Mechanical seal principle and material analysis1

Mechanical seal principle and material analysis

1. The working principle of the mechanical seal The mechanical seal, also known as the mechanical seal, is a dynamic seal for the rotating shaft. The mechanical seal has reliable performance, small leakage, long service life, low power consumption, no need for frequent maintenance of pump mechanical seals, and can be adapted to production process automation and high temperature, low temperature, high pressure, vacuum, high-speed seal factories and various strong corrosion It can meet the sealing requirements of harsh working conditions such as volatile media and media containing solid particles. The mechanical seal is a leakage-proof shaft seal achieved by one or several pairs of relative sliding mechanical seals perpendicular to the shaft under the action of fluid pressure and the elastic force (or magnetic force) of the compensating mechanism. device. The mechanical seal is compared with the soft packing seal as follows: The advantages of the mechanical seal: (1) Compared with the soft packing seal, the mechanical seal is reliable, the sealing state is very stable during long-term operation, and the leakage is small, and its leakage is about the same as that of the soft packing seal. 1%; (2) The service life of the mechanical seal is long, generally 1 to 2 years or longer in oil and water media, and the mechanical seal can generally work for more than half a year in chemical media; (3) The wiping power consumption is small, The friction power of the mechanical seal is only 10% to 50% of that of the soft packing seal; (4) When the mechanical seal is used, the shaft or shaft sleeve is basically not worn; (5) The maintenance cycle is long, and the mechanical seal can be automatically compensated after the end face is worn. (6) The mechanical seal has good vibration resistance, and is not sensitive to the vibration of the rotating shaft and the deflection of the shaft to the sealing cavity; (7) It has a wide range of applications, and the mechanical seal can be used in high temperature, low temperature, High pressure, vacuum, different rotation frequencies, and sealing of various corrosive media and abrasive media. Disadvantages of mechanical seals: (1) Mechanical seals are complex and require high processing; (2) The installation and replacement of mechanical seals are troublesome, requiring workers to have a certain technical level; (3) When accidental accidents occur with mechanical seals, deal with It is more difficult; (4) the price of mechanical seals is high. Preparations before the mechanical seal: (1) Check whether the model and specifications of the mechanical seal meet the requirements of the design drawings, and whether all parts (especially the sealing surface and auxiliary sealing ring) are damaged, deformed, cracked, etc. If there is any defect, must be replaced or repaired. (2) Check whether the matching size, roughness and parallelism of each part of the mechanical seal meet the design requirements. (3) When using a small spring mechanical seal, check whether the length and rigidity of the small spring are the same. (4) Before the mechanical seal, check whether the movement, swing and deflection of the main engine meet the technical requirements, whether the mechanical seal cavity meets the installation size, and whether the seal end cover is perpendicular to the shaft. General requirements: the shaft movement is not greater than ±0.5mm; The swing of the shaft (at the sealing ring of the rotating ring) is not more than 0.06mm; the maximum deflection of the shaft is not more than 0.05mm; the allowable difference of the non-perpendicularity of the contact plane between the sealing end cover and the gasket to the center line is 0.03-0.05mm. (5) The mechanical seal should be kept clean when installing, especially the sealing surfaces of the rotating ring and the stationary ring and the surface of the auxiliary sealing ring should be free of impurities and dust. Do not wipe the sealing surface with an unclean cloth. (6) It is allowed to tap the sealing element with a tool to prevent the seal from being damaged. 2. Material of friction pair of mechanical seal According to statistics, about 80% to 95% of the leakage of mechanical seal is caused by the seal end face and friction pair. In addition to keeping the sealing surfaces parallel, the main problem is the material of the friction pair. The friction material should meet the following conditions: (1) High mechanical strength, able to withstand pressure and pressure deformation; (2) Dry wear resistance, high load resistance, and good self-lubrication; (3) Good running-in properties of matching materials , without excessive wear and dual corrosion; (4) good wear resistance, long life; (5) good thermal conductivity and heat dissipation; (6) good high temperature resistance; (7) good thermal crack resistance; (8) ) strong corrosion resistance; (9) small linear expansion coefficient; (10) good machinability, good formability; (11) good air tightness; (12) low density, thermal deformation resistance and good dimensional stability.