Electromagnetic casting method and apparatus

A method and apparatus for electromagnetic continuous or semicontinuous casting of metals and alloys. A variable coolant application system is used to control the rate of heat extraction from the casting to properly position the solidification front at the surface of the casting without otherwise influencing the containment process through modification of the magnetic field.

CROSS REFERENCE TO RELATED APPLICATIONS 
U.S. patent application Ser. No. 921,298, filed July 3, 1978, by Yarwood et 
al., for "Electromagnetic Casting Method and Apparatus", now U.S. Pat. No. 
4,158,379, granted June 19, 1979. 
BACKGROUND OF THE 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. The electromagnetic casting 
process has been known and used for many years for continuously and 
semicontinuously casting metals and alloys. The process has been employed 
commercially for casting aluminum and aluminum alloys. 
PRIOR ART STATEMENT 
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 water to the ingot. Such an apparatus is 
exemplified in U.S. Pat. No. 3,467,166 to Getselev et al. Containment 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. Pat. Nos. 
3,735,799 to Karlson and 3,646,988 to Getselev. In some prior art 
approaches the inductor is formed as part of the cooling manifold so that 
the cooling manifold supplies both cooling to solidify the casting and to 
cool the inductor as exemplified in U.S. Pat. Nos. 3,773,101 to Getselev 
and 4,004,631 to Goodrich et al. 
The non-magnetic screen is utilized to properly shape the magnetic field 
for containing the molten metal as exemplified in U.S. Pat. No. 3,605,865 
to Getselev. A variety of approaches with respect to non-magnetic screens 
are exemplified as well in the Karlson '799 patent and in U.S. Pat. No. 
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. Pat. No. 
3,741,280 to Kozheurov et al. 
While the above described patents describe electromagnetic 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. Pat. No. 3,702,155. In addition of the aforenoted 
patents a further description of the electromagnetic casting process can 
be found by reference to the following articles: "Continuous Casting with 
Formation of Ingot by Electromagnetic Field", by P. P. Mochalov and Z. N. 
Getselev, Tsvetnye Met., August, 1970, 43, pp. 62-63; "Formation of Ingot 
Surface During Continuous Casting", by G. A. Balakhontsev et al., Tsvetnye 
Met., 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 
Experience with Electromagnetic Moulds", by H. A. Meier, G. B. Leconte and 
A. M. Odok, Light Metals, 1977, pp. 223-233. 
In U.S. Pat. No. 4,014,379 to Getselev a control system is described for 
controlling the current flowing through the inductor responsive to 
deviations in the dimensions of the liquid zone (molten metal head) of the 
ingot from a prescribed value. 
The invention herein is particularly concerned with the apparatus for 
applying 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 
or decantation of the liquid metal is likely to result. 
It is known in the art of Direct Chill casting in a water cooled mold to 
utilize a coolant application arrangement 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 "off" 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. Pat. No. 3,441,079 to Bryson and to an article entitled "Direct 
Chill Casting Process for Aluminum Ingots--A New Cooling Technique", by N. 
B. Bryson, Canadian Metallurgical Quarterly, Vol. 7, No. 1, Pages 55-59. 
In the above noted prior U.S. patent application Ser. No. 921,298, filed 
July 3, 1978, there is disclosed an apparatus and process for controlling 
the position of the solidification front during electromagnetic casting. 
The process and apparatus disclosed in our prior application utilizes a 
coolant discharge port arranged to move axially of the ingot independently 
of the electromagnetic containing and forming system. By moving the 
discharge port in an axial direction the solidification front is moved 
correspondingly to adjust its position without modifying the 
electromagnetic containment field. 
SUMMARY OF THE INVENTION 
In accordance with the 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 embodiment by intermittently 
turning the flow of coolant which is applied to the surface of the ingot 
on and off. In accordance with another embodiment the coolant supply is 
servo-controlled to vary the flow rate intermittently in order to properly 
position the solidification front. 
