EP0384174A2 - Method of monitoring the solidification process in continuous casting - Google Patents

Method of monitoring the solidification process in continuous casting Download PDF

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Publication number
EP0384174A2
EP0384174A2 EP90101969A EP90101969A EP0384174A2 EP 0384174 A2 EP0384174 A2 EP 0384174A2 EP 90101969 A EP90101969 A EP 90101969A EP 90101969 A EP90101969 A EP 90101969A EP 0384174 A2 EP0384174 A2 EP 0384174A2
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EP
European Patent Office
Prior art keywords
continuous casting
sensor coils
monitoring
solidification process
levitation coil
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EP90101969A
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German (de)
French (fr)
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EP0384174A3 (en
EP0384174B1 (en
Inventor
Andreas Dr.-Ing. Krause
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KM Kabelmetal AG
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KM Kabelmetal AG
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Priority to AT90101969T priority Critical patent/ATE93424T1/en
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    • 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
    • B22D11/14—Plants for continuous casting
    • B22D11/145—Plants for continuous casting for upward casting
    • 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
    • B22D11/186—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by using electric, magnetic, sonic or ultrasonic means

Definitions

  • the invention relates to a method according to the preamble of patent claim 1.
  • a casting process also known as upward casting, which permits the continuous production of metal strands from the melt, is known, for example, from DE-A-30 49 353. It is essential for this casting process that a certain section of a water-cooled mold or the solidifying metal column located inside the mold is concentrically surrounded by a special induction coil, the so-called levitation coil.
  • This levitation coil generally consists of a larger number, for example 6, of winding groups arranged one above the other, which are coupled to one another in such a way that an upward moving alternating electromagnetic field is formed within the levitation coil as soon as the levitation coil is excited by a three-phase voltage source.
  • the magnetic field of the levitation coil induces eddy currents in the molten metal.
  • the radial and axial components of the magnetic induction generated by the levitation coil have the effect that forces are generated in the axial direction (upward) and in the radial direction on the liquid or already solidified metal through which the eddy currents flow. These forces ensure that the pressure of the melt and the strand shell on the mold wall are reduced and an increase in the casting speed can be achieved by lower frictional forces.
  • the invention is therefore based on the object of specifying a measuring method with which the position and extent of the solidification front can be identified in a simple manner and with sufficient accuracy during the casting process.
  • the invention is based essentially on the knowledge that the electrical conductivity of metals increases during the transition from the molten to the solid state and with decreasing temperature.
  • the electrical conductivity at the solidification point suddenly increases to a significantly higher value than in the molten state.
  • the electrical conductivity also increases significantly in the temperature range at which the metal alloy solidifies.
  • the temperature of the melt decreases with increasing height due to the progressive heat removal within the continuous casting mold.
  • the proportion of solidified metal increases until the central metal column is completely solidified.
  • the distribution of the electrical conductivity changes specifically within the central metal column. This makes it possible Assign a characteristic conductivity distribution to each cross-sectional plane of the mold perpendicular to the direction of movement of the strand.
  • the area of cooling and solidification of the melt within the mold has spread far apart.
  • the length of this area for example when casting round solid profiles, is a multiple of the strand diameter. Accordingly, the conductivity distribution changes slowly over the length of the mold.
  • An essential feature of upward casting is that almost the entire mold length is surrounded by a levitation coil.
  • the excitation frequency is chosen so that the penetration depth of the magnetic field and the strand radius are of the same order of magnitude. This ensures that the outer area of the strand cross-section, in which the solidification begins and which is of interest for the control of the casting process, is penetrated to a sufficient extent by the field of excitation.
  • a secondary field is generated by the eddy currents, which can provide information about the conductivity distribution within the metal column.
  • the continuous casting mold consists, for example, of a tubular body, around which a heat exchanger is arranged in a ring. Since the walls of the heat exchanger and the mold are relatively thin and are made of materials that weaken the magnetic field of the levitation coil as little as possible with high thermal conductivity, the secondary field is also only slightly weakened.
  • the sensor coils arranged concentrically around the central column of the molten metal or the already solidified metal deliver signals (measuring voltages) to a transmitter via the secondary field. After appropriate evaluation of these signals, it is possible to make statements about the position and extent of the solidification front and to control the solidification process directly during the casting process. Fluctuations or changes in the solidification process, which may be noticeable in the increased occurrence of irregularities in the area of the strand cross section near the surface, are thus recognized at a stage before the strand reaches the exit area of the mold.
  • the sensor coils are particularly advantageously located inside the levitation coil and outside the continuous casting molds.
