As will be noted from the drawings, there is left between the core and the mold a space all around, which will be filled by the metal of the casting when poured. Therefore the surface of the core shapes the inside, and the mold itself the outside and ends of the casting.
The molten metal, entering through the vertical “sprue” hole, flows along the “runner” and into the mold through the more or less constricted entrance called the “gate.” The gases formed during pouring and the air with which the mold was filled are driven out through the porous bodies of sand of the mold and core. Had the mold been rammed too hard the gases could not escape through the sand and an imperfect casting would result.
The poured mold is allowed to stand until the metal has solidified and cooled sufficiently, when the casting is “shaken out.” The sand is returned to the molder to be used again. The sprue and runner are broken from the casting, which, after cleaning by “tumbling” with others in a revolving mill, or otherwise, goes to the machining and assembling shops.
Some form of the above general method is everywhere used for the production of all kinds of castings, except for those which can be made by machine at a lower cost for molds.
This kind of molding, which we have termed “hand work,” requires expert molders and is too slow and expensive for the hundreds of standard shapes and sizes of castings which are in great and constant demand. The latter are made on cleverly devised molding machines working with compressed air or by hand power applied through a lever. The pattern is attached to the machine, set and very accurately adjusted by a skilled mechanic. Thereafter the sand is rammed, the runner formed and the pattern drawn by the machine itself, all of these very critical movements being therefore rapidly and unerringly duplicatable any desired number of times by unskilled labor, which has but to put on the parts of the “flasks,” feed in the sand, set the cores, close and remove the mold, and begin the next.
Sometimes there is but one, but for the smaller sizes there are often ten or twenty, and, occasionally, as many as two hundred pieces or castings in a single mold.
CHAPTER XII
MALLEABLE CAST IRON
It almost goes without saying that the capacity to withstand distortion without breaking was the meaning of and the reason for the use of the term “malleable.” But wrought iron is malleable as also is mild steel, and, in Europe fifty years ago (though in general not now) by the term “malleable iron” was meant and understood what we know as wrought iron. You will remember that Bessemer’s paper announcing his great process was entitled “The Manufacture of Malleable Iron and Steel without Fuel.” The first reference was to wrought iron. Bessemer did not succeed in making this by his process but his success in the manufacture of steel was immense. Therefore, while in ordinary conversation such definiteness is not necessary, perhaps, and not usual here, to be safe one should say “malleable cast iron,” and not simply “malleable iron,” for by the latter, many Europeans still understand wrought iron.
Like “Topsy” of “Uncle Tom’s Cabin” fame, the various members of the iron family “just growed.” Therefore a strictly logical classification and nomenclature is hardly to be expected.
It was mentioned in a former article that a process for making malleable the brittle white cast iron was discovered, or at least described, by Reaumur, a Frenchman, about 1722. It is likely that his discovery or acquaintance with it came about through his extended experiments with cementation steel.