How to choose bearing type
Located in Cixi, China, where is one of the biggest bearing manufacturer center in China. There are thousands of bearing factory from big and small.Our place is famous for miniature bearing and precise bearings.We hereby wish to share our experience of choosing suitable bearings.
Generally speaking, the steps for selecting a bearing may be summarized as:
1. According to bearing working conditions (including load direction and load type, speed, lubrication method, coaxiality requirements, positioning or non-positioning, installation and maintenance environment, ambient temperature, etc.), select the basic bearing type, tolerance level and clearance;
2. Determine the bearing model through calculation according to the working conditions, stress and life requirements of the bearing, or select the bearing model according to the use requirements, 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, required life and load capacity. Other factors help determine the final plan of bearing type, structure, size and tolerance level and clearance requirements.
Bearing Type selection
Various types of rolling bearings have different characteristics and are suitable for different use situations of various machines. When selecting the bearing type,
The following factors should generally be considered. Under normal circumstances: choose thrust bearings and angular contact bearings when bearing thrust loads, ball bearings are usually used for high-speed applications, and roller bearings when bearing heavy radial loads. In short, the selection personnel should select the appropriate type from different manufacturers and numerous bearing products.
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, ball bearings are used for small shafts, and roller bearings are used for large shafts. However, when the bearing is restricted in the diameter direction of the machine, needle roller bearings, extra-light and ultra-light series ball or roller bearings are selected; when the axial position of the bearing is restricted in the machine, narrow or special bearings can be selected. Narrow series of ball or roller bearings.
The size, direction and nature of the load on the bearing
Load is the most important factor in selecting bearings. Roller bearings are used to bear heavier loads, and ball bearings are used to bear light or medium loads. Bearings made of carburized steel or bainite quenched can bear shock and vibration loads.
In terms of the direction of the load, deep groove ball bearings, cylindrical roller bearings or needle bearings can be selected when bearing pure radial loads. When bearing a small pure axial load, a thrust ball bearing can be selected; when bearing a larger pure axial load, a thrust roller bearing can be selected. When the bearing is subjected to combined radial and axial loads, angular contact ball bearings or tapered roller bearings are generally used.
Bearing’s self-aligning performance
When the center line of the shaft is different from the center line of the bearing seat, there is an angular error, or the shaft has a relatively large distance between the two supports and the shaft has a small rigidity, which is easy to bend or tilt. Center ball or spherical roller bearings, and outer ball bearings. This type of bearing can maintain normal operation when the shaft is slightly tilted or bent.
The rigidity of the bearing
The rigidity of a 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 it is not necessary to consider in most machines, but in some machines, such as machine tool spindles, bearing rigidity is an important factor. Generally, cylindrical and tapered roller bearings should be used. Because these two types of bearings bear the load, their rolling elements and raceways are in point contact, and the rigidity is poor.
In addition, various types of bearings can also be pre-tightened to achieve the purpose of increasing the supporting rigidity. For example, angular contact ball bearings and tapered roller bearings, in order to prevent shaft vibration and increase supporting rigidity, a certain axial force is often applied in advance during installation to make them compress each other. It is particularly pointed out here that the preload amount should not be too large. When it is too large, the friction of the bearing will increase, the temperature rise will increase, and the service life of the bearing will be affected.
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 refers to the maximum working speed of the bearing (usually r∕min). This causes the bearing temperature to rise, the lubricant dries up, and even causes the bearing to seize.
Generally speaking, deep groove ball bearings, angular contact bearings, and cylindrical roller bearings should be selected for higher speed working occasions; for lower speed working occasions, tapered roller bearings can be selected. The limiting 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 for lower speed occasions.
For the same type of bearing, the smaller the size, the higher the allowable speed. When selecting bearings, care should be taken to keep the actual speed lower than the limit speed.
Bearing movement and axial displacement
Normally, a shaft is supported by two bearings separated by a certain distance. In order to adapt to the different degrees of thermal expansion of the shaft and housing, one bearing should be fixed in the axial direction during installation, and the other bearing should be allowed to move on the shaft (that is, floating support) to prevent the extension or contraction of the shaft. The stuck phenomenon caused by. The floating support usually uses cylindrical roller bearings (formerly 2000 and 32000) and needle roller bearings with no ribs on the inner ring or outer ring. This is mainly because the internal structure of this type of bearing allows proper axial displacement of the shaft and the housing. . At this time, the inner ring and the shaft, the outer ring and the housing hole can adopt a tight fit. When non-separable bearings are used for floating support, such as deep groove ball bearings and spherical roller bearings, the outer ring and the housing hole, or the inner ring and the shaft must be loosely matched during installation, so that the axial direction can be Free swimming.
Facilitate the installation and disassembly of the bearing
When selecting the bearing type, it is necessary to consider whether it is convenient to install and disassemble the bearing, especially for the installation and disassembly of large and super large bearings. General angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and needle roller bearings with separable outer rings are more convenient to install and disassemble. Their inner and outer rings can be mounted on the shaft or in the housing hole respectively. In addition, spherical roller bearings with an adapter sleeve, double-row cylindrical roller bearings and self-aligning ball bearings with a tapered bore in the inner diameter are also easier to install and disassemble.
Other requirements
In addition to the above factors, the working environment temperature of the bearing, bearing sealing, and special requirements for friction torque, vibration, and noise should also be considered.
