The basic components of the carbon packing are as follows. 1 end friction pair (static and moving ring): To maintain the friction surface close to form the sealing surface to prevent leakage of the medium, the static and dynamic rings are required to have good wear resistance, the moving ring can move axially, and the sealing surface wear is automatically compensated. So that it fits well with the static ring (the moving ring should have good followability), and the static and dynamic rings have a floating cushioning effect. 2 elastic components (spring, bellows, serpentine sleeve, diaphragm, etc.): mainly plays the role of pre-tightening, compensation and buffering. It is also an important factor for generating a reasonable specific pressure on the sealing face of carbon packing. It is required to always maintain elasticity. Overcoming the friction of the auxiliary seal transmission member and the inertia of the moving ring, etc., ensuring that the end face friction pair is well fitted and the follower of the moving ring, and the material requires corrosion resistance and fatigue. 3 Auxiliary seals (O-rings, V-rings, wedge rings and other special-shaped seal rings): The carbon packing should play the role of sealing the static ring and the moving ring, and also play the role of floating buffer, requiring the assistance of the static ring. The sealing element can ensure the sealing between the static ring and the gland and the floating ring. The auxiliary sealing element of the moving ring can ensure the sealing between the moving ring and the shaft or the sleeve and the floating of the moving ring. Materials are required to be heat or cold resistant and compatible with the media.
Transmission parts (drive pin electric drive ring, transmission seat, transmission sleeve, transmission key, transmission lug or jaw connector): play the role of transmitting the torque of the shaft to the moving ring, the transmission pin and pressure of the intermediate transmission The ring-drive ring, the drive pin-spring seat act as a transmission, and the carbon packing material requires wear resistance and corrosion resistance. 5 Fasteners (tightening screws, spring seats, gland, assembly sleeve, bushing): To play the role of positioning, fastening and loading of static and dynamic rings, it is required to position correctly and ensure that the friction pair sealing surface is correct. The position and maintain a good fit to the spring specific pressure. At the same time, it is required to be easy to disassemble, easy to place and reuse. At the point of fitting with the auxiliary seal, pay attention to the guide side angle and the amount of compression of the seal ring. In particular, it should be noted that the dynamic ring-assisted seal and the bushing are required to be corrosion-resistant and wear-resistant, and if necessary, a hard-faced layer is used. Carbon packing seals typically have four sealing locations (channels). A is the end face seal, the moving ring of the rotating ring and the end face of the stationary ring cooperate with each other to slide relative to each other, also known as the main seal in the mechanical seal device, which is the key to determine the mechanical seal performance and life; B is the static ring 7 and pressure Seal between the end faces of the cover 4; C is the seal between the moving ring 3 and the mating surface of the shaft (or bushing) 9. Because it can move axially with the compensating ring and seals, it is also called the secondary seal. When worn, the carbon packing can only follow the axial movement of the compensating ring in a slight amount, which is actually a relatively static seal; D is the seal between the gland and the end face of the pump casing. B, D, C are static seals. These leakage channels are relatively easy to block, and are generally not easy to leak. A is the opposite end rotary seal. As long as the design is reasonable, the leakage can be achieved. The mechanical seal has high requirements for the processing of the sealing end face (flatness: 0.009 mm, surface roughness: hard ring Ra ≤ 0.1 μm, soft ring Ra ≤ 0.2 μm).
In order to maintain the necessary lubricating film between the sealing faces of the carbon packing, the pressing force per unit area on the end face must be strictly controlled, and the unit pressure on the end face is too large to form a stable lubricating liquid film, which accelerates the wear of the end face. The unit pressure on the end face is too small and the amount of leakage increases. Therefore, in order to obtain good sealing performance and long life, when designing and installing the mechanical seal, it is necessary to ensure that the end unit pressure value is within the most appropriate range. (1) According to the contact state of the sealing end face, the end face contact state of the mechanical end face seal is different, mainly including contact mechanical seal, non-contact carbon packing seal and semi-contact mechanical seal. The contact condition of the sealing surface is determined by the rough (uneven) gap between the nominal (average) gap of the sealing end face of a certain surface roughness and the lubrication condition of the sealing surface. The contact type carbon packing seal is a mechanical seal which is pre-compressed by the elastic element, and the sealing fluid pressure and the elastic element pressing force make the sealing surface microprotrusion contact. This type of sealed end face has a small nominal gap (h is a few to 2 μm) and is mostly operated under mixed lubrication and boundary lubrication.
