Valve sealing surface is often subject to media corrosion, erosion, wear, so it is easy to damage the valve parts, such as pneumatic ball valves, electric butterfly valves these automatic valves due to frequent opening and closing and fast opening and closing speed, the quality of its good or bad directly affects the service life of the valve.
The basic requirements of the valve sealing surface is the valve in the specified working conditions to ensure a safe and reliable seal, therefore, the valve sealing surface materials should have the following characteristics:
(1) good sealing performance, that is, the sealing surface should be able to well prevent the leakage of media;
(2) a certain strength, the seal surface should be able to withstand the pressure difference in the medium under the action of the seal than the value of the pressure formed;
(3) Corrosion resistance, the sealing surface in corrosive media and the long-term role of stress, should have a strong corrosion resistance to adapt to the design requirements;
(4) resistance to abrasion, the valve seal is a dynamic seal, the process of opening and closing between the seal are friction
(5) resistance to erosion, the sealing surface should be able to resist the scouring of high-speed media and the impact of solid particles;
(6) good thermal stability, sealing surface at high temperatures, there should be sufficient strength and oxidation resistance, at low temperatures, there should be good resistance to cold brittle performance;
(7) good processing performance, easy to manufacture and repair, the valve role of common parts, to ensure that there is economic value.
Valve sealing surface material conditions of use and the selection of principles of sealing surface materials into two categories of metal and non-metal, commonly used materials for the following conditions:
(1) rubber . Generally used for low pressure soft seal gate valves, diaphragm valves, butterfly valves, check valves and other valve sealing surface.
(2) Plastic. Plastic used for sealing surface are nylon, polytetrafluoroethylene, with good corrosion resistance, small coefficient of friction and other characteristics of soft seal ball valves are more applications.
(3) Barclay’s alloy. Also known as bearing alloy, with good corrosion resistance and good wear ability. Suitable for low pressure, temperature of -70 a 150 ℃ ammonia disconnecting valve sealing surface.
(4) Copper alloy. Its wear resistance is good, there is a certain degree of heat resistance. Suitable for globe valves, cast iron gate valves and check valves, etc., generally used for low pressure, temperature not higher than 200 ℃ of water and steam.
(5) Chromium-nickel stainless steel. It has good corrosion resistance, erosion resistance, heat resistance. Suitable for steaming nitric acid and other media.
(6) Chromium stainless steel. Its good corrosion resistance, usually used in high pressure, temperature is not higher than 450 ℃ oil, water vapour and other media on the valve.
(7) High chromium overlay steel. It has good corrosion resistance and process hardening properties, and is used in high pressure, high temperature oil, steam and other media.
(8) Nitriding steel . It has good corrosion resistance and resistance to abrasion, usually used in thermal power station gate valve, the ball of hard seal ball valve can also choose this material.
(9) Cemented carbide. It has good corrosion resistance, erosion resistance and resistance to abrasion and other comprehensive performance, long service life, is a more ideal sealing materials. Commonly used tungsten drillchin alloy and drill-based alloy overlay welding electrodes, etc., can be made of ultra-high pressure, ultra-high temperature sealing surface, suitable for oil, oil and gas, hydrogen and other media.
(10 ) Spray welding alloys. There are cobalt-based alloy, nickel-based alloy, Chin-based alloy materials, with good corrosion resistance, wear resistance and other properties.
In order to ensure the safety and reliability of the valve sealing surface, the choice of sealing surface materials must be determined according to the specific working conditions. If the medium is more corrosive, the choice of materials, should first meet the corrosive performance, and then meet other performance requirements; gate valve sealing surface should pay attention to the choice of materials with good resistance to abrasion;
safety valves, throttle valves and regulating valves sealing surface is most susceptible to media erosion, should be selected with good corrosion resistance materials; seal ring and body inlay structure, should consider the hardness of the material for the sealing surface; temperature and pressure of the general valve, try to use good sealing performance of rubber and plastic for sealing surface; in the selection of sealing surface materials, should pay attention to the valve seat sealing surface hardness should be as high as possible than the valve sealing surface hardness some.