The Friction of radially loaded hybrid spindle bearings under high speeds

Friction losses are an important parameter for evaluating the operational behaviour of high-speed rolling bearings. Especially in machine tool applications, the bearings are subjected to high radial loads, which lead to increased forces in the rolling contact and thus to increased bearing friction. At high speeds, hybrid spindle bearings are typically used, consisting of ceramic balls and steel raceways, which are characterised by better frictional behaviour compared to steel bearings. A precise knowledge of the friction characteristics, especially at high speeds, makes it possible to improve friction models and to extrapolate them to spindle bearings of other types and sizes, geometries and other operational conditions. In the following article, a new straight forward method to measure the frictional torque in spindle bearings is presented. A rigidly arranged hybrid spindle bearing pair of the type 7008 was tested over varying speeds and radial loads evaluated in a characteristic diagram. The influence of oil air and grease lubrication was investigated. Based on the test parameters, a current friction calculation  method was presented and validated. The influence of outer race control and minimized power dissipation is discussed.