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Structure and advantages of rotary shaft lip seal (oil seal)

Release time:

2019-07-03 12:30

Source:

Structure and advantages of rotary shaft lip seal (oil seal)
 
Rotary shaft lip sealUsually called oil seal, it is widely used in gearboxes, drive axles and other components of construction machinery, such as the front and rear output shafts of the gearbox, the main reducer of the drive axle, wheel sides, etc. Its function is to isolate the oil cavity from the outside world. Seal oil internally and prevent dust externally. At present, a large number of rotary shaft lip seal oil seal structure types are more, and its basic structure includes rubber seal part, metal skeleton or metal shell and metal spring.
 
Sealing mechanism of 1. oil seal The sealing of oil seal is formed by interference fit between a flexible sealing element (leather, rubber, polytetrafluoroethylene, polytrifluoroethylene or polyimide, etc.) and the rotating shaft. Its sealing mechanism is: dry friction, boundary lubrication and fluid lubrication coexist on the contact surface between the oil seal lip and the shaft at the same time, and they are produced alternately.
 
Dry friction produces wear and fluid lubrication produces leakage. Under boundary lubrication, a stable hydrodynamic oil film is formed between the interface of the oil seal lip and the shaft. The thickness of the oil film is about 00025mm; this oil film is used for lubrication. It also plays a sealing role. If the oil film is too thick, the fluid will leak; if the oil film is too thin, the fluid lubrication film cannot be formed and the lip will wear out.
 
2. to the shortcomings of the existing oil seals 1. In terms of structural design, because a large number of oil seals currently used are directly interference fit with the rotating shaft seals to achieve dynamic sealing, they affect the eccentricity, size deviation, and non-roundness of the rotating shaft., Surface roughness, etc. have very strict requirements:
1) the eccentricity of the shaft, the eccentricity of the size directly affects the distribution of the contact stress of the oil seal lip, usually within 0.3mm (shaft diameter of 50 ~ 80mmm, oil seal line speed of 10~15 m/s), but in many cases it is difficult to do. For example, the technical requirements for the assembly of the oil seal seal of the drive axle main reducer: the eccentricity of the center line of the input flange to the center line of the oil seal seat hole is as small as more than 0.1mm. However, since the center line of the seat hole depends on the center position of the mating stop of the bearing seat and the bracket, and the center line of the input flange depends on the center position of the mating spline with the driving spiral bevel gear, the offset of the two center lines is difficult to control within the range of 0.1mm.
 
2) the size of the shaft deviation: only the correct selection of the size of the shaft deviation is possible to obtain a good performance of the sealing effect. An excessively large shaft will increase the contact load on the lip end, while an excessively small shaft will cause insufficient sealing pressure on the lip end contact surface. Too much pressure will cause premature seal failure, while too little contact pressure will cause leakage.
 
3) The out-of-roundness of the shaft: The out-of-roundness of the shaft is likely to cause deformation or loss of elasticity of the elastomer sealing lip according to the irregular movement of the shaft, thereby causing fatigue damage.
 
4) The surface roughness of the shaft is generally Ra1.6 ~ 3.2um. The surface is too smooth, which is not conducive to the formation and maintenance of the oil film. The sealing ring is dry and rubbed, causing leakage; too rough, friction and wear will increase, which will also cause early failure of the oil seal.
 
Structure and Advantages of 3. New Oil Seal
 
The main feature of the new oil seal is that an oil seal inner hub covered with a layer of wavy rubber is designed between the rotating shaft and the oil seal lip. When working, the inner hub rotates with the coaxial, and the oil seal is on its lip and the inner hub. Dynamic sealing is realized between the outer surface. Its advantages are:
 
1. The inner hub part of the oil seal is covered with a layer of wavy rubber, which can adapt to the relatively large eccentricity of the rotating shaft (usually only about 0.5mm) and the large range of size deviation of the shaft, and has better axial and Radial cushioning performance. This kind of oil seal shows good sealing performance in the muddy water test under the condition of shaft eccentricity of 0.5mm and speed of 800rpm; at the same time, it also shows a very long service life in the life test of 5000km.
 
2. Since the seal is realized between the oil seal lip and the inner hub, it does not require high roundness and surface roughness of the shaft, and is not sensitive to slight damage to the shaft surface, which improves the reliability of the oil seal.
 
3. Coated with a layer of rubber on the inner hub, which can make the oil seal firmly installed on the shaft. If the rubber surface is coated with grease before installation, the installation will become easier. 4. A labyrinth channel is designed between the oil cavity and the outside world, and two dust-proof lips are arranged in the channel to keep the main lip at a distance from dust and water, and extend the service life of the oil seal.

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