DINTECHNICAL INFORMATION

Friction torque

The friction torque is a very important criteria for the correct operation of a bearing. It depends on the load applied on the balls, the rotational speed and the properties of the lubricant.

These factors have an influence on the resistance to rotation of the bearing, which is composed as follows:

● The resistance to rolling, depending on the roughness and the geometry of the raceway and the balls, as well as of the applied load.

●The resistance generated by the rubbing seal (if present), depending on the surface finish of the outside diameter of the inner ring, as well as of the rotational speed.

● The resistance generated by the cage, depending on the geometrical form and the machining quality of the cages.

 ● The resistance generated by the lubricant, depending on the lubricant viscosity and filling quantity as well as the rotational speed. At low speed and with fine instrument oil this resistance is insignificant. It will be higher at low temperatures and high viscosity of the lubricant. Grease lubricated bearings will show, according to the grease type and filling, a much higher friction torque than oil lubricated bearings.

On the other hand, two types of friction torque may be considered: the starting torque, necessary to initiate the rolling movement of the bearing, and the rotation torque necessary for keeping the bearing in motion.

The international standards do not describe how to measure the friction torque. However, WIB is in a position to define adequate parameters, corresponding to specifically requested applications, in order to satisfy the customer's requests concerning the friction torque.

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