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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746- ix. mining industry and metal production op sweden.
The regenerators are generally placed under the furnace, and from them the
gas and air are conducted through separate flues into the furnace. The roof of
the furnace is always laid with Dinas-brick, as are also the gas and air-ports
and the inner surfaces of the walls. The figure below shows a Swedish
open-hearth furnace.
Acid open-hearth process. At the different open-hearth works the composition
of the charge varies very considerably according to the supply of raw-material
at hand and the purpose for which the iron is intended. There are, for inst,
open-hearth works which use 73 % pig iron and 7 % wrought iron scrap and 20
’/• iron ore, and others which use 74 % scrap and 26 % pig iron without addition
of ore.
First the pig iron is charged cold, or the pig iron together with a small
proportion of scrap, and after this is melted, scrap is charged in smaller
quantities according as the refining proceeds, and finally ore to hasten the refining.
Open hearth Furnace.
The pig iron is always charged cold, for during the melting period silicon
and the largest part of manganese are oxidized, but after the iron has been melted,
the oxidizing of the silicon proceeds very slowly in acid open-hearth, and thus
there is no time saved at all by charging the pig iron in a molten state on the
furnace, rather the contrary’; but in the basic process the case is reversed, as
above mentioned, and both time and fuel may be saved by charging the pig iron
in liquid form. A small percentage of silicon in the iron after the melting
period is, however, advantageous, inasmuch as the boiling (the escape of carbonic
oxide) becomes less violent. By the contact of the slag high in iron with the
melted metal, the carbon in the iron is oxidized and escapes as carbonic oxide
with bubbling.
But the oxidizing capacity of the slag depends on its composition and
temperature, thus namely that the slag, in order to act oxidizing, must have a greater
percentage of iron at a lower temperature than what is required at a higher.
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