Note: Descriptions are shown in the official language in which they were submitted.
10492Z4
BACKGROUND OF THE INVENTION
This invention reIates to a method and apparatus for
casting a plurality of ingots. ~Iore particularly, this invention
relates to a method and apparatus for casting a plurality of ingots
from one or more electrodes and for eliminating the formation of
deep molten cores in the ingots.
For a long time, the manufacture of ingots according
to any one of several consumable electrode processes was gener-
ally limited to melting or remelting an eIectrode into an ingot
whose cross-sectional area was larger than that of-the electrode.
typically, the maximum ratio of electrode cross-sectional area to
ingot cross-sectional area ranged up to about 80%. Although it
was desirable to manufacture an ingot having a cross~sectional
area smaller than the cross-sectional area of the electrode,
metallurgical and economic restrictions made this dificult to
achieve.
A method and apparatus are known for castinga plur-
ality of ingots which allows the ratio of the electrode cross-
sectional area to the ingot cross-sectional area to exceed 100%.
The method and apparatus permit casting a plurality of ingots
while avoiding the aforementioned metallurgical and economic
restrictions.
The cost of ingot manufacture by electroslag remelt-
ing or other processes is in part a function of the rate of
solidification of the ingot. In addition, the metallurgical
quality of the ingot is a function of the solidification rate.
The solidification rate, in turn, is a function of the ingot
~0~92;~4
1 cross-sectional area. The smaller the ingot cross~sectional area,
the lower the permissible solidification rate and, consequently,
the smaller the number of pounds of ingot which can be cast per
minute. Stated otherwise, the tolerable solidification rate for
a given alloy is determined by the metallurgical characteristics
and quality standards established by specification and, as a
general rule, the tolerable solidification rate decreases with
decreasing ingot cross-sectional area. Low ingot solidification
rates, however, result in poor furnace utilization, increasing
the unit cost of producing ingots.
Furthermore, the cost of manufacturing the electrode
used in a consumable electrode process increases as the electrode
diameter decreases. Consequently, the manufacture of small ingots
by consumable electrode processes and, in particular, the electro-
slag remelting process, had not been widely adopted for use in
the manufacture of ingots of small cross-sectional area.
An apparatus and process are known for manufacturing
small ingots by consumable electrode processes using electrodes
of relatively wide diameters. In one application, a molten metal
pool is formed by melting an electrode according to classic elec-
troslag remelting principles. The process entails suspending an
electrode so that its lower end is immersed in a liquid slag bath.
The lower end of the electrode is melted by passing current through
the electrode and slag so that molten metal droplets form on the
electrode and drop through the slag layer to form a molten metal
bath. A plurality of ingots may be withdrawn from the molten
metal bath.
10492Z4
1 Although the above method and apparatus permits the
economical casting of a plurality of ingots, during casting an
ingot may develop a deep mol~en metal core. The deep molten metal
core causes a decrease in the rate of solidification of the ingot
and, therefore, is undesirable. It is believed that the reason
for the formation of the deep molten metal core is the attractive
forces generated by the electrical current flowing in adjacent
ingot mold sections.
It is well-known that an attractive force is generated
between adjacent conductors which carry current in the same di-
rection. For adiacent ingot sections, it is believed that the
flow of electrical current in each ingot mold section creates an
attractive force, and the force causes molten metal to flow out of
an ingot mold section and back into the molten metal pool in the
main mold section. As a result, the molten metal is circulated in
the ingot mold section, and the circulation of the molten metal
interfers with the gradual advance of the solidification front,
i.e., the interface between the molten metal and the solidified
ingot in the ingot mold section. The solidification front, then,
remains relatively deep within the ingot mold section, and the
ingot being cast has a deep molten metal core.
BRIEF SUMMARY OF THE INVENTION
Briefly, in the present invention, a method and appar-
atus are provided for casting a plurality of ingots. The invention
includes forming a pool of molten metal in a main mold section
having a larger cross-sectional area than the total cross-
sectional area of a plurality of ingot mold sections in direct,
1~49:~Z4
1 open communication therewith, directing an eLectrical current
through an eIectrode and a conductor, the conductor being located
outside the ingot moLd sections, casting the plurality of ingots
from the molten metal pool by flowing the molten metal into the
ingot mold sections while preventing the molten metal from freez-
ing at the interface between the main mold section and the ingot
mold sections, and preventing the electrical current through the
conductor from entering the molten metal in the ingot mold sec~
tions.
