Various types of bearings have different characteristics due to their different designs.
Due to the variability and complexity of specific installation locations and bearing applications, there is no fixed way to select a bearing type.
In order to adapt to the specific installation position and application conditions of a particular host, it is recommended to comprehensively consider the following main factors when selecting a bearing type.
Criteria for selection of bearings
1. Space allowed
In mechanical design, the shaft size is typically determined first and then the bearing is selected based on the shaft size.
Generally, ball bearings are used for small shafts. Cylindrical roller bearings, spherical roller bearings, and tapered roller bearings are used for large shafts (although ball bearings can also be used).
If the radial space of the bearing installation position is limited, a bearing with a smaller radial section height should be used.
Examples of such bearings include needle 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 position is limited, a bearing with a smaller width can be used.
2. Bearing load
Load size is often the deciding factor in bearing size selection.
The load capacity of roller bearings is greater than that of ball bearings of the same dimensions.
Generally, ball bearings are suitable for light or medium loads, while roller bearings are suitable for supporting heavy loads.
For pure radial loads, deep groove ball bearings and cylindrical roller bearings can be chosen.
For pure axial loads, thrust ball bearings and cylindrical roller thrust bearings can be selected.
When there is a combination of radial and axial loads, angular contact ball bearings or tapered roller bearings are generally selected.
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 is a large deformation of the shaft or housing and poor alignment, spherical ball bearings and spherical roller bearings can be selected.
If the axial load is large and the radial load is small, angular contact thrust ball bearings and four-point contact ball bearings can be selected.
If self-aligning performance is required, spherical roller thrust bearings can be selected.
3.R rotation rate
The working speed of a bearing mainly depends on the permissible operating temperature.
Bearings with low frictional resistance and less internal heating are suitable for high-speed operation.
By supporting only radial loads, deep groove ball bearings and cylindrical roller bearings can reach higher speeds.
If you have combined loads, angular contact ball bearings should be selected.
High precision angular contact ball bearings with special design can reach very high speeds.
The rotational speed of thrust bearings is lower than that of radial bearings.
4. Rotation accuracy
For most machines, bearings with grade 0 tolerance are sufficient to meet the requirements of the main motor.
However, when there are strict requirements on the rotational accuracy of the shaft, such as machine tool spindles, precision machines and instruments, deep groove ball bearings, angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and ball bearings Axial angular contact bearings with higher tolerance levels must be selected.
5.R Healthiness
The stiffness of a bearing is determined by its elastic deformation under load. In general, this deformation is very small and can be ignored. But in some machines, such as machine tool spindle systems, the static stiffness and dynamic stiffness of the bearing have a great influence on the system characteristics.
Generally, roller bearings have greater rigidity than ball bearings. The rigidity of all types of bearings can also be improved through appropriate “pre-tightening”.
6. Noise and vibration
Noise and vibration from the bearing itself is generally very low. However, for small and medium-sized motors, office machines, household appliances and instruments that have special requirements for noise and running stability, low-noise bearings are generally used.
7. Axial movement
The most common configuration for bearings is to install a set of axially positioned “fixed bearings” on one end of the shaft and a set of axially movable “floating bearings” on the other end to prevent the shaft from binding due to thermal expansion and contraction. .
The commonly used “floating bearing” is a cylindrical roller bearing without a rib on the inner 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 may adopt an interference fit.
Sometimes a non-separable deep groove ball bearing or a spherical roller bearing can be selected as a floating bearing, but a clearance fit must be selected when the inner ring matches the shaft or the outer ring matches the bore from the box. during installation, to ensure that the inner or outer ring has sufficient freedom of axial movement.
8.F friction torque
The frictional resistance of a ball bearing is lower than that of a roller bearing, and the frictional resistance of a radial contact bearing is lower under pure radial load.
Similarly, under pure axial load, the frictional resistance of an axial contact bearing is small. Under the combined load, the frictional resistance of an angular contact bearing whose contact angle is close to the load angle is smaller.
In instruments and machines that require low frictional torque, it is more appropriate to choose ball bearings or cylindrical roller bearings.
Furthermore, bearings with low friction torque must avoid contact seals. At the same time, it is suggested to use oil drop lubrication, oil-air lubrication or other lubrication methods that lead to reduced wear.
9. Installation and removal
When bearings with cylindrical inner bores are used in machines that require frequent installation and disassembly, it is recommended to use separable angular contact ball bearings, tapered roller bearings, separable cylindrical roller bearings, needle roller bearings and thrust bearings .
Bearings with tapered inner holes can be installed on the journal or cylindrical journals with the aid of clamping or dismounting bushings, making installation and disassembly more convenient.
Conclusion
In the bearing selection process, considering factors such as durability and precision is essential to achieving optimal performance and longevity. Durability refers to the ability of bearings to withstand various loads and operating conditions without succumbing to wear or failure.
Accuracy, on the other hand, refers to the accuracy of a bearing's rotation and the minimization of noise and vibration during operation.
To ensure durability, it is crucial to select the appropriate bearing size, material and type based on specific requirements and operating conditions. Evaluating factors such as speed, temperature and lubrication can significantly impact the lifespan and overall performance of a bearing.
Additionally, adherence to ISO-approved methodologies for bearing sizing can help ensure appropriate load ratings and life expectancy for a given application.
Accuracy in bearing selection is achieved by examining application requirements such as desired rotational accuracy, speed and loading conditions. Selection of bearings with appropriate tolerances and clearances, along with compatible sealing and adequate lubrication, contributes to greater precision and reliability.
In conclusion, a thorough understanding of bearing selection criteria is necessary for successful implementation across multiple industries. By considering durability and accuracy in the selection process, engineers and designers can optimize system performance and extend bearing life.
As a result, potential mechanical problems and costly maintenance processes can be reduced, ultimately leading to the overall success of countless projects and applications.
