EP0744117A1 - Process for operating coreless induction melting and/or holding furnaces and electric switching unit suitable therefor - Google Patents

Process for operating coreless induction melting and/or holding furnaces and electric switching unit suitable therefor

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Publication number
EP0744117A1
EP0744117A1 EP95910392A EP95910392A EP0744117A1 EP 0744117 A1 EP0744117 A1 EP 0744117A1 EP 95910392 A EP95910392 A EP 95910392A EP 95910392 A EP95910392 A EP 95910392A EP 0744117 A1 EP0744117 A1 EP 0744117A1
Authority
EP
European Patent Office
Prior art keywords
induction
melting
frequency
induction coil
switching unit
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.)
Granted
Application number
EP95910392A
Other languages
German (de)
French (fr)
Other versions
EP0744117B1 (en
Inventor
Dieter Schluckebier
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Otto Junker GmbH
Original Assignee
Otto Junker GmbH
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Filing date
Publication date
Application filed by Otto Junker GmbH filed Critical Otto Junker GmbH
Publication of EP0744117A1 publication Critical patent/EP0744117A1/en
Application granted granted Critical
Publication of EP0744117B1 publication Critical patent/EP0744117B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/067—Control, e.g. of temperature, of power for melting furnaces
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/22—Furnaces without an endless core
    • H05B6/24—Crucible furnaces
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2213/00—Aspects relating both to resistive heating and to induction heating, covered by H05B3/00 and H05B6/00
    • H05B2213/02—Stirring of melted material in melting furnaces

Definitions

  • the present invention relates to a method for the operation of coreless induction melting and / or holding furnaces, in which, in melting operation at an induction frequency of> 100 Hz, a slight stirring movement in the melt and in melting or holding operation in contrast thereto Induction frequency reduced by a maximum of 50%, which is always> 50 Hz, results in a greater stirring movement in the melt, and an electrical switching unit for coreless induction melting and / or heating furnaces with an induction frequency in the range from mains to medium telfrequency, which have at least one one-part or multi-part induction coil arranged around a furnace crucible and an electrical voltage supply device with a frequency converter or converter.
  • a coreless induction crucible furnace is known from DE-PS 27 48 136, which can be operated both at the mains frequency and at a higher frequency. Such a furnace is preferably operated at medium frequency in order to rapidly melt the metal introduced into the crucible in the solid state. In contrast, if the already melted metal is to be stirred vigorously and if necessary slag and alloy treatments are to be carried out with the melt, then in such a case a lower frequency, e.g. Mains frequency, applied.
  • a lower frequency e.g. Mains frequency
  • the capacitor capacity and / or the inductance present in the resonant circuit are increased or decreased.
  • the inventive method can also provide that the capacitance and / or the inductance of the resonant circuit be increased or decreased by at least 1/3 of their respective total value.
  • An even more intensive melt bath mixing can be obtained by increasing or decreasing the capacitance and / or the inductance of the resonant circuit by twice the total value.
  • the sub-claims 4 to 6 contain particularly advantageous procedures according to the invention.
  • the present invention is based on the object of designing a coreless induction melting and / or holding furnace in accordance with the type mentioned at the outset in such a way that it can be acted upon alternately with different frequencies, the technical outlay compared to the known ovens should be low.
  • This object is achieved with such an induction melting and / or holding furnace according to the invention in that at least one capacitor is provided within the electrical conduction path between the induction coil (s) and the frequency converter, the capacitor (s) being connected the induction coil (s) is (are) electrically connected in parallel and, together with this (s), forms an electrical resonant circuit, the natural frequency of which is matched to the respective induction frequency, and electrical within the line path mentioned Switching elements are seen, by means of which the capacitance and / or the inductance of the resonant circuit and thus its natural frequency can be adjusted in steps.
  • the solution according to the invention has the further advantage that it can be implemented inexpensively and in a space-saving manner.
  • the switching elements are designed such that when they are actuated, capacitors and / or induction coils which are first connected in series with one another are connected in parallel with one another and vice versa.
  • Either individual capacitors or induction coils can be switched over individually in the manner mentioned, or such a switchover for capacitors and induction coils can be carried out simultaneously.
  • the natural frequency of the resonant circuit can accordingly be increased or decreased by a factor of 2. This frequency change can be increased even further by either using several capacitors or induction coils or by switching both modules simultaneously.
  • the switching unit according to the invention can also provide that at least two switching elements can be locked against one another by means of an electrical or electromechanical locking device.
  • Such a lock is particularly useful when several capacitors and / or induction coils are provided, which can be switched over by several switching elements. Make duck necessary, whereby not all switching elements may be actuated simultaneously.
  • the switching unit according to the invention can also be designed such that the induction coil (s) is / are divided by means of at least one tap.
  • This version is an alternative to two separate induction coils.
  • the switching unit according to the invention can also be designed such that only a part of the turns of the induction coil ⁇ ) is supplied with the supply voltage.
  • This operating mode can also be controlled via switching elements in which, for example, a voltage division of a plurality of capacitors connected in series with one another, which are arranged overall in parallel with the induction coil (s), takes place.
  • This partial loading serves in particular to save energy when the induction furnace is kept warm.
  • a particularly advantageous embodiment of the switching unit according to the invention can provide that the part of the turns of the induction coil which is located in the vicinity of the melt pool surface is supplied with the supply voltage.
  • This operating mode is particularly useful in the stirring and holding mode of the induction furnace, since the efficiency of power transmission to the melt is greatest in the area of the melt pool surface.
  • the switching unit according to the invention can also be designed such that at least two electrically separate induction coil parts are provided and that at least the upper induction coil part is acted upon by the entire capacitance of the capacitors.
  • the capacitor capacity is increased to the extent necessary to achieve optimum efficiency.
  • the oscillating circuit of the induction furnace is changed, ie the oscillating frequency of the oscillating circuit is reduced. Overall, the frequency of the feed current of the furnace can thus be reduced in a desired manner in a simple manner and the stirring movement in the molten bath can be increased.
