Note: Descriptions are shown in the official language in which they were submitted.
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BACKGRO~N~ OF THE IN~ENTION
This invention relates to an improved process and
apparatus for electromagnetically casting metals and alloys.
The 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
~or casting aluminu~ and aluminum alloys.
P~IOR A~T STATEMENT
The electromagnetic casting apparatus comprises a three
part mold consisting of an inductor, a non-magnetic screen and
a manifold for applying cooling water to the ingot. Such an
apparatus is exemplified in U.S. Patent No. 3r467,166 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.
A large bod~ of prior art relating to various aspects of
the electromagnetic casting process and apparatus is descrlbed
in the prior art statement of U~S. Patent No. 4,161,206 and,
therefore, will not be repeated here.
The present invention is particularly related to the
process and apparatus for controlling the electromagnetic
casting sys'cem. Various approaches have been described in
the prior art for controlling the excitation o~ the inductor
ln a manner so as to provide ingots of uniform cross section.
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 dimensions of the
lia~uid zone (molten metal head) of the ingot from a prescribed
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value. In Getselev, U.S. Patent No. 4,014,379 the inductor
voltage is controlled to regulate the inductor current in
response to measured variations in the level of the sur~ace of
the liquid zone of the ingot. Control of the inductor voltage
is achieved by an amplified error signal applied to the field
winding of a ~requency changer.
In Russian Patent 537,750 to Getselev an alternative
control approach is described wherein the potential on the
inductor is regulated to reduce a de~iation of the phase angle
from a programmed value.
In U.S. Patent No. ~,161,206 to Yarwood et al. a control
s~ystem for electromagnetic casting is utilized for ~inimizing
variations in the gap between the molten metal and the inductor.
In this approach a reactive electrical parameter of the
inductor which varies with the magnitude of the gap is
determined and compared to reference Yalues to generate an
error signal for controlling the inductor excitation.
In Russian Patent 273,226 to KabakoY there is disclosed
a control system for controlling the metal level in the
electromagnetic casting mold. A metal level measuring coil
has a relay connected to the ingot withdrawal mechanism via
a regulator. At the start of casting the withdrawal mechanism
is in its initial position. The regulator is connected to an
actuator which starts the feed of met,al into the mold. When
the metal level reaches the height of the sensing coil~ a
signal is transmitted to the regulator which throws the rela~
and operates the withdrawal mechanism to withdraw the ingot
fr~m the mold.
In Russian Patent 338,297 to Irkutsk the electromagnetic
casting mold is ~itted with measuring coils to control the
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metal leYel in the mold. The amount of metal flowing into
the mold is controlled by a value co~pounded with an actuator.
No description is given in this patent o~ any automated feed~
back of the sensed signal from the coil to the actuator. In
fact, the ackuator appears to be manually operated.
The approaches for controlling molten metal head
described in the Russian patents to Kabakov and Irkutsk are
deficient in that control is based solely on the sensed upper
level of the molten metal head. Therefore, these control
systems do not take into account changes in the molten metal
head due to fluctuations in the position of the solid liquid
interface between the molten metal and the solidified casting.
These changes in the interface position occur because of
instabilities in ~he withdrawal mechanism, instabilities in
the coolant application system~ etc. The result of increasing
or reducing the helght of the molten metal head whether due to
a repositioning of the solid liquid interface or the upper
surface of the molten metal or both is to increase or decrease,
respectively, the hydrostatic pressure exerted by the molten
metal head. These changes in hydrostatic pressure must be
offset by the control system for controlling the excitation
of the inductor.
The system described in Yarwood et al. has been shown to
be effecti~Je for providing solidified castings of more uniform
cross section by overcoming the instabilities associated with
changes in hydrostatic pressure of the molten metal head. It
is, of course, desirable that any control system for con-
trolling the inductor excitation operate over its most
preferred range of control. Therefore, it is highly
undesirable to have any long term changes in hydrostatic
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pressure due to changes in the height of the molten metal
head. Consequently, it has been found desirable to provide
some control in addition to the electrical control of the
inductor excitation which could reduce the variation in molten
metal head height during a casting run.
S~MMARY OF THE INVENTION
In accordance with the present invention, a process and
apparatus is provided for controlling the molten metal head
height during a casting run. The system of this invention
does not require actual measurement of the position of the
liquid-solid interface or the top surface of the molten metal.
