GREASES hhhEhhE EEEEEEA project was initiated to develop a methodology for predicting the L1O life of grease products under a laboratory testing environment. The LIO life value is

AD-R165 963 DEVELOPING AN ACCELERATED ENDUANCE TEST FOR GREASES - V/1ASTATUS REPORT(U) ARMY BELVOIR RESEARCH DEVELOPMENTRW ENGINEERING CENTER FORT DELVOIR VA I RMEE RUG 6?

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~ United States ArmyBelvoir Research. Develooment & Engineering CenterFort Belvoir. Virginia 22060-5606 -S

Report 2453

Developing an AcceleratedEndurance Test forGreases-A Status Report

Authored By:

In-Sik Rhee

Report Date:

August 1987

Approved for public release; distribution unlimited.

c", I 1 ' 1987

87 10 . 065

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I,"; CLAS SIIED

REPORT DOCUMENTATION PAGE M',8o P'o

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UNCLASSIFIED

2a ECR - C AS C:. C0% AJ'-CRI'y 3 DSR 8,- O% AwA .Ai L., 0 QECRApproved for Public Release; distribution

42 DECASSFCA- O% DOVORADG SC..EDLiL Unlimited

SERFORM NG O, RGA\,ZA 0% 4EPOR %4,MBERS . S MONTOR %G ORGAAZN O' E0 05 .:VSE,-

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6,a A M E OF PERFORM NG :QCA' ZA- ON 60 CF; CE S 'BO. 7a %AME OF ,O'.7 0R:NG OPGA'. ZA' 0%- Fuels & Lubricants Div., Matis, ifao ,locabe)

Fuels, Lubes Laboratory STRBE-VF

6c A.DRESS Cry. Stare an 2'PC,.oe) o ADDRESS C:ry, State and ZtP Code)

Ft. Belvoir, VA 22060-5606

Sa AlIE 'OF D'46 SPOSOR".6 8b ;;: CE S 'ISO" 9 PROCPEMET %S-R ME'j- DE'YFCA7CN ','SE2ORGANIZA' ON (It appicable)

8c. ADDRESS (C ty, State. and ZIP Code) '0 SOL!PCE OF :,1D NG NuiOSERSPROGRAM :RO,ECT -ASK ,ORK %,"ELEMENT NO NO NO ACCESSON %O

% "L- (include Security C;assiticarionJDEVELOPING AN ACCELERATED ENDURANCE TEST FOR GREASES--A STATUS REPORT

*2 PERSONAL Ai7-O)R(S)In-Sik Rhee

13a TYPE OF REPORT 113b TIME COVERED -4 DATE OF RE ORT (eear, Month, Oay) 15 PAGE CO04Interim Report FROM _ To Aug 1987

'6 SUPPLEMENTARY NOTAT ON

7 COSAT. CODES '3 SBEC" -ERMS Continue on reverse i necessary and oentify by block number)

S',ELD GROUP SlE-GROuP

'9 A STRAC" Continue on reverse if necessary and ;aentty by Mlock number)" The objective of this study was to develop a grease endurance test method which can be

utilized in the comprehensive test methodologies being developed for predicting the

performance life of military grease under laboratory environment. In an initial study, the

ASTM D3527 test method, "Life Performance of Automotive Wheel Bearing Grease" has been

evaluated because it is supposedly simulating an operating environment and has widespread

applications. The results show that this method has-poor precision, long-endurance test time

and poor simulation of field conditions. In particular, the termination criteria used in th.method tend to extend grease life. solve t,,e 'rl;-em, " te: t Itie te'-- :'ic- r i :.r'i ,et.

developed based on the softening of grease, which reduced the test time and distinz'aished

between a good and a poor grease as well as the current method is able to JD. 71 define T-e

LlO life of MIL-G-10924 grease, baseline tests were conducted usinz the AST'l D35- 2 ethodThe LIO life of this grease is less than 20 h. Such a grease is no,_ satistsaCt:rv .,nivehicles with wheel bearings that are equipped with disc braves.

DO FORM 1473,sa~ '74 VAR~ Si ' -UA, rOrre C 'o~ 31 -Is~

CONTENTS

Section Page

I IN T R O D U C T IO N ................................................................................. 1

II OVERALL REVIEW OF ASTM D3527 METHOD .........................................

