Gasket sealing structures are widely used in various types of machinery and equipment, especially in various pressure vessels, pipelines and valves. The simplest gasket is a flat gasket, and the entire gasket is composed of the same material, which is used as a static seal for the general joint surface of mechanical equipment, such as the sealing of gearboxes.
An ideal gasket structure should have a plastic layer on the surface and an elastomer on the surface. The plastic surface layer ensures that it is sealed and close to each other or even fitted, while the layer allows to compensate for a little separation of the sealing surface and often maintain 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, polytetrafluoroethylene (PTFE) has good plasticity, excellent chemical corrosion resistance and a wide working temperature range (-190~ 250 ° C), and is widely used in static sealing flat gaskets. However, due to some reason, its poor resilience and tendency to cold flow limit its simple use. The use of a combination structure can overcome this drawback. On the one hand, it can protect the gasket from corrosion of fluid media or avoid contact pollution of food and pharmaceutical industrial products. On the other hand, it improves the poor rebound and cold flow problems caused by the simple use of PTFE.
My country is rich in asbestos resources. Asbestos can be loosened by mechanical or chemical treatment. Fully loosened asbestos fibers have high tensile strength and large surface area, good adsorption performance, cannot burn, and good heat resistance. The maximum safe use temperature is 500~ 550 ℃, this temperature can basically meet the needs of industrial workers, and asbestos is cheap. The disadvantage is that asbestos dust pollutes the environment and is harmful to the human body. Pay attention to environmental protection.
Asbestos rubber sealing products can be divided into the following 3 categories:
①Gaskets – plate and sheet sealing products used on pipe flanges and container flanges;
②Washers – molded and sealed products used in pumps, valves and kettles;
③Packing – rope and fleece sealing products used on pumps, valves, and kettles.
Asbestos rubber sheet is a sealing material used for pipe flanges rolled by asbestos, rubber and compounding agents, high-pressure vessel flanges and various contact surfaces.
Oil-resistant asbestos rubber sheet is a pipe flange, a high-pressure vessel flange and a sealing material used for various contact surfaces that are rolled with asbestos, oil-resistant rubber and compounding agents as the main raw materials. Reinforced asbestos rubber sheet is composed of asbestos rubber sheet and one or more layers of galvanized steel wire mesh (or embroidered steel wire mesh). It is generally divided into two types: 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, a layer of steel wire mesh should be added for every 1mm increase in the thickness of the product. The steel wire mesh should be sandwiched in the corresponding second and third parts 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 pressure fields. Thin gaskets can play the role of metal gaskets, and can also be said to play the role of “plane and plane” direct sealing. At this time, the roughness and flatness of the sealing surface should be very high.
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, general asbestos rubber sheets can no longer meet the needs. They should have high temperature resistance, high pressure resistance, oil resistance, non-combustible, good elasticity, and can adapt to large fluctuations in temperature and pressure, and should have a long service life and excellent sealing performance. Therefore, only reinforced asbestos rubber sheets and the following asbestos steel sheets, wound gaskets, etc. can meet these requirements.
The choice of gasket material mainly depends on the following three factors: temperature pressure medium metal gasket material
- Carbon steel: The recommended maximum working temperature does not exceed 538 ° C, especially when the medium is oxidizing. High-quality thin carbon steel plates are not suitable for equipment used to manufacture inorganic acid, neutral or acidic salt solutions. If carbon steel is subjected to stress, the accident rate of equipment used in hot water conditions is very high. Carbon steel gaskets are usually used for high-concentration acids and many alkali solutions. Brinell hardness is about 120.
- 304 stainless steel 18-8 (chromium 18-20%, nickel 8-10%), the recommended maximum working temperature does not exceed 760 ℃. In the temperature range of -196~ 538 ℃, stress corrosion and grain boundary corrosion are prone to occur. Brinell hardness 160.
