This paper introduces the technical ideas of the development of electroplating valves

This paper introduces the technical ideas of the development of electroplating valves

Three yuan ethylene propylene fire pipe card sealing rubber ring, 63-65 Shaw A,15MPA, constant pressure less than 25% of the cost-effective compound design. Fluid (gas, liquid) sealing is a necessary general technology in various industrial fields, not only construction, petrochemical, shipbuilding, machinery manufacturing, energy, transportation, environmental protection and other industries can not do without sealing technology, aviation, aerospace and other forefront industries are closely related to sealing technology. The field of application of sealing technology is very advanced. All devices involving fluid storage, transportation and energy conversion have sealing problems.
First, determine the performance indicators of the advantages and disadvantages of sealing materials
1 Tensile properties
Tensile properties are the first properties to be considered for sealing materials, including tensile strength, constant elongation stress, elongation at break and long-term deformation at break. Tensile strength is the relatively large stress of a sample from tensile to fracture. The constant elongation stress (constant elongation modulus) is the stress reached at specified elongation. Elongation is the deformation of the specimen under a specified tensile force, and is the ratio of the increment of elongation to the original length. Elongation at break is the elongation of the specimen at break. The long tensile deformation is the residual deformation between the marks after tensile fracture.
2 the hardness
Hardness indicates the ability of the sealing material to resist external force into the sealing material, is also one of the basic properties of the sealing material. The hardness of the material is related to other properties to a certain extent. The higher the hardness, the greater the strength, the smaller the elongation, the better the wear resistance, and the worse the low temperature resistance.
3 Compression performance
Rubber seals are usually in a compressed state. Due to the viscoelasticity of rubber materials, the pressure will decrease with time when compressed, which is manifested as the relaxation of compressive stress. After removing the pressure, it cannot return to the original shape, which is manifested as compression deformation for a long time. This phenomenon is more obvious in high temperature and oil medium, which is directly related to the durability of the sealing ability of the sealing product.
4 Low temperature performance
To measure the low temperature characteristics of rubber seals, the following two methods of testing low temperature performance are introduced:
(1) Low temperature retraction temperature: the sealing material is stretched to a certain length, and then fixed, quickly cooled to below freezing temperature, reach equilibrium, release the test piece, and at a certain rate of temperature, record pattern retraction of 10%, 30%, 50% and 70% of the temperature to TR10, TR30, TR50, TR70. The material standard takes TR10 as the index, which is related to the brittle temperature of rubber.
(2) Low temperature flexure: after the sample is frozen to the specified time at the specified low temperature, it is reciprocally bent according to the specified Angle, and the advantages and disadvantages of the sealing ability of the seal after the repeated action of dynamic load at low temperature are investigated.
5 Oil or medium resistance
Sealing materials in addition to contact with petroleum base, double esters, silicone grease oil, in the chemical industry sometimes also contact acid, alkali and other corrosive media. In addition to corrosion in these media, at high temperature will also lead to expansion and strength reduction, hardness reduction; At the same time, plasticizer and soluble material in the sealing material are extracted, resulting in mass reduction, volume reduction, causing leakage. Generally at a certain temperature, after soaking in the medium for a number of times, the quality, volume, strength, elongation and hardness of the change are determined to evaluate the advantages and drawbacks of the oil resistance or medium resistance of the sealing material.
6
Resistance to aging
Sealing material by oxygen, ozone, heat, light, moisture, mechanical stress will cause performance deterioration, known as the aging of sealing materials. Aging resistance (also known as weather resistance) can be expressed by the change of strength, elongation and hardness of the aging pattern after aging. The smaller the rate of change, the better the aging resistance. Note: WEATHER RESISTANCE refers TO plastic products due to sunlight, temperature changes, wind and rain and other external conditions of the influence, and the appearance of fading, disCOLoration, cracking, powder and strength decline and a series of aging phenomenon. Among them, ultraviolet radiation is the key factor to promote plastic aging.