III THE LOADING REQUIREMENT ON THE ASTM D3527 METHOD .............. 5

IV NEW TERMINATION CRITERIA FOR THE ASTI D3527 METHOD ........... 11

V THE REQUIREMENT OF L10 LIFE OF GAA IN THE ASTM D3527M E T H O D ..................................................................................... 16

VI DISCUSSION AND CONCLUSIONS ................................................... 19

BIBLIO G RA PH Y ............................................................................. 20

Figure

1 Termination Profile of the ASTM D3527 Method ........................ 4

2 Life of MIL-G-10924C Grease at Two Different Loading Systems ................... 6

3 Life of MIL-G-10924C Grease in the Modified ASTM D3527 Method ............ 7-8

4 Life of M IL-G-10924C Grease in the SKF Method ...................................... 9-10

5 Oxidation Stability T.st Results of the Candidate Grease forM IL-G-10924E in the PDSC M ethod .................................................. 15-16

6 Life of High Dropping Point Grease, MIL-G-10924D .............................. 17-18

Table

I Grease Endurance Test Conditions in the Modified AST.I D352,M ethod and the SKF M ethod ...............................................................

2 The Physical and Chemical Properties of Tested Grea c ................................. 12

3 G rease Life in Both Term ination C riteria ............................. . . ................ 12

C..

:1 o n s st ncy T e t R su l s ... .. ... ... .. ... .. ... .. ... ... .. ... .. ... ... .. ... .. ... i

Section 1. INTRODUCTION

The US Army is presently using a multi-purpose National Lubricating Grease Institute(NLGI) Number 2 consistency grease covered by Military Specification \IIL-G-1092.4.D,"Grease Automotive and Artillery (G.AA)," as the standard grease for all Armvvehicles, artillery, and ground equipment operated worldwide.[1) With rapid advances inautomobile technology, the operational and system requirements of military vehicles andequipment have imposed demands for increased capabilities of the lubricating greases. Tomeet these additional requirements, research is being conducted to develop new perfor-mance criteria that will be required for the -E" revision to MIL-G-10924. One of themajor thrusts in executing this research effort is the development of comprehensive testmethodologies which can be utilized to predict performance life of these militarygreases.

A project was initiated to develop a methodology for predicting the L1O life of greaseproducts under a laboratory testing environment. The LIO life value is a means of defin-ing the minimum life and is an expression meaning the 90 percent reliable grease life inbearings. A research plan was subsequently established for the following three phases:

Phase I: Develop the mathematical modeling system to evaluate functional performance

of grease products.

Phase 11: Select or develop accelerated endurance testing method(s).

Phase III: Correlate laboratory test methodology with field performance.

In one of our previous research efforts, the maximum likelihood (,ML) computer pro-

gram for the two-parameter Weibull probability distribution was developed to meet theprimary objective of Phase I.[2] To provide meaningful input data, the current researcheffort is directed toward developing the grease endurance testing procedure \vhich isplanned in Phase II.

For the last three decades, numerous ball-bearing and roller-bearinL, zrease endurancetests have been devised for laboratory evaluation of grease. Some of them \%ere used tostandardize specific test procedures in the grease industry, while others were used inindividual laboratories for grease development. Among these standard methods, theAmerican Society for Testing and Materials (ASTNi) D3527 test method. "Life Perfor-mance of Automotive Wheel Bearim, Grease," is widelv used in the zrea,,e manutactur-ing and automotive industries. Because of its application and simulation of an operiatiuLen'ironment, a study was conducted to evaluate the ASTNI D352- method prior to

being incorporated into NIIL-G-10924D. This report describes the advantage, and di,ad\an-tages of this method, our findings, and the results of a feasibility ,tudy conduc1CJ todexeiop an accelerated endurance test using this method.

