How to measure bearing axial clearance
When selecting bearing clearance, the following aspects should be considered:
1. The working conditions of the bearing, such as load, temperature, speed, etc.;
2. Requirements for bearing performance (rotational accuracy, friction torque, vibration, noise);
3. When the bearing and the shaft and the housing hole are in an interference fit, the bearing clearance is reduced;
4. When the bearing is working, the temperature difference between the inner and outer rings will reduce the bearing clearance;
5. Reduced or increased bearing clearance due to different expansion coefficients of shaft and housing materials.
According to experience, the most suitable working clearance for ball bearings is close to zero; roller bearings should maintain a small amount of working clearance. In components requiring good support rigidity, FAG bearings allow a certain amount of preload. It is specially pointed out here that the so-called working clearance refers to the clearance of the bearing under actual operating conditions. There is also a kind of clearance called original clearance, which refers to the clearance before the bearing is installed. The original clearance is greater than the installed clearance. Our choice of clearance is mainly to choose the appropriate working clearance.
The clearance values stipulated in the national standard are divided into three groups: basic group (group 0), auxiliary group with small clearance (group 1, 2) and auxiliary group with large clearance (group 3, 4, 5). When selecting, under normal working conditions, the basic group should be preferred, so that the bearing can obtain the appropriate working clearance. When the basic group cannot meet the use requirements, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for the interference fit between the bearing and the shaft and the housing hole. The temperature difference between the inner and outer rings of the bearing is large. The deep groove ball bearing needs to bear a large axial load or needs to improve the self-aligning performance. Reduce the friction torque of NSK bearings and other occasions; the small clearance auxiliary group is suitable for occasions requiring higher rotation accuracy, strictly controlling the axial displacement of the housing hole, and reducing vibration and noise. 1 Fixing the bearing
After determining the type and model of the bearing, it is necessary to correctly design the combined structure of the rolling bearing to ensure the normal operation of the TIMKEN bearing.
The combined structure design of the bearing includes:
1) Shafting support end structure;
2) The cooperation of bearings and related parts;
3) Lubrication and sealing of bearings;
4) Improve the stiffness of the bearing system.
1. Fixed at both ends (one-way fixed at both ends) For short shafts (span L<400mm) under normal working temperature, the fulcrum is often fixed by one-way at both ends, and each bearing bears axial force in one direction. As shown in the figure, in order to allow a small amount of thermal expansion of the shaft during operation, the bearing should be installed with an axial clearance of 0.25mm-0.4mm (the clearance is very small, and it is not necessary to draw it on the structure diagram).
Features: Limit the bidirectional movement of the axis. Suitable for shafts with little change in operating temperature. Note: Considering the thermal elongation, leave a compensation gap c between the bearing cover and the outer end face, c=0.2~0.3mm. 2. One end is fixed in both directions and one end is swimming. When the shaft is long or the working temperature is high, the thermal expansion and shrinkage of the shaft is large.
The fixed end is subjected to bidirectional axial force by a single bearing or bearing group, while the free end ensures that the shaft can swim freely when it expands and contracts. In order to avoid loosening, the inner ring of the floating bearing should be axially fixed with the shaft (a circlip is often used). Features: One fulcrum is fixed in both directions, and the other fulcrum moves axially. The deep groove ball bearing is used as a floating fulcrum, and there is a gap between the outer ring of the bearing and the end cover. Cylindrical roller bearings are used as the floating fulcrum, and the outer ring of the bearing should be fixed in both directions.
Applicable: Long axis with large temperature change.