The clearance of a rolling bearing refers to the maximum distance that can be moved between the inner and outer rings of a bearing in the case of no load, that is, when the bearing is not assembled in the shaft or bearing box, the inner or outer ring of the bearing is fixed, and then the movement of the non-fixed side moves in the radial or axial direction. According to the direction of movement, the radial motion is called radial clearance, and the axial motion is called axial clearance.

1. The radial clearance of bearings will change correspondingly in different states, so it can be divided into original clearance, assembly clearance and working clearance:

(1) The original clearance refers to the clearance in the free state after the complete set of bearings is assembled in the machine and equipment. It is determined by processing and assembly of the manufacturer.

(2) Assembly clearance, also known as matching clearance, is the clearance when the bearing, shaft and bearing seat are assembled but not yet working. The main reason is that interference assembly, either enlarging the inner ring or shrinking the outer ring, or both, makes the assembly clearance smaller than the original clearance.

(3) Working clearance, also known as effective clearance, refers to the actual clearance existing in the bearing under the condition that the bearing is assembled in the main engine and realizes stable operation of corresponding temperature rise under corresponding load effect. Work clearance is smaller than the original clearance, but compared with the assembly clearance, mainly because of working with maximum temperature rise of the inner ring, thermal expansion of the largest, reduce bearing clearance, at the same time, mainly because of the effect of load, the rolling element and raceway contact caused by elastic deformation, the bearing clearance increases, more or less than the actual assembly clearance, depends on the comprehensive efficacy of the two factors.

Two, when the bearing clearance is too small, it is easy to appear that the bearing temperature is too high, and then the speed is fast, there may be a burning problem. If it is operated in high temperature and high speed environment for a long time, there may be bearing lock problem, and cause contusion and damage to the bearing supporting shaft or housing bearing position. When the bearing clearance is too large, the operation will cause the channeling of the rotor. Therefore, the size of bearing clearance can directly interfere with the running accuracy, rotational flexibility, vibration, noise and other performances of bearings. The clearance that does not meet the standard will cause the bearing to fail to function at the initial stage. Therefore, for the bearing used in vacuum transmission, the clearance change caused by various reasons such as temperature change and the clearance change caused by transfer film and trace wear debris in solid lubrication bearing should be considered in the whole process.

Third, the selection of clearance

(1) The radial clearance of the ball bearing should be close to zero. The rigidity of the roller bearing is greater than that of the ball bearing. In order to avoid the radial jam caused by the temperature difference between the inner and outer rings, the roller bearing should retain a certain radial clearance. For bearings with rigid or rotational accuracy requirements, such as automobile wheel hub double-row angular contact ball bearings, it is necessary to apply a certain preloading force to form a "negative clearance".

(2) Light load, high speed, high precision, low working temperature occasions

Four, clearance measurement

Bearing clearance is measured by a special clearance measuring instrument, also can make full use of the feeler or micrometer to measure.

Check with a feeler to verify the maximum load position of the rolling bearing, insert the feeler between the rolling body and the outer (inner) ring which is 180° with it, and the thickness of the feeler which is suitable for the tightness is the radial clearance of the bearing. This specific method is widely used in aligning bearings and cylindrical roller bearings; With the micrometer measurement, first set the micrometer to zero, and then lift the rolling bearing outer ring, the reading of the micrometer is the radial clearance of the bearing