Rather, it relies upon the sensing of an electrical parameter
or signal from the inductor excitation and control syskem
which changes as the hydrostatlc pressure of the molten metal
head changes. The electrical signal which is sensed as aboYe
is applied to a controller which adjusts the flow of molten
metal into the mold in response thereto.
In particular, the present invention is directed to a
process and apparatus for casting metals by electromagnetically
~orming molten metal into a desired casting shape. The
electromagnetic forming is accomplished by means of an
inductor which applies a magnetic field to the molten metal.
The magnetic field serYes to define a containment zone for
the molten metal. A system is. provided for controlling and
applying an alternating current to the inductor to generate
the magnetic field.
In accordance with this invention, the aforenoted
apparatus is improved by proYiding a system for controllin-g
the hydrostatic pressure exerted by the molten metal in the
39 containment zone. This is accomplished by sensing an
electrical signal derived from the system for controlling
and applying the alternating current to the inductor. The
electrical signal which is sensed is one which changes in
correspondence to changes in the hydrostatic pressure of
the molten metal in the containment zone. In response to
the sensed electrical signal, the flow rate of molten metal
into the containrnent zone is controlled.
The electrical signal which is sensed may comprise
any of a number of possible signals including but not limited
to: the error signal which is applied to the power supply to
control the inductor excitation, or any of the voltage
frequency or current signals applied to the inductor, or
internal signals applied within the power supply such as
bus voltage control ~ignals. The sole criteria ~or select-
ing the appropriate signal is that it be one which varies
in correspondence with a variation in the hydrostatic
pressure of the molten metal head.
Accordingly, it is an object of this invention to
reduce the variation in hydrostatic pressure e~erted by the
molten metal in the containment zone of an electromagnetic
casting system.
It is a ~urther object of this invention to
accomplish this result without the necessity of sensing
either the height of the molten metal head or the interface
between the molten metal and the solidifying casting.
In accordance with a particular embodiment of
the invention there is provided an apparatus for casting
materials. The apparatus includes means for electro-
magnetically forming molten rnaterial into a desired casting
shape. The electromagnetic forming means includes means for
applying a magnetic field to the molten material, -the
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magnetic field defining a containment zone for the molten
materialu In accordance with the invention, there is
provided a means for controlling the hydrostatic pressure
exerted by the molten material in the containment zone.
The hydrostatic pressure control means includes means for
sensing changes in the hydrostatic pressure of the molten
material in the containment zone and means automatically
responsive to the hydrostatic pressure sensing means for
controlling the amount of molten material in the contain-
ment zone.
From a different aspect, and in accordance with -~
the invention, there is provided a process for castin~
materials. m e process includes the steps of electro-
-magnetically forming molten material into a desired cast-
ing shape, the electromagnetic forming step including
applying a magnetic field to the molten material. me
magnetic field defines a containment zone for the molten
material. The hy~rostatic pressure exerted by the molten
material in the containment zone is controlled. The control
steps include sensing changes in the hydrostatic pressure
of the molten material in the containment zone, and
controlling the amount of the molten material in the
containment zone responsive automatically to the sensing
of the hydrostatic pressure changes.
m ese and other objects will become more apparent
from the following description and drawings.
Figure 1 is a schematic representation of an electro-
rnagnetic casting apparatus in accordance with the present
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invention; and
Figure 2 is a partial schematic representation of an
electromagnetic casting apparatus showing further details of
the molten metal hydrostatic pressure control system.
Figure 3 is a partial schematic representation of an
electromagnetic casting apparatus showing an alternative
hydrostatic pressure control system.
DETAILED DESCRIPTI'ON'O'F'P~EFERRED EMBODI~ENTS
.
Referring now to Figure 1, there is shown by way of
example an electromagnet~c casting apparatus of this
invention.
The electromagnetic casting mold 10 is comprised of an
inductor 11 which is water cooled3 a cooling manifold l2 for
applylng cooling water to the peripheral surface' 13 of the
metal being cast Cj and a non-magnetic screen 14. Molten
metal is continuously introduced into the mold 10 during a
casting run using a trough 15 and down spout 16 and molten
metal head control I in accordance with this invention. The
inductor Il is excited by an alternating current from a power
source 17 and control system 18 which preferably is of the
type described in the aforenoted Yarwood et al. U.S. Patent
No. 4,161,206.
