Selecting bearing size using the rating life equations

Three primary methods for calculating bearing rating life are:
  • Basic rating life

    The basic rating life, as defined in ISO 281:2007, is the least complex method of calculating bearing rating life. Its single criterion is subsurface fatigue.
  • SKF rating life

    For modern high quality bearings, the basic rating life determined for a given application can deviate significantly from the actual bearing life. Bearing life in a particular application depends on a variety of influencing factors including lubrication, the degree of contamination, proper installation and other environmental conditions as well as specific bearing design aspects.

    The SKF rating life takes into account the fatigue load limit, the lubrication conditions and solid particle contamination level in the bearings.
  • SKF Generalized Bearing Life Model

    The SKF Generalized Bearing Life Model (GBLM) provides an even more flexible and comprehensive method of calculating bearing rating life. This method separates the terms related to surface failure modes from the general subsurface rolling contact fatigue term. It treats them separately and then integrates them into the calculation for overall rolling bearing rating life.

    The subsurface fatigue is calculated with classical Hertzian rolling contact fatigue theory.

    For evaluating the risk of surface fatigue, the GBLM considers additional performance factors not covered by any other method for calculating bearing rating life. It treats the complexity of surface failure modes being considered with advanced tribological models.

    More information about the Generalized Bearing Life Model and tools for practical application will be available in the future.

The basic rating life method is usually adequate for selecting Y-bearing or Y-bearing unit size, as it is based on experience. In the absence of previous experience regarding requisite life and operational reliability, the guideline values listed in table 1 for the basic rating life L10h can be used.
To fully exploit the life of a Y-bearing or a Y-bearing unit, the modified life equation in accordance with ISO 281:2007 should be used to calculate the SKF rating life or the SKF Generalized Bearing Life Model.
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