Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF TIIE INVENTION
This invention relates to an improved process and
apparatus for electromagnetically casting metals and alloys
particularly heavy metals and alloys such as copper and
copper alloys. ~he electromagnetic casting process has been
known and used for many years for continuously and semi-
continuously casting metals and alloys. The process has been
employed commercially for casting aluminum and aluminum
alloys.
PRIOR ART STATE~ENT
The electromagnetic casting apparatus comprises a three
part mold consisting of a water cooled inductor, a non-
magnetic screen and a manifold for applying cooling ~rater
to the ingot. Such an apparatus is exemplified in U.S.
Patent Mo. 3,467,166 to Getselev et al. Gontainment of the
molten metal is achieved without direct contact between the
molten metal and any component of the mold. Solidification
of the molten metal is achieved by direct application of
water from the cooling manifold to the ingot shell~
The cooling manifold may direct the water against the
ingot from above, from within or from below the inductor
as exemplified in U.S. Patent Nos. 3,735,799 to ~arlson
and 3,646,988 to Getselev~ In some prior art approaches
the inductor is formed as part of the cooling manifold so
tha~ the cooling manifold supplies both cooling to solidify
the casting anà to ccol the inductor as exemplified in U.S~
Patent Nos. 3,773,101 to Getselev and 4,004,631 to Goodrich
et al.
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~ he non-l~agnetic screen is utilized to properly shape
the magnetic field for containing the molten metal as
exemplified in U.S. Patent No. 3,605,865 to Getselev. A
variety of approaches with respect to non-magnetic screens
are ex~mplified as ~ell in the Xarlson ' 799 patent and in
U.S. Pztent Mo. 3,985,179 to Goodrich et al. Goodrich et al.
' 179 describes the use of a shaped inductor to shape the
field. Similarly, a variety of inductor designs are set
forth in the aforenoted patents and in U.S. Patent No~
o 3,741,280 to Kozheurov et al.
T~hile the above described patents describe electro-
magnetic casting molds for casting a single strand or ingot
at a time the process can be applied to the casting of more
than one strand or ingot simultaneously as exemplified in
U.S. Patent No. 3,702,155. In addition to the aforenoted
patents a further description of the electromagnetic casting
process can befound by reference to the following articles:
"Continuous Casting with Formation o~ Ingot by Electro-
magnetic Field", by P.P. Mochalov and ~.M. Getselev, Tsvetnye
~Iet., Au~ust, 1970, 43, pp. 62-63; "Formation of Ingot
Surface During Continuous Casting", by G.A. Balakhontsev et
al., Tsvetnye ~Iet., August, 1970, 43, pp. 64-65; "Casting
in an Electromagnetic Field", by Z.N. Getselev, J. Of Metals,
October, 1971, pp. 38-59; and '~Alusuisse ~xperience with
Electromagnetic Mouldsl', by H.A. Meier, G.B. Leconte and A.
M. Odo~, Light Metals, 1977, pp. 223-233.
In U.S. Patent No. 4,014,379 to Getselev a control
system is described for controlling the current flowing
through the inductor responsive to deviations in the dimen-
sions of the liauid zone ~molten metal head~ of the ingot
from a prescribed value.
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The invention herein ls particularly concerned with the
apparatus for applyinæ cooling water to the ingot for
solidification. It is known for electromagnetic casting that
the solidification front between the molten metal and the
solidifying ingot at the ingot surface should be maintained
within the zone of high magnetic field strength. Namely, the
solidification front should be located within the inductor.
If the solidification front extends above the inductor, cold
folding is likely to occur. On the other hand, if it recedes
to below the inductor, a bleed out o~ decantation of the
liquid metal is likely to result.
It is known in the art OI' Direct Chill casting in a
water cooled mold to utili~e a coolant application arrange-
ment wherein the cooling water applied to the mold and ingot
is periodically interrupted or pulsed on a cyclic basis. By
varying the ratio of water "on" to water l-off'l time, good
control over the rate at which the coolant removes heat from
the ingot can be achieved. This pulse cooling process is
amply illustrated by reference to U.S. Patent No. 3,441,079
~o Bryson and to an article entitled"Direct Chill Casting
Process for Aluminum Ingots - A New Coolin~ Techniaue"~ by
N.B. Bryson, Canadian Metallurgical Quarterly~ Vol. 7, No.l,
Pages 55-59.
