Fig. 24. Die-castings illustrating the Extremes of Shrinkage
It is the opinion of the Van Wagner Co. that die-casting costs can be materially reduced if designers will bear this point in mind when bringing out new designs. Even though it is often possible to cast special pieces, incorporating several parts in one, and thereby accomplishing what seems to be a great stunt to the designer, it is sometimes more practicable to make the piece in several sections and later assemble it. Not only is this simpler for the die caster, but it is also more economical for the customer. Such points as avoiding thin sections, including large fillets at corners, as well as taking account of the under-cut problem, are simply matters of common sense, but they can profitably be considered by the designer.
The Van Wagner Die-casting Machine
The first essential to good die-casting is a good casting machine. Perhaps the best known types of casting machines are of the familiar plunger type, of which there are several varieties, the pneumatic type and the rotary or automatic type. (For descriptions of various types of die-casting machines, see “Die Casting Machines,” Machinery’s Reference Book No. 108.) For the economical production of die-castings, however, the hand-operated machines are rather too slow, and automatic machines are applicable only to a class of work which may be made in very large quantities. For these reasons, therefore, the Van Wagner Co. employs the compressed air type of die-casting machine which was patented by Mr. E. B. Van Wagner in 1907. In the casting department of the Van Wagner shop, illustrated in [Fig. 17], there are installed about thirty machines. [Fig. 27] shows a die-casting machine in the open position. [Fig. 26] shows a closer view of the die-operating mechanism and [Fig. 25] is presented to give a general idea of the construction of the entire machine.
Fig. 25. Drawing illustrating Principle of Van Wagner Die-casting Machine
By referring to the line illustration [Fig. 25], which shows the Van Wagner pneumatic die-casting machine in part, and comparing this illustration with [Fig. 26], which shows the general appearance of the die-operating and other mechanism of the casting machine, a good idea may be obtained of its construction and working. At A may be seen the base of the machine in which is located the melting pot B. This melting pot is heated by means of fuel oil passing through the supply pipe C to the burners C1. A vent pipe D is provided to take away the gases incident to combustion. The pressure for “shooting” the metal into the die cavity is supplied by air through the supply pipe E. A valve controls this air supply. The pressure is regulated to suit the particular casting or die, the proper amount being determined by experiment. Similarly, an air exhaust pipe F, which may be seen directly above the supply pipe, sub-divides into two tubes which extend to the die cavity to exhaust the air before the metal is admitted. There are two methods of overcoming the presence of air in the die cavity—the exhaust method and the venting method, and it is the former that is here described.
Fig. 26. View of Machine showing Die-operating Mechanism