Die Casting Machines
Hot Chamber Diecasting Machines
Hot chamber machines (Fig.1) are used primarily for zinc, and low melting point
alloys which do not readily attack and erode metal pots, cylinders and plungers.
Hot Chamber Machine.
In the hot chamber machine, the injection mechanism is immersed in molten metal
in a furnace attached to the machine. As the plunger is raised, a port opens
allowing molten metal to fill the cylinder. As the plunger moves downward
sealing the port, it forces molten metal through the gooseneck and nozzle into
the die. After the metal has solidified, the plunger is withdrawn, the die
opens, and the resulting casting is ejected.
Hot chamber machines are rapid in operation. Cycle times vary from less than one second for small components weighing less than one ounce to thirty seconds for a casting of several pounds. Dies are filled quickly (normally between five and forty milliseconds) and metal is injected at high pressures (1,500 to over 4,500 psi). Nevertheless, modern technology gives close control over these values, thus producing castings with fine detail, close tolerances and high strength.
Cold Chamber Diecasting Machines
Cold chamber machines differ from hot chamber machines primarily in one respect; the injection plunger and cylinder are not submerged in molten metal. The molten metal is poured into a "cold chamber" through a port or pouring slot by a hand or automatic ladle. A hydraulically operated plunger, advancing forward, seals the port forcing metal into the locked die at high pressures. Injection pressures range from 3,000 to over 10,000 psi for aluminium alloys.
Cold Chamber Machine.
In a cold chamber machine, more molten metal is poured into the chamber than is needed to fill the die cavity. This helps sustain sufficient pressure to pack the cavity solidly with casting alloy. Excess metal is ejected along with the casting and is part of the complete shot.
Operation of a "cold chamber" machine is a little slower than a "hot chamber" machine because of the ladling operation. A cold chamber machine is used for high melting point casting alloys because plunger and cylinder assemblies are less subject to attack since they are not submerged in molten metal.