Forged steel cold as the characteristics of the pneumatic valve and material selection of pneumatic valve in low temperature

forged steel cold by the pneumatic valve is suitable for low temperature liquid handling equipment management system management system, has the characteristics of flexible switch, reliable seal, also can be used to other management systems of low temperature and cryogenic medium. 。 At room temperature by the use of pneumatic valve is refers to the medium temperature - ~ c, pneumatic valve body material is different also. Low temperature by the pneumatic valve is mainly refers to the use of medium temperature in - ~ - - - - - - Degree of the cryogenic liquid medium by the pneumatic valve in the system.
forged steel cold by the pneumatic valve, cryogenic pneumatic valve, in particular, its working temperature is extremely low. In the design of this kind of pneumatic valves, besides should follow the design principle of pneumatic valves commonly, there are some special requirements.
a, cryogenic pneumatic valve design requirements: according to the conditions of use, the design of the cryogenic pneumatic valve has the following requirements: pneumatic valves in medium at low temperature and ambient temperature should have the ability to work long hours. Pneumatic valves should not be a low temperature system of a significant source of heat. This is because the heat flow in addition to the lower thermal efficiency, such as flow too much, still can make internal fluid evaporation rapidly, produce abnormal booster, dangerous. Low temperature medium should not produce harmful to the hand wheel operation and packing seal performance. Direct contact with the low temperature medium pneumatic valve assembly should have explosion and fire prevention structure. Work under low temperature of the pneumatic valve assembly does not lubrication, so you need to take structure measures, in order to prevent the friction abrasion.
2 and material selection of cryogenic pneumatic valve
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pneumatic valve body material at low temperature ( Main body material selection should consider the factors from metallographic, metal material in addition to have a face-centered cubic lattice austenitic steel, copper, aluminum, etc, general steel under low temperature condition will appear low temperature brittleness, and reduces the strength and service life of the pneumatic valve. Select the material first to choose suitable for working under low temperature of the material. Aluminum will not appear in the low temperature low temperature brittleness, but because of the hardness of aluminium and aluminium alloy is not high, aluminum sealing surface wear resistance, abrasion resistance is poor, so in the use of low temperature pneumatic valve has certain limitation, only use in low pressure and small pneumatic valves.
working in low temperature materials to ensure the low temperature performance, main is to ensure that the cold shock strength. Pneumatic valve internal parts must pass the correct material, make its have enough cold impact strength, to prevent rupture. C and Cr alloy steel under - ℃ when soon lose impact strength, so use temperature limit - respectively ℃ and - ℃. For Ni content. % of nickel steel can be used to - ℃, Ni content % nickel steel can be used to - ℃. Austenitic stainless steel, nickel, monel alloy, hartz alloy, titanium, aluminum alloy and bronze can be used to lower temperature ( - ℃.
in addition, the material selection of cryogenic pneumatic valve should also consider the following factors:
the minimum use of pneumatic valve temperature; Metal material at low temperature keep working conditions required by the mechanical properties, especially the impact toughness, relative stability of elongation and the organization; In the case of low temperature and oil free, has good abrasion resistance; Good corrosion resistance; Also need to consider when connected by welding materials, welding performance.
　　( Pneumatic valve, pneumatic valve cover, pneumatic valve seat, pneumatic disc ( Ram, material selection of the main principles of material selection of parts were: the temperature above - ℃ when choose ferritic steel; Temperature is below - ℃ when choose austenitic steel; Low pressure and small pneumatic valve can choose materials such as copper and aluminum. When the design choose proper material according to the minimum working temperature.
　　( Pneumatic valve stem and material selection of fastener above -
temperature ℃, using Ni, pneumatic valve stem and bolt material, Cr - Mo alloy steel, such as the proper heat treatment, in order to improve the tensile strength and prevent thread bites, etc. Temperature is below - ℃, using austenitic stainless acid-resistant steel manufacturing. But - Acid-resistant steel hardness is low, will cause the pneumatic valve stem and packing scratch each other, the filler leaks. So, pneumatic valve lever must be hard chrome plated surface ( Plating thickness. - 。 Mm, or nitride and ni-p plating processing, in order to improve surface hardness. In order to prevent the nut and bolt killed, nut generally using Mo steel or Ni steel, at the same time in the screw thread surface with molybdenum disulfide.
and low temperature pneumatic valve selection of gasket, packing materials, with lower temperature, fluorine plastic shrinkage is very big, can make the sealing performance, easy to cause leakage. Asbestos packing is inevitable permeable leakage. Rubber is swelling for liquefied natural gas (LNG), cannot be used in low temperature. At low temperature in the design of pneumatic valve, on the one hand, by the structural design to ensure that make packing is in close to the work under the environment temperature, for example, USES the long neck pneumatic valve cover structure, make the stuffing box.