Friction torque in a modified angular contact ball bearing operating at low axial loads

Friction torque in an angular contact ball bearing is dependent on the motion of the balls, lubricant viscosity and quantity, rotational speed and applied loads. To evaluate the friction torque in a ball bearing, the SKF methodology includes the geometrical parameters, lubricant viscosity and type of lubrication, operation speeds and applied loads (radial and axial). As is indicated in the SKF catalogue, the above-mentioned methodology can be used for applied loads equal to or larger than the recommended minimum load indicated. For very low applied loads and for dry or limit conditions, the SKF catalogue doesn't indicate the adequate models to estimate the friction torque. Also, the presence of the cage is not directly included in the SKF methodology. Based on the spin down methodology, the authors performed experimental investigations on a 7205B modified angular contact ball bearing, by using only three balls with and without the cage. Experimental friction torques on the outer race has been obtained in dry conditions and the results were compared with the results obtained from the SKF catalogue. Important differences have been obtained. Also, it was evidenced that at very low loads the presence of the cage leads to an increase in the friction torque with more than one order of magnitude.