Valve casting forming performance: casting temperature using 1540 ~ 1570 ℃, casting forming performance is better, casting shrinkage is generally 2% to 2.5% of wall thickness. Should consider the design of pressure, pouring riser and the choice of modeling materials. When the casting size deviation, can be corrected after heat treatment, after correction of parts by heat treatment requirements for additional heat treatment.
Compared with other gray iron casting process, the valve casting manufacturing process has the following characteristics:
① valve casting manufacturing process and inspection process is more complex.
Valve casting blank is a complex structure called thin-walled shell pieces. The castings require a smooth surface, cast a word clear, especially to have a dense defect. In order to meet the above requirements, casting should take a series of technical measures, such as the use of high refractibility modeling materials and control of sand water, modeling should be layered to ensure sand hardness, the use of reasonable cap system and strict control Pouring speed and temperature. Due to the high technical requirements, the casting process of the valve casting is much more complicated than the general casting.
In addition, the valve casting in addition to check the size, location accuracy and appearance, and some have for the microstructure, mechanical properties, corrosion resistance and non-destructive testing and other tests, so the valve casting inspection process is more complex.
② valve casting on the machine to install more difficult
Valve casting structure, the shape is more complex, some parts are thin, slender pieces, poor rigidity. When machining on the machine, positioning and clamping are more difficult, so often need a complex special fixture.
Some valve parts, the positioning of the base surface of the lower precision, high surface roughness, and sometimes even the use of non-processing surface positioning. And the processing of sealing surface and other parts of the accuracy and surface roughness requirements are very high, it is difficult to ensure the quality of processing. Therefore, in order to meet the needs of the process, often need to improve the accuracy of the positioning surface and reduce the surface roughness, or in the non-processing surface processing of the positioning surface, which increases the complexity of the valve manufacturing process.
③ difficult to machine processing
Due to the wide variety of valve materials castings, in addition to a variety of cast iron, carbon steel, most of its high strength, corrosion resistance and high hard material cutting performance are poor, it is difficult to achieve the required parts of the processing accuracy and surface roughness The The valve casting sealing surface geometric shape accuracy and surface roughness requirements are high, thus increasing the difficulty of the valve casting machining. At the same time, the valve casting material cutting performance is poor, but also to the valve casting processing methods, tool materials, cutting the amount of technology and equipment, and so brought a lot of new problems.