Assembly and disassembly of precision bearing

1Requirements of precision bearing for matching parts

Because the precision of precision bearing itself is less than 1 μ m, it is required that the matching parts (shaft, bearing seat, end cover, retaining ring, etc.) have high dimensional accuracy and shape accuracy. Especially, the precision of mating surface should be controlled within the same level as that of bearing, which is very important and easy to be ignored.

Note that if the matching parts of the precision bearing fail to meet the above requirements, the error of the precision bearing after installation will be several times or even more than 10 times larger than that of the original bearing, which is totally not considered as a precision bearing. The reason is that the error of matching parts is often not simply superimposed on the bearing error, but is amplified by different multiples.

2. Matching of precision bearing

In order to ensure that the bearing will not produce excessive deformation after installation, it is necessary to:

(1) The roundness of the shaft and the seat hole and the perpendicularity of the shoulder should be in accordance with the corresponding accuracy of the bearing.

(2) It is necessary to calculate not only the interference of the rotating ring, but also the proper fit of the fixed ring.

The ignition interference of the rotating ring should also be small in the possible range. As long as the influence of thermal expansion at working temperature and centrifugal force at high speed is ensured, the creep or sliding of tight fitting surface will not be caused. According to the size of working load and bearing size, the minimum clearance fit or interference fit is selected for the fixed ring. Too loose or too tight is not conducive to maintain the original accurate shape.

(3) If the bearing operates at high speed and the working temperature is high, special attention should be paid to the matching of the rotating ring not to be too loose to prevent eccentric vibration, and the fit of the fixed ring should not have clearance, so as to prevent the ring from deformation under load and to stimulate vibration.

(4) The condition of small interference fit for the fixed ring is that both sides of the matching surface have high shape accuracy and small roughness, otherwise it will make installation difficult and disassembly more difficult. In addition, the influence of spindle thermal elongation should be considered.

(5) If the main shaft with double angular contact ball bearing is used, the half load is light, and if the interference is too large, the axial preload will be significantly larger, which will cause adverse effects. The main shaft of double row short cylindrical roller bearing and tapered roller bearing have relatively large load, so their fit interference is relatively large.

3. Methods to improve the actual fitting accuracy

In order to improve the actual matching accuracy of bearing installation, it is necessary to use the measuring method and measuring tools that do not deform the bearing to measure the fitting surface dimensions of the bearing inner hole and outer circle. All the measuring items of the inner diameter and outer diameter can be measured, and the measured data can be comprehensively analyzed. Based on this, the bearing installation of shaft and seat hole can be precisely matched Size of mounting part. The actual measurement of the corresponding size and geometry of the shaft and seat hole should be carried out under the same temperature condition as that of the bearing.

In order to ensure a higher actual matching effect, the surface roughness of the shaft and seat hole matching with the bearing should be as small as possible.

During the above measurement, two groups of marks indicating the maximum deviation direction should be made respectively on the outer circle and inner hole of the bearing and the corresponding surface of the shaft and seat hole, on both sides close to the assembly chamfer, so that the maximum deviation of the matching two sides can be aligned with the same orientation during actual assembly, so that the deviation of both sides can be partially offset after assembly.

The purpose of making the two groups of directional marks is to consider the compensation of the deviation comprehensively, which not only improves the rotation accuracy of the supports at both ends, but also partially eliminates the coaxiality error of the seat hole and the journal at both ends between the two supports. The surface strengthening measures such as sandblasting and inserting inner hole with precision plug with larger diameter are beneficial to improve the matching accuracy.