Page 88 - Rollingbearings

B.3 Bearing size

The size of a bearing must be suficient to • speed limit of contacting seal lips – this Therefore, the two main criteria that can
ensure that it is strong enough to deliver the can determine the maximum allowable be used for determining appropriate bearing
required/expected life under deined operating speed, which affects operating tempera- size are:
conditions. ture, thereby affecting life
A bearing can be viewed as a system of • lubricant life – when the lubricant deteri- • Size selection based on rating life,
components: raceways, rolling elements, orates, the resulting poor relubrication page 88
cage, seals (if present) and lubricant (ig. 1). condition quickly reduces bearing life This is based on the required bearing life,
The performance of each component con- taking into account the possible effects of
tributes to or determines the performance The operating conditions of the application rolling contact fatigue, and requires calcu-
and life of the bearing (diagram 1). Consider determine which of these factors most lation of the basic rating life, L , or SKF
10
these aspects: inluence the performance and life of the rating life, L 10m , for the bearing.
bearing.
• rolling contact fatigue (RCF) on the rolling This section provides guidance on deter- • Size selection based on static load,
elements and raceways – this is the pri- mining the required bearing size. page 104
mary aspect that dictates bearing life in The effect of RCF or permanent deforma- This is based on the static load that the
most applications tion on rolling elements and raceways is bearing can accommodate, taking into
Bearing size and raceways because of heavy loads act- cage type and material are not related to deformation, and requires calculation of
directly related to bearing size. Effects of
• permanent deformation of rolling elements
account the possible effects of permanent
the static safety factor, s , for the bearing.
bearing size. In capped bearings, the effects
ing on the bearing, while it is stationary or
0
oscillating slowly, or high peak loads acting
of the lubricant and integral seal are only
on the bearing while it is rotating
B.3 • cage type or cage material – these may indirectly related to bearing size.
limit the operating speed or the permissible
acceleration or temperature 1)

Fig. 1
Bearing system life
L bearing = f (L raceways , L rolling elements , L cage , L lubricant , L seals )

1) Special cage executions are often available for
bearing types that are commonly used in appli-
cations where such challenging conditions are
present.

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