Selecting the correct preload
When selecting the preload for a bearing system, the degree of stiffness increases marginally once preload exceeds a given optimum value. When exceeding the optimum value, friction and the resulting increase in heat can substantially reduce bearing service life and negate any benefits (diagram 1). Excessive preload involves a risk that the operational reliability of a bearing system is compromised. Because of the complexity normally required to calculate an appropriate preload, SKF recommends contacting the SKF application engineering service.
When adjusting preload in a bearing system, it is also important that the established preload value, determined either by calculation or by experience, is attained with the least possible scatter. To reduce scatter when mounting tapered roller bearings, for example, the shaft should be turned several times, if possible, so that the rollers are not skewed and the roller ends are in contact with the guide flange of the inner ring. Turning the shaft also enables the rollers to make full contact with the outer ring and avoids damage to the raceways. When the rollers are not fully settled into position, a much smaller preload than the requisite value results.