Differences between valve manufacturing process and other mechanical manufacturing processes:
① It is difficult to install valve parts on the machine tool
The structure and shape of the main parts of the valve are relatively complex. Some parts are thin and slender, with poor rigidity. When machining on a machine tool, positioning and clamping are difficult, so complex special fixtures are often required.
For some valve parts, the accuracy of the positioning base surface is low, the surface roughness is high, and sometimes the non machined surface is used for positioning. The precision and surface roughness of the machined sealing surface and other parts are required to be very high, so it is difficult to ensure the processing quality. Therefore, in order to meet the needs of the process, it is often necessary to improve the accuracy of the positioning base surface and reduce the surface roughness, or to machine the positioning base surface on the non machined surface, which increases the complexity of the valve manufacturing process.
② The manufacturing process and inspection process of valve blanks are relatively complex.
The casting blanks of valves are thin-walled shells with complex structures. The castings shall have smooth surface, clear casting characters, especially dense defects. In order to meet the above requirements, a series of process measures should be taken during casting, such as selecting molding materials with high fire resistance and controlling the moisture content of molding sand, focusing on layered compaction to ensure the hardness of sand mold, adopting a reasonable pouring cap mouth system, and strictly controlling the pouring speed and temperature. Due to high technical requirements, the casting process of valve blanks is far more complex than that of ordinary castings.
In addition, in addition to checking the size, position accuracy and appearance of valve blanks, some of them are also inspected for metallographic structure, mechanical properties, corrosion resistance and nondestructive testing, so the inspection process of valves is also complex. Machining is difficult.
③ Due to the wide variety of valve materials, except for various cast iron and carbon steel, most of the high-strength, corrosion resistant and hard materials have poor cutting performance, which makes it difficult to make the parts reach the specified machining accuracy and surface roughness. However, the requirements for the geometric shape accuracy and surface roughness of the valve sealing surface are very high, which increases the difficulty of valve machining.
At the same time, the poor cutting performance of valve materials has brought many new problems to valve processing methods, tool materials, cutting parameters, process equipment, etc
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