What is the reason why oil seals can be sealed?

Sealing mechanism of oil seals

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

However, static non leaking oil seals may still leak during operation.
The dynamic sealing mechanism is as follows:

During normal operation, oil first enters the narrow band of contact between the oil seal and the shaft through capillary action and the pumping effect of rough tissue (the roughness of the oil seal narrow band and the shaft). When someone enters this contact surface, the pumping effect begins to take effect. The cascaded micropumps on the atmospheric side have high potential pumping capacity, forming fluid dynamic pressure balance on this basis. Now, the seal operates on the oil film while maintaining a sealed state, which is in a lean oil lubrication state. This is the microscopic model of the sealing mechanism of oil seals.

The macro model is as follows: in reality, the oil seal rarely maintains a j perpendicular to the axis during operation, and the entire seal is generally inclined; Or it could be manufacturing errors, such as angular eccentricity or non parallel holes and axes in the cavity. The final performance is that when the shaft rotates, the oil seal performs a low amplitude reciprocating axial movement relative to the shaft, with a frequency of shaft speed, and the stroke depends on the magnitude of angular eccentricity. There is a phenomenon where reciprocating seals with asymmetric pressure distribution pump oil towards areas with steeper contact pressure gradients.
When installed in the forward direction, the sealing side slope is steep, and the pumping effect can achieve sealing; Reverse installation does not meet the requirements, static type does not leak, and leakage occurs during operation.
Combining micro and macro aspects, the dynamic sealing mechanism of oil seals is the result of the combined action of micro rough structure and macro sealing lip inclination, which together provide the dynamic sealing effect of oil seals.

Oil seal, also known as lubricating oil seal, is commonly used in various mechanical bearings to isolate the oil chamber from the outside and seal the internal sealing oil and external dust. It belongs to a type of contact dynamic seal.

Early oil seal materials were generally leather; Leather with good tanning properties is soft, elastic, and has good oil resistance, making it widely used. The current oil seal materials mainly consist of various types of rubber. For example, nitrile rubber, acrylic rubber, polyurethane rubber, silicone rubber, fluorine rubber, and polytetrafluoroethylene rubber.