轴承论文中英文资料外文翻译文献.docx
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轴承论文中英文资料外文翻译文献.docx
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轴承论文中英文资料外文翻译文献
中英文资料外文翻译文献
EXTENDINGBEARINGLIFE
Abstract:
Natureworkshardtodestroybearings,buttheirchancesofsurvivalcanbeimprovedbyfollowingafewsimpleguidelines.Extremeneglectinabearingleadstooverheatingandpossiblyseizureor,atworst,anexplosion.Butevenafailedbearingleavescluesastowhatwentwrong.Afteralittledetectivework,actioncanbetakentoavoidarepeatperformance.
Keywords:
bearingsfailureslife
Bearingsfailforanumberofreasons,butthemostcommonaremisapplication,contamination,improperlubricant,shippingorhandlingdamage,andmisalignment.Theproblemisoftennotdifficulttodiagnosebecauseafailedbearingusuallyleavestelltalesignsaboutwhatwentwrong.
However,whileapostmortemyieldsgoodinformation,itisbettertoavoidtheprocessaltogetherbyspecifyingthebearingcorrectlyinThefirstplace.Todothis,itisusefultoreviewthemanufacturerssizingguidelinesandoperatingcharacteristicsfortheselectedbearing.
Equallycriticalisastudyofrequirementsfornoise,torque,andrunout,aswellaspossibleexposuretocontaminants,hostileliquids,andtemperatureextremes.Thiscanprovidefurthercluesastowhetherabearingisrightforajob.
1Whybearingsfail
About40%ofballbearingfailuresarecausedbycontaminationfromdust,dirt,shavings,andcorrosion.Contaminationalsocausestorqueandnoiseproblems,andisoftentheresultofimproperhandlingortheapplicationenvironment.Fortunately,abearingfailurecausedbyenvironmentorhandlingcontaminationispreventable,andasimplevisualexaminationcaneasilyidentifythecause.
Conductingapostmortemil1ustrateswhattolookforonafailedorfailingbearing.Then,understandingthemechanismbehindthefailure,suchasbrinellingorfatigue,helpseliminatethesourceoftheproblem.
Brinellingisonetypeofbearingfailureeasilyavoidedbyproperhandingandassembly.Itischaracterizedbyindentationsinthebearingracewaycausedbyshockloading-suchaswhenabearingisdropped-orincorrectassembly.Brinellingusuallyoccurswhenloadsexceedthematerialyieldpoint(350,000psiinSAE52100chromesteel).Itmayalsobecausedbyimproperassembly,Whichplacesaloadacrosstheraces.Racewaydentsalsoproducenoise,vibration,andincreasedtorque.
Asimilardefectisapatternofellipticaldentscausedbyballsvibratingbetweenracewayswhilethebearingisnotturning.Thisproblemiscalledfalsebrinelling.Itoccursonequipmentintransitorthatvibrateswhennotinoperation.Inaddition,debriscreatedbyfalsebrinellingactslikeanabrasive,furthercontaminatingthebearing.Unlikebrinelling,falsebinellingisoftenindicatedbyareddishcolorfromfrettingcorrosioninthelubricant.
Falsebrinellingispreventedbyeliminatingvibrationsourcesandkeepingthebearingwelllubricated.Isolationpadsontheequipmentoraseparatefoundationmayberequiredtoreduceenvironmentalvibration.Alsoalightpreloadonthebearinghelpskeeptheballsandracewayintightcontact.Preloadingalsohelpspreventfalsebrinellingduringtransit.
Seizurescanbecausedbyalackofinternalclearance,improperlubrication,orexcessiveloading.Beforeseizing,excessive,frictionandheatsoftensthebearingsteel.Overheatedbearingsoftenchangecolor,usuallytoblue-blackorstrawcolored.Frictionalsocausesstressintheretainer,whichcanbreakandhastenbearingfailure.
Prematurematerialfatigueiscausedbyahighloadorexcessivepreload.Whentheseconditionsareunavoidable,bearinglifeshouldbecarefullycalculatedsothatamaintenanceschemecanbeworkedout.
Anothersolutionforfightingprematurefatigueischangingmaterial.Whenstandardbearingmaterials,suchas440CorSAE52100,donotguaranteesufficientlife,specialtymaterialscanberecommended.Inaddition,whentheproblemistracedbacktoexcessiveloading,ahighercapacitybearingordifferentconfigurationmaybeused.
Creepislesscommonthanprematurefatigue.Inbearings.itiscausedbyexcessiveclearancebetweenboreandshaftthatallowstheboretorotateontheshaft.Creepcanbeexpensivebecauseitcausesdamagetoothercomponentsinadditiontothebearing.
