Static sealing usually refers to the sealing between two static surfaces, and it mainly uses gaskets.
(1) Materials of gaskets
(a) Non-metal gaskets: They are gaskets made from materials such as paper, linen, cowhide, asbestos products, plastic, rubber, etc. Paper, linen and cowhide have capillary pores and are easy to penetrate, so they must be impregnated with oil, wax or other impermeable materials when used. Generally, they are rarely used for valves.
Asbestos products include asbestos tapes, ropes, plates, and asbestos rubber sheets. Among them, the asbestos rubber plate has a compact structure, good pressure resistance, and temperature resistance. It is widely used in the valve and the flange connection between the valve and pipe. Plastic products have good corrosion resistance and are commonly used. They can be classified into polyethylene, polypropylene, soft polyvinyl chloride, polytetrafluoroethylene, nylon 66, nylon 1010 and so on. Rubber products have a soft texture, and various rubbers are resistant to acids, alkalis, oils, and seawater. They include natural rubber, styrene butadiene rubber, nitrile rubber, neoprene rubber, isobutyl rubber, polyurethane rubber and fluorine rubber.
(b) Metal gaskets: Generally speaking, metals have high strength and high-temperature resistance. However, this is not the case with lead, and only the characteristics of its resistance to dilute sulfuric acid are adopted. Commonly used metals for gaskets are brass, copper, aluminum, low carbon steel, stainless steel, Monel, silver, nickel, etc.
(c) Composite gaskets: they are gaskets such as metal sheath (internal asbestos) gaskets, combined wave gaskets, spiral wound gaskets, etc.
(1) Materials of gaskets
(a) Non-metal gaskets: They are gaskets made from materials such as paper, linen, cowhide, asbestos products, plastic, rubber, etc. Paper, linen and cowhide have capillary pores and are easy to penetrate, so they must be impregnated with oil, wax or other impermeable materials when used. Generally, they are rarely used for valves.
Asbestos products include asbestos tapes, ropes, plates, and asbestos rubber sheets. Among them, the asbestos rubber plate has a compact structure, good pressure resistance, and temperature resistance. It is widely used in the valve and the flange connection between the valve and pipe. Plastic products have good corrosion resistance and are commonly used. They can be classified into polyethylene, polypropylene, soft polyvinyl chloride, polytetrafluoroethylene, nylon 66, nylon 1010 and so on. Rubber products have a soft texture, and various rubbers are resistant to acids, alkalis, oils, and seawater. They include natural rubber, styrene butadiene rubber, nitrile rubber, neoprene rubber, isobutyl rubber, polyurethane rubber and fluorine rubber.
(b) Metal gaskets: Generally speaking, metals have high strength and high-temperature resistance. However, this is not the case with lead, and only the characteristics of its resistance to dilute sulfuric acid are adopted. Commonly used metals for gaskets are brass, copper, aluminum, low carbon steel, stainless steel, Monel, silver, nickel, etc.
(c) Composite gaskets: they are gaskets such as metal sheath (internal asbestos) gaskets, combined wave gaskets, spiral wound gaskets, etc.
(2) Performance of commonly used gaskets
According to specific conditions, gaskets are often replaced when valves are used. Commonly used gaskets are rubber flat gaskets, rubber O rings, plastic flat gaskets, PTFE covered gaskets, asbestos rubber gaskets, metal flat gaskets, metal special shaped gaskets, metal covered gaskets, wave gaskets, winding gaskets, etc.
Rubber flat gaskets: They are easy to deform and do not require effort when pressed. However, they have poor pressure and temperature resistance. They are only used in places where the pressure is low and the temperature is not high. Natural rubber has certain acid and alkali resistance, and the use temperature should not exceed 60℃; chloroprene rubber can also be resistant to certain acids and alkalis, and its use temperature is 80℃; nitrile rubber is oil resistant and can be used up to 80℃; fluororubber has good corrosion resistance and its temperature performance is also better than that of general rubber; it can be used in the medium at a temperature of 150℃.
Rubber O shaped gaskets: their cross-sectional shape is a perfect circle, with a certain degree of self-tightening effect. Their sealing effect is better than the flat gasket, and their pressing force is smaller.
Plastic flat gaskets: The most outstanding feature of plastics is that they have good corrosion resistance, and most plastics have poor temperature resistance. PTFE is the king of plastics. It not only has excellent corrosion resistance, but also has a wide temperature resistance range. It can be used for a long time within temperatures between -180℃ and +200℃.
PTFE covered gaskets: In order to give full play to the advantages of PTFE and make up for its poor elasticity, PTFE covered rubber or asbestos rubber gaskets are adopted. In this way, it not only has the same corrosion resistance as the PTFE flat gasket, but also has good elasticity, which enhances the sealing effect and reduces the packing force.
Asbestos rubber gaskets: they are made of asbestos rubber plates, and they have good heat resistance, cold resistance, chemical stability, abundant supply, and low prices. They are composed of 60% to 80% asbestos and 10% to 20% rubber, fillers, vulcanizing agents and so on. When asbestos rubber gaskets are used, the packing force does not have to be great. Because asbestos rubber gaskets can adhere to metal, it is best to coat the surface with a layer of graphite powder to avoid laborious disassembly.
