In the support portion of the machine, in order to prevent the bearing inner ring and the shaft, the outer ring and the outer ring hole from sliding relative to each other during the operation of the machine, a simple and effective method must be adopted. Especially for the thin-walled ferrules of the ultra-light and ultra-light series bearings, the proper tight fit can make the bearing rings have a uniform force during operation, so that the bearing capacity of the bearing rolling elements can be fully utilized. However, the selected bearing fit cannot be too tight, because the elastic expansion of the inner ring and the contraction of the outer ring will reduce the internal clearance of the bearing until it completely disappears, thus affecting the normal operation of the bearing.
1. Bearing matching
(1) Bearings with cylindrical bores
The main factors that should be considered when choosing a bearing fit are as follows:
1 type of load
According to the load acting on the bearing, the load on the ferrule can be divided into three types: fixed load, swing load and swing load.
Fixed load
The resultant radial load is absorbed by the local area of the ferrule raceway and is correspondingly transmitted to the corresponding local area wind of the shaft or housing mating surface. This load is called a fixed load.
The fixed load is characterized by a synthetic radial load that is relatively stationary with the ferrule. A ferrule that is subjected to a fixed load is generally available with a looser fit.
b. swing load
The resultant radial load vector acting on the bearing ring rotates in the circumferential direction of the raceway, is in turn received by the various parts of the raceway, and is correspondingly transmitted to various parts of the surface of the shaft housing bore. This type of load is called a swing load, also known as a cyclic load.
The slewing load is characterized by a synthetic radial load vector and a relative rotation of the ferrule. Filters or interference fits should be used for the ferrules that bear the slewing load and the shaft or housing bore. If the gap is used for the installation, slippage will occur between them, which will cause the contact surface to wear and friction, and the temperature will rise sharply and the bearing will be damaged quickly. The size of the wanted excess is determined by the operation. When the bearing is working under load, the principle of “crawling” on the mating surface of the shaft or the casing hole is not caused.
C. Swing load
The resultant radial load vector acting on the bearing ring is relatively oscillated in a certain area of the ferrule raceway, is received by a certain area of the raceway, and is transmitted to a certain area of the surface of the shaft or the casing hole, or acts on the bearing The upper load is the impact load and the vibration load, and the load direction or value often changes. This load is called the swing load, and is also called the directional load.
When the bearing is subjected to the oscillating load, especially when subjected to heavy loads, the inner and outer rings should be interference fit. When the inner ring is swung and rotated, the inner ring is usually fitted with a swing load. However, sometimes the outer ring must be able to move the bearing outside the outer casing or its load is light, and a slightly looser fit than the swing load can be used.
2 load size
Under the action of the radial component of the load, the bearing ring is compressed in the radial direction, which is easy to cause the looseness of the fit, especially in the case of heavy swing load, which is prone to slip. Therefore, for heavy load applications, it should generally be tighter than the light load and normal load applications. In short, the heavier the load, the greater the interference fit should be.
3 working temperature
When the bearing is running, because the working temperature of the ferrule is usually higher than the temperature of the adjacent parts, the inner ring of the bearing may loosen with the bearing due to thermal expansion, and the outer ring may affect the axial clearance of the bearing due to thermal expansion, so, in the selection When mating, care must be taken to consider the temperature difference between the ferrules and the direction of their heat conduction.
4 rotation accuracy
When the requirements for the rotation accuracy and smoothness of the bearing are high, in order to eliminate the influence of the elastic deformation and vibration of the bearing components, the clearance fit should be avoided as much as possible.
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