Note: Descriptions are shown in the official language in which they were submitted.
~lO(~Z~31
1 In the ~roduction of various high-strength alloy steels,
tool steels and some superalloys it is conventional practice to
melt in an electric furnace and from the electric furnace melt
produce castings. The castings are then subsequently used as an
electrode for further refining of the alloy by vacuum consumable
arc melting thereof. In the casting operation the molten metal
from a transport ladle is cast into a plurality of open-ended
molds which are removably positioned on mold stools, with the
mold stool closing the bot~om end of the mold in preparation for
casting. Upon solidification of the cast metal, the mold is
lifted vertically to slide it from the casting, and the casting
is thereafter removed from the mold stool for further processing,
such as by vacuum arc melting for further refining.
During the casting operation the stream of molten metal
from the ladle initially stri~es the mold stool at the bottom of
the mold and after repeated operation causes erosion of the mold
- stool surface. This results in the mold stool having a relieved
portion on its surface area surrounded by the mold. As a result
of this erosion the mold stools must either be frequently re-
placed or reconditioned which adds significantly to the cost of
the casting operation. Other~iise the molten metal being cast will
solidify in the relieved portion of the mold stool to form a pro-
truding knob on the bottom of the casting. This knob must be
removed as a step in preparing the casting for further processing,
as by the use of the casting as an electrode in vacuum arc melt-
ing. This removal of the knob reduces the product yield. This
problem with mold stools, which is caused by erosion during
casting, also results with closed-bottom and plug-bottom molds.
It is accordingly an object of the present invention
to provide an ingot casting method whereby the relieved portion
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1 of the mold stool or mold bottom resulting from erosion during
casting may be efficiently repaired for each casting operation,
thereby increasing product yield and adding significantly to the
life of the mold stool or mold bottom.
This and other objects of the invention as well as a
more complete understanding thereof may be obtained from the
following description and drawings, in which:
FIGURE 1 is a schematic showing of an open-ended ingot
mold positioned on a mold stool having a relieved portion on the
surface thereof resulting from erosion during casting; and
FIGURE 2 is a schematic showing similar to that of FIG.
1 wherein one embodiment of the invention is shown.
Broadly, in the practice of the invention, prior to the
casting operation the relieved portion of the mold stool is filled
with metal particles, preferably steel shot, and thereafter the
relieved portion of the mold stool is covered with a plate. Con-
sequently, during casting the molten metal is essentially pre-
vented from entering the relieved portion of the mold stool and
~he particles do not significantly comingle with the molten metal
during casting. Comingling of the metal particles to a signif-
icant extent would cause the bottom comingled portion of the cast-
ing to be of an unsatisfactory composition requiring removal and
scrapping thereof prior to further processing of the ingot as by
consumable electrode melting. For the purpose at least one metal
plate~ preferably steel, is placed over the relieved portion of
the mold stool and within the surface area thereof enclosed by
the mold, Preferably the plate has a specific gravity at least
equal to that of the metal being cast to prevent the plate from
float~ng in the metal ~eing cast prior to solidification of the
metal, In this manner, after solidification and removal of the
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1 mold from the ingot casting it is not necessary to remove any
significant portion of the casting bottom to ready the casting
for use as an electrode in subsequent vacuum arc melting oper-
ations. In the conventional practice wherein the casting bottom
was characterized by a protruding kno~ resulting from the metal
solidified in the relieved portion of the mold stool it was
necessary, prior to using the ingot in vacuum arc melting, to
remove this protruding knob along with significant portions of
the usable ~ody of the ingot casting. The removal of this cast
tO material significantly decreased the product yield of each
casting.
Any portion of the metal cover plate and steel shot
adhering to the casting bottom need not ~e removed prior to use
of the ingot casting as an electrode for vacuum arc melting.
Characteristic of the vacuum arc melting practice, there is pro-
vided in the bottom o~ the vacuum arc furnace a quantity of
starter material in the form of machined chips and turnings.
This material is used so that during the initial production of
the arc from the electrode bottom the furnace bottom is protected
from deterioration resulting from the burning action of the arc.