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 rnagnetic field and produce forces which
apply a magnetic pressure to the molten metal head 19 to
contain it in the zone defined by the magnetic field so that
it solidifies in a desired ingot C cross section.
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An air gap d exists dur~ng 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 haYe 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 may
comprise a separate element as shown or may, if desired, be
incorporated as a unitary part of the manifold for applying
the coolant~
Initially, a conventional ram 21 and bottom block 22 ~s
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.
Solidi~ication Or the molten metal which is magnetically
contained in the mold 10 is achieve~d 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 withir. the confines of the
inductor 11. ~he water may be applied to the ingot surface
13 above, within or below the inductor 11 as desired.
If desired any of the prior art mold constructions or
other known arrangements of the electromagnetic casting
apparatus as described in the Background of the Invention
could be. employed.
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The present invention is concerned with the control of
the casting process and apparatus in order to provide cast
ingots C, which have a substantially uniform cross section
over the length of the ingot and which are formed of metals
and alloys such as copper and copper base alloys. This is
accomplished in accordance with the present invenkion by
controlling the molten metal head in the casting zone so as
to maintain a substantially uniform hydrostatic pressure.
The molten metal head 19 corresponds to the pool of molten
metal arranged aboYe the solidifying ingot C which exerts the
aforenoted hydrostatic pressure in the magnetic containment
zone. In a vertical casting apparatus 10 as in Figure 1, the
molten metal head 19 extends from the top surface 23 of the
molten metal pool to the solid/liquid interface or solidifi-
cation front 24 and further includes a limited contribution
associated with the molten metal in and above the down spout
6.
In the prior art as noted in the bac~ground of this
application~ various systems ha~e been described with the aim
of provlding cast ingots by the electromagnetic casting
process which have substantially uniform cross sections. In
these approaches the excitation of the inductor 11 is con-
trolled in a way so as to c~oDensate fo~ any variations in the molten
metal head 19 in order to maintain uniform dimensions in the
cast in~ot. The approach suggested in U.S. Patent No.
4, L61,206 to Yarwood et al. is particularly preferred in
accordance with the present invention and has been found to
provide ingots of substantially uniform cross section.
With any of these approaches some parameter of the
casting process or system 10 is sensed in order to generate
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an error signal which is applied to the power supply 17
which excites the inductor 11 in order to control the inductor
current in a way so as to overcome variations in the hydro-
static pressure of the molten metal head 19. Any such control
system will optimally operate at peak efficiency over a given
range of such a sensed parameter. In a~y casting apparatus,
however, there can be trends or changes which can shift the
range of the sensed parameter over a ~eriod of time adversely
with respect to its optimum control range.
Therefore, in accordance with this invention longer term
changes in the molten mekal head 1~ and more particularly the
hydroskatic pressure exerted by the molten metal head, are
o~ercome by controlling the flow o~ the molten metal into the
containment zone so as to maintain the hydrostatic pressure
within desired limits. This should enable the control system
_ for the excitation of the inductor 11 to operate within its
optimum ranges of control and should also reduce the
instabilities associated with change~ in hydrostatic pressure -
of the system, particularly long term instabilities.
The prior art control systems for controlling the
excitation of the inductor 11 even if effective for their
purposes are not effective for preventing long term changes in
hydrostatic pressure associated with the molten metal head 19.
The two Russian patents to Getselev described in the background
of this application utilize sensing coils for sensing metal
head height and attempt to control the flow of molten metal
into the containment zone. These approaches take into account
only changes in the hydrostatic pressure associated with
changes in the top surface 23 of the molten metal head 19.
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In contrast to the approaches adopted by Getselev, the
present invention is directed to an integrated approach.