Asbestos rubber plates have four colors, that is, gray, red, prunosus and green. Gray asbestos rubber plates are used for low pressure (Grade XB-200 with pressure resistance less than and equal to 16 kg/cm² and resistance to a temperature of 200℃). Red asbestos rubber plates are used for medium pressure (Grade XB-350 with pressure resistance up to 40kg/cm2 and resistance to a temperature of 350℃). Prunosus asbestos rubber plates are used for high pressure (Grade XB-450 with pressure resistance 100kg/cm2 and resistance to a temperature of 450℃). Green asbestos rubber plates are used for oils, and their pressure resistance performance is also very good.
Metal flat gaskets: metal flat gaskets made from lead are resistant to a temperature of 100℃, aluminum 430℃, copper 315℃, low carbon steel 550℃, silver 650℃, nickel 810℃, Monel nickel copper 810℃, and stainless steel 870°C. Among them, lead has poor pressure resistance; aluminum can withstand 64kg/cm², and other materials can withstand high pressure.
Metal anisotropic gaskets
Lens gaskets: they have the effect of self-tightening, which are used for high-pressure valves.
Oval gaskets: they also belong to high-pressure self-tightening gaskets.
Cone double gaskets: they are used for high-pressure internal self-tightening sealing. In addition, there are square, rhombus, triangle, have shapes of a tooth, swallow-tail, B and C, which are generally only used in high and medium pressure valves.
Metal covered gaskets: the covered materials include aluminum, copper, low carbon steel, stainless steel and Monel alloy. The filling materials include asbestos, polytetrafluoroethylene and glass fiber. Metal not only has good temperature and pressure resistance but also good elasticity.
Wave gaskets: they have the characteristics of small pressing force and a good sealing effect. The combination of metal and non-metal is often adopted.
Spiral wound gaskets: a thin metal belt and a non-metallic belt are tightly attached, and winded into a multi-layer circular shape with a wavy cross-section, which has good elasticity and airtightness. The metal belt can be made from 08 steel, 0Cr13, 1Cr13, 2Cr13, 1Cr18Ni9Ti, copper, aluminum, titanium, Monel, etc. Non-metallic belt materials include asbestos and polytetrafluoroethylene.
(3) New sealing materials and new sealing technologies
Liquid sealing: With the rapid development of the polymer organic synthesis industry, liquid sealants have appeared in recent years, which are used for static sealing; this new technology is usually called liquid sealing. The principle of liquid sealing is to make use of the adhesiveness, fluidity and monomolecular film effect of the liquid sealant. The thinner the film is, the greater the tendency for natural recovery becomes. Under appropriate pressure, the liquid sealing can function as a gasket. Therefore, the sealant is also called a liquid gasket.
PTFE raw material sealing: PTFE is also a high-molecular organic compound, it is called the raw material before being sintered into a product, which has soft texture and a monomolecular film effect. Tapes made of raw materials are called raw material tapes, which can be rolled into a reel for long-term storage. It can be formed freely when it is used. As long as there is pressure, a ring shaped film that evenly plays a sealing role can be formed. As the gasket between the valve body and valve bonnet in the valve, you can pry the valve without taking out the valve disc or valve plate, and insert the raw material into it. It has small pressing force, and it is not sticky to the hands or flange surface. It's easy to replace the PTFE raw material. It is most suitable for tongue and groove flanges. PTFE raw materials can also be made into tube and rod shapes for sealing.
Metal hollow O rings: they have good elasticity, small pressing force, self-tightening effect, and a variety of metal materials can be selected to adapt to low-temperature, high-temperature and strong corrosive media.
Graphite plate gaskets: In people's impression, graphite is a brittle substance, which lacks elasticity and toughness, but specially treated graphite has a soft texture and good elasticity. In this way, the heat resistance and chemical stability of graphite can be displayed in the gasket's material; and this gasket has a small compression force and an exceptionally superior sealing effect. This kind of graphite can also be made into belts, which can be combined with metal belts to form spiral wound gaskets with excellent performance. The appearance of graphite plate sealing rings and graphite metal spiral wound gaskets is a major breakthrough in high-temperature corrosion resistant sealing.
Rubber flat gaskets: They are easy to deform and do not require effort when pressed. However, they have poor pressure and temperature resistance. They are only used in places where the pressure is low and the temperature is not high. Natural rubber has certain acid and alkali resistance, and the use temperature should not exceed 60℃; chloroprene rubber can also be resistant to certain acids and alkalis, and its use temperature is 80℃; nitrile rubber is oil resistant and can be used up to 80℃; fluororubber has good corrosion resistance and its temperature performance is also better than that of general rubber; it can be used in the medium at a temperature of 150℃.
Rubber O shaped gaskets: their cross-sectional shape is a perfect circle, with a certain degree of self-tightening effect. Their sealing effect is better than the flat gasket, and their pressing force is smaller.
