轴承机械类毕业设计外文翻译样本

轴承寿命分析摘要自然界苛刻工作条件会导致轴承失效，但是如果遵循某些简朴规则，轴承正常运转机会是可以被提高。在轴承使用过程当中，过度忽视会导致轴承过热现象，也也许使轴承不可以再被使用，甚至完全破坏。但是一种被损坏轴承，会留下它为什么被损坏线索。通过某些细致观测工作，咱们可以采用行动来避免轴承再次失效。核心词：轴承失效寿命1.轴承失效因素轴承失效有如下各种因素，然而轴承寿命实验却是所有机械实验中最故意义。实验者必要控制实验过程以保证成果。其她失效模式在Tallian[19.2]中有详细阐述。下边几段就详细阐述了可以影响寿命实验成果几种失效模式。23章中，从EHL观点讨论了润滑条件对寿命实验成果影响，同步尚有其她润滑条件会影响实验结论，一方面是润滑剂接触面积，受到轴承尺寸，转速，润滑剂流动性等因素影响，润滑剂在轴承表面形成润滑层厚度普通不大于0.05~0.5um，不不大于这个薄层厚度固体微粒会残留在接触面上，从而划伤润滑沟道和轴承滚动面。从而大大缩短轴承耐用性。关于这点Sayles和MacPherson以及其她人均有详细论证。因而，为了保证明验成果咱们必要选用适当级别润滑剂。润滑剂选取由工况决定，实验时也如此。如果工况选取范畴不拟定，就必要考虑到接触面积对实验成果影响。23章中讨论了不同接触面积对轴承失效寿命实验成果影响。潮气是影响润滑成果另一种重要因素，长时间在水中和油中被腐蚀不但对外观质量有影响，还会影响到滚动表面轴承寿命。关于这点Fitch等人[19.7]有过论证。并且，虽然是仅有50~100PPM（百万分之一）水汽含量也会产生有害影响，甚至产生表面看不出痕迹腐蚀。这是由于轴承沟道和滚动面之间会产生氢脆现象，从23章中也可以看出在润滑实验中湿气是如此重要一种因素。因而在轴承寿命实验成果中必要考虑到潮气影响。为了减少对寿命减少影响，潮气含量最多不能超过40PPM。润滑剂化学成分也是需要考虑。大多数商业润滑油包括许多为特定目而开发专有添加剂。例如，为了提高抗磨损性能，为了能达到极限压力，或者耐热性，还可以在边际润滑油膜状况下提供边界润滑还能为边界润滑提供一种边界润滑层。这些添加剂同步也能即时或者逐渐地影响滚动轴承耐用性。为了避免添加剂成为加速寿命实验条件，咱们必要小心以保证测试润滑剂添加剂不会受到恶化。为了保证同组产品寿命实验成果有连贯性，最佳在整个寿命实验中都用同一供应商原则润滑剂。为了得到一种合理成果，记录学规定做诸多组寿命实验。因而一种轴承寿命实验需很长时间。实验人员必要保证整个实验过程持续性，由于任何微小变化都会影响实验成果，因而这个过程是很复杂。甚至这些微小变化在导致重大变化之前都不会被注意到。一旦发生这样状况，就没机会补救了。只能在更好控制条件下重新做实验。例如说：添加剂稳定性会影响到整个实验条件。当前已经懂得了某些添加剂在长期使用时会导致大量额外损耗。这些易退化添加剂会影响轴承表面润滑条件，从而影响轴承寿命。普通对润滑剂做化学检测时是不会检测添加剂成分。因而，如果一种润滑剂用于长时间轴承寿命实验话，生产者应当定期更换实验样品，例如一年一次。用来详细评估润滑剂使用规定。实验时还要控制是恰当温度。润滑层（油膜）厚度对温度影响是相称敏感，大多数装机实验是在原则工业环境下进行，在这一年实验时间中环境温度变化是非常大。同步，个别轴承受温度变化影响是会影响到整个系统常规制造公差。因而，所有轴承受温度变化影响会直接影响到寿命实验数据精确性。因而为了保证明验数据连贯性，必要监控并实时调节每个轴承使用温度。因而对于轴承寿命实验时±3ºC温度公差被以为是可接受。用于轴承寿命实验硬件装备磨损是另一种需要监控恒量。用于重载实验轴和轴承内圈都会受到很大载荷。重复拆装轴承会对轴表面产生损害。这样变化会影响几何形状。轴外径和轴承内径都会受腐蚀影响。腐蚀是由于震动产生微粒被氧化而产生。这样也会减少轴承寿命实验时间。同步这样机构也会在装配面上产生重大几何形变，从而影响轴承内径，最后成为减少寿命重要因素。轴承缺陷检测也是寿命实验重要考察因素。轴承缺陷最早是由原材料上微小裂纹引起。这样缺陷在实验中是没法检测。为了检测这个缺陷就需要使这个缺陷递增到能影响轴承参数数量级别。例如说噪音，温度，震动等缺陷。可以在系统中应用这些技术办法来检查缺陷。而具备这样能力系统可以从初期就检测出在多样化工作条件复杂系统中用来测试用缺陷轴承。而当前还没有一种单一系统能检测出所有轴承缺陷。因而将来有必要选取一种能在轴承受到微小伤害之前就停下机器监控系统。缺陷递增速率是相称重要。如果在实验结束时缺陷限度和理论计算出是一致，唯一区别就是实验中对缺陷检测总是落后于理论计算。原则轴承钢在耐久性实验中缺陷递增速度是相称快。并且这个递增还不是重要因素，考虑到有代表性耐久性实验数据都是经记录学分析后得到。有也不一定，例如某些表面硬度不同钢材或是专为实验用生产钢材。因而在分析成果时候就必要考虑是原则轴承钢还是专门实验用钢材。耐久性实验最后成果有效性是由元素-金相分析验证。轴承会通过高倍光学显微镜，高倍电子扫描显微镜，高倍电子显微镜，化学元素分析等各种办法来分析。生产时浮现会导致缺陷元素以及残留在表面发生化学变化后来会导致缺陷元素（如S，P等有害元素）等都会影响轴承寿命。这些检查办法都是用来保证明验得出数据是真实有效。Tallian将所有轴承失效黑白图片汇编起来【19.8】，可觉得判断各种类型失效提供根据。当前Tallian已经将其更新为【19.9】，其中加入了彩色图片。元素-金相实验可以提供一种精准证据，使实验成果处在可控制状况下，同步检测有疑点和争议地方。当轴承从实验机上取下来时候可以现做一种初步研究，将会在30倍显微镜下观测失效某些。而正常显微图片请看19.2~19.6中图片。、图19.2是球轴承沟道表面失效图片。图19.3是滚子轴承沟道由于未校准而导致表面开裂图片。