Malleable Iron
By depriving cast iron of a portion of its carbon it may be converted into malleable or wrought iron, becoming ductile and tenacious, and capable of being hammered or rolled into thin sheets or drawn into fine wire. Malleable or wrought iron has a fibrous texture, but if it is subjected to repeated jarring or blows it becomes again brittle, and can only be restored by heating and reworking. The ordinary processes of converting cast iron into malleable are: refining, puddling, shingling, hammering, and rolling. The refining-furnace consists of a flat hearth covered with sand, around which are metal troughs through which a constant stream of water is kept running, to prevent the sides from melting; tuyeres set in the direction of the hearth connect with the blowing-engine. The cast iron is melted with coke on the hearth, and a blast of air which blows directly over it causes the carbon of the iron to unite with the oxygen of the incoming air and pass away as carbonic-oxide gas. Oxygen also unites with the silicon present to form silica, and with the iron to form the oxide. A slag of silicate of iron is also produced by the silica of the sand uniting with the oxide of iron. When the molten mass has been sufficiently refined it is run out on cast-iron plates, which are kept cool by streams of water. This process only partially decarbonizes the iron; it is then broken into pieces and passed to the puddling-furnace, where it is again melted and brought up to a high temperature, when it is subjected to the action of a current of air, by which means the carbon burns to carbonic acid, a portion of the iron is oxidized, and this oxide unites with the silicon in the iron and forms a fusible slag. The workmen by means of long bars keep up a constant stirring or puddling of the mass, so that the whole may be exposed to the air, and to intimately mix the oxide with the metal. After a time the iron loses its fluidity, blue flames appear on the surface, it becomes pasty, and finally falls to pieces. The fire is now quickened, and the loose masses unite. They are then gathered by the puddler into balls, which are at once conveyed to the squeezer, or shingling hammer, where the slag is pressed out and the metal formed into a bloom, which is at once passed through the roughing-rolls, and finally the finishing-rolls, which is some instances completes the operation. The quality of the iron is improved by taking the bars from the roughing-rolls and cutting them into lengths, to be reheated in piles or fagots, and then rolled or hammered out together. See PUDDLED STEEL.