%

S -r - - -

Section II. OVERALL REVIEW OF ASTM D3527 METHOD

The method covers a laboratory procedure for evaluating the high-temperature (160: C)ASTM D3527 under specified conditions. The significance of this method is that it dif-ferentiates among wheel bearing greases having distinctly different high-temperaturecharacteristics only. The current precision is as follows:

Repeatability = 0.8 XReproducibility = 1.2 XIWhere X = average of the two test results

The basic configuration of the test apparatus consists of a simulated front wheel hub-spindle-bearings assembly, a heater, a dc-motor, a tachometer, an elapsed time meter. atorque meter, and a temperature monitor. Two tapered roller bearings were used as thetest specimens in this procedure: LM67048-LM67010 for the inboard bearing, andLM I 1949-LMI1910 for the outboard bearing. Both bearings are currently utilized insmall vehicles. For the test, three main parameters (temperature, load, and speed) wereapplied to this method. Initially, a test temperature of 150-C was selected at the out-board bearing because wheel bearing temperatures associated with front disc brakesystems higher than 150'C were encountered.[3] In 1985, the test temperature was raisedfrom 150 to 160°C at the outboard bearing to provide a more severe test condition. Thetest speed selected was 1,000 rpm. The thrust load of only 25 lbf (representing the vehi-cle curb and axial cornering weight) was applied to the test bearings because the test ap-paratus developed was based on modifications of the ASTM D1263, "Leakage Tenden-.cies of Automotive Wheel Bearing Grease," method.[4] This preload was adapted froma wheel bearing adjusting nut torque value used in light trucks. With these testparameters, grease life was determined when the drive motor torque exceeded a presettorque limit for 30 seconds in 20 hours on, 4 hours off cycle operation.

The advantage of this method was to comprehensively evaluate all individual physicalproperties of greases directly related to high temperature and shear, using a simulatedfront wheel bearing system and a dynamic laboratory bench-type test apparatus. Thedisadvantage of this method was its poor precision. For this reason, this method did nothave the capability to distinguish between the greases having similar high-temperatureproperties. Finally, the test results provided limited correlation to field performance.

Since this method was issued, it had not been extensively utilized in grease research anddevelopment and specifications because of its poor precision, long endurance test time.and questionable correlation with field vehicle operation condition,. The ASTMI Com-mittee D2 Subsection B0.04 on Automotive Greases is currentlv .e~eloping a Cha,i,Grease and Wheel Bearing Grease specification to co,.er lubricatmng !rcalc Ntutahlc torthe periodic relubrication of commercial vehicles.[5] In thi, \hccl bcarin,',p2cificat on.the ASTNI D35" method P, listed %iIh its minimum requircment 8S1) hour,, Dluc to ihemethod', poor precision, the follo% inL paragraph 1, iclIded to ti1t !h1, rlqmlrente1i:

"The test reqiiiremewls (lit/fits) M.i VL0I il /isSkc! tltLtlU(i te' as*C /icr jje aSe 1iuu I,.

flhinilnfhl) or mlaxvi?7 (ICCe'ptcth/e valueis '/ria! (lit/'(IiCl test 111'suls. \o uIdllt

corrections for test ,Dre'ct ioi, such cas Iescrlth'd mn the -1S TV D2244. '' t!I,1allo ofTest Data to Determine Conf-1ormance viiih Spe'eilicailon5, '' tire to be a~pp/iedI Inismlchas the pre, ision of the test methods itere takeni 1i110 CheCoW1it? 111Cile deternii1iattu1i Of tiherequi remettS.

Hos ever. the US Army currently uses a modified version of ASTNI D352- In theMI L-G-l0924 specification without the above reser, ation. The currently identified

* problem areas are the termination criteria and the test temperature measuremient techni-que[6.71 According to the ASTNI D3527, the test temperature is measured from thlespindle hole in which the thermocouple is inserted, resulting in a temperature gap of 20to 30 :C between the chamber and spindle. It appears that the test temperature 1, :Iose-to the chamber temperature instead of the spindle temperature because the test sprecimen

* (\ heel beacrig hub system) is fully open in the chamber and the heat transfer I"*facilitated by hot air in the chamber. Therefore, the actual test temperature I, a')NUrmed

to be higher than 160 C.

The problems associated \%Vi the ASTNI termination criteria used in this method are:

e As a consequence of the cy clic operation, the resulting grease life is probablylongzer than the actual life of the 2rease.

* Test results are unrepeatable.

* Since the torque rarely reaches the preset torque limit, there is a termina-tion problem.

* The test is terminated at room temperature rather than the test temperature.

* The termination profile of the ASTNI D352' method is shown in Figure I . The'eproblems directly affect precision. To sole these problems, the ASTNI GO .05 SLIbKcC-

tiLn is ,tdy possible modification to this test machine. Ever since this miethod 1 -1been issued. there ha\e been informal reports of frequent equipment problen>-,.