Instead of sensing head height: of the molten metal head 19,
an electrical parameter is sensed which is derived from the
control and/or current application system 17, 18 of the
apparatus 10. The means for controlling and exciting the
inductor 11 can comprise a separate power supply 17 and
electrical control system 18 as shown, or they could be
combined in a single unit. For purposes of the present
invéntion, the signal which is sensed can be derived from
either khe control portion 18 or the power source portion 17
of the control and current application means. The electrical
signal which is sensed is one which varies generally pro-
portionally with changes in hydrostatic pressure of the molten
metal head 19. Therefore,changes in the signal correspond to
changes in the hydrostatic pressure. By determining or
sensing a parameter indicative of hydrostatic pressure as
opposed to head height alone, it is an advantage of the present
invention that changes in the position of the liquid-solid
interface 24 between the solidlrying casting C and the molten
metal pool 19 are also taken into account. This is something
that the prior art systems have not provided for.
In accordance with this inventiong it is presumed that
the control system 18 is effective for providing a cast ingot
of substantially uniform diameter. ~ost control systems 18
operate in one way or another by generating an error signal
which is applied to the power supply 17 in order to change
its output in a direction which will counteract the effect
of changing hydrostatic pressure of the molten metal head 19.
The flow rate of molten metal into the containment zone cannot
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be controlled so precisely so as to aYoid instability or
other variakions in the molten met'al head 19 and its resultant
hydrostatic pressure.
Referring now to Figures 1 and 2~ control system'l8
operates with relati~ely short control cycles so that the
ingot' C diameter neYer changes substantially. Therefore, the
error signaI A as in Figure ~ which i5 generated by the control
system 18 for appllcation to the power supply 17, is one signal
which'corresponds to changes in hydrostatic pressure of the
molten metal head 19. The error signal _ may take any desired
form, for example, it.could be a current, voltage, frequency,
etc. Preferably, in accordance with bhis invention, the error
signal A is a voltage signal which is applied to an appropriate
control input of the power supply 17 to control the output
thereof.
Preferably, ln accordance with this invention the power
supply 17 comprises a solid state power supply as are known
; in the art, although a motor generator could be utilized if
desired. In such a solid state power supply 17 various
internal signals B result from the application of the error
signal A ~to the control input~of the supply. For example, in
a solid state power supply 17 where an incoming AC voltage is
rectified to a DC voltage which ig then chopped tG re~ulate
the volta~e and then inverted to provide an AC output of the
desired f'requency and voltage, a bus voltage which is used to control
the voltage output of the supply 17 is a si'gnal B which
corresponds to the error signal A and, therefore, to changes
in hydrostatic pressure. Similarly, various other signals B
could be extracted from the power supply 17 at any point from
the error signal' A input to the output of the supp].y so long
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as they correspond to changes associated with the error
slgnal and, therefore, chan~es in hydrostatic pressure.
Finally, the output signals 0 of the power supply 17 which
are applied to the lnductor 11 and which correspond to changes
in hydrostatic pressure can be used. This applies, of course,
only to those output signals 0 which are varied in response to
changes in the error signal A. In the apparatus o~ this
invention one such output signal 0 would be the current in the
inductor 11. Alternatively, the voltage applied to the
inductor 11 or in a variable frequency supply 17 the frequency
could be sensed.
The present apparatus 10 is preferably directed to an
arrangement wherein the frequency is fixed and only the
voltage and current on the inductor 11 is varied. HoweYer,
if desired, power supplies wherein the frequency is not fixed
could be employed and thereby changes in frequency could be
utilized as a signal 0. It is apparent from the foregoing
that the signal which is sensed A, B, or 0 as desired in
~ accordance with this invention to determine changes in hydro-
static pressure can be derived from either the control system
18 or the power supply 17 for exciting the inductor 11.
Referring again to the apparatus of Figures l and 2, the
inductor 11 is connected to an electrical power source or
supply 17 which provides the necessary controlled current and
voltage at a desired frequency. A typical power supply circuit
may be considered as two subcircuits 25 and ~6. An external
circuit 25 consists essentially of a solid state generator
providing an electrical potential across the load or tank
circuit 26 which includes the inductor 11. This latter
circuit 26 except for the inductor 11 is sometimes referred to
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1 ~7Q()17
as a heat station and includes elements such as capacitors
and transformers.
In accordance with this invention, the generator circuit
25 is preferably a solid state inverter. A solid state
inverter is preferred because it is possible to provide a
selectable frequency output over a range of frequencies. This
in turn makes it possible to control the penetration depth of
the current in the load. Both the solid state inverter 25 and
the tan~ clrcuit or heat station 26 may be of conventional
design. Pre~erably, the power supply is provided with front
end DC voltage control in order to separate the ~oltage and
frequency functions of the supply.