3.304L stainless steel carbon content does not exceed 0.03%. Recommended maximum working temperature does not exceed 760 ℃. Corrosion resistance is similar to 304 stainless steel. Low carbon content reduces the precipitation of carbon from the lattice, and the grain boundary corrosion resistance is higher than that of 304 stainless steel. Brinell hardness is about 140.
4.316 stainless steel 18-12 (chromium 18%, nickel 12%), about 2% molybdenum is added to 304 stainless steel, and its strength and corrosion resistance are improved when the temperature increases. When the temperature increases, it has higher creep resistance than other ordinary stainless steels. The recommended maximum working temperature does not exceed 760 ° C. Brinell hardness is about 160.
5.316L stainless steel The recommended maximum working temperature does not exceed 760 ℃~ 815 ℃. The carbon content does not exceed 316 stainless steel and has better stress resistance and grain boundary corrosion. Brinell hardness is about 140.
6.20 alloy 45% iron, 24% nickel, 20% chromium and a small amount of molybdenum and copper. Recommended maximum working temperature does not exceed 760 ℃~ 815 ℃. Especially suitable for manufacturing equipment resistant to sulfuric acid corrosion, Brinell hardness is about 160.
7. Aluminum Aluminum (content not less than 99%). Aluminum has excellent corrosion resistance and processability, suitable for the manufacture of double-clamped gaskets. Brinell hardness is about 35. Recommended maximum operating temperature does not exceed 426 ℃.
8. The composition of red copper is close to pure copper, and it contains a small amount of silver to increase its continuous working temperature. The recommended maximum working temperature does not exceed 260 ° C. Brinell hardness is about 80.
9. Brass (copper 66%, zinc 34%), under most working conditions, has good corrosion resistance, but is not suitable for acetic acid, ammonia, salt and acetylene. Recommended maximum operating temperature does not exceed 260 ℃. Brinell hardness about 58.
10. Hastelloy B-2 (26-30% molybdenum, 62% nickel and 4-6% iron). Recommended maximum working temperature does not exceed 1093 ℃. Has excellent heat resistance to hydrochloric acid corrosion of concentration. Also has excellent resistance to wet hydrogen chloride gas corrosion, sulfuric acid, phosphoric acid and reducing salt solution corrosion performance. High strength under high temperature conditions. Brinell hardness about 230.
11. Hastelloy C-276 16-18% molybdenum, 13-17.5% chromium, 3.7-5% tungsten, 4.5-7% iron, the rest are nickel). Recommended maximum working temperature does not exceed 1093 ℃. Excellent corrosion resistance. Excellent corrosion resistance to various attempted cold nitric acid or boiling nitric acid with a concentration of 70%, good resistance to hydrochloric acid and sulfuric acid corrosion and excellent stress corrosion resistance. Brinell hardness is about 210.
12. Inconel 600 nickel-based alloy (77% nickel, 15% chromium and 7% iron). Recommended maximum operating temperature does not exceed 1093 ℃. It has high strength under high temperature conditions and is usually used in equipment that needs to solve stress corrosion problems. At low temperature conditions, it has excellent co-processing performance. Brinell hardness is about 150.
13. Monel 400 (30% copper, nickel recommended maximum working temperature does not exceed 815 ℃. Except for strong oxidizing acids, it has excellent corrosion resistance to most acids and alkalis. It is prone to stress corrosion cracking in fluoric acid, mercury chloride, and mercury media, so it is not suitable for use in the above media. It is widely used in equipment for the manufacture of hydrofluoric acid. Brinell hardness is about 120.
14. Recommended maximum working temperature does not exceed 1093 ℃. Under high temperature conditions, it has excellent corrosion resistance.
