mixer, power supply cord, and safety goggles are stored

there also. The left-hand compartment is reserved for the

12 analysis packets and microwipe tissues supplied with the

kit. The lid was modified to accommodate the laminated

step-by-step instruction sheet (see Figure 3) in the lefthand side. Also included in the lid are the oil pipette

and the color comparison chart. The color comparison

chart is intended for use only in the event the spectrophotometer becomes inoperable.

A detailed operating manual was prepared and a copy was

included with each kit. The pages of the manuals were

laminated for protection from oil and chemical spills and

other possible flight-line hazards.

459
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461
During the course of this research several actual used

oil samples were analyzed by the colorimetric method.

Atomic absorption, colorimetric, and particle size independent data for 29 used oil samples are compared in Table 1.

The particle size independent method was developed at the

Air Force Materials Laboratory to minimize the effect of

large metal particles on the analysis of used jet engine

oils for wear metal content.

Comparison of the atomic absorption and colorimetric data

in Table 1 shows the following:

(1) The colorimetric data were >1 ppm higher for

13 samples.

(2) The colorimetric and atomic absorption data were

equal (<1 ppm difference) for 13 samples.

(3) The colorimetric data were >1 ppm lower for

three samples.

Since the first Air Force field test for the colorimetric

kit was done on aircraft engines which have threshold limits

of 8 ppm iron, particular attention was paid to used oil

samples containing <15 ppm iron. Table 2 displays the

comparative results for 19 used oil samples analyzed by

atomic absorption, particle size independent, and the

five-step colorimetric method using 3N H2SOZ+. Comparison

of the colorimetric and atomic absorption data show the

following

(1) The colorimetric data were higher (>1 ppm

higher) for four samples.

(2) The colorimetric and atomic absorption data

were equal (<1 ppm difference) for 12 samples.

(3) The colorimetric data were lower (>1 ppm lower)

for three samples.

This shows that the colorimetric and atomic absorption data

agree very well for oil samples containing less than 15 ppm

iron.

In summary, when considering Tables 1 and 2, it can be said

that the 3N colorimetric method did better than atomic

absorption (AA) analysis in 48% of the samples analyzed,

and as well as or better than AA in 90% of the samples

analyzed.

462
I

TABLE 1. COMPARATIVE RESULTS FOR IRON ANALYSIS OF USED

OIL SAMPLES BY ATOMIC ABSORPTION, COLORIMETRIC

,

AND PARTICLE SIZE INDEPENDENT METHODS

Iron Content (ppm)

Sample Atomic Colorimetric Particle Size

Number Absorption 3N Acid Independent

P-44 35.1 43.6 mm P-62 26 .

3

29 .

4

28

P-64 26.0 30.4 27

P-65 15.0 15.3 16

P-78 11 .

8

9 .

8

16

P-81 6 .

5

3 .

7

P-86 7 .

1

6 .

6

10

P-87 2 .

9

3 .

7

P-88 33.9 40.8 42

P-90 12.4 12.2 13

P-91 11 .

0

19.5 19

R-424 12.7 14.3 13

R-429 6 .

5

5 .

9

R-437 2 .

0

1 .

3

R-443 7.0 6.5

R-452 3.1 2.8 -

H-51 16.8 18 .

7

H-58 2 .

0

1 .

4

3

H-63 20.7 26.6 25

H-64 7.6 8 .

2

10

H-65 12 .

3

13 .

3

18

H-68 7.7 7 .

2

9

F-17 30.9 58.2 49

F-18 60.5 44.5 115

F-23 16.1 55.9 64

F-34 6.2 5.7 7

F-37 3.3 9.6 13

F-38 3.2 2.1 5

F-39 22.0 27.1 33

463
TABLE 2. COMPARATIVE RESULTS FOR IRON ANALYSIS OF USED

OIL SAMPLES CONTAINING <15 ppm IRON BY ATOMIC

ABSORPTION, COLORIMETRIC, AND PARTICLE SIZE

INDEPENDENT METHODS

Iron Content (ppm)

Sample Atomic Colorimetric Particle Size

Number Absorption (3N Acid) Independent

P-65

P-78

P-81

P-86

P-87

P-90

P-91

15.0

11.8

6.5

7

2

12

1

9

4

11.0

R-424

R-429

R-437

R-443

R-452

12

6

2

7

3

7

5

0

0

1

H-58

H-64

H-65

H-68

2

7

12

7

0

6

3

7

F-34

F-37

F-38

6.2

3.3

3.2

15

9

3

6

3

12

19

3

8

7

6

7

2

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16

10

13

19

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6

2

3

9

3

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8

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2

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2

3

10

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464
six colorimetric kits and 1,500 analysis packets were

delivered to the Air Force for use in field tests designed

and administered by the Materials Laboratory. The tests

were successfully performed at Myrtle Beach and Luke Air

Force Bases on A-10 and F-15 aircraft. Most of the data

obtained from monitoring these aircraft were in the concentration range of 0 to 5 ppm iron. However, there was one

case where an engine experienced abnormal bearing wear.

The CIK picked up this abnormality at the same time as the

atomic emission instrument and earlier than the atomic

absorption instrument. Detailed results are presented in

a technical report (AFWAL-TR-80-4022 ) prepared by the

Materials Laboratory.

The six Colorimetric Iron Kits used in the Air Force field

test described above were refurbished and 2,000 additional

analysis packets were prepared for testing by the Air Force

in Europe. This test is currently in progress, and initial

response to the training sessions was very favorable.

In conclusion, the Colorimetric Iron Kit provides a simple,

on-the-spot test for iron, a major wear metal in jet

engine lubricating oil. The CIK has been packaged so it

is portable, safe, and easy-to-use (can be used by nontechnical personnel) . Some major characteristics of the

portable kit are

:

(1) Rapid - single analyses requires '^^8 minutes;

two analyses require ^^12 minutes.

(2) Accurate - results comparable to atomic

absorption data.

(3) Precise - repetitive analysis of used oil

showed good precision.

(4) Portable - packaged in a 23.5 x 10 x 8.5 inch

carrying case weighing 25 pounds.

(5) Inexpensive - lower cost than current AF-OAP

instrumentation

.

The Colorimetric Iron Kit provides a viable aid to the

AF-OAP program. The kit is capable of providing rapid

analyses in situations where sending a sample to a AF-OAP

laboratory is impractical or would cause delays in aircraft mission performance.

465
FERROGRAPHY STANDARDIZATION

Peter B. Senholzi

Manager, Applications Engineering

Mechanical Technology Incorporated

Annapolis, Maryland 21401

Abstract: Wear particle technology is a recent development in the equipment wear field. This technology is based on the analysis of wear debris

as a nondestructive reflection of the surface wear condition of the

respective monitored wear process. This monitoring approach can be

applied to everything from simple wear testing to sophisticated multicomponent wear systems. Wear particle analysis technology is rapidly

establishing itself as a valuable tool in both the wear prevention and wear control arenas.

Ferrographic analysis is a relatively new approach to the analysis of wear debris. Until recently, this technique has been utilized as a research tool in a limited number of laboratory facilities. However,

as a result of initial successful utilization, ferrographic technology

is receiving ever increasing interest. This increasing interest level

has raised serious questions with respect to standardization and repeatability.

This paper describes an effort to quantify and apportion analytical

ferrography repeatability/nonrepeatability . Under a program sponsored

by the Office of Naval Research, four leading laboratories contributed

controlled ferrographic analysis data. This data has been analyzed and

the resulting repeatability/nonrepeatability assessed with respect to

analysis variables.

Key words: Diagnostics; Health monitoring; Wear debris analysis; Ferrography; Wear; Tribology.

Introduction ; Wear particle technology is a relatively recent development in the equipment wear field. This technology is based on the

analysis of wear debris as a nondestructive reflection of the surface wear condition of the respective monitored wear process. This monitoring approach can be applied to everything from simple wear testing

to sophisticated multi-component wear systems. Wear particle analysis

technology is rapidly establishing itself as a valuable tool in both

the wear prevention and wear control arenas . In order to fully realize

the potential of wear particle analysis technology, additional re- search efforts must be implemented in order to enhance and expand the

technology.

466
Ferrographic analysis is a relatively new approach to the analysis of wear debris. Until recently, this technique has been utilized as a research tool in a limited number of laboratory facilities. However, as a result of initial successful utilization, ferrographic technology is

receiving increasing interest. This increasing interest level has raised

serious questions with respect to standardization and repeatability.

This paper deals with the standardization of analytical ferrography.

Primary emphasis will be directed at the quantification of ferrographic

repeatability as well as the identification of respective significant

contributing factors.

Background ; Analytical ferrography is based on the magnetic precipitation

and subsequent analysis of wear debris from a lubricant sample. The

approach utilized involves passing a volume of lubricant over a glass substrate which is supported over a magnetic field. Permanent magnets are arranged in such a way as to create a varying field strength over the

length of the substrate. This varying strength results in the precipitation of wear debris (magnetic and f erro-magnetic) in a distribution

with respect to size over the substrate length (approximately 55 mm)

.

Once rinsed and fixed to the substrate, this deposit serves as an ex- cellent media for optical analysis of the wear particulates.

Ferrographic substrate deposit analysis involves the characterization of

debris quantity, size distribution, elemental composition, and morphology.

This total analysis effort involves both quantitative and qualitative

assessments

.

