Basic rating life

Composite bushings and thrust washers

The basic rating life of a composite plain bearing is expressed in number of oscillations or revolutions, or in operating hours. It represents the operating period under test conditions that is ended when one of the criteria for the end of the basic rating life is reached. Those criteria can be:

  • increase in operating clearance 
  • plastic deformation of the sliding layer 
  • fatigue
A distinction is made between the basic rating life and the service life actually achieved.
The basic rating life is a guideline value that will be attained or exceeded by the majority of a large number of apparently identical bearings under the same test conditions.
The service life actually achieved by apparently identical bearings under identical operating conditions has been found to differ both in laboratory endurance tests and in service at operating conditions. These include not only the magnitude and type of load but also other factors such as contamination, corrosion, load and movement cycles of high frequency and shock loads. These factors are difficult or even impossible to quantify.

Bronze, polyamide and filament wound bushings and strips

It is not meaningful to try to calculate the basic rating life for these products. In practice, the various influences and factors that affect the service life actually achieved, interact in a very complex manner and are not always completely quantifiable. 

For additional information in case of inadequate experience with regard to the probable life of a bushing or in choosing an appropriate bushing size, contact the SKF application engineering service.

SKF logo