1、12FTM03AGMA Technical PaperGear Lubrication -Gear Protection Also atLow Oil TemperatureBy M. Hochmann, KlberLubrication Mnchen KGGear Lubrication - Gear Protection Also at Low OilTemperatureDr. Michael Hochmann, Klber Lubrication Mnchen KGThe statements and opinions contained herein are those of the
2、 author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractTo find out if the high-performance gear oils of today are able to reliably protect gears and rolling bearings ingearboxes against damage also at a reduced oil temperature of 40
3、 C, different high-performance gear oilswere examined on a FZG back-to-back gear test rig as well as on a FE8 bearing test rig by modifying thestandardized test methods. It has been shown that the advanced additive technologies used in todayshigh-performance gear oils are capable of inducing the req
4、uired reactions on the surfaces of gears andbearings also at 40 C, thus providing reliable damage protection even under these operating conditions.Copyright 2012American Gear Manufacturers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-034-63 12FT
5、M03Gear Lubrication - Gear Protection Also at Low Oil TemperatureDr. Michael Hochmann, Klber Lubrication Mnchen KGIntroductionInpractice, industrialgears areoftenoperatedwithlower oiltemperatures thanwouldnormally begeneratedin a fully loaded gearbox. Lower temperatures prevail, for instance, whilea
6、 gearbox is beingtaken back intouse after prolonged standstill, i.e. during the time it takes for the oil to heat up from ambient temperature toservice temperature. Similarly, when a gearbox is being operated below its full load capacity, with reducedspeed, or with frequent stop-and-go, the operatin
7、g temperature of theoil willbe lower than it would beunderfull load. Such applications require gear oils that reliably protect gears and rolling bearings against damagenot only at full-load operating temperatures, but also at lower ones. The oil temperature influences the bulktemperature of the gear
8、s and bearings as well as the flash contact temperature 3, 10. Besides theroughness of the mating surfaces, the applied load etc., the flash temperature is strongly influenced by thecircumferentialspeed. Comparedtoahigher speed, at a lower speed whichmostly occurs at theoutput of agearbox, the oil t
9、emperature, the bulk temperature of gears and bearings, and the flash temperatureapproximate each other more closely. Naturally, a reduction of the oil temperature leads to a substantial in-crease of oil viscosity during operation and hence to the formation of a thicker lubricant film in the contact
10、zone. Lubricant film thickness calculations conducted for typical gearbox applications, however, show thateven at oil temperatures as low as 40C the gearbox will still operate under mixed or boundary lubricationconditions depending on the other operating conditions. This means that the formationof a
11、gear oilreactionlayer on the component surfaces is vital to protect the friction bodies against damage.Typical gear failuresFigure 1showstypicallimitsoftheload-carryingcapacityforcasehardenedgearsaccordingtoNiemann11.Intherangeof slowandmedium circumferentialspeeds, themicropittingrisk is increased,
12、 comparedtoverylow circumferential speeds where the risk of slow speed wear prevails.Figure 1. Typical limits of load-carrying capacity for case hardened gears4 12FTM03Micropitting failure of gearsMicropitting is a type of fatigue failure occurring on hardened tooth flanks of highly loaded gears 11.
