pa1778data.pdf
pa1778data.pdf
pa1778data.pdf
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U.S. STEEL DUQUESNE WORKS<br />
HAER No. PA-115<br />
(Page 179)<br />
example, a power failure occurred during the reducing stage of<br />
the heat, oxygen could be used to shape the reducing slag and<br />
melt all alloy additions prior to tapping. 3<br />
A very important addition to the teeming process occurred in<br />
1956 with the installation of a vacuum degassing or casting unit.<br />
The first such unit employed in the United States, it prevented<br />
the formation of gas (especially hydrogen) generated internal<br />
defects such as cavities and fissures in heavy forging ingots.<br />
This made it possible, for example, to produce ingots which could<br />
be forged at the Homestead Works into rotors for large electric<br />
generators. Because of the high speed at which such rotors spun,<br />
they were subjected to unusually severe stress. Consequently,<br />
the internal structure of the steel was of critical importance to<br />
the successful operation of turbines.<br />
The unit consisted of a 17'-0" diameter x 31'-0" high<br />
pouring chamber complete with a retractable roof which was set<br />
into a pit located at the southwestern end of the pouring aisle.<br />
The base, roof, and cylinder sections of the chamber were sealed<br />
by heavy rubber rings. An aluminum diaphragm sealed the pouring<br />
port, which was located on the roof of the chamber. Air was<br />
removed from the pouring chamber by four nearby vacuum pumps.<br />
The vacuum casting process began by setting an ingot mould<br />
upon the base of the chamber. Ingot moulds as large as 95" in<br />
diameter with a capacity of 360,000 lbs. were often teemed in<br />
this manner by successively tapping all three electric furnaces<br />
while the casting process was conducted. After the ingot mould<br />
was put into place, the retractable roof was closed and sealed.<br />
The vacuum pumps then removed the air from the chamber and a<br />
teeming ladle of molten metal was picked up by a E.O.T. crane and<br />
set over the pouring spout. As the steel began to flow from the<br />
bottom of the teeming ladle, the aluminum diaphragm was melted,<br />
allowing the molten metal to pour in the form of countless<br />
droplets into the mould. The process was monitored by a closed<br />
circuit television hook-up during the teeming period and the<br />
chamber was kept airtight by the continued use of the vacuum<br />
pumps. When the monitor indicated that the teeming process was<br />
complete, the vacuum in the chamber was broken and the ingot was<br />
removed. It took at least two days for the largest ingots to<br />
cool before they could be further processed. 4<br />
Between 1957 and 1960, the electric furnace plant underwent<br />
a major expansion. Each of the original electric furnaces were<br />
rebuilt and enlarged. The two 70-ton furnaces were enlarged to<br />
85 tons and their 35-ton capacity counterpart was enlarged to 45<br />
tons. In addition, the 20-ton electric furnace located in the<br />
furnace building of Open Hearth Number Two was reconstructed to