  • FIG. 1 shows an induction crucible furnace with a switching unit according to the invention, by means of which a reduction in the induction frequency can be achieved by increasing the capacitor capacitance for the entire coil;
  • FIG. 2 shows a representation according to FIG. 1, in which a reduction in the induction frequency is achieved only by switching on the capacitor capacitance in the upper coil part;
  • FIGS. 1 and 2 shows a representation corresponding to FIGS. 1 and 2, in which the induction frequency is reduced by increasing the capacitor capacity and the inductance of the furnace coil;
  • Fig. 4 is a Fig. 1 to 3 corresponding representation, in which a reduction in the induction frequency Increasing the inductance of the coil is achieved as well
  • Fig. 5 is a Fig. 1 to 4 corresponding representation, in which a reduction in the induction frequency
  • FIG. 1 shows schematically a coreless induction crucible furnace 1 with an induction coil 3 surrounding the furnace crucible 2.
  • the induction coil 3 is connected to a three-phase network 7 via lines 4, 5 and a frequency converter or oscillating circuit converter 6.
  • capacitors are 8.9. provided that can be connected to each other in series with the help of a switch 10 - and thereby parallel to the induction coil 3 - on the lines 4,5.
  • the capacitors 8.9 can also be connected with the aid of switches 11, 12 and lines 13, 14 in such a way that the Capacitors 8, 9 are each electrically parallel to one another, but overall they are also electrically parallel to the induction coil 3.
  • the induction coil 3 of the coreless induction crucible furnace 1 is connected to the resonant circuit converter 6 via the lines 4, 5.
  • a capacitor 15 is connected between lines 4, 5.
  • Approximately halfway up the induction coil 3 has a tap 16, between which and the line 4 further capacitors 17, 18, 19 can be connected with the aid of switches 20, 21, 22.
  • the operating frequency can only be reduced in the upper half of the induction coil, or the stirring movement and the power can only be increased in the upper half of the furnace of the melt.
  • the induction coil 3 also has a centrally arranged tap 16.
  • the induction coil 3 can be connected to the resonant circuit converter 6 via the lines 4, 5.
  • the capacitors 8.9 are connected in series between the lines 4.5.
  • the switch 23 and a further switch 25 are actuated, the switch 23 not being able to be closed by means of a locking mechanism, the capacitors 8, 9 are connected in parallel with the upper half of the induction coil 3. In this case, both the capacitance of the capacitor and the inductance of the induction coil are increased.
  • FIG. 4 shows an application example of the invention, in which the inductance is doubled in the case of a two-part induction coil 3a, 3b.
  • the switch 23 In normal melting operation, the switch 23 is closed and the two coil parts 3a, 3b are thus supplied with the supply voltage. In the state shown, that is to say when switch 23 is not closed, only coil part 3a is switched on. In this case, the operating frequency is reduced by a factor of 2.
  • FIG. 5 shows a coreless induction crucible furnace, in which partial coils 3a, 3b are provided, which are connected to the three-phase network 7 via lines 4, 5 and via the resonant circuit converter 6.
  • a capacitor 15 is connected in parallel with the partial coils 3a, 3b.
  • the two partial coils 3a, 3b can be acted upon in parallel by the resonant circuit converter 6.
  • the partial coils 3a, 3b are connected in series to the resonant circuit converter 6 via switches 27, 28.
  • the switch 26 on the one hand and the switches 27, 28 on the other hand are interlocked so that the switches 27, 28 can only be closed when the switch 26 is open.

Abstract

PCT No. PCT/DE95/00175 Sec. 371 Date Oct. 7, 1996 Sec. 102(e) Date Oct. 7, 1996 PCT Filed Feb. 10, 1995 PCT Pub. No. WO95/22238 PCT Pub. Date Aug. 17, 1995In a process for the operation of coreless induction melting and/or holding furnaces-in which there results in the melting operation at a relatively high induction frequency (as compared to the mains frequency) a slight stirring motion in the melt, but a high degree of effectiveness for the melting process, and in the melting and holding operation at a correspondingly lower induction frequency there results a greater stirring motion in the melt, but a lower degree of effectiveness for the melting process-it is provided that at least one capacitor switched in parallel to the induction coil(s) is provided, which capacitor(s), together with the induction coil(s), form a resonant circuit; and that in the transition from the melting operation with slight stirring motion in the melt to the melting or holding operation with greater stirring motion, or in the reverse transition, the capacitor capacitance and/or the inductance present in the resonant circuit is increased, or as the case may be, decreased.

Description

VERFAHREN ZUM BETRIEB VON KERNLOSEN INDUKTIONSSCHMELZ- UND/ODER -WARMHALTEÖFEN SOWIE DAFÜR GEEIGNETE ELEKTRISCHE SCHALTEINHEIT METHOD FOR THE OPERATION OF CORELESS INDUCTION MELTING AND / OR HOT HOLDING OVENS AND ELECTRICAL SWITCHING UNIT SUITABLE FOR THIS
Beschreibungdescription
Die vorliegende Erfindung betrifft ein Verfahren zum Be¬ trieb von kernlosen Induktionsschmelz- und/oder -warmhal- teöfen, bei denen im Schmelzbetrieb bei einer Induktions¬ frequenz von > 100 Hz eine geringe Rührbewegung in der Schmelze und im Schmelz- oder Warmhaltebetrieb bei einer demgegenüber um maximal 50 % abgesenkten Induktionsfre¬ quenz, die immer > 50 Hz ist, eine größere Rührbewegung in der Schmelze resultiert, sowie eine elektrische Schaltein¬ heit für kernlose Induktionschmelz- und/oder -warmhalteöfen mit einer Induktionsfrequenz im Bereich von Netz- bis Mit¬ telfrequenz, welche mindestens eine ein- oder mehrteilige, um einen Ofentiegel herum angeordnete Induktionsspule sowie eine elektrische Spannungsversorgungseinrichtung mit einem Frequenzumformer bzw. -Umrichter aufweisen.The present invention relates to a method for the operation of coreless induction melting and / or holding furnaces, in which, in melting operation at an induction frequency of> 100 Hz, a slight stirring movement in the melt and in melting or holding operation in contrast thereto Induction frequency reduced by a maximum of 50%, which is always> 50 Hz, results in a greater stirring movement in the melt, and an electrical switching unit for coreless induction melting and / or heating furnaces with an induction frequency in the range from mains to medium telfrequency, which have at least one one-part or multi-part induction coil arranged around a furnace crucible and an electrical voltage supply device with a frequency converter or converter.
