1、04FTM7A Short Procedure to EvaluateMicropitting Using the New AGMADesigned Gearsby: Dr. K.J. Buzdygon and Dr. A.B. Cardis, Exxon-MobilResearch and Engineering CompanyTECHNICAL PAPERAmerican Gear ManufacturersAssociationA Short Procedure to Evaluate Micropitting Using theNew AGMA Designed GearsDr.Kev
2、inJ.BuzdygonandDr.AngelineB.Cardis,Exxon-MobilResearchandEngineering CompanyThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractEncouraging results from a prototype mic
3、ropitting test using specially designed gears (20:30 tooth ratio, tiprelief, and a 560 mm radius pinion crown) on the standard FZG test rig were reported at the 1998 AGMA FallTechnical Meeting. Subsequently, the authors company purchased several sets of these experimentalAGMA test gears and attempte
4、d to develop a new test procedure to evaluate micropitting as an alternative toFVA Procedure 54. The new relatively short test procedure involves running the test gears on the standardFZGtestrigwithoilcirculationfor168hoursatloadstage10and1500rpm.The5-gallonreservoiroftestoiliskept at 60 C throughou
5、t the test. The oil is cleaned by an in-line filter (200 =6 m) before it is injected into thegear mesh at 2 liters/minute. At the end of test, the gears are rated for micropitting, weight loss, pitting, andscuffing. The most common damage mode was micropitting, with only occasional occurrences of pi
6、tting andno occurrences of scuffing. Other modes of failure such as gear tooth bending did not occur at theseconditions. The involute profile deviation of the gear teeth was not measured.FivecommerciallyavailableISOVG320gearoils,withperformanceintheFVAProcedure54micropittingtestranging from FLS 9-lo
7、w to FLS 10-High, were evaluated using this procedure. The degree of micropittingcoverage ranged from 34% to 7% in the new test procedure. Micropitting generally originated inthe middleofthe gear tooth, instead of the root or tip. Overall, there was excellent correlation of the degree of micropittin
8、gdamage between the new test procedure and FVA Procedure 54.Copyright 2004American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October, 2004ISBN: 1-55589-830-01A SHORT PROCEDURE TO EVALUATE MICROPITTINGUSING THE NEW AGMA DESIGNED GEARSKevin J. Buzdygon an
9、d Angeline B. CardisExxonMobil Research and Engineering CompanyIntroductionThe American Gear Manufacturers Association(AGMA) has developed a new gear design for thestudy of surface fatigue life using the FZG geartest rig. The objective of the AGMA project is todevelop a gear surface fatigue life mat
10、hematicalmodel that will include lubricant and additiveeffects. Typical inspection properties oflubricating oils such as viscosity index, acidnumber, and elemental analysis are not asufficient basis for estimating the ability of thelubricant to provide protection from surfacedistress such as scuffin
11、g, pitting and micropitting. Pitting and micropitting are forms of rolling contactfatigue, which are strongly influenced by lubricantbase stock type and additive chemistry. Althoughmany studies have been reported over the years1,2, 3, the relationship still must be determinedthrough testing of each
12、oil formulation. Fewestablished methods are available to evaluatepitting and micropitting. One method that is usedto evaluate pitting is described in FVA InformationSheet No. 2/IV.11The most commonly used testto evaluate micropitting is described in FVAInformation Sheet No. 544(commonly called FVAPr
13、ocedure 54). This micropitting test can takeseveral months to complete, and therefore is notconvenient for the purpose of screening newtechnology. A screening test was developedusing a roller disc machine5. Althoughsuccessfully used to produce useful data, theequipment is not readily available and r
14、equiresskilled technical support to prepare testspecimens, run the test, and interpret results.Another test method was recently reported whichuses modified gear geometry and differentmetallurgy, but is run on the standard FZG testrig6,7. This test is run at only one load stage withrating after 100 h
15、ours and again after anadditional 300 hours. Although results reportedare promising, this test has not been widely usedperhaps due to limited availability of test gears. Aneed still exists in the industry for a reliable,simple, and widely available screening test formicropitting performance of lubri
