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PRELOAD
Preload is the force that is applied to a
bearing assembly during installation to remove the axial play and
to further compress the bearing to provide both axial and radial
stiffness. It is an important design parameter, affecting rotational
performance and lifetime of a bearing assembly. After preload, the
resulting ball contact angle α must be
considered
Standard preload - Inner rings
pressed
together (maximum stiffness) |
Outer rings pressed together
(less stiffness) |
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| PRELOAD ASSEMBLY
METHODS |
Deadweight: A fixed weight is
set against the bearing ring while adhesive cures to retain
the bearings. This system is used in many applications, and
gives well-controlled torque values as well as maximum
stiffness. Disadvantages are cure time and special handling of
adhesive in mass-production. Care must be taken to allow for
relative thermal expansion effects if different materials are
used in mating parts (see Thermal
Expansion chart.)
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| Spring:
Spring (typically belleville-type) is used to press inner
rings together, or a wavy-washer/spiral spring is used to push
outer rings apart. This system is easy to assemble, but has
minimum stiffness since the spring can move after assembly so
that the stiffness of the assembly is controlled by the spring
rate rather than bearing raceway/ball elasticity. Thermal
effects from relative expansions of mating parts are
minimized. Spring preload is often used in high speed
applications. |
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Solid clamping: Component
parts are machined to precise dimensions to remove axial play
when races are clamped together. In theory, this system is
easy to assemble, has few components and good stiffness.
However, due to the wide range of axial play, it is almost
impossible to achieve in practice. Unless components and
bearings are matched to a high precision the resulting
assembly may be damaged through raceway brinelling or may not
have adequate preload. (Note: precision matched bearings are
available as Duplex Pairs). |
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Note: SWC has a
great deal of experience in the design and manufacture of preloaded
bearing assemblies. Our engineers are available to offer design,
testing and prototyping services.
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