At first glance, the valve has few components, a simple structure, and average precision, making it a simple part in the mechanical industry. However, the core sealing part of the valve requires particularly high standards. The manufacturing process of valves is complex and technically difficult. What process characteristics do we need to pay attention to?
1. Manufacturing materials
Due to the wide variety and specifications of valves, such as general valves including 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, low-temperature valves, etc., all of which are used in various fields of the national economy. Their usage scenarios vary greatly, such as high temperature and high pressure, low-temperature cryogenic, flammable and explosive, highly toxic, and highly corrosive media, which impose strict requirements on the material of valves.
In addition to cast iron, carbon steel, and alloy structural steel, a large amount of CrNi stainless steel, CrMoAl nitriding steel, CrMoV heat-resistant steel, CrMnN acid resistant steel, precipitation hardening steel, duplex stainless steel, low-temperature steel, titanium alloy, Monel alloy, Inconel alloy, Hastelloy alloy, and G0CrW hard alloy are also widely used. The poor casting, welding, and processing properties of these high alloy materials pose great difficulties to the manufacturing process. Moreover, most of these materials are valuable materials with high alloy, high strength, and high hardness, which poses many difficulties in material selection, preparation, and procurement. Some materials are difficult to procure and supply due to their small usage.
2. Structure of casting blanks
Most 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 defects such as pores, shrinkage cavities, sand inclusions, cracks, etc. Therefore, its casting process is complex and the heat treatment technology is difficult. In the mechanical industry, the casting difficulty of pressure bearing thin shell castings for valves is much more complex and challenging than that of castings for other mechanical components.
3. Mechanical processing technology
Due to the poor cutting performance of most high-strength, high hardness, and high corrosion resistant materials, such as high alloy stainless steel and acid resistant steel, which have disadvantages such as 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 machining tools, processes, and equipment. In addition, the valve sealing surface also has high requirements for machining accuracy, fitting angle, smoothness, and matching sealing pairs, which brings great difficulties to mechanical processing.
4. Process arrangement of valve components
The main components of the valve are not many, the structure is relatively simple, and the machining accuracy of most sizes is not high. The exterior is relatively rough, which gives people the impression of being a simple machine. In fact, the heart sealing part of the valve is its own, with high requirements for the "three degrees" (flatness, smoothness, hardness) of its sealing surface, as well as the zero to zero fit of the sealing pair composed of two sealing surfaces, in order to meet the zero leakage requirements of the airtight test. This rough benchmark to ensure zero to zero requirements for the heart area is the major technical difficulty in valve processing.
5. Testing and Inspection of Valves
Valves are important components for opening, closing, and regulating pressure pipelines, and the operating conditions of pressure pipelines vary greatly, including high temperature and high pressure, low temperature and deep freezing, flammability and explosiveness, and high toxicity and strong corrosion. However, the testing and inspection conditions for valve manufacturing cannot meet the same requirements as the working conditions. Various international and domestic valve testing standards stipulate that tests are conducted using gas or water as the medium under conditions close to room temperature. There is a fundamental hidden danger that valve products that pass normal factory tests may encounter difficulties in meeting usage requirements due to material selection, casting quality, and seal failure under harsh actual working conditions, and may also result in major quality accidents. No wonder some veteran valve experts who have worked their entire lives become more restrained and worried as they age.