Note: Descriptions are shown in the official language in which they were submitted.
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Background of he Invention
This invention relates to a method of' casting
steel ingots. It relates especially to the casting of' steel
ingots into ingot molds whose internal surfaces have been
coated with a coating containing a mixture of' finely divided
selected oxides and fluorides.
The use of mold coatings on the internal surfaces
of ingot molds to either improve the surface quality of the
solidified ingot or to prevent the ingot from adhering to
ingot mold is well known and a large variety of materials
and techniques for applying such materials have been tried
by steelmakers in the past. Heretof'ore such coatings have
been expensive, difficult to apply and of' questionable value
in improving the quality of the ingot, especially in the
critical subsurface region immediately below the surface of
the ingot.
Summary of the Invention
It is therefore an object of this invention to
provide a method of casting steel ingots which will produce
steel ingots having superior surface and subsurface quality.
It is a further object of this invention to
provide a method of casting steel ingots using an ingot mold
coating which is relatively inexpensive.
It is a still further object of this invention to
provide a method of casting steel ingots using a mold coating
that is easy to apply and does not require special equipment
or techniques.
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Other and further objects of this invention will
become apparent from the following deseription and claims.
According to the present invention the foregoing
objects are attained by applying to the internal surfaces of
an ingot mold a coating of a liquid dispersion containing a
mixture of finely divided oxides and fluorides, drying the
coating and ~hen teeming molten steel into the coated mold.
Description of Preferred Embodiment
The invention is espeeially suited for use with
cast iron open ended ingot molds of the type used for
easting earbon and alloy steel ingots at most steel pro-
dueing plants. In practice, a liquid dispersion or slurry
is prepared using a mixture of finely divided oxides and
fluorides, the amounts of whieh are selected to provide
eertain desirable physieal and chemical properties to the
eoating when melted by the molten steel.
A satisfaetory slurry has been used eomprised of a
mixture of aluminum oxides, ealeium oxides, silica and
ealeium fluoride in substantially the ~ollowing proportions
by weight:
A123 22%
CaO - 22.8%
CaF2 _ 15.6%
to whieh has been added suf~ieient water to enable the
slurry to be sprayed or brushed on the interior sur~aees of
the ingot mold. Other liquids su¢h as alcohol could be used
instead o~ water as the liquid vehicle if desired. It is
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not necessary or even desirable to add any binder materials
to the slurry since it has been observed that the above
mixture tightly adheres to the surface of the ingot mold
after the liquid which has evaporated.
The exact proportions of aluminum oxide, calcium
oxide, silica and calcium fluoride can be varied for the
proportions given so long as the resulting mixture has a
plastic deformation point between 600C and 1200C, and a
flowidity between 5 and 31 centimeters.
The term "plastic deformation point" and "flowidity"
of the mixture as used in this specification and claims are
defined in United States Patent No. 3,649,249.
The apparatus used to determine the "flowidity" of
the compositions of the present invention is illustrated in
United States Patent No. 3,649,249 in Figure 2. This
apparatus consists of a split mold comprising half mold
sections, casters machines of low carbon steel. The mold
sections when operatively assembled, as by clamping together
the two half mold sections form a vertically disposed funnel
or conical portions having an internal diameter of about
three inches and an external diameter of 3 5/8 inches at the
upper end and an internal diameter of 5/8 inches at the
lower or discharge end thereof. The internal surface of the
conical porti3n forms an angle of 39.5 with the vertical
axis of the conical portion. A conical recess formed by the
conical portion is adapked to receive the test sample of
molten meterial. A rectangular base section connects with
the lower end of the conical portion and defines a
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cylindrical well having a diameter of 5/8 inch and a depth
of 3/4 inch. The base section has a rectangular section
extending horizontally from one side thereof with an axial
bore or conduit extending therethrough and having a circular
cross-section 1/4 inch in diameter and a length of about 20
inches. The conduit intersects the lateral cylindrical well
adjacent the lower end of the well and provides an outlet
passage for the test material introduced into the conical
recess which serves as a funnel to feed the test material
into the conduit until the sample solidifies in the conduit.
The term "flowidity" as used in the specification
is the distance in inches which the test material flows
through the conduit before solidifying when 200 grams of the
test material at a temperature of 2,600F is rapidly poured
into the conical recess. The pouring technique and the
timing of the test procedure should be standardized to
obtain consistent results. The temperature of the mold,
within normal operating limits has little effect on the
; measured flowidity.
The flat "plastic deformation point" of the slag
as the term is used in the specification is determined by
heating about a 20 gram piece of the solidified test material
which is obtained from the above flowidity test at a rate of
50F per minute and pressing a graphite rod (or an aluminua
or other suitable rod) against the piece of test material at
frequent intervals as the temperature rises and the
temperature at which the pieGe of slag plastically deforms
under a slight pressure is the "plastic deformation point".
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It is preferred to use an unfused mixture of the
oxides because of its lower cost. A prefused mixture could
be used equally well in producing this invention but at
greater expense due to the cost of preparing.
It is prelerred to apply the slurry mixture to a
warm ingot mold so that the heat of the mold will assist in
drying the coating. The slurry is applied so that the
resulting dried coating is at least 0.3 millimeters thick.
Based on the mixture set forth above this would equal about
1 kilogram o~ the mixture per square meter of surface area
coated.
While the exact mechanism of this invention is not
known it is believed this mixture as it melts acts as a
lubricant between the ingot and mold allowing contraction o~
the thin ingot skin without stressing the skin which would
cause cracks. The molten mixture also apparently has the
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ability to pick-up surface and subsurface impurities and
inclusion forming material from the molten steel and retain
them while the ingot solidifies.
The use of this practice has pro~ided a 911%
reduction in the length of surface cracks and an 83% reduction
in the sum of inclusion diameters at or :near the surface of
the ingot.
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