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 - Pig iron
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wrought iron.
723
The fuel being free from siflphur, it is more economical to get rid of the sulphur
by roasting the ores carefully than by means of basic slag in the blast furnace,
which always requires a high temperature to melt, and this the more so as the
roasting has the advantage that the compact and refractory magnetites, which,
as a rule, are the ores chiefly used, thereby are rendered more porous and
consequently easier to reduce, thus melting with smaller consumption of fuel. The
slags have about the same basicity as the minerals belonging to the
pyroxen-group, thus also crystallizing in the same forms as these; well developed angite
crystals frequently occur in the slags.
In slags with a high percentage of magnesia olivenite crystals are found, and
in those containing much lime, wolastonite crystals. The slag is only used for
mailing slag-bricks, which are made simply by letting the slag run from the blast
furnace direct into moulds of pig iron.
The pig iron produced varies in quality according to the use for
which it is intended: for refining in hearth, Bessemer, or Open hearth
process. The largest part of foundry iron is imported; only a small
part of what the country requires is manufactured here. On account
of the perfect roasting of the ores, the Swedish pig iron is exceptionally
free from sulphur, seldom reaching O03 %, but frequently being almost
entirely free from sulphur.
Moreover, the percentage of phosphorus is generally low, but as
the country has a good supply of ores high as well as low in
phosphorus, it is possible to obtain from them pig iron of very varying
phosphorus percentages. A great deal of the ores in Central Sweden
has a percentage of only one to two thousand parts of phosphorus, as
for inst. certain Dannemora ores, from which pig iron with a phosphorus
percentage of only 0-oi2 to O020 may be produced. It is not possible
to get lower, inasmuch as the charcoal contains some little phosphoric
acid, which alone gives the iron an amount of phosphorus of O010 to
0*020 %, according to the quality of the charcoal and the quantity in
which it is used. Pig iron intended for steel making, as a rule, contains
no more than O02 to 0-02 5 % of phosphorus.
In 1865, the making of manganese iron or so-called Spiegel-eisen
was begun and is still carried on at the furnace of Schisshyttan. As
fuel for this purpose is used a mixture of charcoal and coke, and an
iron ore consisting of magnetite and knebelite. The amount of manganese
in Spiegel-eisen varies from 12 to 18 %.
Several manganese ores in Central Sweden contain 1 to 5 % of
manganese and a very low percentage of phosphorus, making a most
excellent pig iron for the Bessemer and Open hearth processes. The
ores in Northern Sweden (Lappland), on the contrary, do not contain
any manganese, but occasionally indeed some titanium, though generally
in but small quantities and rarely to such an amount that the
consumption of charcoal is thereby increased.
The consumption of charcoal in the Swedish blast furnaces varies
considerably according to the quality of the charcoal and the ore, as also
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