Principle and structure of mechanical seal1

Principle and structure of mechanical seal

Mechanical seals rely on one 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, the shaft is kept attached to the mechanical seal factory and matched with auxiliary seals to prevent leakage. sealing device. The common mechanical seal 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 components , the anti-rotation pin 7 is fixed on the gland 9 to prevent the stationary ring from rotating. Rotating rings and stationary rings can often be called compensation rings or non-compensation rings according to whether they have axial compensation capability. There are four channels A, B, C and D for the possible leakage of fluid in the mechanical 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. The B 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 seal factory leakage channels are relatively easy to block. The most commonly used static sealing elements are rubber O-rings or polytetrafluoroethylene V-rings, while rotating rings or static rings as compensation rings are used as auxiliary seals, and sometimes rubber, polytetrafluoroethylene or metal bellows that have the function of elastic elements are used Structure. 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 and slide relative to each other. It is the main seal in the mechanical seal device, and it is also the key to determine the performance and life of the mechanical seal. Therefore, the processing requirements for the sealing 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 cavity end face must be strictly controlled. If the pressure is too large, it is difficult to form a stable lubricating liquid film, which will accelerate the end face. wear; if the pressure is too low, the leakage will increase. Therefore, in order to obtain good sealing performance and sufficient 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 the soft packing seal, the mechanical seal has the following advantages: 1. The seal is reliable in the 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; ②Long service life can generally reach 1-2 years or more in oil and water media, and can usually reach more than half a year in chemical media; ③The friction power of the mechanical seal is small in friction power consumption, and the friction power of the mechanical seal is only that of the soft packing seal 10% to 50%.