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Die casting metal casting is introduced in detail, please
It is also known as die casting, the liquid metal is poured into a mold, in order to get the casting a casting method. The mold is made of metal and can be repeatedly used many times (hundreds of times to thousands of times), also called permanent casting.
The structure of the metal type:
Generally, the metal type is made of cast iron and cast steel. The inner cavity of the casting can be used not only with metal core, but also in sand core. There are many kinds of metal structure, such as the horizontal type, the straight type and the compound type. The vertical type is easy to open gate and casting out; the level of type used to produce thin wheel shaped castings; composite type half type is composed of two types of vertical parting by hinge connected together, half type horizontal plate fixed, casting is mainly used in complex casting.
The technological characteristics of the metal mold casting:
The metal type has fast heat conduction speed and no retreat, which makes the casting easy to produce defects such as insufficient pouring, cold septum, crack and white mouth. In addition, the scour of the metal type which is repeatedly subjected to the burning of hot metal will reduce the service life. Therefore, the following auxiliary process measures should be adopted.
Preheated metal type:
The preheating metal type before pouring can slow down the cooling capacity of the mold, be beneficial to the filling of metal liquid and the graphitization process of cast iron. The cast iron parts are produced and the metal type is preheated to 250~350 centigrade; the production of nonferrous metal parts is preheated to 100~250 degrees C
Brush paint:
In order to protect the metal form and facilitate the exhaust, the refractory coating is usually sprayed on the metal surface so as to avoid the metal type directly eroded by metal liquid and heat. Because the adjustment of coating thickness can change the cooling rate of each part of the casting and is beneficial to the discharge of gas in the metal type. Different coatings should be sprayed with different alloys. Such as casting Aluminum Alloy, should be painted by zinc oxide powder, talcum powder and water glass coating; of gray cast iron should be composed of graphite powder, talcum powder, refractory clay powder and peach gum and water paint
Metal mold has strong thermal conductivity, so when metal casting is used, the casting temperature of the alloy should be 20~30 C higher than that of the sand mold. In general, the aluminum alloy is 680 C to 740 C, the cast iron is 1300 C to 1370 C, and the tin bronze is 1100~1150 C. The upper limit of the thin wall parts and the lower limit for the thick wall parts. The wall thickness of iron castings is not less than 15mm to prevent white mouth tissue
Open type:
The more late the open type, the greater the shrinkage of the castings in the metal type, and the difficulty in taking out the casting, and the large internal stress and crack are produced in the casting. Usually the casting temperature of the cast iron is 700~950 degrees C, and the opening time is 10~60 seconds after pouring.
Advantage：
Compared with sand casting, metal casting has the following advantages:
Good reuse, "one type of casting", saving the molding material and molding time
Because of the strong cooling ability of the metal type to the castings, the structure of the castings is dense and the mechanical properties are high
The size accuracy of the castings is high, the tolerance grade is IT12 to IT14, the surface roughness is low, and the Ra is 6.3m
The working conditions of metal casting are improved without sand or less sand.
Shortcomings and limitations:
The manufacturing cost of metal type high, long cycle, strict technical requirements, is not suitable for small batch production of castings, mass production is mainly suitable for non-ferrous alloy castings, such as aircraft, automobile, engine, motorcycle etc. with aluminum piston, cylinder body, cylinder cover, oil pump shell and copper alloy bushing and sleeve etc.. Black alloy castings are also limited to medium and small castings with relatively simple shapes.