13、 Thisfailure consists of very small cracks and pores on the surface of tooth flanks. Micropitting looks greyish andcauses material loss and a changein theprofile form of thetooth flanks, which canlead topitting andbreak-down of the gears. A typical micropitting gear failure of an industrial gear box
14、 is shown in Figure 2. In thiscase, misalignment was the reason for micropitting formation.The formation of micropitting depends on different influences. Besides material, surface roughness, andgeometry of the tooth flanks, it is the lubricant and the operating conditions which have a major influenc
15、e onmicropitting formation. See Table 1.Inmoderngearboxes, thegears areoftenhighlyloadedandrununderconditions ofmixedlubrication. Inthiscase, thetoothflanks of thematinggears arenot fully separatedby thelubricant film and theadditives of thelubricant have to protect the tooth flanks against micropit
16、ting formation.Wear failure of gearsWear is an abrasive material removal occurring on the tooth flanks of gears. This failure proceedscontinuously and causes material loss and a change in the profile form of the tooth flanks, which can lead tobreakdown of the gears. Typical wear on the tooth flanks
17、of an industrial gear is shown in Figure 3.Alsothewearbehaviordependsondifferentinfluences. Besidessurfacehardness,material,andgeometryofthe tooth flanks, it is again the lubricant and the operating conditions which have a major influence on wearbehavior. See Table 2.Figure 2. Micropitting gear fail
18、ure of an industrial gear boxTable 1. Influences on the micropitting load-carrying capacityLubricantChemistry of the base oilViscosity of the base oilType and amount of additivesTooth flank surfaceRoughnessSurface textureSurface hardnessOperating conditionsNormal and frictional loadCircumferential s
19、peedTemperature5 12FTM03Figure 3. Wear on an industrial gearTable 2. Influences on the wear behaviorLubricantChemistry of the base oilViscosity of the base oilType and amount of additivesTooth flank surfaceSurface hardnessProfile modification (tip relief)MaterialOperating conditionsNormal and fricti
20、onal loadCircumferential speedTemperatureFailures of rolling bearingsGear damage is also often caused by high rolling bearing wear or premature fatigue of rolling bearings 14.Failures based on material or production mistakes are very seldom. But type, condition, and quantity oflubricanthasamaininflu
21、enceonbearingfailuresaswellashardorliquidcontamination13. Figure 4showsthe typical failures on a rolling bearing.The additives contained in gear oils may have a decisive effect on rolling bearing damage.Figure 4. Typical rolling bearing failures6 12FTM03Test equipmentInvestigation of micropitting lo
22、ad-carrying capacity and wear behavior of gearsThe test runs conducted to determine the micropitting load-carrying capacity and the wear behavior of gearoils on gears were performed on a FZG back-to-back gear test rig 6. The setup schematic of the FZGback-to-back gear test rig is shown in Figure 5.T
23、he FZG back-to-back gear test rigutilizes arecirculating power loop principle, also knownas afour-squareconfiguration,inordertoprovideafixedtorque(load)toapair oftest gears. Thetest gearboxanddrivegear-box are connected with two torsion shafts. One shaft is divided into two parts and contains a load
24、 couplingused to apply the torque (load) through the use of weights hung on the loading arm. Heating and coolingelements are used to control the oil temperature as required by the operating test conditions.In order to investigate themicropitting load-carryingcapacity, test gears typeC-GF of the stan
25、dardmicropit-tingtestaccordingtoFVA54/78areused. Theslowspeedwearbehaviorisinvestigatedbyusingtestgearstype C-PT according to DGMK 377-01 2 The geometrical data and manufacturing details of the test gearstype C-GF and type C-PT are shown in Table 3 and Table 4.Figure 5. FZG back-to-back gear test ri
