Ifyou'reusinggreaseaslubrication,becarefultolookatthegrease'sspeedrating. Theoilwon'thaveenoughtimetore-adherewiththethickeningaftertheball(oranother rollingelement)passesoverit,whichwillresultinthebearingoverheatingifyour bearingrotatesfasterthanthegreaserating
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Let'squicklygothroughthesciencebehindbearinglubricationfirst.Skiddingwill alwaysresultfromtherelativemotionbetweentheballandtheracetrackinaballbearing becausetheracewayiscurved.Inordertoavoidmetal on metalskidding,aprotective coatingoflubricantmustbepresentbetweentheballsandraceway.
Directmetal to metalcontactwillhappenintheabsenceofsufficientlubrication, resultinginfrictionthatgeneratesharmfulheat Lookingatthebearingandnoticing discolourationontheballandracewaywillusuallyrevealthisissue.
Duetotheexpansionofthebearingringbroughtonbyheat,whichincreasesthestress placedonthebearing,itmayalsomanifestasanoverloadingfailure.Ifyou'reusing greaseaslubrication,becarefultolookatthegrease'sspeedrating Theoilwon'thave enoughtimetore-adherewiththethickeningaftertheball(oranotherrollingelement) passesoverit,whichwillresultinthebearingoverheatingifyourbearingrotatesfaster thanthegreaserating
8CommonBearingProblemsandPrevention
Thesystemasawholecouldcollapsecatastrophicallyifabearingoverheats. Don'tforgettocheckthegreaselifeaswell.Whenthegrease'sshelflifehasrunout,it willbegintobreakdownandstopformingthatrepeatingoilfilmastheballsrolloverit.
Lubricationhasthepotentialtobebothablessingandapainintheneck.Itcomesasno surprisethatconcernswithbearinglubricationaretherootofproblems1-3.Oneofthe maincausesofbearingissuesislubrication.Themajorityofindividualsareawarethata bearing'sballsshouldnevercontactitsracewaydirectly.Knowinghowmuchorhow littlelubricantabearingneedsisdifficult.
1.Duetolesslubrication
2.TheGreaseRatingisExceededbyYourBearing
8CommonBearingProblemsandPrevention
MaintainBearingCleanliness
Herearesomesuggestedpractisestopreventcontaminationifyourapplicationoperates in"dirtier"environments:
4.BearingPollution
Lookattheracewaysandseeifyoucannoticeanindentationoracratertoidentify bearingcontamination.Aroundthecrater,sharpedgesaretypicallyleftbyhard contamination,whereassmootheredgesaretypicallyleftbysoftcontamination.
Cratersdevelopontheracewayastheballscontinuetorollovertheparticles,which causesmachinevibrationandexcessiveheatproduction
Whenchoosingthelubrication,takeintoaccountthesystemlife,temperatures,viscosity, andspeedtomaximisethelubricant'slifespan.
Theviscosityofthegreasemaysignificantlydropatexcessivesystemtemperatures, makingitimpossibleforthegreasetoremainwhereitisneededinthebearing Ontheotherhand,ifthesystemtemperatureistoolow,theviscositymaybecometoo thick,puttingadditionalstrainonthebearingasittriestopushthroughandseparatethe oilandthickenerwhentheballspassoverthegrease.
A"comettail"mightalsobevisibleononeofthecrater'ssides.Thisresultedfromthe ballstrikingthecrater'sedgebeforeflatteningitasittravelledbackout
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Contaminationisanothertypicalreasonforbearingfailure Whendebrisentersthe bearingracetrackwhileitisrunningandgetswedgedbetweentheballsandtheraceway, contaminationoccurs.
Byselectingalubricantthatmaintainsasufficient,thickcoatingattheoperating temperatureofyourapplication,youmayguardthebearingfromlubricationproblems.
3.TheGreaseRatingisExceededbyYourBearing
Includeanon-contactlabyrinthsealinthedesignofyourapplication.Tofurthershield thebearingfromcontamination,labyrinthsealsareinstalledinfrontofthebearing.
Ontheoutsiderace,wherethedeformationismostvisibleandrightatthepinchpoint, youshouldbeabletoseealoadzone.
5.UnbalancedBearings
Pressurizethebearingcompartmenttoforceanypollutionthatmayhaveenteredthe racewaysoutifcleanpressurisedairisavailable.
Shaftimbalancesresembleradialloadsbutarereversedintheirproperties. Giventhattheradialloadisstationarywithrespecttotheinnerrace,the
Systemswithaspinningshaftandexcessiveradialloadwillexhibitconsistent deformationintheinnerraceway.
