The so-called bearing clearance refers to the movement of the bearing when the inner ring or outer ring of the bearing is fixed when it is not installed on the shaft or bearing housing, and then the unfixed side moves radially or axially. According to the moving direction, it can be divided into radial clearance and axial clearance. Clearance is also very important for the use of bearings, so we must not ignore this.
Six items of bearing clearance:
1. The size of the running clearance (called working clearance) has an impact on the rolling fatigue life, temperature rise, noise, vibration and other properties of the bearing.
2. When measuring the bearing clearance, in order to obtain a stable measurement value, the specified measurement load is generally applied to the bearing. Therefore, the measured value is larger than the real clearance (called theoretical clearance), which increases the elastic deformation caused by the measured load. For roller bearings, because the elastic deformation is small, it can be ignored.
3. The internal clearance of the bearing before installation is generally expressed by theoretical clearance.
4. The clearance after deducting the expansion or contraction of the ferrule caused by interference fit when the bearing is installed on the shaft or in the housing from the theoretical clearance is called "installation clearance". The clearance after adding or subtracting the dimensional variation caused by the temperature difference inside the bearing on the installation clearance is called "effective clearance".
5. The bearing is installed with the clearance when it is placed under a certain load, that is, the effective clearance plus the elastic deformation caused by the bearing load, so it is called "working clearance".
6. When the working clearance is slightly negative, the fatigue life of the bearing is long, but with the increase of the negative clearance, the fatigue life decreases significantly. Therefore, when selecting the bearing clearance, it is generally appropriate to make the working clearance zero or slightly positive. In addition, when it is necessary to improve the rigidity of the bearing or reduce the noise, the working clearance should be further taken as a negative value, while when the bearing temperature rises violently, the working clearance should be further taken as a positive value, etc., which must be analyzed in detail according to the service conditions.
