Gasket sealing structure is widely used in various mechanical equipment, especially various pressure vessels, pipelines and valves. The simplest gasket is the flat gasket, and the whole gasket is made of the same material, which is used for static sealing of general joint surfaces of mechanical equipment, such as the sealing of gear boxes.
The ideal gasket structure should be that the surface layer is plastic and the inner layer is elastic The plastic surface layers ensure sealing, and are close to each other or even embedded, while the inner layer allows to compensate for a little separation of the sealing surfaces, and usually maintains a certain amount of compressive stress on the seal. Many combination gaskets are based on this idea or slightly modified, but the principle is the same. For example, PTFE has good plasticity, excellent chemical corrosion resistance and wide working temperature range (-190 ~ 250℃), and is widely used in static sealing flat pads. However, for some reasons, its poor resilience and cold flow tendency limit its simple use. The combined structure can overcome this shortcoming. On the one hand, it can protect the pad from the corrosion of fluid medium or avoid the contact pollution of food and medicine. On the other hand,
Types, Materials and Application Scope of Non-metallic Gaskets Types and Material Pressure of Gaskets
MPa temperature
Suitable medium at 20℃
Teflon gasket Teflon plate ≤ 3.0- 108-250 concentrated acid, alkali, solvent and oil.
Rubber asbestos gasket high pressure rubber asbestos board
Medium pressure rubber asbestos board
Low pressure rubber asbestos board ≤6.0
≤4.0
≤ 1.5 ≤450
≤350
200 or less concentration of acid, alkali, solvent and oil.
Oil-resistant rubber asbestos board ≤ 4.0- 180-250 air, compressed air, inert gas, steam, ammonia, shift gas, coke oven gas, cracking gas, water, seawater, liquid ammonia, condensed water, ≤90% sulfuric acid (mass fraction), salts, ammonium nitrate solution, sulfur ammonia solution, methylamine solution, etc.
Type, material and application scope of combined gasket; Gasket type, material pressure.
MPa temperature
Suitable medium at 20℃
Metal strip wound with gasket: stainless steel.
Non-metallic belt: asbestos belt,
Ptef，
Flexible graphite belt for internal combustion engine ≤6.4 ≈600.
Metal clad flat gasket
Corrugated gasket metal: low carbon steel, aluminum,
Stainless steel and alloy steel
Non-metal: asbestos board, rubber asbestos board, PTFE board, ceramic fiber ≤6.4 ≈600 steam, hydrogen, compressed air, natural gas, cracking gas, shift gas, oil products, solvents, residual oil, wax oil, slurry oil, heavy oil, propylene, caustic soda, molten salt heat carrier, acid, alkali, salt solution, liquefied gas and water.
Types, Materials and Application Scope of Metal Gaskets Type of Gasket Material Pressure
MPa temperature
Suitable medium at 20℃
Metal flat gasket
Low carbon steel, stainless steel, alloy steel ≥4.0 ≈600 steam, hydrogen, compressed air, natural gas, cracking gas, shift gas, oil, solvent, residual oil, wax oil, slurry oil, heavy oil, propylene, caustic soda, molten salt carrier, acid, alkali, alkali solution, liquefied gas and water.
Metal octagonal pad
Metal lens pad
Metal oval pad 10 steel, 10cr 13, alloy steel, stainless steel, etc. ≥6.4 ≈600 Steam, hydrogen, compressed air, natural gas, cracked gas, shift gas, oil, solvent, residual oil, wax oil, slurry oil, heavy oil, propylene, caustic soda, molten salt carrier, etc.
Asbestos rubber sealant
China is rich in asbestos resources. Asbestos can be released by mechanical or chemical treatment. The completely released asbestos fiber has high tensile strength, large surface area, good adsorption performance, incombustibility and good heat resistance. The maximum safe use temperature is 500 ~ 550℃, which can basically meet the needs of industrial workers. Besides, asbestos is cheap. Its disadvantage is that asbestos dust pollutes the environment and is harmful to human body. Attention should be paid to environmental protection.
Asbestos rubber sealing products can be divided into the following three categories:
① Gaskets-plate and sheet sealing products used on pipeline flanges and container flanges;
② Gasket-used for molding and sealing products of pumps, valves and kettles;
③ Packaging belts and velvet sealing products for pumps, valves and kettles.
Asbestos rubber sheet is a sealing material for pipeline flanges, high-pressure container flanges and various contact surfaces rolled by asbestos, rubber and additives.
Oil-resistant asbestos rubber sheet is a sealing material for pipeline flanges, high-pressure container flanges and various contact surfaces, which is made of asbestos, oil-resistant rubber and compounding agent as the main raw materials through calendering.
Reinforced asbestos rubber sheet consists of asbestos rubber sheet and one or more layers of galvanized steel wire mesh (or stainless steel wire mesh). Generally divided into oil-resistant reinforcing plate and high-pressure reinforcing plate. The number of layers of steel wire mesh is related to the thickness of the product. Generally speaking, for every increase in product thickness of 1mm, a layer of steel wire mesh should be added, and the steel wire mesh should be sandwiched in the corresponding bisection and trisection of asbestos rubber to increase the tensile strength and make it resistant to high temperature and high pressure. Thin gaskets should be used in high temperature and high pressure environment. Thin gasket can play the role of metal gasket, but also can play a "face to face" direct sealing role. At this time, the roughness and flatness of the sealing surface should be high. The thickness of reinforced asbestos rubber sheet is generally not more than 3mm.
With the development of petroleum, chemical industry, aviation and national defense. With the emergence of high-temperature and high-pressure and ultra-high-temperature and high-pressure equipment, management and high-speed, small-volume and high-power development machines, asbestos rubber sheets can no longer meet the needs. They should have the characteristics of high temperature resistance, high pressure resistance, oil resistance, incombustibility, good elasticity, adaptability to large fluctuations of temperature and pressure, long service life and excellent sealing performance. Therefore, only reinforced asbestos rubber sheets and asbestos steel sheets and wound gaskets below them can meet these requirements.