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Processing and Application of the Viton O-ring

 

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Processing and Application of the Viton O-ring
 
      1 Preface
      Viton elastomer of the main chain or a polymer containing fluorine atoms in the side chain carbon atoms, so it has a particularly excellent performance. Here to discuss the fluorine -26 or fluorine -246 (ie, the dimension through fluorine rubber), vinylidene fluoride, hexafluoropropylene binary and ternary (third monomer tetrafluoroethylene) copolymer. Use accounted for more than 90% of the total consumption of fluorine rubber in the world. Viton commissioned by the DuPont test device in 1956, 1958, the completion of 1800 t / year scale production plant since its development is very rapid. In the late 1960s, an annual growth of 20% -30% in the 1970s, the growth rate of 10%, entered the 1980s still maintain a growth rate of 7% -8%, and this trend has been preserved. Viton is used extensively for the production of special sealing products. It is reported that 50% of the fluorine rubber for the rubber seal products; the application of a greater proportion of up to 80%.
      Dimension through Viton rapid development, he has the best overall performance, it has good mechanical strength, thermal stability, the medium resistance is exceptionally good, and processing to facilitate the production process, lower cost, so , it occupies the position of absolute superiority in the fluoroelastomer. Has been widely used in aerospace, aviation, transportation, petroleum, machinery, metallurgy, chemical and other industrial sectors, and in all areas to achieve better economic and social benefits.
      2 the main properties of the fluorine rubber
      (1) The mechanical properties of normal
      26 fluorine rubber with the strength of 20Mpa or; elongation of 150-300%; tear strength between the 20-40KN / m, but it is less flexible.
      Fluorine rubber friction coefficient (0.8), nitrile rubber friction coefficient (0.9 to 1.5) is small.
      (2) high temperature performance
      Fluorine rubber and silicone rubber, high temperature performance, the existing rubber best. F26-41 Viton 200 ~ 250 , long-term and short-term work (see Table 1) at 300 C, the F246 performance of the heat a little better than the F26.

      Table 1. Heat resistance of Viton
            Test temperature (hours)
            204
            23.21 million more than
            3000
            2.601 million
            288 240
            31648

      In anti-aging, fluorine rubber and silicone rubber is superior to other varieties (Table 2)
      .2 A variety of rubber heat aging resistance *
            Rubber types have the ability to work to limit temperature
            Viton 320
            Silastic 320
            Nitrile rubber 180
            Natural rubber 130

      * Rubber in the concentration after 24 to 26 hours aging, the tensile strength 7MPa; 100% elongation as has the ability to work.
      Fluorine rubber tensile strength and hardness decreased with increasing temperature. Changes in tensile strength and hardness characteristics are: rapidly reduced with increasing temperature below 150 C; decreased slowly with increasing temperature between 150 ~ 260 (Table 3).
      Table 3. Viton performance variations at different temperatures.
            Performance of 24 C 150 C 204 C
            Tensile strength MPa16.83.42.0
            Elongation of 100% 33,012,080
            Hardness (Shore A) 756 563

      Based on the above, the fluorine rubber seals used in high temperature conditions, should avoid the role of non-assembly stress in order to avoid early damage under high temperature.
      (3) corrosion resistance
      Viton has excellent corrosion resistance. Excellent stability of its organic liquid fuel oil and lubricants. Good corrosion resistance to most inorganic acids, hydrocarbons, benzene and toluene. Just intolerant of low molecular weight esters, ethers, ketones, and some amines.
      (4) heat water and superheated steam performance
      Rubber hydrothermal stability depends not only on the body material, and have decided with the plastic material. For fluorine rubber, fluorine peroxide cured rubber is better than the plastic material of the amine and phenolic curing system. It should be said, fluorine rubber, heat water and superheated steam performance, it is not as good as the ethylene-propylene rubber, the volume change of less than 10% after 180 24h hot water soak, and physical performance has not changed much.
      (5) compression performance
      Viton for high temperature sealing, compressive deformation is the key to performance. Dimension through fluorine rubber so extremely wide range of applications, and improve its compression deformation inseparable. DuPont, USA from 60 to 70 years of commitment to improve fluorine rubber compression deformation of the anti-patience, and have achieved significant results. Table 4 is DuPont Viton compression deformation of the improvements.
      Table 4. DuPont Viton compression deformation of the improvements
            The year 204 70h
            1964> 80
            196 860
            196 950
            197 030
            197 313

