Pneumatic valve material selection:

1, the metal material; material is a critical factor, such as material properties, creep, thermal expansion coefficient, oxidation resistance, wear resistance, abrasion resistance and thermal heat treatment temperature, which is a matter first of all should pay attention to. At high temperatures, creep and rupture is one of the main factors in material damage, particularly carbon steel, when long-term exposure to 425 ° C above the steel carbide phase may be converted to graphite, and for austenitic stainless steel Only when the carbon content exceeds 0.4%, it can be used more than 528 ° C. Therefore, when used at high temperatures should be calculated separately body material tensile strength, creep, high temperature aging and other parameters. As for the trim design, it should also consider the additional material at high temperature hardness, thermal expansion coefficient with the member, the guide member hot hardness difference, elastic deformation, plastic deformation. In the design, should be given appropriate safety factor and reliability factor to ensure avoidance of damage in a multi-factor generated. And to be familiar with the material under high temperature creep rate to select the appropriate stress, bringing the total creep material within the range of normal life does not extend to allowing it to produce micro cracks or deformation without affecting the normal use of the guide member.
To avoid the pneumatic valve internals (FD-LOK Monoflange needle valve, valve seat) surface abrasion, erosion and cavitation, high temperatures hot hardness of the material to be considered to prevent metal hardness change. In the high differential pressure, most of the energy of the fluid concentrated in trim were released, the inner parts of the valve that might have excessive load, and the high temperature mechanical properties of most materials deteriorate, material softens greatly affect the valve life member. Therefore, the correct choice of appropriate materials, to extend the life of the valve. Also, consider the effect of high temperature aging on the physical properties of materials, such as between toughness and corrosion changes. When the temperature reaches or exceeds the heat treatment temperature, the trim will have annealed, hardness decreased and other issues, in order to prevent changes in hardness of the material, the maximum temperature limit must be selected within a safe range. The same media, at high temperatures, the molecular activity is relatively active, some media have generally corrosive to the body and may trim metal serious corrosion damage, state media with high-speed ion penetration metal interior, so characteristic of the material changes, such as thermal expansion, intergranular corrosion, etc. Therefore, the choice of materials, in addition to cost, should also consider the failure of the multi-factor generated.
High differential pressure at high flow rates, even if the temperature is normal, it should assess the characteristics of the material, and the material to meet the conditions. In general, at room temperature, when the pressure exceeds 15bar, it should spool valve seat material 316 is adjusted to Stellite surfacing alloy or higher requirements, for weak corrosive media, the choice 420QT (quenching and tempering), 440QT like. High differential pressure, high flow rates can lead to serious erosion or cavitation, which is the trim material damage is very large, therefore, the material requirements of the valve body and trim is very high, the spool should consider using stainless steel surface nitriding (HRC70) process, so that it has a strong resistance to erosion, improve accuracy and service life of the valve flow. Oxidation resistance at high temperatures the material, but also a very important parameter. In the temperature cycling, and the choice of materials should avoid repeating material surface oxidation, producing oxide and other issues. Under normal circumstances, the Department of austenitic stainless steel, carbide Department and the Department of special alloy material has good temperature stability, the choice of suitable materials depending on the temperature conditions.
2, non-metallic materials
General non-metallic materials can not withstand high temperatures (300 ° C or more), but flexible graphite can withstand temperatures above 700 ° C, and therefore high-temperature conditions, both static seal or dynamic seal, generally can choose flexible graphite or composite materials, it should be noted that the coefficient of friction increases.