Correct selection of bearing fit is very important to ensure the normal operation of the machine, improve the service life of bearings and make full use of bearing capacity.

● Whether the ring rotates. When the inner or outer ring of the bearing works as a rotating ring, a slightly tighter fit should be used. The size of the interference should make the mating surface not “crawling” under the working load, because once crawling occurs, the mating surface will wear and slide, and the higher the ring speed, the more serious the wear. When bearing is working, if its inner ring or outer ring is not rotating ring, in order to facilitate disassembly and adjustment, it is advisable to choose a loose fit.

● Type of load. A loose transition fit or a smaller clearance fit should be selected for the local load bearing ring, so that the friction torque between the raceways of the ring drives the ring to rotate, so that the force on the ring is uniform and the service life of the bearing is prolonged.

Other factors affecting bearing fit

● The effect of working temperature. When the bearing is working, the temperature of the ring is higher than that of its matching parts due to the influence of friction heating and other heat sources. The thermal expansion of the inner ring will cause the loosening of its fit with the journal, while the thermal expansion of the outer ring will cause the tightening of its fit with the shell hole.

● Influence of rotation accuracy and rotation speed. In order to eliminate the influence of elastic deformation and vibration, clearance fit should be avoided for bearings with large loads and high rotation accuracy. For light load bearings of some precision machine tools, in order to avoid the influence of shape error and shaft on bearing accuracy, clearance is often used. It is generally believed that the higher the rotation speed of bearings, the tighter the fit should be.

● Conditions for mounting and dismounting bearings. Considering the convenience of bearing installation and disassembly, it is appropriate to use a loose fit, which is particularly important for large and very large bearings used in heavy machinery. If convenient assembly and disassembly are required and tight fitting is required, separated bearings can be used, or bearings with taper holes in the inner ring, fixed sleeves and back groove can be used.

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