BRIEF DESCRIPTION OF THE D~AWINGS
For the purpose of illustrating the invention, there
is shown in the drawings forms which are presently preferred; it
being understood, however, that this invention is not limited to
the precise arrangements and instrumentalities shown.
Figure 1 is a transverse sectional view of an electro-
slag furnace for casting a plurality of ingots.
Figure 2 is a plan view of the furnace illustrated in
Figure 1.
Figure 3 is a transverse sectional view of an elec-
troslag furnace constructed in accordance with the principles of
the present invention for performing the processes described herein.
~ Figure 4 is a plan view of another embodiment of a
; furnace constructed in accordance with the principles of the pre- sent invention for performing the processes described herein.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings in detail, wherein like
numerals indicate like elements, there is shown in Figure 1 a
1049ZZ4
1 transverse sectional view of a furnace used for casting a plur-
ality of ingots and designated generally as 10. The furnace 10
includes an outer support shell 12 which houses an upper water
cooled copper jacket 14 used to contain the molten metal 16 and
the molten slag 18. ~he support shell 12 is provided with a re-
fractory bottom 20. The refractory bottom 20 includes a replace-
able refractory upper mold insert sleeve 22 which may be annular
in construction. The water cooled jacket 14 together with the
refractory bottom 20 and its insert 22 define what is herein-
after referred to as the main mold section.
In direct, open communication with the main mold sec-
tion through the refractory sleeve 22, are the water cooled
copper ingot mold sections 24. It is in the copper ingot mold
section 24 that ingots are continuously formed and withdrawn as
solidification proceeds.
An electrode 26 is reciprocably supported with its end
in the molten slag 18 by conventional apparatus for that purpose,
not shown. Electrode 26 may have a cross-sectional area substan-
tially larger than the cross-sectional area of an ingot mold
section 24 and, hence, the cross-sectional area of an ingot 28
formed therein. In certain circumstances, it may be advantageous
to use more than one electrode 26; the present invention contem-
plates the use of one or more electrodes to form the molten metal
pool 16 by fusing under the slag 18. Moreover, the electrodes
may have any convenient cross-sectional area; the electrode cross-
sectional area may be less than, equal to, or greater than the
cross-sectional area of an ingot.
10492Z4
1 The main mold section has a larger cross-sectional area
than that of an ingot mold section 24. It is in the main mold
section that the molten metal pool 16 is formed and the molten
slag-molten metal interface maintained.
The refractory bottom 20 together with the refractory
insert sleeve 22 provide thermal insulation allowing the molten
metal pool 16 to remain molten. If any portion of the pool 16
located above the refractory bottom 20 solidifies, then either the
ingot 28 will jam in the ingot mold section 24 or the surface of
the ingot 28 will tear. To avoid jamming and tearing, the re-
fractory bottom 20 and refractory sleeve 22 sufficiently insulate
the molten metal 16 from the cooling effects of the ingot mold
section 24 and the jacket 14 to prevent solidification at or near
the interface between the ingot mold section 24 and the main mold
section. By preventing the solidification of the molten metal 16
in the main mold section, the metal-slag interface may be main-
tained in the main mold section.
By way of example, but not limitation, the refractory
bottom 20 and refractory sleeve 22 could be made of Zirconia (ZrO2).
Zirconia is advantageous because it can remain in contact with
molten steel for long periods of time with minimum reaction tenden-
cies. Moreover, it can also survive with minimum erosion or solu-
tioning during the molten slag start and molten metal buildup. It
should be understood, however, that the refractory bottom 20 and
refractory sleeve 22 are not limited to being made of Zirconia.
Other refractory products which perform the same function may be
substituted. Indeed, even non-refractory materials which insulate
the molten metal sufficiently to keep it in a molten condition can
1049ZZ4
1 be substituted.
The purpose in using a replaceable sleeve 22 at the
head of the ingot section 24 is so that it can be replaced since
this is the area of maximum wear.
