The iron which is intended for castings is melted in a “cupola furnace,” so called on account of the dome-like shape in which it is built, which has something to do with the more perfect heating of the metal. When the iron is completely melted so that it will run freely, the lower portion of the furnace is opened, and the white-hot stream is received in the casting ladle, or, where it has to be carried for some distance, and the casting is large, in great iron pails carried in a sort of frame by two men. From the casting ladle it is at once poured into the mould.
Mould. Small Casting Ladle.
The mould is a sort of iron box filled with a peculiar sort of sand, into which a wooden pattern of the intended casting is pressed, and the sand firmly rammed down and made solid. There are, in fact, two boxes of sand, each of which is impressed with one half of the thickness of the required casting, so that when they are brought together, and firmly fastened with the pins, as shown in the picture, the patterns which have been taken out have left a half of the impression in each box, each corresponding exactly to the other. A hole in the box receives the melted metal, for which a channel has been left in the sand, that it may freely run into the hollows left by the pattern, and completely fill them; then, when it has sufficiently cooled, the casting is removed, and when the rough edges have been removed, and the irregularities trimmed off, it is ready for use, and may be fitted to its other parts, which have perhaps been separately cast, as in the case of garden seats, fenders, chandeliers, umbrella stands, or ornamental girders and columns.
Furnace Iron. Brush. Trowel. Bellows. Foot Rule. Level. Shovel. Spatera. Hammer. Mould Weight. Rammer.
We have only described solid castings, but as ornamental iron work is generally made hollow, this has to be cast in rather a different way, though the only difference is that what are called “cores” are used. These cores are in fact solid metal patterns made a little smaller than the hollow left by the real pattern, and allowed to remain in the mould. The melted iron then flows between the surface of the core and the surface of the mould, and the casting is hollow, so that when the core is removed the metal is only the thickness of the space left between the two surfaces. You will see what is meant by placing a small teacup inside a larger one, and then pouring water between them.
The tools used by the Ironfounder are not very numerous: the casting ladles and mould have already been mentioned; the uses of the shovel and the mould weight, the rammer, and the furnace iron need no description.
The designers, and pattern makers, and the mould maker have the most important duties, and the latter will have to use a small trowel and a spatera for arranging his sand and loam, a level that it may be perfectly true, and a brush and a pair of bellows for removing any particles of grit from the surface of the channels where the pattern has been impressed.