Aus der DE-PS 27 48 136 ist ein kernloser Induktionstiegel¬ ofen bekannt, der sowohl mit Netzfrequenz als auch mit ei- ner höheren Frequenz betrieben werden kann. Dabei wird ein solcher Ofen vorzugsweise mit Mittelfrequenz betrieben, um das im festen Zustand in den Schmelztiegel eingebrachte Me¬ tall schnell einzuschmelzen. Soll demgegenüber das bereits erschmolzene Metall kräftig durchgerührt und gegebenenfalls Schlacken- und Legierungsbehandlungen mit der Schmelze durchgeführt werden, so wird in einem solchen Falle vor¬ zugsweise eine niedrigere Frequenz, z.B. Netzfrequenz, an¬ gewandt.A coreless induction crucible furnace is known from DE-PS 27 48 136, which can be operated both at the mains frequency and at a higher frequency. Such a furnace is preferably operated at medium frequency in order to rapidly melt the metal introduced into the crucible in the solid state. In contrast, if the already melted metal is to be stirred vigorously and if necessary slag and alloy treatments are to be carried out with the melt, then in such a case a lower frequency, e.g. Mains frequency, applied.
Ein Nachteil dieses bekannten Induktionsschmelz- und -warm- halteofens sowie des Verfahrens zu seinem Betrieb ist darin zu sehen, daß zwei verschiedene Stromnetze vorhanden sein müssen, um die dort gestellte Aufgabe, nämlich den Betrieb in zwei Frequenzbereichen, zu lösen. Der apparative Aufwand ist folglich erheblich, da praktisch zwei getrennte Schaltanlagen eingesetzt werden müssen.A disadvantage of this known induction melting and holding furnace and the method for its operation is to be seen in the fact that two different power grids must be available in order to perform the task, namely the operation in two frequency ranges. The outlay on equipment is consequently considerable since practically two separate switchgear assemblies have to be used.
Ebenfalls zwei Versorgungseinrichtungen mit verschiedenen Frequenzen benötigt die Lösung nach der britischen Patent¬ schrift Nr. 508 255 (Fig. 9). In diesem Falle wird eine aus zwei Teilspulen bestehende Induktionsspule gleichzeitig an eine Versorgungseinrichtung niedrigerer Frequenz und an eine solche höherer Frequenz angeschlossen. Zu dem hohen Aufwand, wie er bei dem aus der erstgenannten Patentschrift bekannten Gegenstand betrieben werden muß, gesellt sich im Falle der britischen Patentschrift noch der zusätzliche Nachteil, daß jedes Netz durch besondere Filter geschützt werden muß, damit die Frequenz des einen Netzes nicht nega¬ tiv auf das andere einwirkt.The solution according to British Patent No. 508 255 (FIG. 9) also requires two supply devices with different frequencies. In this case, an induction coil consisting of two sub-coils is connected simultaneously to a supply device of lower frequency and to such a higher frequency. In the case of the British patent, there is the additional disadvantage that each network must be protected by special filters so that the frequency of the one network does not become negative acting on the other.
Aufgabe der vorliegenden Erfindung ist es daher, ein Vei— fahren zum Betrieb eines gattungsgemäßen Ofens anzugeben, bei dem mit nur geringem technischen Mehraufwand ein Be¬ trieb mit mehreren Frequenzen ermöglicht wird, wobei diese zusätzlichen Aufwendungen kostengünstig und auf kleinem Raum realisierbar sind.It is therefore an object of the present invention to provide a method for operating a generic furnace, in which operation with multiple frequencies is possible with only a small additional technical effort, these additional expenses being inexpensive and achievable in a small space.
Diese Aufgabe wird bei dem erfindungsgemäßen Verfahren da¬ durch gelöst, daß mindestens ein zu der(den) Induktions- spule(n) elektrisch parallel geschalteter Kondensator voi— gesehen ist, der(die) zusammen mit der(den) Induktions- spule(n) einen elektrischen Schwingkreis bildet(n),This object is achieved in the method according to the invention by providing at least one capacitor which is electrically connected in parallel with the induction coil (s) and which, together with the induction coil (s) ) forms an electrical resonant circuit,
und daß beim Übergang von Schmelzbetrieb mit geringerer Rührbewegung in der Schmelze auf Schmelz- oder Warmhaltebe¬ trieb mit größerer Rührbewegung bzw. beim umgekehrten Über¬ gang die Kondensatorkapazität und/oder die im Schwingkreis vorhandene Induktivität erhöht bzw. erniedrigt werden.and that during the transition from melting operation with less stirring movement in the melt to melting or holding operation with greater stirring movement or with the opposite transition, the capacitor capacity and / or the inductance present in the resonant circuit are increased or decreased.
Das erfindungsgemäße Verfahren kann ferner vorsehen, daß die Kapazität und/oder die Induktivität des Schwingkreises wenigstens um 1/3 ihres jeweiligen Gesamtwertes erhöht bzw. erniedrigt werden.The inventive method can also provide that the capacitance and / or the inductance of the resonant circuit be increased or decreased by at least 1/3 of their respective total value.
Es hat sich als nützlich und ausreichend erwiesen, die Ka- pazität bzw. die Induktivität wenigstens um den genannten Betrag zu erhöhen.It has proven useful and sufficient to increase the capacitance or inductance at least by the amount mentioned.
