At first glance, there are not many valve parts, simple structure, and average precision. They are simple parts in the machinery industry, but the core sealing parts of the valve are particularly demanding. The valve manufacturing process is complex and technically difficult. Which process characteristics should we pay attention to?
1. Manufacturing materials
Due to the wide variety of valves and specifications, for example, general valves include gate valves, globe valves, check valves, ball valves, butterfly valves, and hydraulic control valves; industrial valves include special valves such as solenoid valves, regulating valves, pressure reducing valves, high temperature and high pressure valves, and cryogenic valves. , Are used in various fields of the national economy, and their use occasions are very different, such as high temperature and high pressure, low temperature and cryogenic, inflammable and explosive, highly toxic, strong corrosive media and other working conditions, which put forward strict requirements on the material of the valve.
In addition to cast iron, carbon steel, alloy structural steel, CrNi stainless steel, CrMoAl nitrided steel, CrMoV heat-resistant steel, CrMnN acid-resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy are also widely used , Inconel, Hastelloy and G0CrW cemented carbide, etc. These high-alloy materials have poor casting, welding, and processing performance, which brings great difficulties to the manufacturing process. In addition, these materials are mostly high-alloy, high-strength, and high-hardness precious materials, and there are many difficulties in material selection, material preparation, and procurement. Some materials are difficult to purchase and supply due to their small usage.
2. The structure of the casting blank
Most of the valve blanks are made of thin-shell castings with complex structures, which not only require good appearance quality, but also dense internal quality and good metallographic structure, without pores, shrinkage holes, sand inclusions, cracks and other defects . Therefore, the casting process is complicated and the heat treatment technology is difficult. In the machinery industry, the difficulty of casting the pressure-bearing thin shell castings of valves is much more complicated and difficult than the castings of other mechanical components.
3. Mechanical processing technology
Since most of the high-strength, high-hardness, and high-corrosion-resistant materials have poor cutting performance, such as high-alloy stainless steel and acid-resistant steel, they all have the disadvantages of high toughness, high strength, poor heat dissipation, high chip viscosity, and strong work hardening tendency. It is difficult to achieve the required dimensional accuracy and smoothness, which brings certain difficulties to the machining tools, processes and equipment. In addition, the valve sealing surface has high requirements for machining accuracy, matching angle, smoothness and matching sealing pairs, which brings great difficulty to mechanical processing.
4. Process arrangement of valve parts
The main parts of the valve are not many, the structure is relatively simple, the machining accuracy of most sizes is not high, and the exterior is relatively rough, which gives the impression of a simple machine. In fact, the heart sealing part of the valve is extremely precise. The "three degrees" (flatness, smoothness, hardness) of the sealing surface is very demanding, and the fit of the sealing pair composed of two sealing surfaces must reach zero to zero. In order to meet the zero leakage of the air tightness test. This kind of rough reference to ensure the precise zero-to-zero requirement of the heart part is the biggest process difficulty in valve processing.
5. Valve test and inspection
Valves are important opening and closing and regulating components of pressure pipelines, and the working conditions of pressure pipelines are very different, such as high temperature and high pressure, low temperature and deep cold, inflammable and explosive, highly toxic and strong corrosion. However, the test and inspection conditions for valve manufacturing cannot meet the same requirements as the working conditions. Various international and domestic valve test standards stipulate that the test is performed with gas or water as the medium under conditions close to normal temperature. There is a fundamental hidden danger, that is, the valve products that pass the normal factory test may encounter problems such as material selection, casting quality and seal damage, which may be difficult to meet the requirements of use, and major problems may occur under harsh actual conditions. Quality accidents. It is no wonder that some old valve experts who have been working for a lifetime have become more cautious and worried as they grow older.