16、cants.Two types of test gears are availablecommercially to evaluate pitting and micropitting.FZG Type C-PT test gears (16:24 tooth ratio,surface finish Ra=0.30.1 micrometers) are usedto test for pitting performance according to FVAInformation Sheet No. 2/IV. FZG type C-GF gears(16:24 tooth ratio, su
17、rface finish Ra=0.50.1micrometers) are used to test for micropittingaccording to FVA Information Sheet No. 54. Hhnet. al.12provide a detailed summary of the varioustest gears used in pitting, micropitting, andscuffing tests. The AGMA prototype test gearsare somewhat different, with a 20:30 tooth rat
18、io,and surface finish Ra=0.5-0.8 micrometers. TheAGMA gears are designed with tip relief, whichthe FZG Type C-PT and C-GF gears do not have.The tip relief is meant to avoid hard contact at thetips of the gear and pinion teeth. The AGMAgears are also CBM form finished, whichproduces a different surfa
19、ce texture compared tothe other types of gears. Additional design detailsof the AGMA test gears are provided elsewhere8.The AGMA test gears represent modern gearingdesign more closely than FZG Type C-PT or C-GF gears8. Results of prototype testing of thenew AGMA test gears were reported at the 1998A
20、GMA Fall Technical Meeting9. Additionalinformation about the test design and initial testresults can be obtained from AGMA8,9,10.A subsequent batch of AGMA test gears wasproduced and limited quantities were madeavailable to interested organizations with theunderstanding that test results would be re
21、portedto AGMA in generic form. M. Hoeprich13conducted a study using the AGMA test gears in ashort duration, high load test (load stage 12).Even though the test ended early due to toothbreakage, important information regarding thedetailed failure mechanism was derived fromstudy of the other teeth. Si
22、gnificant micropittingand pitting were observed on the pinion and gearteeth13. 2In 2001, the authors company purchased a smallnumber of these test gears. Since the companysexpertise is better aligned with lubricant testingthan metallurgical evaluations, it was decided todevelop a short lubricant scr
23、eening test formicropitting resistance, rather than to studyfatigue failure mechanisms.Test ProcedureThis test procedure uses the FZG-26Falex/Strama variable drive FZG gear testmachine. Test oil was contained in atemperature-controlled five-gallon reservoir ofstainless steel construction. Five gallo
24、ns of testoil was maintained at 60C and circulated at 2liters/minute. The oil passed through a 4 inchfilter (Beta ratio = 200 at 6 m) before beingsprayed into the gear mesh. The entire system(gear box, reservoir and all piping) was cleanedwith Stoddard solvent and then flushed with testoil before ea
25、ch test run. The test gears wereinspected for damage, and weighed beforetesting. The test gears were loaded to a powerlevel of stage 10 (372.6 Nm pinion torque) and themotor speed set at 1500 rpm throughout theduration of the 168 hour test. This corresponds toa pinion speed of about 2250 rpm. Based
26、on theinitial test work with these gears9,10,13andconsidering the conditions of the popular FVA 54procedure4, it was thought that these testconditions would effectively promote micropittingin a reasonable amount of time.The pinion gear was weighed and rated twice,once after 48 hours (6.5x106cycles)
27、and againafter 168 hours (2.3x107cycles). A qualifiedCoordinating Research Council (CRC) raterexamined the pinion gear for scuffing,micropitting, pitting, and spalling. Micropitting,also known as grey flecking or grey staining, is aknown fatigue phenomenon that occurs inHertzian contacts that operat
28、e inelastohydrodynamic or boundary lubricationregimes, usually in conjunction with a combinationof sliding and rolling. A “micropit“ is usually lessthan 25 m deep and less than 0.01 mm2. A “pit“is defined here as metal removal from the geartooth surface that is ABCDE F GLubricant CharacterizationISO
29、 Viscosity Grade 320 320 320 320 320 320 68ApplicationIndustrial GearIndustrial GearIndustrial GearIndustrial CirculatingIndustrial GearIndustrial CirculatingAutomotive GearBase Oil Type Mineral Synthetic Synthetic Synthetic Synthetic Mineral SyntheticAntiwear Additive Chemistry ashless sulfur-phosp
30、horousashless sulfur-phosphorousashless sulfur-phosphorousashless phosphorousmixed metal sulfur-phosphorousmixed metal sulfur-phosphorousmixed metal sulfur-phosphorousTypical Lubricant Performance CharacteristicsFVA Procedure 54 Fail Stage 8 Fail Stage 9Fail Stage 10 -HighFail Stage 10 - HighPass St
