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1、07FTM15 Experience with a Disc Rig Micropitting Test by: Dr. M.G. Talks, QinetiQ Ltd., and W. Bennett, Defence Equipment and Support MoD TECHNICAL PAPER American Gear Manufacturers Association Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing C
2、o/5910770001 Not for Resale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,- Experience with a Disc Rig Micropitting Test Dr. Miles G. Talks, QinetiQ, Ltd., and W. Bennett, Defence Equipment and Support, MoD The statements and opinions contained herein a
3、re those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract The experimental work carried out was aimed at developing a test method that was able to consistently produce micropitting damage and could discriminate betwee
4、n a good oil (i.e., one that rarely produces micropitting in service) and a poor oil (i.e., one that does produce micropitting in service). The small-scale 3-Disc test rig that was used for this work employs 3 discs to apply the test load to a 12mm-diameter test roller. This test geometry allows a l
5、arge number of stress cycles (typically 600,000 to 800,000cycles/h) tobe generated at the contact track on the roller. The disc rig control system allows test parameters such as entrainment velocity, contact stress and slide/roll ratio at the disc/roller contacts to be accurately and independently c
6、ontrolled. This enables the effect of key parameters to be studied in isolation, which is something that cannot be easily achieved using conventional gear test rigs. Theearlyworkcarriedoutusingthediscrigwasaimedatproducingmicropittingdamagebyoperatingtherig at contact conditions similar to those use
7、d in the FZG micropitting gear test method. These early tests confirmed that the damage produced to the roller track exhibits characteristics that are typical of micropitting damage,andshowedthattheseverityofthemicropittingproducedwasaffectedbytheamountofrunning-in carried out on the roller prior to
8、 applying the full test load. A test procedure has been developed which provides a good level of repeatability and which allows discriminationbetweenoilswhichproducemicropittinginserviceandthosewhichdonot.Inaddition,astudy of the effect of slide/roll ratio (SRR) has shown that the severity of microp
9、itting damage increases as SRR increased, whereas at 0% SRR no micropitting occurred and, at negative SRRs,microcracking occurredbut not micropitting. This is the way that SRR seems to affect micropitting in gears. Copyright 2007 American Gear Manufacturers Association 500 Montgomery Street, Suite 3
10、50 Alexandria, Virginia, 22314 October, 2007 ISBN: 978-1-55589-919-6 Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,- 1
11、 Experience with a Disc Rig Micropitting Test Authors: Dr. Miles G. Talks (QinetiQ Ltd, UK) and Mr. W. Bennett (Defence Equipment 60% SRR; 1.7GPa contact pressure; 0.45 mm Ra discs; and 90C oil temperature. In all of the five tests, a smallamountofmicropittingwasproducedafterthe firsthourof testing,
12、about halfof theroller trackwas Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,- 7 micropitted after 10 hours and virtu
13、ally all of the track was micropitted after 20 hours and 30 hours. The mean track profile losses obtained during the tests are shown in Figure 6. In four ofthe fivetests, theprofilelosswasbetween8.6and10.5mm. Inthe fifth test, the profile loss was a little higher (14 mm) after the same test period.
14、Figure 6. Profile losses for the five repeatability tests carried out using Oil A Discussion Achievement of the initial objectives Establishmicropittingasthedominantdamagetype For all of the tests carried out using a positive value of SRR, where roller track damage occurred it took theformofaxialmic
15、rocracks(i.e.,cracksorientated across the track). These were typically up to about 50 mm long in the early stages of the test, but these subsequently developed and joined up to form mi- cropits that were typically about 50 mm wide and 300 mm long. Examination of the sectioned roller track using opti
16、cal microscopy (after coating the track with electroless nickel to stabilize it and pre- ventthelossofloosemicrocrackedsurfacematerial during sectioning and polishing) revealed micro- crackswhichpropagatedatashallowangleof(typi- cally20to30degrees)tothesurfacebeforebranch- ing towards the surface(Fi
17、gure 7).These characteristics are typical of the micropitting pro- cess (7), (8) and indicate that the damage that was produced during this study is, indeed, micropitting. In addition, the appearance of the micropitted sur- face (e.g., as shown in Figure 5) is very similar to typical micropitting da
18、mage produced in the FVA testandothergear-basedmicropittingtests.7,8 Figure 7. A typical section of the micropitting damage to the roller track (NB: The coloured area is the electroless nickel coating which was applied to stabilize the surface) Achieve an acceptable level of repeatability The result
19、s of the five repeatability tests showed that the level of the micropitting damage produced after 30 hours of testing was consistent andrepeat- ableintermsofappearanceandprofile loss. Infour of the five tests, the profile loss results were very consistent. The mean profile losses after 30 hours of t
20、esting for each of these tests was within 10% of the average mean profile loss for the four tests. In the fifth test, the mean profile loss after 30 hours was 40% higher than the average for the other four tests. These results indicatethat thetest methodis capable of generating micropitting results
21、that have an acceptable level of repeatability. Achieve adequate discrimination between the two reference oils Theresultsofthisstudyhaveshownthattheseveri- ty of the micropitting produced in the disc rig test is affected by many factors. These include contact stress, SRR, surface roughness, oil type
22、 and disc/ roller running-in conditions.These are factors which have been found to affect micropitting in gears. Itisreasonabletoexpectthatiftheoperating conditions used in the disc rig are too aggressive, severe micropitting damage will be produced with both of the reference oils and discrimination