0thermorelikelycreepindicatorsarescratches,scuffmarks,ordiscolorationtoshaftandbore.Topreventcreepdamage,thebearinghousingandshaftfittingsshouldbevisuallychecked.
Misalignmentisrelatedtocreepinthatitismountingrelated.Ifracesaremisalignedorcocked.Theballstrackinanoncircumferencialpath.Theproblemisincorrectmountingortolerancing,orinsufficientsquarenessofthebearingmountingsite.Misalignmentofmorethan1/4·cancauseanearlyfailure.
Contaminatedlubricantisoftenmoredifficulttodetectthanmisalignmentorcreep.Contaminationshowsasprematurewear.Solidcontaminantsbecomeanabrasiveinthelubricant.Inaddition。
insufficientlubricationbetweenballandretainerwearsandweakenstheretainer.Inthissituation,lubricationiscriticaliftheretainerisafullymachinedtype.Ribbonorcrownretainers,incontrast,allowlubricantstomoreeasilyreachallsurfaces.
Rustisaformofmoisturecontaminationandoftenindicatesthewrongmaterialfortheapplication.Ifthematerialchecksoutforthejob,theeasiestwaytopreventrustistokeepbearingsintheirpackaging,untiljustbeforeinstallation.
2Avoidingfailures
Thebestwaytohandlebearingfailuresistoavoidthem.Thiscanbedoneintheselectionprocessbyrecognizingcriticalperformancecharacteristics.Theseincludenoise,startingandrunningtorque,stiffness,nonrepetitiverunout,andradialandaxialplay.Insomeapplications,theseitemsaresocriticalthatspecifyinganABEClevelaloneisnotsufficient.
Torquerequirementsaredeterminedbythelubricant,retainer,racewayquality(roundnesscrosscurvatureandsurfacefinish),andwhethersealsorshieldsareused.Lubricantviscositymustbeselectedcarefullybecauseinappropriatelubricant,especiallyinminiaturebearings,causesexcessivetorque.Also,differentlubricantshavevaryingnoisecharacteristicsthatshouldbematchedtotheapplication.Forexample,greasesproducemorenoisethanoil.
Nonrepetitiverunout(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,becomingimbeddedintheracesandactingasanabrasivebetweenmetalsurfaces.Fendingoffdirtwithsealsandshieldsillustratessomemethodsforcontrollingcontamination.
Noiseisasanindicatorofbearingquality.Variousnoisegradeshavebeendevelopedtoclassifybearingperformancecapabilities.
NoiseanalysisisdonewithanAnderonmeter,whichisusedforqualitycontrolinbearingproductionandalsowhenfailedbearingsarereturnedforanalysis.Atransducerisattachedtotheouterringandtheinnerraceisturnedat1,800rpmonanairspindle.Noiseismeasuredinandirons,whichrepresentballdisplacementinμm/rad.
Withexperience,inspectorscanidentifythesmallestflawfromtheirsound.Dust,forexample,makesanirregularcrackling.Ballscratchesmakeaconsistentpoppingandarethemostdifficulttoidentify.Inner-racedamageisnormallyaconstanthigh-pitchednoise,whileadamagedouterracemakesanintermittentsoundasitrotates.
Bearingdefectsarefurtheridentifiedbytheirfrequencies.Generally,defectsareseparatedintolow,medium,andhighwavelengths.Defectsarealsoreferencedtothenumberofirregularitiesperrevolution.
Low-bandnoiseistheeffectoflong-wavelengthirregularitiesthatoccurabout1.6to10timesperrevolution.Thesearecausedbyavarietyofinconsistencies,suchaspocketsintherace.Detectablepocketsaremanufacturingflawsandresultwhentheraceismountedtootightlyinmultiplejawchucks.
Medium-handnoiseischaracterizedbyirregularitiesthatoccur10to60timesperrevolution.Itiscausedbyvibrationinthegrindingoperationthatproducesballsandraceways.High-handirregularitiesoccurat60to300timesperrevolutionandindicatecloselyspacedchattermarksorwidelyspaced,roughirregularities.
ClassifyingbearingsbytheirnoisecharacteristicsallowsuserstospecifyanoisegradeinadditiontotheABECstandardsusedbymostmanufacturers.ABECdefinesphysicaltolerancessuchasbore,outerdiameter,andrunout.AstheABECclassnumberincrease(from3to9),tolerancesaretightened.ABECclass,however,doesnotspecifyotherbearingcharacteristicssuchasracewayquality,finish,ornoise.Hence,anoiseclassificationhelpsimproveontheindustrystandard.
GEARANDSHAFTINTRODUCTION
Abstract:
Theimportantpositionofthewhe
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