Charcoal and the General Steel Making Process

When one thinks of charcoal, we normally think of the most important historical use of wood charcoal; as the main ingredient in gunpowder. However, it was of major importance in metallurgical operations as a reducing agent, primarily in the manufacture of steel. The most common use in the modern era for charcoal is as a fuel source, but still has industrial application. The Charcoal Hearth Process was vitally important in the early industrial steel age.

Only a good quality of pig iron (nearly always charcoal pig) is used, as the process is expensive, and is employed only for a high grade of wrought iron. The pig iron is often given a preliminary refining to eliminate most of the silicon. The hearths are usually built of unlined cast-iron plates, at least in part water-cooled. Brick-work is avoided as the silica would enter the slag. The processes may be classified according to the number of times the metal is melted down before the tuyere, into single melting, double melting, and triple melting (or German or breaking up); into Walloon and non-Walloon.

The hearth may be covered or uncovered; if the latter it is called an open fire or open hearth; if the former, a closes hearth. The bloom, after rolling, is called finer's bar (cor- responding to muck bar in puddling), and after piling and rerolling, finished charcoal bar. German general steel  is an obsolete name for the product obtained by melting white or refined pig in a charcoal hearth; it may also be made of poorer quality. In the Bohemian process, mottled or even gray pig is used, and the blooms are reheated in the same hearth. Charcoal is first charged, and on top of this some slag and the pig which is melted down slowly, the iron cake which is formed being frequently raised up. The cinder is tapped at intervals. Finally the bloom is welded to the end of a rod and taken to the hammer; any particles of iron that remain in the hearth are retreated.

The use of charcoal in steel making rapidly diminished with the introduction of coke, anthracite smalls, etc. for industrial processes.

Straightening Machine for Steel Making