What is a sealing gasket
What is a sealing gasket?
Sealing gasket is a kind of sealing spare parts used in machinery, equipment and pipelines as long as there is fluid. It uses internal and external materials to seal. The sealing gasket is made of metal or non-metal plate material through cutting, stamping or cutting. It is used for sealing connection between pipes and between parts of machinery and equipment. According to the material, it can be divided into metal sealing gasket and non-metal sealing gasket. Metal gaskets include copper gaskets, stainless steel gaskets, iron gaskets, aluminum gaskets, etc. Non metallic ones include asbestos gasket, non asbestos gasket, paper gasket, rubber gasket, etc.
Gasket sealing plays a very important role in modern industrial enterprises. The quality of sealing is directly related to the continuity of production, property safety, energy conservation and environmental protection, as well as people’s physical and mental health. Therefore, people pay more and more attention to the development of gasket. With the rise of modern industry, especially modern petroleum, chemical industry, atomic energy industry and large-scale power stations, pressure vessels are developing towards high temperature, high pressure, high vacuum, cryogenic, large-scale and multi series. New requirements are constantly put forward for gasket sealing. Various new materials and new structures are emerging, and their sealing performance is also very different. In addition, the fluctuation of pressure, the change of temperature, the relaxation of bolt preload, the inclination and dislocation of flange, the defects of sealing surface and the corrosion of medium will have a great impact on the sealing effect. Therefore, how to correctly select the appropriate sealing gasket according to the working conditions and how to correctly install it are the key to ensure the sealing effect.
Classification of sealing gaskets
Cotton rubber plate gasket
Asbestos rubber gasket is made of asbestos fiber and rubber as the main raw materials, supplemented by rubber compounding agent and filler through mixing, hot roll forming, vulcanization and other processes. Asbestos rubber gasket can be divided into ordinary asbestos rubber gasket and oil resistant asbestos rubber gasket according to its formula, process performance and purpose. According to the temperature and pressure used, it can be divided into low-pressure asbestos rubber gasket, medium pressure asbestos rubber gasket and high-pressure asbestos rubber gasket. It is applicable to the sealing of water, steam, oil, solvent, medium acid and alkali. Asbestos gasket is mainly used in the sealing of medium and low pressure flange connection.
Rubber gasket has the properties of oil resistance, acid and alkali resistance, cold and heat resistance and aging resistance. It can be directly cut into sealing gaskets of various shapes. It is widely used in medicine, electronics, chemical industry, antistatic, flame retardant, food and other industries.
Rubber gasket the sheet rubber products that seal between two stationary surfaces of metal flanges or other connecting parts are collectively referred to as rubber gaskets. It can be made by molding or vulcanized film. It can be widely used in various mechanical equipment, such as gasket, sealing, buffer and so on.
In terms of form, common rubber washers include: rubber flat washer, rubber O-ring, plastic flat washer, PTFE wrapped washer, asbestos rubber washer, metal flat washer, metal special-shaped washer, metal wrapped washer, corrugated washer, wound washer, etc.
- (1) Rubber flat washer: easy to deform and effortless to compress, but poor pressure and temperature resistance. It is only used in places with low pressure and low temperature. Natural rubber has certain acid and alkali resistance, and the service temperature should not exceed 60 ℃; Neoprene can also resist some acid and alkali, and the service temperature is 80 ℃; Nitrile rubber is oil resistant and can be used up to 80 ℃; Fluororubber has good corrosion resistance and better temperature resistance than ordinary rubber. It can be used in 150 ℃ medium.
- (2) Rubber sealing washer: the section shape is round and has a certain self tightening effect. The sealing effect is better than that of flat washer and the pressing force is smaller.
- In terms of material, the main products of rubber pads are: silicone pads, nitrile rubber pads, fluororubber pads and other rubber pads. Rubber gasket has the properties of oil resistance, acid and alkali resistance, cold and heat resistance and aging resistance. It can be directly cut into sealing gaskets of various shapes. It is widely used in medicine, electronics, chemical industry, antistatic, flame retardant, food and other industries.
