1) Machinery has various working conditions. In order to meet these specific use requirements, different types of bearings are needed to ensure actual needs. According to the shape of the rolling element, rolling bearings can be roughly divided into ball bearings and roller bearings; according to the main direction of the load, they can be divided into radial bearings and thrust bearings. Table 1 is a comparison of the general characteristics of ball bearings and roller bearings. Table 1 Comparison of general characteristics of ball bearings and roller bearings According to the national standard GB/T272-93, the commonly used types of rolling bearings can be found in the database.

2) Selection of rolling bearing types There are many types of rolling bearings. When selecting, the following factors can be considered to make a selection.

1. The size, direction and nature of the load: ball bearings are suitable for light loads, and roller bearings are suitable for heavy loads and impact loads. When the rolling bearing is subjected to pure axial load, thrust bearings are generally selected; when the rolling bearing is subjected to pure radial load, deep groove ball bearings or short cylindrical roller bearings are generally selected; when the rolling bearing is subjected to pure radial load and small axial load, deep groove ball bearings, angular contact ball bearings, tapered roller bearings and self-aligning balls or self-aligning roller bearings can be selected; when the axial load is large, angular contact ball bearings and tapered roller bearings with large contact angles can be selected, or radial bearings and thrust bearings can be combined together, which is particularly suitable for extremely high axial loads or special requirements for greater axial rigidity. 2. Allowable speed: There are great differences due to different types of bearings. Generally speaking, bearings with low friction and low heat generation are suitable for high speeds. When designing, it is necessary to strive for the rolling bearing to work under conditions below its limit speed. 3. Rigidity: When the bearing is under load, elastic deformation will occur at the contact between the bearing ring and the rolling element. The deformation is proportional to the load, and the ratio determines the size of the bearing rigidity. Generally, the rigidity of the bearing can be improved by preloading the bearing; in addition, in the bearing support design, considering the combination and arrangement of the bearings can also improve the bearing support rigidity.

4. Self-aligning performance and installation error: After the bearing is installed in the working position, it is often installed and positioned poorly due to manufacturing errors. At this time, the bearing is often subjected to excessive load due to shaft deflection and thermal expansion, causing early damage. Self-aligning bearings can overcome the defects caused by installation errors by themselves, so they are suitable for such purposes.

5. Installation and disassembly: Tapered roller bearings, needle roller bearings and tapered roller bearings, etc., are bearings with separable inner and outer rings (so-called separable bearings), which are easy to install and disassemble.