26、gTable 3. Manufacturing details of the test gears type C-GF and type C-PTDimension Symbol UnitNumerical valueType C-GF Type C-PTBasic materialPinion 16MnCr5 16MnCr5Wheel 16MnCr5 16MnCr5Surface hardnessPinion 750 HV1 750 HV1Wheel 750 HV1 750 HV1Case hardening depth at550 HV1Pinion mm 0.8 - 1.0 0.8 -
27、1.0Wheel mm 0.8 - 1.0 0.8 - 1.0Core strengthPinion N/mm21000 - 1250 1000 - 1250Wheel N/mm21000 - 1250 1000 - 1250Flank roughnessPinion Ra mm 0.300.10 0.300.10Wheel Ra mm 0.300.10 0.300.107 12FTM03Table 4. Geometrical data of the test gears type C-GF and type C-PTDimension Symbol UnitNumerical valueT
28、ype C-GF Type C-PTShaft center distance a mm 91.5 91.5Module m mm 4.5 4.5Number of teethPinion z1 16 16Wheel z2 24 24Effective face width b mm 14 14Helix angle deg 0 0Pressure angle deg 20 20wdeg 22.44 22.44Profile shift coefficientPinion x1 0.1817 0.1817Wheel x2 0.1715 0.1715Tip diameterPinion da1m
29、m 82.46 82.46Wheel da2mm 118.36 118.36Transverse contact ratio 1.44 1.44Tooth correctionPinionWithout tip and root relief, no longitudinal crowningWheelInvestigation of the wear behavior of rolling bearingsThetestrunsconductedtodeterminethewearbehaviorofgearoilsonrollingbearingswereperformedonanFE8b
30、earingtestrig5requiredforlubricatingoilsCLPaccordingtoDIN51517-34. Theschematicsetupofthe FE8 bearing test rig is shown in Figure 6.The wear behavior of rolling bearings is investigated with test bearings type Daccording to DIN 51819-35.Thegeometricaldataandmanufacturingdetails ofthetestbearings typ
31、eD(81212accordingtoDIN722)aregiveninTable5.Figure 6. FE8 bearing test rig8 12FTM03Table 5. Geometrical data and manufacturing details of the test bearings type DDimension Symbol Unit Numerical valueInner diameter d mm 60.0Outer diameter D mm 95.0Width T mm 26Basic materialRoller 100Cr6Cage BrassTest
32、 proceduresTo determine the performance capacities of gear oils with regard to the prevention of micropitting and wear,they are today subjected to standardized tests under critical lubricating conditions and temperatures as arecommonly encountered in practice. The micropitting resistance ingears is
33、analyzed inthe FZG micropittingtest according to FVA 54/7 8 at an oil temperature of oil=90C. Meanwhile it has become increasinglycommontoconduct micropittingtests also at a reducedoil temperatureof oil=60Cin order to determineifmicropittingcanbereliablypreventedalsoattheselowertemperatures,whichare
34、encountered, forexample,inwindturbinegearboxes. TheslowspeedwearbehaviorofgearsisanalyzedintheFZGweartestaccordingtoDGMK 377-012 at oiltemperatures of oil=90Cand120C. Theinfluenceof temperatureis thustakenintoaccount, albeit onarather highlevel. Thewear behavior of rollingbearings is examined inthe
35、FE8weartest according to DIN 51819-3 5 at an oil temperature of oil=80C.FZG micropitting test (GF-C/8.3/90 or GF-C/8.3/60)Themicropittingload-carryingcapacityofgearscanbecalculatedaccordingtoISOTR15144-17,wheretheinfluence of lubricant, operating conditions, and surface roughness is considered with
36、the specific lubricantfilm thickness. For this purpose, the specific lubricant film thickness of a practical gear is compared with aminimumrequiredspecificlubricantfilm thickness. Thelatter isthespecificfilm thicknesswherenomicropit-tingriskisgivenforalubricantandcanbedeterminedbyperformingamicropit
37、tingtestaccordingtoFVA54/78.ThemicropittingtestGF-C/8.3/90orGF-C/8.3/60accordingtoFVA 54/7consists of aloadstagetest andanendurancetestperformedonaFZGback-to-backgeartestrig6. TestgearstypeC-GFrunatacircumferen-tialspeedof vt= 8.3m/s andalubricanttemperatureofoil=90Cor60C. Theloadandthetest periodsa
38、revaried.Intheloadstagetest, theload is increased stepwisefrom loadstage LS 5 toload stageLS 10with arunningtimeof16hperloadstage. Aftertheloadstagetest,anendurancetestwitharunningtimeof80hinloadstageLS 8 and 580 h in load stage LS 10is performed. Thepinion torqueand thecorresponding Hertzianpres-su
39、reofthedifferentloadstagesaregiveninTable 6. InloadstageLS10thetestgearsarehighlyloaded. Theendurance limit of the material is about Hlim= 1400 N/mm2.Table 6. Load stages of the micropitting testLoad stage Pinion torque, T1,Nm Hertzian pressure, pc,N/mm2LS 5 70.0 795.1LS 6 98.9 945.1LS 7 132.5 1093.
