How to choose the base material of mechanical seal
21/02/22 11:10:02
The sealing performance and service life of the
mechanical seal are related to the mechanical shaft seal material of each part, especially the material of the end seal (friction pair), the material of the auxiliary seal and the material of the spring.
1. Material of end face seal friction pair
Friction pair materials include graphite, ceramics, surfacing hard alloy, tungsten carbide alloy, SiC, filled polytetrafluoroethylene, tin bronze, steel-bonded hard mechanical seal alloy, stainless steel, phenolic plastic, nylon, etc. The properties of commonly used materials are as follows:
1. Tungsten carbide alloy Tungsten carbide, titanium carbide and other metal carbides with high hardness and high melting point are formed by pressing and sintering by adding binder powder metallurgy. The advantage is that the hardness and strength are very high. Wear resistance, high temperature resistance, corrosion resistance, low coefficient of linear expansion, the disadvantage is that it is brittle and difficult to process. Tungsten carbide is a widely used end face sealing material, and it is mostly used as the static ring of medium and low speed mechanical seals and the moving ring of high speed mechanical seals.
2. Graphite The advantages of graphite are good corrosion resistance and self-lubrication, small friction coefficient, good thermal shock resistance and easy processing. The disadvantage is that the mechanical strength is low and there are pores. These two shortcomings of graphite can be improved by impregnation and carburization. Impregnated graphite can be divided into impregnated resin and impregnated metal. Resin-impregnated graphite has good corrosion resistance, but not high temperature resistance (temperature resistance is about 170-200°C); impregnated metal graphite has good temperature resistance (impregnated bronze, aluminum, lead, etc. can withstand high temperature up to 400-500°C), but it is corrosion-resistant Poor sex. Graphite is a widely used non-metallic material, which is used as the moving ring of medium and low speed mechanical seals and the static ring of high speed mechanical seals. Good graphite looks dense to the naked eye, and it doesn't take off powder when you touch it, and it doesn't stain your fingers black.
3. Ceramics The advantages of ceramics are good corrosion resistance, high hardness, and good wear resistance. The disadvantages are high brittleness and high hardness that make it difficult to process. The most widely used are alumina ceramics and cermets. Ceramics are mostly used in corrosive media, medium and low speed occasions.
4. Overlay welding of hard alloy on the sealing surface of carbon steel, chrome steel and chromium-nickel steel, the advantages are high hardness, good wear resistance, good temperature resistance (below 500 ℃), corrosion resistance or The cavitation is good, but the disadvantage is that it is easy to produce pores, slag inclusions and uneven surface hardness.
2. Materials of auxiliary sealing ring
The requirements for auxiliary sealing materials are good elasticity, small friction coefficient, good wear resistance, heat resistance and low temperature resistance, resistance to medium corrosion, dissolution and aging, etc. In addition, good residual deformation after compression and long-term use is also required. Commonly used auxiliary sealing ring materials are rubber and polytetrafluoroethylene, in addition to soft polyvinyl chloride.
1. Polytetrafluoroethylene The advantages of polytetrafluoroethylene are chemical stability, oil resistance, solvent resistance, excellent moisture resistance, low friction coefficient, and suitable for various corrosive media. The disadvantage is that its elasticity is worse than that of rubber, and it is easy to deform.
2. Rubber Rubber has good elasticity, cushioning, shock absorption, heat resistance, and corrosion resistance. The rubber sealing ring has good sealing effect and is the most widely used. Commonly used rubbers are silicone rubber, nitrile rubber, neoprene and fluorine rubber.
3. Elastic element material
1. Spring material The requirements for the spring material are: good elasticity and medium corrosion resistance. Commonly used spring materials are stainless spring steel (1Cr18Ni9Ti, etc.), chrome steel (3Cr13, 4Cr13, etc.), carbon cable spring steel (60si2Mn, etc.) and phosphor bronze.
2. Bellows material The requirements for the bellows material are: good welding performance, greater elasticity, and certain corrosion resistance. Commonly used bellows materials include iron-based, copper-based, nickel-based alloys, and titanium materials. Generally, nickel-chromium austenitic strips in titanium-based materials are mainly used, especially 1Cr18Ni12Mo2Ti. High-nickel elastic alloy is considered to be an ideal material for making bellows, and aluminum-containing materials will encounter difficulties when using general welding techniques. At present, AM350 (approximately Cr16Ni45MnMo3N) is a solid solution, low strength, low hardness and high elongation.
