Al-Si alloy has good casting properties. After modification, inoculation and heat treatment, it has good comprehensive mechanical properties, corrosion resistance and good cutting performance. It is the most famous and most widely used alloy among cast aluminum alloys. It is widely used in military, industrial, railway transportation and other fields, especially in aviation, aerospace, ships Weapons and other heavy industries play a very important role.
Differential pressure casting is also called back pressure casting or differential pressure casting. The formation mode of differential pressure casting is divided into: lower tank pressurization method and upper tank decompression method. The equipment used in the differential pressure casting process adopts the upper tank decompression method. Based on the low-pressure casting equipment, a tank is added to the middle diaphragm and the mold is placed in the upper tank. Before pouring, inject dry compressed air into the lower tank and the upper tank. When the inflation pressure reaches the parameter setting value, close the air inlet valve of the lower tank and the interworking valve of the upper and lower tanks; When pouring, open the vent valve of the upper tank to form a pressure difference between the upper tank and the lower tank. Under the action of the pressure difference, the metal liquid in the crucible enters the mold cavity through the liquid riser. After the mold filling and pressurization are completed, close the vent valve of the upper tank and maintain the pressure for a certain time; The molten metal crystallizes and solidifies under high pressure, which inhibits the precipitation of hydrogen atoms in the molten aluminum and improves the feeding capacity of the pouring system. This greatly reduces the pinhole, shrinkage cavity and shrinkage porosity in the differential pressure casting, so as to obtain the differential pressure casting with compact structure and high mechanical properties; After the solidification of the liquid metal in the mold, open the interworking valve of the upper and lower tanks and the exhaust valve of the upper tank for exhaust. The non solidified liquid metal in the riser flows back to the crucible by gravity.
(1) For the hot spot with complex structure and special shape during solidification of differential pressure casting, if it is not easy to place chill, chill sand can be used to replace chill; Chilled sand has large heat capacity and thermal conductivity. It can be placed in a part of the mold or core.
(2) For the local structure of differential pressure casting, because the middle wall thickness is large, the wall thickness at both ends is small, and the effective feeding distance of riser is less than its height or length, subsidies can be added to the differential pressure casting. The effective measures to eliminate the shrinkage cavity and porosity of differential pressure castings are to artificially set the wedge-shaped feeding channel, and then cooperate with the pouring system and cold iron to realize the sequential solidification from top to bottom.