      (6) low temperature performance
      Fluorine rubber, low temperature performance it can maintain flexibility in extreme temperatures from -15 to -20 . As the temperature decreases, its tensile strength is larger, seem tough at low temperatures. Measuring 2mm thick standard sample, its brittle temperature at about -30 ; thickness 1.87mm -45 C; thickness of 0.63mm for the -53 C; thickness of 0.25mm to -69 . The Viton working temperature slightly lower than the brittle temperature. Use temperature of -40 ~ 205 C as specified in the U.S. military standard MIL-25879D. Foreign fluorine rubber used in the aero-engine temperature limits of -35 .
      (7) resistance to weathering and ozone resistance
      VitonA natural storage for 10 years after the performance is still satisfactory. Air ozone concentration of 0.01% after 45 days the role of no obvious cracks. Its resistance to weathering and ozone resistance is satisfactory.
      (8) The electrical properties
      Fluorine rubber, electrical insulation is not very good, is only suitable for low-frequency low-voltage use. Temperature of its electrical properties, from 24 to rise to 184 C, the insulation resistance dropped by 35,000 times.
      (9) gas permeability
      The gas solubility of the fluorine rubber is relatively large, the rate of diffusion is relatively small, the total gas permeability is very small. Fluorine rubber, fillers, filling the gap inside of the rubber vulcanizates gas permeability is smaller, is very beneficial for vacuum sealing. With the moderate, the Viton solve the 10-7Pa vacuum seal.
      (10) flame resistance
      Fluorine rubber in a fire can burn, away from the fire, self-extinguishing.
      3 with Viton
      The formula of a fluorine rubber, raw rubber, acid scavenger, curing agent, accelerator, and the composition of the reinforcing fillers, processing aids.
      (A) raw rubber
      Basically the same as the performance of domestic fluorine rubber, Viton and abroad, but some differences in processing performance, poor processing performance of the domestic rubber, mainly high Mooney viscosity, the corresponding impact plastic raw material processing poor mobility.
      Domestic fluorine rubber 26 is equivalent to DuPont VitonA, the fluoroelastomers equivalent to VitonB 246, fluorine rubber raw rubber abroad, many of them have good curing agent has been added to 3M Company, USA and Japan Daikin supply of fluorine rubber curing agent.
      (2) curing agent
      Vulcanized fluorine rubber to a certain degree of crosslinking, it has a good performance. Fluorine rubber vulcanization pro-nuclear test
      Agent ion addition mechanism can also be a free radical mechanism peroxide or ray.
      Amines (1 #, 3 # vulcanizing agent) vulcanized fluorine rubber, you can solve the general product requirements; 2 curing agent can solve the processing of the mortar.
      In seal products if it is a smaller compression deformation value should be preferred phenolic compounds as curing agent. Such as hydroquinone, bisphenol A, bisphenol AF, and is equipped with the appropriate accelerator, suitable for high-level performance requirements.
      Solve the resistance to the corrosive medium, it is recommended that the use of peroxide vulcanized fluorine rubber.
      (3) acid scavenger
      The acid scavenger is also known as stabilizer. In order to solve the the Viton process to produce hydrogen fluoride on the corrosion of metals and pollution, so that the curing reaction smoothly. Of Ca (OH) 2 and so on. Commonly used
      Of MgO, CaO, ZnO, PbO, two Dibasic lead phosphate, the amount of 5 to 10. They join their own characteristics: MgO heat resistance, good; of PbO
      Acid resistance; of CaO deformation small; favorable to eliminate air bubbles; of ZnO and dibasic lead phosphate, plastic flow has been improved, good water resistance; Ca (OH) 2 deformation small by adding Ca (OH) 2 and The activity of MgO in the phenolic curing system, available to low compression deformation of the rubber. In short, we must select the appropriate acid scavenger, to meet the performance requirements.
      (4) reinforcing filler
      Viton is a self-reinforcing properties of rubber. Performance requirements and different purposes of need reinforcement, fill the system to adjust its functionality and cost adapt to the needs of users. The general amount of between 10-30. The most commonly used reinforcing filler generally thermal cracking method of carbon black (N-990), spray carbon black, silica, calcium sulfate, barium sulfate, calcium oxide, carbon fibers, etc.
      Canada's imports of N990 carbon black or spray carbon black, a black products have achieved a better process and the corresponding physical properties.
      After adding 20 parts of carbon fiber fluorine rubber, rubber mobility, processing sulfide complex shapes, their appearance in the N-990 and the spray of carbon black, smooth surface. Thermal conductivity of carbon fiber plastic material, suitable for the use of high-speed movement of rubber. It should be specified in the high cost to join carbon fiber, its low elongation.
      Color fluorine rubber products, silica, titanium dioxide, calcium fluoride, calcium carbonate, and is equipped with the corresponding pigment to get the plastic material. However, in the processing of compression type seal products in the selection of the color of raw materials, pay attention to the reasonable match of the pigments with high temperature, but also control the compression deformation of the plastic material to make products to meet the compressed work under.
      (5) processing aids
      Processing aids is a big step forward in recent years, fluorine rubber processing, it is under the premise does not affect the play of rubber, fluorine rubber mixing process can improve and prevent scorch, improving the mobility of the rubber and pressure performance and processing to prevent the sticky roller, sticky mode, play the role of external mold release agents.
      Fluorine rubber processing fluorine wax, low molecular weight polyethylene, zinc stearate, Ws2

 

 

 
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