  • the windings of the sensor coil then have a diameter that lies between the inside diameter of the levitation coil and the outside diameter of the continuous casting mold.
  • the sensor coils can also be arranged in the space between the levitation coil and the heat exchanger wall or in the mold lining.
  • the sensor coils preferably consist of one or more turns of a thin insulated wire.
  • the wire is spirally wound in several turns on the outer surface of the heat exchanger outer wall in one or more layers as closely as possible.
  • the two wire ends of each sensor coil are led to a transmitter, which processes the voltage signal occurring at the wire ends during operation in a suitable manner.
  • the voltage induced in each sensor coil by the alternating field of the levitation coil is a function of the frequency, the current intensity of the current flowing through the levitation coil and the conductivity distribution within the central metal column. Furthermore, the induced voltage is dependent on the geometry of the sensor coils and levitation coil as well as their arrangement to one another.
  • the cooling of the liquid or solidified metal column leads to an increase in conductivity.
  • This increase in conductivity is indicated by a decrease in the amplitude of the measuring voltage while the excitation field strength remains the same.
  • the cause of the change in a measurement signal cannot be clearly identified if only a single sensor coil is used. Therefore, at least two sensor coils are preferably arranged one above the other and the measuring voltages supplied to the transmitter are compared with each other.
  • the measurement voltage which occurs when the metal is in the molten state is expediently chosen as the reference signal.
  • the further cooling of the strand above a temperature at which the solidification begins then only leads to a relatively small decrease in the voltage amplitude at a sensor coil during the temperature changes usually occurring during the casting process, while the entire course of the solidification by a significantly more pronounced drop in the voltage amplitude is marked.
  • the conductivity distribution during the cooling and solidification of the melt within the continuous casting mold results in a profile of measuring voltages on the sensor coils arranged one above the other, with which the position and the extent of the solidification front can be determined with sufficient accuracy. In this way, an uneven solidification course during the casting process can be recognized immediately.
  • An impermissible migration of the solidification front from the desired position in the casting direction can be recognized by the fact that the measuring voltages which are fed to the transmitter from the sensor coils arranged further in the casting direction have higher values.
  • a short-term sticking of the still thin strand shell deviating from normal operation at a certain position within the continuous casting mold is manifested, for example, by a significant drop in the measuring voltage in the sensor coil responsible for the location of the fault.
  • Another advantage of the method according to the invention is that even casting errors, such as cracks, can be identified from the comparison of the measurement signals of a plurality of sensor coils before the strand has left the mold and larger quantities of defective material have been generated.
  • the figure shows a schematic representation of a cross section through a tubular continuous casting mold 1 arranged in an upright position, which is surrounded by a heat exchanger 3 in an annular manner for cooling the liquid metal 2.
  • Coolant with a high flow rate is continuously fed in at the coolant inlet 4, flows through the heat exchanger 3 and is discharged again in the upper part of the heat exchanger 3 at the coolant outlet 5.
  • the levitation coil is designated by 6, the turns of which are arranged essentially perpendicular to the axis of the continuous casting mold 1 between the coolant inlet 4 and the coolant outlet 5 and are connected to a multiphase voltage source, not shown.
  • the alternating electromagnetic field of the levitation coil 6 induces eddy currents in the liquid metal 2, which cause the metal column 7 and the liquid metal to experience an upward lifting effect.
  • sensor coils 8 are arranged one above the other such that their distance from the outer wall of the heat exchanger 3 is the same.
  • 6 sensor coils 8 are shown, the measurement voltage profile of which permits overall sufficient information about the course of the solidification front 9. For higher demands on the accuracy of the identification of the position and extent of the solidification front 9, it is advantageous to provide sensor coils 8 at a distance of at least 1 cm.
  • the levitation coil 6 and the sensor coils 8 have a concentric position around the cylindrical continuous casting mold 1, the inside diameter of which is approximately 20 mm.
  • the sensor coils 8 are each arranged within the levitation coil 6 at a height at which the mean turn of each turn group is located, which is excited with the same phase in each case.
  • the diameter of the levitation coil 6 is approximately 41 mm, while the turns of an excitation phase have a height of 24 mm.
  • the excitation frequency was 2,000 Hz.
  • Each of the 6 sensor coils 8, which are wound from 8 turns of a thin insulated copper wire has a diameter of approximately 35 mm.
  • the effective values in the vicinity of the solidification front 9 were in the range from 86 to 95%.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Continuous Casting (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
  • Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

Abstract

For trouble-free progress of the casting process in continuous casting, as accurate data as possible on the position and extent of the solidification front within the continuous casting mould surrounded by an electromagnetic moving field are required. <??>The method according to the invention for monitoring the solidification process uses the signals of at least two sensor coils arranged concentrically around the continuous casting mould. The signals are fed to a measuring transducer and processed in an appropriate manner. The arrangement of the sensor coils within the levitation coil generating the moving field is particularly preferred.