Eine noch intensivere Schmelzbaddurchmischung kann dadurch erhalten werden, daß die Kapazität und/oder die Induktivi- tat des Schwingkreises um den zweifachen Betrag ihres Gesamtwertes erhöht bzw. erniedrigt werden.An even more intensive melt bath mixing can be obtained by increasing or decreasing the capacitance and / or the inductance of the resonant circuit by twice the total value.
Die Unteransprüche 4 bis 6 enthalten besonders vorteilhafte Verfahrensweisen gemäß der Erfindung. Insbesondere hat es sich als besonders wirtschaftlich erwiesen, daß nur der obere Teil - insbesondere die obere Hälfte - der Induk¬ tionsspule zur intensiven Durchmischung der Metallschmelze in Badspiegelnähe eingeschaltet wird und die vorhandene, für die gesamte Ofenspule ausgelegte Kondensatorkapazität auf diese Teilspule aufgeschaltet wird.The sub-claims 4 to 6 contain particularly advantageous procedures according to the invention. In particular, it has proven to be particularly economical that only the upper part - in particular the upper half - of the induction coil is switched on for intensive mixing of the molten metal in the vicinity of the bath level and the existing capacitor capacity designed for the entire furnace coil is connected to this partial coil.
Ferner liegt der vorliegenden Erfindung die Aufgabe zu¬ grunde, einen kernlosen Induktionsschmelz- und/oder -warm¬ halteöfen gemäß der eingangs genannten Gattung in der Weise auszubilden, daß er abwechselnd mit verschiedenen Frequen¬ zen beaufschlagt werden kann, wobei der technische Aufwand gegenüber den bekannten Öfen gering sein soll.Furthermore, the present invention is based on the object of designing a coreless induction melting and / or holding furnace in accordance with the type mentioned at the outset in such a way that it can be acted upon alternately with different frequencies, the technical outlay compared to the known ovens should be low.
Diese Aufgabe wird bei einem derartigen Induktionsschmelz- und/oder -warmhalteöfen erfindungsgemäß dadurch gelöst, daß innerhalb des elektrischen Leitungsweges zwischen der(den) Induktionsspule(n) und dem Frequenzumformer mindestens ein Kondensator vorgesehen ist, wobei der(die) Kondensator(en) zu der(den) Induktionsspule(n) elektrisch parallel geschal- tet ist(sind) und zusammen mit diesem(n) einen elektrischen Schwingkreis bildet(n), dessen Eigenfrequenz auf die jewei¬ lige Induktionsfrequenz abgestimmt ist, und wobei innerhalb des genannten Leitungsweges elektrische Schaltelemente vor- gesehen sind, mittels derer die Kapazität und/oder die In¬ duktivität des Schwingkreises und damit dessen Eigenfre¬ quenz stufenförmig einstellbar sind.This object is achieved with such an induction melting and / or holding furnace according to the invention in that at least one capacitor is provided within the electrical conduction path between the induction coil (s) and the frequency converter, the capacitor (s) being connected the induction coil (s) is (are) electrically connected in parallel and, together with this (s), forms an electrical resonant circuit, the natural frequency of which is matched to the respective induction frequency, and electrical within the line path mentioned Switching elements are seen, by means of which the capacitance and / or the inductance of the resonant circuit and thus its natural frequency can be adjusted in steps.
Aufgrund dieser Maßnahmen geringen technischen Aufwandes wird ermöglicht, den Induktionsofen trotz nur einer Strom¬ versorgungseinrichtung mit verschiedenen Frequenzen zu be¬ aufschlagen. Die erfindungsgemäße Lösung hat weiterhin den Vorteil, daß sie sich kostengünstig und raumsparend reali- sieren läßt.As a result of these measures of low technical complexity, it is possible to charge the induction furnace with different frequencies despite only one power supply device. The solution according to the invention has the further advantage that it can be implemented inexpensively and in a space-saving manner.
Erfindungsgemäß kann ferner vorgesehen sein, daß die Schal¬ telemente derart ausgebildet sind, daß bei deren Betätigung zunächst zueinander in Reihe geschaltete Kondensatoren und/oder Induktionsspulen zueinander parallel geschaltet werden und umgekehrt.According to the invention it can further be provided that the switching elements are designed such that when they are actuated, capacitors and / or induction coils which are first connected in series with one another are connected in parallel with one another and vice versa.
Dabei können entweder einzelne Kondensatoren oder Induk¬ tionsspulen für sich genommen in der genannten Weise umge- schaltet werden oder eine derartige Umschaltung für Konden¬ satoren und Induktionsspulen kann gleichzeitig vorgenommen werden. Bei einer Umschaltung zweier gleich großer 'Kondensatoren von Reihen- auf Parallelschaltung kann dem¬ nach die Eigenfrequenz des Schwingkreises um den Faktor 2 erhöht bzw. erniedrigt werden. Diese Frequenzänderung kann dadurch noch weiter gesteigert werden, daß entweder mehrere Kondensatoren oder Induktionsspulen verwendet werden oder beide Baugruppen gleichzeitig geschaltet werden.Either individual capacitors or induction coils can be switched over individually in the manner mentioned, or such a switchover for capacitors and induction coils can be carried out simultaneously. When two capacitors of the same size are switched from series to parallel connection, the natural frequency of the resonant circuit can accordingly be increased or decreased by a factor of 2. This frequency change can be increased even further by either using several capacitors or induction coils or by switching both modules simultaneously.
Die erfindungsgemäße Schalteinheit kann ferner vorsehen, daß mindestens zwei Schaltelemente mittels einer elektri¬ schen bzw. elektromechanisehen Verriegelung gegeneinander sperrbar sind.The switching unit according to the invention can also provide that at least two switching elements can be locked against one another by means of an electrical or electromechanical locking device.
