EP0143144B1 - Arrangement and method for heating by induction with several inductor workpieces, in particular tubes and rods - Google Patents

Arrangement and method for heating by induction with several inductor workpieces, in particular tubes and rods Download PDF

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Publication number
EP0143144B1
EP0143144B1 EP84102925A EP84102925A EP0143144B1 EP 0143144 B1 EP0143144 B1 EP 0143144B1 EP 84102925 A EP84102925 A EP 84102925A EP 84102925 A EP84102925 A EP 84102925A EP 0143144 B1 EP0143144 B1 EP 0143144B1
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EP
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Prior art keywords
resonant circuit
individual
source
circuits
disconnected
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EP84102925A
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German (de)
French (fr)
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EP0143144A2 (en
EP0143144A3 (en
Inventor
Hans Matthes
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SMS Elotherm GmbH
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AEG Elotherm GmbH
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Priority to AT84102925T priority Critical patent/ATE35760T1/en
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Publication of EP0143144A3 publication Critical patent/EP0143144A3/en
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    • 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
    • H05B6/08—Control, e.g. of temperature, of power using compensating or balancing arrangements
    • 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

Definitions

  • the invention relates to a device for inductive heating of workpieces, in particular tubes or rods, with a plurality of inductors which, with capacitors, form a plurality of individual resonant circuits fed by a common alternating current source, the power supply thereof by means of a control device as a function of a setpoint deviation of the workpiece temperature individually and / or can be switched on or off in groups, the control device only switching on the power supply of one or more individual resonant circuits when the voltage of the AC power source disappears at least for the instant of switching.
  • the AC power source is formed by a three-phase network, to the phases of which the inductors are connected separately.
  • the individual inductors are preferably switched on and off at the moment the voltage of the corresponding phase passes zero. Since individual inductors can be switched off in accordance with the heating of the workpiece, there is an asymmetrical load for the three-phase network.
  • each inductor is assigned its own generator.
  • Such a device also offers the possibility of regulating the power supply not only by switching off the inductors, but also via the generator. With such a facility, however, the higher installation effort is accepted.
  • the invention has for its object to provide a device of the type mentioned, in which, with good controllability of the power supply to the inductors, there are no harmful effects from switching the inductors on and off.
  • the alternating current source is a controlled parallel resonant circuit converter, the rectifier valves of which can then be controlled into the blocking state by the control device containing a device for adjusting the control angle of the rectifier valves when a single resonant circuit is switched on or the last one is in operation
  • the control device containing a device for adjusting the control angle of the rectifier valves when a single resonant circuit is switched on or the last one is in operation
  • Individual resonant circuit is to be switched off can only be controlled to a reduced output voltage of the AC source when one of the switched-on individual resonant circuits is to be switched off, the reduced output voltage approximately corresponding to the expected reduced power output of the AC source after the individual resonant circuit has been switched off.
  • the use of a parallel resonant circuit converter ensures, in addition to convenient control of the power supply, that the network is not loaded asymmetrically in a three-phase supply system.
  • the measures according to the invention also prevent the switching on and off of the individual inductors from being harmful to the parallel resonant circuit converter, e.g. in the form of overvoltages or by tipping.
  • the aim is to move the workpiece to be transported over the heating section with a certain temperature gradient, so that the workpiece arriving at the exit of the heating section has the optimum temperature for subsequent processing.
  • the main patent can achieve the desired temperature gradient in the quasi-stationary state with the device.
  • the use of the parallel resonant circuit converter also ensures that the network is not loaded asymmetrically in a three-phase supply system. In addition, it is prevented that the switching on and off of the individual inductors has a detrimental effect on the parallel resonant circuit converter, for example in the form of overvoltages or tipping.
  • the impedances of the resonant circuits assigned to the individual sections of the heating pieces remain constant.
  • the impedances of the individual resonant circuits change during the heating. This means that if the converter output voltage remains unchanged, it will be overloaded due to the high current consumption of the resonant circuits.
  • the energy supply to the resonant circuits assigned to the individual sections of the heating section takes place in dependence on the size of the temperature deviation from a predetermined temperature curve over the heating section in such a way that by controlling the on-time, the on-time and the Switch-on sequence of the oscillating circuit (s) to which the oscillating circuit (s) with the greatest setpoint deviation is supplied more energy than the oscillating circuit (s) with smaller setpoint deviation, the sum of the Energy supplied to resonant circuits is kept to the nominal power of the converter if possible.
  • the method according to the invention it is possible to operate the converter practically at nominal power during the entire heating-up phase, because the various possibilities for controlling the energy supply to the individual resonant circuits always allow the individual impedances of the resonant circuits to be used to compile a total impedance that enables the converter to operate with full output voltage, so that vibration effects on the network are minimal and there is a maximum network cos. Since it is possible with the method according to the invention to heat the workpiece in the stationary state in accordance with the predefined temperature curve, there is practically no longer any scrap. Furthermore, the method makes it possible to keep the workpiece which has not been transported further warm with the predetermined temperature gradient over the heating path when the operation is interrupted. In order to achieve a sliding temperature transition in the individual sections of the workpiece at the end of the heating-up phase of the workpiece, the workpiece is transported at a predetermined temperature.
  • an embodiment of the invention provides, including that Control the output voltage of the converter in such a way that the nominal current of the converter is not exceeded.
  • a three-phase-fed converter U for a medium-frequency voltage feeds a plurality of resonant circuits connected in parallel, each consisting of a capacitor C 1 , C 2 , C n and an inductor L 1 , L 2 , L n connected in parallel.
  • An electronic switch S 1 , S Z , S n is arranged in the power supply line of each resonant circuit C 1 , L 1 , C 2 , L 2 , C n , L n .
  • the inductors L 1 , L 2 , L n are designed as ring coils and enclose a rod-shaped workpiece W to be heated.
  • a temperature sensor F 1 , F 2 , F n for the workpiece temperature in the area of the respective inductor is assigned to each inductor L I , L 2 , L n .
  • the temperature sensors F 1 , F 2 , F n supply the actual temperature to a comparison stage V, to which the setpoints of setting elements G 1 , G 2 , G n are also supplied.
  • the comparison stage V supplies an actuating signal to a decision element E, which controls a device GW for setting the rectifier control angle a.
  • the medium frequency voltage of the converter U is fed to the device GW for control purposes.
  • the device described works in the following way: After closing the switches S 1 , S 2 , S n , the converter U is switched on, so that the workpiece W begins to heat up. As soon as the temperature determined by a temperature sensor F 1 matches the target temperature set on the setting element G 1 , the comparison stage V emits an actuating signal to the decision element E, which determines whether at least one inductor L 2 is still present after the inductor L 1 has been switched off. L n is switched on. If this is the case, the decision element E gives the device GW for setting the rectifier control angle an actuating signal for reducing the medium-frequency voltage of the converter U, which corresponds to the expected reduced power consumption of the inductor L. As soon as the medium frequency voltage is reduced accordingly, the decision element E sends an actuating signal to the switch S 1 , which interrupts the current supply to the resonant circuit C 1 , L 1 .
  • the decision element E determines that after the power supply to the resonant circuit L 1 , C 1 has been interrupted, no further resonant circuit is connected to the converter U, the medium-frequency voltage is not reduced further, but the converter U is switched off. Switching off the converter U is also necessary every time a further resonant circuit is switched on.
  • the comparison stage is expanded to a programmed control and regulating device.
  • the comparison stage V can determine the impedance of the associated resonant circuits and, taking into account the setpoint / actual value deviation of the temperature, control the energy supply to the individual resonant circuits in such a way that the converter can be operated with maximum output voltage without overloading . If a workpiece that is uniformly cold over its length is assumed in the heating section, the output impedances of all resonant circuits are the same. When the three resonant circuits are switched on at the same time, the energy supply to all resonant circuits is the same.

