While forges or fires are of many shapes and sizes the principles of their cor...Iraction remain the same. An ordinary blacksmith forge is a fireplace in the bottom of which there is a tuyere for admitting a blast of air to blow the fire. Where the air blast is furnished by a hand bellows the pipe leading therefrom to the tuyere is open throughout. Where a power-driven blower furnishes the blast, there is a valve in the pipe for regulating the same.
The usual form of tuyere consists of a single blast pipe, opening into the bottom of the fire pit. This may be a simple nozzle as in Fig. 2, with the blast regulated by a damper in the pipe; or, it may have a regulator at the month of the tuyere as in Fig. 8. Sometimes the tuyere has several openings, and is then in the form of a grate. Whatever its form, it should be possible to clean it from below, in order that coal and clinkers falling into it may be removed.
A common form of forge is shown in Fig. 4. It is built of brick and the chimney rises from one side. A bonnet (A) placed above the chimney opening increases its draft. The fire is at one side and only comparatively light work can be done in it. An improved form of forge is shown in Fig. 5. In this the fire is at the center. The smoke and gases are carried off through a bonnet suspended from above. With this construction it is possible to work on all sides of the fire and long bare may be heated at any point.
The Fuel used in the forges thus far described is invariably bituminous coal. It is desirable that the coal should be as free as possible from sulphur and earthy matter. Sulphur gives off choking fumes that are disagreeable and it has an injurious effect upon the iron. Earthy matter produces clinker and chokes the tuyeres. A coal that contains a great deal of gas is also undesirable. Gas distilled from coal Cannot be honied in an open fire. Formerly, almost all blacksmith coal was imported. Now, however, such coal as that mined in the Cum-berland region is admirably adapted to the purpose. Cumberland coal averages about the following composition:
93.81 per cent.
1.82 per cent.
2.77 per cent.
1.60 per cent.
100.00 per cent.
From this it will be seen that carbon stands very high and that the losses due to the distillation of hydro-carbon gases must be very low. Anthracite coal is used in special furnaces, which will be described later. Charcoal and coke are also used in limited quantities.
The Blast is furnished to the fires of a blacksmith shop by blowers of various kinds. For many years the ordinary bellows was used. This has been superseded by the fan blower which is now almost universally used, even for hand power.
Such a fan blower is shown in Fig. 6. It is formed of a thin cast iron shell in which there are a set of rapidly revolving blades.
These blades set up a current of air which presses against the side of the shell and escapes through the tangential opening. The pressure of the blast used for an open blacksmith fire varies from about 2 to 7 ounces per square inch. The lower pressure is used for a tight fire and light work. The higher pressure is suitable for heavy classes of work.