NASA/TMm2001-210670

EHL Transition Temperature Measurements

on a Geostationary Operational Environmental

Satellite (GOES) Filter Wheel Bearing

Mark J. Jansen

AYT Research Corporation, Brook Park, Ohio

William R. Jones, Jr. and Stephen V. Pepper

Glenn Research Center, Cleveland, Ohio

Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland

Bradley A. Shogrin

Jet Propulsion Laboratory, Pasadena, California

January 2001
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NASA / TM--2001-210670

EHL Transition Temperature Measurements

on a Geostationary Operational Environmental

Satellite (GOES) Filter Wheel Bearing

Mark J. Jansen

AYT Research Corporation, Brook Park, Ohio

William R. Jones, Jr. and Stephen V. Pepper

Glenn Research Center, Cleveland, Ohio

Roamer E. Predmore

Goddard Space Flight Center, Greenbelt, Maryland

Bradley A. Shogrin

Jet Propulsion Laboratory, Pasadena, California

National Aeronautics and

Space Administration

Glenn Research Center

January 2001
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Available electronically at http://gltrs.grc.nasa.gov/GLTRS
EHL Transition Temperature Measurements on a Geostationary Operational

Environmental Satellite (GOES) Filter Wheel Bearing

Mark J. Jansen

AYT Research Corporation

Brookpark, Ohio

William R. Jones, Jr. and Stephen V. Pepper

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio

Roamer E. Predmore

National Aeronautics and Space Administration

Goddard Space Flight Center

Greenbelt, Maryland

Bradley A. Shogrin

Jet Propulsion Laboratory

California Institute of Technology

Pasadena, California

ABSTRACT

The elastohydrodynamic lubrication (EHL) transition

temperature was measured for a Geostationary

Operational Environmental Satellite (GOES) sounder

filter wheel bearing in a vacuum tribometer. Conditions

included both an 89 N (20 lb.) hard and soft load, 600

RPM, temperatures between 23°C (73°F) and 85°C

(185°F), and a vacuum of approximately 1.3xlo 5 Pa.

Elastohydrodynamic to mixed lubrication started to occur

at approximately 70°C (158°F).

INTRODUCTION

The Geostationary Operational Environmental Satellite

(GOES) program provides constant and reliable weather

data to the United States. The key element in the

program are satellites that operate in geosynchronous

orbit and monitor the United States, Atlantic, Pacific, and

Central and South America. One of the main

instruments on the satellite is the Sounder unit, which is

used to measure vertical atmospheric temperature and

moisture profiles, surface and cloud top temperature,

and ozone distribution [1].

The GOES Sounder utilizes a filter wheel (FW)

consisting of 19 spectral bandpass filters mounted on a

29.2 cm (11.5") aluminum disk. The disk is rotated at a

constant 600 RPM by a synchronous hysteresis motor.

Infrared radiation passes through the filters and strikes

detectors. By sensing the amount of energy passing

through each filter, the spectral make-up of earth's

infrared radiation is determined. Proper operation

requires that the wheel's wobble and jitter be minimized.

The assembly utilizes a duplex bearing pair (MPB 1219).

These bearings have 440C diamond polished,

passivated races, TiC coated 440C balls, and polyimide

cages. The HIRS sounder for Tiros has a similar

bearing system. The cage is impregnated with 130 mg

of a perfluoropolyether (Krytox 143AB). In addition,

20 mg of free oil is added to each bearing. Required

orbital life is 5 years and design life is 7 years.

Operating conditions were predicted to be 8°C (46°F) to

38°C (100°F) with a preload of 89 N (20 lb.). Under

these conditions, the bearings should operate in the EHL

regime. The FW successfully passed a six-year

qualification test at these temperatures.

After GOES 8 launch, telemetry indicated that the FW

motor housing was operating at temperatures to 53°C

(127°F) each day and at one point had reached 59°C

(138°F). Concern was raised about shortened FW life

due to possible lubricant loss and/or transition from EHL

into mixed lubrication.

