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Causes and solutions of quality problems in the assembly of bearing seals

Update:23-09-2020
Summary:

The sealing ring of the bearing is a commonly used part […]

The sealing ring of the bearing is a commonly used part in the assembly structure of the bearing. The assembly quality of the sealing ring will directly affect the sealing performance of the bearing or affect the life of the bearing. When a bearing is in use, a lot of damage is related to the quality of the bearing seal assembly. What are the reasons for the common quality problems of the bearing seal assembly in our daily life? China Bearing Network (abbreviation: Bearing Network) will share relevant reasons and solutions based on the knowledge of bearing assembly.

Under normal circumstances, the reasons for the quality problems in the assembly process of the bearing seal ring are as follows: ①The seal ring rotates; ②The seal ring does not fit; ③The seal ring is easy to fall off; ④The bearing outer ring causes large cracks; ⑤Bearing The inner ring is stuck; ⑥The inner lip of the sealing ring bites back when the bearing rotates or flips.

1. The bearing seal ring is turned

Rotation of the bearing seal ring means that the inner and outer rings of the bearing also move relative to each other in the radial direction during the rotation. Usually, the seal ring cannot rotate when it is installed in the seal groove. The main reason is that the size of the rib of the bearing seal ring is too small, and the interference between the inner lip of the seal ring and the outer spherical surface of the inner ring is greater than the interference between the rib of the seal ring and the seal groove step of the outer ring, that is, the friction between the seal ring and the step The force is less than the friction between the sealing ring and the outer spherical surface,

The solution is: appropriately increase the size of the bearing seal ring rib and increase the size of the inner lip of the seal ring on the premise of ensuring the quality of the seal ring assembly.

2. The bearing sealing ring does not fit

Non-fitting of the bearing seal ring means that the inner lip of the seal ring is tilted and does not fit tightly to the outer spherical surface of the inner ring after the seal ring is assembled. The non-fitting of the sealing ring will reduce the sealing performance of the bearing, thereby affecting the quality of the product. The reasons for this phenomenon are: ①The inner lip of the sealing ring is too small; ②The inner lip of the sealing ring is too thin and easy to deform; ③The sealing ring cannot be reset after installation.

Deal with differently according to different causes:

① If the flared mouth caused by too small interference of the inner lip of the bearing seal ring, the interference of the inner lip of the seal ring must be increased. The unilateral interference F is calculated according to the following formula;

F=(D2-D1)/2+e

Where: D2-diameter size of sealing ring lip; D1-diameter size of inner ring section; e-unilateral interference of conventional lower sealing ring lip.

②The horn mouth caused by the deformation of the inner lip of the bearing seal ring is mainly caused by the inner lip being too thin, and the seal ring is deformed during the injection and unloading process. Therefore, the thickness of the inner lip of the seal ring must be increased in this case ;

③The bell mouth caused by the bearing sealing ring not resetting, the head A point of the sealing ring is stuck in the sealing groove during the bearing swing and cannot return to the original state . The outer diameter of the sealing ring must be reduced or Reduce the width of the seal head.

3. The bearing seal is easy to fall off

Shedding of bearing seal ring means that the seal ring falls out of the seal groove. The firmness of the sealing ring after assembly is verified by a drop test. The reason for the sealing ring falling off is: the interference between the sealing ring flange and the outer ring seal groove step is too small, and the sealing ring head is straight at the flange. The length is too small.

Therefore, increase the size of the seal ring rib and lengthen the length a of the straight section of the seal ring head near the rib to increase the firmness of the assembly, and at the same time, properly add in the limited space of the existing seal groove The large sealing ring rib width b increases the contact area of ​​the sealing ring in the groove. The larger the contact area, the greater the friction between the sealing ring and the outer ring. When the bearing swings, the sealing ring is less likely to loosen and rotate. The higher the firmness.

 

 

4. Large cracks in the bearing outer ring

Due to assembly requirements, there is an axial seam on the outer diameter of the bearing outer ring. After the seal ring is installed, the axial seam of the outer ring will increase due to the amount of interference. When the axial seam of the outer ring increases to a certain extent , It will cause the user's bearing installation difficulties, so the size of the outer ring gap should be strictly controlled, usually about 0.5mm is appropriate. For bearings with rib positioning, the interference between the rib of the seal ring and the seal groove of the outer ring should be appropriately reduced without affecting the assembly quality, thereby reducing the gap between the outer diameter of the outer ring.

5. The inner ring of the bearing is stuck

After the bearing is installed in the sealing ring, the inner ring cannot rotate flexibly or even cannot rotate. This phenomenon is called the inner ring jam.

The main method is to reduce the interference between the lip of the seal ring and the spherical surface of the inner ring, that is, increase the inner diameter d of the seal ring to reduce the amount of contact between the lip of the seal ring and the spherical surface. The second is to reduce the waist size e of the sealing ring to make the lips of the sealing ring more elastic and reduce the contact pressure between the sealing ring and the inner ring spherical surface. In addition, when designing the seal ring, the opening angle α should not be too large. The opening angle gradually increases from α to β, and the straight line distance is from point A to point B. The contact area between the line BC and the inner ring is S1+S2 The contact area of ​​S2 is completely larger than the contact area S1 of the straight line AC and the inner ring.

Under the same condition of the lip interference, the larger the area of ​​the seal ring contacting the inner ring spherical surface, the greater the bearing resistance to rotation and the easier it is to jam. At the same time, the lip of the sealing ring will be severely worn and cannot be used normally. Therefore, appropriately reducing the opening angle α can also increase the flexibility of bearing rotation. According to actual application verification, the opening angle α is generally about 45°.

6. The inner lip of the sealing ring bites back when the bearing rotates or flips

The phenomenon that the bearing exceeds its swing angle during rotation and the seal ring lip is involved in the inner spherical surface of the outer ring when reset is called back bite of the seal ring.

For this phenomenon, the main solution is to reduce the amount of interference between the lip of the seal ring and the spherical surface of the inner ring; the second is to appropriately increase the rigidity and elasticity of the inner lip of the seal ring, that is, increase the thickness of the lip part. Shaded part S) and reduce the waist size e of the sealing ring. Only if the lip of the sealing ring has sufficient rigidity and elasticity, the back bite will not occur when the bearing swings.

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