Popular Technology; or, Professions and Trades. Vol. 2 (of 2)

by Edward Hazen

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.

7. Several moulders work together in one foundery, and, when they have completed a sufficient number of moulds, they fill them with the liquid metal. The metal for small articles is dipped from the hearth or crucible of the furnace with iron ladles defended on every side with a thin coating of clay mortar, and poured thence into the moulds. But in casting articles requiring a great amount of iron, such as cannon, and some parts of the machinery for steam engines, the iron is transferred to the moulds, in a continued stream, through a channel leading from the bottom of the crucible. In such cases, the moulds are constructed in a pit dug in the earth near the furnace. Large ladles full of iron are, in some founderies, emptied into the moulds by the aid of huge cranes.

8. Although the moulders have their distinct work to perform, yet they often assist each other in lifting heavy flasks, and in all cases, in filling the moulds. The latter operation is very laborious; but the exertion is continued but a short time, since the moulds, constructed during a whole day, can be filled in ten or fifteen minutes.

9. Iron-founderies are usually located in or near large cities or towns, and are supplied with crude iron, or pig metal, from the blast furnaces in the interior. The metal is fused either with charcoal or with pit coal. In the former case, an artificial blast is necessary to ignite the fuel; but in the latter, this object is often effected in air furnaces, which are so constructed that a sufficient current of air is obtained directly from the atmosphere.

10. The practice of making castings of iron is comparatively modern; those of the ancients were made of brass, and other alloys of copper. Until the beginning of the last century, iron was but little applied in this way. This use of it, however, has extended so rapidly, that cast iron is now the material of almost every kind of machinery, as well as that of innumerable implements of common application. Even bridges and rail-roads have been constructed of cast iron.