The Design of Rolling Bearing Mountings

18 Surface grinding spindleOperating dataGrinding motor power 220 kW; maximum speed375 min –1 ; weight of spindle, rotor and grinding spindlehead 30 kN; maximum grinding pressure 10 kN.Bearing selectionThe spindle is supported at the grinding spindle headby a double-row cylindrical roller bearing FAGNN3060ASK.M.SP. The thrust ball bearing FAG51164MP.P5 arranged above this bearing absorbs thethrust component of the grinding pressure. The upperend of the spindle is fitted with a double-row cylindricalroller bearing FAG NN3044ASK.M.SP and athrust ball bearing FAG 51260M.P6. The cylindricalroller bearing provides radial guidance; the thrust ballbearing carries the weight of the rotor, spindle, andspindle head. To increase axial rigidity this bearing isadjusted with Belleville spring washers against thelower thrust ball bearing.Bearing dimensioningRigid spindle guidance in the radial direction is ensuredby accurately dimensioned mating parts, tightfits of the rings, and a light preload of the cylindricalroller bearings. The inner rings are pushed along thetapered bearing seat until the roller-and-cage assemblyruns under a light preload (5 µm). Surface finish anddimensional accuracy of the workpiece mainly dependon the axial rigidity of the spindle headstock and of therotary table. Therefore, the rigidity of the thrust bearingsis especially important. To increase the rigidity, thethrust bearings are preloaded to 40 kN by Bellevillespring washers at the upper end of the spindle. Sincethe combined weight of spindle, rotor, and spindlehead is 30 kN, the lower thrust bearing is preloaded to10 kN. Rigid, clearance-free spindle guidance also inthe axial direction is, therefore, guaranteed. The nominalrigidity is 2.5 kN/µm; the spindle deviates axiallyby only 4 µm with the maximum grinding pressure of10 kN.Lubrication, sealingThe headstock bearings are lubricated for life withFAG rolling bearing grease Arcanol L74V. A gap-typeseal suffices at the upper spindle end since the headstockis protected by a cap.A shaft seal prevents grease from penetrating into themotor. The lower bearings are sealed at the motor endwith a gap-type seal and at the spindle head with a gaptypeseal preceded by a labyrinth.18: Bearing arrangement of a surface grinding spindleFAG 30