CA1170017A - Electromagnetic casting process and apparatus - Google Patents
Electromagnetic casting process and apparatusInfo
- Publication number
- CA1170017A CA1170017A CA000368209A CA368209A CA1170017A CA 1170017 A CA1170017 A CA 1170017A CA 000368209 A CA000368209 A CA 000368209A CA 368209 A CA368209 A CA 368209A CA 1170017 A CA1170017 A CA 1170017A
- Authority
- CA
- Canada
- Prior art keywords
- molten material
- controlling
- hydrostatic pressure
- containment zone
- inductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
- B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/01—Continuous casting of metals, i.e. casting in indefinite lengths without moulds, e.g. on molten surfaces
- B22D11/015—Continuous casting of metals, i.e. casting in indefinite lengths without moulds, e.g. on molten surfaces using magnetic field for conformation, i.e. the metal is not in contact with a mould
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Continuous Casting (AREA)
- Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An apparatus or process for casting metals by electromagnetically forming molten metal into a desired shape by applying a magnetic field to the molten metal.
The magnetic field defines a containment zone for the molten metal. The hydrostatic pressure exerted by the molten metal in the containment zone is sensed and in response thereto the flow of molten metal into the containment zone is controlled. This minimizes changes in the hydrostatic pressure.
An apparatus or process for casting metals by electromagnetically forming molten metal into a desired shape by applying a magnetic field to the molten metal.
The magnetic field defines a containment zone for the molten metal. The hydrostatic pressure exerted by the molten metal in the containment zone is sensed and in response thereto the flow of molten metal into the containment zone is controlled. This minimizes changes in the hydrostatic pressure.
Description
13062~M3 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 0~
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 1 1 7QV ~ ~
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 I :!7Q~
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 . - 5 -0 ~
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 - 5a -,, 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.
1 ~ 7~3 V ~
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.
11 l ~Q~
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 ~ 1 7~Q ~ ~
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.
3o 117~
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 1 ~ 7 (~ O ~
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 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 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.
l0062-r~s i 1 7 ~ 7 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 ' ~14 10062-~B
~ 1 7~
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 l?~7~01 ~
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 Q ~ ~ ~
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.
~ 10062~MB
0 ~ ~
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 ~7~0~
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 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.
~ ~'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 3 ~ 7 ~ 3 1 ~
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.
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 0~
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 1 1 7QV ~ ~
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 I :!7Q~
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 . - 5 -0 ~
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 - 5a -,, 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.
1 ~ 7~3 V ~
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.
11 l ~Q~
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 ~ 1 7~Q ~ ~
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.
3o 117~
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 1 ~ 7 (~ O ~
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 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 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.
l0062-r~s i 1 7 ~ 7 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 ' ~14 10062-~B
~ 1 7~
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 l?~7~01 ~
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 Q ~ ~ ~
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.
~ 10062~MB
0 ~ ~
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 ~7~0~
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 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.
~ ~'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 3 ~ 7 ~ 3 1 ~
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.
Claims (26)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an apparatus for casting materials comprising:
means for electromagnetically forming molten material into a desired casting shape, said electromagnetic forming means including means for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; the improvement wherein said apparatus further comprises:
means for controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control means comprising:
means for sensing changes in the hydrostatic pressure of said molten material in said containment zone; and means automatically responsive to said hydrostatic pressure sensing means for controlling the amount of molten material in said containment zone.
means for electromagnetically forming molten material into a desired casting shape, said electromagnetic forming means including means for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; the improvement wherein said apparatus further comprises:
means for controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control means comprising:
means for sensing changes in the hydrostatic pressure of said molten material in said containment zone; and means automatically responsive to said hydrostatic pressure sensing means for controlling the amount of molten material in said containment zone.
2. An apparatus as in claim 1 wherein said control means controls said amount of said molten material in a manner so as to minimize changes in said hydrostatic pressure.
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3. In an apparatus for casting materials comprising:
means for electromagnetically forming molten material into a desired casting shape, said electromagnetic forming means including: an inductor for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; and means for controlling and applying an alternating current to said inductor to generate said magnetic field the improvement wherein said apparatus further comprises:
means for controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control means comprising:
means for sensing an electrical signal derived from said means for controlling and applying said alternating current, said electrical signal being one which changes in correspondence about to changes in said hydrostatic pressure of said molten material; and means responsive to said sensed electrical signal for controlling the amount of said molten material in said containment zone.
means for electromagnetically forming molten material into a desired casting shape, said electromagnetic forming means including: an inductor for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; and means for controlling and applying an alternating current to said inductor to generate said magnetic field the improvement wherein said apparatus further comprises:
means for controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control means comprising:
means for sensing an electrical signal derived from said means for controlling and applying said alternating current, said electrical signal being one which changes in correspondence about to changes in said hydrostatic pressure of said molten material; and means responsive to said sensed electrical signal for controlling the amount of said molten material in said containment zone.
