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FAG Bearing Coordination

Writer: Eric Bearing Limited

For the thin-walled rings of extra-light and ultra-light series bearings, the proper tight fit can be used to make the bearing rings evenly stressed during operation, so that the bearing capacity of the rolling elements of the bearings can be fully exerted. However, the selected FAG bearing should not be too tight, because the elastic expansion of the inner ring and the shrinkage of the outer ring will reduce the internal clearance of the bearing until it completely disappears, thus affecting the normal operation of the FAG bearing.    Below photo is NJ415M1.C3  bearings in ERIC BEARING LTD stock , need more information , pls click here 

1. FAG bearing fit selection

(1) Bearing with cylindrical bore

The main factors that should be considered when choosing the fit of FAG bearings are as follows:

①Type of load

According to the load acting on the FAG bearing, the load on the ring can be divided into three types: fixed load, slewing load and swing load.

a. Fixed load

The resulting radial load is borne by the local area of ​​the ferrule raceway and is transmitted to the corresponding local area of ​​the shaft or housing mating surface accordingly. This load is called a fixed load.

The characteristic of the fixed load is that the resultant radial load is relatively static with the ferrule. A ferrule that bears a fixed load can generally use a looser fit.

b. Swing load

The synthetic radial load vector acting on the bearing ring swings relatively in a certain area of ​​the ring raceway, is borne by a certain area of ​​the raceway, and is transmitted to a certain area of ​​the surface of the shaft or housing hole, or acts on the bearing The load on the load is an impact load, a vibration load, and the direction or value of the load often changes. This load is called a swing load, which is also called a directional load.

When the FAG bearing is subjected to a swing load, especially when it is under heavy load, the inner and outer rings should adopt an interference fit. When the inner ring swings and rotates, usually the inner ring adopts the fit of the slewing load. However, sometimes the outer ring must be able to move toward the bearing inside the housing or its load is light, and a slightly looser fit than the slewing load can be used.

c. Slewing load

The resultant radial load vector acting on the bearing ring rotates along the circumferential direction of the raceway, and is sequentially received by various parts of the raceway and transmitted to various parts of the surface of the shaft housing hole accordingly. This load is called slewing load, also known as cyclic load.

The characteristic of the slewing load is the relative rotation of the synthetic radial load vector and the ferrule. The ferrule that bears the slewing load and the shaft or housing hole should be filtered or interference fit. If the clearance fit installation is used, slippage will occur between each other, which will result in friction of the contact surface, friction and heat generation, and the temperature will rise sharply, and the bearing will soon be damaged. The size of the desired interference depends on the operating conditions. The principle is that the bearing does not cause a "crawling" phenomenon on the mating surface of the shaft or housing hole when the bearing is working under load.  FAG deep groove ball bearings are our hot sale products , if you need , pls contact ERIC BEARING LTD . 

②The size of the load

Under the action of the radial component of the load, the FAG bearing ring will be compressed in the radial direction, which is easy to cause loosening of the fit, especially in the case of heavy slewing load, it is easy to produce a slip phenomenon. Therefore, for heavy load occasions, it should usually be tighter than light load and normal load occasions. In short, the heavier the load, the greater the interference.

③Working temperature

When the bearing is running, because the working temperature of the ring is usually higher than the temperature of the adjacent parts, the inner ring of the bearing may loosen from the bearing due to thermal expansion, and the outer ring may affect the axial clearance of the bearing due to thermal expansion. When fitting, the temperature difference between the ferrules and the direction of heat conduction must be considered.

④Installation and disassembly

In many complex structural applications, in order to facilitate installation and disassembly, clearance fit is required. Depending on the bearing operation, if an interference fit installation is necessary, separate bearings (cylindrical roller bearings, needle roller bearings, tapered roller bearings and thrust bearings that can be installed on the inner and outer rings, respectively) or tapered The bearing with inner hole can make the assembly and disassembly easy.

⑤Rotation accuracy

When the requirements on the bearing's rotation accuracy and running stability are high, in order to eliminate the influence of the elastic deformation and vibration of the bearing components, the gap fit should be avoided as much as possible.

⑥Structure and material of shaft and shell

If the openings of the shaft and casing (box) are irregularly shaped, it will cause abnormal deformation of the inner and outer rings of the bearing and uneven stress. For the split shell (box) body, the interference fit with the outer ring of the bearing should not be an interference fit, but the outer ring should not rotate in the hole of the shell (box). 

When the bearing is installed on a thin-walled, light alloy shell (box) hole or hollow shaft, in order to ensure that the bearing has sufficient support surface, it should be installed on a thick-walled shell (box) body, cast iron shell (box) body or solid The selected fit on the shaft is tighter.

⑦Axial displacement of non-fixed end bearing

This displacement refers to the requirement that a bearing ring mounted on the non-fixed end can have a certain play in the axial direction. Usually, the ferrule (usually the outer ring) that bears a fixed load is installed with clearance fit. If cylindrical roller bearings (type 2000 and 3200) with no ribs on the inner ring or outer ring or needle roller bearings are installed on the non-fixed end, the inner and outer rings are installed with interference fit.

(2) Bearing with conical inner hole

The bearing with conical inner hole is more convenient to install and remove. It can be directly installed on the tapered journal or the outer sleeve with tapered cylindrical surface (adaptive sleeve, withdrawal sleeve), and then the middle sleeve The cylinders are mounted together on a cylindrical shaft.

The fit between the outer ring of the bearing and the hole of the casing (box) is the same as the rule of the cylindrical inner hole bearing.

Non-separable bearings with adapter sleeves or withdrawal bushes can be used for bearings with large tolerances, but the shape and position tolerances of the shaft must be strictly controlled.

2. Coordination of FAG bearings with shaft and housing

The bearing and the shaft use the base hole system, and the bearing and the housing use the base shaft system. The fit between the bearing and the shaft is different from the tolerance fit system adopted in the machine manufacturing industry. The inner diameter tolerance of the bearing is mostly a negative tolerance. Therefore, under the same fit conditions, the fit ratio between the inner diameter of the bearing and the shaft is usually closer. Although the bearing outer diameter tolerance is a negative tolerance, its tolerance value is different from the general tolerance system.