What Is Bearing Preload?

Bearing preload is the force acting on the bearing by axial adjustment relative to another bearing before applying the “use” load (external load), or the force generated by the “negative clearance” (internal preload) formed by the size of the raceway and rolling elements in the bearing.

The main purposes of bearing preload are as follows:

1. Improve the guiding accuracy of the bearing. The shaft supported by the preloaded bearing has higher guiding accuracy because the flexure capacity of the shaft under load is limited by the preload. Preloaded differential bearings have higher guiding accuracy and higher rigidity, which means that accurate and constant meshing can be maintained, and the additional dynamic force is very small, so the running noise is low and the meshing gear has a longer life.
2. Improve rigidity. The rigidity of the bearing is defined as the ratio of the force acting on the bearing to the elastic deformation of the bearing. Within a certain load range, the elastic deformation of the preloaded bearing is smaller than that of the non-preloaded bearing.
3. Low-noise operation. The smaller the bearing running clearance, the better the guidance of the rolling elements in the load-free zone, and the lower the noise when the bearing is running.
4. Compensation for wear and subsidence. During operation, the wear and subsidence of the bearing increase the clearance, but this can be compensated by preload. Compensate for wear and subsidence during operation and extend the service life.
5. Extend the service life. In some cases, the bearings are arranged in pairs and preloaded to improve the operating reliability and extend the service life. Because the appropriate amount of preload can improve the load distribution of the bearing, it can increase its service life.