Accordingly, it is an object of this invention to provide an improved 
method and apparatus for the electromagnetic casting of metals and alloys. 
It is a further object of this invention to provide an improved method and 
apparatus as above for controlling the position of the solidification 
front. 
These and other objects will become more apparent from the following 
description and drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 1 there is shown by way of example an electromagnetic 
casting apparatus in accordance 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 
introduced into the mold 10 during 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 inductor 11 produces a magnetic field which 
interacts with the molten metal head 19 to produce eddy currents therein. 
These eddy currents in turn interact with the magnetic field and produce 
forces which apply a magnetic pressure to the molten metal head 19 to 
contain it so that it solidifies in a desired ingot cross section. 
An air gap exists during casting, between the molten metal head 19 and the 
inductor 11. The molten metal head 19 is formed or molded into the same 
general shape as the inductor 11 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 14 is to fine tune and balance the 
magnetic pressure with the hydrostatic pressure of the molten metal head 
19. The non-magnetic screen 14 can comprise a separate element as shown, 
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 of the mold 10 to allow 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 withdrawn at a desired casting rate. 
Solidification of 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 
FIG. 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 boundary 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 maximum magnetic flux density which usually 
comprises the plane passing through the electrical centerline 26 of the 
inductor 11. In this way, the maximum 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 ingot 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 extraction resulting from the cooling 
water application. The location of the front 25 can be characterized with 
reference to its height "d" above the location of the coolant application 
plane 27. Hence, the plane of cooling water application 27 can be 
referenced to the electrical centerline 26 of the inductor. That distance 
"d" depends on a multiplicity of factors. "d" decreases with 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 follows, 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 necessary to adjust the casting speed in 
order to adjust the position of the solidification front 25 to the 
favorable location corresponding to the plane through the centerline 26 of 
the inductor 11. However, in practice other factors such as cracking and 
formation 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 controlling 
the rate at which heat is extracted from the solidifying ingot. This 
technique allows adjustment of the position of the solidification front 25 
location independent of casting speed and alloy properties. 
In the embodiment of FIG. 1 a solenoid valve 30 has been inserted in the 
inlet pipe 31 to the coolant application manifold 12. The solenoid valve 
30 is connected to an adjustable timer 32 which actuates it 
intermittently. 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 of this 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 of heat transfer 
leading to an overall reduction in the average rate of heat removal from 
the solidifying ingot C as compared to a continuous flow. This has the 
effect of retarding the onset of solidification as compared to the 
continuous application of coolant and thereby lowers the position of the 
solidification front 25. Any changes in the flow rate or continuity of 
water application affect the position of the solidification front 25 
without influencing 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 extraction from the solidifying 
ingot. 
The timer 32 comprises an adjustable timer of conventional design which is 
arranged to actuate via wires 33 the electrically operated solenoid valve 
30 in the input conduit 31 to the coolant application manifold 12. The 
timer 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 of 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 FIG. 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 
FIG. 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-amplifier 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. Normally such control for pulse 
cooling operations would be between valve positions intermediate the fully 
open and fully closed positions. The servo-amplifier and controller 43 
actuate the servo-controlled valve 40 to provide 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. 
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 application 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/off operation of the 
valve 30 or of the periods of high and low flow of the valve 40 usually 
occurs prior to a casting run. However, if desired, the adjustment may 
occur during a casting run to correct a mispositioning of the 
solidification front 25. 
In the embodiment of FIG. 2 it is also possible to utilize in conjunction 
with the solidification front 25 position control system 30 or 40 of this 
invention the solidification front position control system 50 of our prior 
application U.S. Ser. No. 921,298, filed July 3, 1978. The use of both 
systems in conjunction should provide a wider range of adjustment and 
increase the sensitivity of the adjustment. 
