Page 197 - Rollingbearings

External sealing
Seal selection criteria Seal types Fig. 1
Multi-stage labyrinth seal
Seals for bearing applications should provide The purpose of a seal is to retain lubricant
maximum protection with a minimum and prevent any contaminants from entering
amount of friction and wear, under the pre- into a controlled environment
vailing operating conditions Because bear- There are several basic seal types:
ing performance and service life are so
closely tied to the effectiveness and cleanli- • non-contact seals
ness of the lubricant, the seal is a key com- • contact seals
ponent For additional information on the • static seals
inluence of solid contaminants on bearing
performance, refer to Contamination factor, Non-contact radial shaft seals form a nar-
η , page 104 row gap between the stationary and the
c
Many factors must be considered when rotating component The gap can be
selecting the most suitable seal for a par- arranged axially, radially or in combination
ticular bearing-shaft-housing system These Non-contact seals, which range from simple Fig. 2
include: gap-type seals to multi-stage labyrinths Radial shaft seal
(ig. 1), do not wear
• the lubricant type: oil or grease Seals in contact with sliding surfaces are
• the contaminant type: particles or luid or called contact seals and are used to seal
both passages between machine components
• the circumferential speed at the seal lip that move relative to each other, either lin-
• the shaft arrangement: horizontal or early or circumferentially
vertical The most common contact seal is the
• possible shaft misalignment or delection radial shaft seal (ig. 2), which is installed
• run-out and concentricity between a stationary and a rotating
• available space component
• seal friction and the resulting temperature Seals between stationary surfaces are
increase called static seals Their effectiveness Sealing, mounting and dismounting
• environmental inluences depends on the radial or axial deformation of
• cost their cross section when installed Gaskets Fig. 3
• required operating time (ig. 3) and O-rings (ig. 4) are typical ex- Gasket
• maintenance requirements amples of static seals

For additional information, refer to Power
transmission seals, (skf com/seals)
B.8

Fig. 4
O-ring

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