During the operation of rolling bearings, friction occurs due to the effects of preloading and working load. The main forms of friction are as follows:

(1) Rolling friction caused by elastic hysteresis: The ball rolls along the surface of the raceway under the action of a load, causing elastic deformation of the material below the contact surface. After contact elimination, the main part of elastic deformation is restored. However, when the load increases, the total deformation corresponding to a given stress is always less than the deformation when the load decreases, which is called elastic hysteresis and reflects a certain energy loss, manifested as rolling friction resistance.

(2) Friction caused by differential sliding: If the tangential force of any unit area on the contact surface is proportional to the contact pressure, the frictional torque caused by differential sliding when the rolling element rolls along the bearing raceway can be deduced.

(3) Friction caused by self rotating sliding: For rolling bearings, the ball may rotate around the normal of the contact surface along the raceway of the ring during operation. The sliding caused by this becomes spin sliding. Simultaneously generating frictional force and torque through spin sliding.

(4) Viscous friction of lubricants: Lubricants and lubrication methods have a significant impact on bearing friction and friction torque. Due to the action of lubricants, an elastic hydrodynamic lubrication film is formed between the rolling element and the steel wire raceway, and the friction coefficient of each sliding contact area changes. When the bearing is running, the rolling element is subjected to flow resistance through a space filled with a mixture of oil and gas, which becomes disturbance resistance and generates friction force and frictional torque.