Eine derartige Verriegelung bietet sich besonders dann an, wenn mehrere Kondensatoren und/oder Induktionsspulen vorge¬ sehen sind, die eine Umschaltung durch mehrere Schaltele- ente erforderlich machen, wobei nicht sämtliche Schaltele¬ mente gleichzeitig betätigt werden dürfen.Such a lock is particularly useful when several capacitors and / or induction coils are provided, which can be switched over by several switching elements. Make duck necessary, whereby not all switching elements may be actuated simultaneously.
Die erfindungsgemäße Schalteinheit kann ferner so ausgebil- det sein, daß die Induktionsspule(n) mittels wenigstens ei¬ ner Anzapfung geteilt ist(sind).The switching unit according to the invention can also be designed such that the induction coil (s) is / are divided by means of at least one tap.
Diese Ausführung stellt eine Alternative zu zwei getrennten Induktionsspulen dar.This version is an alternative to two separate induction coils.
Die erfindungsgemäße Schalteinheit kann weiter so ausgebil¬ det sein, daß lediglich ein Teil der Windungen der Induk¬ tionsspule^) mit der Vorsorgungsspannung beaufschlagt ist.The switching unit according to the invention can also be designed such that only a part of the turns of the induction coil ^) is supplied with the supply voltage.
Dieser Betriebsmodus läßt sich ebenso über Schaltelemente ansteuern, bei denen beispielsweise eine Spannungsteilung mehrerer zueinander in Reihe geschalteter Kondensatoren, die insgesamt parallel zu der(den) Induktionsspule(n) ange¬ ordnet sind, erfolgt. Diese Teilbeaufschlagung dient insbe- sondere der Energieeinsparung beim Warmhaltebetrieb des In¬ duktionsofens.This operating mode can also be controlled via switching elements in which, for example, a voltage division of a plurality of capacitors connected in series with one another, which are arranged overall in parallel with the induction coil (s), takes place. This partial loading serves in particular to save energy when the induction furnace is kept warm.
Eine besonders vorteilhafte Ausgestaltung der erfindungsge¬ mäßen Schalteinheit kann vorsehen, daß der in der Nähe der Schmelzbadoberfläche liegende Teil der Windungen der Induk¬ tionsspule^) mit der Versorgungsspannung beaufschlagt ist.A particularly advantageous embodiment of the switching unit according to the invention can provide that the part of the turns of the induction coil which is located in the vicinity of the melt pool surface is supplied with the supply voltage.
Dieser Betriebsmodus bietet sich insbesondere im Rühr- und Warmhaltebetrieb des Induktionsofens an, da die Effizienz der Kraftübertragung auf die Schmelze im Bereich der Schmelzbadoberfläche am höchsten ist.This operating mode is particularly useful in the stirring and holding mode of the induction furnace, since the efficiency of power transmission to the melt is greatest in the area of the melt pool surface.
Anstelle der Teilung der Induktionsspule mittels einer An¬ zapfung kann die erfindungsgemäße Schalteinheit auch so ausgeführt sein, daß mindestens zwei elektrisch getrennte Induktionsspulenteile vorgesehen sind und daß wenigstens der obere Induktionsspulenteil mit der gesamten Kapazität der Kondensatoren beaufschlagt ist. Beim Übergang von Schmelzbetrieb mit höherer Frequenz, d.h. mit geringer Rührbewegung in der Schmelze, auf Schmelz¬ oder Warmhaltebetrieb mit einer größeren Rührbewegung wird hierbei die Kondensatorenkapazität über das zur Erzielung eines optimalen Wirkungsgrades erforderliche Maß erhöht. Dabei wird der Schwingkreis des Induktionsofens verändert, d.h. die Schwingfrequenz des Schwingkreises herabgesetzt. Insgesamt kann somit auf einfache Weise die Frequenz des Speisestroms des Ofens in gewünschter Weise herabgesetzt und die Rührbewegung im Schmelzbad erhöht werden.Instead of dividing the induction coil by means of a tap, the switching unit according to the invention can also be designed such that at least two electrically separate induction coil parts are provided and that at least the upper induction coil part is acted upon by the entire capacitance of the capacitors. In the transition from melting operation with a higher frequency, ie with a small stirring movement in the melt, to melting or holding operation with a larger stirring movement, the capacitor capacity is increased to the extent necessary to achieve optimum efficiency. The oscillating circuit of the induction furnace is changed, ie the oscillating frequency of the oscillating circuit is reduced. Overall, the frequency of the feed current of the furnace can thus be reduced in a desired manner in a simple manner and the stirring movement in the molten bath can be increased.
Im folgenden Teil der Beschreibung werden das erfindungsge¬ mäße Verfahren sowie die erfindungsgemäße Schalteinheit an- hand von in Figuren dargestellten Ausführungsbeispielen nä¬ her erläutert.In the following part of the description, the method according to the invention and the switching unit according to the invention are explained in more detail on the basis of exemplary embodiments shown in the figures.
Im einzelnen zeigen:In detail show:
Fig. 1 einen Induktionstiegelofen mit einer Schaltein¬ heit gemäß der Erfindung, mittels der eine Absen¬ kung der Induktionsfrequenz durch Erhöhung der Kondensatorkapazität für die gesamte Spule er¬ reichbar ist;1 shows an induction crucible furnace with a switching unit according to the invention, by means of which a reduction in the induction frequency can be achieved by increasing the capacitor capacitance for the entire coil;
Fig. 2 eine Darstellung gemäß Fig. 1, bei der eine Ab¬ senkung der Induktionsfrequenz durch Zuschalten von Kondensatorkapazität nur im oberen Spulenteil erreicht wird;FIG. 2 shows a representation according to FIG. 1, in which a reduction in the induction frequency is achieved only by switching on the capacitor capacitance in the upper coil part;
Fig. 3 eine Fig. 1 und 2 entsprechende Darstellung, bei der eine Absenkung der Induktionsfrequenz durch Erhöhung der Kondensatorkapazität und der Induk¬ tivität der Ofenspule erreicht wird;3 shows a representation corresponding to FIGS. 1 and 2, in which the induction frequency is reduced by increasing the capacitor capacity and the inductance of the furnace coil;
Fig. 4 eine Fig. 1 bis 3 entsprechende Darstellung, bei der eine Absenkung der Induktionsfrequenz durch Erhöhung der Induktivität der Spule erreicht wird sowieFig. 4 is a Fig. 1 to 3 corresponding representation, in which a reduction in the induction frequency Increasing the inductance of the coil is achieved as well
Fig. 5 eine Fig. 1 bis 4 entsprechende Darstellung, bei der eine Absenkung der Induktionsfrequenz durchFig. 5 is a Fig. 1 to 4 corresponding representation, in which a reduction in the induction frequency
Erhöhung der Induktivität bei einer zweigeteilten Spule erreicht wird.Increasing the inductance is achieved with a two-part coil.
