super precision bearings

LIFE CALCULATION FOR SUPER PRECISION BEARINGSEquivalent Load withVarying Loads andSpeedsFor bearing arrangements that aresubject to varying loads andspeeds, the equivalent load is calculatedfrom the individual loadsand speeds with their correspondingpercentage of time:3n 1and the mean speed n m from:q 1q 1q 2P =P 13 ·n·100+ P 23 · · + ... [kN]m 100n m = n 1 · + n 2 · + ... [min -1 ]100 100n 2n mq 2Static Equivalent Load P 0For super precision bearings thestatic load, i.e. loading in the absenceof ring rotation, is rarelychecked. The stress index f s as ameasure of the static load is obtainedfromf s = C 0 /P 0f sC 0P 0= static stress index= static load rating [kN]= static equivalent load [kN]For the modified life calculation,factor f s* is also obtained from thefollowing equations, however usingthe dynamic loads.In order to maintain the accuracyof the bearings, the static stress indexshould be higher than 3.0.Only with an extremely short-termand centric axial load (tool ejectionforce), f s ≥ 1 is admissible for hybridbearings.Angular Contact ThrustBall BearingsP 0 = 3.98 · F r + F aThe static stress index should behigher than 2.5.Double Direction Angular ContactThrust Ball BearingsSpindle BearingsP 0 = F aContact angle α = 15°P 0 = F r [kN]for F a /F r ≤ 1.09P 0 = 0.5 · F r + 0.46 · F a [kN]for F a /F r > 1.09Contact angle α = 25°P 0 = F r [kN]for F a /F r ≤ 1.31The static stress index should behigher than 2.5.FD Bearings andCylindrical Roller BearingsP 0 = F rThe static stress index should behigher than 3.0.P 0 = 0.5 · F r + 0.38 · F a [kN]for F a /F r > 1.31Where there are several bearings,the load is calculated for the individualbearing.An axial load is evenly distributedon the loaded bearings.RTC BearingsP = F aP = F rfor the axial roller rowfor the radial roller rowThe static stress index should behigher than 3.0.FAG · 136