Description

Die Erfindung betrifft ein Verfahren nach dem Oberbegriff des Patentanspruchs 1.The invention relates to a method according to the preamble of patent claim 1.

Ein auch als Aufwärtsstranggießen bezeichneter Gießprozeß, der die kontinuierliche Erzeugung von Metallsträngen aus der Schmelze gestattet, ist beispielsweise aus der DE-A-30 49 353 bekannt. Wesentlich für diesen Gießprozeß ist, daß ein be­stimmter Abschnitt einer wassergekühlten Kokille beziehungs­weise die sich im Innern der Kokille befindliche erstarrende Metallsäule konzentrisch von einer speziellen Induktionsspule, der sogenannten Levitationsspule, umgeben ist. Diese Levita­tionsspule besteht in der Regel aus einer größeren Anzahl, beispielsweise 6, übereinander angeordneter Wicklungsgruppen, die so miteinander gekoppelt sind, daß sich innerhalb der Levitationsspule ein aufwärts bewegendes elektromagnetisches Wechselfeld ausbildet, sobald die Levitationsspule von einer dreiphasigen Spannungsquelle erregt wird. Das Magnetfeld der Levitationsspule induziert in der Metallschmelze Wirbel­ströme. Die radiale und axiale Komponente der durch die Le­vitationsspule erzeugten magnetischen Induktion bewirken, daß auf das von den Wirbelströmen durchflossene flüssige oder bereits erstarrte Metall Kräfte in axialer Richtung (aufwärts) und in radialer Richtung erzeugt werden. Diese Kräfte sorgen dafür, daß der Druck der Schmelze und der Strangschale auf die Kokillenwand vermindert werden und so durch geringere Reibungskräfte eine Steigerung der Gießgeschwindigkeit er­zielt werden kann.A casting process, also known as upward casting, which permits the continuous production of metal strands from the melt, is known, for example, from DE-A-30 49 353. It is essential for this casting process that a certain section of a water-cooled mold or the solidifying metal column located inside the mold is concentrically surrounded by a special induction coil, the so-called levitation coil. This levitation coil generally consists of a larger number, for example 6, of winding groups arranged one above the other, which are coupled to one another in such a way that an upward moving alternating electromagnetic field is formed within the levitation coil as soon as the levitation coil is excited by a three-phase voltage source. The magnetic field of the levitation coil induces eddy currents in the molten metal. The radial and axial components of the magnetic induction generated by the levitation coil have the effect that forces are generated in the axial direction (upward) and in the radial direction on the liquid or already solidified metal through which the eddy currents flow. These forces ensure that the pressure of the melt and the strand shell on the mold wall are reduced and an increase in the casting speed can be achieved by lower frictional forces.

Für den reibungslosen Ablauf des Gießprozesses ist es erfor­derlich, eventuelle Abweichungen von der Sollposition der Erstarrungsfront innerhalb der Stranggießkokille verfolgen zu können, um dann durch rechtzeitige Veränderung der Gieß­parameter darauf zu reagieren.In order for the casting process to run smoothly, it is necessary to be able to track any deviations from the set position of the solidification front within the continuous casting mold, in order to then react to them by changing the casting parameters in good time.

Der Erfindung liegt daher die Aufgabe zugrunde, ein Meßver­fahren anzugeben, mit dem während des Gießprozesses auf ein­fache Weise und mit hinreichender Genauigkeit die Lage und Ausdehnung der Erstarrungsfront identifiziert werden kann.The invention is therefore based on the object of specifying a measuring method with which the position and extent of the solidification front can be identified in a simple manner and with sufficient accuracy during the casting process.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß Si­gnale von konzentrisch um die Stranggießkokille angeordneten Sensorspulen einem Meßumformer zugeführt und ausgewertet wer­den. Vorteilhafte Weiterbildungen der Erfindung ergeben sich aus den Unteransprüchen.This object is achieved in that signals from sensor coils arranged concentrically around the continuous casting mold are fed to a measuring transducer and evaluated. Advantageous developments of the invention result from the subclaims.

Der Erfindung liegt im wesentlichen die Erkenntnis zugrunde, daß die elektrische Leitfähigkeit von Metallen beim Übergang von dem schmelzflüssigen in den festen Zustand und mit abneh­mender Temperatur ansteigt. Bei reinen Metallen erhöht sich die elektrische Leitfähigkeit am Erstarrungspunkt sprunghaft auf einen deutlich höheren Wert als im schmelzflüssigen Zu­stand. Bei Legierungen erhöht sich die elektrische Leitfähig­keit ebenfalls deutlich in dem Temperaturbereich, bei dem Er­starrung der Metallegierung einsetzt.The invention is based essentially on the knowledge that the electrical conductivity of metals increases during the transition from the molten to the solid state and with decreasing temperature. With pure metals, the electrical conductivity at the solidification point suddenly increases to a significantly higher value than in the molten state. With alloys, the electrical conductivity also increases significantly in the temperature range at which the metal alloy solidifies.