The control system 18 may be of any desired design
including any of these described in the background of this
application. However, preferably it is a system in accordance
with the U.S. 4~161,206~ Yarwood et al. patent. In that
system a reactive~parameter of the inductor is sensed which
is a function of the gap "d" between the~ molten metal 19 and
the inductor 11. The sensed parameter is compared with a
prese~ value thereof and an error signal A is generated which
is a function of the difference between the magnitude of the
sensed parameter and a preset value thereof. As the sensed
parameter changes, so does the error slgnal A in correspondence
thereto. If the sensed parametqr corresponds about to
inductance, as in the preferred approach of~the Yarwood et al.
patent~ then the control system 18 is adapted;to control the
power supply 17 in a way so as to maintain a substantially
constant inductance and thereby a substantially uniform ingot
cross section.
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The changes in the Yalue of the error signal are a
function of changes in the hy'drostatic pressure of the molte'n
metal head 19. As the molten metal head 19 increases in height
either due to an increase in the height of the upper surface 23
or to a lowering of the solidification front 24 or both,' there
is an increase in hydrostatic pressure. This hydrostatic
pressure increase would normally increase the diameter of the
resultant ingot C. HoweYer~ the control system 18 is
effective to counteract this increase in hydrostatic pressure
by increasing the current applied to the inductor ll. These
changes occur very rapidly, in fractions of a second, so that
the induct~nce and cross section of the ingot appear sub-
stantially constant throughout.
Normally, the molten metal flowing into the containment
zone is controlled manually by a suitable valve which in
copper alloy casting practice is located at the top of the
down spout _ . For other types of metals the valve may be
located in any desired location. For example, for aluminum
casting the valve is normally located toward the botkom of
the down spout. The particular position of the flow control
valve may be selected as desired. Conventionally manual
control of flow rate is performed in response to sensing the
height of the molten metal in the containment zone either
visually or through electrical or electroptical means as are
known in the art.
It is desired in accordance with this invention, however,
that the control of the flow rate be fully automated and
integrated into the control of the casting system 10.
Referring now to Figures l and 2, this is accomplished by
providing a flow control valve 27 somewhere in the molten
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metal distribution system which leads to the mold. Preferably,
it is in the down spout''l6. The flow control valve 27 shown
-
comprises a pin 28 having a conical end 29 which is arranged
to control the flow rate of met'al from the trough 15 into
the down spout 16. The pin 28 is arranged coaxially above the
down spout 16. Raising the pin' 28 increases the flow rate.
Lowering the pin 28 decreases the flow rate. Lowering the pin
28 into contact with the end corners of the down spout'16
._ _
cuts off flow entirelyO
Movement of the valve pin '28 up or down in accordance
with this inventlon is fully automated by means of a suitable
actuator 30 which can be controlled electrically. The
actuator 30 shown in Figures 1 and 2 comprlses a pneumatic
actuator. The pneumatic actuator '30 includes a housing'31
internally of which is supported a flexible diaphragm 32.
~he diaphragm 32 in turn is connected to the valve pin 28 by
means of a rod 33. The valve pln 28 is normally biased to its
closed position by means of a spring 3~ e~tending between t:he
pin 28 and the houslng 31 of the pneumatic actuator'30. Air
is introduced or wlthdrawn from the housing 31 by a voltage
to pressure transducer 35. The magnitude of the air pressure
applied by the transducer 35 to the housing 31 via conduit 36
is directly proportional to the magnitude of the control
voltage signal V input to the transducer 35. Variations in
the signal V cause corresponding variation in the output
pressure of the transducer 35. A suitable transducer 35
comprises a Model T5100 series manufactured by Fairchild, Inc.
of No,rth 'Carolina.
The air pressure from the transducer 35 deflects the
diaphragm 32 as shown in phantom in proportion to the magnitude
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of the air pressure. This causes the pin 28 to be raised
from its fully-closed position. The position of the pin 28
is, therefore, a function of the pressure on the lower side
of the diaphragm 32. As the pressure increases, the
deflection of the diaphragm 32 lncreases and, therefore, khe
flow opening into the casting zone is increased. Similarly,
as the pressure decreases, the flow opening is decreased.
