Types, functions, and application ranges of common gaskets

There are a variety of gaskets, which can be classified into three main categories based on the primary material of their construction: non-metallic, semimetallic, and metallic gaskets. ⑴Non-metallic gaskets. Non-metallic gaskets are soft, corrosion-resistant, and inexpensive, but they have poor temperature and pressure resistance. It is commonly used for flange sealing in medium and low-pressure vessels or pipelines at normal and moderate temperatures. Non-metallic gaskets include rubber gaskets, asbestos gaskets, asbestos-rubber gaskets, flexible graphite gaskets, and polytetrafluoroethylene gaskets, among others. ①Rubber sheet. The main materials used to manufacture rubber gasket sheets include natural rubber, nitrile rubber, neoprene, etc. In addition, special rubbers such as fluororubber are also beginning to be used. Rubber is widely used for sealing containers and pipes due to its dense structure, soft texture, good elasticity, ease of cutting into various shapes, as well as being inexpensive and readily available. However, it cannot withstand high pressures, dissolves and swells in mineral oils, is susceptible to corrosion, and ages easily at high temperatures, losing its elasticity. ②Asbestos. Asbestos materials come in two types: chrysotile and blue asbestos. Wet asbestos has good heat and alkali resistance, high tensile strength, but poor acid resistance; most asbestos rubber sheets are made from it ； Blue asbestos not only has good heat resistance but also excellent acid resistance, which is why it is often used in the manufacture of acid-resistant asbestos rubber sheets. The normal operating temperature for asbestos boards is below 550 degrees. Asbestos tape or asbestos rope can be used for low-pressure containers with a larger diameter. When using asbestos rope, it is usually impregnated with water glass. Such gaskets can also be used in media such as acids, bases, and solvents. ③Asbestos rubber sheet. Asbestos rubber sheets are made by compressing asbestos, rubber, and fillers together. Generally, asbestos fibers account for 60%-85%. Based on their manufacturing processes, properties, and applications, they mainly include high-pressure asbestos rubber sheets, medium and low-pressure asbestos rubber sheets, and oil-resistant asbestos rubber sheets. Asbestos rubber sheets possess suitable properties such as strength, elasticity, and flexibility; using them to make gaskets is both convenient and cost-effective, which has led to their rapid adoption and use in chemical manufacturing enterprises. ④Flexible graphite. Flexible graphite is a novel sealing material with excellent resilience, flexibility, and heat resistance, and it has been rapidly adopted and used in chemical industries. ⑤Polytetrafluoroethylene (abbreviated as PTFE). Polytetrafluoroethylene is known as the \"king of plastics\" because its chemical resistance, heat resistance, cold resistance, and oil resistance surpass those of any other plastic currently available. It does not age easily, does not burn, and has an absorption rate of water that is virtually zero. It has a dense structure and a non-polar molecular structure; it is used as a gasket, allowing the contact surface to remain flat and smooth, without sticking to metal flanges. Apart from being eroded by molten alkali metals and fluorine-containing gas, it can resist corrosion by a variety of acid, alkali, salt, and oil-based solution media. PTFE gaskets include pure PTFE, filled PTFE, or expanded PTFE, among others. ⑵Semi-metal gaskets (also known as metal composite gaskets). Non-metallic materials have advantages such as good flexibility, compressibility, and low bolt load capacity. But its main drawback is its low strength and poor resilience, making it unsuitable for high-pressure and high-temperature environments. Therefore, taking into account the high strength and good resilience of metal materials. The ability to withstand high temperatures. A gasket is formed to combine the two structures. That is, a semimetallic gasket. Semi-metallic gaskets mainly include metal-clad gaskets, metal-wound gaskets, metal corrugated ring gaskets, and metal toothed ring gaskets. ①Metal gasket (metal composite gasket). This gasket has a non-metallic core, with an outer coating thickness of 0. 25-0. 5mm thick metal sheet. Based on the coating status, it can be divided into full coating, semi-coating, wave-shaped coating, and double-layer coating, etc. Metal sheets are selected based on the material’s elastoplasticity, heat resistance, and corrosion resistance. The main materials include copper, galvanized iron sheet, stainless steel, titanium, Monel alloy, etc. Copper, galvanized iron sheet, and stainless steel are the most commonly used. As the core material for metal gaskets, heat resistance is the main criterion for evaluation. Aspiral board or low-rubber asbestos board, carbon fiber or ceramic fiber with good high-temperature resistance, as well as flexible graphite sheets are generally used. Another advantage of metal-clad gaskets is that they can be made into various types of gaskets. It can meet the sealing requirements of various heat exchanger tube boxes and non-circular pressure vessels, whereas other composite gaskets cannot. ②Metal wound gaskets. A metal wound gasket is formed by alternately winding thin metal corrugated strips with non-metallic materials such as asbestos or flexible graphite in a spiral pattern, and then welding the starting and ending points of the metal strips together. It is also known as a spiral gasket abroad. ⑶Metal gasket. Under harsh operating conditions such as high temperature and pressure, as well as frequent load cycles, various metal materials remain the preferred choices for gaskets. Commonly used materials include copper, aluminum, low-carbon steel, stainless steel, chromium-nickel alloy steel, and titanium Monel alloys. To reduce bolt loads and ensure a compact structure, in addition to using narrow-width metal flat washers whenever possible, ring washer structures with linear contact characteristics are the preferred form. ①Flat metal gasket. For parallel use, there are two types: wide shims and narrow shims. Wide gaskets, due to the high pre-tension requirements, tend to cause deformation of the bolt flanges when the pressure exceeds 1. It is rarely used on flanges with smooth surfaces at 96 MPa. Narrow gaskets are easy to preload, at a pressure of 6. 27-9. Used on pipes at 8MPa. ②Wavy metal gasket. The thickness of the metal plate in wave-shaped metal gaskets is generally 0. 25-0. 8mm。 The gasket thickness is generally 40%-50% of the wavelength. Suitable for smooth sealing surfaces, pressure 3. Used on pipes at 34 MPa. ③Toothed metal gasket. Toothed metal gaskets are commonly used in 6. 77-9. On a pipeline of 8MPa. The tooth tip distance is about 1. 5mm, with tooth tip and tooth root angles both at 90 degrees. Its sealing performance is better than that of flat gaskets, and the compression force required is also lower than that of flat gaskets.