Adjustment means setting the bearing internal clearance, see section Mounting - Bearings with a cylindrical bore, or setting the preload of a bearing arrangement.
The radial preload usually used for cylindrical roller bearings, double row angular contact ball bearings and sometimes for deep groove ball bearings, for example, is achieved by using a sufficient degree of interference for one or both of the bearing rings to reduce the initial internal clearance of the bearing to zero so that in operation there will be a negative clearance, i.e. preload.
Bearings with a tapered bore are particularly suitable for radial preloading since, by driving the bearing up on to its tapered seat, the preload can be applied to within narrow limits.
Axial preload in single row angular contact ball bearings, tapered roller bearings and also deep groove ball bearings is produced by displacing one bearing ring axially in relation to the other by an amount corresponding to the desired preload force. There are two main groups of adjustment methods that differ in the principle on which they are based: individual adjustment and collective adjustment.
Individual adjustmentWith individual adjustment, each bearing arrangement is adjusted separately using nuts, shims, spacer sleeves, deformable sleeves etc. Measuring and inspection procedures provide that the established nominal preload force is obtained with the least possible deviation. There are different methods depending on the quantity of bearings to be measured
- adjustment using preload path
- adjustment using friction torque
- adjustment using direct force measurement.
Individual adjustment has the advantage that individual components can be produced to Normal tolerances and the desired preload can be achieved with a reasonably high degree of accuracy.
Adjustment using preload pathThis method of adjustment is frequently used when the components of a bearing arrangement are pre-assembled. The preload is achieved, for example, for a pinion bearing arrangement by
- fitting intermediate rings between the outer and inner rings of the two bearings (fig 1)
- inserting shims between a housing shoulder and a bearing outer ring or between the casing and the housing (fig 2), the housing being in this case the flanged angled insert
- fitting a spacer ring between a shaft shoulder and one of the bearing inner rings (fig 3) or between the inner rings of the two bearings.
The width of the shims, intermediate rings or spacer rings is determined by
- the distance between the shaft and housing shoulders
- the total width of both bearings
- the preload path (axial displacement) corresponding to the desired preload force
- a correction factor for the preload path to take account of the thermal expansion in operation
- the manufacturing tolerances of all related components, established by measuring the actual dimensions before mounting
- a correction factor to take account of a certain loss of preload force after a certain period of operation.
This method of adjustment is based on the relationship between the preload force and the elastic deformations within the preloaded system. The requisite preload can be determined from a preload force/preload path diagram (diagram 1).