The framework oil seal structure consists of three parts: oil seal body, reinforced framework and self tightening spiral spring. The sealing body is divided into bottom, waist, edge and sealing lip according to different parts. Generally, the inner diameter of the framework oil seal in free state is smaller than that of the shaft, that is, it has a certain "interference amount". Therefore, when the oil is sealed into the oil seal seat and shaft, the pressure of the oil seal edge and the contraction force of the self tightening spiral spring will produce a certain radial tightening force on the shaft. After a period of operation, the pressure will rapidly decrease or even disappear. Therefore, the spring can compensate the self tightening force of the oil seal at any time.

Sealing principle: because there is an oil film controlled by the oil seal edge between the oil seal and the shaft, the oil film has the characteristics of fluid lubrication. Under the action of the liquid surface tension, the stiffness of the oil film just makes the contact end of the oil film and air form a crescent surface, which prevents the leakage of the working medium, so as to realize the sealing of the rotating shaft. The sealing capacity of oil seal depends on the thickness of oil film on the sealing surface. If the thickness is too large, the oil seal will leak; if the thickness is too small, dry friction may occur, which will cause wear of oil seal and shaft; if there is no oil film between sealing lip and shaft, it is easy to cause heat and wear.

Therefore, during installation, some oil must be applied on the sealing ring, and the skeleton oil seal must be vertical to the axis line. If not, the sealing lip of the oil seal will drain the lubricating oil from the shaft, which will lead to excessive wear of the sealing lip. In operation, the lubricant in the shell seeps a little bit to form an oil film on the sealing surface.