4. An apparatus as in claim 3 wherein said control means controls said amount of said molten material in a manner so as to minimize changes in said hydrostatic pressure.
5. An apparatus as in claim 3 wherein said sensed electrical signal comprises an error signal used to regulate the output of said means for controlling and applying said alternating current.
6. An apparatus as in claim 3 wherein said sensed electrical signal comprises at least one of current, voltage or frequency signals applied to said inductor.
7. An apparatus as in claim 6 wherein said sensed electrical signal comprises the current in said inductor.
8. An apparatus as in claim 3 wherein said means responsive to said sensed electrical signal comprises;
control circuit means for receiving said sensed electrical signal and for generating a desired corresponding output signal; and means operable in response to said output signal of said control circuit means for increasing or decreasing the amount of molten material in said containment zone.
control circuit means for receiving said sensed electrical signal and for generating a desired corresponding output signal; and means operable in response to said output signal of said control circuit means for increasing or decreasing the amount of molten material in said containment zone.
9. An apparatus as in claim 8 wherein said means for increasing or decreasing said flow of molten material into said containment zone comprises a valve means arranged in a molten material distribution means for transporting said molten material to said containment zone; and means for actuating said valve means to increase or decrease said molten material flow and wherein said molten material comprises a metal.
An apparatus as in claim 9 wherein said valve means is arranged to control the flow of molten material in a downspout of said distribution means.
11. An apparatus as in claim 10 wherein said valve means comprises a valve member arranged for movement axially of said downspout and wherein said actuating means is operatively connected to move said valve member axially of said downspout to increase or decrease said molten metal flow.
12. An apparatus as in claim 11 wherein said actuating means includes: pneumatic means for moving said valve member axially of said downspout; and transducer means for receiving said output signal and for generating a pneumatic output for application to said pneumatic means for moving said valve member, said pneumatic output being proportional to said output signal.
13. An apparatus as in claim 12 wherein said transducer means comprises a voltage to pressure transducer and wherein said output signal comprises a voltage signal and wherein said means for moving said valve member comprises; a housing including a flexible diaphram internally thereof defining within said housing a pressure chamber, said pneumatic output from said transducer means being connected to said chamber; and said diaphram being connected to said valve member.
14. An apparatus as in claim 11 wherein said actuating means includes; means for moving said valve member axially of said downspout, said moving means comprising a servo or stepping motor; and means for controlling said servo or stepping motor in correspondence to said output signal.
15. An apparatus as in claim 8 wherein said control circuit means comprises a proportional controller.
16. An apparatus as in claim 15 wherein said proportional controller includes a set point function and a rate function.
17. An apparatus as in claim 8 wherein said means for controlling and applying said alternating current to said inductor includes means for determining about a reactive parameter of said inductor and for comparing said reactive parameter to a predetermined value thereof for generating an error signal, said error signal being utilized to control the -output of said means for applying said alternating current; and wherein said error signal comprises said sensed electrical signal for controlling said flow of molten material into said containment zone.
18. In a process for casting materials comprising:
electromagnetically forming molten material into a desired casting shape, said electromagnetic forming step including:
applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; the improvement wherein said process further comprises:
controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control step comprising;
sensing changes in the hydrostatic pressure of said molten material in said containment zone; and responsive automatically to said sensing of said hydrostatic pressure changes controlling the amount of said molten material in said containment zone.
electromagnetically forming molten material into a desired casting shape, said electromagnetic forming step including:
applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; the improvement wherein said process further comprises:
controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure control step comprising;
sensing changes in the hydrostatic pressure of said molten material in said containment zone; and responsive automatically to said sensing of said hydrostatic pressure changes controlling the amount of said molten material in said containment zone.
19. A process as in claim 18 wherein said controlling of said amount of said molten material is in a manner so as to minimize changes in said hydrostatic pressure.
20. In a process for casting materials comprising;
electromagnetically forming molten material into a desired casting shape, said electromagnetic forming step including: providing an inductor for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; and controlling and applying an alternating current to said inductor to generate said magnetic field, the improvement wherein said process further comprises:
controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure controlling step comprising:
sensing an electrical signal derived from said step of controlling and applying said alternating current, said electrical signal being one which changes in correspondence about to changes in said hydrostatic pressure of said material; and responsive to said sensed electrical signal, controlling the amount of said molten material in said containment zone.
electromagnetically forming molten material into a desired casting shape, said electromagnetic forming step including: providing an inductor for applying a magnetic field to said molten material, said magnetic field defining a containment zone for said molten material; and controlling and applying an alternating current to said inductor to generate said magnetic field, the improvement wherein said process further comprises:
controlling the hydrostatic pressure exerted by said molten material in said containment zone, said hydrostatic pressure controlling step comprising:
sensing an electrical signal derived from said step of controlling and applying said alternating current, said electrical signal being one which changes in correspondence about to changes in said hydrostatic pressure of said material; and responsive to said sensed electrical signal, controlling the amount of said molten material in said containment zone.
