Depending on the applications, there might be a need to preload the bearing arrangement i.e. apply a negative operating clearance.
In applications like machine tool spindles, automotive differentials and electric motors, where preload enhances stiffness or running accuracy, SKF recommends applying preload with springs if an adjustment nut is not available. Springs should also be used under very light or no-load conditions to provide a minimum load on the bearing (→ Requisite minimum load).
Preload can be expressed as a force or as a distance (path), but is typically expressed as a force.
Depending on the adjustment method, preload is also indirectly related to the frictional moment in the bearing.
Empirical preload values can be obtained from proven designs and can be applied to similar designs. For new designs, SKF recommends calculating the preload force and checking its accuracy by testing the application. In general, all influencing factors in operation cannot be fully identified in the design stage and adjustments may be necessary. The accuracy of the calculation depends on how closely the estimated operating temperature and elastic behaviour of the associated components – most importantly the housing – coincide with the actual conditions in operation.