Quantitative assessments are derived for quantity and size distribution

characterization utilizing a light reflected/light transmitted type

densitometer. These assessments are registered by indicating the percentage of blocked area in a particular microscopic field of view.

Readings are taken over the length of the substrate in order to characterize debris size distribution.

Elemental composition and morphological debris assessments are very

qualitative in nature. They involve the manual characterization of debris

deposits relying on observations conducted through an optical microscope.

This deposition and assessment process involves numerous variables. Such

aspects as sample preparation, sample dilution, sample volume, sample

viscosity, debris concentration, densitometer type, densitometer calibration, measurement approach, measurement indexing, and debris distribution, all affect ferrographic assessment results. These aspects can be

generally categorized in three groups: technique/procedure; equipment;

operator.

In the initial stages of ferrographic analysis, it was left up to each

individual laboratory to address these analysis variables.

467
During the mid 1970's, a government sponsored international committee was established under The Technical Cooperative Program (TTCP) with the objective of fostering equipment health monitoring. A prime emphasis area

of this committee was wear particle analysis and specifically ferrographic

analysis. As part of this committee's efforts, lubricant samples were

distributed among participating laboratories for wear debris analysis. Upon

comparing sample analyses, it became apparent that slide variations

existed between laboratory results. Further investigations revealed that

at least a portion of this variation was due to individually developed/

tailored ferrographic procedures. No variation apportionment could be

made, however, between procedure, operator, and equipment. Thus, a severe standardization and repeatability problem was identified. This problem

was intensified by the fact that ferrography was being applied by an ever increasing number of organizations in a variety of applications.

As a first step in attacking the problems of analytical ferrographic

standardization, the Navy under an Office of Naval Research program proceeded to generate a preliminary detailed ferrographic procedure. Due to

procedural controversies, dual procedural approaches were included for

density lighting technique and density reading indexing approaches.

In order to verify this procedure, clarify controversial dual approaches,

quantify repeatability, and identify respective significant contributing

factors, two "round robin" sample analysis exercises were established

between several major wear particle analysis facilities.

Standardization Program : As mentioned above, in order to verify the preliminary Navy Analytical Ferrographic Standardized Procedure, a joint program was developed and supported by several leading wear debris laboratories. A two phase "round robin" approach was instituted. Each phase

consisted of the analysis of fluid samples as well as the analysis of premade ferrograph slides. This analysis was limited to analytical ferrography and did not include either direct reading or in-line ferrographic

techniques

.

Primary analysis variables addressed under this "round robin" exercise were procedure, equipment, and operator/location. Secondary addressed

variables include: fluid type; debris concentration; debris size distribution; ferroscope type; ferrogram slide location; microscope lighting

approach; and slide indexing approach. Round robin test design incorporated both primary and secondary variable treatment.

Statistical Approach : Respective ferrographic analysis data was submitted to a central location from each participating laboratory for each

round robin phase. This data consisted of sets of density readings for

each sample/slide, indexed with respect to ferrogram slide location.

Supporting information for each set was also submitted which included

such items as volume of fluid analyzed, dilution ratio, lighting approach,

indexing approach, operator, and sample number. Statistical analyses were performed on these data sets in order to determine repeatability as

468
well as apportion nonrepeatability among the competing significant variables .

A four facet statistical format was applied to this data base. These

four facets included data plots (slide position versus normalized density) , analysis of variance, coefficient of variation analysis, and a graphical regression analysis. Examples of these four treatments are presented in Figure 1 through 4 respectively.

Expected outputs of this multifaceted statistical approach are summarized

as follows

:

• Data Plots • Coefficient of Variation Analysis

Trending Analysis Repeatability Assessment

Scatter Comparison Repeatability Apportionment

Quantitative Comparisons

• Graphical Regression Analysis

• Analysis of Variance Bias

Variable Significance Discrimination

Quantitative Comparisons

Scatter

Trending Analysis

Results and Conclusions : Based on the statistical analysis as described

above, the following results and conclusions have been generated. These

results and conclusions are presented with respect to the primary and

secondary analysis variables as covered earlier in this paper.

1. Lighting Technique ; Both transmitted and reflected lighting

approaches were considered with respect to analytical ferrography density measurements.

A. Mean reflected density reading is higher than transmitted.

B. Trends the same.

C. Standard deviation the same.

D. Coefficient of variation the same.

E. Standardize on reflected approach.

2. Indexing Technique ; Both a fixed density reading slide indexing approach (conventional) and a floating slide indexing

approach (new method) were considered.

A. Mean conventional density reading is the same as the new

method.

B. Trends the same.

C. Standard deviation the same.

D. Coefficient of variation the same.

E. Standardize on conventional approach.

3. Equipment ; Both Reichert and Olympus Ferroscopes were considered

under this round robin effort.

469
A. Mean Reichert equipment density reading is the same as the

Olympus

.

B. Trends the same.

C. Standard deviation the same.

D. Coefficient of variation the same.

E. Minimal equipment effect on variation.

4. Slide Position : Repeatability with respect to the indexed

location on the ferrogram was considered. Debris size is a function of this slide location.

A. Minimal effect on variation.

5. Sample Type ; Hydraulic fluid, mineral oil, and synthetic lubricant samples were considered.

A. Minimal effect on repeatability.

B. Hydraulic samples consistently higher variation.

6. Sample Debris Concentration ; Light, medium, and heavy debris

sample concentrations were considered.

A, Light and heavy concentrations have most effect on repeatability/variation

.

7. Intra-Laboratory ; Repeatability within each laboratory was considered.

A. Trends agree.

B. Good repeatability Phase I Phase II Phase II

Stage I Stage I Stage II

Mean COV 19% 5% 4%

C. Procedure improved intralaboratory variation.

8. Inter-Laboratory ; Repeatability between all participating laboratories was considered.

A. Trends agree.

B. Poor repeatability Phase I Phase I Phas.e II Phase II

Stage I Stage II Stage I Stage II

Mean COV 50% 57% 37% 39%

C. Poor Discrimination

Mean Discrimination .91 1.5 .84 2.3

D. Inconsistent inter-laboratory bias.

E. Procedure has little effect on inter-laboratory variation.

F. The prime source of inter-laboratory variation appears to be

the ferroscope densitometer as opposed to either the operator

or the sample procedure variables.

470
Summary ; The results of this analysis have served to Indicate that the preliminary Navy Standardized Ferrography Procedure has served to greatly

improve the repeatability of analytical ferrographic analysis within an individual laboratory. However, repeatability between laboratories re- mains poor due to an equipment problem with the ferroscope densitometer.

This problem could be addressed by the development of an effective densitometer calibration standard.

These results should not be construed as an effectiveness criticsm of

either ferrographic analysis or wear debris analysis technology. Both of

these interrelated technical fields have proven their effectiveness in

both the maintenance and research conununities

.

The Navy Analytical Ferrography Standardized Procedure resulting from this

effort will be published by the Office of Naval Research in the near future.

References ;

1. Wescott, V.C., et al, "Oil Analysis Program," U.S. Naval Air Engineering

Center, Final Report on Contract Number N00156-74-C-1682 , FoxboroTrans Sonics Report, 1975.

2. Scott, D., and Seifert, W.W. , "Ferrography - A New Tool For Analyzing

Wear Conditions," Fluid Power Testing Symposium, 1976.

3. Dalah, H., and Senholzi, P.B., "Characteristics of Wear Particles

Generated During Failure Progression of Roller Bearings," ABLE Paper

presented at ASLE Annual Meeting, 1976.

4. Senholzi, P.B., and Bowen, C.R., "Oil Analysis Research," National

Conference on Fluid Power, October 1976.

5. Senholzi, P.B., "Oil /malysis/Wear Particle Analysis," Mechanical

Failures Prevention Group, 1977.

6. Senholzi, P.B., "Oil Analysis/Wear Particle Analysis II," Institute

of Mechanical Engineers, 1978.

7. Maciejewski, A.S., "Oil Analysis Aspects of Tribology," Fluid Power

Research Conference, 1979.

8. Naval Air Engineering Center Report No. 92-0458, "Sample Preparation/

Ferrogram Procedure/Ferrogram Analysis," August 8, 1980.

9. Naval Air Engineering Center Tribology Laboratory Ferrogram Analysis

Report, November 7, 1977.

10. Bowen, E.R., and Westcott, V.C., "Wear Particle Atlas," Contract

No. N00156-7A-C-1682, U.S. Naval Air Engineering Center, Controlling

Office, July, 1976.

471
FIGURE 1

DATA PLOTS

MTI

PH887

FERROGRAPHY DATA

DENSITY VS SLIDE POSITION

LAB 1 SYNTHETIC

LIGHT

TRANSMITTED

NEW METHOD

Y = -0.081 X + 1.322

YBAR = 0.836 SY = 0.347

SYX = 0.232 R = 0.743

Y = LEAST SQUARED EQUATION

YBAR = AVERAGE DENSITY READING

SY = STANDARD DEVIATION

SYX = STANDARD ERROR OF ESTIMATE

R = CORRELATION COEFFICIENT
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475
A CONTINUOUS CORROSIVITY MONITORING DEVICE FOR THE MARINE ENVIRONMENTS

V. Agarwala

Naval Air Development Center

Warminster, Pennsylvania 18974

INTRODUCTION

Currently the assessment of corrosivity of an environment is made

on the projected figures obtained on a cumulative basis from outdoor,

longterm exposure tests. Tests such as salt fog, total or alternate

immersion, are primarily designed from such projections to produce an accelerated laboratory test environment. Although these test methods

have been quite successful in evaluating various materials, they are

too often indiscriminately used. In situations where rapid weather

changes control the nature of the environment or the locations are inaccessible, a true evaluation of the corrosivity of the environment

is not possible. Any extrapolation of the results obtained from

laboratory tests may be inaccurate at best, and deceptive, at worst.

