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Hacker, Robert W. (ed.) / The Wisconsin engineer
Volume 53, Number 4 (January 1949)

Pipkorn, Russell
[Continuous casting],   pp. 6-8


Page 8


its surface finish requires only light finishing operations.
         Evolution of Continuous Steel Casting
  The actual beginnings of the successful continuous cast
steel operation began about six years ago, when the Re-
public Steel Corporation began its development work un-
der the Williams Patents. In 1944 the Babcock & Wilcox
Company and Republic began their discussions which led
to a formal agreement in 1946. Then came the experimental
plant at Beaver Falls which was established to experiment
with standard commercial sections. From this plant came
the first successful commercial steel billets.
    Molten steel being transferred from the regular electric
  furnace by transfer ladle to the inductively heated holding
  and pouring ladle.
  Because of the possibilities, and necessities, other com-
panies have entered the field in the experiment. Many
developments, however, are either dormant at present or
of little success. The Babcock & Wilcox-Republic combina-
tion has been successful because of the knowledge and ex-
perience of the former company in the field of heat trans-
fer at high rates and the latter company's knowledge of
the steel industry.
  The British, too, because of the necessity to modernize
their facilities, are investigating its possibilities and have
continued on their own rather than depend on the Ameri-
can efforts.
                   Successful Process
  The Beaver Falls plant casts an eliptical section of
about thirty square inches at a rate of 400 pounds per min-
ute. Casts are made two or three times a week.
  The operation begins at the top of a 75 foot tower where
steel is delivered from the company's regular electric fur-
naces by transfer ladle to an inductively heated holding
and pouring unit. The usual supply is 5,000 pounds per
cast.
  The molten metal is poured from the holding ladle
into a tundish which is designed to strain out the slag, and
8
then enters the water cooled mold. The important factor
for the successful operation of the mold is that it must
not be wetted by the steel. To accomplish this the steel
must have a strong negative meniscus (like mercury). This
is an indication that the mold is clean and the process
is properly functioning. This condition is checked by a
mirror arrangement above the mold.
  A small amount of hydrocarbon is introduced in the
mold to eliminate free oxygen above the mold, because
any oxide present promotes wetting. Argon, because of
its high density and inactivity with iron, is introduced
above the liquid to prevent oxidation. The steel is in con-
tact wth the mold for only a few inches since, as it cools,
the metal shrinks away from the mold. The steel loses
heat by conduction only while it is in contact with the
mold and by radiation and conduction below the shrink
point. This latter process is aided by the gas which fills this
gap between steel and mold. This gas has been analyzed
and found to be about fifty per cent hydrogen. The steel
must get its strength to withstand further movement and
surface quality while in contact with the mold.
  From the mold the metal passes through an insulated
chamber which arrests and controls the speed of further
cooling. Below this chamber is the mechanism which con-
trols the rate of withdrawal of the steel billet. The billet
passes an oxy-acetylene torch which moves along with the
billet for a short distance while the billet is being cut
to a specified length which could be as long as 35 feet.
The cut-off section of the billet is then lowered into a
horizontal position by a special cradle arrangement. The
billets are then ready to proceed to the finishing opera-
tions.
                 Problems Encountered
  The mold, as was mentioned, is the basis for a good
billet. The mold surface must be smooth and remain clean
throughout the operation. A number of metals have been
tried and successfully used. The thicknesses of the mate-
rial, however, depends upon the rate of heat conductance.
One-sixteenth inch steel, one-quarter inch copper and
three-sixteenth inch brass have been used. Stainless or heat
resisting steels, seemingly logical choices, were unsuccessful
because they have wetting characteristics. Brass has been
found to have the best structural and fabricational advan-
tage. Cooling must be supplied to the mold in such a man-
ner that the coolant is in contact on all surfaces. In order
that proper cooling was obtained-no deterioration of the
mold and reasonable casting speeds-water flows as high
as 500 gallons per minute were used, giving only a few
degrees of temperature rise. A special system of flow
design was required to prevent cavitation in the mold.
  Slag influences the quality of the steel. To eliminate it
the tundish was placed between the pouring ladle and
mold. Originally a preheated tundish was used, but with
this type the metal has a tendency to begin freezing since
the slower it moves tkrough the tundish, the better is
the slag elimination. A new electrically heated tundish
will solve the freezing problem and increase slag elimina-
                  (please turn to page 20)
                  THE WISCONSIN ENGINEER


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