For purposesof achieving a homogeneous vacuum arc melting ingot
structure the initial portion of the vacuum arc melt, constitut-
ing the striker chips and the inital vacuum arc melted material
com~ining therewith is discarded. This discard results from
the conventional cropping operation imparted to the end of the
work piece produced ~rom the vacuum arc melted ingot during su~-
sequent operations such as forgoing or rolling. It may be seen,
the~efore f that with the practice of the invention not only do
savings result from the standpoint of increased product yield
and prolonged mold stool life but in addition there is no special
28~
1 preparation, such as a cropping action, necessary to remove
any significant amount of metal from the ~ottom of the ingot
prior to vacuum arc melting~ The only operation necessary to
ready the ingot fc;r use as an electrode in vacuum arc melting is
the prior practice of subjecting it to a lathe-turning operation
in which a concentric surface portion is removed and a longitud-
inal taper imparted to the ingot casting.
With reference to the drawings, FIG, 1 shows an assem-
bly 10 including a vertical open-ended ingot mold 12 having
side lugs 14 to facilitate removal and transport~ as by the use
of an over-head crane, In typical preparation for an ingot
casting operation the mold 12 is shown positioned on a mold stool
16, which mold stool has a relieved portion 18 caused by erosion
during casting. With this relieved portion ~eing present, after
casting and upon solidification molten metal will form a pro-
truding knob on the bottom of the casting, This knob must be
removed prior to using the casting as an electrode in vacuum arc
melting, This of course significantly detracts from the product
yield and overall efficiency of the operation, FIG, 2 shows the
~o identical structure of FI~. 1 with the relieved portion 18 of the
mold stool filled with steel shot 20 and ~Jith the relieved portion
then covered with a steel plate 22. The shot 20 effectively
repai~s the relieved portion for the casting operation, thereby
preventing the formation of undesirable protruding knobs and
- the plate 22 prevents comingling of the steel shot 20 with the
molten metal being cast, The shot 20 during casting and as a
result of the heat from the cast metal fuses together and to the
surface of the relieved portion or cavity to fill the same~ If
significant comingling is permitted the comingled portion of
the ingot casting will not be of the required composition, and
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1 thus removal of this portion will ~e required ~efore further
processing.
Prior to the use of the invention, conventional mold
stools used in the production of electric furnace melted high
strength alloy steels required replacedment after a~out 8 to 10
castings, and all of the castings prior to use as electrodes in
vacuum arc melting operations required that the ~ottoms thereof
- ~e trimmed ~y torch cutting to remove the protrusion caused by
metal entering the relieved portion of the mold stool. By the
- 10 use of conventional steel shot of the typical composition .9~
car~on, .~ silicon, ~75~ manganese and ~alance iron with metal
plates covering the eroded portion of the mold stool 26 castings
have ~een made in accordance with the invention with the same
stools with on additional detectahle erosion. Initially, and
prior to the use of the invention, the stools contained cavities
ranging from 1" to 7" in depth. By the use of steel shot wlthin
the relieved portion of the mold stool covered with a steel plate
in accordance with the practice of the invention, the,molten
metal ~uic~ly solidified without entering the relieved portion
of the mold and comingling with the shot. Hence, product yield
is maximized and the life of the mold stool is prolonged~
It has ~een found that if the steel shot is nonuniform
in size consist, the shot will sinter together during the casting
operation to fill, at least partially the relieved portion and
will not be pulled from the mold stool with the casting upon
lifting of the solidified casting therefrom. Hence it is pre-
ferred in the practice of the invention that the shot ~e of a
nonuniform size consist of for example -8 to +70 mesh U.S.
Standard.
Although the invention has ~een descri~ed as ~lsed in
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1 manufacture of ingot castings for subsequent use as electrodes
in vacuum arcmelting operations, the invention is useful in any
casting operation wherein erosion of the mold stool or mold
bottom is encountered and by using the invention increased pro-
duct yield and increase stool life result.
Although the-invention has been described as being
used with mold stools having relieved surface portions caused by
erosion during casting, nevertheless the invention would also
find utility with mold stools and mold bottoms initially con-
structed with cast surface cavities. In this instance, theinvention could be used during the initial castings with mold
stools of this type.
The term mold bottom as used herein refers to mold
stools and mold bottoms of both the integral and plug-bottom
type.
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