The effect of bearing clearance on bearings

The clearance of rolling bearings refers to the maximum distance between the inner and outer rings of bearings that can move without load, that is, when the bearings are not assembled in the shaft or bearing box, the inner ring or the outer ring is fixed, and then the amount of movement when the unfixed party moves radial or axial. According to its direction of movement, the radial movement is called radial clearance, and the axial movement is axial clearance.

1. The radial clearance of the bearing will change relative to each other in different states, so it can be divided into original clearance, assembly clearance and working clearance:

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

(2) Assembly clearance, also called matching clearance, is the clearance when the bearing, shaft and bearing seat are assembled and not yet working. Mainly because interference assembly, or make the inner ring, or make the outer ring, or both, so that the assembly clearance is smaller than the original clearance.

(3) Working clearance, also known as effective clearance, refers to the actual clearance existing in the bearing after it is assembled in the main engine, under the condition that the corresponding temperature rise is stable under the corresponding load effect. The working clearance is smaller than the original clearance, but compared with the assembly clearance, mainly because the inner ring temperature rise is the largest, the thermal expansion is the largest, so that the bearing clearance is reduced, at the same time, mainly because of the effect of load, the rolling body and raceway contact causes elastic deformation, so that the bearing clearance is increased, the actual than the assembly clearance is larger or smaller, depends on the comprehensive effect 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 the speed is faster, there may be burning problems. If long-term operation in high temperature, high-speed environment, there may be bearing locking problem, and cause damage to the bearing supporting shaft or housing bearing position. When the bearing clearance is too large, the rotor will shift during operation. Therefore, the size of the bearing clearance can directly interfere with the running accuracy, rotation flexibility, vibration, noise and other performance of the bearing. The clearance that does not meet the standard will cause the bearing to be ineffective at the beginning. Therefore, for the bearings used for vacuum transmission, the change of clearance caused by temperature change and other various reasons should be considered in the whole process of use, as well as the change of clearance caused by transfer film and micro debris in solid lubrication bearings.

Three, the choice of clearance

(1) The radial clearance of ball bearings should be close to zero, and the rigidity of roller bearings is larger than that of ball bearings. In order to avoid radial stuck due to the temperature difference between inner and outer rings, roller bearings should retain a certain radial clearance. For bearings with rigidity or rotation accuracy requirements, such as automotive hub double row angular contact ball bearings, a certain amount of preload should be applied to form a "negative clearance".

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

Four, clearance measurement

Bearing clearance measurement using a special clearance measuring instrument, also can make full use of feeler or dial meter to measure.

Check with a feeler to verify the maximum load position of the rolling bearing. Insert a feeler between the 180° rolling body and the outer (inner) ring. The thickness of the feeler with appropriate tightness is also the radial clearance of the bearing. Such a specific method is commonly used in aligning bearings and cylindrical roller bearings; To measure with a dial meter, the dial meter is zeroed first, and then the outer ring of the rolling bearing is jacked up. The reading of the dial meter is also the radial clearance of the bearing.