图19.4是一种球轴承由于外圈表面锈蚀而导致外圈开裂图片。图19.5是表面凹陷残骸详细图片。图19.6是一种由于热变形导致内圈游隙变化图片。最后4张图片不是用正的确验办法得到有效失效模式。然而，这些错误数据需要从有效失效数据中剔除掉，从而得到能对的评估寿命实验有效数据。2.避免失效办法解决轴承失效问题最佳办法就是避免失效发生。这可以在选用过程中通过考虑核心性能特性来实现。这些特性涉及噪声、起动和运转扭矩、刚性、非重复性振摆以及径向和轴向间隙。扭矩规定是由润滑剂、保持架、轴承圈质量（弯曲某些圆度和表面加工质量）以及与否使用密封或遮护装置来决定。润滑剂粘度必要认真加以选取，由于不适当润滑剂会产生过大扭矩，这在小型轴承中特别如此。此外，不同润滑剂噪声特性也不同样。举例来说，润滑脂产生噪声比润滑油大某些。因而，要依照不同用途来选用润滑剂。在轴承转动过程中，如果内圈和外圈之间存在一种随机偏心距，就会产生与凸轮运动非常相似非重复性振摆（NRR）。保持架尺寸误差和轴承圈与滚珠偏心都会引起NRR。和重复性振摆不同是，NRR是没有办法进行补偿。在工业中普通是依照详细应用来选取不同类型和精度级别轴承。例如，当规定振摆最小时，轴承非重复性振摆不能超过0.3微米。同样，机床主轴只能容许最小振摆，以保证切削精度。因而在机床应用中应当使用非重复性振摆较小轴承。在许多工业产品中，污染是不可避免，因而惯用密封或遮护装置来保护轴承，使其免受灰尘或脏物侵蚀。但是，由于轴承内外圈运动，使轴承密封不也许达到完美限度，因而润滑油泄漏和污染始终是一种未能解决问题。一旦轴承受到污染，润滑剂就要变质，运营噪声也随之变大。如果轴承过热，它将会卡住。当污染物处在滚珠和轴承圈之间时，其作用和金属表面之间磨粒同样，会使轴承磨损。采用密封和遮护装置来挡开脏物是控制污染一种办法。噪声是反映轴承质量一种指标。轴承性能可以用不同噪声级别来表达。噪声分析是用安德逊计进行，该仪器在轴承生产中可用来控制质量，也可对失效轴承进行分析。将一传感器连接在轴承外圈上，而内圈在心轴以1800r/min转速旋转。测量噪声单位为anderons。即用um/rad表达轴承位移。依照经验，观测者可以依照声音辨别出微小缺陷。例如，灰尘产生是不规则噼啪声；滚珠划痕产生一种持续爆破声，拟定这种划痕最困难；内圈损伤普通产生持续高频噪声，而外圈损伤则产生一种间歇声音。轴承缺陷可以通过其频率特性进一步加以鉴定。普通轴承缺陷被分为低、中、高三个波段。缺陷还可以依照轴承每转动一周浮现不规则变化次数加以鉴定。低频噪声是长波段不规则变化成果。轴承每转一周这种不规则变化可浮现1.6~10次，它们是由各种干涉（例如轴承圈滚道上凹坑）引起。可察觉凹坑是一种制造缺陷，它是在制造过程中由于多爪卡盘夹太紧而形成。中频噪声特性是轴承每旋转一周不规则变化浮现10~60次。这种缺陷是由在轴承圈和滚珠磨削加工中浮现振动引起。轴承每旋转一周高频不规则变化浮现60~300次，它表白轴承上存在着密集振痕或大面积粗糙不平。运用轴承噪声特性对轴承进行分类，顾客除了可以拟定大多数厂商所使用ABEC原则外，还可拟定轴承噪声级别。ABEC原则只定义了诸如孔、外径、振摆等尺寸公差。随着ABEC级别增长（从3增到9），公差逐渐变小。但ABEC级别并不能反映其她轴承特性，如轴承圈质量、粗糙度、噪声等。因而，噪声级别划分有助于工业原则改进。BEARINGLIFEANALYSISProceedingsoftheNinthInternationalSymposiumonMagneticBearings.Kentucky.USA.,(August):3-61.WHYBEARINGSFAILAnindividualbearingmayfailforseveralreasons；however，theresultsofanendurancetestseriesareonlymeaningfulwhenthetestbearingsfailbyfatigue-relatedmechanisms.Theexperimentermustcontrolthetestprocesstoensurethatthisoccurs.SomeoftheotherfailuremodesthatcanbeexperiencedarediscussedindetailbyTallian[19.2].Thefollowingparagraphsdealwithafewspecificfailuretypesthatcanaffecttheconductofalifetestsequence.InChapter23，theinfluenceoflubricationoncontactfatiguelifeisdiscussedfromthestandpointofEHLfilmgeneration.Therearealsootherlubrication-relatedeffectsthatcanaffecttheoutcomeofthetestseries.Thefirstisparticulatecontaminantsinthelubricant.Dependingonbearingsize，operatingspeed，andlubricantrheology，theoverallthicknessofthelubricantfilmdevelopedattherollingelement-racewaycontactsmayfallbetween0.05and0.5m.Solidparticlesanddamagetheracewayandrollingelementsurfaces，leadingtosubstantiallyshortenedendurances.Thishasbeenamplydemonstratedbyandandothers.Therefore，filtrationofthelubricanttothedesiredlevelisnecessarytoensuremeaningfultestresult.Thedesiredlevelisdeterminedbytheapplicationwhichthetestingpurportstoapproximate.Ifthisdegreeoffiltrationisnotprovided，effectsofcontaminationmustbeconsideredwhenevaluatingtestresults.Chapter23discussestheeffectofvariousdegreesofparticulatecontamination，andhencefiltration，onbearingfatiguelife.Themoisturecontentinthelubricantisanotherimportantconsideration.Ithaslongbeenapparentthatquantitiesoffreewaterintheoilcausecorrosionoftherollingcontactsurfacesandthushaveadetrimentaleffectonbearinglife.IthasbeenfurthershownbyFitch[19.7]andothers，however，thatwaterlevelsaslowas50-100partspermillion(ppm)mayalsohaveadetrimentaleffect，evenwithnoevidenceofcorrosion.Thisisduetohydrogenembrittlementoftherollingelementandracewaymaterial.SeealsoChapter23.Moisturecontrolintestlubricationsystemsisthusamajorconcern，andtheeffectofmoistureneedstobeconsideredduringtheevaluationoflifetestresults.Amaximumof40ppmisconsiderednecessarytominimizelifereductioneffects.Thechemicalcompositionofthetestlubricantalsorequiresconsideration.Mostcommerciallubricantscontainanumberofproprietaryadditivesdevelopedforspecificpurposes；forexample，toprovideantiwearproperties，toachieveextremepressureand/orthermalstability，andtoprovideboundarylubricationincaseofmarginallubricantfilms.Theseadditivescanalsoaffecttheenduranceofrollingbearings，eitherimmediatelyorafterexperiencingtime-relateddegradation.Caremustbetakentoensurethattheadditivesincludedinthetestlubricantwillnotsufferexcessivedeteriorationasaresultofacceleratedlifetestconditions.Alsoforconsistencyofresultsandcomparinglifetestgroups，itisgoodpracticetoutilizeonestandardtestlubricantfromaparticularproducerfortheconductofallgenerallifetests.Thestatisticalnatureofrollingcontactfatiguerequiresmanytestsamplestoobtainareasonableestimateoflife.Abearinglifetestsequencethusneedsalongtime.Amajorjoboftheexperimentalististoensuretheconsistencyoftheappliedtestconditionsthroughouttheentiretestperiod.Thisprocessisnotsimplebecausesubtlechangescanoccurduringthetestperiod.Suchchangesmightbeoverlookeduntiltheireffectsbecomemajor.Atthattimeitisoftentoolatetosalvagethecollecteddata，andthetestmustberedoneunderbettercontrols.Forexample，thestabilityoftheadditivepackagesinatestlubricantcanbeasourceofchangingtestconditions.Somelubricantshavebeenknowntosufferadditivedepletionafteranextendedperiodofoperation.ThedegradationoftheadditivepackagecanaltertheEHLconditionsintherollingcontent，alteringbearinglife.Generally，thenormalchemicaltestsusedtoevaluatelubricantsdonotdeterminetheconditionsoftheadditivecontent.Thereforeifalubricantisusedforendurancetestingoveralongtime，asampleofthefluidshouldbereturnedtotheproduceratregularintervals，sayannually，foradetailedevaluationofitscondition.Adequatetemperaturecontrolsmustalsobeemployedduringthetest.ThethicknessoftheEHLfilmissensitivetothecontacttemperature.Mosttestmachinesarelocatedinstandardindustrialenvironmentswhereratherwidefluctuationsinambienttemperatureareexperiencedoveraperiodofayear.Inaddition，theheatgenerationratesofindividualbearingscanvaryasaresultofthecombinedeffectsofnormalmanufacturingtolerances.Bothoftheseconditionsproducevariationsinoperatingtemperaturelevelsinalotofbearingsandaffectthevalidityofthelifedata.Ameansmustbeprovidedtomonitorandcontroltheoperatingtemperaturelevelofeachbearingtoachieveadegreeofconsistency.Atolerancelevelof3Cisnormallyconsideredadequatefortheendurancetestprocess.Thedeteriorationoftheconditionofthemountinghardwareusedwiththebearingsisanotherarearequiringconstantmonitoring.Theheavyloadsusedforlifetestingrequireheavyinterferencefitsbetweenthebearinginnerringsandshafts.Repeatedmountinganddismountingofbearingscanproducedamagetotheshaftsurface，whichinturncanalterthegeometryofamountedring.Theshaftsurfaceandtheboreofthehousingarealsosubjecttodeteriorationfromfrettingcorrosion.Frettingcorrosionresultsfromtheoxidationofthefinewearparticlesgeneratedbythevibratoryabrasionofthesurface，whichisacceleratedbytheheavyendurancetestloading.Thismechanismcanalsoproducesignificantvariationsinthegeometryofthemountingsurfaces，whichcanaltertheinternalbearinggeometry.Suchchangescanhaveamajoreffectinreducingbearingtestlife.Thedetectionofbearingfailureisalsoamajorconsiderationinalifetestseries.Thefatiguetheoryconsidersfailureastheinitiationofthefirstcrackinthebulkmaterial.Obviouslythereisnowaytodetectthisoccurrenceinpractice.Tobedetectablethecrackmustpropagatetothesurfaceandproduceaspallofsufficientmagnitudetoproduceamarkedeffectonanoperatingparameterofthebearing：forexample，noise，vibration，and/ortemperature.Techniquesexitfordetectingfailuresinapplicationsystems.Theabilityofthesesystemstodetectearlysignsoffailurevarieswiththecomplexityofthetestsystem，thetypeofbearingunderevaluation，andothertestconditions.Currentlynosinglesystemexiststhatcanconsistentlyprovidethefailurediscriminationnecessaryforalltypesofbearinglifetests.Itisthennecessarytoselectasystemthatwillrepeatedlyterminatemachineoperationwithaconsistentminimaldegreeofdamage.Therateoffailurepropagationisthereforeimportant.Ifthedegreeofdamageattestterminationisconsistentamongtestelements，theonlyvariationbetweentheexperimentalandtheoreticallivesisthelaginfailuredetection.Instandardthrough-hardenedbearingsteelsthefailurepropagationrateisquiterapidunderendurancetestconditions，andthisisnotamajorfactor，consideringthetypicaldispersionofendurancetestdataandthedegreeofconfidenceobtainedfromstatisticalanalysis.Thismaynot，however，bethecasewithotherexperimentalmaterialsorwithsurface-hardenedsteelsorsteelsproducedbyexperimentaltechniques.Caremustbeusedwhenevaluatingtheselatterresultsandparticularlywhencomparingtheexperimentalliveswiththoseobtainedfromstandardsteellots.Theultimatemeansofensuringthatanendurancetestserieswasadequatelycontrolledistheconductofapost-testanalysis.Thisdetailedexaminationofallthetestedbearingsuseshigh-magnificationopticalinspection，higher-magnificationscanningelectronmicroscopy，metallurgicalanddimensionalexaminations，andchemical evaluationsasrequired.Thecharacteristicsofthefailuresareexaminedtoestablishtheiroriginsandtheresidualsurfaceconditionsareevaluatedforindicationsofextraneouseffectsthatmayhaveinfluencedthebearinglife.Thistechniqueallowstheexperimentertoensurethatthedataareindeedvalid.The“DamageAtlas”compiledbyTallianetal.[19.8]containingnumerousblackandwhitephotographsofthevariousbearingfailuremodescanprovideguidanceforthesetypesofdeterminations.ThisworkwassubsequentlyupdatedbyTallian[19.9]，nowincludingcolorphotographsaswell.Thepost-testanalysisis，bydefinition，afterthefact.Toprovidecontrolthroughoutthetestseriesandtoeliminateallquestionableareas，theexperimentershouldconductapreliminarystudywheneverabearingisremovedfromthetestmachine.Inthisportionoftheinvestigationeachbearingisexaminedopticallyatmagnificationsupto30forindicationsofimproperorout-of-controltestparameters.ExamplesofthetypesofindicationsthatcanbeobservedaregiveninFigs.19.2-19.6.Figure19.2illustratestheappearanceofatypicalfatigue-originatedspallonaballbearingraceway.Figure19.3containsaspallingfailureontheracewayofarollerbearingthatresultedfrombearingmisalignment，andFig.19.4containsaspallingfailureontheouterringofaballbearingproducedbyfrettingcorrosionontheouterdiameter.Figure19.5illustratesamoresubtleformoftestalteration，`wherethespallingfailureoriginatedfromthepresenceofadebrisdentonthesurface.Figure