by 
All kinds of bearings have different characteristics and are suitable for different applications of various machines. When selecting the bearing type, the following factors should generally be considered. Generally, thrust bearing and angular contact bearing are selected for bearing thrust load, ball bearing is usually used for high-speed applications, and roller bearing is selected for bearing heavy radial load.
In mechanical design, the size of the shaft is generally determined first, and then the rolling bearing is selected according to the size of the shaft. Usually, ball bearings are used for small shafts and roller bearings are used for large shafts. However, when the bearing is limited in the diameter direction of the machine, needle roller bearings, ultra light and ultra light series ball or roller bearings are selected; When the axial position of the bearing in the machine is limited, narrow or ultra narrow series ball or roller bearings can be selected.
Load is the main factor in the selection of bearings. Roller bearings are used to bear heavy loads, ball bearings are used to bear light or medium loads, and bearings made of carburized steel or bainite quenching can bear impact and vibration loads. In terms of load direction, when bearing pure radial load, deep groove ball bearing, cylindrical roller bearing or needle roller bearing can be selected. When bearing the small pure axial load of NSK bearing, thrust ball bearing can be selected;
When bearing large pure axial load, thrust roller bearing can be selected. When the bearing bears the combined radial and axial load, angular contact ball bearing or tapered roller bearing is generally selected. For cantilever support structures, tapered roller bearings or angular contact ball bearings are often used in pairs.
When the center line of the shaft is different from the center line of the bearing seat, there is an angle error, or the rigidity of the shaft is small due to the large distance between the two supports of the shaft, which is easy to bend or tilt under force, the self-aligning ball or self-aligning roller bearing with good self-aligning performance and outer ball bearing can be selected. This type of bearing can maintain normal operation when the shaft is slightly tilted or bent.
The rigidity of bearing refers to the force required for bearing to produce unit deformation. The elastic deformation of rolling bearing is very small, which can not be considered in most machines, but in some machines, the bearing rigidity is an important factor. Generally, cylindrical and tapered roller bearings should be selected. Because when these two kinds of bearings bear load, their rolling elements and raceways belong to point contact and have poor rigidity. In addition, various bearings can also be preloaded to increase the support rigidity. For example, angular contact ball bearings and tapered roller bearings, in order to prevent shaft vibration and increase support rigidity, a certain axial force is often applied in advance during installation to make them compact with each other.
Each bearing model has its own limit speed, which is determined by physical characteristics such as size, type and structure. The limit speed refers to the high working speed of the bearing (usually R / min). Exceeding this limit will lead to the increase of bearing temperature, the drying of lubricant and even the seizure of the bearing. The speed range required for the application helps to determine what type of bearing to use. D is the bearing size, which usually refers to the pitch diameter of the bearing. When selecting the bearing, use the average value of the bearing inner diameter and outer diameter, in mm. A limiting speed factor (DN) is obtained by multiplying the pitch diameter d by the shaft rotation speed in R / min. DN is very important in the selection of bearing type and size. The product catalogue of most bearing manufacturers provides the limit speed value of their products. Practice has proved that it is better to work under 90% of the limit speed.
Usually, a shaft is supported by two bearings at a certain distance. In order to adapt to different degrees of thermal expansion of shaft and shell, one bearing shall be fixed axially and the other bearing shall be movable on the shaft (i.e. movable support) during installation, so as to prevent jamming caused by shaft elongation or contraction. Cylindrical roller bearings (original 2000 and 32000) and needle roller bearings without retaining edge on the inner or outer ring are usually selected for traveling support, which is mainly because the internal structure of such bearings allows proper axial displacement between the shaft and the housing.
At this time, the inner ring and the shaft, the outer ring and the housing hole can be tightly matched. When the non separable bearing is used as the traveling support, such as deep groove ball bearing and self-aligning roller bearing, the outer ring and housing hole must be allowed in the installation of INA Bearing, or the inner ring and shaft must be loosely matched to make it move freely in the axial direction. Tapered roller bearings, self-aligning roller bearings and deep groove ball bearings basically belong to positioning type. When used as non positioning, they are installed with loose fit. All thrust roller bearings are positioning bearings.
When selecting bearing types, consideration must be given to whether the installation and disassembly of bearings are convenient, especially for the installation and disassembly of large and extra large bearings. The general angular contact ball bearing, tapered roller bearing, cylindrical roller bearing and needle roller bearing with separable outer ring can be installed and disassembled conveniently. Their inner ring and outer ring can be installed on the shaft or in the shell hole respectively. In addition, self-aligning roller bearings with tapered holes in the inner diameter, self-aligning roller bearings with tight sleeves, double row cylindrical roller bearings and self-aligning ball bearings are also easier to install and disassemble.
In addition to the above factors, the working environment temperature of the bearing, bearing seal and special requirements for friction torque, vibration, noise, etc. shall also be considered.