Low pressure die casting of light metals - using controlled escape of gas from die cavity to prevent porosity in casting

摘要

Light metals are cast at low pressure in a die cavity with a cross-section changing with a height; molten metal in a chamber (1) is forced by a constant gas pressure (P1) into a runner with ingates leading to the base of the die cavity, which has a top air vent channel. To prevent porosity in the casting, the air vent channel is connected to a second gas source with pressure (P2) which is initially at least equal to P1; molten metal is then fed towards the die and P2 is reduced to below P1 and then altered to a program so a constant flow of the molten alloy is attached in the parts of the die cavity with different heights. The pref. plant pref. includes air and gas valves with an electronic master controller fitted with a memory store contg. the desired program of gas pressures, and actuating a reversible motor driving a main valve. The molten metal or alloy rises at the optimum speed in each part of the die cavity so turbulence of the melt is avoided and air, gas or vapour can escape without being trapped in the mould, thereby causing blowholes, pores etc.