In Fig. 1 ist schematisch ein kernloser Induktionstiegel- ofen 1 mit einer den Ofentiegel 2 umgebenden Induktions¬ spule 3 dargestellt. Die Induktionsspule 3 ist über Leitun¬ gen 4,5 sowie über einen Frequenzumformer bzw. Schwing- kreisumrichter 6 an ein Drehstromnetz 7 angeschlossen. Außerdem sind Kondensatoren 8,9. vorgesehen, die mit Hilfe eines Schalters 10 zueinander in Reihe - und dabei parallel zur Induktionsspule 3 - an die Leitungen 4,5 geschaltet werden können. Um die Kapazität der Kondensatoren 8,9 auf das Vierfache zu erhöhen und damit die Frequenz um die Hälfte zu senken, können die Kondensatoren 8,9 außerdem mit Hilfe von Schaltern 11,12 sowie Leitungen 13, 14 in der Weise verschaltet werden, daß die Kondensatoren 8,9 jeweils zueinander elektrisch parallel, insgesamt jedoch auch elek¬ trisch parallel zu der Induktionsspule 3 liegen.1 shows schematically a coreless induction crucible furnace 1 with an induction coil 3 surrounding the furnace crucible 2. The induction coil 3 is connected to a three-phase network 7 via lines 4, 5 and a frequency converter or oscillating circuit converter 6. In addition, capacitors are 8.9. provided that can be connected to each other in series with the help of a switch 10 - and thereby parallel to the induction coil 3 - on the lines 4,5. In order to increase the capacitance of the capacitors 8.9 to four times and thus reduce the frequency by half, the capacitors 8.9 can also be connected with the aid of switches 11, 12 and lines 13, 14 in such a way that the Capacitors 8, 9 are each electrically parallel to one another, but overall they are also electrically parallel to the induction coil 3.
In dem Ausführungsbeispiel gemäß Fig. 2 ist die Induktions¬ spule 3 des kernlosen Induktionstiegelofens 1 über die Lei¬ tungen 4,5 an den Schwingkreisumrichter 6 angeschlossen. Zwischen den Leitungen 4,5 ist ein Kondensator 15 zuge¬ schaltet. Etwa auf halber Höhe besitzt die Induktionsspule 3 eine Anzapfung 16, zwischen der und der Leitung 4 weitere Kondensatoren 17,18,19 mit Hilfe von Schaltern 20,21,22 zu¬ geschaltet werden können. In diesem Falle kann die Be¬ triebsfrequenz lediglich in der oberen Induktionsspulen¬ hälfte gesenkt bzw. die Rührbewegung und die Leistung nur in der oberen Ofenhälfte der Schmelze erhöht werden.In the exemplary embodiment according to FIG. 2, the induction coil 3 of the coreless induction crucible furnace 1 is connected to the resonant circuit converter 6 via the lines 4, 5. A capacitor 15 is connected between lines 4, 5. Approximately halfway up the induction coil 3 has a tap 16, between which and the line 4 further capacitors 17, 18, 19 can be connected with the aid of switches 20, 21, 22. In this case, the operating frequency can only be reduced in the upper half of the induction coil, or the stirring movement and the power can only be increased in the upper half of the furnace of the melt.
In dem Anwendungsbeispiel gemäß Fig. 3 besitzt die Induk¬ tionsspule 3 ebenfalls eine mittig angeordnete Anzapfung 16. Mit Hilfe eines Schalters 23 kann die Induktionsspule 3 über die Leitungen 4,5 an den Schwingkreisumrichter 6 ange¬ schlossen werden. Die Kondensatoren 8,9 sind dabei zwischen den Leitungen 4,5 in Reihe geschaltet. Bei Betätigung des Schalters 23 und eines weiteren Schalters 25, wobei über eine Verriegelungsmimik der Schalter 23 nicht geschlossen werden kann, werden die Kondensatoren 8,9 in Parallelschal¬ tung mit der oberen Hälfte der Induktionsspule 3 verbunden. In diesem Falle wird sowohl die Kapazität des Kondensators als auch die Induktivität der Induktionsspule erhöht.In the application example according to FIG. 3, the induction coil 3 also has a centrally arranged tap 16. With the help of a switch 23, the induction coil 3 can be connected to the resonant circuit converter 6 via the lines 4, 5. The capacitors 8.9 are connected in series between the lines 4.5. When the switch 23 and a further switch 25 are actuated, the switch 23 not being able to be closed by means of a locking mechanism, the capacitors 8, 9 are connected in parallel with the upper half of the induction coil 3. In this case, both the capacitance of the capacitor and the inductance of the induction coil are increased.
