Bearing clearance has a significant impact on bearing life, temperature rise, noise, etc. Therefore, it is necessary to select an appropriate clearance based on working conditions and performance requirements. The clearance of bearings is divided into radial clearance and axial clearance, which respectively represent the displacement of one sleeve fixed and the other sleeve from one extreme position to another along the radial and axial directions. The radial clearance of bearings includes the original clearance in the free state before bearing installation, the assembly clearance after installing the main shaft and bearing seat, and the working clearance formed under load during operation. For ball bearings, the suitable working clearance is close to zero; For roller bearings, a small amount of working clearance can be maintained. In components that require good support rigidity, bearings should have a certain amount of preload. This is the principle for determining the radial clearance of bearings.
For centripetal thrust ball bearings and tapered roller bearings, they are usually installed face to face or back to back, with the internal clearance or preload determined by the axial position of a certain bearing ring. Starting from the zero clearance condition, the specified clearance can be obtained by adjusting the thickness of the gasket on the outer ring of the bearing or by loosening or tightening the back nut on the shaft. There is a fixed relationship between the axial and radial clearance of this type of bearing, and meeting one of these values is sufficient.
When selecting bearing clearance, the following aspects should also be considered:
1. The working conditions of the bearing, such as load, temperature, speed, etc;
2. Requirements for the performance of bearings, such as rotational accuracy, friction torque, vibration and noise, etc;
3. When the bearing is in an interference fit with the shaft and housing hole, it leads to a decrease in bearing clearance;
4. During bearing operation, the temperature difference between the inner and outer rings leads to a decrease in bearing clearance;
5. Due to the different expansion coefficients of the shaft and shell materials, the bearing clearance decreases or increases;
6. Due to the large temperature difference between the inner and outer rings of the bearing, deep groove ball bearings need to withstand large axial loads or improve their centering performance, which requires increasing the limit speed and reducing bearing friction torque;
When the basic group cannot meet the usage requirements, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for interference fit between bearings, shafts, and shell holes, while the small clearance auxiliary group is suitable for situations that require high rotational accuracy, strict control of axial displacement of shell holes, and reduction of vibration and noise.