In Getselev et al. '166 the coolant applica'ion manifold
is assciated with the screen portion of the mold and they
are arranged for simultaneous movement relative to the
inductor. This is not a suitable system for adjusting the
water application plane since movement of the coolant manifold
entails corresponding movement of the screen which results
in undesirable modification in the field shape of the mold
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`and hence, in the resulting ingot shape. In Getselev '988
there is disclosed a moveable manifold mounted below the
inductor. This system would appear adequate for high con-
ductivity alloys especially where low casting speeds are
used, However, the apparatus described provides a minimum
separation between the plane of water application and the
inductor mid-plane comprising one-half the height of the
inductor. If this apparatus were applied to copper alloys
of moderate or fairly low conductivity, then in order to
properly position the plane of coolant application, it would
be necessary to use an impractically short inductor height
unless restrictively low casting speeds were employed.
SUMMARY OF THE INVE~TIO~
In accordance with one method and apparatus of
this invention the position of the solidification front at
the surface of the ingot being electromagnetically cast is
adjusted by controlling the coolant application to vary the
rate at which heat is extracted from the ingot. This is
accomplished in accordance with one e~bodiment by inter-
mittently turning the flow of coolant which is applied tothe surface of the ingot on and o~f. In accordance with
another embodiment of the coolant supply is servo-controlled
to vary the rate intermittently in order to properly posi-
tion the solidification front.
In accordance with a particular embodiment of
the invention there is provided, in an apparatus for con-
tinuously or semicontinuously casting metals: means for
electromagnetically forming molten metal into a desired
casting and means for cooling said molten metal to form a
shell of said casting by applying coolant directly to said
casting; the improvement ~herein, said apparatus further
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includes: means for controlling the position of a solidi-
fication front at the outer surface of said casting, said
means for controlling said position of said solidification
front comprising means for providing a pulsed flow of coolant
from said cooling means for said application directly to
said casting,
From a different aspect, and in accordance with
the invention, there is provided, in a process for con-
tinuously or semicontinuously casting metal$, the steps
comprising: electromagnetically forming molten metal into
a desired casting; and cooling said molten metal to form a
shell of said casting by applying coolant directly to said
casting; the improvement wherein, said process further
includes: controlling the position of a solidification
ront at the outer surface of said casting, said controlling
step comprising providing a pulsed flow of coolant in said
cooling step for said direct application to said casting,
Accordingly, it is an object of this invention to
provide an improved method and apparatus for the electro-
magnetic casting of metals and alloys.
It is a further object of this invention to pro-
vide an improved method and apparatus as above for control-
ling the position of the solidification front.
These and other objects will become more apparent
from the following description and drawings.
BRIEF DES~RIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of an
electromagnetic casting apparatus in accordance with one
embodiment of this invention; and
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Figure 2 is a schematic representation of an
electromagnetic casting apparatus in accordance with a
different embodiment of this invention.
DETAILED DESCRIPTIO~ OF PREFERRED EMBODIMENTS
Referring now to Figure 1 there is shown by way
of example an electromagnetic casting apparatus in accord-
ance with one embodiment of this invention.
The electromagnetic casting mold 10 is comprised
of an inductor 11 which is water cooled, a coolant manifold
12 in accordance with this invention for applying cooling water
to the peripheral surface 13 of the metal being cast C, and
a non-magnetic screen 14. Molten metal is continuously
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introduced into the mold 10 durlng a casting run, in the
normal manner using a trough 15 and down spout 16 and
conventional molten metal head control~ The inductor 11 is
excited by an alternating current from a suitable power
source (not shown~.
The alternating current in the inducotr ll produces a
magnetic field Trhich interac-ts with the molten metal head l9
to produce eddy currents therein. These eddy currents in
turn interact .~ith the magnetic field and produce forces
~hich apply a magnetic pressure to the molten metal head l9
to contain it so that it solidifies in a desired ingot cross
section.
