Allowable Space:

During mechanical design, the shaft dimensions are typically determined first, and then bearings are selected based on these dimensions. Generally, small shafts use ball bearings, while large shafts use cylindrical roller bearings, spherical roller bearings, or tapered roller bearings (sometimes ball bearings can also be used). If the radial space for bearing installation is limited, bearings with smaller radial section heights should be used, such as needle roller bearings, certain series of deep groove ball bearings, angular contact ball bearings, cylindrical roller or spherical roller bearings, and thin-section bearings.

Bearing Load:

The load size is usually the determining factor in selecting bearing dimensions. Roller bearings have higher load-carrying capacities compared to ball bearings of the same outer dimensions. Typically, ball bearings are suitable for light or medium loads, while roller bearings are suitable for heavy loads.

For pure radial loads, deep groove ball bearings and cylindrical roller bearings can be used.

For pure axial loads, thrust ball bearings and thrust cylindrical roller bearings can be used.

For combined loads (both radial and axial), angular contact ball bearings or tapered roller bearings are generally chosen.

When the radial load is large and the axial load is small, deep groove ball bearings and cylindrical roller bearings with retaining rings on both the inner and outer rings can be used.

If there are significant shaft or housing deflections and poor alignment during installation, self-aligning ball bearings or self-aligning roller bearings can be used.

For large axial loads and small radial loads, thrust angular contact ball bearings or four-point contact ball bearings can be used. If alignment performance is also required, thrust self-aligning roller bearings can be chosen.

Rotational Speed:

The working speed of rolling bearings mainly depends on their allowable operating temperature. Bearings with low friction and less internal heating are suitable for high-speed applications. When bearings only bear radial loads, deep groove ball bearings and cylindrical roller bearings can achieve high speeds. For combined loads, angular contact ball bearings are recommended. Special high-precision angular contact ball bearings can achieve extremely high speeds. All types of thrust bearings have lower speeds compared to radial bearings.

Rotational Precision:

For most machinery, bearings with tolerance grade 0 are sufficient to meet the main requirements. However, when strict precision is required for shaft rotation, such as in machine tool spindles, precision machinery, and instruments, bearings with higher tolerance grades, such as deep groove ball bearings, angular contact ball bearings, tapered roller bearings, cylindrical roller bearings, and thrust angular contact ball bearings, should be selected.

Rigidity:

The rigidity of rolling bearings is determined by the elastic deformation that occurs when they bear loads. In general, this deformation is very small and can be neglected. However, in some machinery, such as machine tool spindle systems, the static and dynamic stiffness of bearings significantly affect the system's characteristics. Generally, roller bearings have higher stiffness than ball bearings. All types of bearings can be improved to some extent through proper preloading.

Noise and Vibration:

Bearings themselves generally produce low levels of noise and vibration. However, for machinery with special requirements for low noise and smooth operation, such as small electric motors, office equipment, household appliances, and instruments, low-noise bearings are usually chosen.

Axial Movement:

The most common bearing configuration is to install a "fixed bearing" with axial positioning at one end of the shaft and a "floating bearing" with axial movement at the other end to prevent jamming caused by thermal expansion and contraction of the shaft.

Common "floating bearings" are cylindrical roller bearings without retaining rings on the inner or outer ring. In this case, the fit between the inner ring and the shaft or the fit between the outer ring and the housing hole can be a clearance fit. Sometimes, non-separable deep groove ball bearings or self-aligning roller bearings can be used as floating bearings, but in such cases, the fit between the inner ring and the shaft or the fit between the outer ring and the housing hole should be a clearance fit to ensure sufficient axial movement of the inner or outer ring.

Friction Torque:

Ball bearings have lower friction resistance than roller bearings. When subjected to pure radial loads, radial contact bearings have lower friction resistance, while axial contact bearings have lower friction resistance under pure axial loads. For combined loads, bearings with contact angles close to the load angle (e.g., angular contact ball bearings) have the least friction resistance. For instruments and machinery requiring low friction torque, ball bearings or cylindrical roller bearings are more suitable.

Installation and Disassembly:

Bearings with cylindrical bore are preferred for machinery where installation and disassembly are frequent. Separable angular contact ball bearings, tapered roller bearings, separable cylindrical roller bearings, needle roller bearings, and thrust bearings are suitable choices. Bearings with tapered bore can be mounted on shafts or on cylindrical shafts with the help of adapter sleeves or withdrawal sleeves, making installation and disassembly convenient.

In conclusion, bearing selection is a comprehensive process that requires careful analysis of equipment working conditions, load situations, environmental influences, and maintenance requirements, among other factors. By choosing the appropriate bearing type, size, and material, engineers can enhance equipment performance and reliability while reducing the risk of failures, thus providing better mechanical equipment solutions.