Maintaining the correct preload
When selecting the preload force for a bearing arrangement it should be remembered that the stiffness is only marginally increased when the preload exceeds a given optimum value, whereas friction and consequently heat generation increase and there is a sharp decrease in bearing service life as a result of the additional, constantly acting load. Diagram 1 indicates the relationship between bearing life and preload/clearance. Because of the risk that an excessive preload implies for the operational reliability of a bearing arrangement, and because of the complexity of the calculations normally required to establish the appropriate preload force, it is advisable to consult the SKF application engineering service.
It is also important when adjusting preload in a bearing arrangement, that the established value of the preload force, determined either by calculation or by experience, is achieved with the least possible scatter. This means, for example, for bearing arrangements with tapered roller bearings, that the bearings should be turned several times during adjustment so that the rollers do not skew and so that the roller ends are in correct contact with the guide flange of the inner ring. If this is not the case, the results obtained during inspection or by measurements will be false and the final preload can be much smaller than the requisite value.