The accuracy of precision bearings after installation

Apr 02, 2021

Leave a message

After the bearing is installed in the host, if you measure the radial runout of the spindle, you can find that the measured value of each revolution has a certain change; when the measurement is performed continuously, it can be found that the change will be approximately repeated after a certain number of revolutions. appear. The index to measure the degree of this change is the cyclic rotation accuracy. The number of revolutions required for the approximate repetition of the change represents the "quasi-period" of the cyclic rotation accuracy. The magnitude of the change in the quasi-period is large, which is the poor cyclic rotation accuracy. .

If the main shaft is properly preloaded and the speed is gradually increased to close to the working speed, the "run-in" function of the bearing can be implemented, which can improve the cycle rotation accuracy of the main shaft.

A factory trial-produced a precision instrument. The main shaft used a 6202/P2 bearing and its accuracy still failed to meet the requirements. After that, the journal was thickened and a raceway was made on it to replace the inner ring, and the steel ball was measured by the size. Each group of three steel balls is separated by an interval close to 120°. Because one layer of processing surface is reduced, one layer of mating surface is reduced, and the rigidity of the shaft-bearing system is improved. The nearly equidistant distribution of the grain steel balls improves the rotation accuracy of the shaft, thus meeting the accuracy requirements of the instrument.

After installing the angular contact ball bearing into the main shaft, the installation accuracy verification sequence is as follows (take a common lathe with a shaft diameter of 60-100mm as an example):

(1) Measure the size of the shaft and the bearing seat hole to determine the matching accuracy of the bearing. The matching requirements are as follows:

The inner ring and the shaft adopt an interference fit, and the interference is 0～+4μm (0 under light load and high precision); the outer ring and the bearing seat hole adopt a clearance fit, and the clearance is 0～+6μm (but the bearing at the free end When using angular contact ball bearings, the gap can also be increased); the roundness error of the shaft and the seat hole surface is below 2μm, the end face parallelism of the spacer used in the bearing is below 2μm, and the runout of the inner end of the shaft shoulder facing the outer end face is less than 2μm; The runout of the bearing seat hole shoulder to the axis is less than 4μm; the runout of the inner end of the spindle front cover facing the axis is less than 4μm.

Thoroughly clean the bearing with clean cleaning kerosene. For grease lubrication, first pour an organic solvent containing 3% to 5% grease into the bearing for degreasing and cleaning, and then use a grease gun to fill the bearing with a certain amount of grease (accounting for 10%～15% of the bearing space volume); heat the bearing to raise the temperature by 20～30℃, install the bearing into the shaft end with a hydraulic machine; press the adapter sleeve on the shaft and press the bearing end face with appropriate pressure to make it axial Positioning; Wrap the belt of the spring balance on the outer ring of the bearing, and use the method of measuring the starting torque to verify whether the specified preload has a large change (even if the bearing is correct, the preload is also due to the fit or the deformation of the cage The possibility of change).

Heat the seat hole to raise the temperature by 20～30℃, use continuous and gentle pressure to install the bearing-shaft assembly into the seat hole; adjust the front cover so that the tightening amount of the front cover is 0.02～0.05μm, taking the outer end surface of the bearing seat as As a benchmark, touch the head of the dial indicator on the surface of the journal, rotate the shaft to measure its runout, and the required error is less than 10μm; position the dial indicator on the shaft, and the head of the dial against the inner surface of the rear seat hole, rotate the shaft To measure the coaxiality of the front and rear housing holes of the bearing housing.

(4) Place the free end bearing selectively at a position that may offset the deviation, and install it to the rear support position of the bearing seat to offset the mutual roundness deviation and coaxiality deviation as much as possible.

4. Installation of double row short cylindrical roller bearings with tapered bore

When installing NN3000K series tapered bore double row short cylindrical roller bearings, you must pay attention to the correct match between the inner diameter of the bearing and the taper of the shaft. In the case of low production volume, the coloring method can be used for contact verification, but when the production volume is large , It is best to use a precise taper gauge to check.

When installing the bearing on the tapered shaft, the inner ring should be adjusted to an appropriate position in the axial direction so that the radial clearance is close to zero.