How to choose best bearings with 8 points?
In general, the steps for selecting best bearings may be summarized as:
1. According to best bearings operating conditions (including load direction and load type, speed, lubrication method, concentricity requirements, positioning or non-locating, installation and maintenance of the environment, ambient temperature, etc.), select the basic bearing types, tolerance levels and clearance;
2. According to best bearings working conditions and force conditions and life requirements, determine the bearing model by calculation, or according to the use requirements, select the bearing model, and then verify the life;
3. Check the rated load and limit speed of the selected best bearings.
The main considerations in selecting a bearing are the limiting speed, the required life and load capacity, and other factors that will help determine the final type of bearing type, structure, dimensions and tolerance levels and clearance requirements.
Various types of rolling bearings have different characteristics and are suitable for different uses of various machines. When selecting the bearing type,
The following factors should generally be considered. Under normal circumstances: Thrust bearings and angular contact bearings are used for thrust loads. Ball bearings are usually used for high-speed applications. When heavy radial loads are applied, roller bearings are used. In short, the selection personnel should choose the right type from different manufacturers and many bearing products.
• The space and position of the machinery occupied by the best bearings
In the 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 small shafts use ball bearings, large shafts use roller bearings. However, when the bearing is limited in the diameter direction of the machine, needle roller bearings, special light and ultra-light series ball or roller bearings are selected; when the bearing is limited in the axial position of the machine, narrow or special Narrow series ball or roller bearings.
• The size, direction and nature of the load on the best bearings
Load is the most important factor in selecting a bearing. Roller bearings are used for heavier loads. Ball bearings are used for lighter or medium loads. Carburized steel or bainite-quenched bearings can withstand shock and vibration loads.
With respect to the direction of the applied load, deep groove ball bearings, cylindrical roller bearings or needle roller bearings can be used when subjected to pure radial loads. The thrust ball bearing can be used when the pure axial load is small, and the thrust roller bearing can be used when the pure axial load is large. When the bearing bears radial and axial joint loads, angular contact ball bearings or tapered roller bearings are generally used.
• Bearing alignment performance
When the center line of the shaft is different from the center line of the bearing seat, there is an angle error, or the shaft rigidity is small due to the large distance between the two bearings of the shaft, and when the force is bent or tilted easily, the tune with good alignment performance can be selected. Ball or spherical roller bearings, and ball bearings. This type of bearing maintains normal operation when the shaft is slightly tilted or bent.
The performance of best bearings alignment is related to the different degrees of allowable shafts. The greater the value of different shaft degrees, the better the alignment performance.
• Bearing rigidity
The rigidity of the best bearingsrefers to the magnitude of the force required to deform the unit by the bearing. Rolling bearing elastic deformation is very small, in most machines can not be considered, but in some machinery, such as machine tool spindle, bearing rigidity is an important factor, generally should use cylindrical and tapered roller bearings. Because these two types of bearings are under load, their rolling elements are in point contact with the raceways and their rigidity is poor.
In addition, all types of bearings can also be pre-tightened to increase the rigidity of the support. Such as angular contact ball bearings and tapered roller bearings, in order to prevent shaft vibration, increase the support rigidity, often in the installation of a certain amount of axial force in advance, so that they compact each other. Here specifically pointed out that the amount of preloading should not be excessive. 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.
• best bearings 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 operating speed of the best bearings (usually r∕min), beyond which the limit will be exceeded. Causes the bearing temperature to rise, the lubricant to dry up, even causes the bearing to be stuck.
The speed range required for the application occasion helps to decide what type of bearing to use. D is the bearing size. It usually refers to the diameter of the pitch circle of the bearing. When selecting the bearing, use the average value of the inside and outside diameter of the bearing in mm.
A limit rotational speed factor (DN) is obtained by multiplying the pitch circle diameter D by the shaft rotation speed (in r/min). DN is very important when selecting the bearing type and size. Most bearing manufacturers’ product catalogs provide the limit speed value of their products. Practice has proved that it is better to work under 90% of the limit speed.
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 limiting speed is generally only 80% of the limiting speed when the bearing uses a high quality recirculating oil system, but for oil mist lubrication system, the limiting speed is generally higher than the same basic lubrication system. 50% higher.
The design and structure of the cage also affect the rotational speed of the bearing, because the rolling elements are in sliding contact with the cage surface. The more expensive, well-designed cages made of high quality and low friction material not only allow rolling The body is separated and helps maintain the lubricant film in the sliding contact area. However, inexpensive cages such as stamped cages usually only keep the rolling elements apart. As a result, they are subject to accidental and distressing sliding contact, which leads to a lower limit speed.
In general, deep groove ball bearings, angular contact bearings, and cylindrical roller bearings should be used in high-speed working environments. In low-speed applications, tapered roller bearings can be used. 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 speed limit and can only be used for lower speed applications.
For the same type of bearing, the smaller the size, the higher the allowable rotation speed. When selecting bearings, care should be taken to keep the actual speed below the limit speed.
• the best bearings movement and axial displacement
Normally, a shaft is supported by two bearings at a certain distance. In order to adapt to different degrees of thermal expansion effects of the shaft and the housing, one bearing should be fixed in the axial direction during installation, and the other bearing can be moved on the shaft (ie, the floating support) to prevent the shaft from being extended or contracted. Caused stuck. Floating bearings usually use cylindrical roller bearings with inner or outer rings without ribs (formerly Type 2000 and Type 32000) and needle roller bearings. This is mainly due to the fact that the internal structure of such bearings allows proper axial displacement of the shaft and the housing. . At this point, the inner ring and the shaft, the outer ring and the housing hole can be tightly fitted. When the non-separable bearing is used for floating support, such as deep groove ball bearings and self-aligning roller bearings, the outer ring and the housing hole must be allowed in the installation, or the inner ring and the shaft must be loosely fitted so that the shaft can be axially Free to swim.
Tapered roller bearings, self-aligning roller bearings and deep groove ball bearings basically belong to the positioning type. When used as a non-positioning device, they are loosely fitted. All thrust roller bearings are positioning bearings.
• Convenient for mounting and dismounting of bearings
When selecting the type of bearing, it is necessary to consider whether it is convenient to install and disassemble the bearing, and it is especially important to install and disassemble the large and extra large bearings. General outer ring detachable angular contact ball bearings, tapered roller bearings, cylindrical roller bearings and needle roller bearings, installation and removal more convenient, their inner and outer rings can be installed on the shaft or the housing hole. In addition, self-aligning roller bearings, double-row cylindrical roller bearings and self-aligning ball bearings with inner bores with tapered bore, adapter sleeves are also easier to install and remove.
• other request
In addition to the above factors, the best bearings operating temperature, bearing seals, and special requirements for frictional torque, vibration, and noise must also be considered.
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