Page 28 - Rollingbearings

A.1 Bearing basics
Integral sealing Fig. 20 Fig. 21
Shield Contact seal
Integral sealing can signiicantly prolong
bearing service life because it keeps lubricant
in the bearing and contaminants out of it.
SKF bearings are available with various
capping devices:

• Shields
There is a small gap between the shield
and inner ring. Bearings itted with shields
Bearing basics (ig. 20) are used where the operating
conditions are relatively clean, or where
low friction is important because of speed
or operating temperature considerations.

A.1 • Seals Low-friction seal Fig. 22 Non-contact seal Fig. 23
Bearings with seals are preferred for
arrangements where contamination is
moderate. Where the presence of water or
moisture cannot be ruled out, contact seals
(ig. 21) are typically used. These seals
make positive contact with the sliding
surface on one of the bearing rings. Low-
friction seals (ig. 22) and non-contact
seals (ig. 23) can accommodate the same
speeds as bearings with shields, but with
improved sealing effectiveness.

Suficient internal clearance in a bearing Fig. 24
Internal clearance during operation is important. Preload Bearing internal clearance
(clearance below zero) is possible for certain
bearing types.
Bearing internal clearance (ig. 24) is deined To enable selection of the appropriate Radial internal
clearance
as the total distance through which one initial internal clearance to achieve the desired
bearing ring can be moved relative to the operational internal clearance, bearings are
other in the radial direction (radial internal available in different clearance classes. ISO
clearance) or in the axial direction (axial has established ive clearance classes for
internal clearance). many bearing types. SKF uses designation
In almost all applications, the initial clear- sufixes to indicate when the bearing internal
ance in a bearing is greater than its operating clearance differs from Normal (table 1).
clearance. The difference is mainly caused by
two effects:

• Bearings are typically mounted with an Axial internal
interference it on the shaft or in the hous- clearance
ing. The expansion of the inner ring or the
compression of the outer ring reduces the
internal clearance.
• Bearings generate heat in operation. Dif-
ferential thermal expansion of the bearing
and mating components inluences the
internal clearance.

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