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首页 机械类专业英语翻译

机械类专业英语翻译.doc

机械类专业英语翻译

无言的小恋人
2019-06-14 0人阅读 举报 0 0 暂无简介

简介:本文档为《机械类专业英语翻译doc》,可适用于外语资料领域

EXTENDINGBEARINGLIFEBearingsfailforanumberofreasons,butthemostcommonaremisapplication,contamination,improperlubricant,shippingorhandlingdamage,andmisalignmentTheproblemisoftennotdifficulttodiagnosebecauseafailedbearingusuallyleavestelltalesignsaboutwhatwentwrongHowever,whileapostmortemyieldsgoodinformation,itisbettertoavoidtheprocessaltogetherbyspecifyingthebearingcorrectlyinThefirstplaceTodothis,itisusefultoreviewthemanufacturerssizingguidelinesandoperatingcharacteristicsfortheselectedbearingEquallycriticalisastudyofrequirementsfornoise,torque,andrunout,aswellaspossibleexposuretocontaminants,hostileliquids,andtemperatureextremesThiscanprovidefurthercluesastowhetherabearingisrightforajobWhybearingsfailAboutofballbearingfailuresarecausedbycontaminationfromdust,dirt,shavings,andcorrosionContaminationalsocausestorqueandnoiseproblems,andisoftentheresultofimproperhandlingortheapplicationenvironmentFortunately,abearingfailurecausedbyenvironmentorhandlingcontaminationispreventable,andasimplevisualexaminationcaneasilyidentifythecauseConductingapostmortemilustrateswhattolookforonafailedorfailingbearingThen,understandingthemechanismbehindthefailure,suchasbrinellingorfatigue,helpseliminatethesourceoftheproblemBrinellingisonetypeofbearingfailureeasilyavoidedbyproperhandingandassemblyItischaracterizedbyindentationsinthebearingracewaycausedbyshockloadingsuchaswhenabearingisdroppedorincorrectassemblyBrinellingusuallyoccurswhenloadsexceedthematerialyieldpoint(,psiinSAEchromesteel)Itmayalsobecausedbyimproperassembly,WhichplacesaloadacrosstheracesRacewaydentsalsoproducenoise,vibration,andincreasedtorqueAsimilardefectisapatternofellipticaldentscausedbyballsvibratingbetweenracewayswhilethebearingisnotturningThisproblemiscalledfalsebrinellingItoccursonequipmentintransitorthatvibrateswhennotinoperationInaddition,debriscreatedbyfalsebrinellingactslikeanabrasive,furthercontaminatingthebearingUnlikebrinelling,falsebinellingisoftenindicatedbyareddishcolorfromfrettingcorrosioninthelubricantFalsebrinellingispreventedbyeliminatingvibrationsourcesandkeepingthebearingwelllubricatedIsolationpadsontheequipmentoraseparatefoundationmayberequiredtoreduceenvironmentalvibrationAlsoalightpreloadonthebearinghelpskeeptheballsandracewayintightcontactPreloadingalsohelpspreventfalsebrinellingduringtransitSeizurescanbecausedbyalackofinternalclearance,improperlubrication,orexcessiveloadingBeforeseizing,excessive,frictionandheatsoftensthebearingsteelOverheatedbearingsoftenchangecolor,usuallytoblueblackorstrawcoloredFrictionalsocausesstressintheretainer,whichcanbreakandhastenbearingfailurePrematurematerialfatigueiscausedbyahighloadorexcessivepreloadWhentheseconditionsareunavoidable,bearinglifeshouldbecarefullycalculatedsothatamaintenanceschemecanbeworkedoutAnothersolutionforfightingprematurefatigueischangingmaterialWhenstandardbearingmaterials,suchasCorSAE,donotguaranteesufficientlife,specialtymaterialscanberecommendedInaddition,whentheproblemistracedbacktoexcessiveloading,ahighercapacitybearingordifferentconfigurationmaybeusedCreepislesscommonthanprematurefatigueInbearingsitiscausedbyexcessiveclearancebetweenboreandshaftthatallowstheboretorotateontheshaftCreepcanbeexpensivebecauseitcausesdamagetoothercomponentsinadditiontothebearingthermorelikelycreepindicatorsarescratches,scuffmarks,ordiscolorationtoshaftandboreTopreventcreepdamage,thebearinghousingandshaftfittingsshouldbevisuallycheckedMisalignmentisrelatedtocreepinthatitismountingrelatedIfracesaremisalignedorcockedTheballstrackinanoncircumferencialpathTheproblemisincorrectmountingortolerancing,orinsufficientsquarenessofthebearingmountingsiteMisalignmentofmorethan·cancauseanearlyfailureContaminatedlubricantisoftenmoredifficulttodetectthanmisalignmentorcreepContaminationshowsasprematurewearSolidcontaminantsbecomeanabrasiveinthelubricantInaddition。insufficientlubricationbetweenballandretainerwearsandweakenstheretainerInthissituation,lubricationiscriticaliftheretainerisafullymachinedtypeRibbonorcrownretainers,incontrast,allowlubricantstomoreeasilyreachallsurfacesRustisaformofmoisturecontaminationandoftenindicatesthewrongmaterialfortheapplicationIfthematerialchecksoutforthejob,theeasiestwaytopreventrustistokeepbearingsintheirpackaging,untiljustbeforeinstallationAvoidingfailuresThebestwaytohandlebearingfailuresistoavoidthemThiscanbedoneintheselectionprocessbyrecognizingcriticalperformancecharacteristicsTheseincludenoise,startingandrunningtorque,stiffness,nonrepetitiverunout,andradialandaxialplayInsomeapplications,theseitemsaresocriticalthatspecifyinganABEClevelaloneisnotsufficientTorquerequirementsaredeterminedbythelubricant,retainer,racewayquality(roundnesscrosscurvatureandsurfacefinish),andwhethersealsorshieldsareusedLubricantviscositymustbeselectedcarefullybecauseinappropriatelubricant,especiallyinminiaturebearings,causesexcessivetorqueAlso,differentlubricantshavevaryingnoisecharacteristicsthatshouldbematchedtotheapplicationForexample,greasesproducemorenoisethanoilNonrepetitiverunout(NRR)occursduringrotationasarandomeccentricitybetweentheinnerandouterraces,muchlikeacamactionNRRcanbecausedbyretainertoleranceoreccentricitiesoftheracewaysandballsUnlikerepetitiverunout,nocompensationcanbemadeforNRRNRRisreflectedinthecostofthebearingItiscommonintheindustrytoprovidedifferentbearingtypesandgradesforspecificapplicationsForexample,abearingwithanNRRoflessthanumisusedwhenminimalrunoutisneeded,suchasindiskdrivespindlemotorsSimilarly,machinetoolspindlestolerateonlyminimaldeflectionstomaintainprecisioncutsConsequently,bearingsaremanufacturedwithlowNRRjustformachinetoolapplicationsContaminationisunavoidableinmanyindustrialproducts,andshieldsandsealsarecommonlyusedtoprotectbearingsfromdustanddirtHowever,aperfectbearingsealisnotpossiblebecauseofthemovementbetweeninnerandouterracesConsequently,lubricationmigrationandcontaminationarealwaysproblemsOnceabearingiscontaminated,itslubricantdeterioratesandoperationbecomesnoisierIfitoverheats,thebearingcanseizeAttheveryleast,contaminationcauseswearasitworksbetweenballsandtheraceway,becomingimbeddedintheracesandactingasanabrasivebetweenmetalsurfacesFendingoffdirtwithsealsandshieldsillustratessomemethodsforcontrollingcontaminationNoiseisasanindicatorofbearingqualityVariousnoisegradeshavebeendevelopedtoclassifybearingperformancecapabilitiesNoiseanalysisisdonewithanAnderonmeter,whichisusedforqualitycontrolinbearingproductionandalsowhenfailedbearingsarereturnedforanalysisAtransducerisattachedtotheouterringandtheinnerraceisturnedat,rpmonanairspindleNoiseismeasuredinandirons,whichrepresentballdisplacementinμmradWithexperience,inspectorscanidentifythesmallestflawfromtheirsoundDust,forexample,makesanirregularcracklingBallscratchesmakeaconsistentpoppingandarethemostdifficulttoidentifyInnerracedamageisnormallyaconstanthighpitchednoise,whileadamagedouterracemakesanintermittentsoundasitrotatesBearingdefectsarefurtheridentifiedbytheirfrequenciesGenerally,defectsareseparatedintolow,medium,andhighwavelengthsDefectsarealsoreferencedtothenumberofirregularitiesperrevolutionLowbandnoiseistheeffectoflongwavelengthirregularitiesthatoccurabouttotimesperrevolutionThesearecausedbyavarietyofinconsistencies,suchaspocketsintheraceDetectablepocketsaremanufacturingflawsandresultwhentheraceismountedtootightlyinmultiplejawchucksMediumhandnoiseischaracterizedbyirregularitiesthatoccurtotimesperrevolutionItiscausedbyvibrationinthegrindingoperationthatproducesballsandracewaysHighhandirregularitiesoccurattotimesperrevolutionandindicatecloselyspacedchattermarksorwidelyspaced,roughirregularitiesClassifyingbearingsbytheirnoisecharacteristicsallowsuserstospecifyanoisegradeinadditiontotheABECstandardsusedbymostmanufacturersABECdefinesphysicaltolerancessuchasbore,outerdiameter,andrunoutAstheABECclassnumberincrease(fromto),tolerancesaretightenedABECclass,however,doesnotspecifyotherbearingcharacteristicssuchasracewayquality,finish,ornoiseHence,anoiseclassificationhelpsimproveontheindustrystandard如何延长轴承寿命轴承失效的原因在球轴承的失效中约有是由灰尘、脏物、碎屑的污染以及腐蚀造成的。污染通常是由不正确的使用和不良的使用环境造成的,它还会引起扭矩和噪声的问题。由环境和污染所产生的轴承失效是可以预防的,而且通过简单的肉眼观察是可以确定产生这类失效的原因。通过失效后的分析可以得知对已经失效的或将要失效的轴承应该在哪些方面进行查看。弄清诸如剥蚀和疲劳破坏一类失效的机理,有助于消除问题的根源。只要使用和安装合理,轴承的剥蚀是容易避免的。剥蚀的特征是在轴承圈滚道上留有由冲击载荷或不正确的安装产生的压痕。剥蚀通常是在载荷超过材料屈服极限时发生的。如果安装不正确从而使某一载荷横穿轴承圈也会产生剥蚀。轴承圈上的压坑还会产生噪声、振动和附加扭矩。类似的一种缺陷是当轴承不旋转时由于滚珠在轴承圈间振动而产生的椭圆形压痕。这种破坏称为低荷振蚀。这种破坏在运输中的设备和不工作时仍振动的设备中都会产生。此外,低荷振蚀产生的碎屑的作用就象磨粒一样,会进一步损害轴承。与剥蚀不同,低荷振蚀的特征通常是由于微振磨损腐蚀在润滑剂中会产生淡红色。消除振动源并保持良好的轴承润滑可以防止低荷振蚀。给设备加隔离垫或对底座进行隔离可以减轻环境的振动。另外在轴承上加一个较小的预载荷不仅有助于滚珠和轴承圈保持紧密的接触,并且对防止在设备运输中产生的低荷振蚀也有帮助。造成轴承卡住的原因是缺少内隙、润滑不当和载荷过大。在卡住之前,过大的摩擦和热量使轴承钢软化。过热的轴承通常会改变颜色,一般会变成蓝黑色或淡黄色。摩擦还会使保持架受力,这会破坏支承架,并加速轴承的失效。材料过早出现疲劳破坏是由重载后过大的预载引起的。如果这些条件不可避免,就应仔细计算轴承寿命,以制定一个维护计划。另一个解决办法是更换材料。若标准的轴承材料不能保证足够的轴承寿命,就应当采用特殊的材料。另外,如果这个问题是由于载荷过大造成的,就应该采用抗载能力更强或其他结构的轴承。蠕动不象过早疲劳那样普遍。轴承的蠕动是由于轴和内圈之间的间隙过大造成的。蠕动的害处很大,它不仅损害轴承,也破坏其他零件。蠕动的明显特征是划痕、擦痕或轴与内圈的颜色变化。为了防止蠕动,应该先用肉眼检查一下轴承箱件和轴的配件。避免失效的方法解决轴承失效问题的最好办法就是避免失效发生。这可以在选用过程中通过考虑关键性能特征来实现。这些特征包括噪声、起动和运转扭矩、刚性、非重复性振摆以及径向和轴向间隙。扭矩要求是由润滑剂、保持架、轴承圈质量(弯曲部分的圆度和表面加工质量)以及是否使用密封或遮护装置来决定。润滑剂的粘度必须认真加以选择,因为不适宜的润滑剂会产生过大的扭矩,这在小型轴承中尤其如此。另外,不同的润滑剂的噪声特性也不一样。举例来说,润滑脂产生的噪声比润滑油大一些。因此,要根据不同的用途来选用润滑剂。在轴承转动过程中,如果内圈和外圈之间存在一个随机的偏心距,就会产生与凸轮运动非常相似的非重复性振摆(NRR)。保持架的尺寸误差和轴承圈与滚珠的偏心都会引起NRR。和重复性振摆不同的是,NRR是没有办法进行补偿的。在工业中一般是根据具体的应用来选择不同类型和精度等级的轴承。例如,当要求振摆最小时,轴承的非重复性振摆不能超过微米。同样,机床主轴只能容许最小的振摆,以保证切削精度。因此在机床的应用中应该使用非重复性振摆较小的轴承。在许多工业产品中,污染是不可避免的,因此常用密封或遮护装置来保护轴承,使其免受灰尘或脏物的侵蚀。但是,由于轴承内外圈的运动,使轴承的密封不可能达到完美的程度,因此润滑油的泄漏和污染始终是一个未能解决的问题。一旦轴承受到污染,润滑剂就要变质,运行噪声也随之变大。如果轴承过热,它将会卡住。当污染物处于滚珠和轴承圈之间时,其作用和金属表面之间的磨粒一样,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的一种方法。

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