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The preload of the crossed roller bearing means that after the bearing is installed on the bearing seat and the shaft, certain measures are taken to produce a quantitative pre-deformation between the rolling elements in the bearing and the inner and outer rings, so as to keep the inner and outer rings in the same position. pressed state. The purpose of preloading the crossed roller bearing is to: increase the rigidity of the support; reduce vibration and noise; prevent the sliding of the rolling elements relative to the inner and outer raceways caused by the moment of inertia. Depending on the application, the bearing arrangement must have a positive or negative operating clearance. In most cases, the working clearance is positive, that is, when the bearing is running, there is a certain residual clearance, although it may be a small clearance.
On the other hand, there are many applications that require negative operating clearance—that is, negative preload—to increase the rigidity or rotational accuracy of the bearing arrangement. For example, spindle bearings of machine tools, CNC machine tool turntable bearings, thin-walled cross-roller bearings of robot arms, pinion bearings in automobile transmission shafts, small motor bearings, or bearing arrangements for reciprocating motion, etc. In some applications, if the imported bearing is under no or only small load, and operates at high speed, preload should be carried out on the bearing arrangement, such as by spring to carry out bearing preload. In this case, the role of preload is to provide a small load to the bearing to prevent the rolling elements from sliding and causing damage to the imported bearing.
The preload form can be radial or axial according to different bearing types. For example, cylindrical roller bearings, due to their design, can only be preloaded in the radial direction, while thrust ball bearings and thrust cylindrical roller bearings can only be preloaded in the axial direction. Single row angular contact ball bearings and tapered roller bearings are generally axially preloaded and are usually paired with another imported bearing of the same type back-to-back or face-to-face. And deep groove ball bearings are usually also subjected to axial preloading. In order to achieve the purpose of preloading, a radial internal clearance larger than that of the ordinary group should be used, so that it can have a larger than zero clearance like an angular contact ball bearing. Contact angle.
The preload is generally adjusted (or set according to this temperature) during installation at ambient temperature. If the temperature rise of the shaft is greater than that of the bearing seat during operation, the preload will increase. And the face-to-face configuration adds more preload than the back-to-back configuration. When the shaft is thermally expanded, the diameter of the shaft increases (radial expansion) and also stretches (axial expansion).
Whether in a face-to-face or back-to-back arrangement, under the influence of radial expansion, the bearing arrangement's clearance will decrease, i.e. the preload will increase. In face-to-face bearing arrangements, the preload will increase further under the influence of axial expansion, but the preload in back-to-back bearing arrangements will therefore decrease. In a back-to-back bearing arrangement, if there is a given distance between the bearings and the bearing and related components have the same coefficient of thermal expansion, the effects of radial and axial expansion on the preload will cancel each other out, so no preload will occur. Variety.
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