Referring to Figure 2, there is shown a plan view of
the furnace 10 illustrated in Figure 1. Although three cylindri-
cal ingot mold sections 24 are illustrated in Figures 1 and 2, it
should be understood that this is merely by way of example. The
furnace may also be constructed with 2, 4 or more ingot mold sec-
tions 24. Moreover, the cross-sectional shape of an ingot mold
section 24 could be other than cylindrical, if desired.
For starting the process described in U,S. patent
3,782,445 using the furnace 10 illustrated in Figures 2 and 3,
starting plugs 30 are inserted into each of the ingot mold sec-
tions 24 so that a good electrical connection is provided for
each of the ingots 28 to be formed by withdrawal of molten metal
from the pool 16.
The electode 26 is positioned above the refractory
bottom 20 and within the copper jacket 14, and molten slag 18 is
poured into the main mold section until its level rises to the tip
of the electrode 26. Thereafter, the melting process begins. If
desired, the refractory bottom 20 and refractory sleeve 22 can be
preheated such as by use of a torch prior to the addition of the
molten slag 18.
During the first few minutes, the electrode 26 melts
at a predetermined ratel thereby covering the main mold section
refractory bottom 20 with molten metal 16. After the pool of mol-
ten metal 16 is formed, ingot withdrawal is initiated and, sub-
10492Z4
1 sequently, maintained at a rate equivalent to the melt off rateof the electrode 26 Ingot withdrawal can be accomplished by any
conventional means such as by lowering the ingot 28 from a fixed
ingot mold section 24 or by raising the ingot mold section 24
from a fixed ingot 28. Both processes and apparatus for accomp-
lishing the same are known and therefore need not be described in
detail. Thus, a plurality of ingots 28 can be simultaneously
formed from a common pool of molten metal 16.
Control of the rate of formation of the ingots 28
depends substantially in part upon the position of the molten
metal-slag interface. Since there is only one such interface,
control problems are substantially reduced as compared with trying
to maintain a molten metal-slag interface in each of the ingot mold
sections 24. Since there is only one molten metal-slag interface,
conventional controls can be used.
Although the main mold section and the ingot mold
sections 24 are preferably made of water cooled copper, it should
be understood that water cooled steel or other known types of molds
that are compatible with the process could be used. Still further,
the process is not limited to the use of consumable electrodes.
It is contemplated that non-consumable electrodes or other methods
of forming the molten metal 16 in the main mold section could be
used with equal facility. Moreover, furnaces operated in accord-
ance with the processes described herein may be used either for
continuous casting of a plurality of ingots or for the manufacture
of individual ingots.
As previously indicated, one of the major advantages
of the process and apparatus described above with respect to
~0492Z4
1 Figures 1 and 2 is that a plurality of ingots 28 can be made from
a common pool of molten metal 16. The process permits the use of
one or more electrodes 26 meIting at a relatively high rate while
each ingot 28 is being cast at a relativeIy slower rate. Stated
otherwise, in casting a plurality of ingots, the rate of casting
each ingot is not strictly controlled by the rate at which the
molten metal pool 16 is formed.
It has been found, however, that in casting a plur-
ality of ingots by the above described method and apparatus, a
deep molten metal core 32 forms within each ingot mold section 24.
It is believed that the principal réason for the formation of the
deep molten metal core 32 is an attractive force generated by the
flow of electrical current through the solidifying ingots 28. It
is well-known that adjacent conductors which carry current in the
` same direction generate attractive forces. In the above-described
method and apparatus, the flow of molten metal 16 in adjacent ingot
mold sections 24 may be likened to adiacent electrical conductors.
Thus, in Figure 1, there are shown two separate current paths,
marked A and B, between electrode 26 and starting plugs 30 in
ingot mold sections 24. Since the current paths A and B extend
through separate ingot mold sections 24 and are parallel, the
effect is to create attractive forces between the molten metal 16
within adjacent ingot mold sections 24. The attractive forces
cause molten metal to be ejected from the top of the ingot mold
sections 24 and into the molten metal pool 16 in the main mold
section.
lO~9'ZZ~
1 The ejection of the molten metal from the ingot mold
sections 24 into the molten metal pool 16 in the main mold section
above is attended by a molten metal circulation indicated by the
arrows labeled C in Figure 1. The circulation of the molten metal
16 within the ingot mold sections 24 interfers with the gradual
advance of the solidification front and results in the deep molten
metal cores 32.
