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.
739
The bottom is either built with specially formed bricks with a certain number
of holes in each (strainer-bottom) or else so-called Bessemer-tuyeres are used, which
sre cylindrical and made of fire clay, having each 10—12 small holes, the tuyeres
being fixed into the bottom. Both ways are about equally common. The
strainer-bottoms have a large number of tuyere-holes, 150 to 200, each 6 to 8 millimeters
in diameter; when Bessemer-tuyeres are used, the number of holes is less, 90
to 120, but the diameter of the holes larger, 12 to 15 millimeters. The total
area of these holes varies from 35 to 50 sq. cm. per ton of pig iron and is thus
large in comparison to what is used in other countries. This is also necessary,
the converter being small, as the charge cannot be larger than one cast from
the blast furnace, or 3 to 4 tons, and the pig iron is to have a comparatively
low percentage of silicon, both of which circumstances tend to lowering the
temperature in the converter and to making the steel too cold, in case the tuyere
area be not large, so that the blow can be done in a short time. — The
pressure of the blast varies from 500 to 1,000 millimeters mercury.
Bessemer Converter.
The carrying ont of the process. From the blast furnace the iron is
tapped into a ladle, and a sample is taken out and cast in a small mould. The
ladle with the iron is weighed and is then brought to the converter, which is
now turned into a horizontal position, after which the iron by means of an iron
spout, lined with fire-clay, is poured into the converter.
Meantime the iron sample has cooled and been broken, and from the
appearance of its fracture is estimated its percentage of silicon and the
blast-pressure which ought to be used at the beginning of the blow.
If the iron sample is completely grey, the highest pressure possible, or
1,000 millimeters mercury or more, is generally used, for, on account of the high
percentage of graphite, the tuyeres have a tendency to fill up, and much blast
is required for the oxidation of the silicon; but on the other extreme, or in case
of entirely white iron, a very low pressure is used instead, for instance, 600
millimeters. Thus, after a blast pressure has been applied corresponding to the nature
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