The corrosion problems of naval aircraft are of a very severe and

varied nature. In particular, sulfur from the carrier stack gases

combined with sea spray provides a uniquely hostile environment

(reference (a)). The aggressive naval aircraft carrier and marine

environments not only undermine the structural integrity of the

aircraft but also affect the navigational and communication systems as well. Inaccessible and critical functional areas of aircraft are very

sensitive to even the slightest corrosion damage. An assessment of

corrosion problems in such systems is almost impossible through the

conventional corrosion tests. Corrosion of avionics, gear and gear

housings, bearings and wing flaps etc. are well documented failures.

In addition, the present trend to miniaturization and large scale

integration of computer hardware in aircraft will even further increase

their susceptibility to corrosion. Therefore, it is important that an assessment of the actual corrosivity of the environment be made before

any laboratory testing procedure can be developed to simulate the

environment

.

In the present work a probe has been developed using well known

techniques, (references (b) - (g)) which can monitor the corrosivity of

the environment on a continuous basis and also can be placed in areas which are otherwise inaccessible. This probe is a series of

electrochemical galvanic cells comprised of plates of two different

metals such as aluminum and steel or steel and copper sandwiched

together alternately separated by an electrical insulator and

encapsulated in epoxy. When short circuited through an external

electronic circuit of a zero-resistance ammeter, the condensed

476
moisture and the pollutants in the environment create an electrolyte

(thin liquid film) on the surface of these plates which completes the

circuit and develops a galvanic potential between the two. The

magnitude of this cell current gives a measure of the corrosivity of

the condensed film (the environment). The concepts of this technique

were originally investigated by Sereda (reference (b)) who used

platinum and zinc as the galvanic couple to measure the time of wetness

during atmospheric exposure. Sereda' s time of wetness measuring

technique was arbitrarily based on a potential of 0.2V (a voltage drop

across a lOM il resistor) as a timer was started when the potential drop

exceeded 0.2V. Sereda chose this as a reference voltage developed by

the Pt/Zn couple when exposed to an environment which contained 85%

R.H. Tomashov and co-workers (reference (c)) independently utilized a similar approach and developed closely spaced galvanic cells for

monitoring time of wetness of panels exposed to a high humidity

environment. Later Kucera and Mattsson (reference (d)) modified this

technique and the principles used earlier by Sereda and Tomashov to

develop galvanic cells of copper and steel and suggested that they can

be used to monitor atmospheric corrosion rates. Lauer and Mansfeld

(reference (f)) and Mansfeld and Kenkel (reference (g)) further

explored Kucera and Mattsson 's suggestions and designed several

galvanic couples made up from copper, steel, aluminum and zinc metals.

More recently, Mansfeld (reference (h)) made a study of the effect of

weather conditions and correlated the output of the couples with the

corrosion rate. In the present work a study has been made to develop a wider use of this technique for specifically measuring the severity of

the marine weather and the pollutants of the naval environment on corrosion behavior of steels and aluminum alloys.

EXPERIMENTAL DETAILS

PROBE DESIGN AND INSTRUMENTATION

The design of the probe was based on the approach used by earlier

investigators (references (e) - (g)). Three galvanic couples,

copper-steel, copper-aluminum and steel-aluminum were made from

approximately 1 mm thick sheet metal stock of commercial purity.

"Virgin" teflon of 0.75 mm thick was used as insulators. Ten pieces

(5 X 2.5 X 0.1 cms) of each of the two dissimilar metals (one as a cathode and the other as an anode) were sandwiched together alternately

and insulated by the teflon spacers. Two holes were drilled through

this assembly for inserting nylon bolts to hold it together. All

similar metal pieces (e.g., copper to copper or steel to steel) were short-circuited by thin electrical conductors and ended with two

terminals, one for the cathode (e.g., copper) and the other for the

anode (e.g., steel). The whole array of these plates was then thinly

coated with stop off lacquer on the sides and potted in epoxy resin

leaving only one long edge surface and the two wire terminals exposed.

The potted assemblies were then sufficiently cured at room temperature

before the exposed edge of the probe was surface ground and polished to

477
a 600 grit finish. The total exposed area of the probe was approxiately 5 cm ^ for each metal.

The galvanic cell current output from the probe was recorded on a periodic basis (short intervals) using the electronic devices such as a zero resistance ammeter (Z.R.A.), an anlog to digital converter; i.e.,

a digital panel meter (DPM) of very high impedance and a data logger.

The schematic of the set up is shown in Figure 1. The ZRA was put

together by using a potentiostat (Aardvark Model PEC-1) in which the

voltage between the working (W) and reference (R) terminals was set to zero. A standard resistance box was connected between the reference

(R) and counter (C) terminals for converting the galvanic current,

Ig, into a potential drop for amplification and recording purposes.

The digital data logging system used was a commercially available

instrument from Precision Digital (Model 1040). The data logger was programmed to record probe output every 10 minutes during exposure.

The choice of digital recording instruments eliminated the use of a log

converter in this study as current variations of up to three orders of

magnitude could be conveniently recorded without changing the

resistance between (R) and (C). A lOK^l resistor was adequate to give a current range of luA to 1mA in naval environments.

ELECTROCHEMICAL CONCEPTS

The principles involved in the use of this corrosivity monitoring

probe are those of corrosion of galvanically coupled metals. The

driving force in the galvanic corrosion is the difference in electrode

potentials between two dissimilar metals where the more active metal

becomes the anode and the other the cathode. Usually the cathode or cathodic metal corrodes very little or not at all and corrosion of the

anode or anodic metal is increased significantly. In other words, both

metals are polarized so that each corrodes at a new rate. The extent

of this polarization potential,")] , of both the anodic and cathodic

metals determines the magnitude of galvanic current flowing between two

disimilar metals and is expressed by the Stern-Geary equation

^g

= ^corr (10)

'''' - (10) (1)

After a series expansion and neglecting the higher terms assuming

d }] and being small, the equation (1) can be written as

^g = Wr X 2.3/^7] I (2)

where C'":, and ^'.-^ are the Tafel slopes of the cathodic and anodic

polarization respectively (reference (i)). However, when applied to

478
corrosion reactions in which the cathodic (reduction) reaction is under

diffusion control (i.e., at the limiting current) and the IR drop is

significant as one would expect in the atmospheric corrosion phenomena,

the situation is equivalent to a large or infinite value of in

equation (2).

Hence, the equation (2) can be simplified as

But, for a particular couple at some steady state, the polarization

potential/} *fj becomes a constant. Hence

Ig = Constant X Icorr

i.e., the galvanic current, Ig becomes the corrosion current of the

anode. This relationship is also in agreement with Mansfield and

Kenkel (reference g)). However, it is important to note that the

corrosion current, Icorr' does depend upon the electrochemical nature

of the cathodic metal as it alters the value of i^j^ in equation (3).

In this analysis it has been assumed that the cathodic metal behaves

more like an oxygen depolarizer therefore it undergoes the least

corrosion. The extent by which the polarization potential , shifts

is primarily dependent upon three important environmental variables,

temperature, relative humidity and corrosivity (i.e., nature of the

environment such as presence of O2, salts, acids and other gaseous

and particulate matter). In other words, the output of a galvanic

probe will be dependent upon these parameters. Experimentally the

observed changes will be directly related to the corrosive nature of

the environment.

The details of the mechanism of galvanic corrosion phenomena are described elsewhere (references (c), (g), (i), (j)> and (k)). Probably

the best explanation of how a galvanic couple behaves in a corroding

system is offered by the mixed potential theory (reference (j)).

PROCEDURES

The experimental program to explore the applicability of the

corrosion monitoring probes utilized two laboratory environments and one natural environment to achieve three different exposure conditions:

(1) a continuous high humidity (near 100% R.H.) environment; (2) an accelerated laboratory corrosion test environment; and (3) an aircraft

carrier. The galvanic probes used to study these environments were copper/steel, copper /aluminum and steel/aluminum. Both copper and

aluminimi were commercially pure metals and the steel used was an AISI

479
1040 grade. Use of the three different galvanic probes for testing was made to determine the effect to potential difference as the driving

force on the galvanic current developed in various media and to

determine the performance of one metal over another in so far as the

corrosion of anodic metal was concerned.

Near 100% relative humidity in the test chamber was created by

passing compressed air through two vessels containing deionized water

one after another and by using gas bubblers (fritted glass tubes). The

humidity and temperature of the chamber were monitored by a digital

humidity and temperature measurement system manufactured by Thunder

Scientific Corporation (Model HS-1CHDT-2R) . In experiments where

chloride and acid were introduced into the chamber, the air bubbling

vessels contained 1% NaCl and 6M HCl solutions respectively, instead of

deionized water. With this procedure approximately 0.2 gm/m-^ of NaCl

and 4 gms/m^ of HCl could be present at any time in the chamber. The

galvanic current transient curves (dotted) shown in Figures 2-4

represent the results of these test conditions.

