Introduction to Common Materials for Mechanical Seals

The sealing performance and service life of mechanical seals are related to the materials of various mechanical seals, especially the materials of end seals (friction pairs), auxiliary seals, and springs.

1、 Material of end face sealing friction pair

Friction materials include graphite, ceramics, hard sealing alloys for welding, tungsten carbide alloys, SiC, filled with polytetrafluoroethylene, tin bronze, steel bonded hard alloys, stainless steel, phenolic plastics, nylon, etc. The properties of commonly used materials are as follows:

1. Tungsten carbide alloy is formed by pressing and sintering metal carbides with high hardness and melting point, such as tungsten carbide and titanium carbide, using powder metallurgy with binders. The advantage is that it has high hardness and strength. Wear resistant, high temperature resistant, corrosion-resistant, low coefficient of linear expansion, but the disadvantage is brittleness and difficult processing. Tungsten carbide is the most widely used end face sealing material, commonly used as the static ring for medium and low-speed mechanical seals and the dynamic ring for high-speed mechanical seals.

2. The advantages of graphite are good corrosion resistance and self-lubricating properties, low friction coefficient, good heat shock resistance, and easy processing. The disadvantage is low mechanical strength and porosity. These two drawbacks of graphite can be improved by impregnation and carburizing methods. Immersion graphite can be divided into two types: resin immersion and metal immersion. Resin impregnated graphite has good corrosion resistance, but is not resistant to high temperatures (about 170-200 ℃); Immersion metal graphite has good temperature resistance (immersion bronze, aluminum, lead, etc. can withstand high temperatures up to 400-500 ℃), but poor corrosion resistance. Graphite is the most widely used non-metallic material, used as the dynamic ring for medium and low-speed mechanical seals and the static ring for high-speed mechanical seals. Good graphite appears dense to the naked eye and does not cause significant powdering or blackening when touched by fingers.

3. The advantages of ceramic ceramics are good corrosion resistance, high hardness, and good wear resistance. The disadvantages are high brittleness and high hardness, making it difficult to process. The most commonly used materials are alumina ceramics and metal ceramics. Ceramics are commonly used in corrosive media and at medium to low speeds.

4. Hard alloy welding is applied to the sealing surfaces of carbon steel, chromium steel, and chromium nickel steel. The advantages of hard alloy welding are high hardness, good wear resistance, good temperature resistance (below 500 ℃), and good corrosion or cavitation resistance. The disadvantages are that it is prone to porosity, slag inclusion, and uneven surface hardness.

2、 Material of auxiliary sealing ring

The requirements for auxiliary sealing materials are good elasticity, low friction coefficient, wear resistance, heat resistance, and low temperature resistance, as well as resistance to medium corrosion, dissolution, and aging. In addition, it is also required to have good residual deformation after compression and long-term use. The commonly used auxiliary sealing ring materials are rubber and polytetrafluoroethylene, in addition to soft polyvinyl chloride.

1. The advantages of polytetrafluoroethylene are excellent chemical stability, oil resistance, dissolution resistance, and moisture resistance, low friction coefficient, and suitability for various corrosive media. The disadvantage is that its elasticity is worse than rubber and it is prone to permanent deformation.

2. Rubber has good elasticity, cushioning, vibration absorption, heat resistance, and corrosion resistance. Rubber sealing rings have good sealing effect and are widely used. Commonly used rubbers include silicone rubber, nitrile rubber, chloroprene rubber, and fluororubber.

3、 Elastic element material

1. The requirements for spring materials are good elasticity and resistance to medium corrosion. Common spring materials include stainless spring steel (1Cr18Ni9Ti, etc.), chromium steel (3Cr13, 4Cr13, etc.), carbon cable spring steel (60si2Mn, etc.), and phosphor bronze.

2. The requirements for corrugated pipe materials are: good welding performance, high elasticity, and certain corrosion resistance. The commonly used materials for corrugated pipes include iron-based, copper based, nickel based alloys, and titanium materials. Generally, nickel chromium austenitic strips in titanium based materials are the main ones, with 1Cr18Ni12Mo2Ti being the most commonly used. High nickel elastic alloy is considered an ideal material for making corrugated pipes, and materials containing aluminum may encounter difficulties when using general welding techniques. At present, the most commonly used corrugated pipe material abroad is AM350 (approximately Cr16Ni45MnMo3N), which belongs to solid solution, low strength, low hardness, and high elongation.