For the production of wrought iron in the ordinary way, two distinct sets of processes are required; first the extraction of the metal from the “ore” that is brought up from the mine, which metal is cast iron; and secondly the conversion of this cast iron into malleable or bar iron, by remelting, puddling, and forging. Bar iron is turned into steel by placing it in contact with charcoal in a peculiar kind of furnace.
When the ore is taken from the mine it is first burnt or calcined, and then removed to a blast furnace to be smelted. These blast furnaces are generally built of brick, and look like small towers. The ore is mixed with limestone, which causes it to melt more easily, and the fire is lighted with pit coal or coke. The melted metal sinks to the bottom of the furnace in consequence of its weight, while the limestone and dross float on the top, and are allowed to run off when they cool into a mass of what is called “slag.”
The melted metal is run off from the bottom of the furnace, either into moulds for some sort of castings, or into a large furrow made in a bed of sand. This large furrow has several smaller furrows on each side of it, and has received the name of the “sow;” the smaller furrows being called “pigs;”—and the iron when it is formed in this shape to be afterwards made malleable is called “pig iron.”
The pig iron is taken to other and smaller furnaces called puddling furnaces, the bottoms of which are lined with clay mixed with the slag just mentioned, and forming a substance which the puddlers call “bull-dog,” though it would be difficult to discover why it received that name.
About four hundred weight of the pigs is placed in the furnace, and as it melts the puddler stands at the furnace mouth with a long iron rod bent at the end, and stirs it about, until it comes to resemble several great balls of iron paste. These balls are removed, and fall into iron trucks pushed along a small railway by boys, who wheel them at once to the “shingling hammer,” an immensely powerful hammer worked by steam, and this beats the iron into small square bars called “blooms.”
The blooms are next carried to the rolling mill, which is a pair of great rollers cut into grooves of various sizes, and between these grooves the bars are squeezed, as the rollers turn round, until they become much longer and narrower, when they are known as “forged bars.”
Some of the rolling mills, however, are plain cylinders without grooves, and when a slab of white-hot iron is placed between these it comes out from the pressure in a great broad sheet of metal.
These operations require great bodily strength as well as considerable skill on the part of the workmen, who are obliged to seize the heated metal with long tongs, and to catch it in the same way as it comes out from the mill.
Casting Ladle.