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　　Casting valves have casting body. Generally speaking, casting valves are usually applied in medium of low pressure, such as PN16, PN25, PN40, but sometimes can also be used in medium of high pressure, like 1500Lb, 2500Lb. For casting valves, their size is usually 50mm or above. Forged valves have forged body, and are generally used on high-grade pipelines. For forged valves, their size is DN50mm or below.

　　Casting is the process of smelting metal into liquid that meets certain requirements, then pouring it into the mold. After cooling, solidifying and clearing, the casting having a predetermined shape, size and performance is obtained. It is the basic process of the modern machinery manufacturing industry. The casting is low in cost. For parts with complicated shape, especially with complex internal cavity, it is financially preferred . At the same time, it has sound adaptability and good comprehensive mechanical properties. But during casting production, a lot of materials and equipments are require such as metal, wood, fuel, mould, metallurgical furnace, sand mixer, molding machine, core machine, falling sand machine, shot blasting machine, cast iron plate, and etc. It will also produce a lot of harmful dust, gas, and noise that pollutes the environment.

　　The casting process usually has three steps. The first is preparing mould. Mould is a container that makes the liquid metal into a solid casting. There are several types of mould, including sand mould, metal mould, ceramic mould, mould, graphite mould. The moulds have different service life. Some moulds are just used for one time, but some are semi-permanent or permanent. The mould is the main factor that decides the quality of castings. The second step is melting and casting. Materials have cast iron, cast steel and cast non-ferrous alloys. The last step is the treatment and inspection of casting. Treatment includes removing foreign objects on casting surface , cutting pouring risers, planishing burrs and other projections, as well as heat treatment, shaping, anti-rust treatment and roughing.