Die Temperatur der Schmelze nimmt aufgrund fortschreitendem Wärmeentzugs innerhalb der Stranggießkokille mit zunehmender Höhe ab. Abhängig von der jeweils erreichten Position erhöht sich auch der Anteil des erstarrten Metalls, bis schließlich die zentrale Metallsäule vollständig erstarrt ist. Entspre­chend der fortschreitenden Abkühlung des Metalls sowie der Änderung der Phasenanteile während der Erstarrung, ändert sich die Verteilung der elektrischen Leitfähigkeit spezifisch innerhalb der zentralen Metallsäule. Damit wird es möglich, jeder Querschnittsebene der Kokille senkrecht zur Bewegungs­richtung des Strangs eine charakteristische Leitfähigkeits­verteilung zuzuordnen.The temperature of the melt decreases with increasing height due to the progressive heat removal within the continuous casting mold. Depending on the position reached, the proportion of solidified metal increases until the central metal column is completely solidified. In accordance with the progressive cooling of the metal and the change in the phase components during solidification, the distribution of the electrical conductivity changes specifically within the central metal column. This makes it possible Assign a characteristic conductivity distribution to each cross-sectional plane of the mold perpendicular to the direction of movement of the strand.

Als Folge der relativ hohen Gießgeschwindigkeit ist der Be­reich der Abkühlung und Erstarrung der Schmelze innerhalb der Kokille weit auseinandergezogen. Die Länge dieses Be­reichs beträgt beispielsweise beim Gießen von runden Voll­profilen ein Mehrfaches des Strangdurchmessers. Die Leit­fähigkeitsverteilung ändert sich also dementsprechend lang­sam über die Länge der Kokille. Ein wesentliches Merkmal des Aufwärtsstranggießens ist, daß nahezu die gesamte Kokillen­länge von einer Levitationsspule umgeben ist. Die Erreger­frequenz wird so gewählt, daß die Eindringtiefe des Magnet­felds und der Strangradius die gleiche Größenordnung aufwei­sen. Damit ist sichergestellt, daß der äußere Bereich des Strangquerschnitts, in dem die Erstarrung einsetzt und der für die Kontrolle des Gießprozesses von Interesse ist, in hinreichendem Ausmaß von dem Erregerfeld durchdrungen wird. Dabei wird von den Wirbel strömen ein Sekundärfeld erzeugt, das Informationen über die Leitfähigkeitsverteilung inner­halb der Metallsäule liefern kann.As a result of the relatively high casting speed, the area of cooling and solidification of the melt within the mold has spread far apart. The length of this area, for example when casting round solid profiles, is a multiple of the strand diameter. Accordingly, the conductivity distribution changes slowly over the length of the mold. An essential feature of upward casting is that almost the entire mold length is surrounded by a levitation coil. The excitation frequency is chosen so that the penetration depth of the magnetic field and the strand radius are of the same order of magnitude. This ensures that the outer area of the strand cross-section, in which the solidification begins and which is of interest for the control of the casting process, is penetrated to a sufficient extent by the field of excitation. A secondary field is generated by the eddy currents, which can provide information about the conductivity distribution within the metal column.

Die Stranggießkokille besteht beispielsweise aus einem rohr­förmigen Körper, um den ein Wärmetauscher ringförmig ange­ordnet ist. Da die Wände des Wärmetauschers und der Kokille relativ dünn sind und aus Materialien gefertigt werden, die bei hoher Wärmeleitfähigkeit das Magnetfeld der Levitations­spule möglichst wenig schwächen, wird auch das Sekundärfeld nur wenig abgeschwächt. Die konzentrisch um die zentrale Säule der Metallschmelze beziehungsweise des bereits erstarrten Me­talls angeordneten Sensorspulen liefern Signale (Meßspannungen) über das Sekundärfeld an einen Meßumformer. Nach entsprechen­der Auswertung dieser Signale ist es möglich, Aussagen über die Position und Ausdehung der Erstarrungsfront zu machen und den Erstarrungsverlauf während des Gießprozesses direkt zu kontrollieren. Schwankungen oder Veränderungen im Erstarrungs­verlauf, die sich im verstärkten Auftreten von Unregelmäßig­keiten im oberflächennahen Bereich des Strangquerschnitts bemerkbar machen können, werden somit bereits in einem Stadi­um erkannt, bevor der Strang den Austrittsbereich der Ko­kille erreicht.The continuous casting mold consists, for example, of a tubular body, around which a heat exchanger is arranged in a ring. Since the walls of the heat exchanger and the mold are relatively thin and are made of materials that weaken the magnetic field of the levitation coil as little as possible with high thermal conductivity, the secondary field is also only slightly weakened. The sensor coils arranged concentrically around the central column of the molten metal or the already solidified metal deliver signals (measuring voltages) to a transmitter via the secondary field. After appropriate evaluation of these signals, it is possible to make statements about the position and extent of the solidification front and to control the solidification process directly during the casting process. Fluctuations or changes in the solidification process, which may be noticeable in the increased occurrence of irregularities in the area of the strand cross section near the surface, are thus recognized at a stage before the strand reaches the exit area of the mold.

