AGMA 92FTM8-1992 The Role of Reliability for Bearings and Gears《可靠性对于轴承和齿轮的重要性》.pdf
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1、92 FTM 8The Role of Reliability forBearings and Gearsby: Charles A. MoyerThe Timken CompanyAmerican Gear Manufacturers AssociationTECHNICAL PAPERThe Role of Reliability for Bearings and GearsCharles A. Moyer (retired)The Timken Company, Canton, OhioThe statements and opinions contained herein are th
2、ose of the author and should not be construed as an official action oropinion of the American Gear Manufacturers Association.ABSTRACT:Life prediction or performance assessment is primarily done for bearings or gears with recognition of the significant roleof stress level to such assessments. Reliabi
3、lity or probability of performance is known to relate to the stress-liferelationship but the details as to how these interact are not often clearly defined.This paper details the experimental basis for the relationship between stress (load), life and reliability for bearings andgears considering the
4、 similarity and differences of their respective systems. The role of stress level and life scatter interms of the Weibull distribution will be addressed. The background and equations to calculate the reliability factors, asincluded in both bearing and gear standards, are then developed.Copyright 199
5、2American Gear Manufacturers Association1500 King Street, Suite 201Alexandria, Virginia, 22314October, 1992ISBN: 1-55589-588-3The Role of Reliability for Bearings andGearsby Charles A. MoyerWithin any vital operating equipment, the S_reliability of the components that make _ _up the unit must be kno
6、wn if any sound 2predictions of life or stress capability_re to be made. Reliabilty of course is k_. t _not an independent quality or factor of _any component, whether it be bearing or _._gear. The interdependenceof these three _ _ :_-_ _kfactors,life,stress(orloadleveland “reliability was demonstra
7、ted years ago _.interlinking plots in what Weibull Ncalled the complete fatigue diagram.p _ .EoSection 1 on the figure is the typical -I 0 0._s (;0 0.2sS/N curve with S representing stress on a ._/./_J_/y _D2 _4 _0blinear scale and N representing life instress cycles on a log scale. The curves o - ,
8、0zlabeled P are the full range of /_/,7 ._._/jprobabilty that can theoretically occur /from PrO (100% reliability) to P=I (zero / ,_. _-_ /./_04reliability). All testing or real life _“ ,_ _,_component operations fall within theseextremes. For a given stress and expected ,n_or determined life, a pro
9、bability or i _Nreliability value must exist. Forbearings and gears one tends to consider Fig. 1 The Complete Fatigue Diagram (i).only a few specific curves represented bysection i of the diagram.In sections 2 and 3 of Fig. i, other eventually used in gear and bearingrepresentations of the stress-li
10、fe- standards, they have been developed fromreliability relationship are illustrated, tests. The S/N curves are based onFor this figure the spacing of the curves fatigue tests and the reliability-life orand the log or linear scales are reliability-stress relationships dependarbitary. In actuality th
11、e underlying on related or additional testing, usuallydistributions or scales are determined by with multiple tests at each of severalexperiment. And when curves are drawn and stress levels.Reliability-Life for Bearings 70 )leof 229 85mm boreThe reliability-life relationship forbearings has been gen
12、erated from multipletests run on all types of rolling elementbearings. Bearing life has been expressedas B-IO or L-IO for years and is L-IO inthe latest bearing standards (2)(3)(4).L-IO is defined as basic rating life inmillions of revolutions so that for a (-_group of apparently identical rolling Z
13、bearings, operating under the same _conditions, 90 percent are expected to meet or exceed rating life and ten cr 99percent are expected to fail earlier.Thus, reliability in the broader sense is O0the percentage of an identical group that E-will reach or exceed a specified life. Z ILJJFor an individu
14、al bearing its reliability 0is the probability that it will reach or rrexceed the specified life. LUO_ 99._It has been determined that lives ofidentical bearing groups could be Irepresented by the Weibull distributionas shown in Fig. 2. In 1972 the bearingload ratings and fatigue life standards(5)(6
15、) incorporated the concept of lifeadjustment factors so that applicationlife (L-na) could be more closelyassessed rather than rating life (L-IO) 0.01.02 .04.06 .I .2 .4 .6 1.0 2.0that assumed operating conditions thatwould only lead to classical subsurfacerolling contact fatigue. The reliability REL
16、ATIVE LIFEfactor a(1) as given in the referenceswas based on a Weibull dispersion Fig. 2 Typical Weibull Distribution Plot.parameter or slope of 1.5. It can bedetermined with the equation: extensive Weibull analysis presented by4.483,in(lOO/R)i/l.5 Tallian(7) in 1962. Tallians data was ona(1) = i 93
17、 test groups of 2520 bearings coveringwhere, about 30 years of testing,of which 91a(1) = a life ratio giving values percent were ball bearings. In theother than 1.0 for other reliabilities; surival range of 40 to 90 percent, thea(1)=l.O for L-IO life. fatigue failures fit the WeibullR = reliability
18、as expressed in distribution very well with a Weibullterms of percent survival, slope (m) of 1.0, very close to the 1.125m = Wsibull slope = 1.5 for (9/8) value of m that is used in theequation i. standard ball bearing rating equations.However, in the survival range of 95 toA generalized equation fo
19、r any value of 99.9 percent a deviant line, showingWeibull slope may also be useful and is: excess life held for the early failures,was put through the lowest life bearingsa(1) = 9.4912*in(lOO/R) I/m 2 giving a Weibull slope here of 1.5. Fig.3 from reference (7) shows a Weibull plotWith a Weibull sl
20、ope of 1.5 a(1) valuesfrom 90 to 99.97 percent survival. Thus,are normally presented in tabular form asfor at least ball bearings, a Weibulltaken from references (2)(3) for ball andslope of 1.5 seemed suitable for equationroller bearings: 2 or would justify equation i above.Table i: Reliability a(1)
21、 ValuesReliability % L-ha a_l) A sizeable group of tapered roller90 L-IO 1.00 bearings, representing standard95 L-5 0.62 production lots over a five year period,have been fatigue tested with SAE 2096 L-4 0.5397 L-3 0.44 mineral oil of closely controlled98 L-2 0.33 viscosity and inlet oil temperature
22、controlled at 38C(I00 F). The test99 L-I 0.21 bearings ranged in size from 12.0 to 85.0mm bore Considering the similiarity ofAs Table 1 indicates, reliability wasonly considered for values greater than the test conditions, it was possible to90 percent This was partly from the express the bearings“ l
23、ives as a ratio of“ experimentallife to expected life or as90 ._a / 70Compositesampleof 346595 “ 80_TaperedRollerBearings2095 bearings spalledJj 90m= 1“6r=O99(crrcef)99 -o _ 95. -/-/ .d Z 98-, / _ _rr99.9 “ _JO 99.5-/ 1 :“ 99 97 “,././ !. 0 oX_l _1 QOl _1 LO _r“WFig. 3 Life Distribution: Early Failu
24、res 95 _ J * ITallian, Reference (7) / 1 lzrelative life. The expected life for each 198/ / i i : I ,! rsize bearing was determined using that 99.99 . I _ I , Ibearings specific rating and its test 0.01 .02 ,04.06 .I .2 .4 .6 1.0 2.0loads. The resulting Weibull distributionis given in Fig. 4 (8). Th
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