There are seven factors to consider in the selection of bearings.
All kinds of rolling bearings have different characteristics and are suitable for different use of all kinds of machinery.
In general, thrust bearing and angular contact bearing are used when bearing thrust load. High-speed applications usually use ball bearings; When bearing heavy radial load, roller bearings are used.
1. The space and position of the machine occupied by 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. Usually the small shaft selection of ball bearings, the large shaft selection of roller bearings. However, when the bearing is limited in the direction of the diameter of the machine, needle roller bearings, ultra-light, and ultra-light series of the ball or roller bearings are selected; When the bearing is limited in the axial position of the machine, narrow or extra-narrow series of the ball or roller bearings can be selected.
2. The size, direction, and nature of the load on the bearing
Load is the most important factor in the selection of bearings. Roller bearings are used to withstand heavier loads, ball bearings are used to withstand lighter or moderate loads, and bearings made of carburized carbon steel or bainitic quenching can withstand impact and vibration loads.
In terms of the direction of load, when bearing pure radial load, deep groove ball bearings, cylindrical roller bearings, or needle roller bearings can be used. When bearing a small pure axial load, the thrust ball bearing can be selected; When bearing a large pure axial load, the thrust roller bearing can be used. When a bearing bears radial and axial combined load, an angular contact ball bearing or tapered roller bearing is generally used.
3. Self-aligning performance of bearings
When the center line of the shaft is different from the center line of the bearing seat, there is an Angle error, or the rigidity of the shaft is small because of the large distance between the two supports of the shaft, and it is easy to be bent or tilted by force, the self-aligning ball or self-aligning roller bearings with good self-aligning performance can be selected, as well as external ball bearings. This kind of bearing can keep working normally when the shaft is slightly tilted or bent.
The quality of bearing self-aligning performance is related to the allowable different coaxiality. The greater the value of different coaxiality, the better the self-aligning performance.
4. Rigidity of bearings
The rigidity of the bearing refers to the size of the force required by the bearing to produce unit deformation. Rolling bearing elastic deformation is very small, in most machinery can not be considered, but in some machinery, such as machine tool spindle, bearing rigidity is an important factor, generally should choose cylindrical and tapered roller bearings. Because these two kinds of bearings under load, the rolling body and raceway belong to point contact, the rigidity is poor.
In addition, all kinds of bearings can also be pretightened to increase the rigidity of the support. Such as angular contact ball bearings and tapered roller bearings, in order to prevent the vibration of the shaft, increase the rigidity of the support, often in the installation of a certain amount of axial force is applied in advance, so that they compress each other. But the preload can not be too large, otherwise it will increase bearing friction, increase temperature rise, affect the service life of bearings.
5. Speed of bearings
Each bearing model has its own limit speed, which is determined by physical characteristics such as size, type and structure. Exceeding this limit will cause bearing temperature to rise, lubricant to dry up, and even make bearing stuck. Practice has proved that it is better to work under the condition of 90% limit speed.
The ultimate speed of grease lubricated bearings is lower than that of oil lubricated bearings. It must be noted that for grease lubricated bearings, their limit speed is generally only 80% of the bearing's limit speed when using a high-quality repeating cycle oil system, but for oil mist lubrication systems, their limit speed is generally 50% higher than the same basic lubrication system. The design and structure of cage also affect the ultimate speed of bearing.
6. Bearing swimming and axial displacement
Normally, a shaft is supported by two bearings spaced a certain distance apart. In order to adapt to the influence of different degrees of thermal expansion of the shaft and the shell, one bearing should be fixed in the axial direction when installing, and the other bearing should be able to swim on the shaft (that is, the swimming support), in order to prevent the phenomenon of jamming caused by the elongation or contraction of the shaft.
7. Easy to install and disassemble bearings
When selecting bearing types, it is also necessary to consider whether it is convenient to install and disassemble, especially the installation and disassembly of large and extra-large bearings.
Bearing is an important part of mechanical equipment.
Reasonable selection, correct operation, and maintenance can effectively improve the performance and service life of bearings and equipment.