It is well known to be resistant to chloride ions and has excellent resistance to nitric acid corrosion in a wide temperature and concentration range. Titanium is rarely used in most alkali solutions and is suitable for oxidation conditions. Brinell hardness is about 216. Non-metallic gasket material:
1. Natural rubber NR has good corrosion resistance to weak acids and alkalis, salts and chloride solutions, and poor corrosion resistance to oils and solvents. It is not recommended for ozone media. Recommended working temperature -57 ℃~ 93 ℃. 2. Neoprene CR Neoprene is a synthetic rubber, suitable for corrosion resistance to moderately corrosive acids, alkalis and salt solutions. It has good corrosion resistance to commercial oils and fuels. But its corrosion resistance is poor in strong oxidizing acids, aromatic hydrocarbons and chlorinated hydrocarbons. Recommended working temperature -51 ℃~ 121 ℃.
3. Cyanide butadiene rubber NBR cyanide butadiene rubber is a synthetic rubber, suitable for good corrosion resistance to oil, solvents, aromatic hydrocarbons, basic hydrocarbons, oil and natural gas in a wide temperature range. It has good corrosion resistance to hydroxides, salts and near-neutral acids. However, its corrosion resistance is poor in strong oxidizing media, chlorinated hydrocarbons, ketones and lipids, and the recommended working temperature is 51 ° C~ 121 ° C.
4. Fluororubber fluororubber rubber compound is made of binary and ternary fluorine raw rubber filled with compounding agent and vulcanizing agent. In addition to excellent heat resistance, medium resistance, and good physical and mechanical properties, it also has low compression set, good elasticity and long service life. Fluororubber has outstanding heat resistance (200~ 250 ℃) and oil resistance. It can be used to manufacture cylinder liner sealing rings, rubber bowls and rotating lip sealing rings, which can significantly improve the service time. Recommended working temperature -40 ℃~ 232 ℃.
5. Chlorosulfonylated polyethylene synthetic rubber has good corrosion resistance to acid, alkali and salt solutions, and is not affected by climate, light, ozone, commercial fuels (such as diesel and kerosene, etc.). But not suitable for aromatic hydrocarbons, chlorinated hydrocarbons, chromic acid and nitric acid. Recommended working temperature -45 ℃~ 135 ℃.
6. Silicone rubber Silicone rubber has outstanding high and low temperature resistance, and can be used for a long time at 150 ° C without performance change; it can be used continuously for 10,000 hours at 200 ° C, and can maintain its unique use at a working temperature of -70~ 260 ° C. The advantages of elasticity, ozone resistance, weather resistance, etc., are suitable for making sealing gaskets required in thermal mechanisms, such as sealing bushings, valve gaskets, oil seals (suitable for aqueous media), etc. Special silicone rubber can make oil seals.
7. Ethylene propylene rubber has good corrosion resistance to strong acid, strong alkali, salt and chloride solutions. But it is not suitable for oils, solvents, aromatic hydrocarbons and hydrocarbons. Recommended working temperature -57 ℃~ 176.
8. Graphite This material is an all-graphite material that does not contain resin or inorganic substances. It can be divided into graphite materials with or without metal elements. The material can be bonded so that pipe gaskets with a diameter of more than 600MM can be manufactured. It has very excellent corrosion resistance to many acids, alkalis, salts and organic compounds and heat transfer solutions, and even high temperature solutions. It cannot be melted, but will sublimate when it exceeds 3316 ° C. The use of this material in strongly oxidizing media should be used with caution under high temperature conditions. In addition to being used for gaskets, this material can also be used to make non-metallic winding tape in fillers and winding gaskets.
9. Porcelain fiber and porcelain fiber formed into strip is an excellent gasket material suitable for high temperature and low pressure working conditions and light flange conditions. The recommended working temperature is 1093 ° C, which can make non-metallic winding tape in winding gaskets.
10．聚四氟乙烯集中了大多数塑料垫片材料的优点，包括耐温从-95℃~232℃。除游离氟和碱金属外，对化学物品、溶剂、氢氧化物和酸具有优异的耐蚀性能。PTFE材料能充填玻璃，其目的是降低PTFE的冷流性和蠕变性。