Frictional torque and temperature

Frictional torque of rolling bearings varies under changing load and lubrication conditions. When grease is used as a lubricant, the grease resistance must be added to the bearing frictional torque. When adequate lubrication under normal loading conditions (Cr/P>12,Fa/Fr<0.2), the frictional torque of a bearing can be express as follows:

whereby:

• M: FRICTIONAL TORQUE (N•mm)
• F: BEARING LOAD (N)
• d: SHAFT DIAMETER (mm)
• μ: =0.0015 COEFFICIENT OF FRICTION

Friction and grease resistance can increase the bearing temperature. In the initial stages of operation, the internal bearing temperature rises rapidly: as the heat dissipates to the shaft and housing and the cooling effect of the lubricant begins to take effect, the temperature stabilizes. Constant high temperatures lead to a reduction in bearing clearance, a deterioration of the running accuracy and of the lubricant and thereby a reduction in bearing life. It is important to consider the effect of temperature increases when selecting the bearing.