An air gap exists during casting, bet~reen the molten
metal head l9 and the inductor ll. The molten metal head l9
is formed or molded into the same general shape as the
inductor ll thereby providing the desired ingot cross section.
The inductor may have any desired shape including circular
or rectangular as required to obtain the desired ingot C
cross section.
The purpose of the non-magnetic screen lLI is to fine
tune and balance the magnetic pressure with the hydrostatic
pressure of the molten metal head l9. The non-magnetic screen
14 can comprise a separate element as sho~rn, or it may comprise
a part of the manifold 12 for applying the coolant as desired.
Initially, a conventional ram 21 and bottom block 22
is held in the magnetic containment zone o the mold lO to
allo~ the molten metal to be poured into the mold at the
start of the casting run. The ram 21 and bottom block 22 are
then uniformly~wi~lhdraNn at a desired casting rate.
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Solidification o~ the molten metal which is magnetically
contained in the mold 10 is achieved by direct application
of water from the cooling manifold 12 to the ingot surface
13. In the embodiment which is shown in Figure 1 the water
is applied to the ingot surface 13 within the confines of
the inductor 11. The water may be applied to the ingot
surface 13 from above, within or below the inductor 11 as
desired.
The solidification front 25 of the casting comprises
the 7coundary between the molten metal head 19 and the
solidified ingot C. It is most desirable to maintain the
solidification front 25 at the surface 13 of the ingot C at or
close to the plane of ma~imum magnetic flux density which
usually comprises the plane passing through the electrical
centerline 26 of the inductor 11. In this way, the magimum
magnetic pressure opposes the maximum hydrostatic pressure of
the molten metal head 19. This results in the most efficient
use of power and reduces the possibility of cold folds or
bleed outs.
The location of the solidification front 25 at the
in~ot surface 13 results from a balance of the heat input
from the superheated liquid metal 19 and the resistance
heating from the induced currents in the ingot surface layer,
with the longitudinal heat e~traction resulting from the
cooling water application. The location of the front 25 can
be characteri~ed with reference to its height "d" above the
location of the coolant application plane 27. Hence, the
plane of coolant water application 27 can be referenced to
the electrical centerline 26 of the inductor. That distance
3 "d" depends on a mul~iplicity of facfvors. "d" decreases with
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increasing: latent heat of solidification of the alloy being
cast; specific heat of the alloy; electrical resistivity of
the alloy; molten metal head height; inductor height; melt
superheat; inductor current amplitude; inductor current
frequency; casting speed; and with decreasing alloy
conductivity and visa versa.
For a given alloy, the physical properties, latent heat
of solidification, specific heat, thermal conductivity, and
electrical resistivity are more or less fixed. Normal
electromagnetic casting practice would fix the inductor 11
current frequency within limits, the geometrical arrangement
of the inductor 11 and its height, the molten metal head 19
height and the inductor 11 current amplitude. It. ~ollows,
therefore, that the only remaining major process control
variable affecting the position of the solidification front
25 at the surface 13 of the ingot C is the casting speed.
Therefore, it would be necessar~ to adjust the casting speed
in order to ad~ust the position of the solidification front
25 to the favorable location corresponding to the plane
through the centerline 26 c~ the inductor 11. However, in
practice other ~actors such as cracking and ~ormation of
undesirably coarse microstructures limit the range of casting
speeds which can be used.
In accordance with this invention the problem of
maintaining the solidification front at its desired position
is overcome by controllin~ the rate at which heat is e~tracted
from the solidifying ingot and/or by ad~usting the plane of
T.Yater application with respect to the inductor. These
techniques allow adjustment of the position of the solidifi-
cation front 25 location independent of casting speed and
alloy properties.