Second, the material of commonly used valve seals is introduced
1 Nitrile butadiene rubber (NBR)
It is an irregular copolymer of butadiene and acrylonitrile monomer synthesized by emulsion polymerization. Its molecular structure formula is as follows: – (CH2-CH=CH) M – (CH2-CH2-CH) N-CN, nitrile butadiene rubber ** was developed in Germany as early as 1930. It is a copolymer of butadiene and 25% acrylonitrile. Because of its aging resistance, heat resistance and wear resistance are better than natural rubber, it has been paid more attention by the rubber industry. During the Second World War, with the rapid development of weapons and equipment, the demand for heat – and oil-resistant nitrile rubber as war readiness materials increased sharply. Up to now, more than 20 countries have produced NBR, 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, accounting for about 80% of the demand for all oil resistant rubber. Nitrile butadiene rubber in the 1950s has made great development, so far there are more than 300 brands, according to the content of acrylonitrile, in 18% ~ 50% acrylonitrile content range can be divided into: The content of acrylonitrile was 42% for extremely high nitrile grade, 36% to 41% for high nitrile grade, 31% to 35% for medium high nitrile grade, 25% to 30% for medium nitrile grade, and less than 24% for low nitrile grade. Industrial use of relatively large is low nitrile grade nitrile -18 (combined with acrylonitrile content of 17% ~ 20%), medium nitrile grade nitrile -26 (combined with acrylonitrile content of 27% ~ 30%), high nitrile grade butanitrile -40 (combined with acrylonitrile content of 36% ~ 40%). The increase of acrylonitrile content can significantly improve the oil resistance and heat resistance of NBR, but not more is better, because the increase of acrylonitrile content will also reduce the low temperature performance of rubber.
Nitrile butadiene rubber is mainly used in the manufacture of petroleum based hydraulic oil, lubricating oil, kerosene and gasoline in the work of rubber products its working temperature is -50-100 degrees; Short-term work can be used for 150 degrees, in air and ethanol glycerin antifreeze working temperature of -45-100 degrees. The aging resistance of nitrile is poor, when the ozone concentration is high, it will rapidly aging and cracking, and it is not suitable for long-term work in high temperature air, nor can it work in the fire resistance hydraulic oil of phosphate ester
General physical characteristics of nitrile butadiene rubber:
(1) nitrile rubber is generally black, the color can be adjusted according to customer needs, but must increase some costs, and may affect the use of rubber.
(2) nitrile rubber has a slight rotten egg taste.
(3) According to the oil resistance characteristics of nitrile rubber and the use of temperature range to determine whether the material of the seal is nitrile rubber.
Silicone rubber (Si or VMQ)
It is a linear polymer with Si-O bond unit (-Si-O-Si) as the main chain and organic group as the side group. Due to the development of aviation, aerospace and other forefront industries, there is an urgent need for high temperature and low temperature resistant rubber sealing materials. Early use of natural, butadiene, chloroprene and other general rubber can not meet the needs of industrial development, so in the early 1940s in the United States two companies began to put into production of dimethyl silicone rubber, is the first silicone rubber. Our country also researched successfully and put into production in the early 1960s. After decades of development, the variety, performance and yield of silica gel have been greatly developed.
The main characteristics of silica gel:
(1) heat resistance silica gel high temperature stability performance. Can be used at 150℃ for a long time, the performance will not change significantly; It can work for more than 10,000 hours continuously at 200℃, and can even be used for a short time at 350℃.
(2) Cold resistance 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℃ and -70℃. The general temperature of silica gel is -50℃.
(3) oil resistance and chemical resistance of silica gel to ethanol, ** and other polar solvents and food oil tolerance is very good, only cause a small expansion, mechanical properties will not be reduced; The tolerance of silica gel to low concentration of acid, alkali and salt is also good. When placed in 10% sulfuric acid solution for 7 days, the volume change rate is less than 1%, and the mechanical properties are basically unchanged. But silica gel is not resistant to concentrated sulfuric acid, alkali, carbon tetrachloride and toluene and other non-polar solvents.
(4) strong aging resistance, silica gel has obvious ozone resistance and radiation resistance is not comparable to ordinary rubber.
(5) Dielectric properties Silica gel has very high volume resistivity (1014 ~ 1016 ω cm) and its resistance value remains stable over a wide range. Suitable for use as insulation material under high voltage conditions.
(6) Flame retardant performance silica gel will not burn immediately in case of fire, and its combustion produces less toxic gas, and the products after combustion will form insulating ceramic, so silica gel is an excellent flame retardant material.