In accordance with this embodiment of the invention as shown in FIG. 2 the 
coolant manifold 42 is arranged above the inductor and includes at least 
one discharge port 51 for directing the coolant against the surface 13 of 
the ingot or casting C. The discharge port 51 can comprise a slot or a 
plurality of individual orifices for 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 to pulse cooling for controlling 
the solidification 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 11 and the non-magnetic screen 14 are all arranged coaxially 
about the longitudinal axis 52 of the ingot C. In the preferred embodiment 
shown 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 11 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 independently of the inductor 11 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 inductor 11. This is a significant departure 
from the approaches described in the prior art wherein the non-magnetic 
screen 14 is supported by the coolant manifold 12 and both are arranged 
for simultaneous movement in the axial sense. 
By moving the discharge port 51 of the coolant manifold independently of 
the non-magnetic screen 14 in accordance with this invention it is 
possible to adjust the position of the solidification front 25 without 
modifying the magnetic containment field. In the preferred embodiment 
shown in FIG. 2 the discharge port 51 is arranged for axial movement 
between the non-magnetic screen 14 and the inductor 11 along the path 62 
as shown in phantom. 
Another feature of this embodiment of the present invention is that the 
coolant manifold or at least that portion of the manifold which enters the 
magnetic field is formed of a material which 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 FIG. 2 the coolant manifold 42 includes three 
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 
between 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 between 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 51. The manifold 42 including the 
extended third chamber 56 is arranged for movement along vertically 
extending rails 60 so that the extended portion 53 of the manifold can be 
moved between the inductor 11 and the screen 14 along the path 62 as shown 
in phantom. 
Axial adjustment of the discharge port 51 position is provided by means of 
cranks 63 mounted to screws 64. The screws are rotatably secured to the 
manifold 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 down. 
The coolant is discharged against the surface of the casting in the 
direction indicated by arrows 66 to define the plane of coolant 
application. By 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 typically cast in 6".times.30" cross sections at 
speeds at from about 5 to 8" per minute. Over this restricted speed range 
the preferred and most preferred water application zones for three common 
copper alloys have been calculated as follows: 
TABLE I 
______________________________________ 
Calculated Water Cooling Application Zone 
Alloy Preferred Most Preferred 
______________________________________ 
C 11000 -1/2" .fwdarw. -2" 
-3/4" .fwdarw. -2" 
C 26000 0 .fwdarw. -11/4" 
-1/4" .fwdarw. -1" 
C 51000 +3/8" .fwdarw. -3/4" 
+1/8" .fwdarw. -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 inductor. 
While it is most preferred in accordance with 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 which 
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 56 need be 
formed from non-conductive material, whereas the chambers 54 and 55 could 
be formed from any desired material. 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 with 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 beginning of a 
casting run in order to position the solidification front 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 11 and 
screen 14 so that its change in position does not affect the magnetic 
field or the containment process. 
It should be apparent from the foregoing description that as compared to 
cooling with a continuous full flow, pulse cooling is only effective to 
lower the solidification front 25. However, in accordance with this 
invention when operating in a pulse cooling 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 embodiment of 
the invention with respect to FIG. 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 maximum level achievable by adjustment 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 
the effect of markedly 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 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 solidification of the alloy being cast; the specific heat of the 
alloy; the metal superheat; the casting speed, etc. 
The method and apparatus of this invention is particularly adapted to the 
continuous or semicontinuous casting of metals and alloys. Further details 
of the apparatus and method of electromagnetic casting can be gained from 
a consideration of 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 metals and alloys including nickel and 
nickel alloys, steel and steel alloys, aluminum and aluminum alloys, etc. 
It is apparent that there has been provided in accordance with this 
invention an electromagnetic casting apparatus and method which fully 
satisfies the objects, means and advantages set forth hereinbefore. While 
the invention has been described in combination with specific embodiments 
thereof, it is evident that many alternatives, modifications and 
variations will be 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 
broad scope of the appended claims.