Ihe transducer 35 receives the input control signal from the flcw
control system 37 which is connected to the power source 17 and
control system 18 of the casting apparatus 10. The flow
control system 37 is best shown in Figure 2. It comprises a
set point control amplifier 38, one input 39 of which is
connected to a variable voltage source 40 which is utilized
to set the control point of the amplifier 38. The other
input 41 to the amplifier is connected to receive the desired
signal A, B, or 0 as described above, which is sensed from
within the control and excitation system 17, 18 of the
inductor 11. The sensed signaI A, B~ or 0, which is applied
to the control input 41 of the amplifier is compared by the
amplifier to the variable voltage source set point signal P
to generate the output signal V which is proportional to
the difference therebetween. The output signaI V from the
amplifier 38 causes the transducer 35 to increase or decrease
the deflection of the diaphragm 32 to correspondingly increase
or decrease the flow rate of metal from the trough 15 into ?
the down spout 16.
The flow control system 37 preferably is of the pro-
portional type wherein the differential between t~e set point
signaI P and the input signal A, B, or 0 from the control
system and power source 17 and 18 is measured and amplified
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by a desired factor. The controller 37 preferably includes a
reset function which serves to long term average the sensed
signal A, B, or 0. In this way, the flow control system 37
will comprise an integrating control arrangement wherein the
flow rate change cycles are from 2 to 10 times the cycle time
associated with the power supply control system 18O For
example, the flow rate change cycles will range in time in
seconds rather than in fractions of a second, preferably 2 to
10 seconds.
If the casting apparatus 10 is to be one which may be
sub~ect to drastic changes in flow rate, then the controller
37 preferably also includes a rate function whic~ is
particularly useful at start-up. The rate function of the
controller 37 adds a factor to the control output signal V
which would be a function of the rate of change in the input
error slgnal A, B, or 0.
The specific details of the controller 37 do not form
part of the present invention, and any desired set point
controller 37 which is adapted to receive the sensed hydro-
static preasure error signal A, B, or 0 and compare it with a
prede~termined value thereof to generate an error signal for
controlling the transducer 35 could be used.
It is not necessary in accordance with this invention to
utilize a pneumatic actuator 30~ It would be fully appropriate
to use in place thereof either a stepping motor or a servo
control motor 42 as in Figure 3 and in place of the transducer
35, an approprlate servo amplifier 43 which ~ould receive
the error signal V from the set point amplifier 38. The pin
type flow control valve 27 is arranged for movement in a
frame not shown vertically and axially of the down spout 16.
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A rack 44 is connected to the pin 28 and ls associated with a
pinion gear 45 which is driven by the servo motor 42 which
in accordance with this embodiment could be either a servo
motor or a stepping motor. The servo motor 42 is actuated by
the output signal V' froTn the servo amplifier 43 in response
to the error signal V from the set point amplifier whic.h is applied
at the input 46 to the servo amplifier.
A~cordingly, it is a unique aspect of this invention that
a hydrostatic pressure change signal A, B, or 0 from the
con~rol and excitation system 17 and 18 for the inductor 11
is utilized to control the flow rate of the molten metal into
the containment zone of the casting machine 10. The signals
A, B, or 0 which are sensed in accordance with this invention
can be sensed in any desired conventional fashion. For
example, as shown in Figure 2, the error signal A from the
~~ control system 18 can be sensed by a parallel connection 47
to the output 48 of the control system 18 so that the output 48
thereof is applied to both the power supply 17 and the flow
rate controller by suitably connecting terminal 49 to
terminal 50 as by a wire 59 shown i~ phantcm.
If the current in the inductor 11 is to be sensed, this
can be accomplished through the use o.f a current transformer
51 whose output is current to voltage scaled at S to provide
a corresponding voltage signal at terminal 5c which is
connected to terminal 50.
The voltage or frequency across the inductor could be
sensed by means of a dlfferential amplifier ,3, filter 54
and frequency to voltage converter 55 as described in U.S.
