1. The bearing fit is generally a transition fit, but under special circumstances, an interference fit is optional, but it is rare. Because the match between the bearing and the shaft is the match between the inner ring of the bearing and the shaft, the base hole system is used. Originally, the bearing should be completely zero. We can also think so in actual use. When the minimum limit size is matched, the inner ring rolls, which damages the g surface of the shaft, so our bearing inner ring has a lower deviation tolerance of 0 to several μ to ensure that the inner ring does not rotate, so the bearing generally chooses transition fit. Even the transition fit should not exceed the 3-wire interference.

Generally, level 6 is selected for the matching accuracy level. Sometimes it depends on the material and processing technology. In theory, level 7 is a bit low. If it is matched with level 5, grinding is required .

The general selection is: the inner ring of the bearing and the shaft should be matched with the shaft to choose k6, and the outer ring of the bearing and the hole should be matched with the hole to choose K6 or K7.

Second, the matching tolerance standard of the bearing and the shaft

1. When the bearing inner diameter tolerance zone and the shaft tolerance zone form a fit, the tolerance code that was originally a transition fit in the general base hole system will become an over-win fit, such as k5, k6, m5, m6, n6, etc., However, the amount of overwin is not large; when the bearing inner diameter tolerance is matched with h5, h6, g5, g6, etc., it is not a clearance but an overwin fit.

2. The bearing outer diameter tolerance zone is also a special tolerance zone because the tolerance value is different from the general reference shaft. In most cases, the outer ring is fixed in the housing hole. It needs to be adjusted according to the requirements, and its fit should not be too tight, and it is often matched with H6, H7, J6, J7, Js6, Js7, etc.

Three. Examples

Under normal circumstances, the shaft is generally marked with 0~+0.005. If it is not removed frequently, it is +0.005~+0.01 interference fit. Okay, if you want to disassemble and assemble frequently, it is a transition fit. We also need to consider the thermal expansion of the shaft material itself during rotation, so the larger the bearing is, the better the clearance fit is -0.005 to 0, and the maximum clearance fit should not exceed 0.01. Another one is the interference of the moving coil and the clearance of the static ring.

Fourth, fit tolerance (fit tolerance)

refers to the sum of the hole and shaft tolerances that make up the fit. It is the amount of variation that allows for clearance or interference. The size of the tolerance zone and the position of the tolerance zone for the hole and shaft make up the fit tolerance. The size of the hole and shaft fit tolerance indicates the fit accuracy of the hole and the shaft. The size and position of the hole and shaft fit tolerance zone indicate the fit accuracy and fit nature of the hole and shaft. The size of the fit tolerance u003d the size of the tolerance zone; the size and position of the fit tolerance zone u003d the nature of the fit.

5. Selection of tolerance grades

The tolerance grades of the shaft or bearing seat hole matched with the bearing are related to the bearing accuracy. For the shaft matched with the P0 grade precision bearing, the tolerance level is generally IT6, and the bearing seat hole is generally IT7. For occasions with higher requirements on the stability of the rotary machine (such as electric motors, etc.), the shaft should be selected as IT5, and the bearing seat hole should be IT6.

Six. Selection of tolerance zone

The equivalent radial load P is divided into 'lightThe relationship between C is: light load P≤0.06C normal load 0.06C

1, shaft tolerance zone

Install radial bearings and For the tolerance zone of the shaft of angular contact bearing, refer to the corresponding tolerance zone table. For most occasions, when the shaft rotates and the radial load direction does not change, that is, when the bearing inner ring rotates relative to the load direction, a transition or interference fit should generally be selected. When the shaft is stationary and the radial load direction is unchanged, that is, when the inner ring of the bearing is static relative to the load direction, transition or small clearance fit can be selected (too much clearance is not allowed).

2. Tolerance zone of housing bore

For the tolerance zone of housing bore for radial bearings and angular contact bearings, refer to the corresponding tolerance zone table. When selecting, pay attention to avoid clearance fits for outer rings that oscillate or rotate in the direction of load. The size of the equivalent radial load also affects the fit selection of the outer ring.

3. Selection of bearing housing structure

Unless there are special needs, the bearing housing of rolling bearing generally adopts an integral structure. The split bearing housing is only difficult to assemble. Or when the advantage of convenience in assembly is the main consideration, but it cannot be used for tight or more precise fits, such as K7 and tighter fits than K7, and for seat holes with a tolerance class of IT6 or more , split bearing housings shall not be used.