Pump valve castings of a wide range of processing materials, and its surface treatment technology and process applications in different materials will produce different results, the casting of castings for casting substrate and surface treatment technology substrate pretreatment technology, On the basis of the traditional process, different casting materials are put forward suitable processing technology, so as to improve the performance of castings and improve the life of castings.
Structural characteristics of Ni-Cr type valve castings
1. To prevent the formation of coarse grains, should be avoided as thick sections and local metal agglomeration. In the process can also be used metal-type valve casting and other methods to refine the grain.
2. To reduce the casting stress, to prevent thermal cracking, the wall thickness should be as uniform as possible, the transition is smooth, a nickel-chromium stainless steel valve body a sprue 2 a riser 3 a Ling iron to avoid hindering castings shrink prominent part. From the perspective of preventing oxide film and inclusions, it is hoped that transitional gentleness will not cause turbulence.
3. For some stainless steel castings (such as pump body, valve body, etc.) which require higher air tightness and withstand greater pressure, the structure should be designed according to the principle of solidification in order to ensure the shrinking effect. For example, some thick flanged part of the pump valve casting, the valve body wall thickness designed to have a certain slope, so that the thicker closer to the flange. Setting the riser on the flange and placing the cold iron on the valve seat can form the order of solidification so that the riser can effectively supplement parts of the valve body to avoid shrinkage and ensure good air tightness.
Pump valve casting heat treatment technology is to improve the pump valve casting another direction of development is to combine the traditional heat treatment process and advanced surface treatment technology to improve the service life of the casting. Such as the chemical heat treatment method carbonitriding, and conventional quenching and tempering process combined with NQN (ie carbonitriding - quenching - carbonitriding) composite strengthening, not only get a higher surface hardness, but also effective hardening Layer depth increases, distribution of hardness gradient distribution is reasonable, the tempering stability and corrosion resistance increased. Through continuous improvement of casting heat treatment technology, China's valve casting industry will usher in new technology opportunities for development, but also to promote better development of the industry.