pa1778data.pdf

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