How to select bearings
There are many types and sizes of rolling bearings. In order to make the mechanical device play the expected performance, it is very important to choose the most suitable bearing.
In order to select a bearing, it is necessary to analyze many factors, conduct research and evaluate the procedures for selecting bearings from various angles. There are no special specifications, but the general sequence is as follows:
(1) Master the use conditions of mechanical devices and bearings, etc.
(2) Clarify the requirements for bearings
(3) Select the type of bearing
(4) Select the bearing configuration method
(5) Select bearing size
(6) Select bearing specifications
(7) Select the installation method of the bearing
1. Bearing load
Load sizeis usually the deciding factor in selecting the size of the bearing. Roller bearings have greater carrying capacity than ball bearings with the same external dimensions. Usually ball bearings are suitable for light or medium loads, and roller bearings are suitable for heavy loads.
For pure radial load, deep groove ball bearings and cylindrical roller bearings can be selected. For pure axial load, thrust ball bearings and thrust cylindrical roller bearings can be selected. When there is radial load and axial load (combined load), angular contact ball bearings or tapered roller bearings are generally used. If the radial load is large and the axial load is small, deep groove ball bearings and cylindrical roller bearings with ribs on the inner and outer rings can be selected. If there are large shaft or housing deformation and poor installation centering at the same time, self-aligning ball bearings and spherical roller bearings can be selected. If the axial load is large and the radial load is small, thrust angular contact ball bearings can be selected. If the four-point contact ball bearing requires self-aligning performance, thrust spherical roller bearings can be selected.
2. Rotation accuracy
For most machinery, the use of 0-level tolerance bearings is sufficient for use, but when there are strict requirements on the rotation accuracy of the shaft, such as machine tool spindles, precision machinery and instruments, deep groove ball bearings with higher tolerance levels should be selected. Angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and thrust angular contact ball bearings.
3. Noise and vibration
The noise and vibration of the bearing itself are generally very low. But for small and medium motors, office machinery, household appliances, and instruments that have special requirements for noise and smooth operation, low-noise bearings are usually used.
The rigidity of a rolling bearing is determined by the amount of elastic deformation that occurs when it bears a load. Under normal circumstances, this amount of deformation is very small and can be ignored, but in some machinery, such as machine tool spindle systems, the static and dynamic stiffness of the bearing Great influence on the characteristics of the system. Roller bearings have higher stiffness than ball bearings. Various types of bearings can also improve their rigidity to varying degrees through proper "preloading".
5. Rotation speed
The working speed of the rolling bearing mainly depends on its allowable operating temperature. Bearings with low friction resistance and less internal heating are suitable for high-speed operation. When only bearing radial load, deep groove ball bearings and cylindrical roller bearings can be used to achieve higher speeds. When bearing combined loads, angular contact ball bearings should be used. Specially designed high-precision angular contact ball bearings can reach extremely high speeds. The speed of various thrust bearings is lower than that of radial bearings.
6. Allowable space
In mechanical design, the size of the shaft is generally determined first, and then the bearing is selected according to the size of the shaft. Generally, ball bearings are used for small shafts; cylindrical roller bearings, spherical roller bearings, and tapered roller bearings are used for large shafts. If the radial space of the bearing installation part is restricted, a bearing with a smaller radial section height should be used. Such as needle roller bearings, some series of deep groove ball bearings, angular contact ball bearings, cylindrical roller or spherical roller bearings and thin-walled bearings. If the axial space of the bearing installation part is restricted, a bearing with a smaller width dimension can be used.
7. Friction torque
The friction resistance of ball bearings is smaller than that of roller bearings. When pure radial load is applied, the friction resistance of radial contact bearing is small; when pure axial load is applied, the friction resistance of axial contact bearing is small; when combined load is applied, the bearing is in contact Angular contact bearings whose angles are close to the load angle have the least frictional resistance. In instruments and machinery that require low friction torque, ball bearings or cylindrical roller bearings are more appropriate.
8. Axial movement
The common configuration of bearings is to install a set of axially positioned "same bearings" on one end of the shaft, and install a set of axially movable "floating bearings" on the other end to prevent thermal expansion and contraction of the shaft. Stuck phenomenon. The frequently used "floating bearing" is a cylindrical roller bearing with no ribs on the inner ring or outer ring. At this time, the inner ring and the shaft or the outer ring and the housing hole can be fitted with an interference fit. Sometimes non-separable deep groove ball bearings or spherical roller bearings can be used as floating bearings, but when installing the inner ring and shaft or outer ring and the housing hole, clearance fit should be selected to ensure that the inner ring or outer ring has Enough freedom of axial movement.
9. Installation and removal
Bearings with cylindrical bores are used in machines that are frequently installed and disassembled. Separate angular contact ball bearings, tapered roller bearings, separable cylindrical roller bearings, needle roller bearings, thrust bearings, etc. should be preferred. The bearing with a conical inner hole can be installed on the shaft journal, or on the cylindrical shaft journal with the aid of an adapter sleeve or a withdrawal sleeve, which is very convenient for installation and disassembly.
Bearing conditions and environmental conditions
Correctly grasping the location of the bearing in the mechanical device and the conditions of use and environmental conditions are the prerequisites for choosing a suitable bearing. For this, it is necessary to obtain the following data and information:
(1) Function and structure of mechanical device
(2) Where to use the bearing
(3) Bearing load (size, direction)
(4) Rotation speed
(5) Vibration and shock
(6) Bearing temperature (ambient temperature, temperature rise)
(7) Ambient atmosphere (corrosiveness, cleanliness, lubricity)