Patent 4,161,206. In this approach the differential
amplifier 53 is utilized to provide a volta3e across the
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induc~or 11 signal at terminal 56. The output of the
differential amplifier 53 alternatlvely is fed to a filter
circuit 54 for exkracting khe fundamental frequency. The
output of the filter 54 is fed to a frequency to voltage
converter 55. The output signal of the frequency to voltage
converter 55 at terminal 57 comprises a signal proportional
to the frequency of the applied current. Hydrostatic pressure
control signals B ~rom within the power source 17 such as the
control bus voltage are provided at terminal 58. In practice
selectively only one of the control signals A, B, or 0 is
connected to terminal 50 as by a wire connecting that terminal
to any of the signal terminals 49, 56, 57, and 58. A suitable
wire connection 59 is shown in phantom connecting terminals 49
and _ as an example.
The means for sensing the signals A, B, or 0 referred to
above can be any desired means including a volt meter, a
current meter or any other suitable instrument.
In operation the apparatus 10 o~ the present invention
will sense changes in the hydrostatic pressure of the molten
metal head 19. If the magnitude of the hJdrostatic pressure
change signal A, B~ or O increases or decreases with time~
depending on whether the hydrostatic pressure is increasing
or decreasing, then the set point control arplifier 38 will
provide an appropriate control signal V for controlling the
actuator 30 of the flow control valve 27. If for example
there is an increase in hydrostatic pressure associated with
an increased flow of molten metal into the containment zone
the effect on the control system 18 for the inductor 11
would be to increase the current to overcome the higher
hydrostatic pressure. This current increase would be sensed
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at any of the points as described above, either as the current
output signal O itsel~ or some other corresponding signal
which could be traced all the way back to the change signal A
which caused the increased current. The change signal A, B,
or O is applied to the set point control a~plifier 38 to
generake an output signal V from the ampli~ier which would
cause the flow control valve 37 to reduce the flow of molten
metal into the mold. This in turn would reduce the hydrostatic
pressure and cause the control system 18 for the power supply
17 to reduce the current in the inductor. This would result
in a change signal A, B, or O which would be fed back to the
flow control system 37 and the two systems 18 and 37 will
interact until a quiescent or near quiescent condition is
obtained. If some change in the flow of molten metal into the
mold destroys this quiescence, then the same control inter-
ackion will occur again until a more quiescent condition is
achieved.
Of course, it is recognized that the control system 18
for the power supply 17 is reactin~ or cycling in fractions
of a second whereas the control system 37 for the molten
metal flow rate is reacting or cycling in seconds. In this
way it ls posslble to control the flow rate into the
casting zone in such a manner as to have khe control system
~or the power supply operate within its optimum range of
control. The net result of the dual control of both the
output of the power supply 17 and the flow rake of molten
metal into the mold fully automatically as described should
be to provide cast ingots of even more uniform cross section
than would be obtained by the use of a control system 18 of
the Yarwood et al. patent or other system alone.
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~ ~'7~`0~ ~
In the figures common elements haYe the same reference
numbers.
The flow control 37 could be slmilar to the Model 7355
three mode proportloning controllers manufactured by Honeywell,
Inc.g Minneapolis, Minnesota.
While the castin~ as described above has been described
as an ingot, it could comprise any desired type of con-
tinuously or semi-continuous~ cast shape, such as rods, bars,
etc. While the invention has been described by reference to
copper and copper base alloys, it is believed that the
apparatus and process 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. While the control circuitry has been described in an
anolog format, it should be apparent that digital circuitry
could be substituted including the-use of appropriate micro-
processing as desired.
Instead of controlling the flow of molten metal into the
mold by means of a valve 27 in the downspout 16 the valve
2I could be located in the trough 15 though this is deemed
less desirable. Further, in place of a va~ve 27 the pour
rate of the furnace which provides the molten metal can be
controlled by any desired means. For example, if a conven-
tional tilt type furnace is utilized the rate at which the
furnace is tilted could be controlled in a manner similar
to the way the valve 27 in the embodiments described above
is controlled. This approach again is not preferred because
it is too far upstream of the mold. Ideally, the valve
should be located as far downstream in the distribution systern
as possible in order to reduce the time interval necessary
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to change the rate of flow of molten metal into the mold.
The terms molten metal flow or flow rate as used
herein refer to the volumetric flow rate of the molten metal.
~ t is apparent that there has been provided in
accordance with this invention an electromagnetic casting
process and apparatus 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 alter-
na~ives, modifications and variations as fall within the
spirit and broad scope of the appended claims.
