Metal casting, also known as hard mold casting, it is the liquid metal into the metal mold, in order to obtain a casting casting method. The mold is made of metal and can be used repeatedly (several hundred to several thousand times). Metal casting can produce the castings, Metal Casting in terms of weight and shape there are certain restrictions, such as the ferrous metal can only be a simple shape of the casting; casting weight can not be too large; wall thickness is also limited, smaller castings wall thickness Can not cast out.
Metal casting, the working temperature of the mold, the pouring temperature of the alloy and the casting speed, the time of casting in the mold, and the use of the coating, Metal Casting the impact on the quality of the casting is very sensitive and requires strict control.
The characteristics of metal casting are as follows.
(1) has a higher dimensional accuracy (IT12 ~ IT16) and a smaller surface roughness (Ra6.3μm ~ 12.5μm), the machining margin is small.
(2) due to the good thermal conductivity of the metal type, cooling speed, Metal Casting casting grain smaller, good mechanical properties.
(3) can achieve "a type of casting" to improve labor productivity. And save modeling materials, can reduce environmental pollution and improve working conditions.
Metal casting is mainly used for large-scale production of non-ferrous metal castings such as copper alloy, aluminum alloy, such as piston, connecting rod, cylinder head, bearing, bushing and so on. Cast iron parts of the metal casting has also been developed, but its size is limited to 300 mm or less, Metal Casting the quality does not exceed 8kg, such as iron floor and so on.
Metal casting advantages:
1, metal type can be used many times, pouring up to tens of thousands of times without damage, it can save man-hours and a lot of modeling materials;
2, metal processing precision, cavity deformation is small, cavity wall smooth, Metal Casting so the shape of the castings accurate, high dimensional accuracy, surface roughness value is small;
3, metal heat transfer quickly, casting cooling speed, and thus fine grain, good mechanical properties;
4, high productivity, no dust, labor conditions improved.
Metal casting molding characteristics: metal-type material thermal conductivity than the sand material, no air permeability, no concession. Damage type: ① outside the crack a, caused by the temperature changes caused by the tensile strength of the mold to produce cracks (preheat metal type) b, unreasonable structure c, Metal Casting sand hole inclusions defects d, rough casting stress d, stiffness Too low ② internal cracks a, fatigue stress b, alternating thermal stress ③ deformation, multiple pouring, thin wall, high temperature, pouring a long time (time from the pouring system) ④ burn, wall thickness is too high ⑤ friction The Improve the life of the metal way a, Metal Casting heat treatment to reduce stress b, the right material to ensure the stability of c, a reasonable wall thickness and structure to prevent stress concentration d, pouring system design to be reasonable e, coating performance and spraying process. The role of paint: a, to protect the metal b, adjust the casting parts of the metal in the cooling rate c, to improve the quality of the casting d, appropriate to improve the metal type of exhaust conditions. Paint requirements: a, uniform viscosity b, refractoriness c, small amount of gas d, no chemical reaction e, easy to remove