The purpose of this work was to explore the transition

from EHL to boundary lubrication as a function of

temperature. Therefore, a series of tests were

performed on a replica bearing in a vacuum tribometer

capable of measuring torque and the EHL transition

temperature. Conditions included an 89 N (20 lb.) hard

or soft load, 600 RPM, Krytox 143AB lubricant,

temperatures between 23°C (73°F) and 85°C (185°F),

and a vacuum of approximately 1.3x10 s Pa.

NASA/TM--2001-210670 1
EHL CALCULATIONS

EHL is the regime that describes a bearing where the

balls and races are completely separated by a lubricant

film. EHL film thickness calculations [2], assuming a

fully flooded inlet, were completed using the appropriate

FW bearing parameters including an 89 N (20 lb.) load, a

rotational speed of 600 RPM, and lubricant properties

such as pressure viscosity coefficients, kinematic

viscosity, and density. Minimum film thickness (p.m) at

the inner race-ball contact as a function of temperature

(°C) appears in Figure 1. The transition from EHL to

mixed lubrication would first appear at the inner race, as

the film thickness at the inner race-ball contact is less

than that at the outer race-ball contact. The pressureviscosity coefficient and the absolute viscosity of the oil

are the driving force behind the temperature-thickness

relationship.

0.6 ..........

" 0.4 •

"_ 0,3

FE 0.2 E.

o.1_

0

25 75 125 175

Temperature (°(3)

between 1 and 3. At A-values tess than approximately

one, boundary lubrication ensues with continual asperity

contact and little contribution from fluid films. A-values

were calculated for the MPB 1219 bearing and Krytox

143AB and are shown in Figure 2. Surface roughness

(RRMs)for both the ball and race were assumed to be

0.025 p.m (1 microinch). This surface roughness is for

commercial quality bearings and is the worst-case

scenario; flight quality bearings are expected to have a

lower surface roughness. Based on these values, the Avalue drops below 3 near 95°C (203°F).

15 -- _ m __ _

13 i --

o 11

n- 9

E 7

5

3

25 75 125 175

Temperature (°C)

Figure 2 - Lambda ratio for MPB 1219 bearing and Krytox 143AB as a

function of temperature assuming a race and ball surface roughness of

0.025 _m (1 microinch)

EXPERIMENTAL

Figure 1 - Film thickness as a function of temperature for Krytox 143AB

and a MPB 1219 angular contact bearing assuming a fully flooded

contact

LAMBDA RATIO

Obviously, asperity contact between the ball and race is

a function of both film thickness and surface roughness.

All else being equal, smoother surfaces can operate with

thinner film and still remain in the EHL regime. A

common parameter used to estimate the degree of

surface contact is the lambda (A) ratio. The A-ratio is

calculated by dividing the minimum film thickness by the

composite surface roughness (co), which is the square

root of the sum of the squares of the ball and race

surface roughnesses (R,_s). In general, A-ratios greater

than three indicate complete surface separation. A

transition from full EHL to mixed lubrication (partial EHL

film and some asperity contact) occurs in the A range

APPARATUS

The GOES bearing test facility (Figure 3) [3] was used to

evaluate a FW bearing prepared by ITT to flight

specifications. Bearings were from a lot that was

rejected for minor defects, which did not affect the shortterm tests. Parameters measured include torque,

temperature, cross race resistance, load, and vacuum

level. Cross race resistance is determined by placing a

known resistance in parallel with the bearing. A DC

current source is applied across these resistances to

allow a maximum of 1 mv to be developed across the

fixed resistor for infinite contact resistance. Non-infinite

resistance lowers the potential developed across the

parallel pair to less than 1 mv. The potential is

measured and the resistance is obtained from the circuit

equation. A single bearing (SN 7-1115A) was placed in

the bearing assembly and subjected to a normal run-in

procedure, except that vacuum was used instead of

ambient air. After run-in, the bearing was subjected to a

variety of tests, including the effect of temperature on

film formation and speed on contact resistance.

NASA/TM--2001-210670 2
1.0E+6

E 1.0E+4-

to.9_.

o 1.0E+3 : ........

t-"

_ :

._m i

if/ i

1.0E+2 + .... or"

i

1.0E+1 _ .....