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Thisresultsfromtheshaftspinningpastthebearing'spinchpointwhiletheouterraceway isstill
Inoverloadedbearings,plasticdeformationresultsfromexcessivebearingloads,which raisesthepressurebetweentheballsandthebearingraceway.
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WhatCausesBearingstoOverload
Here'showtodeterminethesourceoftheexcessiveloadifitaffectsyourapplication: Theinnerandouterbearingracewaysbothdeformuniformlyunderexcessiveaxialload.
● shaftinequalities ○
Excessiveloads,aswediscussedbefore,arethemaincauseofoverloadedbearings,but therearealsoother,lessprevalentcauses,suchas: incorrectbearinginstallationresultsinincreasedloading axialforcesproducedbytherollingelement(ifrotatingatveryhighspeeds)
8CommonBearingProblemsandPrevention
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Here'showtotellwhetherthisisoccurringtoyourapplication:
FixingUnbalancedBearings
Ifhighaxialorradialloadsarethecauseofoverloading,addbearingsoralterbearing sizetorelievepressureoneachindividualbearing.
Whenthereisinsufficientforcebetweentherollingelementsandraceways,underloading damagecanoccur.Thiscancausetheballsinthebearingtoskidandslideacrossthe racetrack,whichgeneratesexcessiveheat.High speedapplicationsaremorelikelyto experiencethisformofdamage
Changetoceramicballsifoverloadingiscausedbyfastrotationalspeedsbecausethey havealowerballweight Abearingwithsmallerballs,suchasourKHlineofangular contactballbearings,shouldalsobepurchased.Thecentrifugalforcesatveryhigh speedswillbereducedbythesealternatives.
8CommonBearingProblemsandPrevention
loadeffectedzonewillbeintheinnerrace.Duetotheradialloadspinning aroundit,theouterracewillsustainconsistentdamage.
Dependingonthecause,thefollowingadvicewillhelpyoufixtheissueifyoubelieve youhaveanoverloadedbearing:
Similarsignsofcontaminationandoverloadcanbeseen.Bothproblemsleavecraterson theraceway'ssurface,whichraisethetemperatureorgenerateexcessivevibration.
6.UnstableBearings
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Ifyoucanseemultipledistinctcircumferentiallines(sometimesknownas"Saturn rings")ontheballsofthebearing,youmayhaveaproblemwithunderloadedbearings.
Anangularcontactbearingcanbeoptimisedforaparticulartypeofloadbyadjustingthe contactangle.
7.DamagedBearingCage
Underloadingandrapidacceleration,forinstance,canresultintherollingelements bangingagainstthesidesofthecagepockets.Ifunderloadingistheproblem,increasing preloadcanhelpreducetherelativemovementoftherollingelementinthecagepocket. Forrapidaccelerations,astrongercagematerial,suchasbrassorbronze,canbeused.
Findingandanalysingthesourceofthecagedamageisacrucialfirststepinpreventing furthercagedamage Cagedamagecanalsoresultfromanyofthepreviouslydiscussed problems,suchascontaminationandexcessiveloading.Theseissuescancausetheballs tobouncearoundinthecage'sballpocketandcausecatastrophicdamagetothecage.
Damagetothebearingcageistypicallycausedbyanotherissueintheapplication.
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8CommonBearingProblemsandPrevention
Byreducingtheslipfitorswitchingtoapress fitbetweenthetwomatingcomponents, youcanfixbearingmicro fretting.Thebearingringcanalsobepreventedfromslipping byapplyinganaxialclampingforce.
8.DamagetoBearingsfromMicro-Fretting
Bearingmicro frettingcanappearasmicroscopicrustspotsonthesurfacebutisactually producedbybrownoxidationthatformsasaresultofthefrictioninducedbytherubbing Ithappensinbearingswhenthefitbetweentheouterringandthehousingortheinner ringandtheshaftistoolarge.
Bycorrectlypreloadingyourbearings,youcanavoidunderloadedbearingdamage. Preloadingabearingentailsexertinganaxialforceagainsttheracewaythatis independentoftheapplicationforcetopreventskidding.Amongothertechniques,this canbeaccomplishedviawavespringsorbearingoffsets.
Hightemperaturescanmakesomecages,especiallythosemadeofphenolicmaterial,dry upandbecomebrittle.Whenaball(orotherrollingobject)strikesabrittlecage,itmay bedamagedorevenfail.
Thelikelihoodofbearingissuesandfailuresishigherthanyoumightthink.Hopefully, theseeighttypicalbearingproblemsandtheirfixeswillhelpyourapplicationfrom experiencingabearingfailure.
Contactusifyouwantanengineertoassistyouindeterminingthecauseofabearing failure.Foryourapplication,ourengineerscanprovideassistanceorcarryoutabearing failurestudy
Conclusion:
8CommonBearingProblemsandPrevention
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