1, from the manufacturing materials speaking:
Due to the wide variety of valve specifications, it is used in various fields of the national economy and its use situations vary widely, such as high temperature and pressure, cryogenic cryogenic, flammable and explosive, highly toxic and corrosive media and other working conditions, demanding the material of the valve Request. In addition to cast iron, carbon steel, alloy steel, but also extensive use of CrNi stainless steel, CrMoAl nitrided steel, CrMoVi heat-resistant steel, CrMnN acid-resistant steel, precipitation hardened steel, duplex stainless steel, low temperature steel, titanium, Monel alloy , Because of Nerloy, Hastelloy and G0CrW cemented carbide. These high-alloy materials, casting, welding, processing performance is poor, to the manufacturing process has brought great difficulty. Coupled with these materials are mostly high alloy, high strength, high hardness of precious materials, from the material selection, preparation, procurement, there are many difficulties. Some materials due to the use of small, difficult procurement procurement.
2, from the casting of rough structure speaking:
Most of the valve blank is used in the structure of the complex shell castings require good appearance quality, dense internal organization and good metallurgical structure, can not have pores, shrinkage, sand, cracks and other defects. Therefore, its casting process is complex, heat treatment technology is difficult. In the machinery industry, it is more difficult and more difficult to cast the shell of the valve under pressure than the castings of other mechanical components.
3, from the mechanical processing technology:
Because most of the high strength, high hardness, high corrosion resistance of the cutting performance of materials are not good, such as high alloy stainless steel, acid-resistant steel with toughness, high strength, heat dissipation, chip viscosity and work hardening tendency and other shortcomings, Difficult to meet the required dimensional accuracy and finish, to the machining of tools, processes and equipment has brought great difficulties. In addition, the valve sealing surface in the machining accuracy, with the angle and finish, as well as matching the requirements of pairing is also very high, to bring great difficulty machining.
4, from the valve parts on the process arrangement:
The small number of the main parts of the valve, the structure is relatively simple, most of the size of the machining accuracy is not high, the external rough, which gives the impression of a simple mechanical. In fact, the heart of the valve sealing parts but extremely sophisticated, the sealing surface demanding, flatness, smoothness, hardness, and seal the formation of the two sealing surface to pay the coincidence have reached zero to zero in order to meet the gas seal test zero leakage. This rough benchmark to ensure precision zero-zero requirements, is the valve processing the most difficult process.
5, from the valve test and inspection on:
The valve is an important opening and closing of the pressure pipe, regulating components, and the pressure pipe working conditions are ever-changing, high temperature and pressure, cryogenic cryogenic, flammable, highly toxic and highly corrosive. However, the valve manufacturing test and inspection conditions can not meet the same requirements of the working conditions, the international and domestic standards for testing various valves are close to room temperature conditions, using air or water as a medium for testing. One of the most fundamental problems is that the valve products that have passed the normal factory test can not meet the requirements due to materials, castings, seals and other problems under severe actual working conditions, and serious quality accidents can occur. No wonder some old valve experts who worked for a lifetime, the older the more formal, the more dry the more worried.
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