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. Specifically, in machine tool applications, the bearings are subjected to high radial loads and high speeds, which lead to increased forces in the rolling contact and, as a result, increased bearing friction. In this high-speed application, hybrid spindle bearings, typically made of ceramic balls and steel raceways, show better frictional behaviour compared to full steel-made bearings. Therefore, precise knowledge of the friction characteristics of high-speed hybrid bearings can improve friction models and generalise them to spindle bearings with different types, geometries, and operating conditions. In this article, a new straightforward and cost-efficient method for measuring the frictional torque in spindle bearings is presented. A rigidly arranged 7008 hybrid spindle bearing pair was tested up to rotational speeds of 24,000 rpm and high radial loads of 3 kN. The effects of oil-air and grease lubrication are discussed in characteristic diagrams of the tested bearings. Then, based on the test results, a friction calculation model is presented and validated for the outer race control and minimised power dissipation regarding the influence of radial forces.

Automated summary

Friction losses are important for evaluating the behavior of high-speed rolling bearings, particularly in machine tool applications where high radial loads and speeds increase forces and friction. Hybrid spindle bearings, made of ceramic balls and steel raceways, demonstrate better friction behavior compared to full steel bearings. Accurate understanding of the friction characteristics of high-speed hybrid bearings can improve friction models for different types of spindle bearings. This article presents a cost-efficient method for measuring friction torque in spindle bearings and discusses the effects of lubrication. A friction calculation model is also proposed and validated based on test results to control outer race and minimize power dissipation.