Effect of bearing preload
The main reasons to apply bearing preload are to
- enhance stiffness
- reduce running noise
- enhance the accuracy of shaft guidance
- compensate for wear and settling (bedding down) processes in operation
- provide long service life.
Bearing stiffness (in kN/μm) is defined as the ratio of the force acting on the bearing to the elastic deformation in the bearing. The elastic deformation caused by a load in preloaded bearings is smaller for a given load range than in bearings which are not preloaded.
The smaller the operational clearance in a bearing, the better the guidance of the rolling elements in the unloaded zone and the quieter the bearing in operation.
Accurate shaft guidance
Preloaded bearings provide more accurate shaft guidance because preload restricts the ability of the shaft to deflect under load. For example, the more accurate guidance and the increased stiffness afforded by preloaded pinion and differential bearings means that the gear mesh will be kept accurate and remain constant, and that additional dynamic forces will be minimized. As a result, operation will be quiet and the gear mesh will have a long service life.
Compensating for wear and settling
Wear and settling processes in a bearing arrangement during operation increase the clearance but this can be compensated for by preload.
Long service life
In certain applications preloaded bearing arrangements can enhance operational reliability and increase service life. A properly dimensioned preload can have a favourable influence on the load distribution in the bearings and therefore on service life, see section Maintaining the correct preload.