There are many materials for commonly used seals in valves. Today I will introduce several commonly used materials to you.
1. Polyurethane elastomer (PU) is a polymer made of polyisocyanate, polyether polyol or polyester polyol or/and small molecule polyol, polyamine or water and other chain extenders or crosslinking agents. In 1937, Professor Otto Bayer in Germany first discovered that polyisocyanate and polyol compound could be polyaddition reaction to produce polyurethane, and based on this, it entered industrial application. The temperature range of polyurethane elastomer is -45℃—110℃, and it can have high elasticity and strength, excellent wear resistance, oil resistance, fatigue resistance and vibration resistance in a wide range of hardness, especially for lubrication Both oil and fuel oil have good anti-swelling properties, and are known as "wear-resistant rubber".
Polyurethane elastomer has excellent comprehensive properties and has been widely used in metallurgy, petroleum, automobile, mineral processing, water conservancy, textile, printing, medical treatment, sports, grain processing, construction and other industrial sectors.
2. Nitrile-butadiene rubber (NBR) is an irregular copolymer synthesized by emulsion polymerization of butadiene and acrylonitrile monomer. Its molecular structure is: -(CH2-CH=CH)m-(CH2-CH2-CH)n -CN
Nitrile-butadiene rubber was first developed in Germany in 1930. It is a copolymer of butadiene and 25% acrylonitrile. Because of its aging resistance, heat resistance and abrasion resistance, which are superior to natural rubber, it has been valued by the rubber industry. During the Second World War, with the rapid development of weapons and equipment, the demand for heat-resistant and oil-resistant nitrile rubber as war supplies increased sharply. So far, more than 20 countries have produced nitrile rubber, with an annual output of 560,000 tons, accounting for 4.1% of the world's total synthetic rubber. Due to its excellent heat resistance, oil resistance and mechanical properties, it has now become the main product of oil-resistant rubber. It accounts for about 80% of all oil-resistant rubber demand.
NBR has made great progress in the 1950s, and there are more than 300 grades so far. According to the content of acrylonitrile, it can be divided into: acrylonitrile content > 42% within the range of 18% to 50% acrylonitrile content It is extremely high cyanide grade, 36%~41% is high cyanide grade, 31%~35% is medium high cyanide grade, 25%~30% is medium cyanide grade, and below 24% is low cyanide grade. The most widely used industrially are low cyanide grade butylcyanide-18 (combined acrylonitrile content 17%~20%), medium cyanide grade butylcyanide-26 (combined acrylocyanide content 27%~30%), high cyanide grade Butylcyanide-40 (combined with acrylocyanide content 36% to 40%). The increase of acrylonitrile content can significantly improve the oil resistance and heat resistance of nitrile rubber, but not more is better, because the increase of acrylonitrile content will reduce the low temperature performance of rubber at the same time.
NBR is mainly used in the manufacture of rubber products working in petroleum-based hydraulic oil, lubricating oil, kerosene and gasoline. It is -45-100 degrees. Nitricyanide has poor aging resistance. When the ozone concentration is high, it will rapidly age and crack. It is not suitable for long-term work in high-temperature air, nor can it work in phosphate ester fire-resistant hydraulic oil.
General physical characteristics of nitrile rubber: 1) NBR is generally black, and the color can be adjusted according to customer needs, but some costs will be added, and the use effect of the rubber may be affected. 2) NBR has a slight smell of rotten eggs. 3) Judging whether the material of the seal is NBR according to the oil resistance characteristics of NBR and the operating temperature range.
3. Silicone rubber (Si or VMQ) is a linear polymer with silicon-oxygen bond units (-si-o-si) as the main chain and organic groups as side groups.
Due to the development of cutting-edge industries such as aviation and aerospace, there is an urgent need for high-temperature and low-temperature-resistant rubber sealing materials. The early-used general-purpose rubbers such as natural, nitrile, and neoprene can no longer meet the needs of industrial development. Therefore, in the early 1940s, two companies in the United States began to produce dimethyl silicone rubber, which is the earliest silicone rubber. my country also successfully researched and put it into production in the early 1960s. After decades of development, the variety, performance and output of silica gel have greatly developed.
The main characteristics of silica gel:
1) Heat resistance Silicone has good high temperature stability. It can be used for a long time at 150°C without significant change in performance; it can work continuously for more than 10,000 hours at 200°C, and can even be used at a high temperature of 350°C for a short time.
2) Low phenyl silica gel and medium phenyl silica gel have good low-temperature elasticity when the cold resistance coefficient is above 0.65 at -60°C and -70°C. The general use temperature of silica gel is -50 ℃.
3) Oil resistance and chemical medium resistance Silicone has good resistance to polar solvents such as ethanol and acetone and food oil, causing only a small expansion and basically no reduction in mechanical properties; silica gel is resistant to low-concentration acids and alkalis , Salt tolerance is also good, placed in 10% sulfuric acid solution for 7 days, the volume change rate is less than 1%, and the mechanical properties basically do not change. However, silica gel is not resistant to non-polar solvents such as concentrated sulfuric acid, concentrated alkali, carbon tetrachloride and toluene.
