The fan bearings’s life

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1、Inaccordancewiththeinformationyouprovide，theOperatingtemperatureis25°,sothistemperaturewillnotaffectthefan'sservicelife.Thefanbearingsarevulnerablepartsinthissystem,soWefocuseonthelifeofthebearing.Weallknowthatfollowingthesystemrotate,therotorofthefanwillgenerateacentrifugalforce.Whenthefanwork

2、ingintherotatingsystem,Itissubjecttothreepartsforces.Thefirstisthefan'sownunbalancedforce.thesecondisaerodynamicforce,Itiscausedbytheairflowstatechange.Thelastpartisthecentrifugalforce.Tosimplifytheproblem,weonlyexaminedthecentrifugalforce.ThecentrifugalforceFcanbedisintegratedintoaaxialcompone

3、ntFandaverticaldownwardcacomponentF(seethepicture1).r6ε10⎛ftC⎞Lh=⎜⎟(1)60n⎝P⎠Forballbearingε=3nistheballbearingrotatevelocityCisthebasicrateddynamicloadfisthetemperaturecoefficient(seethetable1)tPistheequivalentdynamicloadBythepicture2wecanhave'P=XFr1+YFa(2)Becausetheweightoftherotorissmall,Ihav

4、eignoredtheeffectofrotorweight.'axialcombineforceFa=Fa0−Fa(3)2F=Fsin(θ)=mwrsin(θ)(4)ac2F=Fcos(θ)=mwrcos(θ)(5)rcr=690mm,w=12.56r/s,rotorweightm≈14g,F≈5.2Na0'SoF=.039NF=.147NFa=.211NarBecauseitisdifficultytocalculateF,Imagnifyitasfollow:r1F

5、293Nr1AccordingtothedatawhichthebearingcompanyNMBprovide,weTakeC=560NSo,accordingtotheformula(1),wecanhavethebearing’slifeinthissystemis:6ε6310⎛ftC⎞10⎛560⎞6Lh=⎜⎟=⎜⎟=7.7*10h60n⎝P⎠60*15000⎝.293⎠Thelifeofourfanis70000h,andtheLh>>70000h,soIthinktherotationofthesystemaffectthefanslightly.But,inthisr

6、esultIhaveigoredsomething.So,therealityresultmaybedifferent.Table1-temperaturecoefficientftBearingworking≤120125150175200225250300350temperature(℃)temperature1.000.950.900.850.800.750.700.60.5coefficientftPSfansFaRotatingCentrifugalforceXcitecenterFcPSF'rFaFa0Radiiis690mmRotatingspeed(Rotatingc

7、entertois0.5s/rotPScenter)12degreePicture1Fr1Fr2Fa0Fa0OFabearing1bearing2FrPicture2