In the accelerated laboratory corrosion testing, a salt fog cabinet

meeting the requirements of ASTM B117-73, Appendix I, was used. A 5%

NaCl solution was sprayed into the chamber as a continuous mist to

simulate nearly wet conditions as experienced on naval aircraft

carriers. In the tests where SO2 laden salt fog was required, SO2

gas was introduced in the cabinet for one hour four times a day while

salt fog was continuously sprayed. The details of this testing are described elsewhere (reference (1)). The probe exposure data obtained

by this accelerated laboratory corrosion testing are shown as continuous curves of galvanic current transients in Figures 2-4.

In the aircraft carrier exposure tests, the probe was installed on

a radar tower about 20 feet above the flight deck of the aircraft

carrier, USS JOHN F. KENNEDY (reference (m)). The galvanic current

measuring instruments were located in the radar room to isolate them

from the flight deck. The sensitivity of the recording system was set

low so that at high relative humidity (> 85%), the output of the probe was low (1-2 microamps). This way the full scale range setting on the

recording system could measure up to 500 microamps. The probe output

was recorded for a period of eight months, from June 1978 to March

1979, during which the carrier was deployed to the Mediterranean. At

the end of the mission, the current transient records were analyzed and

condensed as shown in Figure 5. The probe used in this study was a stee 1 /aluminum couple.

RESULTS AND DISCUSSION

The galvanic current-exposure time output for the three probes,

copper/steel, copper/aluminum and steel/aluminum, evaluated here in

various corrosive environments are shown in Figures 2, 3 and 4,

respectively. It has been shown that after an initial surface

480
conditioning of the probes which may take 5-10 hours, the probe output

tends to become steady and depending upon the environment present in

the chamber, the galvanic currents take an orderly relative position on

the scale of corrosivity. Generally, it was found that as the

corrosivity of the environment was increased the galvanic current

measured by the probes also increased in the same order. This order of

corrosivity was independent of the metals uised in the probe but

differed in magnitude depending on the couple. A comparative

evaluation of their performance in various environments has been

summarized in Table I. On comparison it was noted that the

steel/aluminum probe was a little less sensitive to environmental

variables. However, when the environment was of a highly acidic nature

as in the case of 100% R.H + HCl (cf. Table I and Figure 4), the

steel /aluminum probe showed an order of magnitude increase when

compared to copper /stee 1 . The copper /aluminum probe also showed a correspondingly higher output in the acid environment. Here, the

logical explanation lies in the behavior of aluminum which becomes very

active at very low pH and high chloride ion concentrations. This was

also confirmed by the fact that almost the same corrosion potentials were measured for these couples (copper /aluminum and steel/aluminum)

when immersed in a 3.5% NaCl solution (cf. Table II). A review of the

electrochemical data obtained for three metal systems shown in Table II

also indicated that as compared to the corrosion potentials of the

couples, the open circuit potentials of the uncoupled anodic metals do

not change significantly. It can therefore be concluded that in

galvanic coupling the cathodic metal is mostly polarized and the

galvanic current measured is largely due to the corrosion of the anodic

member of the couple only; concurrent results were also reported by

Walker (reference (n)). Although these results refer to an immersed

state, it is believed that similar electrochemical polarization occurs

on thin electrolyte films (condensed environment on the probe surface)

as well, except for some kinetic effects which originate due to

concentration limiting diffusion parameters. An earlier study by the

author (reference (o)) relates to these conclusions.

Based on the results obtained by the corrosivity monitoring probes

as summarized in Table I, the environments can be arranged as follows

in the order of increasing corrosivity:

Moisture (Moisture + CI) ^ (Moisture +SO2)

^ Salt Spray < (Salt Spray + SO2) < (Salt Spray + SO2 + Soak)

The increase in corrosivity from one environment to the next was almost

an order of magnitude with the exception of the one which contained

HCl. Some parallel tests on panels exposed to these environments also

exhibited similar behavior and confirmed the results as shown by the

probe output.

481
The condensed data of the aircraft carrier exposure test (reference

(m)) after replotting, as shown in Figure 5, exhibit several periods of

high corrosion activity (currents). In the first 40 days the

steel /aluminum probe showed very little corrosion activity (less than

S.-t-fA) indicative of normal marine weather and similar to those obtained

from the probe in 5% salt spray environment (cf. Table I). Between 40

to 160 days there appeared to be periods of wetness resembling the data

obtained in salt spray and SO2 test environment. However, in the

last 100 days of deployment considerable corrosive activity was recorded with galvanic currents as high as 500,<YA at some instance.

This correlates with the reports from carrier personnel that the

weather in the first four months of deployment was generally mild,

whereas that of the last four months was characterized by stonns and

high seas. It also correlates with corrosion rates exhibited by the

aluminimi alloys exposed on the carrier when inspected at four months

and eight months. Exfoliation attack was slight at four months and severe after eight months exposure (reference (m)). High current peaks were indicative of extremely corrosive conditions such as those created

in the laboratory by periods of high acidity, chloride, SO2 and

almost wet conditions. In addition, the deposition of particulate

matter such as heavy metals, soot and grease on the surface of the

probe may have further accelerated the corrosion effects

significantly. A qualitative analysis (AES) of the smut deposited on the probe showed detectable amounts of Cu, Ni, Pd, Cr, Fe and Mn. It

has been reported by LaQue (reference (p)) that the presence of heavy

metals like copper in sea water can accelerate corrosion of aluminum

significantly. The results shown by the copper/aluminum galvanic probe

in the laboratory accelerated test (cf. Table I) seem to substantiate

this conclusion.

The results obtained by the probe in the carrier exposure tests were indicative of the diversities of environment where the weather in

question changed frequently from very wet and corrosive to almost

normal or calm. It then raises a question whether the corrosivity

monitoring probe was actually responding to such changes in the carrier

environment. To affirm that, the galvanic probes were subjected to a cyclic accelerated environmental test. It was comprised of a 30 minute

spray of synthetic sea water (ASTM Dl 141-75, Section 6) in the spray

cabinet followed by a 30 minute flow of SO2, gas (flow rate of 1 cc/min/ft^ of cabinet volume) and all activity stopped for the next

two hours (called the soak period). At the end of the soak period the

cycle starts all over again and continues, repeating every three

hours. The probe exposure data obtained from these tests are shown in

Figure 6. The Ig vs. time curves demonstrate a good correlation with

the changing nature (corrosivity) of the environment in the cabinet.

The gap in the arrows in Figure 6 indicates that the peak corrosivity

of the environment was repeated after approximately three hours which

coincided well with the cyclic period regulated in the cabinet. The

gap in the arrows in Figure 6 indicates that the peak corrosivity of

the environment was repeated after approximately three hours which

482
coincided well with the cyclic period regulated in the cabinet. The

variations in the time of occurrence of these peaks were probably the

result of initial surface stabilization of the probe and the frequency

with which the cabinet cover was open. In subsequent long exposure

tests these variables were better regulated. It was noted (cf. Figure

6) that the steel /aluminum probe was not as sensitive to the

environmental changes as the other two. In order to determine the

behavior of this probe on a long term basis, this test was continued

for a period of five days. The results obtained from the copper/steel

probe were even more interesting. As shown in Figure 7, the Ig vs. exposure time curve is made up of maxima and minima of the corrosion

currents which were consistently repeated after every three hours and

became very reproducible as the exposure continued. The ascending part

of the curve coincided with the time when SO2 gas was flowing into

the cabinet after salt spray had ceased. Thus, the peaks correspond to

the point in time where the probe experienced the highest SO2

concentration; i.e, maximum acidity and maximum wetness as the salt fog

continues to remain in the chamber for at least 1/2 hour after its flow

has stopped. The extrapolated dotted lines in the curve (cf. Figure 7) were drawn to make the corrections in the curve, because during those

periods, the cabinet cover was opened for examination which probably

allowed the environment to escape (change) and therefore affected the

results. The steady state values of the maxima and minima varied from

100 to 300 A showing extremely high corrosive environmental changes. In

Table I a comparative summary of the performance of various probes used

in the cyclic test has been given. From the actual panel exposure

testing it was observed that this synthetic sea salt + SO2 + soak

cycle environment was probably the most corrosive of all accelerated

laboratory corrosion testing environments (cf. Table I ) and the type

of attack produced had the closest resemblance to that obtained in he

carrier environment.

CONCLUSIONS

Based on the principles of galvanic action a corrosion monitoring

probe has been developed and evaluated for its usefulness in measuring

the severity of the environment quantitatively. A comparative study of

three galvanic probes, copper/steel, copper /aluminum and steel/aluminum

showed that the copper/steel probe was most responsive to most

varieties of environments in terms of its corrosion sensitivity and

reproducibility when used on a continuous basis. In a simulated

accelerated cyclic corrosion test environment, the corrosion monitoring

ability of the probe was found to be in agreement with the cyclic

corrosive nature of the environment. The aircraft carrier exposure

results obtained by the probe indicated a very high corrosion activity

caused by the presence of high wetness, sea salt, SO2 and deposition

of particulate matter (most probably heavy metals).

483
ACKNOWLEDGEMENTS

The author gratefully acknowledges the generous financial support

of the Independent Research Board of the Naval Air Development Center,

the Naval Air Systems Command, and the Commander, Naval Air Altantic

Fleet for the opportunity to perform the aircraft carrier exposure

tests. The author is thankful to Mr. K. Briegel for experimental work

and Dr. J. J. De Luccia and Mrs. S. J. Ketcham for their helpful

suggestions

.