BEARING FIXTURE

1.0E+0 ...... ' ......

0 100 200 300 400 500 600

Speed (RPM)

Figure 4 - Resistance as a function of speed using 89 N hard load,

vacuum ~1.3x10 ' Pa, 23°C

Figure 3 - GOES bearing test rig and bearing fixture

EFFECT OF SPEED

At the end of run-in, a torque trace was performed

(0.5 rpm and 27 N (6 lb.) load). This was for comparison

with the low speed dynamometer trace made at the

FW manufacturer. Sinusoidal traces were obtained both

CCW and CW. This is in contrast to the flat traces from

the FW manufacturer. It is suspected that this may be

due to an alignment problem in the bearing test rig. At

any rate, the average torque for the NASA data was

approximately 3.2x10 .3 Nm (0.45 in-oz.) compared to the

ITT result of 3.1x10 3 Nm (0.43 in-oz.).

Contact resistance as a function of speed using an 89 N

(20 lb.) hard load appears in Figure 4. A hard loaded

system meant that the bearing was held rigidly, with a

load applied through a screw mechanism. A soft load

allowed the bearing a degree of freedom and was

implemented with a dead weight. The transition

between EHL and mixed lubrication occurred between

100 and 200 rpm at room temperature (23°C).

EFFECT OF TEMPERATURE

The effect of temperature on torque and contact

resistance was observed at a constant speed of

600 RPM. A thermocouple was spot welded to the

bottom of the inner race and an infrared heat lamp was

directed on the bearing assembly through the window.

The temperature-time trace is shown in Figure 5.

90

80

3O

20 c

0 100 200 300

Time (min)

Figure 5 - Heating rate of GOES test facility using heat lamp and 89 N

hard load

NASA/'rM--2001-210670 3
As can be seen, a heating rate of approximately

0.5°C/min (0.8°F/min) was attained. Torque and

resistance as a function of temperature appear in

Figures 6a and 6b, respectively. This was the first time

this facility was operated above room temperature using

a hard load. The hard load is effected by a precision

screw mechanism below the test rig [3], which simulates

the condition in the filter wheel. The elevated

temperatures caused the bearing to unload, reaching

30 N (6.8 lb.) at 82°C (180°F). The transition from EHL

to mixed lubrication occurred about 70°C (158°F).

6.0E-3

5.5E-3

5.0E-3

4.5E-3

E

zv 4.0E-3

=e 3.5E-3

E

o 3.0E-3

2.5E-3

2.0E-3

O

1.5E-3 r ...........

1.0E-3 ; ....

20 40 60 80 1O0

Temperature (°C)

A second test was performed on the same bearing using

a soft 89 N (20 lb.) load. A soft load is applied by

disconnecting the screw mechanism and replacing it with

deadweight. This type of loading is not affected by

temperature. In this test, an aluminum shroud was

placed around the bottom of the test fixture to mask the

torque and load sensors from the infrared lamp. The

heating rate 0.35°C/min (0.45°F/min) (Figure 7) was

neither as efficient nor as linear. Start up torque was

lower, 4.6x10 3 Nm (0.65 in-oz), but the final value at

85°C (185°F) was 2.6x10 a Nm (0.37 in-oz), which was

similar. There was a drop of contact resistance (Figure

8) at 54°C (130°F), but the rapid decrease occurred at

approximately 70°C (158°F).

RESULTS

INSPECTION

Inspection of the bearing components at low

magnification (10x) showed no unusual features,

evidence of surface distress, or other damage. There

was no obvious ball banding or tracking. There was a

thin, non-uniform layer of oil on the ball surface. The

infrared signature of this layer was identical to virgin

Krytox 143AB.

