Working principle of mechanical seal for slurry pump
Mechanical seal is a kind of rotating shaft dynamic seal, which is characterized by that the dynamic seal face is perpendicular to the rotating axis, so the centering during installation is very important. The mechanical seal has the advantages of long service life and good sealing performance due to the axial wear compensation mechanism composed of elastic elements, auxiliary sealing rings, etc.
Four points a, B, C and D in the figure are possible leakage points. Among them, B, C and D are static sealing points, which can easily rely on the compression of sealing ring to prevent leakage. The most difficult and important sealing point is the dynamic seal between the dynamic ring and the static ring. Due to the effect of medium pressure and spring force, there is a certain compression force on the sealing end face, forming a small gap between the sealing end face of the moving ring and the static ring, and keeping a layer of liquid film in the gap, the gap is very small, the resistance of medium passing through is very large, thus preventing the leakage of liquid; the existence of liquid film can lubricate the friction pair, reduce wear, and ensure the sealing effect. The dynamic and static rings are the core parts of mechanical seals. Due to the wear and heat generated by relative sliding, the materials of dynamic and static rings are required to have wear resistance, high thermal conductivity and other necessary mechanical properties. The most important is wear resistance, especially in the case of short-term dry friction, it must have good working ability. Generally, when selecting materials, the dynamic and static rings are matched with one hard one soft pair. Only in special cases, such as when the medium contains solid particles, can the hard pair be used. The common friction pair materials in China are graphite, cemented carbide, ceramics and bronze, etc. Graphite is mostly used as static ring. In order to overcome the shortcomings of high porosity and low strength, graphite impregnated with resin or metal is generally used. The impregnated resins include phenolic resin, barking resin, epoxy resin, etc. The impregnated metals are Babbitt, bronze, aluminum, etc. The cemented carbide used as the moving ring is generally tungsten carbide, which is characterized by high hardness and strength, good wear resistance and high temperature resistance, low coefficient of linear expansion, but it is brittle, easy to break and difficult to process. Alumina ceramics are commonly used as actuation rings, which have the advantages of high regularity and wear resistance, and especially corrosion resistance. They are brittle and prone to hot cracking.