484
REFERENCES

S. J. Ketcham, Materials Performance , 16, 38 (1977).

P.J. Sereda, ASTM Bulletin No. 228, pp. 53 (1958); ibid .

,

No. 238 , pp. 61 (1959); ibid., No. 246, pp. 47 (1950).

N. D. Tomashov, Theory of Corrosion and Protection of Metals , The McMillan Co., New York, 1966, pp. 375.

V. Kucera and E. Mattsson, ASTM Special Technical Presentation on Corrosion in Natural Environments , 558, 1974, pp. 239.

P. J. Sereda, ibid., pp. 7.

G. Lauer and F. Mansfeld, Corrosion , 26, 504 (1970).

F. Mansfeld and J. V. Kenkel, Corrosion Science , 16 , 111 (1976);

Corrosion , 33, 13 (1977).

F. Mansfeld, Werksto ff . u .Korrosion , 30, 38 (1979).

H. H. Uhlig, Corrosion and Corrosion Control , John Wiley, N.Y.,

1965

M. G. Fontana and N. D. Greene, Corrosion Engineering , McGraw

Hill, N.Y., 1967.

R. Baboian, Electrochemical Techniques for Corrosion , NACE T-3L

Publication, pp. 73-78, 1977.

S. J. Ketcham, Naval Air Development Center Report No.

NADC-77252-30 , 1977.

E. J. Jankowsky, S. J. Ketcham and V. S. Agarwala, Naval Air

Development Center Report No. NADC- 79 251-60 , 1979.

M. S. Walker, Corrosion/78 Conference , NACE, Texas, Paper No.

171 (1978).

V. S. Agarwala and N. D. Greene, Corrosion Research Conference , Corrosion/ 76 , NACE, Houston, Texas.

F. L. LaQue, ECS Corrosion Monograph Series on Marine Corrosion

Causes and Prevention, John Wiley & Sons, N.Y., 1975, pp. 95-122.

485
TABLE I. EFFECTS OF ENVIRONMENTAL VARIABLES ON PROBE OUTPUT

Probe Output, Ig, ^A

Environment

100% R.H.

100% R.H. + CI

-b

100% R.H. + C-HCl

100% R.H. + SO2

5% NaCl Spray

5% NaCl Spray + SO2

Syn, Sea Water + SO2 + Soak (Cyclic Test)

Copper/

Steel

0.01

0.1

28

1.5

7.5

140

120-300

Copper/ Steel/

Aluminum Aluminum

0.01

0.5

260

^10. 01

0.01

220

3 0.5

8 1.5

80 7

80-200 15-30

a Ig values at steady-state after 20 hours of

initial exposure,

b Cl~ in the test chamber carried by the air when

purged through 1% NaCl solution.

£ HCl in the test chamber carried by the air when

purged through 6MHC1 solution.

486
TABLE II. OPEN-CIRCUIT POTENTIALS (Ecorr,) CORROSION RATES

(Icorr.) AFTER 24 HOURS IN 3.5% NaCl SOLUTION (IMMERSED).

1 11 a Ecorr..V Galvanic E^orr., V Icorr.

Material (Vs SCE) Couple Vs SCE A/cm^

Aluminum (CP.) -0.730 Steel/Al -0.740 12

AISI 1040 Steel -0.610 Cu/Al -0.720 30

Copper (CP.) -0.240 Cu/Steel -0.680 20

a Corrosion rates refer to the anodic member of the

couples only.

1 ^ 11

^corr. ^corr. ^^fer to potentials of uncoupled anodes

and cathodes, and galvanic couples after one hour immersion

respectively.

487
< 1 — D PM

1

GALVANIC

PROBE

W 'R C

1

I POTENTIOSTAT

j

ANALOG BCD

CONVERTOR

Z.R.A.

FIGURE 1. ENVIRONMENTAL CORROSIVITY MONITORING PROBE AND

THE RELATED INSTRUMENTATION SCHEMATIC.

488
FIGURE 2. GALVANIC CURRENT TRANSIENTS OF COPPER/ STEEL PROBE

EXPOSED TO VARIOUS LABORATORY SIMULATED

ENVIRONMENTS

.

489
FIGURE 3. GALVANIC CURRENT TRANSIENTS OF COPPER/ALUMINUM

PROBE EXPOSED TO VARIOUS LABORATORY SIMULATED

ENVIRONMENTS

.

490
FIGURE 4. GALVANIC CURRENT TRANSIENTS OF STEEL/ALUMINUM

PROBE EXPOSED TO VARIOUS LABORATORY SIMULATED

ENVIRONMENTS

.

491
50 100 150 200 250

EXPOSURE TIME. DAYS

FIGURE 5. GALVANIC CURRENT TRANSIENTS OF STEEL/ALUMINUM

PROBE EXPOSED TO AN AIRCRAFT CARRIER ENVIRONMENT.

492
FIGURE 6. A SIMULATED CARRIER EXPOSURE TEST (SOAK CYCLE)

DEMONSTRATING PROBE SENSITIVITY TO ENVIRONMENTAL

CHANGES

.

493
FIGURE 7. PERFORMANCE OF COPPER/STEEL PROBE IN AN ALTERNATING

CORROSIVE ENVIRONMENT (SOAK CYCLE) OVER A LONG

PERIOD OF EXPOSURE SHOWING THE CYCLIC NATURE OF THE

ENVIRONMENTAL CORROSIVITY TEST.

494
IMPROVING MAINTENANCE. MANPOWER UTILIZATION

Warren W. Lee

The Emerson Consultants, Inc.

30 Rockefeller Plaza

New York, New York 10112

Abstract: Managing the Maintenance function is extraordinarily difficult. Many factors contribute to this difficulty. Labor problems are complex because of craft lines. Efficiency is hard to achieve. It is

difficult to schedule men and materials to jobs because of the constant

interruption of emergencies. Overtime is commonly too high. Foreman

usually are inadequately trained and receive little management support.

The most difficult problem may be that of developing management understanding of the methods of maintenance cost control and an organization

that desires and is able to control maintenance costs.

As a result of the many factors that make the management of maintenance

difficult, some maintenance organizations handle maintenance on a breakdown basis rather than on a planned basis.

Breakdown maintenance is inefficient. With breakdown maintenance,

foremen are trapped into becoming dispatchers. Craftsmen can't develop

a work rhythm because they must go after tools and materials, wait on other crafts or wait on decisions. With breakdown maintenance, the

Maintenance Department operates as a standby workforce.

Planned maintenance is more efficient. Crafts can be coordinated. Repair parts and materials can be provided. Production equipment availability can be arranged. Efficient ways of doing work can be developed.

Bottlenecks can be anticipated and broken. When interruptions are avoided, craftsmen develop a work rhythm. Preventive maintenance is an important element of planned maintenance.

Before reviewing how to establish improved maintenance work procedures,

we should review the problems normally associated with a breakdown

maintenance organization so we will recognize what needs to be changed.

Then we can discuss a program for change.

Work Practices and Procedures That Limit Maintenance Efficiency

Most of the practices that limit maintenance efficiency are susceptible

to change by Management. When we look at maintenance operations, we

find maintenance work is always impeded by bottlenecks. If these bottlenecks are removed, worker productivity improves. When we examine

these bottlenecks, we find most result from omissions by foremen. If

495
Management takes care of these omissions, Maintenance worker productivity increases. Consider the following examples:

1. Maintenance crews commonly are slow about getting to work. Foremen

who assign all work in the morning may take one and a half hours to

get to the last assignment. The craftsman may not be told exactly

what is wrong or what Management expects him to do. Instructions

may be vague.

The craftsman may have difficulty finding the job. He may not find

the person who initiated the job, or find someone to tell him what

is needed. We frequently find Maintenance workers starting late,

(from one-half to one and one-half hours after the whistle) for reasons that are primarily Management's fault.

2. A second common problem is that the equipment is not ready to work

on when the Maintenance people get to the job site. As a result,

they are left standing around through no fault of the Maintenance

crew.

3. Inadequate planning is a third problem area. A job may not have

been investigated and planned. Assisting crafts may not have been

coordinated. A pump mechanic may have to wait for the electrician

or for a pipefitter to break connections or for a crane to lift the

pump. If these craftsmen work for different foremen, there is no easy way for the primary craftsman to arrange this coordination,

particularly if the needed man is busy on another job. The result

is a crew standing around because management didn't coordinate the

job.

4. Repair materials are a problem in some organizations. Spare parts

may not be in stock. Tools and materials required for the job may

not have been identified and delivered. That leaves it up to the

craftsman to determine what is needed and find a way to get it.

The plant may have no material delivery system, or no catalog from

which to order stock materials. Or the catalog may be poor, com- pletely unusable by a maintenance craftsman. Or a foreman's signature may be required to release materials. Then the crew must stop

work and send one or more men to the storeroom. These constant interruptions make it difficult for craftsmen to develop a work

rhythm. Again, the problem is not the worker's. It is Management's

problem.

5. Increasing complexity of equipment is a problem. Machine speeds are increased. Sophisticated controls are added. Greater skills are needed to maintain this equipment. Few organizations have the

training programs necessary to upgrade Maintenance employees' skill

levels. A mechanic without adequate skills cannot be fully productive.