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Section iii. THE LOADING REQUIREMENT ON THE ASTM 1)3527 METHOD

The primary objective of this study was to establish a comparati e baseline for loadin2requiements (i.e., test severity) of the three major test parameters (temperature, load,,,and speed) to be used in the laboratory grease endurance test procedure. The equipmenttargeted for use in developing this wear-life projection was the AST.! D3_527 test ap-paratus. Because of questions concerning test parameters, the major focus on this ap-paratus was the radial load (vehicle weight) which had been used as a test parameter inpreviously conducted grease investigations using the SKF grease test procedure. [8.9.10]

For this reason, a study was conducted to determine whether the radial load should beconsidered as a test parameter in the grease endurance test procedure. This task was per-formed using the differences of two test methods (ASTNI, SKF). The major differencesof these methods were the load treatment on the test bearing, termination criteria, andtest operation (continuous vs. cycle operation). To make a comparison, the grease en-durance tests were performed according to the Modified ASTM D3527 test method. Thegrease used in these tests was a qualified NIIL-G-10924C grease evaluated previously us-ing the SKF grease test method. Table 1 presents test conditions.

Thirteen data points were generated using the four ASTNI D3527 test devices. Due tothe poor precision, the MIL-G-10924C "grease life" was determined using the MIL com-puter program. The LIO life of the MIL-G-10924C grease was projected to be 238 hours.This L1O life value was approximately eight times longer than that previously obtainedfrom the SKF method which gave an LIO life of 32 hours. This implied that the greaselife also depends on the load as well as the temperature. Therefore, the results indicatedthat the radial load (vehicle weight) should be used as a test parameter in the grease per-formance test. These test results are plotted to make a comparison in Figure 2, and theirtest results are provided in Figures 3 and 4.

Table 1. Grease Endurance Test Conditions in the Modified ASTNI 3527 Method andthe SKF Method

Modified ASTM SKi-

Test temperature 121 C 121 CSpeed 0 rpm 80) rpmThrust load 25 lbf- (fxed) 560 l t- h applid cji 5

minute,, for le) ,econd,,duranzon i

R, dial load none 1.8"5 lh t lfill)Te,,t bearing,, Tapered roller hearm-L ,ame 1b VT\IOperation Cycle (20 hour, on, :onMTMOU,

4 hour, oft

Termination criteria Torque \ihrAtnou, Fi rn-up, \olsc.[ln -t ' HfurL'

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7

ESTIMATES FOR THE CL\AI LATI\E \ EIB IL DISTRIMI TI()\

F(X) = I -E\P - " ) 'B)

ESTIMATE AND TWO-SIDED 90o CONFIDENCE INTER\ \1 ,FOR DISTRIBUTION P-\RANIETERS

SHAPE (BETA) PA\RANIETER = 3.5328 SCALE P-\RAMETER = 4.963LOWER LIMIT = 2.510 LOWER LIMIT -,3)2LPPER LIMIT = -4.9310 UPPER LIMIT = 516.0136

ESTIMATED COVARIANCE NI\TRIX OF PARAIETER ESINIl \ILS

SCALE SHAPESCALE 1405.878- 9.11 1SHAPE 9.011) .5128

ESTIMATE AND TWO-SIDED 901 CONFIDENCE I\TERV\ X S\1'FOR DISTRIBUTION PERCENTILES

PERCENTILEPERCENTAGE ESTIMATE LOWER LIMIT LPPER I 1\111

1.0 122 -4 201I5.0 194 137 2-t,

10.0 238 17820.0 294 23450.0 406 3480.0 474 415 54

90.) 5"0 499 65195 0 614 533 --

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ESTIMATES FOR THE CUMULATIVE WEIBLLL DISTRIBUTrION

F(X) = I-EXP -X AA) B)