Referring to Figure 3, the present invention provides
a method and apparatus for casting a plurality of ingots from a
common molten metal pool 16 while avoiding the formation of deep
metal cores in the ingots 28. In particular, a starter plug 38
is disposed between adjacent ingot sections 24 to provide a good
electrical connection with electrode 26. The starter plug 38
is surrounded in part by the refractory bottom 20 of the main mold
section which separates adjacent ingot mold sections 24. Any
suitable starter plug, known in the industry, may be inserted in
the invention according to methods well-known in the art.
A water cooled copper conductor 40 is electrically
connected to starterplug 38 and depends downwardly therefrom be-
tween adjacent ingot mold sections 24. In this manner, electricalcurrent is directed from electrode 26 through molten metal pool
16 to the starter plug 38 and conductor 40 without entering an ingot
mold section 24.
Using a conventional crucible drive, not shown, the
main mold section and ingot mold sections 24 attached thereto may
be driven upwardly as the ingots 28 are cast. Initially, ingot
mold sections 24 are supported by support table 36 which is pro-
vided with an annular opening 44 through which copper conductor 40
-10-
10492Z4
1 extends. Conductor 4Q terminates below opening 44 where it is
electrically connected to the return buses 42 of a conventional
power supply, not shown, by suitable power conductors available
in the industry.
The current paths A and B, shown extending through
ingot mold sections 24 in Figure 1, are eIiminated by inserting
starter plug 38 and copper conductor 40 as described. A single
current path, then, labeled D in Figure 3, is created; the path
extends from electrode 26 through starter plug 38 and copper
conductor 40 to the return buses 42 of the power supply. The
solidified portions of the ingots 28, then, are effectively iso-
A lated electrically, and current will ~KU~ flow through the ingots
in the mold sections 24. Thereby the molten metal circulation
aris.ng from multiple current paths is avoided. Gonsequently,
, the gradual solidification of the molten metal 16 in the ingot
I ld sections 24 will nto be impeded by the flow of current
through the molten metal pool 16, and the deep molten metal
cores 32, shown in Figure 1, will not form. This is indicated
in Figure 3 by the relatively shallow solidification front 34.
The unimpeded solidification of the ingots 28 permits
the ingots to be cast at a greater rate and, accordingly, results
in increased furnace utilization and decreased production costs.
At the same time, the metallurgical quality of the ingot is pre-
served.
Although described in terms of the electroslag remelt-
ing process, it should be understood that the invention herein can
be applied to other electrode remelting processes, such as a vacuum
arc process, or to a non-consumable electrode process. Electro-
slag remelting is somewhat slower than othe`r known processes for
-11-
1049ZZ4
1 continuous casting of a plurality of ingots, but it results in a
better product; better quality alloys result at a slower solidifi-
cation rates. In electroslag remelting, slower solidification
rates occur because the slag blanket on top of the molten metal
helps maintain heat in the pool of molten metal. Moreover, the
slag blanket prevents freezing from the edge of the pool of molten
metal at the slag-metal interface.
Although the conductor 40 is described as being made
of copper, it should be understood that other conductive materials
are also suitable for providing the single current path through the
electrode 26, the starter plug 38 and the conductor 40. In addi-
tion, although current has been referred to as flowing from the
electrode 26 to the conductor 40, the direction of current flow
is not a limitation; the current may be alternating or direct o
either polarity in practicing the present invention.
Further, the invention described herein is not limited
to a method and apparatus which uses only one starter plug 38 and
conductor 40 to provide the single current path D. Instead, as
shown in the embodiment of the invention depicted in Figure 4, a
plurality of conductors 40 may be used to generate a plurality of
current paths through the molten metal pool. Each current path,
however, is prevented from enterng an ingot mold section 24; the
currents keep the molten metal pool in the molten stateJ and the
plurality of ingots can be cast without the formation of the deep
molten metal cores 32.
1049Z24
The present invention may be embodied in other speci-
fic forms without departing from the spirit or essential attributes
thereof and, accordingly, reference should be made to the appended
claims, rather than to the foregoing specification as indicating
the scope of the invention.
-13-
