Friction torque in thrust ball bearings lubricated with polymer greases of different thickener content

•The friction torque of rolling bearings lubricated with grease was measured.•The friction behaviour of different greases was investigated.•Tests performed with fresh greases of different thickener content.•A rolling bearing friction torque model was optimized to the experimental results.•The higher the thickener content, the smaller is the friction torque at low speeds.

In this work a series of experimental tests were performed in thrust ball bearings lubricated with polymer greases. The tested greases were formulated with the same base oil but different thickener content. A multi-purpose lithium thickened grease was also tested as reference.The friction torque was measured at constant temperature and load, while varying the rotational speed. The coefficients of friction under boundary and full film lubrication were numerically calculated through the optimization of a rolling bearing friction torque model to the experimental measurements. The results show that the higher the thickener content, the smaller is the friction torque generated by the lubricating greases, phenomenon which was found to be especially important at low speeds and low specific film thickness.