496
6. Inadequate preventive maintenance is a common problem. This not

only results in excessive downtime of production equipment, but it

increases the work that Maintenance must do. Instead of minor adjustments, Maintenance gets saddled with major repairs.

When Maintenance doesn't perform preventive maintenance, the result

is a great deal of breakdown maintenance. A high percentage of

breakdown maintenance not only is inefficient, it forces Maintenance

into the business of standby maintenance.

There is no way to develop efficiency in a maintenance organization

that is habituated to standby maintenance, to standing by to fix

breakdowns. It is not enough just to repair equipment when it

breaks down. Maintenance must avoid repair jobs where possible.

This requires avoiding breakdowns through preventive maintenance

procedures. It requires solving problems by design change, through

changed operating procedures, or by retiring or replacing obsolete

equipment that is responsible for excessive maintenance costs.

7. Supervisory practices are another area for problems. Foremen may

spend little time at the job site. Their time may be taken up with

meetings, with paperwork, or with planning. They frequently end up

as dispatchers, depending on the men to find the job, and to decide

what needs to be done.

Some organizations support this Management philosophy. They take

the attitude that the craftsman is paid to know the job, that fore- men are a vestigial anomaly that will eventually disappear.

I think it is significant that we find such crews never achieve the

productivity of those with close and effective supervision.

8. Overtime causes many problems. Sometimes such problems are not re- cognized as symptoms of excessive overtime. It is fruitless to try

to solve symptoms.

The following are examples of problems arising from excessive overtime:

0 Supervisors develop a pay problem. Morale falls. Paying supervisors for overtime is not the answer.

0 It becomes difficult to find hourly employees who will accept

promotion to supervisory positions.

0 Men get locked into higher standards of living. Then they must

decide between taking care of their families and looking out

for the company's interest. Frequently, they find that they

must schedule overtime in order to maintain their social lives.

497
0 Absenteeism increases. Men become more prone to illness (possibly because they have more money).

0 Productivity and efficiency decrease. Studies indicate that two

weeks may be the maximum period during which efficiency can be

maintained under a heavy overtime schedule.

9. Modifications and alterations can account for major expenditures.

When Management controls are inadequate, equipment may be modified

without adequate analysis. Built-ins, cabinets and closets may

spring up everywhere.

A related problem is Management's failure to separate maintenance

repair costs from other services such as janitors, power plant and

utilities operation, unloading cars and trucks, providing relief

operators and providing clean-up crews. When Management can't isolate all these costs, when they are lumped together as maintenance

costs, there is no way to analyze operations. Under these conditions, effective control of maintenance costs is impossible.

10. The relationship between Maintenance and the user of maintenance

services may need to be improved. The users may not feel con- strained to help Maintenance in ways that lower maintenance costs.

The user may feel no restraint on requests for service, no concern

for giving Maintenance the time to do the planning and scheduling

needed for efficient maintenance. If the additional cost of emer- gencies affects only the Maintenance budget, the user may not be

concerned about Maintenance overtime or preventive maintenance.

11. Responsibilities for job priorities can present a problem. There is

a basic conflict between Maintenance's need for time to plan and

schedule work so that maintenance costs will be minimized and the

user's desire for immediate repairs. Immediate repair requires a standby Maintenance crew. Organizations following this practice

are bloated. Efficient maintenance requires time to plan and

schedule.

How can these conflicting needs be balanced?

Management must recognize that this conflict exists and organize to

handle it. They must develop an effective priority system. This

is difficult. The user should have the right to say when repairs

are needed. But good men dislike broken down equipment.

There are two requirements for an effective solution of this conflict:

0 A strong Maintenance Planning and Scheduling Organization.

0 Dynamic use of job priority (set by the user).

498
Planning and Scheduling strives always to get time to plan. This

conflicts with the user's legitimate desire for repairs to be made

"NOW". But the structure is there to handle such conflicts. Most

problems can be solved at a low level (planner and user). But the

organization and procedures are present to carry problems as high

as needed. It is the top man who must decide whether to increase

staff or live with the potential delays.

Contractual Problems That Limit Maintenance Efficiency

We have been reviewing common causes of low productivity. As you can

see, most are Hanagement problems. Most can be eliminated by Management action. Most are simple to identify and not too difficult to cure.

Let's consider some more complex problems that interfere with Maintenance Management--problems that bottleneck maintenance productivity

but are so difficult of solution that most managements ignore them.

1. First consider craft barriers. Do your labor agreements rigidly

define the work a specific craft may do? The difference between

organization is surprising. In some, mechanics regularly do most

of the work related to a job. In others, several crafts may be

required for a simple task. For example, a pipefitter and an electrician may be required to help an instrument man remove an instrument. The work may be well within the instrument mechanic's

ability, but past practice requires three crafts.

Consider how inefficient this becomes. If the job isn't planned,

waiting time becomes excessive. If it is planned, planning and

coordination costs become excessive, because the planner must com- municate with several crafts. Between planner and foremen, they

may waste more time than it takes to do the job.

Who is responsible for preventing an increase in craft barriers?

Who is responsible for developing a plan, for negotiating an "incidental work" agreement, and for enforcing the agreement after it

is made?

2. Another difficult problem area is maintaining Management's rights

under the contract. We expect foremen to operate effectively in

the face of growing Union strength. Do we train them in the de^

tails of the contract? Do we consult with them before negotiations? Is it any wonder that foremen end up taking actions that

Management subsequently decides not to support?

After Management has failed to train their supervisors and then

finds it undesirable to support their actions, we get an inevitable

499
result. The foremen decide to play it safe and minimize their ex- posure by "managing" as little as possible,

3. Another difficult problem is controlling entry into the Maintenance

work force. Some organizations have no apprentice program, no series of examinations that a craftsman must pass. As a result, un- suitable people can get into Maintenance. Once in the Maintenance

organization, there frequently is no way to get these people out

and little way to upgrade them. In time, such practices will

weaken the entire group.

A Program For Change - The Route To Efficient Maintenance

We have reviewed the problems that make Maintenance Management difficult, both the obvious problems that yield to direct action and the

complex problems that are harder to solve. Our purpose has been to

spotlight the problems that face Maintenance Management so that we can tailor our solutions to these problems. Here are the steps that

we have found to be successful for accomplishing a turnabout of the

Maintenance function:

First, identify your problems. Look for the obvious problems I've

listed here. Determine their trends and evaluate their seriousness.

Measure your productivity with work sampling. Reduce your findings

to writing.

Second, develop a plan for change. Get the plan approved by Management. Schedule each step you will take and assign responsibility for

each step.

The following actions are those we have found to be effective for

identifying and removing those bottlenecks that limit the productivity

of Maintenance organizations.

1. Develop a sound organization that recognizes the functions that

must be accomplished and structures the organization- for their ac- complishment. Chief among these structures are separation of

planning and work execution, proper relationship between Stores and

Maintenance, proper relationship between the user and Maintenance,

provision of needed Engineering functions and relating the work

force to specific areas of large installations.

2. Establish effective procedures that make it easy to initiate, exe- cute and control Maintenance work. Following are the procedures

that we have found most effective:

0 Preplan the jobs so that needed materials may be identified and

supplied and crafts and equipment may be coordinated.

500
0 Assign work the day before in order to avoid the morning startup delays.

0 Assign more than one job so that the craftsman always knows

where his next job will be. That way he does not need to

stretch out the current assignment. He won't need to return to

the shop for his next job and, if the foreman is absent, be

forced to wait.

0 Get the foreman out on the job with the clearly identified goal

of finding and eliminating the bottlenecks. He should understand that his goal is to help his men do the job efficiently,

not "look down their collar."

0 Provide Materials Management that includes:

- Effective stock control (expensive to establish, but profitable)

- Good warehouse procedures

- An adequate catalog so that Maintenance people can tell what

material is available and can order it by telephone.

- And last, a delivery system that will get material to the

craftsman rather than requiring him to come after it.

0 Establish a priority system. The user should set priorities.

The Maintenance Planner only negotiates priorities. However,

he can approach the user this way: "I have this many people to

schedule. Which jobs do you want tomorrow?"

Most priorities are set at a low level (user versus planner).

Some rise for Management consideration when the user can't ac- cept delay. Management must decide between accepting such

delays or providing extra staff.

0 Control facilities modifications and alterations. First line user supervisors should be able to authorize major repairs but

only limited dollar alterations. Alterations should be approved by Engineering. Approvals should be monitored by Planning. The work order provides the control vehicle.

0 Establish work sampling. This is the most meaningful measure of

the suitability of staffing level. Monitor other measures of

Maintenance performance such as downtime, equipment failures,

labor hours, overtime levels, and the like.

These are the principal procedures that usually need attention. Do

not neglect the more difficult problems.

501
3. Establish overtime controls. Hold total overtime to a low level

(10% maximum). Identify causes of overtime and the amount per

cause. Apply effort where it is needed. Reduce emergencies.

Schedule for week-ends. Minimize scheduled overtime.

