17. When the hearth has become full of iron, the metal is let out, at one corner of it, into a bed of sand, called a pig-bed, which is from twenty to thirty feet in length, and five or six in width. One concave channel, called the sow, extends the whole length of the bed, from which forty or fifty smaller ones, called pig-moulds, extend at right angles. The metal, when cast in these moulds, is called pig-iron, and the masses of iron, pigs.
18. Pig-iron, or, as it is sometimes called, crude iron, being saturated with carbon and oxygen, and containing also a portion of scoria, is too brittle for any other purpose than castings. Many of these, such as stoves, grates, mill-irons, plough-irons, and kitchen utensils, are commonly manufactured at blast furnaces, and in many cases nearly all the iron is used for these purposes. In such cases, the metal is taken in a liquid state, from the hearth, in ladles.
19. In Great Britain and Ireland, and perhaps in some other parts of Europe, iron-ore is smelted with coke, a fuel which bears the same relation to pit-coal, that charcoal does to wood. It is obtained by heating or baking the coal in a sort of oven or kiln, by which it becomes charred. During the process, a sort of bituminous tar is disengaged from it, which is carefully preserved, and applied to many useful purposes.
THE IRON-FOUNDER.
1. The appellation of founder is given to the superintendent of a blast-furnace, and likewise to those persons who make castings either of iron or any other metal. In every case, the term is qualified by a word prefixed, indicating the metal in which he operates, or the kind of castings which he may make; as brass-founder, iron-founder, or bell-founder. But whatsoever may be the material in which he operates, or the kind of castings which he may produce, his work is performed on the same general principle.
2. The sand most generally employed by the founder is loam, which possesses a sufficient proportion of argillaceous matter, to render it moderately cohesive, when damp. The moulds are formed by burying in the sand, wooden or metallic patterns, having the exact shape of the respective articles to be cast. To exemplify the general manner of forming moulds, we will explain the process of forming one for the spider, a very common kitchen utensil.
3. The pattern is laid upon a plain board, which in this application is called a follow board, and surrounded with a frame called a flask, three or four inches deep. This is filled with sand, and consolidated with rammers, and by treading it with the feet. Three wooden patterns for the legs are next buried in the sand, and a hole is made for pouring in the metal.
4. One side of the mould having been thus formed, the flask, with its contents, is turned over, and, the follow board having been removed, another flask is applied to the first, and filled with sand in the same manner. The two flasks are then taken apart, and the main pattern, together with those for the legs, removed. The whole operation is finished by again closing the flasks.
5. The mode of proceeding in forming moulds for different articles, is varied, of course, to suit their conformation. The pattern is often composed of several pieces, and the number and form of the flasks are also varied accordingly. Cannon-balls are sometimes cast in moulds of iron; and to prevent the melted metal from adhering to them, the inside is covered with pulverized black lead.
6. Rollers for flattening iron are also cast in iron moulds. This method is called chill-casting, and has for its object the hardening of the surface of the metal, by the sudden reduction of the temperature, which takes place in consequence of the great power of the mould, as a conductor of heat. These rollers are afterwards turned in a powerful lathe.