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Due to the variability and complexity of the specific installation of the bearing, it is recommended to comprehensively consider the following main factors when selecting the bearing type.
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, the small shaft adopts ball bearing; Cylindrical roller bearing, self-aligning roller bearing and tapered roller bearing (sometimes ball bearing can also be selected) are selected for the main shaft. If the radial space of the bearing installation position is limited, the bearing with a small radial section height shall be used. Such as needle roller bearings, some series of deep groove ball bearings, angular contact ball bearings, cylindrical roller or self-aligning roller bearings and thin-wall bearings. If the axial space of the bearing installation part is limited, the bearing with smaller width can be used.
The magnitude of the load is usually the determining factor in the selection of bearing size. General selection skills are:
(1) The bearing capacity of roller bearings is larger than that of ball bearings with the same overall dimensions. Generally, ball bearings are suitable for light or medium load, and roller bearings are suitable for heavy load;
(2) Load mode: deep groove ball bearing and cylindrical roller bearing can be selected for pure radial load;
(3) Thrust ball bearing and thrust cylindrical roller bearing can be selected for pure axial load;
(4) When there is radial load and axial load (combined load), angular contact ball bearing or tapered roller bearing is generally selected;
(5) If the radial load is large and the axial load is small, deep groove ball bearings and cylindrical roller bearings with retaining edges on the inner and outer rings can be selected;
(6) In case of large deformation of shaft or shell and poor installation alignment, self-aligning ball bearing and self-aligning roller bearing can be selected;
(7) If the axial load is large and the radial load is small, the thrust angular contact ball bearing can be selected. If the four-point contact ball bearing also requires centring performance, the thrust self-aligning roller bearing can be selected.
The working speed of the rolling bearing mainly depends on its allowable operating temperature. The bearing with low friction resistance and less internal heating is suitable for high-speed operation. When bearing only radial load, deep groove ball bearing and cylindrical roller bearing can achieve high speed. If bearing combined load, angular contact ball bearing should be selected. The specially designed high-precision angular contact ball bearing can achieve extremely high speed. The speed of various thrust bearings is lower than that of radial bearings.
For most machines, the bearings with Class 0 tolerance are sufficient to meet the requirements of the main engine, but when there are strict requirements on the rotation accuracy of the shaft, such as machine tool spindle, precision machinery and instruments, deep groove ball bearings, angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and thrust angular contact ball bearings with higher tolerance levels shall be selected.
The rigidity of rolling bearing is determined by its elastic deformation when bearing load. Generally, this deformation is very small and can be ignored. However, in some machines, such as machine tool spindle systems, the static stiffness and dynamic stiffness of bearings have a great impact on the characteristics of the system. Generally speaking, roller bearings have higher stiffness than ball bearings. The rigidity of various bearings can also be improved to varying degrees through appropriate “pre tightening”.
6. Noise and vibration
The noise and vibration of the bearing itself are generally very low. However, for small and medium-sized motors, office machinery, household appliances, instruments and other machinery with special requirements for noise and running stability, low-noise bearings are usually selected.
The common configuration of bearings is to install a set of axially positioned “fixed bearings” at one end of the shaft and a set of axially movable “floating bearings” at the other end to prevent jamming due to thermal expansion and cold contraction of the shaft. The frequently used “travelling bearing” is a cylindrical roller bearing without retaining an edge on the inner ring or outer ring. At this time, the fit between the inner ring and the shaft or the fit between the outer ring and the housing hole can adopt interference fit. Sometimes, the non-separable deep groove ball bearing or self-aligning roller bearing can also be selected as the travelling bearing, but during installation, the clearance fit shall be selected for the fit between the inner ring and the shaft or the outer ring and the shell hole, so as to ensure that the inner ring or outer ring has enough freedom of axial movement.
The friction resistance of ball bearing is smaller than that of roller bearing. Under pure radial load, the friction resistance of radial contact bearing is small; Under a pure axial load, the friction resistance of axial contact bearing is small; Under combined load, the friction resistance of angular contact bearing with similar bearing contact angle and load angle is small. Ball-bearing or cylindrical roller bearing is more suitable for instruments and machines requiring low friction torque. In addition, contact sealing should be avoided for low friction torque bearings. At the same time, it is recommended to use drip lubrication, oil-gas lubrication or other lubrication methods conducive to wear reduction.
Bearings with cylindrical inner holes are used in machines with frequent installation and disassembly. Separate angular contact ball bearings, tapered roller bearings, separable cylindrical roller bearings, needle roller bearings and thrust bearings should be preferred. The bearing with a conical inner hole can be installed on the journal or sleeved on the cylindrical journal with the help of a tightening sleeve, which is very convenient for installation and disassembly.