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Ir. the embodiment of Figure 1 a solenoid valve 30 has
been inserted in the inlet pipe 31 to the coolant appllcation
mani~old 12. The solenoid valve 30 is connected to an
adjustable timer 32 which actuates it intermittentl~. The
timer 32 and solenoid valve 30 arrangement may be similar to
that as described in the Bryson patent and article set forth
in the background o~ the application. The timer 32 and
solenoid valve 30 allow discontinuous application of the
coolant to the ingot surface 13 which provides intermittent
high and reduced levels OL heat transfer leading to an over-
all reduction in the average rate o~ heat removal from the
solidifying ingot C as compared to a continuous flow. This
has the e~ect of retarding the onset of solidification as
compared to the continuous application of coolant and thereby
lowers the position of the solidi~ication front 25. Any
changes in the flow rate of continuity of water application
affect the position of the solidilication front 25 without
in~luencing the electromagnetic field~
In the apparatus 10 of this invention the coolant is
applied directly to the ingot C surface 13 and the ingot
never comes in contact with the inductor 11 or coolant
application manifold 12. Therefore, by controlling the duration
of the periods of the coolant application pulses and the
duration of the periods between coolant application pulses
one can effectively regulate the rate of heat e~traction
from the solidifying ingot.
The timer 32 comprises an adàustable timer of conven-
tional design which is æ~ranged to actuate via wires 33 the
electrically operated solenoid valve 30 in the input conduit
31 to the coolant application mani~old 12. The timer
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sequentially and repetitively controls the period the valve
30 is open and the period between valve openings when it is
closed, to provide intermittent operation of the valve so as
to cause the coolant applied to the ingot surface 13 to be
pulsed. The respective periods when the valve is open or
closed may be set as desired to obtain the desired rate o~
heat extraction which will properly position the
solidification front 25 in the solidifying ingot C.
Alternatively~ if desired, instead of using an on/off
valving arrangement 30 as described by reference to the
embodiment of Figure 1 one could employ an arrangement
wherein the pulsed flow of the coolant is provided by
intermittently applying two different levels of coolant flow.
Referring to Figure 2 this can be readily accomplished through
the use of a servo-controlled valve 40 in the input conduit
41 of the manifold 42 and a conventional servo-ampli~ier and
controller 43 for adjustably controlling the actuation of the
valve 40 over its range of actuation between its fully open
and fully closed positions. Normall~ such control ~or pulse
cooling operations would be between valve posltions
intermediate the fully open and fully closed positions. The
servo-amplifier and controller 43 actuate the servo-controlled
valve 40 to provlde a pulsed output between two different
levels of coolant flow. The valve 40 is adapted to rapidly
change between its respective high and low coolant flow
positions. The respective periods of high and low flow may
be set as desired by adjustment of the servo-amplifier 43
to provide the desired heat transfer rate to properly
position the solidification front 25.
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Therefore, in accordance with this invention means are
provided for controlling the position of the solidification
front 25 during the electromagnetic casting which comprise
adjusting the coolant application means 12 or 42 to provide
increased or reduced rates of heat extraction from the ingot
C in order to raise or lower the axial position, respectively,
of the solidification front. This is accomplished by any of
a number of means including the intermittent pulsed appli-
cation of the coolant or by intermittently changing the flow
rate of the coolant in a pulsed manner~
The actual adjustment of the respective periods of on/offoperation of the valve 30 or of the periods of hi~h and low
flow of the valve 40 usually occurs prior to a casting run.
However, if desired, the ad~ustment may occur during a casting
run to correct a mispositioning of the solidification front
25.
In the embodiment of Figure 2 it is also possible to
utilize in conjunction with or in place of the solidification
front 25 position control system 30 or 40 the first embodi-
ment of this invention a solidification front position control
system 50 in accordance wi~h an alternative embodiment now
to be described. The use of both systems in conjunction
should provide a wider range of ad~ustment and increase the
sensitivity of the ad~ustment.
In accordance with the alternative embodiment of the
invention as shown in Figure 2 the coolant manifold 42 is
arranged a~ove the inductor and includes at least one dis-
charge port 51 for directing the coolant against the surface
13 of the ingot or casting C. The discharge por~ 51 can
3 comprise a slot or a plurality of individual ori~ices for
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directing the coolant against the surface 13 of the ingot
C about the entire periphery of that surface.