21. A process as in claim 20 wherein said controlling of said amount of said molten material is in a manner so as to minimize changes in said hydrostatic pressure.
22. A process as in claim 21 wherein said sensed electrical signal comprises an error signal used to regulate the output of said controlling and applying said alternating current step.
23. A process as in claim 21 wherein said sensed electrical signal comprises at least one of current, voltage or frequency signals applied to said inductor.
24. A process as in claim 23 wherein said sensed electrical signal comprises the current in said inductor.
25. A process as in claim 21 wherein said molten material comprises a metal and wherein said step of controlling the amount of said molten metal comprises controlling the' flow of said molten metal and wherein said flow control step responsive to said sensed electrical signal comprises: providing a control circuit means for receiving said sensed electrical signal; generating a desired corresponding output signal from said control circuit means; and in response to said output signal from said control circuit means increasing or decreasing the flow of molten metal into said containment zone.
26. A process as in claim 25 wherein said step of controlling and applying said alternating current to said inductor includes:
determining about a reactive parameter of said inductor and comparing said reactive parameter to a predetermined value thereof for generating an error signal, said error signal being utilized to control the output of said step of applying said alternating current; and wherein said error signal comprises said sensed electrical signal for controlling said flow of molten metal into said containment zone.
determining about a reactive parameter of said inductor and comparing said reactive parameter to a predetermined value thereof for generating an error signal, said error signal being utilized to control the output of said step of applying said alternating current; and wherein said error signal comprises said sensed electrical signal for controlling said flow of molten metal into said containment zone.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US11089380A | 1980-01-10 | 1980-01-10 | |
| US110,893 | 1980-01-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1170017A true CA1170017A (en) | 1984-07-03 |
Family
ID=22335502
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000368209A Expired CA1170017A (en) | 1980-01-10 | 1981-01-09 | Electromagnetic casting process and apparatus |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0032442B1 (en) |
| JP (1) | JPS56141943A (en) |
| CA (1) | CA1170017A (en) |
| DE (1) | DE3162710D1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4446909A (en) * | 1981-02-20 | 1984-05-08 | Olin Corporation | Process and apparatus for electromagnetic casting of multiple strands having individual head control |
| US4450890A (en) * | 1981-02-20 | 1984-05-29 | Olin Corporation | Process and apparatus for electromagnetic casting of multiple strands having individual head control |
| US4498521A (en) * | 1981-05-26 | 1985-02-12 | Kaiser Aluminum & Chemical Corporation | Molten metal level control in continuous casting |
| US4415017A (en) * | 1981-06-26 | 1983-11-15 | Olin Corporation | Control of liquid-solid interface in electromagnetic casting |
| DE3148344A1 (en) * | 1981-12-07 | 1983-06-09 | Preh, Elektrofeinmechanische Werke, Jakob Preh, Nachf. Gmbh & Co, 8740 Bad Neustadt | MACHINE FEEDING DEVICE FOR A WARM CHAMBER PRESS MOLDING MACHINE |
| EP0296443A3 (en) * | 1987-06-22 | 1989-11-08 | Zimmermann & Jansen GmbH | Method and device for automatically filling a continuous casting mold |
| CN102398008A (en) * | 2011-11-28 | 2012-04-04 | 苏州有色金属研究院有限公司 | Method for preparing aluminum alloy composite round ingot blank |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2686864A (en) * | 1951-01-17 | 1954-08-17 | Westinghouse Electric Corp | Magnetic levitation and heating of conductive materials |
| US3467166A (en) * | 1967-03-01 | 1969-09-16 | Getselev Zinovy N | Method of continuous and semicontinuous casting of metals and a plant for same |
| DE2757785C3 (en) * | 1977-12-23 | 1981-01-29 | Reinhard W. Dr.-Ing. Zuerich Theiler (Schweiz) | Method and device for measuring the level of an electrically conductive liquid, in particular a metallic melt |
| US4161978A (en) * | 1978-07-19 | 1979-07-24 | Reynolds Metals Company | Ingot casting |
-
1981
- 1981-01-09 DE DE8181300093T patent/DE3162710D1/en not_active Expired
- 1981-01-09 CA CA000368209A patent/CA1170017A/en not_active Expired
- 1981-01-09 EP EP81300093A patent/EP0032442B1/en not_active Expired
- 1981-01-10 JP JP256681A patent/JPS56141943A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0032442A1 (en) | 1981-07-22 |
| EP0032442B1 (en) | 1984-03-21 |
| JPS56141943A (en) | 1981-11-05 |
| DE3162710D1 (en) | 1984-04-26 |
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