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Installation of precision bearings

by:JNSN     2021-12-25
1. The requirements of precision bearings for matching parts. Because the precision of the precision bearing itself is within 1μm, it is required to have high dimensional accuracy and shape accuracy with its matching parts (shaft, bearing seat, end cover, retaining ring, etc.), especially the matching surface Accuracy must be controlled within the same level as the bearing, which is crucial and is most easily overlooked. It must also be noted that if the matching parts of the precision bearing do not meet the above requirements, the precision bearing will often have an error that is several times larger than the original bearing error after installation, or even more than 10 times the error. It is completely impossible to be a precision bearing because of the matching machine. The error of the parts is often not simply superimposed on the error of the bearing, but added after being enlarged by different multiples. 2. In order to ensure that the bearing does not produce excessive deformation after installation, the matching of precision bearings must: (1) The roundness of the shaft and the seat hole and the verticality of the shoulder should be required in accordance with the corresponding accuracy of the bearing. (2) It is necessary to accurately calculate the interference amount of the rotating ferrule as well as the appropriate amount of the fixed ferrule. The burning interference of the rotating ferrule should also be smaller within the possible range. As long as the effect of thermal expansion at the working temperature and the effect of centrifugal force at the maximum speed are ensured, it will not cause creep or slippage of the tight-fitting surface. According to the size of the working load and the size of the bearing, the fixed ring selects a very small clearance fit or an interference fit. Too loose or too tight is not conducive to maintaining the original precise shape. (3) If the bearing is running under high-speed conditions and the working temperature is high, special attention should be paid to not too loose the fit of the rotating ring to prevent eccentric vibration, and there should be no gap in the fit of the fixed ring to prevent the ring from being Deforms under load and excites vibration. (4) The condition of adopting 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 installation difficulties and disassembly more difficult. In addition, the influence of the thermal elongation of the spindle needs to be considered. . (5) The main shaft using paired double angular contact ball bearings usually has a lighter load. 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 fit interference is relatively large. 3. In order to improve the actual matching accuracy during bearing installation, it is necessary to use measurement methods and measurement tools that do not deform the bearing to carry out actual precision measurement of the matching surface dimensions of the inner hole and outer circle of the bearing. The measurement items of the inner diameter and outer diameter are all measured, and the measured data is fully analyzed. Based on this, the size of the bearing installation part of the shaft and the seat hole is precisely matched. The actual measurement of the corresponding size and geometry of the shaft and the seat hole should be carried out under the same temperature conditions as when measuring the bearing. In order to ensure a high actual matching effect, the roughness of the matching surface of the shaft and the seat hole and the bearing should be as small as possible. When making the above measurement, two sets of marks showing the direction of maximum deviation should be made on the outer circle and inner hole of the bearing, and on the corresponding surface of the shaft and the seat hole, on both sides close to the assembly chamfer. In the actual assembly, the maximum deviation of the two matching parties should be aligned in the same direction, 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 deviation can be considered comprehensively, not only to improve the rotation accuracy of each support at both ends, but also to obtain part of the coaxiality error of the seat hole between the two supports and the journals at both ends. eliminate. The implementation of surface strengthening measures on the mating surface, such as sandblasting, using a precision plunger with a slightly larger diameter to plug the primary inner hole, etc., are all conducive to improving the accuracy of the mating.
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