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Installation knowledge of precision bearings

by:JNSN     2022-03-12
1. The requirements of precision bearings for matching parts Since the precision of the precision bearing itself is within 1 μm, it is required to have high dimensional accuracy and shape accuracy of the matching parts (shaft, bearing seat, end cover, retaining ring, etc.), especially the mating surface. Accuracy to be controlled at the same level as the bearing is critical and most overlooked. It must also be noted that if the matching parts of the precision bearing fail to meet the above requirements, the error of the precision bearing is often several times larger than that of the original bearing, or even more than 10 times, after installation, and it is not a precision bearing at all. The reason is that the matching machine The error of the parts is often not simply superimposed on the error of the bearing, but added after being amplified by different multiples. 2. Matching of precision bearings In order to ensure that the bearing does not have excessive deformation after installation, it must be done: (1) The roundness of the shaft and the seat hole and the verticality of the shoulder should be required according to the corresponding accuracy of the bearing. (2) It is necessary to accurately calculate not only the interference fit of the rotating ferrule, but also the proper fit of the fixed ferrule. The burning interference of the rotating ferrule should also be small within the possible range. As long as the influence of thermal expansion at the working temperature and the influence of centrifugal force at the maximum speed are ensured, the creeping or sliding of the tight-fitting surface will not be caused. According to the size of the working load and the size of the bearing, the fixed ring selects a very small clearance fit or interference fit. Too loose or too tight is not conducive to maintaining the original precise shape. (3) If the bearing operates at high speed and the working temperature is high, special attention should be paid to the fit of the rotating ferrule not to be too loose to prevent eccentric vibration, and the fit of the fixed ferrule should not have gaps to prevent the ferrule from being in Deforms under load and excites vibration. (4) The condition for adopting a small interference fit for the fixed ring is that both sides of the mating surface have high shape accuracy and small roughness, otherwise it will cause difficulty in installation and more difficult in disassembly. In addition, the influence of thermal elongation of the main shaft needs to be considered. . (5) For the main shaft using paired double angular contact ball bearings, most of the loads are light. If the fit interference is too large, the internal axial preload will be significantly larger, which will cause adverse effects. The main shaft of the double row short cylindrical roller bearing and the main shaft of the tapered roller bearing have a relatively large load, so the interference is relatively large. 3. Methods to improve the actual fit All measurement items of inner diameter and outer diameter are measured, and a comprehensive analysis of the measured data is made. Based on this, the size of the bearing installation part of the shaft and the seat hole is precisely matched. When actually measuring the corresponding size and geometry of the shaft and seat hole, it should be carried out under the same temperature conditions as when measuring the bearing. In order to ensure a higher actual matching effect, the surface roughness of the shaft and the seat hole and the bearing should be as small as possible. When making the above measurements, two sets of marks that can indicate the direction of the maximum deviation should be made on the outer circle and inner hole of the bearing, as well as the corresponding surfaces of the shaft and the seat hole, on both sides near the assembly chamfer, so that In actual assembly, the maximum deviation of the two matching parties is aligned with the same orientation, so that after assembly, the deviation of the two parties can be partially offset. The purpose of making two sets of orientation marks is that the compensation of the deviation can be comprehensively considered, so that the rotation accuracy of the supports at both ends can be improved, and the coaxiality error of the seat hole between the two supports and the journals at both ends can be partially obtained. eliminate. Implementing surface strengthening measures on the mating surface, such as sandblasting, plugging the inner hole with a precision plunger with a slightly larger diameter, etc., will help improve the mating accuracy.
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