subject: Types and Purposes of Bearing Preload [print this page] Bearing is usually selected to have a small clearance during normal operation, while some bearings are selected to have a negative clearance. When bearings are mounted, various effects can be achieved. This is just called the preload method, which can be applied only to the rolling bearings, not sliding ones.
What is the purpose of bearing preload? There are various purposes as in the different applications. when applied in the precision bearings for position controlling, used for main shaft bearing of machining tools or precision measuring instruments, the preload can be made to precisely determine the position of a shaft in radial and axial directions, and to increase its rotating precision at the same time. Besides, the preload can be done to increase the bearing rigidity in the pinion bearings of main shaft bearing of machining tools or automotive differentials. Moreover, it can also be made to restrict the sliding revolution and sliding rotation of rolling element in the angular contact ball bearings for high frequency motors or cylindrical roller bearings for jet engines.
There are two main types of preload, i.e. a position preload and a constant pressure preload. The former can be further divided into several sub-groups, namely, a method tightly fitting a pair of preloaded bearings, a method adjusting the dimensions of a spacer or seam to obtain the proper preload without using a matched pair of bearings, and a method employing the direct cont-roll of proper degree of fastening force to apply the appropriate amount of preload by measuring the starting friction moment without using spacer or seam. This type can allow a bearing to keep the constant relative position regardless of its operation status. And the second type of preload uses any of coil spring, plate spring, or board spring to apply a proper amount of preload to bearing.
In addition to the above aspects, it is also necessary to know the correlations between the applied load and displacement of bearing to find out correlations between preload and rigidity, and to theoretically determine the proper amount of preload. Although various effects can be achieved by applying the preload appropriately, excessive preload can become the causes for excessive heat generation, increased friction moment, or reduction of bearing life, etc. Therefore the amount of preload should be decided after careful analysis of bearing operating conditions and the purpose of preload, and many other aspects.
