pa1778data.pdf
pa1778data.pdf
pa1778data.pdf
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U.S. STEEL DUQUESNE WORKS<br />
HAER No. PA-115<br />
(Page 177)<br />
first stage or oxidizing period, a charge of cold scrap steel was<br />
melted down and impurities were subseguently eliminated from the<br />
bath. The second stage, or reducing period, involved creating<br />
the required alloy composition in the steel.<br />
The process began with the loading of scrap boxes on the<br />
ground floor of the stockhouse aisle. After each box was loaded<br />
and weighed, it was lifted up by an E.O.T. crane and set on one<br />
of several flat cars located on the scrap makeup floor. The line<br />
of cars were subsequently moved by a Diesel locomotive over<br />
crossover tracks to the charging floor where they were set<br />
alongside the furnaces to be charged. Each box was picked off of<br />
its respective car by the peel of the charging machine and<br />
overturned inside of the furnace through its water cooled<br />
charging door. A thin layer of light scrap was charged first,<br />
followed by heavy scrap, which was placed within or adjacent to<br />
the triangle or "delta" formed by the electrodes. Finally, light<br />
scrap was piled high around the sides of the furnace in order to<br />
protect the roof and side walls from the arc during the high<br />
power melt down period.<br />
When the charging operation was complete, the electrodes<br />
were adjusted into place and the current was turned on. Melt<br />
down usually lasted for three and one-half or four hours, after<br />
which the silicon, manganese, phosphorus, and carbon contained in<br />
the scrap was oxidized, forming a slag which floated on top of<br />
the molten metal. This part of the process lasted for about one<br />
hour. As soon as the oxidizing period was complete, the<br />
electrodes were raised and the current was shut off while the<br />
slag was manually raked off the bath by the manipulation of long<br />
stemmed wooden "rabbles" put through the charging door. During<br />
this period, the furnace was tilted backward to permit the slag<br />
to drain into a cinder pot located on the transfer car running<br />
between the splasher walls. Completion of slag removal made the<br />
heat ready for the reducing stage of the process.<br />
The reducing period began with the addition of a new slag<br />
mixture, composed of burnt lime, fluorspar, silica sand, and<br />
powered coke, to the bath. Before adding the components of the<br />
new slag mixture into the furnace, the charging machine placed<br />
their individual charging boxes into a gas fired drying oven<br />
located on the charging floor, in line with the furnaces.<br />
Powdered coke, which was added to the slag after it became fluid,<br />
supplied the carbon for the formation of calcium carbide. The<br />
presence of calcium carbide in the slag facilitated the removal<br />
of sulphur from the bath and allowed for the addition of alloys<br />
such as manganese, nickel, chromium, vanadium, and tungsten to<br />
the molten metal because it returned their reducible oxides from<br />
the slag to the bath. After a period of approximately two hours