ESTIMATE AND TWO-SIDED 90r0 o CONFIDENCE INTERVALSFOR DISTRIBUTION PARAMETERS

SHAPE (BETA) PARAMETER = 1.5500 SCALE PARAMETER = 134.-94-*LOWER LIMIT =1.1471 LOWVER LIMIT =105

*UPPER LIMIT -2.0943 UPPER LIMIT 17V2.830

ESTIMATED COVARIANCE MATRIX OF PARAMIETER ESTI.MATES

SCALE SHAPESCALE 413.9144 L7054SHAPE 1.7054 .0804

ESTIMATE AND TWO-SIDED 90'ro CONFIDENCE INTERVALSFOR DISTRIBUTION PERCENTILES

PERCENTILEPERCENTAGE ESTIMATE LOWER LIMIT UPPER LIMIT

1.0 7 3 195.0 20 10 40

10.0 32 18 55;20.0 51 33 7950.0 106 81 14070.0 152 120 19390.0 231 179 29-95.0 2-74 208 36099.0 361 261 50099.9 469 319 689

L10 L50LCL MED UCL LCL MED LCL

18 32 55 81 106 1-40

Figure 4. Continued

I10

Section IN. NEW TERMINATION CRITERIA FOR THEASTM D3527 METHOD

The current grease failure criteria used in the ASTNI D352- method originall, %%eredeveloped based on a hardening of grease which, in turn, produced lubricant ,taration.However, it now appears that these criteria can only be utilized when the running torquevalue has a higher value than a steady-state torque ,,alue which developed at the first2 hours of operation. In practice, the running torque value does not al%,ays produce ahigher ,alue than its initial value measured at 2 hours of operation. In our preioustests, evidently, it was observed that the NIIL-G-10924C grease sample underwentchanges at 121 -C in two distinct stages. In the first stage, the grease appeared to oft:enor become semifluid at the given test temperature and speed. The running torqueobserved at this stage was about a quarter of the steady-state torque obtained at thefirst 2 hours of operation; then, hardening of the grease occurred in the later stage. Toprovide more evidence, a lubrication comparison test was conducted using the modifiedASTNI D3527 method used in the MIL-G-10924C grease endurance tests. The lubrica-tion used in this comparison test was the VV-L-800, "General Purpose PreserxatieOil," having similar property as the base stock used in the MIL-G-10924C grease.[ 1]The results showed that the lubrication life marked 9.3 hours, and the running torquevalue was almost identical to that obtained with the MIL-G-10924C grease. It would ap-pear that the grease in question changed its consistency during the test due to thetemperature and shear forces incurred in the first stage. These physical property changesmay affect grease endurance life and lead to subsequent bearing failure. Generally, thedeterioration of grease results from oxidation reactions, a breakdown of grease struc-ture, excess bleeding or separation of oil from the thickener, and contamination.t[12These physical property changes can all be considered as grease failure criteria.

To develop new termination criteria for the ASTNI D3527 method, a feasibility ,ud\\\as conducted using a candidate grease for the "E" revision of MIL-G-10924 Specitia-tion and the .IIL-G-10924C grease used in the SKF tests. The former is a high droppingpoint grease, whereas the latter is a low dropping point grease. The phyIcal andchemical properties of these greases are sho\kn in Table 2. For the feaibilitv .,,ud\. thefollo% inc tentati'e termination criteria were de&eloped haled on the ,oftening of re.,indicated in the preious test results:

TC \l (ST - N, N. ilwre

T ,,ead. -,tate torque .,aLIC ohtained it 2 hour, ,1k2a1 onN = ,'IC of unloaded motor

Holdin, :ime for T(' 1 3e ,nd'

To -iak a .!'eenduran 'C- , v,,"er pe: ';r e. a--e t,

-\ST\I 'erminar;,ri r::er a 'e ,f o: , in )and he en: ,t ', cn ,, :":-:.% : na:,,m ,::, ailo', ,ct pont) at 1 l C and IN) ( . Ih C :e,: r e..t- ac-,r ,. :, I at e

I7

Table 2. The Physical and Chemical Properties of Tested Greases

ASTMI

Test Method Grease

%IIL-G-10924C Candidate Greasefor \IIL-G.10924E

NLGI Consistency Number:Worked 60X D217 2 1'

Lnworked D217 - 3

Thickener Type: Calcium Lithium ComplexBase oil Petroleum Polyalphaolefin

Base oil viscosity at 401C, cSt 13.3 220Cone Penetration (worked 60X): D217 281 305Dropping Point, 'C: D2265 143 260-Oil Separation, 0-o: D1747 5.2 0.62

