Additional effects on the frictional moment
Effects of clearance and misalignment on friction
Changes in clearance or misalignment in bearings influence the frictional moment. The SKF model for calculating the frictional moment considers normal internal operating clearance and an aligned bearing. However, high bearing operating temperatures or speeds might reduce internal bearing clearance, which can increase friction. Misalignment generally increases friction. However, for self-aligning ball bearings, spherical roller bearings, CARB toroidal roller bearings and spherical roller thrust bearings, the corresponding increase of friction is negligible.
For applications that are sensitive to changes in clearance or misalignment, contact the SKF application engineering service.
Effects of grease fill on friction
When a bearing has just been lubricated or relubricated with the recommended amount of grease, the bearing can realize considerably higher frictional values than had been calculated originally. It can be seen as an increase in operating temperature. The time it takes for friction to decrease depends on the speed of the application and how long it takes for the grease to distribute itself within the free space in the bearing.
This effect can be estimated by multiplying the rolling frictional moment by a factor of 2 to 4, where 2 applies for light series bearings (narrow width series) and 4 for heavy series bearings.
However, after the running-in period, the values for the frictional moment in the bearing is similar to, or even lower than the values for oil lubricated bearings. Bearings filled with an excessive amount of grease may show higher values of friction. For additional information, refer to Relubrication, or contact the SKF application engineering service.