Understand The Sealing Principle Of Oil Seals

August 26, 2021
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Sealing mechanism of the oil seal involves two factors.

One is the sealing of the cavity, which is mainly the positioning of the outer edge of the oil seal in the cavity; the other is the dynamic seal where the sealing lip contacts the surface of the rotating shaft, which is the most important function of the oil seal.


The static principle of the outer edge of the oil seal:

The outer edge of the oil seal is to ensure the static seal of the oil seal in the cavity and the stable position in the hole, and it is easy to assemble. Generally, the metal frame is covered by rubber material, which combines the reliable static sealing ability of the elastic body of the rubber wrist with the advantages of the metal frame to support positioning. The outer edge of the oil seal is chamfered to facilitate assembly. In addition, the design of grooves on the outer edge of the oil seal can increase adhesion, avoid the danger of oil seal retreat and skew, and also increase the press fit tolerance, which can improve the reliability of the oil seal static seal.


The dynamic principle of the oil seal lip:

  • The sealing mechanism of the contact area of ​​the sealing lip of the oil seal is extremely important to the sealing function of the oil seal, which depends on: the design after the seal, the structure of the elastic material; the roughness of the shaft surface, etc.
  • The combined effect of the radial force of the sealing lip, the angle design of the sealing lip, and the distance design between the lip tip and the center of the spring produces a contact pressure that is asymmetrically distributed on the axial surface; the pressure on the oil side is the largest and increases steeply; The pressure decays at a small angle on the air side. Under the cooperation of the interference (the inner diameter of the sealing lip is designed to be slightly smaller than the diameter of the shaft under no load condition), this asymmetrical distribution of contact pressure is related to the circumferential ring tightening force generated by the rotation. The combined effect leads to structural deformation in the contact area of ​​the sealing lip. This deformation structure of the sealing elastic body is formed during the test operation of the oil seal, which plays a decisive role in the sealing performance (therefore, the oil seal needs a running-in period for the test operation). The influence of the spiral and the rotation of the shaft result in a pumping action to the oil side due to this deformed structure