Full resolution (JPEG) - On this page / på denna sida - Second part - IX. Mining Industry and Metal Production - 2. The Iron and Steel Industry. By the late Prof. J. G. Wiborgh - Ingot iron (Steel)
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wrought iron.
747
Hagfors Iron Works.
Now, since the percentage of iron in the slag decreases in the same degree that
it oxidizes the carbon, it follows that either fresh oxidized iron must constantly
be added to the slag, or the temperature be increased, unless the refining (the
oxidizing of the carbon) is to cease entirely. Such a case is not to be feared,
however, for after the melting of the iron the furnace temperature always rises
gradually and the slag is supplied with oxidized iron, partly by small drops
of melted iron being thrown up by the bubbling caused by the escaping carbonic
oxide, which drops are immediately burned by the flame to oxide, which is
absorbed by the slag, and partly by a special addition of iron ore in case the
refining proceeds too slowly or shows signs of ceasing.
With rising temperature the percentage of iron in the slag, as a rule,
decreases and consequently gets more acid and thick.
This circumstance makes it possible to judge to a certain degree of the
percentage of carbon in the iron by the appearance of the bubbles formed when
the carbonic oxide leaves the slag, for in the beginning, when the percentage of
carbon is high, the slag is very rich in iron and flows easily and the bubbles
seem high and pointed, but as the percentage of carbon decreases and the
temperature rises, the slag becomes thick, and the bubbles round and flat.
After the first part of the charge is melted, fresh charges of wrought iron
scrap are made with V* an hour’s to 1 hour’s intervals, depending upon the
nature of the boiling. This scrap generally contains some oxidized iron in the
form of rust or scales, which hastens the refining, but as the percentage of carbon
decreases, the oxidizing of the carbon becomes more difficult, wherefore more
powerful oxidizing agents are used, such as rich iron ore, which is added from time
to time, while a sample of the iron is taken between each addition of ore, until
the percentage of carbon has come down to the desired point.
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