super precision bearings

SPEED-DEPENDENT FITSSpeed-Dependent FitsFAG super precision bearings canbe used at maximum speeds.Speed indices of n · d m up to2.0 · 10 6 mm/min are attainablewith grease lubrication, while oillubricatedbearings can attainspeeds as high as 3.0 · 10 6 mm/minand beyond. Such high speedscause high centrifugal forces whichact on the inner rings and causethem to expand.This ring expansion leads to a liftingoff of the inner ring from theshaft and thus to clearance betweeninner ring and shaft.The result is fretting corrosion and,possibly, turning of the ring on theshaft, poor shaft guidance with increasedtendency to vibration andreduced bearing performance dueto possible misalignment. These effectscan be avoided through acorrespondingly tight fit on theshaft.The required interference can beobtained from Diagram 29 orcalculated with the help of theSPICAS 2000 program (see page182). The values determined in thisway yield a fit with a remaining interferenceof 1 µm at maximumspeed.High interference leads to an increasein preload, in particular inthe case of rigid adjusted bearings.This in turn leads to increased heatgeneration in the bearing arrangementas well as losses in terms ofspeed-ability. This preload increasemust be compensated byappropriate measures. With valuesn 2 · f w > 1.2 (red zone in Diagram29), it is advisable to consult theapplication engineering departmentof FAG AC/SP GmbH.The value f w can be obtained fromDiagram 30 (for bearings of type B,HCB and XCB) and Diagram 31(for bearings of type HS, HC andXC). If value n 2 · f w < 1.2, theresulting shaft dimension is asfollows:2422201816Solid shaftHollow shaft 50 %Interference[µm]1410108642Hollow shaft 75 %00 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4n 2 · f wmm 3min 229: Speed-dependent determination of interference shaft/inner ringFAG · 172