pa1778data.pdf

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U.S. STEEL DUQUESNE WORKS
HAER No. PA-115
(Page 177)
first stage or oxidizing period, a charge of cold scrap steel was
melted down and impurities were subseguently eliminated from the
bath. The second stage, or reducing period, involved creating
the required alloy composition in the steel.
The process began with the loading of scrap boxes on the
ground floor of the stockhouse aisle. After each box was loaded
and weighed, it was lifted up by an E.O.T. crane and set on one
of several flat cars located on the scrap makeup floor. The line
of cars were subsequently moved by a Diesel locomotive over
crossover tracks to the charging floor where they were set
alongside the furnaces to be charged. Each box was picked off of
its respective car by the peel of the charging machine and
overturned inside of the furnace through its water cooled
charging door. A thin layer of light scrap was charged first,
followed by heavy scrap, which was placed within or adjacent to
the triangle or "delta" formed by the electrodes. Finally, light
scrap was piled high around the sides of the furnace in order to
protect the roof and side walls from the arc during the high
power melt down period.
When the charging operation was complete, the electrodes
were adjusted into place and the current was turned on. Melt
down usually lasted for three and one-half or four hours, after
which the silicon, manganese, phosphorus, and carbon contained in
the scrap was oxidized, forming a slag which floated on top of
the molten metal. This part of the process lasted for about one
hour. As soon as the oxidizing period was complete, the
electrodes were raised and the current was shut off while the
slag was manually raked off the bath by the manipulation of long
stemmed wooden "rabbles" put through the charging door. During
this period, the furnace was tilted backward to permit the slag
to drain into a cinder pot located on the transfer car running
between the splasher walls. Completion of slag removal made the
heat ready for the reducing stage of the process.
The reducing period began with the addition of a new slag
mixture, composed of burnt lime, fluorspar, silica sand, and
powered coke, to the bath. Before adding the components of the
new slag mixture into the furnace, the charging machine placed
their individual charging boxes into a gas fired drying oven
located on the charging floor, in line with the furnaces.
Powdered coke, which was added to the slag after it became fluid,
supplied the carbon for the formation of calcium carbide. The
presence of calcium carbide in the slag facilitated the removal
of sulphur from the bath and allowed for the addition of alloys
such as manganese, nickel, chromium, vanadium, and tungsten to
the molten metal because it returned their reducible oxides from
the slag to the bath. After a period of approximately two hours