The principle of the sealing shaft of the mechanical seal

The principle of the sealing shaft of the mechanical seal

A mechanical seal is a shaft sealing device that relies on a pair or several pairs of end faces that are perpendicular to the shaft for relative sliding under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism, and is matched with an auxiliary seal to prevent leakage. Mechanical seals are commonly used. The structure is composed of static ring (static ring) 1, rotating ring (moving ring) 2, elastic element 3, spring seat 4, set screw 5, rotating ring auxiliary sealing ring 6 and stationary ring auxiliary sealing ring 8 and other elements. The pin 7 is fixed on the gland 9 to prevent the stationary ring from rotating. The mechanical seal ring and the stationary ring are often also called compensation rings or non-compensation rings according to whether their mechanical seals have axial compensation capability. Mechanical There are four channels A, B, C, and D for the possible leakage of fluid in the seal. The leakage channels C and D are the seals between the static ring and the gland, and between the gland and the shell, both of which are static seals. B The channel is the seal between the rotating ring and the shaft. When the end face is rubbed and worn, it can only follow the compensation ring for a small amount of movement in the axial direction, and it is actually still a relatively static seal. Therefore, these leakage channels are relatively easy. Blocking. The most commonly used static sealing elements are rubber O-rings or polytetrafluoroethylene V-rings, while the rotating ring or static ring as a compensation ring is used as auxiliary seal, and sometimes rubber, polytetrafluoroethylene or The structure of the metal bellows. The A channel is a dynamic seal in which the end faces of the rotating ring and the stationary ring are attached to each other to slide relative to each other. It is the main seal in the mechanical seal device and is also the key to determining the performance and life of the mechanical seal. Therefore, the seal The processing requirements of the end face are very high. At the same time, in order to maintain the necessary lubricating liquid film between the sealing end faces, the pressure per unit area on the end face of the cavity must be strictly controlled. If the pressure is too large, it is difficult to form a stable lubricating liquid film, which will accelerate the wear of the end face; pressure If it is too small, the leakage will increase. Therefore, in order to obtain good sealing performance and sufficient service life, when designing and installing mechanical seals, it is necessary to ensure that the pressure value per unit area of ​​the end face is in the most appropriate range. Compared with soft packing seals, mechanical seals, It has the following advantages: ① The seal is reliable in long-term operation, the sealing state is very stable, and the leakage is very small. According to rough statistics, the leakage is generally only 1/100 of the soft packing seal; ② The service life is long in oil and water Generally, it can last for 1 to 2 years or more in similar media, and it can usually last for more than half a year in chemical media; ③ The friction power of the mechanical seal with small friction power consumption is only 10% to 50% of that of the soft packing seal;