9 Factors to Be Considered In Bearing Selection

Various types of bearings have different characteristics due to different designs.

Due to the variability and complexity of the specific installation location and application of bearings, there is no fixed mode for bearing type selection

In order to adapt to the specific installation position and application conditions of a certain host, it is suggested to consider the following main factors comprehensively when selecting the bearing type.

1. Allowed 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, self-aligning roller bearings and tapered roller bearings are used for large shafts (sometimes ball bearings are also used).

If the radial space of the bearing installation position is limited, the bearing with smaller radial section height should be used.

Such as needle bearings, some series of deep groove ball bearings, angular contact ball bearings, cylindrical roller or self-aligning roller bearings and thin-walled bearings.

If the axial space of the bearing installation position is limited, the bearing with smaller width can be used.

Factors To Be Considered In Bearing Selection

2. Bearing load

Load size load size is usually the decisive factor in the selection of bearing size.

The bearing capacity of roller bearing is larger than that of ball bearing with the same dimension.

Generally, ball bearing is suitable for light or medium load, roller bearing is suitable for bearing heavy load.

Load mode pure radial load can choose deep groove ball bearing, cylindrical roller bearing.

Pure axial load can choose thrust ball bearing, thrust cylindrical roller bearing.

When there is radial load and axial load (combined load), angular contact ball bearing or tapered roller bearing is generally selected.

If the radial load is large and the axial load is small, deep groove ball bearing and cylindrical roller bearing with rib in inner and outer ring can be selected.

In case of large deformation of shaft or shell and poor alignment, self-aligning ball bearing and self-aligning roller bearing can be selected.

If the axial load is large and the radial load is small, thrust angular contact ball bearing and four point contact ball bearing can be selected.

If the self-aligning performance is required, the thrust self-aligning roller bearing can be selected.

Factors To Be Considered In Bearing Selection

3. Rotation rate

The working speed of 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 only bearing radial load, deep groove ball bearing and cylindrical roller bearing can achieve higher speed

If bearing combined load, angular contact ball bearing should be selected.

High precision angular contact ball bearing with special design can achieve very high speed.

The rotation speed of thrust bearing is lower than that of radial bearing.

4. Rotation accuracy

For most machines, the bearing with grade 0 tolerance is enough to meet the requirements of the main engine.

However, when there are strict requirements on the rotation accuracy of the shaft, such as machine tool spindle, precision machinery and instruments, the deep groove ball bearing, angular contact ball bearing, tapered roller bearing, cylindrical roller bearing and thrust angular contact ball bearing with higher tolerance level should be selected.

Factors To Be Considered In Bearing Selection

5. Rigidity

The rigidity of rolling 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 system, the static stiffness and dynamic stiffness of the bearing have great influence on the characteristics of the system.

Generally speaking, roller bearings have higher stiffness than ball bearings.

The rigidity of all kinds of bearings can also be improved by proper “pre tightening”.

6. Noise and vibration

The noise and vibration of the bearing itself are generally very low.

But for small and medium-sized motors, office machinery, household appliances and instruments, which have special requirements for noise and running stability, low-noise bearings are usually used.

7. Axial movement

The most common configuration of bearings is to install a set of axially positioned “fixed bearing” at one end of the shaft and a set of axially movable “floating bearing” at the other end to prevent the shaft from sticking due to thermal expansion and cold contraction.

The commonly used “floating bearing” is the cylindrical roller bearing with no 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 shell hole can adopt interference fit.

Sometimes, non separable deep groove ball bearing or self-aligning roller bearing can be selected as floating bearing, but clearance fit should be selected when inner ring is matched with shaft or outer ring is matched with housing hole during installation, so as to ensure that inner ring or outer ring has enough freedom of axial movement.

Factors To Be Considered In Bearing Selection

8. Friction torque

The friction resistance of ball bearing is smaller than that of roller bearing, and the friction resistance of radial contact bearing is smaller under pure radial load;

The results show that the friction resistance of axial contact bearing is small under pure axial load;

Under the combined load, the friction resistance of the angular contact bearing whose contact angle is close to the load angle is the smallest.

In the instruments and machines that need low friction torque, it is more appropriate to choose ball bearing or cylindrical roller bearing.

In addition, low friction torque bearings should avoid contact seal

At the same time, it is suggested to use oil drop lubrication, oil air lubrication or other lubrication methods which are conducive to reducing wear.

9. Installation and removal

When the bearings with cylindrical inner holes are used in the machinery with frequent installation and disassembly, the separated angular contact ball bearings, tapered roller bearings, separable cylindrical roller bearings, needle roller bearings and thrust bearings should be preferred.

The bearing with conical inner hole can be installed on the journal, or on the cylindrical journal with the help of fixing sleeve or dismounting sleeve, so the installation and disassembly are very convenient.

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