Valve parts is difficult due to the valve installed in the machine tool structure and complicated shape, some valve parts wall thin, long and thin piece, the poor rigidity. On the machine tool processing, the positioning and clamping are difficult, so often require complicated special fixture. Sometimes low precision positioning base surface, the surface roughness is higher, sometimes even using the machining surface. By machining accuracy and surface roughness requirements in areas such as the sealing surface is very high, so difficult to stainless steel needle valve guarantee the quality of the valve. Therefore, in order to meet the needs of the process, often must improve the valve positioning base surface precision and reduce the surface roughness, or located in the machining on the surface of the base level, which adds to the complexity.
Valve compared with other mechanical manufacturing technology, has the following characteristics: valve manufacturing process and inspection process is more complicated valve casting blank is called a complex thin-walled shell structure. The requirements of the casting surface is bright and clean, clear hand type, particularly the density of defects. In order to meet the above stainless steel hydraulic fitting requirements, valve casting should take a series of technological measures, such as molding material selects high refractoriness and control water, moulding should be layered solid in place to ensure that the hardness of sand mould, adopt reasonable pouring cap system and strict control of casting speed and temperature, etc.
Due to the high technical requirements, the valve blank casting process is far more like complex castings. In addition, the blank except for check valve size, location precision and appearance, some mechanical properties, corrosion resistance and nondestructive flaw detection, and other inspection, therefore, the inspection process of the valve has more complex.
Valve mechanical processing is difficult because of all kinds of valve is various, in addition to all kinds of cast iron, carbon steel, the majority of its high strength, high corrosion resistance and hard material cutting performance is very poor, it is difficult to make the parts meet the machining accuracy and surface roughness. And the valve geometry shape is very tall to the requirement of accuracy and surface roughness, thus increased the machining difficulty. At the same time, the valve material cutting performance is stainless steel tube fitting poor, the processing method was given to the valve, cutting tool material, cutting dosage, the respect such as process equipment has brought about many new problems.