Subsequent to an historical review of die-casting, briefly stated, the author covers the subject of present die-casting practices comprehensively and conveys a large amount of specific information. Because many different methods of producing castings exist outside the sand-casting realm, he says that some confusion prevails as to the exact definition of the term “die-casting.” Such castings may be produced in metallic or in non-metallic long-life molds, or in combination with destructible cores. They may be filled by gravity and known as “permanent-mold castings”; or by centrifugal force and known as “centrifugal castings”; or by filling the mold by gravity and, after the outer skin has become chilled, pouring out the excess metal. The last named are known as “slush castings.” On the other hand, a die-casting may be defined as a casting formed in a metallic mold or die, from metal subjected to mechanical or gaseous pressure while in the molten state.
It is important to contrast this last definition with so-called “pressed castings” or drop-forgings in which the pressure is applied while the metal is in a plastic or a semi-plastic condition that makes impracticable the coring of side holes.
In die-castings, the metal being liquid, the pressure is practically uniform in all directions, and complicated coring of holes and of side cavities is therefore easy of accomplishment. The molten metal, coming into contact with the comparatively cold surfaces of the mold, chills immediately and the feed of the metal is maintained under full pressure until the die-casting has solidified completely. The sudden cooling forms a smooth, hard skin on the surface, with a comparatively coarser structure at the center of the walls.
Alloys of comparatively low fusing-points, best adapted to the die-casting process, are divided into groups and their characteristics are stated. The design of die-castings is covered, and the paper treats also of the polishing, enameling and electroplating of die-castings, the methods used for die-castings and the applications and limitations of die-castings in general.
