1

Abstract

The U.S. Environmental Protection Agency (EPA) has funded

a pilot project to assist small and medium-size manufacturers

who want to minimize their generation of waste but who lack

the expertise to do so. In an effort to assist these manufacturers Waste Minimization Assessment Centers (WMACs) were

established at selected universities and procedures were

adapted from the EPA Waste Minimization Opportunity Assessment Manual (EPA/625/7-88/003, July 1988). That document has been superseded by the Facility Pollution Prevention

Guide (EPA/600/R-92/088, May 1992). The WMAC team at the

University of Tennessee performed an assessment at a plant

that manufactures aircraft landing gear. Metal forgings undergo

machining operations to form the various components needed

to manufacture the landing gear. The resulting components are

heat treated offsite, chrome plated offsite, painted, and assembled into the final product. The team’s report, detailing

findings and recommendations, indicated that painting-related

wastes are generated in large quantities and that significant

cost savings could be realized by reactivating the currently

unused electrostatic paint spray system.

This Research Brief was developed by the principal investigators and EPA’s National Risk Management Research Laboratory, Cincinnati, OH, to announce key findings of an ongoing

research project that is fully documented in a separate report

of the same title available from University City Science Center.

Introduction

The amount of waste generated by industrial plants has become an increasingly costly problem for manufacturers and an

additional stress on the environment. One solution to the

problem of waste generation is to reduce or eliminate the

waste at its source.

University City Science Center (Philadelphia, PA) has begun a

pilot project to assist small and medium-size manufacturers

who want to minimize their generation of waste but who lack

the in-house expertise to do so. Under agreement with EPA’s

National Risk Management Research Laboratory, the Science

Center has established three WMACs. This assessment was

done by engineering faculty and students at the University of

Tennessee’s (Knoxville) WMAC. The assessment teams have

considerable direct experience with process operations in manufacturing plants and also have the knowledge and skills needed

to minimize waste generation.

The pollution prevention opportunity assessments are done for

small and medium-size manufacturers at no out-of-pocket cost

to the client. To qualify for the assessment, each client must

fall within Standard Industrial Classification Code 20-39, have

gross annual sales not exceeding $75 million, employ no more

than 500 persons, and lack in-house expertise in pollution

prevention.

The potential benefits of the pilot project include minimization

of the amount of waste generated by manufacturers, and

reduction of waste treatment and disposal costs for participating plants. In addition, the project provides valuable experience for graduate and undergraduate students who participate

in the program, and a cleaner environment without more regulations and higher costs for manufacturers.

Methodology of Assessments

The pollution prevention opportunity assessments require several site visits to each client served. In general, the WMACs

Pollution Prevention Assessment for a Manufacturer of

Aircraft Landing Gear

ENVIRONMENTAL

RESEARCH BRIEF

Richard J. Jendrucko*, Susan D. Morton*, Todd M. Thomas*,

and Gwen P. Looby**

* University of Tennessee, Department of Engineering Science and Mechanics

* University City Science Center, Philadelphia, PA

E AP

United States

Environmental Protection

Agency

National Risk Management

Research Laboratory

Cincinnati, OH 45268

Research and Development EPA/600/S-95/032 August 1995
2

follow the procedures outlined in the EPA Waste Minimization

Opportunity Assessment Manual (EPA/625/7-88/003, July 1988).

The WMAC staff locate the sources of waste in the plant and

identify the current disposal or treatment methods and their

associated costs. They then identify and analyze a variety of

ways to reduce or eliminate the waste. Specific measures to

achieve that goal are recommended and the essential supporting technological and economic information is developed. Finally, a confidential report that details the WMAC’s findings

and recommendations (including cost savings, implementation

costs, and payback times) is prepared for each client.

Plant Background

This plant manufactures aircraft landing gear. It operates 24 hr/

day, year-round to produce over 300 landing gear units annually.

Manufacturing Process

The plant manufactures many different aircraft landing gear

components which are assembled into complete landing gear

units for various commercial and military aircraft models. Raw

materials used by the plant include steel, aluminum, and titanium forgings, fasteners, and bushings. The basic processes

used by the plant are described below in more detail.

