On the other hand, many applications need to have negative clearance job -- negative preload to improve the rigidity of the bearing arrangement or rotating accuracy. For example, machine tool spindle bearings, CNC machine tool turntable YRT turntable bearing robot arm thin-walled cross roller bearings, automobile transmission shaft pinion bearing, small motor bearing, or reciprocating motion of the bearing arrangement. In some applications, if the imported bearings are not or only bear a small load, and run at high speed, should be carried out in the bearing configuration preload, such as through the spring to carry out bearing preload. In this case, the preload is the role of the bearing to provide the minimum load, in order to prevent the rolling body sliding caused by the damage of imported bearings.
Pre tight form
Preload according to different types of bearings can be radial, but also to the axial. For example, cylindrical roller bearing, due to its design, only in the radial preload, and thrust ball bearings and cylindrical roller thrust bearing is only in the axial preload. Single row angular contact ball bearings and tapered roller bearings by the general for axial preload, and usually with another of the same type imported bearings to back-to-back or face to face using a paired. And deep groove ball bearing is usually the same subjected to axial preload, in order to achieve the preload should be used with greater than normal group, the radial internal clearance, the angular contact ball bearings generally have a greater than zero contact angle.
Preload adjustment is generally installed at ambient temperature (or according to the temperature setting), if in the operation, the temperature rise of the shaft than the bearing seat, the preload will increase. But in the face of preload increase is larger than the surface configuration of the back-to-back configuration. In the axial thermal expansion, shaft diameter will increase (radial expansion), elongation (axial expansion) will. Either face to face or back-to-back configuration, under the influence of radial expansion, the clearance of the bearing arrangement can reduce the, namely pre tightening will increase. Face-to-face bearing configuration, under the influence of the axial expansion, preload will further increase, but back-to-back bearing arrangement of pre tight will thus decrease. In back-to-back bearing configuration, if a given distance between bearings, and the bearings and related components have the same coefficient of thermal expansion, radial expansion and axial expansion of influence of preload will offset each other and thus preload will not change.
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