The working principle and composition characteristics of mechanical seal

The two annular parts in the mechanical seal that fit each other and slide relative to each other are called seal rings. The sealing ring that rotates with the shaft is called a dynamic ring; the sealing ring that does not rotate with the shaft is called a static ring. The end face where the moving ring and the static ring are attached to each other is called the sealing face. The sealing end face is perpendicular to the rotation axis, and the sealing link formed by the sealing end face is called the main seal, which is the main sealing part of the mechanical seal.

The other sealing links other than the main seal in the mechanical seal are called auxiliary seals. Usually, elastic seals such as rubber and polytetrafluoroethylene are used to make seals as auxiliary seals, so they are called auxiliary seals. The auxiliary seals can generally be divided into For the dynamic ring seal ring and the static ring seal ring, they not only play the role of auxiliary seal, but also have a buffer function, which is an important condition in mechanical seals. If the vibration of the shaft is not buffered, it will be directly transmitted to the sealing surface. , the sealing surface can not be closely attached and the leakage will increase. The axial force and radial force caused by the vibration of the shaft to the sealing surface will lead to increased wear or even damage to the sealing surface, which will seriously affect the sealing performance. to this end. The mechanical seal should use the elasticity of various auxiliary sealing rings and bellows to buffer the impact of vibration of the shaft on the sealing performance.

The mechanical seal must have the ability to compensate axially so that the seal face can still maintain a good fit after wear. Therefore, the sealing ring with axial compensation ability is called compensation ring, and the sealing ring without axial compensation ability is called non-compensation ring. The components that can move axially with the compensation ring, which are composed of elastic elements (springs, etc.) and related parts (spring seats, push rings, etc.), are called compensation mechanisms.

The driving mechanism of the mechanical seal is formed by driving the moving ring and the shaft - the rotating parts (transmission screws, transmission pins, etc.).

The main seal, auxiliary seal, compensation mechanism and transmission mechanism are the four components that constitute the mechanical seal. Sealing devices often also have cooling, flushing and lubricating parts.

When the mechanical seal is working, the closing force caused by the pressure of the sealing fluid and the elastic force of the elastic element makes the moving ring and the static ring fit each other, and maintains a very thin layer of liquid in the extremely small space between the two ends. membrane. The gap mainly depends on the grinding accuracy, and the thickness of the liquid film varies according to the size of the parts and the friction state. Because this extremely thin liquid film has dynamic pressure and static pressure, it lubricates the end face on the one hand, so that it has a long service life, and on the other hand plays the role of balancing pressure, so as to obtain a good sealing performance.

A mechanical seal can be defined as a device that prevents fluid leakage by keeping at least a pair of end faces perpendicular to the axis of rotation under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and the cooperation of the auxiliary seal, which keep fit and slide relatively.