4. Provide a work order system for Maintenance. The work order should

be designed to accomplish the following functions:

Requesting maintenance work

Approving requests for maintenance work

Planning the job

Opening the computer cost collection account (for the Management Information System)

Requisitioning material (in some cases)

Reporting completion of the job

It should provide for coding the following information as a minimum:

Priority

Production cost center

Identification number of equipment being repaired

Reason for undertaking modifications or new construction

AFE, RFA, or project number if the work order is part of a larger job

The expense classification for budgetary purposes

The names of all authorities approving the request

An estimate of labor, material and total dollars required

to complete the job

The reason the equipment failed or needed repair

5. Provide training as needed for all employees. Train the foremen

and the craftsmen in the technical aspects and best methods of

doing their jobs. Teach the foremen to understand the contract and

to manage within the provisions of the contract. Make sure that

second level Management discharges its responsibility to train the

foremen to know what their jobs are and how to accomplish them.

502
As part of the training program, develop controls over entry Into

the Maintenance Department, Also develop an apprentice training

program that will increase the craftsman's competence. This program should have the ability to reject trainees that aren't going

to develop into suitable journeymen.

6. Establish a good Preventive Maintenance program. Preventive maintenance is more than a lubrication program, more than an inspection

program. It includes the analysis of breakdowns and an attempt to

prevent them. It includes review of equipment design and specifications to identify and avoid equipment known to perform poorly.

It includes finding and eliminating operating procedures that are responsible for excessive maintenance in the organization.

7. Protect the rights of Management versus those of the Union. Pay

close attention to the day-to-day problems that come up between

foremen and the Union. Insure that the positions taken fairly re- flect the contract. Be alert to prevent the Union nibbling away

at Management rights by establishing adverse procedures that the

Union can later claim as "past practice."

Make sure that the foreman understands and exercises Management

rights. Protect him from taking positions that Management may not

be able to support and which may result in Management actions that

destroy the confidence and authority of the foreman.

Prepare for the periodic negotiation of a new contract. The Union,

at national, regional and local levels, plans what they are going

to take away from Management. They develop positions and strategies for the negotiating table. This is their business. They are professionals and spend full time at it.

Management can't hope to negotiate effectively with the Union, to

support its own position adequately, if two weeks before the negotiations the man selected to head up the Management team sits down

and throws together a position paper. This is particularly true

when his primary contact with line management occurs only at negotiating time, or if his contacts have been limited to periods when

line management has gotten into difficulty. When the negotiator's

contacts are thus limited, he loses confidence in line management

to the extent that the two of them have difficulty forming an effective team.

8. Consider negotiating for a reduction in craft barriers. A first

step within reach of most companies is an agreement for the principal craft to perform minor associated tasks or incidental work.

9. Provide a Management Information System if your operation is large

(over 100 Maintenance people) or if your company has several large

plants.

503
The Management Information System requires computerized work order

accounting that communicates with payroll and labor distribution,

with warehouse stock materials accounting, and with outside purchased materials accounting.

Such a Management Information System can help with the control and

management of maintenance.

One Last Reminder

Keep in mind that it is the foreman and his team that gets maintenance

work done. Planners don't do maintenance work. Neither does Management. It is the maintenance mechanic supported by his foreman that

gets the job done.

Few foremen receive the management support they need and deserve.

Few craftsmen receive the support they need and have a right to expect.

Management needs to make some fundamental changes:

0 Eliminate criticism as a mode of dealing with the foreman. He

is the only one of the Management team who is working face to

face with the worker. Criticism too often reflects Management's

lack of understanding of his situation or Management's refusal

to accept their responsibility for helping him become effective.

0 Support the foreman. Support him with training in all the more

obvious areas, but most important, keep the general foreman in

the field showing him how to support his men, training him to

find and break the bottlenecks that slow down the job.

0 Support the craftsmen. Train them in craft skills and recognize and support their pride in these skills. Help them become

master mechanics and maximize their opportunities for selfrealization on the job.

0 Recognize that it is Management's job, not merely to direct, but

to train and support the general foremen.

504
APPENDIX

MECHANICAL FAILURES PREVENTION GROUP

Innovation for Maintenance Technology Improvements

33rd Meeting

April 21-23, 1981

Attendance List

Ricardo R. Ablaza

U.S. Dept. of Transportation

Federal Highway Admin. , HDV-13

400 7th Street, SW

Washington, DC 20590

U.S. Agarwala

Naval Air Development Center

Code 606

Warminster, PA 18974

O.K. Anand

National Science Foundation

1800 G. Street NW

Washington, DC 200Q6

David F. Appleby

Royal Australian Air Force

Office of the Air Attache

Embassy of Australia

1601 Massachusetts Ave.

Washington, DC 20036

J. Ariano

Applied Technology Laboratory

Ft. Eustis, VA 23604

Yayesh Asmerom

Pennwalt Corporation

900 First Avenue

King of Prussia, PA 19406

Phil Badger

Consultant

Box 54

Washburn, lA 50706

M.K. Bernett

Naval Research Laboratory

Washington, DC 20375

Lou Bergan

Atacs Industries

1120 SW 16th Street

Renton, WA 98055

Philip Bloomfield

Pennwalt Corporation

900 First Avenue

King of Prussia, PA 19406

Paul H. Bowen

Westinghouse Electric Corp.

1310 Buleah Road

Pittsburg, PA 15235

A. P. Brackney

Monsanto Company

730 Worcester Street

Indian Orchard, MA 01151

Bobby Brown

Naval Air Systems Command

2624 10th Street, NE

Washington, DC 20018

507
Anthony J. Bukowski

Naval Air Propulsion Center

Parkway Avenue

Trenton, NJ 08628

Harry C. Burnett

National Bureau of Standards

Building 223, Room B-166

Washington, DC 20234

Charles E. Burns

Life Cycle Engineering, Inc.

615 Wesley Drive, Suite 212

Charleston, SC 29407

Andy Cal lahan

Endevco

Rancho Viejo Road

San Juan Capistrano, CA 92675

William M. Capece

General Technology

370 Paoli Avenue

Philadelphia, PA 19128

Nikolaos Caravasos

Boeing Vertol

P.O. Box 16858

Philadelphia, PA 19142

B.W. Christ

National Bureau of Standards

1605 Cryogenics Building

Boulder, CO 80303

Bryan D. Cleveland

Southwest Research Institute

P.O. Drawer 28510

6220 Culebra Road

San Antonio, TX 78284

John F. Clayton

Gulf Canada Research & Development

Sheridan Park

Ontario, Canada L5K1A8

Chester M. Dacres

Naval Surface Weapons Center

White Oak, MD 20910

Raymond J. Dallry

Ferrography (Loxboro Analytical)

78 Blanchard Road

Burlington, MA 08103

George DeLong

Resource Management Systems

1250 Sixth Avenue, Suite 300

San Diego, CA 92101

M.J. Devine

General Technology

2560 Prescott Road

Haverton, PA 19083

Stanley W. Doroff

Mechanical Technology, Inc.

2731 Prosperity Avenue

Fairfax, VA 22031

Walter D. Downing

Southwest Research Institute

P.O. Drawer 28510

6220 Culebra Road

San Antonio, TX 78284

J.G. Early

National Bureau of Standards

Materials Building, Room A-113

Washington, DC 20234

Charles Eby

Monsanto Research Corporation

1101 17th Street, NW

Washington, DC 20036

John R. Elliott

U.S. Army/MIT

125 Lowell Street, Apt. 409

Some rvi lie, MA 02143

Francois Envent

ManTech International Corporation

2341 Jefferson Davis Highway

Arlington, VA 22202

Herb Evans

Pennsylvania Instrument

Spring City, PA 19475

508
J. Fay

Advanced Logistics Management, Inc.

1745 South Jefferson Davis Highway

Arlington, VA 22202

Maj-Britt K. Gabel

Wear Sciences

R.D. 7, Box 70, Gabel Road

Coatesville, PA 19320

Jerry H. Garant

U.S. Marine Corps.

M & L Division, Dev. Center

MCDEC

Quantico, VA 22134

Thomas J. Green, Jr.

SEMCO

Div. of Products Research & Chemical Corporation

410 Jersey Avenue

Gloucester City, NJ 08030

Raymond Guyer

SKF Industries

1100 First Avenue

King of Prussia, PA 19406

Robert A. Hall

U.S. Army Applied Technology

Laboratory

Building 401

Fort Eustis, VA 23604

Robert E. Hartwell

RCA

P.O. Box 588

Burlington, MA 01803

H.R. Hegner

ManTech International Corporation

2341 Jefferson Davis Highway

Arlington, VA 22202

R. Curtis Heinen

Southwest Research Institute

P.O. Drawer 28501

6220 Culebra Road

San Antonio, TX 78284

William Hi 11 an Monsanto

1515 Nicholas Road

P.O. Box 8

Dayton, Ohio 45407

Don P. Hodge

U.S. Army

114 Meeks Drive

Aberdeen, MD 21001

Fred W. Hohn

RCA, Mail Stop 9-2

P.O. Box 588

Burlington, MA 01803

G.W. Holbrook

Dow Corning Corporation

Midland, MI 48640

R.R. Hoi den

Hughes Aircraft Company

Building 110, Mail Station 63

P.O. Box 90515

Los Angeles, CA 90009

Kenneith E. Homer

Optimal Systems, Inc.

P.O. Box 1182

Atlanta, GA 30301

Bradford W. Jameson

Monsanto-Bircham Bend Plant

190 Grochmal Avenue

Indian Orchard, MA 01151

Karl -Edward Johansson

Linkoping University

Linkoping Institute of Technology

Dept. of Mechanical Engineering

S-58183 Linkoping, Sweden

Joseph John

I.R.T.

