Sealing mechanism of oil seal  

Static sealing mechanism is relatively simple, the oil seal sealing interface is a narrow ring with a width of 0.1-0.2mm. Under the action of preloading (usually spring), there is an average radial contact pressure of 1N/mm2 between the oil seal and the shaft.  When the lubricating oil pressure is lower than the pressure value, the oil seal prevents it from leaking to the outside world.  

However, static non-leakage oil seal operation may still occur leakage.  

Its dynamic sealing mechanism is as follows:  

In the normal operation process, the oil first through the capillary action and rough structure (roughness of the narrow band of oil seal and shaft) pumping into the narrow band of oil seal and shaft contact.  When something enters this contact, the pumping action comes into play.  The cascade micro pump on the atmospheric side has a high potential pumping capacity, on which the fluid dynamic pressure balance is formed.  Now, the seal runs on the film and remains sealed, and the operation is lean lubrication.  This is the microscopic model of oil seal sealing mechanism.  

The macro model is as follows: in practice, the oil seal seldom keeps absolutely vertical with the axis when running, and the whole seal is generally with a slope;  Or make errors, such as angular eccentricity or the cavity is not parallel to the axis.  The final performance is that when the shaft rotates, the oil seal performs low amplitude reciprocating axial movement relative to the shaft, the frequency is the shaft speed, and the stroke depends on the size of the angular eccentricity.  There is a phenomenon where reciprocating seals with asymmetrical pressure distributions will pump oil to areas with a steeper contact pressure gradient.  As shown below:  

When the forward installation, meet the sealing side slope is steep, pumping can achieve sealing;  Reverse installation does not meet, static leakage, leakage during operation.  

Comprehensive micro and macro, the dynamic sealing mechanism of oil seal is the result of the joint action of micro rough structure and macro seal lip tilt, which together provide the dynamic sealing effect of oil seal.