pa1778data.pdf

U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 167)
track by a dinky to the charging floor of the furnace building
and deposited alongside one of the furnaces. A Wellman-Seaver
charging machine running on wide gauge track adjacent to the
boxes and equipped with a hydraulically operated arm or "peel"
picked the boxes up in sequence and overturned them into the
furnace hearth through its water-cooled charging doors.
Limestone was charged first, followed by iron ore and finally the
scrap. The entire mass was heated for approximately two hours,
or until the scrap was white hot and slightly fused, by burning
natural gas mixed with combustion air over it. During the period
in which the furnace operated, waste gas and combustion air were
passed alternatively through the furnace's regenerative heating
chambers every twenty minutes. Constructed of brick checkerwork,
the regenerative chambers were located below the structural
charging floor and away from the furnace.
When the initial charge was ready, a ladle full of molten
pig iron, drawn from the mixer at the Bessemer plant, was
transported by an E.O.T. crane and charged into the furnace
through a spout inserted into the charging door. Soon after the
molten iron had been charged, a reaction occurred in which almost
all of the silicon, manganese, phosphorus, sulphur, and part of
the carbon was eliminated. All of these materials except the
carbon, which escaped as carbon monoxide and caused an agitation
of the bath, became part of the slag. During the next two or
three hours, about 80 percent of this slag flushed into a slag
pot through a notch located in the back of the furnace. The iron
ore then entered a three to four hour period known as the "ore
boil" during which it reacted with the carbon. Then, for
approximately two or three hours carbon dioxide emitted from the
limestone as it was being decomposed by the heat bubbled through
the bath and exposed part of the metal to the flame, thus
oxidizing it. Known as the "lime boil," this activity completed
the purification begun by the ore reaction and left the carbon
content of the bath somewhat greater than that at which the metal
was to be tapped. If, after a sample of the molten metal was
taken, it was determined that the carbon content was too high or
too low, more pig iron or iron ore was added. In any case, after
about another hour the carbon content was reduced to the proper
level for tapping. The temperature of the bath at tapping was in
the neighborhood of 3000° F., varying according to the
composition and grade of the steel.
Tapping began with the digging out of the clay-loam plug and
dolomite used to seal the tap hole before the furnace was
charged. Molten steel escaped from the tapping hole, which was
located at the lowest level of the hearth, into a teeming ladle
through a removable spout. The ladle was set on a stand below