Mit besonderem Vorteil befinden sich die Sensorspulen inner­halb der Levitationsspule und außerhalb der Stranggießkokil­len. Die Wicklungen der Sensorspule besitzen dann einen Durch­messer, der zwischen dem Innendurchmesser der Levitations­spule und dem Außendurchmesser der Stranggießkokille liegt. Die Sensorspulen können jedoch auch in dem Raum zwischen Le­vitationsspule und Wärmetauscherwand oder in der Kokillen­auskleidung angeordnet sein.The sensor coils are particularly advantageously located inside the levitation coil and outside the continuous casting molds. The windings of the sensor coil then have a diameter that lies between the inside diameter of the levitation coil and the outside diameter of the continuous casting mold. However, the sensor coils can also be arranged in the space between the levitation coil and the heat exchanger wall or in the mold lining.

Vorzugsweise bestehen die Sensorspulen aus einer oder mehreren Windungen eines dünnen isolierten Drahts. In einer bevorzug­ten Ausführungsform wird der Draht spiralförmig in mehreren Windungen auf der Außenoberfläche der Wärmetauscheraußenwand in einer oder mehreren Schichten möglichst eng aufgewickelt. Die beiden Drahtenden jeder Sensorspule werden zu einem Meß­umformer geführt, der das an den Drahtenden während des Be­triebs auftretende Spannungssignal in geeigneter Weise ver­arbeitet.The sensor coils preferably consist of one or more turns of a thin insulated wire. In a preferred embodiment, the wire is spirally wound in several turns on the outer surface of the heat exchanger outer wall in one or more layers as closely as possible. The two wire ends of each sensor coil are led to a transmitter, which processes the voltage signal occurring at the wire ends during operation in a suitable manner.

Die in jeder Sensorspule durch das Wechselfeld der Levita­tionsspule induzierte Spannung ist eine Funktion der Fre­quenz, der Stromstärke des die Levitationsspule durchflie­ßenden Stroms und der Leitfähigkeitsverteilung innerhalb der zentralen Metallsäule. Ferner ist die induzierte Spannung ab­hängig von der Geometrie von Sensorspulen und Levitations­spule sowie ihrer Anordnung zueinander.The voltage induced in each sensor coil by the alternating field of the levitation coil is a function of the frequency, the current intensity of the current flowing through the levitation coil and the conductivity distribution within the central metal column. Furthermore, the induced voltage is dependent on the geometry of the sensor coils and levitation coil as well as their arrangement to one another.

Grundsätzlich führt die Abkühlung der flüssigen oder ver­festigten Metallsäule zu einem Anstieg der Leitfähigkeit. Diese Leitfähigkeitserhöhung wird durch eine Abnahme der Amplitude der Meßspannung bei gleichbleibender Erregungs­feldstärke angezeigt. Die Ursache der Änderung eines Meß­signals läßt sich jedoch nicht eindeutig identifizieren, wenn nur eine einzige Sensorspule verwendet wird. Vorzugs­weise werden deshalb mindestens zwei Sensorspulen überein­ander angeordnet und die jeweils dem Meßumformer zugeführ­ten Meßspannungen einander gegenübergestellt. Als Referenz­signal wird dabei zweckmäßigerweise die Meßspannung gewählt, die beim schmelzflüssigen Zustand des Metalls auftritt. Die weitere Abkühlung des Strangs oberhalb einer Temperatur, bei der die Erstarrung beginnt, führt dann bei den üblicherweise beim Gießprozeß auftretenden Temperaturänderungen nur noch zu einer relativ geringen Erniedrigung der Spannungsamplitude an einer Sensorspule, während der gesamte Verlauf der Erstar­rung durch einen wesentlich deutlicheren Abfall der Span­nungsamplitude gekennzeichnet ist. Die Leitfähigkeitsvertei­lung während der Abkühlung und Erstarrung der Schmelze inner­halb der Stranggießkokille ergibt ein Profil von Meßspan­nungen an den übereinander angeordneten Sensorspulen, mit dem die Position und die Ausdehnung der Erstarrungsfront in hinreichender Genauigkeit bestimmt werden kann. Ein un­gleichmäßiger Erstarrungsverlauf während des Gießprozesses kann auf diese Weise sofort erkannt werden.Basically, the cooling of the liquid or solidified metal column leads to an increase in conductivity. This increase in conductivity is indicated by a decrease in the amplitude of the measuring voltage while the excitation field strength remains the same. However, the cause of the change in a measurement signal cannot be clearly identified if only a single sensor coil is used. Therefore, at least two sensor coils are preferably arranged one above the other and the measuring voltages supplied to the transmitter are compared with each other. The measurement voltage which occurs when the metal is in the molten state is expediently chosen as the reference signal. The further cooling of the strand above a temperature at which the solidification begins then only leads to a relatively small decrease in the voltage amplitude at a sensor coil during the temperature changes usually occurring during the casting process, while the entire course of the solidification by a significantly more pronounced drop in the voltage amplitude is marked. The conductivity distribution during the cooling and solidification of the melt within the continuous casting mold results in a profile of measuring voltages on the sensor coils arranged one above the other, with which the position and the extent of the solidification front can be determined with sufficient accuracy. In this way, an uneven solidification course during the casting process can be recognized immediately.

