SKF - Rolling Bearings

Design considerations
Non-contact seals
The effectiveness of a non-contact seal depends,
in principle, on the sealing action of the
narrow gap between the shaft and housing.
The gap may be arranged radially, axially or in
combination († fig. 46). These seals can be
as simple as a gap-type radial shaft seal or
more complex, like a labyrinth seal. In either
case, because there is no contact, these seals
generate almost no friction and do not wear.
They are not easily damaged by solid con tamin
ants and are particularly well suited for high
speeds and high temperatures.
Contact seals
The effectiveness of a contact seal is determined
by the amount of pressure available to
keep the seal lip in contact with the seal counterface
on the shaft. This pressure († fig. 47)
can be produced either by:
Contact seals are generally very reliable.
Their effectiveness, however, depends on the
surface finish of the counterface, the condition
of the seal lip and the presence of lubricant
between the seal lip and counterface. Friction
between the seal lip and counterface can generate
a significant amount of heat. As a result,
these seals have circumferential speed limits.
They are also susceptible to mechanical damage
as a result of improper mounting, or by
solid contaminants. To protect the seal from
the damage caused by solid contaminants, a
non-contact seal is typically placed in front of
a contact seal.
• the resilience of the seal, resulting from the
elastic properties of the seal material (a)
• the designed interference between the seal
and its counterface (b)
• a tangential force exerted by a garter spring
incorporated in the seal (c)
Fig. 46 Fig. 47
a b c
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