7650 Convoy Court

P.O. Box 80817

San Diego, CA 92138

509
James M. Kelly

HQ, U. S. Marine Corps (Code LMM-3)

HQMC

Washington, DC 20380

A.J. Koury

Naval Air Systems Command

AIR-4114C

Washington, DC 20361

Robert Kincaid

Spectron Carbide, Inc.

Condominio Las Lomas No. 2

Cadparra Heights, PR 00921

J. King

Pennwalt Corporation

900 First Avenue

King of Prussia, PA 19406

George Kitchen

Bell Telephone Laboratories, Inc.

Murray Hill , NJ 07974

E.E. Klaus

The Pennsylvania State University

133 Chemical Engineering Building

University Park, PA 16802

Judi Komaki

Georgia Institute of Technology

Engineering Experiment Station

Atlanta, GA 30332

P.R. Langston

E. I. DuPont deNemours & Co., Inc.

Centre Road Building

Wilmington, DE 19898

Vincent J. Lanza

Metco Inc.

Richard S. Lee

JOAP-TSC (U.S. Army)

Building 780, NAS

Pensacola, FL 32508

W.M. Lee

The Emerson Consultants, Inc.

8806 Chippenham Parkway

Richmond, VA 23235

Rudolph Lenich

Caterpillar Tractor Company

100 NE Adams Street, AB6D

Peoria, IL 61629

H.T. Lootens

U.S. Army

Aberdeen Proving Ground, MD

21005

K. Ludema

University of Michigan

Department of Mechanical Eng.

Ann Arbor, MI 48109

Malte Lukas

Baird Corporation

125 Middlesex Turnpike

Bedford, MA 01730

P.B. MacPherson

Westland Helicopters, Ltd.

Yeovil

Somerset, England

H.P. Martin

Office of Naval Research

Code 470B

800 North Quincy Street

Arlington, VA 22217

1101 Prospect Ave. Dick McLaughlin

Westbury, NY 11590 RCA

P.O. Box 577

Jorn Larsen-Basse Burlington, MA 01778

University of Hawaii

Department of Mechanical Eng.

2540 Dole Street

Honolulu, HI 96822

510
Ronald E. Mead

USAF, AF Logistics Command

611 Pinewood Place

Beavercreek, OH 45430

Robert Mehrabian

National Bureau of Standards

Materials Building, Room B-266

Washington, DC 20234

William Menth

Metco Inc.

1101 Prospect Avenue

Westbury, NY 11590

Robert W. Messier, Jr.

Eutectic Corporation

40-40 172nd Street

Flushing, NY 11358

Victor Middlebrook

Transportation Systems

Consulting Corporation

P.O. Box 230

5 Stanford Street

Huntington Station, NY 11746

D.V. Minuti

Naval Air Development Center

Code 606

Warminster, PA 18974

Ray Misialek

NAVSSES

Philadelphia, PA 19112

Thomas P. Mortimer

Pratt & Whitney Aircraft

400 Main Street, EB 3S4

East Hartford, CT 06108

Thomas A. Nebel

Monsanto - Bircham Bend Plant

190 Grochmal Avenue

Indian Orchard, MA 01151

Bill Needelman

Pall Corporation

30 Sea Cliff Avenue

Glen Cove, NY 11592

Gerald A, Nowotar^ki

Rilsan Corporation

139 Harris town Road

Glen Rock, NJ 07452

John T. Oakley

Techplan Corporation

65 West Street Road

Warminster, PA 18974

Betty O'Keefe

Rilsan Corporation

139 Harristown Road

Glen Rock, NJ 07452

Daniel Pauze

U.S. Army Propulsion

Laboratory (AVRADCOM)

Lewis Research Center, MS 302-2

21000 Brookpark Road

Cleveland, OH 44135

Sal Pera

RCA - Government .Systems Division

P.O. Box 588

Burlington, MA 08803

M. Peterson

Wear Sciences

925 Mallard Circle

Arnold, MD 21012

H.E. Pohlenz

Hughes Helicopters, Inc.

Centinela and Teale Street

Culver City, CA 90230

H. Porter

Advanced Logistics Management

Incorporated

1745 South Jefferson Davis Hwy.

Arlington, VA 22202

S.B. Poteate

Applied Technology Laboratory

Ft. Eustis, VA 23604

511
Robert Pond, Jr.

USNA

117 Glen Aryle

Baltimore, MD 21212

John P. Pruett

Kelly Air Force Base

SA-ALC/MMETS

Kelly, AFB, TX 78241

G.G. Quirk

Monsanto Company

730 Worcester Street

Indian Orchard, MA 01151

Raul A. Raudales

Industrias Ra

P.O. Box 230, Coma ya guela

Honduras, Central America

B.R. Reason

Cranfield Institute of Technology

Cranfield, Bedford MK43 OAL

United Kingdom

N.D. Rebuck

Naval Air Development Center

Code 6061

Warminster, PA 18974

Richard Rio

Mechanical Technology, Inc.

968 Albany-Shaker Road

Latham, NY 12110

Donald J. Rokos

Interlube, Inc.

205 W. Grand Avenue, Suite 125

Bensenville, IL 60106

Harry Rolka

Dow Corning Corporation

Mail Stop 10

Midland, MI 48640

A.W. Ruff

National Bureau of Standards

Materials Building, Room B266

Washington, DC 20234

S. Sarian

ReLuxtrol , Inc.

333 Victory Avenue

South San Francisco, CA 49080

R.L. Scharpf

Applied Technology Laboratory

Ft. Eustis, VA 23604

G.N.D. Seddon

University of Manchester

Simon Engineering Labs.

Oxford Road

Manchester Ml 3 9PL

United Kingdom

Peter Senholzi

Mechanical Technology, Inc.

1656 Homewood Landing Road

Annapolis, MD 21401

J. P. Sharma

Indian Institute of Technology

Hauz Khos

New Delhi, India 110029

Jon A. Shelton

USCPSC

5401 Westbard Avenue

Bethesda, MD 20207

T.R. Shives

National Bureau of Standards

Materials Building, Room All

3

Washington, DC 20234

William Skewis

Eagle Technology Inc.

2300 S. 9th Street

Arlington, VA 22204

Richard M. Slayton

Pratt & Whitney Aircraft

71 Saginaw Street

South Windsor, CT 06074

512
Richard Smith

Shaker Research

Northway 10 Executive Park

Ballston Lake, NY 12019

J.E. Stern

Trident Engineering Associates

1507 Amherst Road

Hyattsville, MD 20783

William C. Stitzel

Armco, Inc.

703 Curtis Street

Middletown, OH 45043

C. Trainer

Interlube Systems

Plymouth, England

Steven VanHoff

Puget Sound Naval Ship Yard

Bremerton, VA 98314

James L. Vannest

Fafnir Bearing Division

Textron, Inc.

37 Booth Street

New Britain, CT 06050

John F. Wagner

Mechanical Technology, Inc.

968 Albany-Shaker Road

Latham, NY 12110

Jeff Warren

NSWC - White Oak (Navy)

Code R34

White Oak, MD 20910

W.A. Willard

National Bureau of Standards

Materials Building, Room A-113

Washington, DC 20234

E. John Wootten

Bruel & Kjaer Instruments, Inc.

185 Forest Street

Marlborough, MA 01752

G. Allan Whittaker

Honeywell , Inc.

2600 Ridgway Parkway

Minneapolis, MN 55413

Anthony Wu

Science Division, C.C.N. A. A.

4301 Connecticut Avenue, NW

Suite 132

Washington, DC 20008

Donald J. Yanusko

Pennsylvania Instrument

Service Corporation

R.D. 1, Box 231

Spring City, PA 19475

Ronald W. Yound

Rockwell International

Rocketdyne Division

6633 Canoga Avenue

Canoga Park, CA 91304

513
MFPG PUBLICATIONS

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March 27, 1969

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514
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November 2-4, 1971

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516
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517
NBS.n4A (REV. 2.8C) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO. SHEET (See instructions) NBS SP 640 October 1982

4. TITLE AND SUBTITLE

Innovation for Maintenance Technology Improvement . Proceedings of the 33rd Meeting

of the Mechanical Failures Prevention Group held at the National Bureau of Standards,

Gaithersburg, MD, April 21-23, 1982.

T. Robert Shives and William A. Willard, Editors

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struct/on s) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

Final

. a

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

Center for Materials Science, National Bureau of Standards, Washington, DC 20234; Naval

Air Systems Command, U.S. Dept. of the Navy, Washington, DC 20360; Office of Naval

Research, U.S. Dept. of the Navy, Arlington, VA 22217; National Aeronautics and Space

Administration, Goddard Space Flight Center, Greenbelt, MD 20771

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 82-600598

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

These proceedings consist of a group of 34 submitted entries (32 papers and 2 abstracts

from the 33rd meeting of the Mechanical Failures Prevention Group which was held at the

National Bureau of Standards, Gaithersburg, Maryland, April 21-23, 1981. The subject

of the symposium was maintenance technology improvement through innovation. Areas of

special emphasis included maintenance concepts, maintenance analysis systems, improved

maintenance processes, innovative maintenance diagnostics and maintenance indicators,

and technology improvements for power plant applications.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

fault detection/location system; lubrication; maintenance; maintenance management;

maintenance technology; manpower utilization; reliability assessment.

13. AVAILABILITY

[X~| Unlimited

[ 1 For Official Distribution. Do Not Release to NTIS

|X I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

518

15. Price

$11.00

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