In Fig. 4 ist ein Anwendungsbeispiel der Erfindung darge¬ stellt, bei dem eine Verdopplung der Induktivität bei einer zweigeteilten Induktionsspule 3a,3b, erfolgt. Im normalen Schmelzbetrieb ist der Schalter 23 geschlossen und damit sind die beiden Spulenteile 3a,3b mit der Versorgungsspan¬ nung beaufschlagt. Im dargestellten Zustand, also bei nicht geschlossenem Schalter 23, ist nur der Spulenteil 3a einge¬ schaltet. In diesem Falle wird die Betriebsfrequenz um den Faktor 2 reduziert.4 shows an application example of the invention, in which the inductance is doubled in the case of a two-part induction coil 3a, 3b. In normal melting operation, the switch 23 is closed and the two coil parts 3a, 3b are thus supplied with the supply voltage. In the state shown, that is to say when switch 23 is not closed, only coil part 3a is switched on. In this case, the operating frequency is reduced by a factor of 2.
Fig. 5 zeigt einen kernlosen Induktionstiegelofen, bei dem Teilspulen 3a,3b vorgesehen sind, die über Leitungen 4,5 sowie über den Schwingkreisumrichter 6 an das Drehstromnetz 7 angeschlossen sind. Parallel zu den Teilspulen 3a,3b ist ein Kondensator 15 zugeschaltet. Durch Schließen eines Schalters 26 können beide Teilspulen 3a,3b in Paral¬ lelschaltung vom Schwingkreisumrichter 6 beaufschlagt wer¬ den. Um die Frequenz der an den Spulenteilen 3a,3b anlie- genden Spannung um ca. 50% zu senken, werden die Teilspulen 3a,3b über Schalter 27,28 in Reihe an den Schwingkreisum¬ richter 6 angeschlossen. Auch hier sind der Schalter 26 ei¬ nerseits und die Schalter 27,28 andererseits gegeneinander so verriegelt, daß die Schalter 27,28 nur dann geschlossen werden können, wenn der Schalter 26 geöffnet ist. 5 shows a coreless induction crucible furnace, in which partial coils 3a, 3b are provided, which are connected to the three-phase network 7 via lines 4, 5 and via the resonant circuit converter 6. A capacitor 15 is connected in parallel with the partial coils 3a, 3b. By closing a switch 26, the two partial coils 3a, 3b can be acted upon in parallel by the resonant circuit converter 6. In order to reduce the frequency of the voltage applied to the coil parts 3a, 3b by approximately 50%, the partial coils 3a, 3b are connected in series to the resonant circuit converter 6 via switches 27, 28. Here, too, the switch 26 on the one hand and the switches 27, 28 on the other hand are interlocked so that the switches 27, 28 can only be closed when the switch 26 is open.

Claims

Ansprüche Expectations
1. Verfahren zum Betrieb von kernlosen Induktionsschmelz- und/oder -warmhalteöfen,1. method for operating coreless induction melting and / or holding furnaces,
bei denen im Schmelzbetrieb bei einer Induktionsfrequenz von > 100 Hz eine geringe Rührbewegung in der Schmelzein which a slight agitation in the melt during melting operation at an induction frequency of> 100 Hz
und im Schmelz- oder Warmhaltebetrieb bei einer demgegen¬ über um maximal 50 % abgesenkten Induktionsfrequenz, die immer > 50 Hz ist, eine größere Rührbewegung in der Schmelze resultiert,and in melting or keeping-warm mode with an induction frequency that is reduced by a maximum of 50%, which is always> 50 Hz, a greater stirring movement results in the melt,
dadurch gekennzeichnet,characterized,
daß mindestens ein zu der(den) Induktionsspule(n) elek¬ trisch parallel geschalteter Kondensator vorgesehen ist, der(die) zusammen mit der(den) Induktionsspule(n) einen elektrischen Schwingkreis bildet(n),that at least one capacitor connected in parallel to the induction coil (s) is provided, which together with the induction coil (s) forms an electrical resonant circuit,
und daß beim Übergang von Schmelzbetrieb mit geringerer Rührbewegung in der Schmelze auf Schmelz- oder Warmhaitebe- trieb mit größerer Rührbewegung bzw. beim umgekehrten Über¬ gang die Kondensatorkapazität und/oder die im Schwingkreis vorhandene Induktivität erhöht bzw. erniedrigt werden.and that during the transition from melting operation with less stirring movement in the melt to melting or hot operation with greater stirring movement or with the reverse transition, the capacitor capacity and / or the inductance present in the resonant circuit are increased or decreased.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Kapazität und/oder die Induktivität des Schwingkreises wenigstens um 1/3 ihres jeweiligen Gesamtwertes erhöht bzw. erniedrigt werden.2. The method according to claim 1, characterized in that the capacitance and / or the inductance of the resonant circuit are increased or decreased by at least 1/3 of their respective total value.
3. Verfahren nach Anspruch 1 oder 2, dadurch ge- kennzeichnet, daß die Kapazität und/oder die Induktivität des Schwingkreises um den zweifachen Betrag ihres Gesamt¬ wertes erhöht bzw. erniedrigt werden. 3. The method according to claim 1 or 2, characterized in that the capacitance and / or the inductance of the resonant circuit are increased or decreased by twice the amount of their total value.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß bei vollem Ofen bzw. nahezu ganz mit Metallschmelze gefülltem Ofentiegel nur ein Teil der Spu¬ lenwindungen, insbesondere derjenige in der Nähe der Schmelzbadoberfläche, an die elektrische Spannungsversor¬ gungseinrichtung des Induktionsofens angeschlossen wird, wobei der übrige Teil der Spule nicht beaufschlagt wird.4. The method according to any one of claims 1 to 3, characterized in that when the furnace is full or almost completely filled with molten metal, only part of the coil turns, in particular that near the melt surface, to the electrical voltage supply device of the induction furnace is connected, whereby the remaining part of the coil is not acted upon.
5. Verfahren nach einem der vorhergehenden Ansprüche, da- durch gekennzeichnet, daß bei mehreren getrennten Induk¬ tionsspulenteilen lediglich die obere bzw. die oberen Teil¬ spulen eingeschaltet werden.5. The method according to any one of the preceding claims, characterized in that in the case of a plurality of separate induction coil parts, only the upper or the upper part coils are switched on.
