Installation of precision bearing

Requirements for matching parts of precision bearings

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

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 or even more than 10 times greater than that of the original bearing after installation, which is not a precision bearing at all. The reason is that the error of the matching parts is often not simply superimposed on the error of the bearing, but amplified by different multiples.

Fit of precision bearing

In order to ensure that the bearing does not produce excessive deformation after installation, the following must be achieved:

(1) The roundness of shaft and seat hole and the perpendicularity of retaining shoulder shall be required according to the corresponding accuracy of bearing.

(2) It is necessary to accurately calculate the interference of the rotating ferrule and the appropriate fit of the fixed ferrule.

The burning interference of rotating ferrule should also be small 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, the creep or sliding of the tight fitting surface will not be caused. According to the working load and bearing size, the fixed ring selects a very small clearance fit or interference fit. Too loose or too tight is not conducive to maintaining the original accurate shape.

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

(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 be difficult to install and more difficult to disassemble. In addition, the influence of thermal elongation of the main shaft needs to be considered.

(5) The main shaft with paired double angular contact ball bearings has light half load. If the fit interference is too large, the internal axial preload will be significantly too large, resulting in adverse effects. The load of the spindle with double row short cylindrical roller bearing and the spindle with tapered roller bearing is relatively large, so the fit interference is also relatively large.

Methods to improve the actual matching accuracy

In order to improve the actual fitting accuracy during bearing installation, it is necessary to use the measurement methods and tools that do not deform the bearing to accurately measure the fitting surface dimensions of the inner hole and outer circle of the bearing, measure all the measurement items related to the inner diameter and outer diameter, and make a comprehensive analysis of the measured data, The size of the bearing installation part of the precision matching shaft and seat hole. When actually measuring the corresponding size and geometry of the matched shaft and seat hole, it shall 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 between the shaft and seat hole and the bearing shall be as small as possible.

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

The purpose of making two groups of orientation marks is to comprehensively consider the compensation of deviation, not only improve the rotation accuracy of the supports at both ends, but also partially eliminate the coaxiality error of the seat hole between the two supports and the journal at both ends. The surface strengthening measures for the mating surface, such as sand blasting and plugging the primary inner hole with a slightly larger diameter precision plug column, are conducive to improving the mating accuracy.