Industrial seal self study guide - SKF.com

BASIC SEAL TYPES (cont.)
A
As a shaft rotates in a stationary
housing, a CRW1 dynamic radial
seal both retains lubricant and
excludes contaminants (fig. 2c).
B
Axial mechanical seals create an
interface along the shaft plane
between matched components.
Usually, one contact face is stationary
while the other rotates with the shaft
(fig. 2d).
At the “interface” point, a thin film
of lubricant separates sealing surfaces
(fig. 2e).
Dynamic “Radial” Seals
A dynamic radial seal creates a barrier or interface between surfaces
in relative motion. For radial lip type seals, the interface is where the
seal touches the shaft. Sealing is accomplished by two surfaces making
contact radially, one usually stationary while the other rotates.
An example of a radial seal is shown in figure 2c. As the shaft rotates
in a stationary housing, a CRW1 seal both retains lubricant and
excludes contaminants. Typical radial seal applications include
gearboxes, drives, motors, pumps and speed reducers.
Axial Mechanical Seals
Axial mechanical seals are face type seals which create an axial
seal interface between matched, radially mounted components. In
operation, one contact face is usually stationary in the housing while
the other moves with the shaft. Sealing pressure is applied in the
axial direction through a spring mechanism. The spring force keeps
the surfaces together.
Axial mechanical seals are generally used where pressure and/or
surface speeds exceed the capabilities of radial shaft seals. Typical
applications are water pumps and most types of pumps used in
chemical processing plants or refineries. Figure 2d is a view of
such an installation.
Other types of axial seals are “non-mechanical” ones, such as V-Rings.
Seal Interface
“Interface” is the point of contact between sealing surfaces (fig. 2e). But
they do not really “contact” at that point, they are separated by a film
of lubricant as thin as 0.00001 in.—a hundred thousandths of an inch.
In metrics, that is 0.25 microns.
The lubricant film prevents rapid wear of the seal lip and/or the shaft
surface. But interface tolerances must be precise to keep the lubricant
from leaking. Uncontrolled conditions of run-out must be prevented.
Any misalignment or eccentricity of interfacing surfaces which exceed
acceptable tolerances must be corrected.
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