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Installation of precision NSK bearings

by:JNSN     2022-03-12
1. The requirements of precision NSK bearings for matching parts Because the precision of precision NSK bearings themselves is within 1μm, it is required that the matching parts (shaft, NSK bearing seat, end cover, retaining ring, etc.) have high dimensional accuracy and shape accuracy, especially It is critical that the accuracy of the mating surface be controlled within the same level as the NSK bearing, and it is also the most easily overlooked. It must also be noted that if the matching parts of the precision NSK bearing fail to meet the above requirements, the error of the precision NSK bearing after installation is often several times larger than that of the original NSK bearing, or even more than 10 times, which is not a precision NSK bearing at all. The reason is that the error of the matching parts is often not simply superimposed on the error of the NSK bearing, but is added after being amplified by different multiples. 2. Matching of precision NSK bearings In order to ensure that NSK bearings do 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 precision of the NSK bearing. (2) It is necessary to accurately calculate the interference fit of the rotating ferrule and the appropriate 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 highest 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 NSK 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 NSK bearing operates at high speed and the working temperature is high, special attention should be paid to the matching 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. 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 NSK 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 NSK bearing and the main shaft of the tapered roller NSK bearing have a relatively large load, so the interference is relatively large. 3. The method of improving the actual fitting accuracy In order to improve the actual fitting accuracy of NSK bearing installation, it is necessary to use the measuring method and measuring tool that does not deform the NSK bearing, to carry out the actual precise measurement of the mating surface dimensions of the inner hole and the outer circle of the NSK bearing. All measurement items related to the inner diameter and outer diameter can be measured, and the measured data can be analyzed comprehensively. Based on this, the size of the NSK bearing installation part of the shaft and seat hole can be 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 NSK bearings. In order to ensure a higher actual matching effect, the surface roughness of the shaft and the seat hole matching the NSK bearing should be as small as possible. When making the above measurement, two sets of marks that can indicate the direction of maximum deviation should be made on the outer circle and inner hole of the NSK bearing, as well as the corresponding surfaces of the shaft and seat hole, on both sides near the assembly chamfer. , so that during actual assembly, the maximum deviation of the two matching parties can be 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 considered comprehensively, so that the rotation accuracy of the two 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 obtained. Partially eliminated. 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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