6. Verfahren nach Anspruch 4 oder 5, dadurch gekennzeich- net, daß an die beaufschlagtetn) obere(n) Teilspule(n) die gesamte Kondensatorkapazität, die sonst beim Schmelzbetrieb mit geringerer Rührbewegung in der Schmelze und beim Beauf¬ schlagen der gesamten Spule verwendet wird, angeschlossen wird.6. The method according to claim 4 or 5, characterized in that to the loaded (upper) sub-coil (s) the total capacitor capacity, which otherwise used in the melting operation with less stirring movement in the melt and when the entire coil is loaded is connected.
7. Elektrische Schalteinheit für kernlose Induk¬ tionschmelz- und/oder -warmhalteöfen mit einer Induktions¬ frequenz im Bereich von Netz- bis Mittelfrequenz,7. Electrical switching unit for coreless induction melting and / or holding furnaces with an induction frequency in the range from mains to medium frequency,
welche mindestens eine ein- oder mehrteilige, um einen Ofentiegel herum angeordnete Induktionsspule sowie eine elektrische Spannungsversorgungseinrichtung mit einem Fre¬ quenzumformer bzw. -Umrichter aufweisen,which have at least one one-part or multi-part induction coil arranged around a furnace crucible and an electrical voltage supply device with a frequency converter or converter,
dadurch gekennzeichnet,characterized,
daß innerhalb des elektrischen Leitungsweges zwischen der(den) Induktionsspule(n) (3;3a,3b) und dem Frequenz¬ umformer (6) mindestens ein Kondensator (8,9;15;17,18,19) vorgesehen ist,that at least one capacitor (8,9; 15; 17,18,19) is provided within the electrical conduction path between the induction coil (s) (3; 3a, 3b) and the frequency converter (6),
wobei der(die) Kondensator(en) zu der(den) Induktions- spule(n) elektrisch parallel geschaltet ist(sind) und zu- -1 ϊ -the capacitor (s) being (are) electrically connected in parallel with the induction coil (s) and -1 ϊ -
sammen mit diesem(n) einen elektrischen Schwingkreis bil- det(n), dessen Eigenfrequenz auf die jeweilige Induktions¬ frequenz abgestimmt ist,together with this forms an electrical resonant circuit, the natural frequency of which is matched to the respective induction frequency,
und wobei innerhalb des genannten Leitungsweges elektrische Schaltelemente vorgesehen sind, mittels derer die Kapazität und/oder die Induktivität des Schwingkreises und damit des¬ sen Eigenfrequenz stufenförmig einstellbar sind.and wherein electrical switching elements are provided within said line path, by means of which the capacitance and / or the inductance of the resonant circuit and thus its natural frequency can be adjusted in steps.
8. Schalteinheit nach Anspruch 7, dadurch gekennzeichnet, daß die Schaltelemente derart ausgebildet sind, daß bei de¬ ren Betätigung zunächst zueinander in Reihe geschaltete Kondensatoren und/oder Induktionsspulen zueinander parallel geschaltet werden und umgekehrt.8. Switching unit according to claim 7, characterized in that the switching elements are designed such that when de¬ ren actuation, capacitors and / or induction coils connected in series with one another are connected in parallel with one another and vice versa.
9. Schalteinheit nach Anspruch 7 oder 8, dadurch gekenn¬ zeichnet, daß mindestens zwei Schaltelemente mittels einer elektrischen bzw. elektro echanisehen Verriegelung gegen¬ einander sperrbar sind.9. Switching unit according to claim 7 or 8, characterized gekenn¬ characterized in that at least two switching elements can be locked against each other by means of an electrical or electro-mechanical lock.
10. Schalteinheit nach einem der Ansprüche 7 bis 9, da¬ durch gekennzeichnet, daß die Induktionsspule(n) mittels wenigstens einer Anzapfung geteilt ist(sind).10. Switching unit according to one of claims 7 to 9, da¬ characterized in that the induction coil (s) is (are) divided by means of at least one tap.
11. Schalteinheit nach einem der Ansprüche 7 - 10, da¬ durch gekennzeichnet, daß lediglich ein Teil der Windungen der Induktionsspule(n) mit der Vorsorgungsspannung beauf¬ schlagt ist.11. Switching unit according to one of claims 7 - 10, characterized by the fact that only a part of the turns of the induction coil (s) is acted upon by the supply voltage.
12. Schalteinheit nach Anspruch 11, dadurch gekenn¬ zeichnet, daß der in der Nähe der Schmelzbadoberfläche lie¬ gende Teil der Windungen der Induktionsspule(n) mit der Versorgungsspannung beaufschlagt ist.12. Switching unit according to claim 11, characterized in that the part of the turns of the induction coil (s) lying in the vicinity of the molten bath surface is acted upon by the supply voltage.
13. Schalteinheit nach einem der Ansprüche 7 bis 12, da¬ durch gekennzeichnet, daß mindestens zwei elektrisch ge¬ trennte Induktionsspulenteile vorgesehen sind. 13. Switching unit according to one of claims 7 to 12, characterized in that at least two electrically separate induction coil parts are provided.
14. Schalteinheit nach Anspruch 13, dadurch gekenn¬ zeichnet, daß wenigstens der obere Induktionsspulenteil mit der gesamten Kapazität der Kondensatoren beaufschlagt ist. 14. Switching unit according to claim 13, characterized gekenn¬ characterized in that at least the upper induction coil part is acted upon by the entire capacitance of the capacitors.
EP95910392A 1994-02-11 1995-02-10 Process for operating coreless induction melting and/or holding furnaces and electric switching unit suitable therefor Expired - Lifetime EP0744117B1 (en)

Applications Claiming Priority (3)

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DE4404412 1994-02-11
DE4404412 1994-02-11
PCT/DE1995/000175 WO1995022238A1 (en) 1994-02-11 1995-02-10 Process for operating coreless induction melting and/or holding furnaces and electric switching unit suitable therefor

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DE59502256D1 (en) 1998-06-25

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