4) Strong aging resistance, silica gel has obvious ozone resistance and radiation resistance, which is incomparable to ordinary rubber.
5) Dielectric properties Silica gel has a very high volume resistivity (1014-1016Ω?cm) and its resistance value remains stable in a wide range. Suitable as insulating material under high voltage conditions.
6) Flame retardant properties: Silica gel will not burn immediately when it encounters fire, and its combustion produces less toxic gas, and the products after combustion will form insulating ceramics, so silica gel is still an excellent flame retardant material.
Based on the above characteristics, silica gel is widely used in seals or rubber parts used in the household appliance industry, such as rubber parts in electric kettles, electric irons, and microwave ovens; seals or rubber parts in the electronics industry, such as mobile phone buttons, DVDs. Shock-absorbing pads, seals in cable joints, etc.; seals on various supplies that come into contact with the human body, such as kettles, water dispensers, etc.
4. Fluorine rubber (FKM or Vtion), also known as fluoroelastomer, is a high molecular polymer containing fluorine atoms on the main chain and side chain carbon atoms.
From the early 1950s, the United States and the former Soviet Union began to develop fluoroelastomers. The first ones put into production are vtionA and Kel-F of DuPont and 3M in the United States. After half a century of development, fluoroelastomers have achieved rapid development in heat resistance, medium resistance, low temperature resistance and technology, and have formed a series of products.
Fluorine rubber has excellent heat resistance, ozone resistance and various hydraulic oil properties. Its working temperature in air is -40~250°C, and its working temperature in hydraulic oil is -40~180°C. Due to the processing of fluorine rubber, the bonding and low temperature properties are worse than general rubber, and the price is more expensive, so it is mostly used in high temperature media that general rubber is not capable of, but it is not suitable for some phosphate ester solutions.
5. Ethylene Propylene Diene (EPDM) is a terpolymer of ethylene, propylene and a small amount of non-conjugated diene olefins.
In 1957, Italy realized the industrial production of ethylene and propylene binary copolymer rubber (EPDM rubber). In 1963, DuPont of the United States added a small amount of non-conjugated cyclic diene as the third monomer on the basis of binary ethylene-propylene rubber, and synthesized low-unsaturation EPDM with double bonds in the molecular chain. Since the main chain of the molecule is still saturated, EPDM maintains the excellent performance of binary ethylene propylene, and at the same time achieves the purpose of vulcanization.
EPDM rubber has excellent ozone resistance, and it will not crack for 2430 hours in an environment with an ozone concentration of 1*10-6; it has good corrosion resistance: alcohol, acid, strong alkali, oxidant, detergent , animal and vegetable oils, ketones, and certain lipids all have good stability (but in petroleum-based fuels and hydraulic oils, they swell severely, and cannot work in environments contacting mineral oils); excellent heat resistance, can be used in - It can be used for a long time at a temperature of 60-120°C; it has good water resistance and electrical insulation.
The natural color of EPDM rubber is beige and has excellent elasticity.
6. Polytetrafluoroethylene (PTFE)
Polytetrafluoroethylene (English abbreviation is Teflon or [PTFE, F4]), known as/commonly known as "Plastic King", Chinese trade name "Teflon", "Teflon" (teflon), "Teflon" , "Teflon", "Teflon" and so on. It is a polymer compound polymerized by tetrafluoroethylene, which has excellent chemical stability and corrosion resistance (it is one of the best corrosion-resistant materials in the world today, and it can withstand other materials except molten metal sodium and liquid fluorine) All chemicals will not change when boiled in aqua regia, and are widely used in various products that require resistance to acids, alkalis and organic solvents), sealing, high lubrication and non-stickiness, electrical insulation, good aging resistance, and excellent temperature resistance ( It can work for a long time at a temperature of +250°C to -180°C). Polytetrafluoroethylene itself is not toxic to humans, but perfluorooctanoic acid ammonium (PFOA), one of the raw materials used in the production process, is considered to have carcinogenic effects.
Temperature -20～250°C (-4～＋482°F), allowing sudden cooling and sudden heating, or alternate operation of cold and hot.
Pressure -0.1～6.4Mpa (full vacuum to 64kgf/cm2) (Fullvacuumto64kgf/cm2)
advantage:
High temperature resistance - the working temperature can reach 250°C.
Low temperature resistance - has good mechanical toughness; even if the temperature drops to -196°C, it can maintain an elongation of 5%.
Corrosion resistance - inert to most chemicals and solvents, resistant to strong acids and alkalis, water and various organic solvents.
Weather resistant - has the best aging life among plastics.
High lubrication - the lowest coefficient of friction among solid materials.
Disadvantages: poor elasticity.
Finally，we are a professional manufacturer of Polyurethane elastomer.Looking forward to cooperating with you.