In combination with the above characteristics, silica gel is *** * used in the household electrical appliances industry seals or rubber parts, such as electric kettle, iron, microwave oven rubber parts; Seals or rubber parts in the electronic industry, such as mobile phone keys, shock pads in DVDS, seals in cable joints, etc.; Seals on all kinds of supplies in contact with the human body, such as water bottles, water dispensers, etc.
3 Fluorine glue (FKM or Vtion)
Also known as fluorine elastomer, is a high polymer containing fluorine atoms on the carbon atoms of the main chain and side chain. From the early 1950s, the United States and the former Soviet Union began to develop fluorinated elastomers. First put into production is the United States DuPont and 3M company’s vtionA and KEL-F after half a century of development, fluorine elastomer in heat resistance, medium resistance, low temperature resistance and process and other aspects have achieved rapid development, and formed a series of products.
Fluorine glue has excellent heat resistance, ozone resistance and a variety of hydraulic oil properties. The operating temperature in the air is -40 ~ 250℃, and the operating temperature in the hydraulic oil is -40 ~ 180℃. Because of the processing, bonding and low temperature performance of fluorine rubber is worse than general rubber, the price is more expensive, so it is more used in high temperature media that general rubber is not competent for, but not for some phosphate ester solutions.
4 EPDM (EPDM)
It is a terpolymer of ethylene, propylene and a small amount of unconjugated diene alkenes. In 1957, Italy realized the industrial production of ethylene and propylene copolymer rubber (binary EPC rubber). In 1963, DuPONT added a small amount of unconjugated circular diene as the third monomer on the basis of binary ethylene propylene, and synthesized low unsaturated ethylene propylene ternary with double bonds on the molecular chain. Because the molecular backbone is still saturated, EPDM retains the excellent properties of binary EPDM while achieving the purpose of vulcanization. Epdm rubber has excellent ozone resistance, in the ozone concentration of 1*10-6 environment is still not cracking 2430 hours; Good corrosion resistance: good stability to alcohol, acid, strong alkali, oxidants, detergents, animal and vegetable oils, ketones, and some lipids (but in petroleum based fuel oil, hydraulic oil expansion is serious, can not work in contact with mineral oil environment); Excellent heat resistance, can be used in -60 ~ 120℃ temperature for a long time; It has good water resistance and electrical insulation ability. Epdm rubber natural color is beige, good elasticity.
5 Polyurethane elastomer
It is a polymer made of polyisocyanate and polyether polyol or polyester polyol or/and small molecule polyol, polyamine or water and other chain extenders or crosslinkers. In 1937, Professor Otto Bayer from Germany first discovered that polyurethane could be produced by the addition of polyisocyanate and polyol compounds, and on this basis, it entered into industrial application. The temperature range of polyurethane elastomer is from -45℃ to 110℃. It has high elasticity and strength, excellent wear resistance, oil resistance, fatigue resistance and shock resistance in a wide range of hardness. Especially for lubricating oil and fuel oil, it has good swelling resistance and is known as “wear-resistant rubber”.
Polyurethane elastomer has excellent comprehensive performance, has been used in metallurgy, petroleum, automotive, mineral processing, water conservancy, textile, printing, medical, sports, food processing, construction and other industrial sectors.
6 Polytetrafluoroethylene (PTFE)
Teflon (English abbreviation Teflon or [PTFE,F4]), is known as/commonly known as “plastic king”, Chinese trade names “Teflon”, “Teflon” (Teflon), “Teflon”, “Teflon”, “Teflon”, “Teflon” and so on. It is made of tetrafluorethylene by polymerization of polymer compounds, with excellent chemical stability, corrosion resistance (is one of the world’s corrosion resistance is relatively good materials, in addition to molten metal sodium and liquid fluorine, can withstand all other chemicals, boiling in aqua rega can not change, *** is used in all kinds of need to resist acid and alkali and organic solvents), sealing, high lubrication non-adhesive, electrical insulation and good anti-aging endurance, excellent temperature resistance (can work in +250℃ to -180℃ temperature for a long time). Teflon itself is not toxic to humans, but ammonium perfluorooctanoate (PFOA), one of the raw materials used in the production process, is thought to be potentially toxic. The temperature is -20 ~ 250℃ (-4 ~ +482°F), allowing sudden cooling and sudden heating, or alternating hot and cold operation. Pressure -0.1 ~ 6.4Mpa (Full vacuum to 64kgf/cm2)