*E~aporation, Ilo: D972 5.3 1.72Oxidation:

Stability, 100 hours D942 2

4 Ball EP. LWI D2596 35.8 50

Table 3. Grease Life in Both Termination Criteria

Candidate GreaseTest Temperature MIL-G-10924C for MIL-G-10924E

LSP* HSP** LSP HSP

120 'C 80 hours 150 hours -> 1,000 hours

160) 'C ->20 hours 57.9.hours 123.8 hours

*LSP: Lo%% ,et pointHSP: High set point (current ASTl D3527 termination criteria)ASTN1 termination criteria:

TC =8 tiniiial torque - unloaded torque) -unloaded torqueHoldiniz time for TC: 30 ,econds

12

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The candidate grease for .IIL-G-10924E Specification did not follow, either terminationcriteria at 121 C. It appeared that the test temperature (121 -C) may be too lo%% to fullystress or deteriorate the high dropping point grease. This grease was terminated by bothset points when tested at 160-C. The grease terminated by the low set point criteria ap-peared to be moderately oxidized and dried with free oil. On the other hand, the failedgrease detccted by the high set point criteria appeared to be completely oxidized andonly residue grease remained in the bearings. The life obtained using the loN% set pointcriteria ,%a, approximately one half of that obtained when using the high set pointcriteria. In the other test, the %IIL-G-10924C grease (low dropping point grease) alsofollo,,ed both set points at 121 -C. The condition of this grease in both tests w.as similarto the condition of the high dropping point grease. At 160-C, this grease only operatedfor 20 hours. Hovever, the actual "life" of this grease was less than 20 hours becausemost grease failures were observed at the initial cycle operation after a 4-hour rest.Therefore, the minimum life of this method can be considered to be 20 hours. Thisgrease ,,a, not suitable to conduct the grease endurance test according to the ASTID352" method because of its low dropping point (143 -C). Evidentlv, the grease com-pletely melted at the test temperature and the tested bearings looked like unlubricatedne%, bearins. Both test results indicated that the tentative termination criteria canreduce the test time to as much as one half of that obtained from the ASTNI termina-tion criteria.

To address %,hether the grease becomes soft or not at the tentative termination criteria.a consistency test was conducted on exposed samples according to the ASTNI D1403,"Cone Penetration of Lubricating Grease using One-Quarter and One-Half Cone ScaleEquipment." Due to the insufficient amount of grease, only the unworked penetrationnumber of the candidate grease for MIL-G-10924E was determined. The test resultsshowed that the un,,orked penetration number measured from the used grease (54.4hours) was softened by a halt NLGI number in comparison to that obtained from thenev grease. It would appear that the decrease in the running torque at this stageresulted from the combination of softening of the grease and adsorption of certain ad-diti,.es on bearing surfaces. The test results are summarized in Table 4.

Table 4. Consistency Test Results

Grease Unworked Penetrarion

New Used (54.4 hoursi

Candidate greasefor MIL-G-10924 " 2s3

NLGI Number

13

To define an additional failure criteria for tested greases, experimental oxidation stabili-ty tests were conducted using the Pressure Differential Scanning Calorimetry (PDSC)method which is being developed within the ASTNI Committee D2 Subsection 09.OE onoxidation.[13] The test results are provided in Figure 5

The test results showed that the MIL-G-10924C grease used in the modified ASTNID3527 test for 80 hours gave 1.4 minutes in induction time which indicates the relativedegree of oxidation in this method. This value was lower than that obtained from thenew grease (16.2 minutes) and equivalent to that determined from the heavy oxidizedresidue grease. The new candidate grease for MIL-G-10924E showed a good oxidationstability at the given test conditions, and the grease used in outboard and inboard bear-ings for 57.9 hours marked 15.3 minutes and 31.9 minutes respectively. Both valueswere higher than those obtained from new MIL-G-10924C grease. Although the greasewas not oxidized at this stage, the result indicated that the grease was being degraded bythe temperature and shear force. Evidently, the induction time obtained from the usedgrease (57.9 hours) was significantly lower than new grease and higher than the residuegrease collected at 123.8 hours.

