Mechanical seal principle and material analysis

Mechanical seal principle and material analysis 1. The working principle of mechanical seal. Mechanical seal, also known as end face seal (Mechanical Seal), is a dynamic seal for a rotating shaft. The mechanical seal has reliable performance, small leakage, long service life and low power consumption. It does not require 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 The sealing requirements of harsh working conditions such as sexual media and media containing solid particles. The mechanical seal is a shaft seal with leakage resistance achieved by one or several pairs of relative sliding perpendicular to the shaft. The end face of the mechanical seal is kept in contact under the action of the fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and is equipped with an auxiliary seal. Device. The comparison between mechanical seal and soft packing seal is as follows: Advantages of mechanical seal: (1) Compared with soft packing seal, mechanical seal is reliable, the sealing state is very stable during long-term operation, and the leakage is small, and its leakage is about that of soft packing seal. 1%; (2) The service life of mechanical seals is long, generally up to 1 to 2 years or longer in oil and water media, and mechanical seals can generally work for more than half a year in chemical media; (3) Wipe power consumption is small, The friction power of the mechanical seal is only 10% to 50% of the soft packing seal; (4) The shaft or sleeve is basically not worn when the mechanical seal is used; (5) The maintenance cycle is long, and the end face of the mechanical seal can be automatically compensated after it is worn. (6) The mechanical seal has good vibration resistance, and is insensitive to the vibration of the rotating shaft and the deflection of the shaft to the seal cavity; (7) The scope of application is wide, and the mechanical seal can be used for high temperature, low temperature, Sealing of high pressure, vacuum, different rotation frequency, and various corrosive media and media containing abrasive particles. Disadvantages of mechanical seals: (1) Mechanical seals are more complicated and require high processing requirements; (2) The installation and replacement of mechanical seals are troublesome, requiring workers to have a certain level of skill; (3) When accidental accidents occur when using mechanical seals, handle More difficult; (4) The price of mechanical seals is high. Preparatory work before 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 are defects, 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 host meet the technical requirements, whether the mechanical seal cavity meets the installation dimensions, and whether the seal end cover is perpendicular to the shaft. General requirements: the shaft movement is not more than ±0.5mm; The amount of shaft swing (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 non-perpendicularity of the contact plane between the sealing end cover and the gasket to the center line is allowed to be 0.03～0.05mm. (5) Keep clean when installing the mechanical seal, especially the sealing surface of the rotating ring and the stationary ring and the surface of the auxiliary sealing ring should be free of impurities and dust. It is not allowed to wipe the sealing surface with a dirty cloth. (6) It is allowed to hit the sealing element with a tool to prevent the sealing element from being damaged. 2. Mechanical seal material friction pair material According to statistics, about 80%-95% of mechanical seal leakage 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. Friction materials should meet the following conditions: (1) High mechanical strength, resistance to pressure and pressure deformation; (2) Dry wear resistance, high load resistance, and good self-lubrication; (3) Good running-in properties of mating materials , No 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, heat-resistant deformation and good dimensional stability. Keywords: seal factory, mechanical seal factory, pump mechanical seal