Brief Introduction of 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-to-end seals (friction pairs), auxiliary seals and springs.

I. Material of end seal friction pair

Friction pair materials include graphite, ceramics, hardfacing seals, tungsten carbide, SiC, filled PTFE, tin bronze, steel-bonded carbide, stainless steel, phenolic plastics, nylon, etc. The properties of common materials are as follows:

1. Tungsten carbide alloys are formed by compaction and sintering by adding binder powder metallurgy, which are metal carbides with high hardness and melting point, such as tungsten carbide and titanium carbide. The advantages are high hardness and strength. Wear resistance, high temperature resistance, corrosion resistance, low linear expansion coefficient, shortcomings are brittle, difficult processing. Tungsten carbide is the most widely used end sealing accessory material. It is mostly used as the static ring of medium and low speed mechanical seals and the dynamic ring of high speed mechanical seals.

2. Graphite graphite has the advantages of good corrosion resistance and self-lubrication, small friction coefficient, good heat shock resistance and easy processing. The disadvantage is low mechanical strength and porosity. These two shortcomings of graphite can be improved by impregnation and carburization. Graphite impregnated can be divided into resin impregnated and metal impregnated. Resin impregnated graphite has good corrosion resistance, but not high temperature resistance (about 170-200 C); metal impregnated graphite has good temperature resistance (bronze, aluminium, lead and other high temperature resistance can reach 400-500 C), but poor corrosion resistance. Graphite is the most widely used non-metallic material, which is used as the moving ring and the static ring of mechanical seals at medium and low speed. Good graphite looks dense to the naked eye. Fingers don't feel very powdered and don't dye black fingers.

3. Ceramic ceramics have the advantages of good corrosion resistance, high hardness and good wear resistance, but the disadvantages are brittleness and high hardness which are difficult to process. Alumina ceramics and metal ceramics are widely used. Ceramics are mostly used in corrosive media, medium and low speed occasions.

4. Surfacing cemented carbide on the sealing surface of carbon steel, chromium steel and Chromium-Nickel Steel has the advantages of high hardness, good wear resistance, good temperature resistance (below 500 C), good corrosion resistance or cavitation corrosion resistance, but the disadvantages are easy to produce pore, slag inclusion and uneven surface hardness.

II. Material of Auxiliary Seal Ring

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

1. Polytetrafluoroethylene (PTFE) has the advantages of chemical stability, oil resistance, solubility resistance, moisture resistance, low friction coefficient and is suitable for various corrosive media. The disadvantage of PTFE is that its elasticity is worse than that of rubber and it is easy to produce permanent deformation.

2. Rubber rubber has good elasticity, cushioning, vibration absorption, heat resistance and corrosion resistance. Rubber sealing ring has good sealing effect and is widely used. The commonly used rubber are silicone rubber, butadiene-fine rubber, chloroprene rubber and fluorine rubber.

3. Elastic Component Materials

1. The requirement of spring material for spring material is good elasticity and medium corrosion resistance. Commonly used spring materials are stainless spring steel (1Cr18Ni9Ti, etc.), chromium steel (3Cr13, 4Cr13, etc.), carbon cable spring steel (60si2Mn, etc.) and phosphor bronze.

2. The requirement of bellows material for bellows material is: good welding performance, greater elasticity and certain corrosion resistance. Commonly used bellows are iron-based, copper-based, nickel-based alloys and titanium materials. Generally, nickel-chromium austenitic strips in titanium matrix are the main materials, especially 1Cr18Ni12Mo2Ti. High nickel elastic alloy is considered to be an ideal material for making bellows. Aluminum-containing materials will encounter difficulties in general welding technology. AM350 (approximate Cr16Ni45MnMo3N) is a kind of solid solution, low strength, low hardness and high elongation.