pa1778data.pdf

U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 68)
furnace, lime combined with the minerals which had been separated
from the ore such as silica, aluminum, and part of the manganese
to form slag. From this point the slag and the liquified iron
trickled down through the interstices of the coke at the
combustion zone of the furnace to the hearth. Both substances
attracted the sulphur and ash of the coke to them during their
downward flow. Due to its lighter weight, the slag formed a
molten layer on top of the iron. As the hearth continued to
fill, the slag, because of its chemical composition, attracted
part of the sulphur in the molten iron to it.
After an interval of several hours, the hearth became full
and the furnace was ready to be tapped. Iron was taken from the
furnace through a tap hole called the iron notch. Located on the
furnace at the level of the cast house floor, the iron notch was
opened by means of an pneumatic air drill. Upon opening, molten
iron, at a temperature of approximately 2600 degrees F., rushed
out of the furnace into a series of clay runners embedded in the
cast house floor before making its way to sand molds located on
the floor or to waiting ladle cars which were located on standard
gauge tracks below the cast house at the end of the runners.
After 1898, molten iron flowed exclusively to the ladle cars.
Shortly after the iron had been tapped, the slag was withdrawn
from the furnace through the slag notch or "monkey." Located 90
degrees from the iron notch on the furnace at a slightly higher
elevation, the "monkey," which was opened by removing a short
iron rod called the bott, allowed the slag to flow from the
furnace into a series of clay runners also embedded in the cast
house floor. The runners led to either a slag pit, or to waiting
cinder pot rail cars, either of which were located below and
outside of the cast house. After tapping, the iron notch was
plugged up by means of a mechanical clay gun and the bott was
reinserted in the "monkey."
Ladle cars filled with molten iron were either taken to a
pig casting machine (after 1898) where it was cast into molds to
be sold on the merchant iron market or to the steelmaking plant
where it was converted into steel by a number of different
steelmaking processes — including the Bessemer, open hearth, or
basic oxygen processes. In either case, the iron had to be
desulphurized because the presence of too much sulphur in
merchant iron caused excessive shrinkage in castings and because
its presence in steel caused cracking across the ingot surface
during rolling. Historically, desulphurization took place
internally within the Bessemer converter or open hearth furnace
itself or externally by adding soda ash or calcium carbide to the
ladle so as to create a slag which could attract the remaining
sulphur to it. 1