Plastic flat gaskets: The most outstanding feature of plastics is that they have good corrosion resistance, and most plastics have poor temperature resistance. PTFE is the king of plastics. It not only has excellent corrosion resistance, but also has a wide temperature resistance range. It can be used for a long time within temperatures between -180℃ and +200℃.
PTFE covered gaskets: In order to give full play to the advantages of PTFE and make up for its poor elasticity, PTFE covered rubber or asbestos rubber gaskets are adopted. In this way, it not only has the same corrosion resistance as the PTFE flat gasket, but also has good elasticity, which enhances the sealing effect and reduces the packing force.
Asbestos rubber gaskets: they are made of asbestos rubber plates, and they have good heat resistance, cold resistance, chemical stability, abundant supply, and low prices. They are composed of 60% to 80% asbestos and 10% to 20% rubber, fillers, vulcanizing agents and so on. When asbestos rubber gaskets are used, the packing force does not have to be great. Because asbestos rubber gaskets can adhere to metal, it is best to coat the surface with a layer of graphite powder to avoid laborious disassembly.
Asbestos rubber plates have four colors, that is, gray, red, prunosus and green. Gray asbestos rubber plates are used for low pressure (Grade XB-200 with pressure resistance less than and equal to 16 kg/cm² and resistance to a temperature of 200℃). Red asbestos rubber plates are used for medium pressure (Grade XB-350 with pressure resistance up to 40kg/cm2 and resistance to a temperature of 350℃). Prunosus asbestos rubber plates are used for high pressure (Grade XB-450 with pressure resistance 100kg/cm2 and resistance to a temperature of 450℃). Green asbestos rubber plates are used for oils, and their pressure resistance performance is also very good.
Metal flat gaskets: metal flat gaskets made from lead are resistant to a temperature of 100℃, aluminum 430℃, copper 315℃, low carbon steel 550℃, silver 650℃, nickel 810℃, Monel nickel copper 810℃, and stainless steel 870°C. Among them, lead has poor pressure resistance; aluminum can withstand 64kg/cm², and other materials can withstand high pressure.
Metal anisotropic gaskets
Lens gaskets: they have the effect of self-tightening, which are used for high-pressure valves.
Oval gaskets: they also belong to high-pressure self-tightening gaskets.
Cone double gaskets: they are used for high-pressure internal self-tightening sealing. In addition, there are square, rhombus, triangle, have shapes of a tooth, swallow-tail, B and C, which are generally only used in high and medium pressure valves.
Metal covered gaskets: the covered materials include aluminum, copper, low carbon steel, stainless steel and Monel alloy. The filling materials include asbestos, polytetrafluoroethylene and glass fiber. Metal not only has good temperature and pressure resistance but also good elasticity.
Wave gaskets: they have the characteristics of small pressing force and a good sealing effect. The combination of metal and non-metal is often adopted.
Spiral wound gaskets: a thin metal belt and a non-metallic belt are tightly attached, and winded into a multi-layer circular shape with a wavy cross-section, which has good elasticity and airtightness. The metal belt can be made from 08 steel, 0Cr13, 1Cr13, 2Cr13, 1Cr18Ni9Ti, copper, aluminum, titanium, Monel, etc. Non-metallic belt materials include asbestos and polytetrafluoroethylene.
(3) New sealing materials and new sealing technologies
Liquid sealing: With the rapid development of the polymer organic synthesis industry, liquid sealants have appeared in recent years, which are used for static sealing; this new technology is usually called liquid sealing. The principle of liquid sealing is to make use of the adhesiveness, fluidity and monomolecular film effect of the liquid sealant. The thinner the film is, the greater the tendency for natural recovery becomes. Under appropriate pressure, the liquid sealing can function as a gasket. Therefore, the sealant is also called a liquid gasket.
PTFE raw material sealing: PTFE is also a high-molecular organic compound, it is called the raw material before being sintered into a product, which has soft texture and a monomolecular film effect. Tapes made of raw materials are called raw material tapes, which can be rolled into a reel for long-term storage. It can be formed freely when it is used. As long as there is pressure, a ring shaped film that evenly plays a sealing role can be formed. As the gasket between the valve body and valve bonnet in the valve, you can pry the valve without taking out the valve disc or valve plate, and insert the raw material into it. It has small pressing force, and it is not sticky to the hands or flange surface. It's easy to replace the PTFE raw material. It is most suitable for tongue and groove flanges. PTFE raw materials can also be made into tube and rod shapes for sealing.
Metal hollow O rings: they have good elasticity, small pressing force, self-tightening effect, and a variety of metal materials can be selected to adapt to low-temperature, high-temperature and strong corrosive media.
Graphite plate gaskets: In people's impression, graphite is a brittle substance, which lacks elasticity and toughness, but specially treated graphite has a soft texture and good elasticity. In this way, the heat resistance and chemical stability of graphite can be displayed in the gasket's material; and this gasket has a small compression force and an exceptionally superior sealing effect. This kind of graphite can also be made into belts, which can be combined with metal belts to form spiral wound gaskets with excellent performance. The appearance of graphite plate sealing rings and graphite metal spiral wound gaskets is a major breakthrough in high-temperature corrosion resistant sealing.
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