Experimental Friction Torque in Miniature Ball Bearings Grease Lubricated

Abstract

The friction torque in the miniature ball bearings grease -lubricated depends on many factors such as grease properties, rotational speed, applied loads and internal geometry. The catalogues of various rolling bearings manufacturers (SKF, Schaeffler, NSK) present empirical relations for determining friction torque in general purpose ball bearings. For miniature and low-load ball-bearings, these relations lead to significant differences in the friction torque compared to the experimentally determined one. To demonstrate these differences, the authors experimentally determined the friction torques in the grease-lubricated 7000 C series angular contact ball bearing.

The experiments were conducted using three types of greases at rotational speeds between 200 and 700 rpm, and an axial load of 3.11 Newtons. The authors used the spin-down methodology and the resulted friction torques (T _exp ) was determined by integrating the dynamic equation into the deceleration process using Python-based software. The input and output parameters were presented for each grease and rotational speed. The dependences between experimental friction torques and angular speeds were shown in logarithmic diagrams, and fitted relations were determined for all three greases.

Based on the SKF methodology, the friction torques was theoretical determined and compared with experimental results. It was observed that the calculated friction torques were (77-88)% lower values than the experiment values.