In order to provide a means in addition or in place of
pulse cooling for controlling the solldification front 25
at the surface 13 of the ingot C without influencing the
containment of the molten metal through modification of the
magnetic field, the coolant manifold 42 with its discharge
port 51 is arranged for movement axially of the ingot C.
The coolant manifold 42, the inductor ll and the non-magnetic
screen 14 are all arranged coaxially about the longitudinal
axis 52 of the ingot C. In the pre~erred embodiment s'nown
the coolant manifold 42 includes an extended portion 53
which includes the discharge port 51 at its free end. The
extended portion 53 of the coolant manifold 42 is arranged
for movement between the non-magnetic screen 14 and the
inductor ll in the direction defined by the axis of the
ingot C.
The inductor 11 and the non-magnetic screen 14 are
supported by conventional means known in the art ~not shown).
The coolant manifold 42 is supported for movement independ-
ently of the inductor ll and the non-magnetic screen 14 so
that the position of the discharge port 51 can be adjusted
axially of the ingot without a concurrent movement of the
non-magnetic screen 14 or the inductor ll. This is a
significant departure from the approaches described in the
prior art ~herein the non-magnetic screen 14 is supported
by the coolant maniT'old 12 and both are arranged for sirnul-
taneous movement -`n the axial sense.
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~ y moving the discharge port 51 of the coolant manifold
independentl~ of the non-magnetic screen 14 in accordance
with this invention it is ~ossible to ad~ust the position of
the solidification front 25 ~ithout modifying the magnetlc
containment field. In the preferred embodiment shown in
Figure 2 the discharge port 51 is arranged for axial movement
bet~een the non-magnetic screen 14 and the inductor ll along
the ~ath 62 as sho~n in phantom.
Another feature of this embodiment of the present inven-
tion is that the coolant manifold or at least that portion
of the manifold which enters the magnetic field is formed
of a material ~hich will not modify the magnetic field~
Preferably, it is formed of a non-conductive material such
as plastic or resinous materials including phenolics.
In the embodiment shown in F~gure 2 the coolant manifold
42 includes ~hree chambers 54, 55 and 56. The coolant enters
the manifold 42 in the first chamber 54. A slot or a
plurality of orifices 57 arranged in the wall 58 bet~,~een the
first chamber 54 and the second chamber 55 serve to enhance
the uniformity of the distribution of the coolant in the
manifold 42. Similarly, slots or orifices 59 bet~een the
second 55 and the third chamber 56 further enhance the
uniformity of distribution of the coolant in the manifold
42. The coolant is discharged from the axially extended
third chamber 56 via the discharge port 5l The manifold
~2 including the extended third chamber 56 is arranged ~or
movement along vertically extending rails 60 so that the
extended portion 53 of the manifold can be moved between the
inductor ll and the screen 14 along the path 62 as shown in
phantom.
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Axial adJustment of the dischar~e port 51 position is
provided by means of cranks 63 mounted to screws 64. The
screws are rotatably secured to the mani~old 42 at one end
and are held in threaded engagement in support blocks 65
which are mounted to the rails 60. In this manner turning
the cranks 63 in one direction or the other will move the
manifold 42 and discharge port 51 axially up or do~m.
The coolant is discharged against the surface o~ the
casting in the direction indicated by arrows 66 to define
the plane of coolant application. B~ moving the discharge
port 51 up or down in the manner described above the plane
of coolant application 27 is also moved up or down respectively
with respect to the centerline 26 of the inductor 11 to
thereby change the distance "d".
Copper alloy ingots are t~pically cast in 6" x 30"
cross sections at speeds at from about 5 to 8" per mlnute.
Over this restricted speed range the preferred and most
pre~erred Nater application zones for three common copper
alloys have been calculated as follows:
TABLE T
Calc_l ted ~ater Coolin~ Application Zone
Alloy Preferred Most Preferred
-
C 11000 - 1/2" ~ - 2" - 3/4" ~ - 2"
C 26000 ) - 1 1/4" - 1/4"
C 51000 *3/8'~ ~ - 3/4" * 1/8" ) - 1/2"
The measurements provided in Table I are for the distance
from the centerline of the inductor to the plane of the
coolant application. The values are negative or positive~
respectively~ depending on whether the plane of coolant
application is arranged below or above the centerline of the
3 inductor.
