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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: Dynaroll 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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