23、 betweenthemwillbepoor. Conversely,ifthecondi- tionsarenotsevereenough,littlemicropittingwillbe produced with either oil and, again, the discrimina- tion will be poor.Consequently, if adequate discrimination between oils is to be achieved, it is important to carry out the tests at an appropriate Cop
24、yright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,- 8 level of severity. For the two reference oils used in this study, and u
25、sing 0.30mm Ra discs, the best dis- crimination was obtained at 60% SRR at the 1.7GPa and 90C test condition.NB:In gears, nearly all of the micropitting damage that develops doessoinregionswhereSRRsofgreaterthan40% occur. It is possible that further development of the test method could result in fur
26、ther improvements in the discrimination but the important feature of the results obtained so far is that the test can discrimi- natebetweentwogearoilswhichareknowntohave differentmicropittingperformancesinservice applications. Comparison of the disc rig results with FZG gear test results Figure 8sho
27、ws theposition ofthe micropittingband after a typical gear-based micropitting test using the FZG C-type gears. The band of micropitting (which has been coloured to highlightits position)is belowthepitchline,intheregionwherehighcontact stresses and high positive values of SRR occur. A graph of profil
28、eloss ina micropittingtest carriedout on Oil A, using the Strama gear test rig, is shown in Figure 9, together with a summary of the SRR val- ues at various positions on the gear flank.This shows that most of the micropitting damage occurs inthededendumofthetestgearin aregion wherea combinationofhig
29、hcontactstresses(about 1.6 GPa) and high SRRs (typically up to about +80%) occurs. The results from the disc rig exhib- ited similar behavior, with the highest levels of micropitting being produced using a high positive SRR (+60%) and contact stresses of 1.7 GPa and 1.85 GPa. Figure 8. Micropitting
30、damage (the coloured band) to an FZG C- -type gear after a typical micropitting test Figure 9. Profile loss of an FZG C- -type micropitting gear after testing with Oil A Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Re
31、sale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,- 9 Conclusions A series of tests carried out using the miniature three-disc test rig has shown that it is able to pro- duce micropitting damage and to achieve an ac- ceptable level of repeatability. In
32、 addition, once a suitable set of test conditions has been identified, it isabletodiscriminatebetweengearoilswhichhave different micropitting performances. Aswithgear-basedmicropittingtests(e.g.,theFVA test), adequate control of the surface roughness of the test specimens is important if acceptable
33、re- peatability and adequate discrimination are to be obtained in the disc rig test. It is possible that the effect of disc roughness is less pronounced athigh- erSRRs(e.g.,60%),however,duetotheoverriding effect of the sliding conditions. Theseverityofthemicropittingdamageproducedin thediscrigvaries
34、ina similarmanner withoperating parameters such as surface roughness, SRR and sliding direction, as it does in gears. Micropitting is not produced under pure rollingconditions andvery little is produced at a negative SRR, which is the same pattern as that observed in gear-based mi- cropitting tests.
35、 Micropittingcanbeproducedusingthediscrigwith- in about 25 million stress cycles, which is compara- ble with thecycles involvedin gear-basedmicropit- ting tests. The disc rig test contact conditions are thus similar in severity to those occurring in test gears. Asthetestrollerissubjectedtoahighstres
36、s cyclerate(typically810,000cycles/h),however,the disc rig test is potentially a much quicker test than gear-based micropitting tests. Becauseofthesmallvolumeoftestoilusedandthe relatively simple specimen design, the miniature disc rig micropitting test should be a useful tech- nique for future asse
37、ssments of gear oils and addi- tives, and gear materials, as well as for studies of coatings and the effects of surface finishing tech- niques. In addition, the disc rig allows more funda- mental studies of micropitting to be carried out at specific combinations of gear parameters (such as contact s
38、tress and SRR). This type of study could not be performed using conventional gear tests. References 1 Shotter, B.A., Micropitting: Its Characteristics and Implications on the Test Requirements of GearOils, ProceedingsoftheInstituteofPetro- leum, No.1, pp 91-103, London, 1981. 2 Ariura,Y.,AnInvestiga
39、tionofSurfaceFailureof SurfaceHardenedGearsby ScanningElectron Microscopy Observations, Wear, 87, pp 305 - 316, 1983. 3 Benyajati, C., An Experimental Study of Micro- pitting Using a New Miniature Test Rig, Pro- ceedings 30thLeeds-Lyon Symposium on Tribology, Lyon, France, pp135-143, Sept 2003. 4 We
40、bster, M.N. and Norbart, C.J.J., An Experi- mental Investigation of Micropitting Using a Roller Disc Machine, Proceedings 50th STLE Annual Meeting, Chicago, Illinois, May 1995. 5 Olver, A.V., Wear of Hard Steelin RollingLubri- cated Contacts, PhD Thesis, Imperial College, London, UK, 1986. 6 FVAInfo
41、rmationSheetNo. 54/I-IV,FVAMicro- pitting Test Method, ForchungsvereinigungAn- treibstechnik E.V., Lyoner Strasse 18, 60528 Frankfurt/Main, Germany. 7 Shaw, B.A. and Evans, J.T., Micro- -pits Under the Microscope, Session 3, Paper 6, BGA DrivesandControlsConference,Telford, Salop, UK, March 1997. 8
42、Brimble,K.,AComparisonofMicro- -pittingPer- formance of Identical Oils Using Standard FZG Test Gears and Helical Test Gears, Session 8, Paper8,Proceedings2001Drivesand Controls, and Power Electronics Conference, London, UK, March 2001. Acknowledgements The authors would like to acknowledge the UKMin
43、- istry of Defence for financingthis work. Theywould also like to thank the MoD, QinetiQ Ltd and theBrit- ishGearAssociation(Project6Consortium)forper- mission to publish this paper. Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=Boeing Co/5910770001 Not for Resale, 07/24/2008 22:47:48 MDTNo reproduction or networking permitted without license from IHS -,-,-