31、age 10 - High not available not availableFZG rating, A/8.3/90 Pass 12 Pass 13 * Pass 13 * Pass 13 * Pass 12 Fail 12 Fail 12Timken OK load, lb 60 60 35 50 60 15 NA4-Ball Weld Load, kg 250 250 200 NA 200 200 NATest Results in AGMA Gear Test (168 hrs/LS10/60C), Pinion DataMicropitting coverage 48 hrs,
32、% 0.0 15.2 0.0 0.7 1.4 1.9 9.4Micropitting coverage 168 hrs, % 34.0 25.6 16.8 16.8 7.2 12.0 21.2Pitting coverage 48 hrs, % 0.0 0.0 0.0 0.0 0.0 0.0 0Pitting coverage 168 hrs, % 4.5 0.16 0.0 0.2 0.05 0.01 0.01Scuffing 48 hrs none none none none none none noneScuffing 168 hrs none none none none none n
33、one noneWeight Loss48 hrs, mg 2 14 17 15 9 6 16Weight Loss168 hrs, mg 505 51 34 45 17 22 54Comnt -One gear tooth spalled -* These oils pass stage 12 according to the standard ISO 14635-1 FZG test procedure. The FZG test was then continued through one additional stage with applied torque of 646.4 Nm,
34、 which is not part of the ISO 14635-1 procedure. If the gears still meet the passing criteria for scuffing at the end of this additional stage, then the term “Pass 13“ is used to describe the result. Great care should be used when interpreting these results because stage 13 is not part of any docume
35、nted FZG scuffing procedure. Table 1Data Summary AGMA Micropitting Test4results. An important next step will be tounderstand the variability of this test method byconducting repeat runs. Perhaps with furtherrefinement in the methodology and additionaltesting, this relatively short micropittingperfor
36、mance test procedure could be used as ascreening tool for the more universally acceptedFVA 54 procedure. Oil A Oil BOil C Oil DOil E Oil FOil GFigure 1Worst Case Pinion Gear Tooth at End of Test5References1 B. A. Shotter, “Micropitting: ItsCharacteristics and Implications on the TestRequirements of
37、Gear Oils”. Proceedings of theInstitute of Petroleum, Volume I (PerformanceTesting of Lubricants), London, 1981, pp. 91-103.2 H. Winter and P. Oster, “Influence ofLubrication on Pitting and Micropitting of Gears”.Gear Technology, Volume 7, Number 2,March/April 1990, pp16-23.3 T. Uneo, Y. Ariuraand T
38、. Nakanishi,“Surface Durability of Case-Carburized Gears On a Phenomenon of Gray-Staining of ToothSurfaces”. ASME paper, No. 80-C2/DET-27, theAmerican Society of MechanicalEngineers, NewYork, 1980.4 “FVA-Informationsblatt Nr. 54 I-IV:Testverfahren zur Untersuchung desSchmierstoffeinflusses auf die E
39、ntstehung vonGrauflecken bei Zahnradern“ FVA-Nr. 54/7 StandJuli 1993.5 Webster, M. N. and Norbart, C. J. J., “AnExperimental Investigation of Micropitting Using aRoller Disk Machine”. Tribology Transaction,Volume 38, Number 4, pp 883-983.6 Theissen, J. “Eignungsnachweise vonSchmierolen fur Industieg
40、etriebe“. Presented at11thInternational Colloquium, January 1998,Esslingen.7 Cardis, A. B. and Webster, M. N., “GearOil Micropitting Evaluation“. AGMA TechnicalPaper 99FTM4, October 1999.8 AGMA Helical Gear Rating Committee,“Tribology Test Proposal.“9 OConnor, B.M., “Preliminary Gear TestProgram, Su
41、mmary of Results to Date“ presentedto AGMA 5AT Helical Gear Rating Committee,Tribology Subcommittee, October, 1998.10 OConnor, B.M., “Preliminary Gear TestProgram Report 2, Results with PrototypeGearsets 005 and 006“ presented to AGMA 5ATHelical Gear Rating Committee TribologySubcommittee, February,
42、 1999.11 “FVA Information Sheet No. 2/IV:Influence of lubricant on the Pitting Capacity ofCase Carburized Gears in Load-Spectra andSingle Stage Investigations.“ July 1997.12 Hhn, B. R., Oster, P., Michaelis, K.,“New Test Methods for the Evaluation of Wear,Scuffing and Pitting Capacity of Gear Lubric
43、ants,“AGMA Technical Paper 98FTM8, October 1998.13 Hoeprich, M. R., “Analysis of Micropittingon Prototype Surface Fatigue Test Gears,“ AGMATechnical Paper 99FTM5, October 1999.Figure 2 Correlation Between FVA 54 Test and New AGMA Gear Test0510152025303540Fail Stage 8Oil AFail Stage 9Oil BFail Stage
44、10 - HighOil CFail Stage 10 - HighOil DPass Stage 10 - HighOil ETypical Result from FVA 54 Micropitting Test NewAGMA GearTest,%Micropitting at 168 hours6Figure 3 Correlation Between FVA 54 Test and Weight Loss in New AGMA Gear Test050100150200Fail Stage 8Oil AFail Stage 9Oil BFail Stage 10 - HighOil CFail Stage 10 - HighOil DPass Stage 10 -HighOil EResult from FVA 54 Micropitting Test ProcedureNew AGMAGearTest, mgwt lossat168hours505 mg
