The characteristics of metal casting are as follows.
(1) There is a higher dimension precision (it12~it16) and a smaller surface roughness (Ra6.3μm~12.5μm), the machining allowance is small.
(2) Because of the good heat conductivity of metal type, the cooling speed is fast, the grains of the castings are finer and the mechanical properties are good.
(3) can realize "one type multiple casts", raise labor productivity. Metal Casting and save molding materials, can reduce environmental pollution, improve working conditions.
However, the trade network points out that the manufacturing cost of metal mold is high, and it is not suitable to produce large and complex thin-walled castings. Metal Casting Because of the fast cooling speed, the surface of cast iron is easy to produce white mouth, which makes the machining difficult. The alloy with high melting point is not suitable for metal casting because of the limit of the melting point of the metal type material.
Metal casting is mainly used for mass production of non-ferrous castings such as copper alloy and aluminum alloy, such as piston, connecting rod, cylinder head, bushing, bushing, etc. Cast iron parts of the metal casting has also developed, but its size limit within the MM, the quality of not more than 8kg, Metal Casting such as the bottom of an electric iron.
Forming characteristics of metal casting: the thermal conductivity of metal-type materials is larger than that of sand-type materials, and there is no permeability and no compromise. Damage form: ① external crack A, the stress caused by the temperature change to the mold tensile strength when the crack (preheating metal type) b, unreasonable structure c, defect of sand hole inclusions D, Metal Casting blank exists casting stress D, low stiffness ② internal crack A, fatigue stress B, alternating thermal stress ③ deformation, multiple pouring, thin wall, high temperature, The pouring time is long (time is fixed by gating system) ④ burns, the wall thick place temperature is too high ⑤ friction. The way to improve the life of metal type A, heat treatment to reduce stress B, Metal Casting correct selection to ensure stiffness C, reasonable wall thickness and structure to prevent stress concentration D, gating system design should be reasonable e, coating performance and spraying technology. The role of paint: A, the protection of metal type B, adjust the casting parts in the metal type of cooling speed C, improve the quality of the casting surface D, Metal Casting appropriate to improve the metal type of exhaust conditions. Coating requirements: A, viscosity of uniform b, fire resistance C, small d, no chemical reaction e, easy to clear