Spindle Bearings

Spindle bearings are single-row angu­lar contact ball bearings with a contact angle between 12° and 25°. They consist of solid inner and outer rings as well as solid window cages and cannot be dismant­led. Compa­red to other bearings, they can be lubri­ca­ted better by smal­ler contact surfaces. For this reason, spindle bearings have become estab­lis­hed for the bearing of fast rota­ting main spind­les of machine tools which are distin­guis­hed from conven­tio­nal angu­lar contact bearings in the accu­racy and small contact surfaces of the balls. To ensure a defi­ned rolling of the balls, spindle bearings always require a prel­oad in axial direc­tion. High-speed bearings (HS bearings) and hybrid bearings (HC bearings) were deve­lo­ped in response to incre­a­sed requi­re­ments, parti­cu­larly for maxi­mum speeds. Hybrid bearings contain cera­mic balls which have a lower density and a higher modu­lus of elasti­city than conven­tio­nal rolling bearing steel. This results in incre­a­sed stiff­ness with the same prel­oad. Howe­ver, this also results in higher Hertzian pres­su­res and lower load ratings since the lower elastic defor­ma­tion of the rolling elements and race­way results in a smal­ler pres­sure ellipse in the contact surface which can be redu­ced by a lower prestres­sing force. In combi­na­tion with steel, the cera­mic mate­rial has very good tribo­lo­gi­cal proper­ties resul­ting in impro­ved fric­tion beha­vior and also impro­ved wear beha­vior compa­red with HS bearings. The ball diame­ter offers further poten­tial for incre­a­sing the speed. Due to the lower peri­pheral speed, smal­ler contact surfaces and lower mass, rolling bearings are there­fore equip­ped with a large number of small balls for maxi­mum speeds. The spindle bearings can be lubri­ca­ted either as lubri­ca­ted for life and sealed grease lubri­ca­tion or as oil/air-oil lubri­ca­tion.

The oil-air lubri­ca­tion can take place directly via the outer rings of the bearing or via an addi­tio­nal lubri­ca­tion chan­nel in the housing. The choice of bearings and lubri­ca­tion stron­gly depends on the speed range and the requi­red rigi­dity during machi­ning. The choice of bearing should there­fore always be defi­ned by the inten­ded use.

Sources: Wake-up, M.+ Brea­ker, C.: Werk­zeug­ma­schi­nen, volume 2, Konstruk­tion und Berech­nung VDI-Verlag, 8th comple­tely revi­sed edition, 2006 Bründ­lein, Esch­mann, Hasbar­gen, Weigand: Die Wälz­la­ger­pra­xis, Wies­ba­den, 1995