The Design of Rolling Bearing Mountings

17 External cylindrical grinding spindleOperating dataInput power 11 kW; speed n = 7,500 min –1 ; runningaccuracy: radially 3 µm, axially 1 µm.Bearing selectionDuring external cylindrical grinding a high cutting capacityis required (for rough grinding) and a high standardof form and surface quality (for fine grinding). Ahigh degree of rigidity and running accuracy as well asgood damping and speed suitability form the main criteriafor the bearing arrangement. These requirementsare met by precision bearings.Sealed universal spindle bearings with small steel balls(HSS) are used:– at the work end: 1 spindle bearing setFAG HSS7020C.T.P4S.QBCL in double-O arrangement as locating bearing– at the drive end: 1 spindle bearing setFAG HSS7020C.T.P4S.DBL in O arrangement asfloating bearingWhere even higher speeds have to be accommodated,it is advisable to use sealed hybrid spindle bearingsHCS with small ceramic balls (lower centrifugalforces).Bearing dimensioningThe required spindle diameter or the specified outsidediameter of the quill determines the bearing size. Thecontact angle of 15° is suitable for high radial rigidity.Damping and running accuracy are improved byarranging four bearings at the work end.Bearing clearanceAll UL universal design bearings are lightly preloadedwhen mounted in O arrangement. Spacers improve thethermal conditions and provide a larger spread at thebearing location. To ensure that the defined bearingpreload is not altered by the spacers, the latter must beidentical in width and flush ground.Lubrication, sealingThe sealed FAG HSS spindle bearings require nomaintenance and are lubricated for life with the FAGrolling bearing grease Arcanol L74.Additional sealing is provided at the grinding wheelend by a labyrinth with defined narrow axial gaps of0.3 ... 0.8 mm. A plain labyrinth seal is sufficient at thedrive end.Machining tolerancesBearing Seat Diameter Form tolerance Axial runout tolerancetolerance (DIN ISO 1101) of abutment shoulderSpindle bearing Shaft +3/–3 µm 1 µm 1.5 µm(work end) Housing -3/+5 µm 2 µm 3.5 µmSpindle bearing Shaft +3/–3 µm 1 µm 1.5 µm(drive end) Housing +5/+13 µm 2 µm 3.5 µm17: Bearing arrangement of an external cylindrical grinding spindle29 FAG