Machining

Steel, aluminum, and titanium forgings are inspected upon

receipt for acceptable quality. Forgings that fail inspection are

returned to the vendor. The acceptable forgings undergo machining operations—sawing, milling, grinding, drilling, boring,

reaming, turning, stamping, forging, and shaping—to achieve

the desired shape and dimension. After machining, the forgings

are sprayed with a protective oil coating that controls corrosion

until the forgings undergo grinding; an alkaline wash solution is

used to remove the oil coating before grinding.

After grinding, the forgings are honed and buffed to smooth

their surfaces; spray-washed with an alkaline cleaner; and

blown dry using compressed air. Another protective coating of

oil is applied to parts which are then stacked on pallets and

shipped offsite to a heat-treating facility.

Heat-treated parts are machined, honed, and deburred after

they are returned to the plant. The parts are cleaned, sprayed

with corrosion-preventing oil, and shipped offsite for hard-chrome

plating. The plated parts are placed in a temporary storeroom

or sent directly to painting and assembly after they are returned to the plant.

Painting and Plating

Aluminum, nickel, and bronze bushings are pressed into the

forgings. Occasionally, touch-up plating is necessary on some

small parts. The touch-up plating is done on an in-house

plating line that consists of six separate tanks for cleaning,

rinsing, and plating. Following touch-up plating, the parts are

cleaned in a cold solvent-cleaning tank.

Next the parts are vapor-degreased and blown dry with compressed air. In preparation for painting, plated surfaces on the

parts are masked with paper and tape to prevent plating in

those areas. A coat of primer pre-mix is then sprayed onto the

parts. The primed parts are transported through an electric

infrared drying oven. After the primer has cured, a finish coat of

paint is applied. The parts are then transferred into the drying

unit for final paint curing and placed in a circulating air cooldown chamber. Lastly, a final layer of clearcoat is applied to all

parts.

After the painting process, a corrosion preventative is applied

to all unpainted surfaces and the parts are palletized and

transported to the assembly area.

Assembly

The landing gear components parts are de-masked and mechanically fastened together to produce complete assemblies.

All hydraulic parts are pressure-tested for oil leaks. Finished

units are sent to the packaging and shipping area.

An abbreviated process flow diagram for the production of

aircraft landing gear is shown in Figure 1.

Existing Waste Management Practices

This plant already has implemented the following techniques to

manage and minimize its wastes.

• Certain operations that generated 1,1,1-trichloroethane and

perchloroethylene waste streams have been eliminated at

this plant.

• A separate employee committee is responsible for tracking

each waste stream in the plant. The goal of each committee

is a 10% reduction in quantity of waste generated.

• Cardboard and paper waste is recycled.

• Fluid evaporators are used to concentrate waste coolant,

thereby reducing the volume of waste shipped offsite.

• Many chemicals and solvents are purchased in bulk to

eliminate disposal of small non-reusable containers.

• Solid paint waste is compacted to reduce its volume before

it is shipped offsite.

• 1,1,1-trichloroethane is no longer used as a hand-washing

agent.

• The temperature of the vapor degreaser has been lowered in

order to reduce evaporative losses of 1,1,1-trichloroethane.

• A recycling unit has been installed in the paint spraying areas

to reclaim waste paint solvent.

Pollution Prevention Opportunities

The type of waste currently generated by the plant, the source

of the waste, the waste management method, the quantity of

the waste, and the waste management cost for each waste

stream identified are given in Table 1.

Table 2 shows the opportunities for pollution prevention that

the WMAC team recommended for the plant. The opportunity,

the type of waste, the possible waste reduction and associated

savings, and the implementation cost along with the simple

payback time are given in the table. The quantities of waste

currently generated by the plant and possible waste reduction

depend on the production level of the plant. All values should

be considered in that context.

It should be noted that the economic savings of the opportunities, in most cases, results from the need for less raw material

and from reduced present and future costs associated with

waste treatment and disposal. Other savings not quantifiable

by this study include a wide variety of possible future costs
3

related to changing emissions standards, liability, and employee health. It also should be noted that the savings given for

each opportunity reflect the savings achievable when implementing each pollution prevention opportunity independently

and do not reflect duplication of savings that may result when

the opportunities are implemented in a package.

