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.
Charcoal Hearth Processes were sometimes but rarely called forge processes and bustling and buzzing are very obsolete terms. These processes are designed for the production of wrought iron charcoal iron usually by refining cast iron occasionally by melting scrap before a tuyere with charcoal for fuel the product being obtained in a pasty condition and containing a certain amount of slag but less than puddled iron. Only the latter method survived the early 20th century in this country.
In general the furnaces or hearths are like the Catalan and bloomary hearths for reducing iron from the ore low rectangular chambers sometimes roofed and with one or more tuyeres. The chief difference is that in refining cast iron much more strongly oxidizing conditions are brought about chiefly by melting the metal down in drops before the tuyere repeatedly if need be so that it passes in a state of minute subdivision and with great surface exposure through a part of the hearth where the atmospheric oxygen is in excess; and by the action of the basic ferruginous slag with which the metal is mixed during the earlier stages and with which it is covered during the later stages to ward off the strongly carburizing tendency of the charcoal.
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 castiron plates at least in part watercooled. Brickwork 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 nonWalloon.
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 http://www.youtube.com/watch?v=GpYoJyiqa4 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.
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