Cylinder gasket is refined from high-quality asbestos fiber, oil resistant fiber, filler and colorant. It is widely used in automobile and motorcycle engine cylinders. The model of corresponding grade can be selected according to working conditions.
Aramid gaskets are widely used for sealing pumps, valves, pipelines and containers used in fluid transportation equipment, such as steam, organic solvents, acids and alkalis.
Composition and characteristics
The sealing product is made of aramid fiber with high strength and high wear capacity as the main material and special materials with good lubricity. This sealing product has excellent lubricity and wear resistance. It can show its outstanding characteristics on the liquid device with solid-liquid phase mixing.
Non asbestos plate gasket
Non asbestos gasket (non asbestos gasket) is a sealing material made of aramid and other organic fibers and plant fibers, nitrile rubber and inorganic minerals calendered at high temperature. Because there are few asbestos fibers, it is suitable for the replacement of non asbestos gasket of asbestos gasket. Non asbestos gasket (non asbestos gasket) not only has high strength, good resilience, but also has super impermeability. It is a good environmental protection material to replace asbestos gasket under high temperature and high pressure.
It is molded with asbestos cloth and other auxiliary materials, which is used for corrosive high pressure and high temperature sealing. Used for reaction kettle, reaction tank, manhole, handhole, etc. Service temperature: – 100 ℃ – + 1000 ℃; Service pressure: PN < 5.0MP.
The utility model relates to a copolymer gum elastomer made of vinylidene fluoride and fluorine-free, propylene fluoride and propylene, which is widely used in national defense industry and civil industry. It is characterized by high temperature resistance, ozone resistance, natural aging resistance, vacuum resistance, fuel oil resistance, lubricating oil resistance, strong oxidant resistance, good drug resistance and electrical insulation performance.
PTFE lined rubber pad. PTFE lined rubber gasket is a PTFE sandwich rubber composite gasket. It has strong anti-corrosion performance and high sealing resilience. It is suitable for anti-corrosion sealing of enamel, glass pipeline and other low-pressure chemical equipment.
Asbestos free gasket
According to its formula, process performance and application, non asbestos gaskets are roughly divided into non asbestos rubber sheet gaskets and non asbestos take-off sheet gaskets. They are a series of non asbestos sealing gaskets made of aramid and other organic fibers and plant fibers, butadiene green rubber and minerals through extension pressing or take-off process. Because the non asbestos gasket series not only has high strength, Moreover, they have good resilience and super impermeability, so they are excellent environmental protection sealing gaskets to replace asbestos gaskets in the field of automobile and industrial machinery.
Industry standard for sealing gasket
- 1. GB4622.2-93 spiral wound gasket pipe flange dimension series
- 2. GB9126.1-88 asbestos rubber sheet for flat steel pipe flange
- 3. GB9126.2-88 asbestos rubber sheet for raised profile steel pipe flange
- 4. GB9126.3-88 asbestos rubber sheet for concave convex steel pipe flange
- 5. GB9129-88 specification for asbestos rubber gaskets for steel pipe flanges
- 6. GB9130-88 specification for metal ring gaskets for steel pipe flange connection
- 7. HGJ70-91 flexible graphite composite gasket for steel pipe flange
- 1. The sealing gasket and flange sealing surface shall be cleaned, and there shall be no scratches, spots and other defects affecting the sealing performance of the connection.
- 2. The outer diameter of the sealing gasket shall be smaller than that outside the flange sealing surface, and the inner diameter of the sealing gasket shall be slightly larger than that of the pipeline. The difference between the two inner diameters is generally twice the thickness of the sealing gasket, so as to ensure that the inner edge of the sealing gasket will not extend into the container or pipeline after compression, so as not to hinder the flow of fluid in the container or pipeline.
- 3. The pre tightening force of the sealing gasket shall not exceed the design provisions to avoid excessive compression and loss of resilience of the sealing gasket.
- 4. When the sealing gasket is compressed, it is best to use a torque wrench. For large bolts and high-strength bolts, it is best to use hydraulic tighteners. The tightening torque shall be calculated according to the compression of the given sealing gasket, and the oil pressure of the hydraulic tensioner shall also be determined through calculation.