Sämtliche Störungen des Erstarrungsverlaufs können an charak­teristischen Signalverläufen festgestellt werden.All disturbances in the solidification process can be determined using characteristic signal processes.

Eine unzulässige Wanderung der Erstarrungsfront aus der Soll­position in Gießrichtung kann daran erkannt werden, daß die Meßspannungen, die dem Meßumformer von den weiter in Gieß­richtung angeordneten Sensorspulen zugeführt werden, höhere Werte aufweisen. Ein vom Normal betrieb abweichendes kurz­fristiges Hängenbleiben der noch dünnen Strangschale an einer bestimmten Position innerhalb der Stranggießkokille äußert sich beispielsweise durch einen deutlichen Abfall der Meß­spannung in der für den Ort der Störung zuständigen Sensor­spule. Ein weiterer Vorteil des erfindungsgemäßen Verfahrens liegt darin, daß aus dem Vergleich der Meßsignale mehrerer Sensorspulen sogar auftretende Gußfehler, wie zum Beispiel Anrisse, identifiziert werden können, noch ehe der Strang die Kokille verlassen hat und größere Mengen fehlerhaften Materials erzeugt worden sind.An impermissible migration of the solidification front from the desired position in the casting direction can be recognized by the fact that the measuring voltages which are fed to the transmitter from the sensor coils arranged further in the casting direction have higher values. A short-term sticking of the still thin strand shell deviating from normal operation at a certain position within the continuous casting mold is manifested, for example, by a significant drop in the measuring voltage in the sensor coil responsible for the location of the fault. Another advantage of the method according to the invention is that even casting errors, such as cracks, can be identified from the comparison of the measurement signals of a plurality of sensor coils before the strand has left the mold and larger quantities of defective material have been generated.

Anhand des in der Figur dargestellten Ausführungsbeispiels wird die Erfindung im folgenden noch näher erläutert.Based on the embodiment shown in the figure, the invention is explained in more detail below.

Die Figur zeigt in schematischer Darstellung einen Quer­schnitt durch eine rohrförmige in aufrechter Stellung ange­ordnete Stranggießkokille 1, die zur Kühlung des flüssigen Metalls 2 von einem Wärmetauscher 3 ringförmig umgeben ist. Kühlmittel mit großer Strömungsgeschwindigkeit wird konti­nuierlich beim Kühlmittelzulauf 4 eingespeist, strömt durch den Wärmetauscher 3 und wird im oberen Teil des Wärmetau­schers 3 beim Kühlmittelablauf 5 wieder abgeleitet. Mit 6 ist die Levitationsspule bezeichnet, deren Windungen im we­sentlichen senkrecht zur Achse der Stranggießkokille 1 zwi­schen Kühlmittelzulauf 4 und Kühlmittelablauf 5 angeordnet und mit einer nicht dargestellten mehrphasigen Spannungs­quelle verbunden sind. Das elektromagnetische Wechselfeld der Levitationsspule 6 induziert in dem flüssigen Metall 2 Wirbelströme, die bewirken, daß die Metallsäule 7 und das flüssige Metall eine nach oben gerichtete Hubwirkung erfahren. In dem Raum zwischen Wärmetauscher 3 und Levitationsspule 6 sind Sensorspulen 8 derart übereinander angeordnet, daß ihr Abstand zur Außenwand des Wärmetauschers 3 gleich ist. Bei­spielhaft sind 6 Sensorspulen 8 dargestellt, deren Meßspan­nungsprofil eine insgesamt ausreichende Information über den Verlauf der Erstarrungsfront 9 zuläßt. Für höhere Anforde­rungen an die Genauigkeit der Identifikation von Lage und Ausdehnung der Erstarrungsfront 9 ist es vorteilhaft, im Ab­stand von mindestens 1 cm Sensorspulen 8 vorzusehen.The figure shows a schematic representation of a cross section through a tubular continuous casting mold 1 arranged in an upright position, which is surrounded by a heat exchanger 3 in an annular manner for cooling the liquid metal 2. Coolant with a high flow rate is continuously fed in at the coolant inlet 4, flows through the heat exchanger 3 and is discharged again in the upper part of the heat exchanger 3 at the coolant outlet 5. The levitation coil is designated by 6, the turns of which are arranged essentially perpendicular to the axis of the continuous casting mold 1 between the coolant inlet 4 and the coolant outlet 5 and are connected to a multiphase voltage source, not shown. The alternating electromagnetic field of the levitation coil 6 induces eddy currents in the liquid metal 2, which cause the metal column 7 and the liquid metal to experience an upward lifting effect. In the space between heat exchanger 3 and levitation coil 6 sensor coils 8 are arranged one above the other such that their distance from the outer wall of the heat exchanger 3 is the same. By way of example, 6 sensor coils 8 are shown, the measurement voltage profile of which permits overall sufficient information about the course of the solidification front 9. For higher demands on the accuracy of the identification of the position and extent of the solidification front 9, it is advantageous to provide sensor coils 8 at a distance of at least 1 cm.