In summary, the grease lubricated in the outboard bearing gave lower induction timethan that obtained from the inboard bearing under the same hub system. This impliedthat the grease used in the outboard bearing (small bearing) failed earlier than greaseobtained from the inboard bearing (large bearing). As the ASTM D3527 method wasdesigned to determine the grease failure life when grease packed in both bearings corn-pletely deteriorates, the grease failure occurring in the outboard bearing actually doesnot signal failure life. Therefore, this developed preliminary termination criteria, basedon the oxidation and hardening of grease, intends to extend grease life and sometimesgive a termination problem. Based on data developed to date, this method needs newtermination criteria which can determine the true grease life. The tentative terminationcriteria reduced the test time and distinguished a good and poor grease as well as thecurrent method is able to do.

14.- 1

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HEAT F-()\%(ni\-

Candidate (j'reaseNIIL-G- 10924C for X[G194

Grea~ec !relse TTC ASTNI greas e TTC ASTNI

fBeariuc lB3 OB IlB 013 IlB OB IlB 13

Y,;uc Ih 212 1.4 - - - 120 31.9 153 0, 6 4

yr ~ ent& et er mi nation cr itert a"*>\IASTM\ terminlation c:riteria

11.Inboard- bearin !(43.: ( Lulhboard bearing.

Figure 5. Continued

Section N . THlE REQUIREMENT OF 1,1t) LIFE, 0' G.A.AIN THE ASI D)3527 MIETHOD)

* To establish the requirement of L 10 life of cuirrent GA.- grease and the future lon,- lifeCArmy grease, ba,,eline tests %%ere con1ducted uPing the ASTNI D35?- method. Of the litte14 quaIi t'ifd produIct> under the \11 L. -(i- IN (4D Amendment I Specificatin, onl1 one hi'.,1dropping point grease %%a,, qualified to perform according to the .- ST\I D35Y2

* method.[1-4] The other grease,, %%ere not included in thl h i\aluatlon due to their lo\werdropping point,, (143 C). Eight data point,, \%erc generated onl the One qui idpro~du2,and its L 10 life wkas determined u,,inu lie NIL compurf program. The baselinle eelife, wilth 90 percent confidence inter\ ak, and it,, numlericll per:enltile life are 'ho\ nMi

* FiL'Ure 6. The L-10 life obtained from th hi> baelinle tet w \ 2 ours. aind thle L;( l ifierepre,,ent i rg thle a'%. erage life) %%a, 1 16 hour,.. Th is L;() life \ as longer than the req;uire -

ment of the draft A-STI %%heel bearing peci fication . The a'.erace life of comem ut onalwheel bearineL 1re ,e is etw ecu l) to 150 h0ur\ . The cUrrenlt l(ow droppline- po01ntgre ase, -Uppried under the ',III -(J-1092-11) Speci fiat loll arc ueuClerall\ ,ati1factor% forart Iler\ and grudeqJuipment. but 110t ec ar1%. in dvc brake whecel heCaring appi-1121tions because the tes)ting ait 100) C pro'.idcd a life Iec>> tha-n 2() hour".

16

U-)

01

* U-) -

-0 L

C (S-DCCD M-0d

HOURS TO FAILURE

Ir

ESTIMATES FOR THE C'T 'LL.-\TIVE \VEIBULL DISTRIBUTION

SF(X) = 1 - EX PI -X .A),N B)

ESTIMATE AND TWO-SIDED 900'o CONFIDENCE INTERVALSFOR DISTRIBUTION PARAMETERS

SH-\PE (BETA) PARAMETER = 2.3637 SCALE PARAMETER = 135.8103LOWER LIMIT = 1.501' LOWER LIMIT 105UPPER LIMIT = 3.203 UPPER LIMIT = 1-6.2104

ESTIMATED COVARIANCE MATRIX OF PARAMETER ESTIMATES

SCALE SHAPESCALE 462.254 4.585SHAPE 4.5875 .4248

ESTIMATE AND TWO-SIDED 90%o CONFIDENCE INTERVALSFOR DISTRIBUTION PERCENTILES

PERCENTILEPERCENTAGE ESTIMATE LOWER LIMIT UPPER LIMIT

1.0 19 75.0 39 19 -8

10.0 52 30 9320.0 72 46 11350.0 116 87 156"0.0 147 114 18990.0 193 149 25095.0 216 164 28599.0 259 188 35,99 9 308 211 448

I 10 L 50LCL MED UCL L.CL NIED UCL

30 52 93 87 116 156

Figure 6. Continued

i4

18

-...... .- .a. - a I*

S. . . .S,

Section VI. DISCUSSION AND CONCLUSIONS

Although the ASTNI D3527 method wkas studied ,ith limited data, it can be con-cluded that this method max be as good as the screening test, but not applicable to usein the Army grease specification without any modification. The reasons are that thismethod has poor precision and definition of the meaning of the test. Based on testresults, grease life also depends on the load as \%ell as the temperature. Therefore, theradial load should be used as a test parameter with the thrust load.

