Basic rating life
For spherical plain bearings, a lubricant film that fully separates the sliding contact surfaces cannot be formed. Therefore, the sliding contact surfaces make direct contact with each other, resulting in a certain and unavoidable degree of wear. This increases the internal clearance in the bearing.
Regarding the life of spherical plain bearings or rod ends, a distinction is made between the basic rating life and the service life. The basic rating life is a theoretical guideline value, used to estimate the service life. Service life depends on the actual operating conditions and is the actual life achieved by the bearing in service.
The basic rating life is based on a large number of laboratory tests. The bearings were tested for an operating period until a specific increase in bearing clearance or friction occurred (table 1). The basic rating life considers several influencing factors and can be expressed in operating hours or the number of oscillating movements (fig. 1). In some cases, however, it is not possible to quantify factors such as contamination, corrosion, and complex kinematic loads. Therefore, the basic rating life can be attained or exceeded by the majority of many apparently identical spherical plain bearings under the same operating conditions. For the calculation methods of the different sliding contact surface combinations as well as calculation examples, refer to the section Basic rating life calculation or to the SKF Bearing Calculator1).
The service life cannot be calculated as it is too complex to determine and evaluate all the influencing factors. Therefore, depending on the application conditions, the service life may differ from the basic rating life.
- 1)By using the SKF Bearing Calculator and its incorporated calculation programs, it is possible to perform the necessary calculations to select a spherical plain bearing with the click of a mouse. The product data necessary for the calculations is automatically put in by selecting a spherical plain bearing or rod end from the product tables. It is then only necessary to fill in the fields for the operating data.