40、9LS 8 171.6 1244.9LS 9 215.6 1395.4LS 10 265.1 1547.39 12FTM03Attheendoftheloadstagetestandtheendurancetestwiththefirsttestgears,theloadstagetestisrepeatedwith new test gears to check repeatability.Aftereachtestperiod,thetestgearsaredisassembledandtheprofileofthetestedflanksismeasuredusinga3D measur
41、ement system.In the load stage test, the failure criterion has been reached once the mean profile form deviation due tomicropitting exceeds the limiting value of 7.5 mm. The load stage in which the failure criterion is reached iscalled failure load stage. An overview regarding the classification of
42、test results obtained in the micropittingtestisgiveninTable7.Lubricants withahighmicropittingload-carryingcapacity reachthefailurecriterionof aprofileform deviationof 7.5 mm due to micropitting in load stageLS 10 of the load stage test (GFT-high).Examples of the evaluation of the micropitting test a
43、re given in Figure 7 and Figure 8.Table 7. Classification of test results of the micropitting testDescription Failure loadstageMicropitted area GF-ClassLow micropitting load-carryingcapacityLS 7 Sometimes morethan 50%GFT-lowMedium micropitting load carryingcapacityLS 8 - LS 9 About 30% GFT-mediumHig
44、h micropitting load-carryingcapacityLS 10 Less than 20% GFT-highFigure 7. Pinion type C-GF with measurement of the profile, nearly no micropitting failureFigure 8. Pinion type C-GF with measurement of the profile, micropitting failure in the range ofthe failure criterion10 12FTM03Intheendurancetest,
45、astagnationofmicropittingformationcomparedwiththemicropittingareaattheendoftheloadstagetestispreferredbutnotrequired. Forahigh-performancegearoilonthebasisofpolyglycolwitha high micropitting performance, a test result is given exemplarily in Figure 9 showing the profile form devi-ationduetomicropitt
46、ing. Theprofileformdeviationofthepinionisbelowthefailurecriterionforthewholeloadstagetest(GFT-high). Intheendurancetest,theprofileformdeviationstagnatescomparedwiththesteptest.FZG slow speed wear test (C/0.05:0.57/90:120/12)TheresultsoftheFZGslowspeedtestaccordingtoDGMK377-012canbeusedforrelativeran
47、kingofgearoilstoareferenceoilandinaddition,specificwearratescITcanbederivedforinclusioninthewearcalculationmethod developed by Plewe 12.The FZG slow speed wear test C/0.05:0.57/90:120/12 according to DGMK 377-01 determines the wearcharacteristicsofgearoilsattwodifferenttemperaturesunder mixedandboun
48、darylubricationconditions2.With an additional test part the influence of circumferential speed can be investigated.TestgearstypeC-PTrunataverylowcircumferentialspeedofvt=0.05m/s. TheloadappliedisloadstageLS12 which is equivalent to a pinion torque of T1= 378.2 Nm. This corresponds to a Hertzian pres
49、sure ofpc= 1853N/mm2inthegear contact. Theoiltemperatureisoil=90Cduringtest part1of220hoursandoil=120Cduringtestpart2of220hours. Intheoptionaltestpart3of140hoursahighercircumferentialspeed of vt=0.57m/sisrunatanoiltemperatureofoil=90C.Thetest is runonamodifiedFZG back-to-back gear testrigaccordingto ISO14635-16usinganadditionalreducergearboxafterthedrivemotorinordertorunverylowspeedsAftereachtestintervalthepinionandthewheel are disassemble
