SKF - Rolling Bearings

Selecting bearing size
A systems approach to
bearing selection
In the SKF life rating equation, the stresses
resulting from external loads are considered
together with the tribological stresses in the
rolling contact area. Understanding the influence
of these combined stress systems on
bearing life enables a more accurate prediction
of how a bearing will perform in its
application.
Due to its complexity, a detailed description
of the theory is beyond the scope of this catalogue.
Therefore, a simplified approach is presented
under SKF rating life († page 64). This
enables users to fully exploit bearing life
potential, to undertake controlled downsizing,
and to recognize the influence of lubrication
and contamination on bearing service life.
Bearing system life
Metal fatigue of the rolling contact surfaces is
a well-known failure mode for rolling bearings.
Metal fatigue can be the result of a variety of
factors including but not limited to excessive
frictional heat, poor or contaminated lubrication
conditions, and heavy external and/or
indeterminate loads.
Therefore, a criterion based on raceway
fatigue is generally sufficient for the selection
and sizing of a rolling bearing for a given application.
International standards such as
ISO 281 are based on metal fatigue of the rolling
contact surfaces. Nevertheless, it is important
to remember that the complete bearing
can be viewed as a system in which the life of
each component, i.e. rolling elements, raceways,
cage, lubricant and seals, when present,
contributes equally and in some cases dictates
the effective endurance of the bearing
(† fig. 1).
In the different sections of this catalogue,
references are made to relevant aspects of the
strength and suitability of other components
of the bearing viewed as a system that need to
be checked to ensure the best performance.
Fig. 1
Bearing system life
L bearing = f (L raceways , L rolling elements , L cage , L lubricant , L seals )
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