Figure 6(a) - Torque as a function of temperature using an 89 N hard

load

7.0E+5

6.8E+5 - e-->__

6.6E+5

'6.4E+5

6.2E+5

6.0E+5

5.8E+5

5.6E+5 -

5.4E+5 -

5.2E+5 -

5.0E+5 -

20 40 60

Temperature (°C)

80 100

Figure 6(b) - Resistance as a function of temperature for 89 N hard

load

9O

80 _p Off

I-_vE _"°_"_7045060 "- __'_ ___

30

Heat Lamp On

20

0 200 400 600 800

Time (min)

Figure 7 - Heating rate of GOES test facility using heat lamp and 89 N

dead weight

NASA/TM--2001-210670 4
8.0E+5 _

7.0E+5

6.0E+5

E 5.0E+5 .....

4.0E+5" - .....

t"

•_ 3.0E+5 ,

rr

2.0E+5

1.0E+5

0.0E+0 - _ - " •

20 40 60 80 100

Temperature(°C)

Figure 8 - Resistance as a function of temperature for MPB 1219

bearing using an 89 N dead weight load, CCW Rotation

RECOMMENDATIONS

1. An actual GOES-FW assembly should be

instrumented and tested in vacuum for motor

housing temperatures to 70°C (158°F). Bearing

temperatures should be monitored and lubricant loss

rates should be determined as a function of

temperature.

2. GOES-8 and GOES-J sounder bearings should

never be operated above 70°C (158°F).

REFERENCES

1. "GOES I-M DataBook", Loral Space Systems, Ref. #S415-19, August, 1996.

2. Hamrock, B.J., Dowson, D., Ball Bearing Lubrication. The

Elastohydrodynamics of Elliptical Contacts, John Wiley &

Sons, Inc., 1981.

3. Jones, W.R., Jr. et al., "The Preliminary Evaluation of

Liquid Lubricants for Space Applications by Vacuum

Tribometery", 28'h Aerospace Mech. Symp., May 18-20,

1994.

CONCLUSION

1. Operation of FW bearings (MPB 1219) lubricated

with Krytox 143AB, preloaded to 89 N (20 lb.), and

operating at 600 RPM and at temperatures less than

70°C (158°F) is not detrimental, since EHL

conditions still exist, as indicated by the infinite

electrical resistance across the bearing.

2. Transition from EHL to mixed lubrication appears to

occur above 70°C (158°F) and will limit bearing

lifetime (possibly to months) at 600 RPM.

3. Experimental measurements of the temperature for

transition from EHL to mixed, agrees well with

theory.

NASA/TM--2001-210670 5
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3, REPORT TYPE AND DATES COVERED

January 2001 Technical Memorandum

4. TITLE AND SUBTITLE

EHL Transition Temperature Measurements on a Geostationary Operational

Environmental Satellite (GOES) Filter Wheel Bearing

6. AUTHOR(S)

Mark J. Jansen, William R. Jones, Jr., Stephen V. Pepper,

Roamer E. Predmore, and Bradley A. Shogrin

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135- 3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

'5. FUNDING NUMBERS

WU-251-30-2E-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12576

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--2001-210670

11. SUPPLEMENTARY NOTES

Mark J. Jansen, AYT Research Corporation, 2001 Aerospace Parkway, Brook Park Ohio 44142; William R. Jones, Jr.

and Stephen V. Pepper, NASA Glenn Research Center; Roamer E. Predmore, NASA Goddard Space Flight Center,

Greenbelt, Maryland 20771; and Bradley A. Shogrin, Jet Propulsion Laboratory, California Institute of Technology,

Pasadena, California 91109. Responsible person, Mark J. Jansen, organization code 5960, 216--433---6054.

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Available electronically at htto://_ltrs.m'c.nasa._ov/GLTRS

This publication is available from the NASA Center for AeroSpace Information. 301-621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The elastohydrodynamic lubrication (EHL) transition temperature was measured for a Geostationary Operational Environmental Satellite (GOES) sounder filter wheel bearing in a vacuum tribometer. Conditions included both an 89 N (20 lb)

hard and soft load, 600 rpm, temperatures between 23 °C (73 °F) and 85 °C (185 °F), and a vacuum of approximately

1.3x 10 -5 Pa. Eiastohydrodynamic to mixed lubrication started to occur at approximately 70 °C (158 °F).

14. SUBJECT TERMS

Elastohydrodynamic; Tribology

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