1. Bearing load
The size, direction and nature of the load on the bearing are the main basis for selecting the type of bearing.
When selecting the type of bearing according to the size of the load, because the main components in the roller bearing are in line contact, it is suitable for bearing a larger load, and the deformation after the load is also small. Ball bearings are in point contact and are suitable for light or medium loads. Therefore, ball bearings should be preferred when the load is small.
When selecting the bearing type according to the direction of the load, thrust bearings are generally used for pure axial loads. Thrust ball bearings can be selected for smaller pure axial loads; thrust roller bearings can be selected for larger pure axial loads. For pure radial loads, deep groove ball bearings, cylindrical roller bearings or needle bearings are generally used. When the bearing is bearing the radial load R and there is a small axial load A, deep groove ball bearings or angular contact ball bearings with small contact angles or tapered roller bearings can be selected; when the axial load is large Angular contact ball bearings or tapered roller bearings with larger contact angles can be selected, or a combination of radial bearings and thrust bearings can be selected to bear the radial load and the axial load respectively.
2. Bearing speed
Under the general speed, the speed has no effect on the selection of the type. Only when the speed is high, it will have a more significant effect. The limit speeds of various types and sizes of bearings are listed in the bearing samples. This limit speed refers to the maximum allowable speed when the load is not too large (P≤0.1C, C is the basic dynamic load rating), the cooling condition is normal, and the maximum allowable speed of the bearing with 0 tolerance. However, since the limit speed is mainly limited by the temperature rise during work, it cannot be considered that the limit speed in the sample is an absolutely unsurpassed limit. If the working speed of the bearing exceeds the limit speed, the following fifth measure can be taken.
From the requirements of the speed on the bearing, the following points can be determined:
1) Compared with roller bearings, ball bearings have a higher limit speed, so ball bearings should be preferred at high speeds;
2) Under the condition of the same inner diameter, the smaller the outer diameter, the lighter the rolling elements, and the smaller the centrifugal inertia force of the rolling elements on the outer ring raceway during operation, so it is more suitable for working at higher speeds. . Therefore, ultra-light, extra-light and light series bearings should be used at high speeds. Bearings of heavy and extra heavy series are only used for low-speed and heavy-duty occasions. If a light series bearing is used and the load capacity cannot meet the requirements, a wide series bearing can be considered, or two light series bearings can be used together.
3) The material and structure of the cage have a great influence on the bearing speed. The solid cage allows a higher speed than the stamped cage.
4) The limit speed of the 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, the tolerance level of the bearing can be increased, or the radial clearance of the bearing can be increased appropriately, the use of circulating lubrication or oil mist lubrication, and the strengthening of the cooling of the circulating oil can be used to improve The telling performance of the bearing. If the working speed exceeds the limit speed more, special high-speed rolling bearings should be used.
3. Bearing's self-aligning performance
When the center line of the shaft does not coincide with the center line of the bearing seat and there is an angular error, or when the shaft is bent or tilted due to force, the axis of the inner and outer rings of the bearing will be tilted. At this time, a self-aligning ball bearing or self-aligning roller bearing with a certain degree of self-aligning performance should be used. This type of bearing can still work normally when the axis of the inner and outer ring has a small relative deviation.
Cylindrical roller bearings and needle roller bearings are most sensitive to the deflection of the bearing, and the load carrying capacity of this type of bearing may be lower than that of ball bearings under deflection. Therefore, when the rigidity of the shaft and the supporting rigidity of the bearing seat hole are low, the use of such bearings should be avoided as much as possible.
4. Bearing installation and removal
Ease of assembly and disassembly is also a factor that should be considered when selecting the bearing type. When the bearing seat has no split surface and the bearing components must be installed and removed in the axial direction, the bearings with separable inner and outer rings (such as N0000, NA0000, 30000, etc.) should be preferred. When the bearing is installed on the long shaft, in order to facilitate disassembly, a bearing with a 1:12 tapered hole in the inner ring (used to be installed on the tightening bush) can be selected.