19.6givesanexampleofatotallydifferentfailuremodeproducedbythelossofinternalbearingclearanceduetothermalunbalanceofthesystem.Thelastfourfailuresarenotvalidfatiguespallsandindicatetheneedtocorrectthetestmethods.Furthermore，thesedatapointswouldneedtobeeliminatedfromthefailuredatatoobtainavalidestimateoftheexperimentalbearinglife.2.AVOIDINGFAILURESThebestwaytohandlebearingfailuresistoavoidthem．Thiscanbedoneintheselectionprocessbyrecognizingcriticalperformancecharacteristics．Theseincludenoise，startingandrunningtorque，stiffness，non-repetitiverunout，andradialandaxialplay．Insomeapplications，theseitemsaresocriticalthatspecifyinganABEClevelaloneisnotsufficient．Torquerequirementsaredeterminedbythelubricant，retainer，racewayquality(roundnesscrosscurvatureandsurfacefinish)，andwhethersealsorshieldsareused．Lubricantviscositymustbeselectedcarefullybecauseinappropriatelubricant，especiallyinminiaturebearings，causesexcessivetorque．Also，differentlubricantshavevaryingnoisecharacteristicsthatshouldbematchedtotheapplication.Forexample，greasesproducemorenoisethanoil．Non-repetitiverunout(NRR)occursduringrotationasarandomeccentricitybetweentheinnerandouterraces，muchlikeacamaction．NRRcanbecausedbyretainertoleranceoreccentricitiesoftheracewaysandballs．Unlikerepetitiverunout，nocompensationcanbemadeforNRR.NRRisreflectedinthecostofthebearing．Itiscommonintheindustrytoprovidedifferentbearingtypesandgradesforspecificapplications．Forexample，abearingwithanNRRoflessthan0.3umisusedwhenminimalrunoutisneeded，suchasindisk—drivespindlemotors．Similarly，machine—toolspindlestolerateonlyminimaldeflectionstomaintainprecisioncuts．Consequently，bearingsaremanufacturedwithlowNRRjustformachine-toolapplications．Contaminationisunavoidableinmanyindustrialproducts，andshieldsandsealsarecommonlyusedtoprotectbearingsfromdustanddirt．However，aperfectbearingsealisnotpossiblebecauseofthemovementbetweeninnerandouterraces．Consequently，lubricationmigrationandcontaminationarealwaysproblems．Onceabearingiscontaminated，itslubricantdeterioratesandoperationbecomesnoisier．Ifitoverheats，thebearingcanseize．Attheveryleast，contaminationcauseswearasitworksbetweenballsandtheraceway，becomingintheracesandactingasanabrasivebetweenmetalsurfaces．Fendingoffdirtwithsealsandshieldsillustratessomemethodsforcontrollingcontamination．Noiseisasanindicatorofbearingquality．Variousnoisegradeshavebeendevelopedtoclassifybearingperformancecapabilities．Whichisusedforqualitycontrolinbearingproductionandalsowhenfailedbeari