The current ASTNI termination criteria developed based on a hardening of greae ga~e atermination problem and tended to extend grease life. The ne\\ developed tentativetermination criteria, based on the softening of grease, reduced the test time as much asone half of that obtained from the current ASTM termination criteria. It also differen-tiated between a good and a poor grease as well as the current ASTN D352- does,Results clearlv show that this approach resolved the problem associated %%ith the currentmethod. Further study of this termination would be beneficial for dexeloping an ac-celerated grease endurance method.

The L1O life of high dropping point grease supplied under .IIL-G-10924D Specificationobtained 52 hours, and L50 life (representing the average life) was 116 hours, \\hich is alonger life than the requirement of the draft ASTNI wheel bearing specification(80 hours). The traditional low dropping point MIL-G-10924D grease provided les, lifethan 20 hours. It appears that this grease is not satisfactory in disc brake whet i hearingapplications.

19.5'

BIBLIOGRAPHY

1. Military Specification SMIL-G-10924D, "Grease Automotive and Artillery (G.AA)."13 June 1983.

2. In-Sik Rhee, "Evaluation of the kl0 Life of Military Greases in Wheel BearingLs byComputer Analysis," ASNIE Failure Prevention and Reliability Conference, 1985.

3. R. MlcClintock, General Motors Research Laboratories, "A Laboratory Study ofW\heel Bearing Grease High-Temperature Life," NLGI 45th Annual Sleeting, 19;9.

i:' 4. D. J. Sargent, E/%I Lubricants, Inc., "A Historical View, of ASTI Mlethod

D35;"-," NLGI 45th .Annual Meeting, October 1977.

hi/i ::5..Minutes of ASTSI Subsection 130.04, 6 .August 1986.

' 6. In-Sik Rhee, Trip Report ASTNI Committee D2 Sleeting2, Louisville, Ki',,'8 July 1986.

*," 7.In-Sik R,iee, Trip Report AST.M Committee D2 Mleeting, Savannah, GA,13 January 1987.

8. CntSic Re DAAK ot0-77-C-0034, Performance Evaluation of Automoti e gheelBearin Greases," Final Report, SKF Inc.

9. Contract No. DAAK 70-79-C-0213, "Performance Evaluation of Automotue oheele Bearing Greses," Final Report, SKF Inc.

10. Contract No. DAAK 70-83-C-0063, "Performance Ealuation OfAT M-\utoie to heelBearin2 Greases," Final Report, SKF Inc.

11. Militar Specification BOV-L-800, "General Purpose Preser19at8e 06.,15 September 1986.

12. O'Connor & Boyd, StaTrdard HAM ook o MLein, S , GA, Ch , I n.

13. ASTI Draft .Method, -Oxidation Resistance of Lubrication, Greaute,o tv \.,Differential Scannn Calorimetry," 4 October 1984.

" I1. Military Qualified Products List of Products Qulfied Under llitar SpecificatiOl'

\MIL-G-10924D and Amendment 1, 26 June 1986.

20

4,- 4 ' .4 4- %' ' % . ':P. -4. - 4 ' ~ -

% ,P2j.A~~..P I~zY::. .'4'4 '

DEPARTMENT OF THE ARMY

I Commander I DirectorUS Armv Materiel Command Propulsion DirectorateATTN: ANICDE-SS U'S Armv Research & Technology-ATTN: A.\ICSNI-%NST Activities (AVSCOMN)5 001 Eisenhower Avenue ATTh,: SAVDL-PL-D (Mr. AcurioAlexandria, VA 22333-0001 21000 Brookpark Road10

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24

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.'.. *~' .. *.. **p* d~* .- '-'. - . . . .. * , * ~ . * * . * - *

NDo