This research brief summarizes a part of the work done

under Cooperative Agreement No. CR-819557 by the University City Science Center under the sponsorship of the U. S.

Environmental Protection Agency. The EPA Project Officer

was Emma Lou George.

Steel, Aluminum,

and Titanium Forgings

Inspection Machining Washing Honing

and Buffing Washing

Compressed

Air

Dry-off

Oil

Spray

Offsite

Heat

Treating

Final

Machining Washing

Final

Grinding,

Honing, and

Deburring

Washing Oil

Spray

Offsite

Chrome

Plating

Onsite

Touch-up

Plating

Bushings

Pressed

in Place

Oil

Spray

Storage

Small Parts

From Storage

Large

Components

From Storage

Cold

Cleaning

Vapor

Degreasing

Masking Priming

Finish Coat Curing

Repainting

De-Masking Cool-down Curing

Storage

Components From

Storage Fastening Testing Packaging

Abbreviated Process Flow Diagram for Manufacture of Aircraft Landing Gear

Figure1. Abbreviated process flow diagram for manufacture of aircraft landing gear.

Table 1. Summary of Current Waste Generation

Annual Quantity Annual Waste

Waste Stream Generated Source of Waste Waste Management Method Generated (lb/yr) Management Cost ($/yr)

Scrap metal Machining Sold to recycler 2,600,000 $-10,460

(credit

received)

Waste coolant Machining Concentrated in evaporator; shipped

offsite to fuels blending program 20,000 40,380

Adsorbent/hydraulic and machining oil Leaks from machines Shipped offsite to controlled landfill 50,000 22,280

Hydraulic and machining oil Periodic machine oil changes Shipped offsite to fuels blending program 20,000 19,060

Abrasive waste Grinding Shipped offsite to landfill 88,000 2,270

Paint liquid waste Painting Shipped offsite to fuels blending program 4,000 15,780

Solid paint waste Painting Incinerated offsite 1,500 13,720
4

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/S-95/032

Table 1. (continued)

Annual Quantity Annual Waste

Waste Stream Generated Source of Waste Waste Management Method Generated (lb/yr) Management Cost ($/yr)

Spent 1,1,1-trichloroethane Vapor degreasing Shipped offsite for recycling 3,000 12,850

Spent paint booth filters Paint booths Incinerated offsite 1,100 14,000

Waste solvent blend Cleaning Incinerated offsite 1,500 8,300

Empty paint containers Painting Shipped offsite for reconditioning 1,800 11,700

Plating liquid waste Touch-up plating Shipped offsite for treatment and disposal 6,000 11,680

Plating solid waste Touch-up plating Incinerated offsite 400 4,110

Evaporated 1,1,1-trichloroethane Vapor degreasing Evaporates to plant air 55,080 0

Evaporated solvent blend Cleaning Evaporates to plant air 34,800 0

Evaporated paint solvent and thinner Painting Evaporates to plant air 900 0

Miscellaneous solid waste Various processes Shipped offsite to landfill 362,000 36,630

Table 2. Summary of Recommended Pollution Prevention Opportunities

Annual Waste Reduction

Net Annual Implementation Simple

Pollution Prevention Opportunity Waste Stream Reduced Quantity (lb/yr) Per Cent Savings ($/yr) Cost Payback (yr)

Reactivate the currently unused electro- Spent paint booth filters 360 33 $36,680 $ 5,500 0.2

static paint spray system in order to improve the paint transfer efficiency.

Install plastic covers with roller tracks Evaporated 49,570 90 22,530 6,960 0.3

on all four sides of the vapor degreas- 1,1,1-trichloroethane

er tank with openings just large enough

for the cables used to suspend the components to reduce evaporative losses of

1,1,1-trichloroethane.

Construct a containment area around the Adsorbent/hydraulic 45,0001 9 12,740 16,750 1.3

bases of the metal working machines to and machining oil

collect waste oil. Use the available wetvacuum to collect the waste oil for disposal

Utilize reusable thin plastic shielding in- Solid paint waste 1,010 67 4,200 2,500 0.6

stead of paper to mask parts prior to the

spray-painting process.

1 Approximately 8,000 lb/yr of waste oil will be collected and disposed of (at a much lower unit cost)