Low-Pressure Casting was the earliest anti-gravity casting technology, which was first used in industrial production in the 1940s. Nowadays, low-pressure casting is mainly used in the production of aluminum alloy and magnesium alloy parts, such as the automotive hub of the automobile industry, the cylinder body, cylinder head, piston, missile shell, impeller, air guide wheel and other castings with complex shapes and high quality requirements.
The common material of low-pressure casting is A356\ZL101\ZL101A,this kind of material is usually applied to auto part, storage part,transformation part,etc.
The pressure on the surface of the molten metal is 0.06~0.12Mpa.This processing has good shrinkage, casting tissue is dense, easy to produce the large thin-walled complex parts, the casting head is not needed , metal yield can be up to 95%.
Low pressure casting can adopt sand type, metal type, graphite type, etc. The filling process is not only different from gravity casting such as metal casting and sand casting, but also different from high pressure and high speed filling pressure casting, which has the following advantages:
1) Pure metal liquid filling type, which improves the purity of the casting. Because the slag generally floats on the surface of the metal liquid, and the low pressure casting by the metal liquid in the lower part of the crucible realizes the filling through the lifting pipe, which completely avoids the possibility of the slag into the cast cavity.
2) The metal liquid filling type is smooth, reducing or avoiding the turnover, impact and splashing phenomenon of the metal liquid when filling the type, thus reducing the formation of less oxide slag.
3) The casting molding performance is good, the metal liquid filling under the pressure action, can improve the fluidity of the metal liquid, is conducive to the formation of clear outline, smooth surface casting, for the formation of large thin-wall casting is more favorable.
4) The casting crystallizes and solidifies under pressure, which can be fully condensed, and the casting structure is compact.
5) Improve the yield of metal liquid, generally do not need to burst, and the same metal in the lifting tube can be returned to the crucible, reuse, so that the yield of metal liquid greatly increased, the yield can generally reach 90%.
6) Convenient production and operation, good working conditions, high production efficiency, easy to achieve mechanization and automation.
Low pressure casting also has some disadvantages, equipment and mold investment is large; in the production of aluminum alloy casting, crucible and lift pipe long time with metal liquid contact, easy to erosion and scrap, will also make the metal liquid iron and performance deterioration.
