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The object of the study was to replace oil mist lubrication which involves high physical complexity in the case of spindle ball bearings for very high speeds by grease lubrication. This has been achieved by the use of balls made of the ceramic material silicon nitride in conjunction with a tribologically matched grease grade.
On the one hand, the low density of this material compared with that of steel distinctly reduces the centrifugal force acting on the balls while, on the other hand, its high modulus of elasticity increases contact rigidity and Hertzian contact pressure. Moreover, there is a smaller contact ellipse which as a favorable effect on such tribological quantities as rolling and sliding friction, lubricant stressing, and starvation.
The high material hardness, which is of the order of DPH 1600, distinctly reduces wear on solid contact under conditions of short-time defective lubrication.
The experiments carried out in the spindle ball bearings test rigs at different speeds and for different lengths of time revealed the advantages of the ceramic balls in the temperature and wear behavior.
spindle bearings, high speed, ceramic balls, grease lubrication
Engineering manager, GMN Georg Müller Nürnberg AG, Nürnberg,