Die Levitationsspule 6 und die Sensorspulen 8 weisen eine konzentrische Lage um die zylindrische Stranggießkokille 1 auf, deren Innendurchmesser etwa 20 mm beträgt. Die Sensor­spulen 8 sind innerhalb der Levitationsspule 6 jeweils in einer Höhe angeordnet, in der auch die mittlere Windung einer jeden Windungsgruppe liegt, die mit jeweils gleicher Phase erregt wird. Der Durchmesser der Levitationsspule 6 beträgt etwa 41 mm, während die Windungen einer Erregerphase eine Höhe von 24 mm aufweisen. Die Erregerfrequenz betrug 2 000 Hz. Jede der 6 Sensorspulen 8, die aus 8 Windungen eines dünnen isolierten Kupferdrahts gewickelt sind, besitzt einen Durch­messer von etwa 35 mm.The levitation coil 6 and the sensor coils 8 have a concentric position around the cylindrical continuous casting mold 1, the inside diameter of which is approximately 20 mm. The sensor coils 8 are each arranged within the levitation coil 6 at a height at which the mean turn of each turn group is located, which is excited with the same phase in each case. The diameter of the levitation coil 6 is approximately 41 mm, while the turns of an excitation phase have a height of 24 mm. The excitation frequency was 2,000 Hz. Each of the 6 sensor coils 8, which are wound from 8 turns of a thin insulated copper wire, has a diameter of approximately 35 mm.

Führt man nun die jeweiligen Signale der Sensorspulen einem Meßumformer zu, so ergeben sich folgende Effektivwerte der gleichgerichteten Meßspannung, wenn als Bezugsgröße das ent­sprechende Signal bei Luft zugrunde gelegt wird: Luft 100 % flüssige Kupferschmelze ca. 1 250 °C 97,9 % erstarrtes Kupfer ca. 1000 °C 82,9 % If the respective signals from the sensor coils are fed to a transmitter, the following effective values of the rectified measuring voltage result if the corresponding signal in air is used as the reference variable: air 100% liquid copper smelt approx. 1 250 ° C 97.9% solidified copper approx. 1000 ° C 82.9%

Während des Gießprozesses, bei dem kontinuierlich ein Strang aus reinem Kupfer erzeugt wurde, lagen die Effektivwerte in der Umgebung der Erstarrungsfront 9 im Bereich von 86 bis 95 %.During the casting process, in which a strand of pure copper was continuously produced, the effective values in the vicinity of the solidification front 9 were in the range from 86 to 95%.

Claims (7)

