Operation of the Die-casting Machine
The metal for the die-casting machine is mixed in the proper proportions for the work in hand by means of a separate furnace, before being poured into the tank of the machine itself. The burners are lighted and the dies are set up on the two die-plates. As soon as the machine has “warmed up,” so that the metal is in a thoroughly melted condition, the sprue-cutting lever T is thrown back, leaving a clear passageway to the die cavities. Lever R is pulled backward, thus bringing die-plate Q up to die-plate M, which operation closes the two halves of the die. Then lever N is thrown forward, thereby bringing the closed die up to the body of the machine, with the nozzle in close contact with the outlet of the cylinder. Next, the gate F is opened, and the man at the compression lever I gives the lever a quick, hard pull, forcing the metal in the cylinder downward and into the dies. The molten metal literally “squirts” into the dies. Gate F is now closed; lever N is pulled back to remove the dies from the cylinder outlet; and the sprue-cutting lever T is pushed forward, cutting off the sprue and pushing it out of the nozzle into the kettle placed beneath it. The lever R is pushed forward, and a finished casting is ejected from the dies.
An important advantage that this machine has over other die-casting machines is the fact that the metal for the castings is taken from the bottom of the melting pot, whereas most other machines use metal from the top of the tank. At the bottom of the tank the metal is always the best, as it is free from impurities and dross; hence, there is little chance for the formation of blow-holes. A handful of rosin thrown into the melting tank occasionally helps to keep the metal clean, but the metal nearest the surface always contains more or less foreign matter.
Fig. 6. Section of Soss Die-casting Machine
While this description of the operation of the die-casting machine may convey the idea that the process is a slow one, as a matter of fact, the time required is, on the average, not over a minute and a half for turning out a finished casting. With the ejection of the casting from the dies, the product is completed, in theory; but in practice there are always a few small thin fins, caused by the air vents or by improperly fitted portions of the dies. It is, however, but the work of a few seconds to break off these fins, and unless there are many of them, or they are excessively thick, they are detrimental neither to the quality nor the quantity of finished castings.