How to choose the right bearing? When selecting a bearing, it depends on several important parameters: bearing load, bearing speed, centering requirements, allowable space, bearing installation and disassembly, tolerance class, and price. Bearings mainly support and reduce friction in the machine, so the accuracy and noise of the bearings are directly related to the use and life of the machine.

In general, the steps to select a bearing may be summarized as:

1. According to the bearing working conditions, including load direction and type, speed, lubrication method, coaxiality requirements, positioning or non-positioning, installation and maintenance environment, ambient temperature, etc., select the basic type of bearing, tolerance level and clearance;

2. According to the working conditions of the bearing and the force and life requirements, determine the bearing model by calculation, or select the bearing model according to the requirements of use, and then check the life;

3. Check the rated load and limit speed of the selected bearing.

The main considerations for selecting a bearing are the limit speed and load capacity. Other factors help determine the final solution for bearing type, structure, size and tolerance class and clearance requirements.

7 factors to consider when choosing a bearing

Various types of rolling bearings have different characteristics and are suitable for different use cases of various machines. In general, thrust bearings and angular contact bearings are used for thrust loads; ball bearings are usually used for high-speed applications, and roller bearings are used for heavy radial loads.

1. The space and position of the bearing

In mechanical design, the size of the shaft is generally determined first, and then the rolling bearing is selected according to the size of the shaft. Ball bearings are usually used for small shafts and roller bearings for large shafts. However, when the bearing is limited in the diameter direction of the machine, needle roller bearings, ultra-light and ultra-light series of ball or roller bearings are used; when the bearing is limited in the axial position of the machine, narrow or special can be used. Narrow series of ball or roller bearings.

2. The magnitude, direction and nature of the load on the bearing

The load is the most important factor in the selection of bearings. Roller bearings are used to withstand heavy loads. Ball bearings are used to withstand light or medium loads. Carburized steel or bainite quenched bearings can withstand shock and vibration loads.

In the direction of the action of the load, deep groove ball bearings, cylindrical roller bearings or needle bearings can be used when subjected to pure radial loads. Thrust ball bearings are available for small pure axial loads and thrust roller bearings for large pure axial loads. Angular contact ball bearings or tapered roller bearings are generally used when the bearings are subjected to combined radial and axial loads.

3. Bearing alignment performance

When the center line of the shaft is different from the center line of the bearing housing, there is an angular error, or the shaft has a small rigidity and the rigidity of the shaft is small, and it is easy to be bent or tilted by force, and the self-aligning with good self-aligning performance can be selected. Ball or spherical roller bearings, as well as outer ball bearings. These bearings remain functional when the shaft is slightly tilted or bent.

The quality of the bearing’s self-aligning performance is related to the different axial degrees allowed. The larger the different axial values, the better the self-aligning performance.

4. Bearing rigidity

The rigidity of the bearing refers to the amount of force required to produce a unit deformation of the bearing. The elastic deformation of rolling bearings is very small and can be ignored in most machines. However, in some machines, such as machine tool spindles, bearing rigidity is an important factor. Cylindrical and tapered roller bearings are generally used. Because these two types of bearings are subjected to load, their rolling elements and raceways are in point contact and have poor rigidity.

In addition, various types of bearings can also be pre-tensioned to achieve the purpose of increasing the rigidity of the support. For example, angular contact ball bearings and tapered roller bearings, in order to prevent the vibration of the shaft and increase the rigidity of the support, a certain axial force is often applied at the time of installation to press them against each other. Here specifically pointed out: the amount of preload should not be too large. When it is too large, the friction of the bearing will increase and the temperature rise will increase, which will affect the service life of the bearing.

5. Bearing speed

Each bearing model has its own limit speed, which is determined by physical characteristics such as size, type and structure. The limit speed is the maximum working speed of the bearing (usually in r/min). This causes the bearing temperature to rise, the lubricant to dry out, and even the bearing to jam.

The range of speeds required for the application will help determine which type of bearing to use. Most bearing manufacturers’ catalogues provide limit values for their products. It has been proven that working at temperatures below 90% of the limit speed is better.

The limit rotation speed of the grease-lubricated bearing is lower than the limit rotation speed of the oil-lubricated bearing, and the oil supply mode of the bearing has an influence on the achievable limit rotation speed. It must be noted that for grease-lubricated bearings, the limit speed is generally only 80% of the limit speed of the bearing using a high-quality recirculating oil system, but for oil mist lubrication systems, the limit speed is generally the same as the basic lubrication system. 50% higher.

The design and construction of the cage also affects the ultimate speed of the bearing, since the rolling elements are in sliding contact with the surface of the cage. Not only can the scrolls be made of expensive, well-designed cages of high quality and low friction material. The body is spaced apart and helps to maintain the lubricating oil film in the sliding contact zone.

However, inexpensive cages such as stamped cages usually only keep the rolling elements apart. As a result, they have accidental and annoying sliding contact, resulting in lower limit speeds.

Generally speaking, in the case of higher speed working, deep groove ball bearings, angular contact bearings and cylindrical roller bearings should be used; in the case of lower speed working, tapered roller bearings can be used. The limit speed of tapered roller bearings is generally about 65% of deep groove ball bearings, 70% of cylindrical roller bearings, and 60% of angular contact ball bearings. Thrust ball bearings have a low limit speed and can only be used in lower speed applications.

For the same type of bearing, the smaller the size, the higher the allowable speed. When selecting a bearing, care should be taken to make the actual speed lower than the limit speed.

6. Bearing movement and axial displacement

Typically, a shaft is supported by a distance between two bearings. In order to adapt to the different degrees of heat rise of the shaft and the outer casing, one bearing should be fixed in the axial direction during installation, and the other bearing can be moved on the shaft (ie, swimming support) to prevent the shaft from being elongated or contracted. The resulting jamming phenomenon.

The floating support usually adopts cylindrical roller bearings (formerly 2000 and 32000) with inner or outer ring without ribs and needle bearings. This is mainly because the internal structure of such bearings allows proper axial displacement of the shaft and the outer casing. . At this time, the inner ring and the shaft, the outer ring and the outer casing hole can be tightly fitted. When using non-separable bearings for swimming support, such as deep groove ball bearings, spherical roller bearings, the outer ring and the outer casing hole must be allowed in the installation, or the inner ring and the shaft should be loosely fitted to make the axial direction Free to swim.

Tapered roller bearings, spherical roller bearings and deep groove ball bearings are basically of the positioning type, and when used as non-positioning, they are loosely mounted. All thrust roller bearings are positional bearings.

7. Easy to install and disassemble the bearing

When selecting the bearing type, it is convenient to install and disassemble the bearing, and it must be considered comprehensively, especially for the installation and disassembly of large and extra large bearings. The general outer ring separable angular contact ball bearing, tapered roller bearing, cylindrical roller bearing and needle roller bearing are convenient to install and disassemble, and their inner and outer rings can be respectively mounted on the shaft or the housing hole. In addition, spherical roller bearings with inner diameter and tapered bore, spherical roller bearings with double-row cylindrical roller bearings and self-aligning ball bearings are also easier to install and disassemble.