1. Verfahren zur Überwachung des Erstarrungsvorgangs beim kontinuierlichen Stranggießen von Metallen mit einer Stranggießkokille, die von einer ein elektromagnetisches Wechselfeld erzeugenden Levitationsspule umgeben ist, und wobei flüssige Metallschmelze von unten in die Stranggieß­kokille eingeführt und als erstarrtes Metallprodukt im oberen Bereich abgezogen wird, dadurch gekenn­zeichnet, daß Signale von konzentrisch um die Strang­gießkokille angeordneten Sensorspulen einem Meßumformer zu­geführt und ausgewertet werden.1. A method for monitoring the solidification process in the continuous continuous casting of metals with a continuous casting mold which is surrounded by a levitation coil which generates an electromagnetic alternating field, and wherein molten metal is introduced into the continuous casting mold from below and drawn off as a solidified metal product in the upper region, characterized in that that signals from sensor coils arranged concentrically around the continuous casting mold are fed to a transmitter and evaluated. 2. Verfahren zur Überwachung des Erstarrungsvorgangs nach An­spruch 1 , dadurch gekennzeichnet, daß sich die Sensorspulen innerhalb der Levitationsspule befinden.2. A method for monitoring the solidification process according to claim 1, characterized in that the sensor coils are located within the levitation coil. 3. Verfahren zur Überwachung des Erstarrungsvorgangs nach An­spruch 1, dadurch gekennzeichnet, daß sich die Sensorspulen zwischen der Stranggießkokille und der Levitationsspule befinden.3. A method for monitoring the solidification process according to claim 1, characterized in that the sensor coils are located between the continuous casting mold and the levitation coil. 4. Verfahren zur Überwachung des Erstarrungsvorgangs nach An­spruch 3, dadurch gekennzeichnet, daß die Sensorspulen in unmittelbarer Nähe des Wärmetauschers an­geordnet sind.4. A method for monitoring the solidification process according to claim 3, characterized in that the sensor coils are arranged in the immediate vicinity of the heat exchanger. 5. Verfahren zur Überwachung des Erstarrungsvorgangs nach einem der Ansprüche 1 bis 4, dadurch gekenn­zeichnet, daß Signale von mindestens zwei Sensor­spulen ausgewertet werden.5. A method for monitoring the solidification process according to one of claims 1 to 4, characterized in that signals from at least two sensor coils are evaluated. 6. Verfahren zur Überwachung des Erstarrungsvorgangs nach einem der Ansprüche 1 bis 5, dadurch gekenn­zeichnet, daß die Sensorspulen in Gießrichtung im wesentlichen den gleichen Abstand voneinander auf­weisen.6. A method for monitoring the solidification process according to one of claims 1 to 5, characterized in that the sensor coils are at substantially the same distance from one another in the casting direction. 7. Einrichtung zur Überwachung des Erstarrungsvorgangs beim Stranggießen mit einer länglichen Stranggießkokille (1), die von einer Levitationsspule (6) umgeben ist, da­durch gekennzeichnet, daß sich zwischen der Stranggießkokille (1) und der Levitationsspule (6) Sensor­spulen (8) befinden, die konzentrisch um die Stranggieß­kokille (1) angeordnet sind und wobei die von den Sensor­spulen (8) einem Meßumformer zugeführten Signale auswert­bar sind.7. Device for monitoring the solidification process during continuous casting with an elongated continuous casting mold (1) which is surrounded by a levitation coil (6), characterized in that there are sensor coils (8) between the continuous casting mold (1) and the levitation coil (6), which are arranged concentrically around the continuous casting mold (1) and the signals supplied by the sensor coils (8) to a transmitter can be evaluated.
EP90101969A 1989-02-23 1990-02-01 Method of monitoring the solidification process in continuous casting Expired - Lifetime EP0384174B1 (en)

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AT90101969T ATE93424T1 (en) 1989-02-23 1990-02-01 METHOD OF MONITORING THE SOLIDIFICATION PROCESS IN CONTINUOUS CONTINUOUS CASTING.

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DE3905516A DE3905516A1 (en) 1989-02-23 1989-02-23 METHOD FOR MONITORING THE STARTERING PROCESS IN CONTINUOUS CONTINUOUS CASTING
DE3905516 1989-02-23

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DE19843354C1 (en) * 1998-09-22 2000-03-09 Ald Vacuum Techn Gmbh Apparatus for oriented solidification of a metal melt cast into a mold shell comprises guide sheets in the liquid metal cooling bath for purposes of controlling the bath flow produced by magnetic fields
US7010835B2 (en) * 2001-10-24 2006-03-14 Tillim Stephen L Parallel handle system and method for designing a parallel handle system
US10022787B2 (en) * 2015-08-24 2018-07-17 Retech Systems, Llc Method and system for sensing ingot position in reduced cross-sectional area molds

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FI900445A0 (en) 1990-01-29
JP2948607B2 (en) 1999-09-13
FI90507C (en) 1994-02-25
ATE93424T1 (en) 1993-09-15
CA2009758C (en) 1995-12-05
JPH02235560A (en) 1990-09-18
EP0384174A3 (en) 1991-03-06
ES2045586T3 (en) 1994-01-16
US5042559A (en) 1991-08-27
CA2009758A1 (en) 1990-08-23
DE3905516A1 (en) 1990-08-30
DE59002415D1 (en) 1993-09-30
FI90507B (en) 1993-11-15
EP0384174B1 (en) 1993-08-25

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