With individual adjustment, each bearing system is adjusted separately using nuts, shims, spacer sleeves, crush sleeves etc. Measuring and inspection procedures provide that the established nominal preload is obtained with the least possible deviation. There are different methods to obtain the required preload:
- axial displacement method
- frictional moment method
- direct force method
The method used depends on, among other things, the application design and the number of bearings to be mounted. Individual adjustment can accommodate enough tolerance stack-up so that if individual components are produced to Normal tolerances, the desired preload can be achieved with a relatively high degree of accuracy.
Axial displacement method
The axial displacement method is based on the relationship between the preload force and the elastic deformations within the bearing system. The requisite preload can be determined from a preload force / axial displacement diagram (diagram 1).
This method of adjustment is frequently used when the components of a bearing system are pre-assembled. The required preload, which is expressed as a linear value, requires measuring total axial displacement (end play) of the shaft relative to a fixed surface. This is typically done with a dial indicator.
Shims, intermediate rings or spacers can then be used to adjust axial displacement to the correct value. The preload is achieved, for example, for pinion arrangement designs by:
- fitting intermediate rings between the inner and outer rings of the two bearings (fig. 1)
- inserting shims between the housing shoulder and the bearing outer ring or between the cartridge and the housing (fig. 2), where the cartridge in this case is the flanged angled insert
- fitting a spacer between a shaft shoulder and one of the bearing inner rings (fig. 3) or between the inner rings of both bearings
The width of the shims, intermediate rings or spacers is determined by:
- the distance between the shaft and housing shoulders
- the total width of both bearings
- the axial displacement corresponding to the desired preload force
- a correction factor for the axial displacement to account for thermal expansion in operation
- the manufacturing tolerances of all related components, established by measuring the actual dimensions before mounting
- a correction factor to account for a certain loss of preload as a result of settling and wear
Frictional moment method
This method is common in series production because it is fast and can be automated. Since there is a relationship between bearing preload and the frictional moment in the bearings, it is possible to stop adjustment when a frictional moment corresponding to the desired preload has been reached. This can be done if the frictional moment is continuously monitored while setting preload. However, the frictional moment can vary from bearing to bearing, and it also depends on the preservative, the lubricant and the sealing method.
Direct force method
As the purpose of bearing adjustment is to obtain a specific preload, it would seem sensible to use a method either to produce or to measure the force directly. However, in practice, the indirect methods of adjustment by axial displacement or frictional moment are preferred as they are simple and can be achieved easily and more cost-effectively.