- 5. When installing the sealing gasket, tighten the nuts in sequence. However, the design value shall not be reached by screwing once. Generally, it shall be cycled at least 2 ~ 3 times so that the stress distribution of the sealing gasket is uniform.
- 6. For pressure vessels and pipelines with flammable and explosive media, safety tools shall be used when replacing sealing gaskets to avoid sparks caused by collision between tools and flanges or bolts, resulting in fire or explosion accidents.
- 7. If there is leakage in the pipeline, the sealing gasket must be replaced or adjusted after pressure reduction. It is strictly prohibited to operate under pressure.
Special installation requirements
- 1. When installing the sealing spiral wound gasket matched with the raised plane flange, pay attention to ensure that the seal is concentric with the pipe. Generally, the external stiffening ring is in contact with the inner circumferential surface of the bolt for positioning, and eccentric installation is not allowed. When installing the basic spiral wound gasket in the sealing surface flange of tenon and groove surface, pay attention to keep the gap consistent with the groove wall surface.
- 2. When installing the metal clad gasket with narrow width, place a certain thickness of steel plate on the outside of the gasket, and then press the flange, so as to avoid expanding the interface (or lap) of the metal shell and damaging the metal clad gasket after the clad filler in the metal gasket is pressed.
- 3. When the working temperature of the flange is higher than 200 ℃, sealant shall be applied between the flange sealing surface and the sealing gasket to prevent sintering between the sealing gasket and the flange sealing surface under high temperature, which will increase trouble for maintenance and replacement of the sealing gasket.
- 4. If the sealing surface is not flat, apply sealant on the sealing surface before installing the sealing gasket. Sealant is generally composed of manganese dioxide, lead, graphite powder and boiled linseed oil (dry oil). The corresponding type and brand of liquid sealant can be selected according to the sealing medium, working temperature and medium pressure.
- 5. For the installation of octagonal metal ring gasket, when the processing of metal ring gasket and flange sealing groove is not ideal, the tight fit can be achieved by matching and grinding. For large-diameter metal ring gasket, it is difficult to match and grind. In order to fill the small unevenness on the metal surface, sealant can be used.
Important factors affecting gasket selection gasket selection is not an easy work, especially in the selection of gasket sealing materials, many factors should be considered. The variables at the flange connection seem to be endless, and all these uncertain factors affect the sealing effect of the gasket. In the past, “temp” (temperature, application, medium, pressure) seemed to be sufficient. However, today, the sealing effect of gasket is affected by flange processing quality, bolt thread embedding amount, flange rotation amount, bolt tension amount, medium filler and flange surface treatment. Therefore, we must comprehensively consider various parameters in order to make an appropriate choice.
In most selection processes, fluid temperature is the primary consideration. This will quickly narrow the selection, especially from 200 ° f (95 ° C) to 1000 ° f (540 ° C). When the system operating temperature reaches the limit of the maximum continuous operating temperature of a specific gasket material, a higher level of material should be selected. This should also be the case at some low temperatures.
The most important parameters in application are the type of flange and the bolts used. The size, number and grade of bolts in the application determine the payload. The effective area compressed is calculated from the contact size of the gasket. The effective gasket sealing pressure can be obtained from the load of the bolt and the contact surface of the gasket. Without this parameter, we will not be able to make the best choice among many materials.
There are thousands of fluids in the medium, and the corrosivity, oxidation and permeability of various fluids are very different. The materials must be selected according to these characteristics. In addition, the cleaning of the system must also be taken into account to prevent the gasket from being eroded by the cleaning fluid.
Each gasket has its maximum limit pressure. The pressure bearing performance of the gasket decreases with the increase of material thickness. The thinner the material, the greater the pressure bearing capacity. The selection must be based on the fluid pressure in the system. If the pressure fluctuates frequently and violently, you need to know the details in order to make a choice.
(5) PT value
The so-called Pt value is the product of pressure (P) and temperature (T). The pressure resistance of each gasket material is different at different temperatures, which must be considered comprehensively. In general, the manufacturer of the gasket will give the maximum PT value of the material.
Source: China Sealing Gaskets Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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