The magnitude, direction and nature of the load on the bearing are the main basis for selecting the bearing type. When selecting the type of bearing according to the load, because the main elements in the roller bearing are in line contact, it is suitable to bear large load and small deformation after bearing. The ball bearing is point contact and should be used to bear light or medium load. Therefore, when the load is small, the ball bearing should be preferred. When the bearing type is selected according to the direction of load, thrust bearing is generally selected for pure axial load.
Thrust ball bearing can be selected for small pure axial load; Thrust roller bearing can be selected for large pure axial load. For pure radial load, deep groove ball bearing, cylindrical roller bearing or needle roller bearing are generally selected. When the bearing bears radial load R and small axial load a, deep groove ball bearing or angular contact ball bearing or tapered roller bearing with small contact angle can be selected; When the axial load is large, angular contact ball bearing or tapered roller bearing with large contact angle can be selected, or the structure of radial bearing and thrust bearing can be selected to bear radial load and axial load respectively.
Under the general speed, the speed does not have any impact on the type selection. Only when the speed is high, it will have a significant impact. The limit speed of various types and sizes of bearings are listed in the bearing samples. This limit speed refers to the large allowable speed when the load is not too large (P ≤ 0.1C, C is the basic rated dynamic load), the cooling conditions are normal, and it is a Class 0 tolerance bearing. However, since the limit speed is mainly limited by the temperature rise during operation, the limit speed in the sample cannot be considered as an absolutely insurmountable limit. If the working speed of the bearing exceeds the limit speed, the following fifth measure can be taken.
1) Compared with roller bearing, ball bearing has higher limit speed, so ball bearing should be preferred at high speed;
2) Under the condition of the same inner diameter, the smaller the outer diameter, the lighter and smaller the rolling element. During operation, the smaller the centrifugal inertia force added by the rolling element on the outer race raceway, so it is more suitable for working at higher speed. Therefore, ultra light, ultra light and light series bearings should be selected at high speed. Heavy and extra heavy series bearings are only used for low-speed and heavy-duty occasions. If a light series bearing is used and the bearing capacity cannot meet the requirements, a wide series bearing can be considered, or two light series bearings can be installed together.
3) The material and structure of cage have a great influence on the bearing speed. Solid cages allow higher speeds than stamped cages.
4) The limit speed of thrust bearing is very low. When the working speed is high, if the axial load is not very large, angular contact ball bearings can be used to bear pure axial force.
5) If the working speed slightly exceeds the limit speed specified in the sample, measures can be taken to improve the bearing performance, such as increasing the tolerance grade of the bearing, appropriately increasing the radial clearance of the bearing, selecting circulating lubrication or oil mist lubrication, and strengthening the cooling of circulating oil. If the working speed exceeds the limit speed more, a special high-speed rolling bearing shall be selected.
When the center line of the shaft does not coincide with the center line of the bearing seat and there is an angle error, or when the shaft is bent or tilted due to force, the axis of the inner and outer ring of the bearing will be tilted. At this time, the self-aligning ball bearing or self-aligning roller bearing with certain self-aligning performance shall be adopted. This kind of bearing can still work normally when the axis of the inner and outer rings has little relative deflection. Cylindrical roller bearing and needle roller bearing are sensitive to bearing deflection, and the bearing capacity of this kind of bearing may be lower than that of ball bearing. Therefore, when the stiffness of the shaft and the support stiffness of the bearing seat hole are low, this kind of bearing should be avoided as far as possible.
Easy assembly and disassembly is also a factor to be considered when selecting the bearing type. When the bearing pedestal has no split surface and the bearing components must be installed and disassembled along the axial direction, the bearings with separable inner and outer rings (such as N0000, na0000, 30000, etc.) shall be preferred. When the bearing is installed on the long shaft, in order to facilitate disassembly, the bearing with cone hole of 1:12 (for installation on the tightening bushing) can be selected.