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) |
| |
| 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.) |
 |
| 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. |
  |
| 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). |
 |
| Note: CIE 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. |
| PRELOAD CALCULATION |
| Once the initial end play has been removed (ball contact angle = ao), then further axial load (preload) will cause axial displacement d at ball contact angle a. Formulae to calculate loaded contact angle a, initial (no load) contact angle ao and axial displacement d under a given preload are as follows: |
 |
| Contact CIE directly to obtain a chart of displacement d and contact angle a vs. preload Fa for a particular bearing. Also see section on Assembly Characteristics for more details. |