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While it is most preferred in accordance wlth this
embodiment of the invention to form the entire manifold 42
from a non-conductive material one could, if desired, form
only that portion of the manifold 42 whlch would interact
with the magnetic field from the non-conductive material
while using other materials such as metals for the remaining
portion of the manifold 42. For example, if desired, only
the chamber need be formed from non-conductive material,
whereas the chambers 54 and 55 could be formed from any
desired mat-erial. The chamber 56 would then be joined to
the chambers 54 and 55 in a conventional manner. Therefore,
in accordance with this embodiment of the invention it is
only necessary that the portion of the coolant application
means which would interact with the magnetic field be formed
from a non-conductive material.
The method of continuously or semicontinuously casting
metals and alloys in accordance ~ith this embodiment of the
present invention involves the adjustment in an axial sense
of the position of the manifold 42 and in particular, the
discharge port 51 therein, prior to the ~eginning of a casting
run in order to position the solidification fro~t 25 at an
appropriate axial position for the alloy being cast. It is
preferred that this adjustment take place prior to the
beginning of the casting run. However, if desired, the
adJustment can be refined during a casting run. The discharge
port 51 must be moved independently of the inductor ll and
screen 14 so that its change in position does not affect the
magnetic field or the containment process~
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It should be apparent from the foregoing description
that as compared to cooling with a continuous full flow, pulse
cooling is onl~ effective to lower the solidification front
25. However, in accordance with this invention when operating
in a pulse coolin~ mode within the ranges of the periods of
coolant application or non-application or the periods of high
or low flow it should be possible to raise or lower the
solidification front over a range of positions with the
highest position comprising that corresponding to non-pulsed
application of the coolant. The embcdlment of the invention
with respect to Figure 2 is, therefore, particularly adapted
to increase the range of adjustment while using the pulsed
coolant application. If it is necessary to raise the
solidification front 25 above a ma~imum level achievable by
ad~ustment of the pulsed cooling, this can be accomplished
by raising the position at which the coolant is applied to
the ingot surface.
With respect to the embodiment of the invention wherein
the pulsed coolant comprises periods of high and low coolant
flow it is preferred that the lower flow rate be selected so
that a steam film is generated which has t~le ef~ect of
mar~edly reducing the rate of heat transfer. This embodiment
of the invention is particularly preferred because it should
provide less abrupt changes in heat transfer at the ingot
surface due to the steam film formation. In such a high/low
pulsed flow mode heat transfer at the high flow periods is by
nucleant boiling; whereas~ in the low flow periods heat
transfer is by film boiling. This provides marked differences
in heat transfer between the pulses of high flow and low flow
thereby allowing for the variation in the rate of heat
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extraction as described above in order to control the position
of solidification front 25~
The actual flow rates of the coolant in either of the
pulsed cooling embodiments set forth above may be set as
desired. They will be a function of a number of variables
including the alloy composition; the latent heat of the
solidfication of the alloy being cast; the specific heat
of the alloy; the melt superheat; the casting speed, etc.
The method and apparatus of this invention is
particularly adapted to the cont~nuous or semicontinuous
casting of metals and alloys. Further details of the
apparatus and method of electromagnetic casting can be gained
from a considerationof the various patents and publications
cited in this application, which are intended to be
incorporated by reference herein.
While the invention has been described with reference
to copper and copper base alloys it is believed that the
apparatus and method described above can be applied to a wide
range of met21s and alloys including nickel and nickel alloys,
2~ steel and steel alloys, aluminum and aluminum alloys, etc.
It is apparent that there has bee provided in
accordance ~Yith this invention an electromagnetic casting
apparatus and method which fully satisfies the ob~ects,
means and advantages set forth herein before. While the
invention has been described in combination with specific
embodiments thereol, ~t is evident that many alternatives,
modifications and variations will ~e apparent to those
skilled in the art in light of the foregoing description.
Accordingly, it is intended to embrace all such alternatives,
modifications and variations as fall within the spirit and
3 broad scope of the appended claims.
