pa1778data.pdf

U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 162)
steel could flow into it. After the ingots were teemed, they
were allowed to stand and cool before they were sent to the
blooming mill's soaking pits. 1
During the period when the Duquesne Works used cupola melted
pig iron, it set a world record for productivity for a two
converter plant by making 38,000 tons of ingots in one month.
The use of cupolas, however, entailed certain disadvantages which
affected the quality of the steel produced. Because the cupolas,
which operated like blast furnaces, used coke as their primary
fuel, much of the sulphur and phosphorus inherent in the coke was
absorbed into the iron. Their presence, which is undesirable in
steel above certain limits, could not be removed by the Bessemer
process. As a result, care had to be taken to use only the best
coke available, in minimal amounts, when charging the cupolas.
These factors, combined with the fluctuation in iron composition,
caused erratic swings in iron temperatures, resulting in
difficulties in controlling the blowing of the converters.
Consequently, the cupolas were abandoned and hot metal was drawn
directly from a 2 00 ton capacity hot metal mixer when the Works
put its newly constructed blast furnace plant in operation.
The cylindrically shaped refractory brick lined mixer stored
molten iron taken from the blast furnaces and conserved its heat
by a continuous rocking motion. In addition to saving the
remelting and handling costs which were associated with cupola
use, the mixer improved the metallurgical composition of the iron
because it was able to store several blast furnace casts at one
time, thereby mixing iron low in some elements with iron that was
high in the same ingredients. Thus, the hot metal delivered to
the converters was of more uniform quality than could otherwise
have been obtained. The design of the Duquesne hot metal mixer,
moreover, represented a significant improvement over the original
box mixer designed by Captain William Jones of the J. Edgar
Thomson Works in 1888. Unlike the two 100 ton capacity box
mixers at the Edgar Thomson Works, which were rocked by a motor
driven gear and pinion arrangement, the Duquesne mixer was
mounted on two sets of racers and rollers which were formed to
its shape and carried the weight of the vessel. A hydraulically
powered plunger, connected to the mixer by means of a link,
rocked or revolved it on the rollers. As such, this design
allowed for mixers of much greater capacities (up to 1300 tons)
than the original box design could accommodate, making the
Duquesne design the standard from which all mixers were
constructed in the future. 2