Abstract

1. Arrangement for heating workpieces (W), especially tubes or rods, by induction, using a plurality of inductors (L1 , L2 , Ln ) which with capacitors (C1 , C2 , C3 ) form a plurality of individual resonant circuits (L1 , C1 ; L2 , C2 , Ln , Cn ) powered by a common a.c. source, the current supply to said resonant circuits being adapted to be connected and disconnected individually and/or in groups by a controlling system (V, E) in response to a deviation in the temperature of the workpiece, said controlling system (V, E) only connecting the supply of current to one or more individual resonant circuits if the voltage from the a.c. source disappears at least for the switching instant, characterised in that the a.c. source is a controlled anti-resonant circuit converter (U) the rectifier valves of which can be moved into the blocking state by the controlling system (V, E) containing a device (GW) for setting the delay angle of the rectifier valves whenever an individual resonant circuit (L1 , C1 ; L2 , C2 ; Ln , Cn ) is to be connected or the last individual resonant circuit in operation is to be disconnected, but which, however, can only be operated to give a reduced output voltage from the a.c. source if one of the connected individual resonant circuits is to be disconnected, said reduced output voltage corresponding roughly to the reduced power output of the a.c. source expected after the individual resonant circuit is disconnected.

Description

Die Erfindung bezieht sich auf eine Einrichtung zur induktiven Erwärmung von Werkstücken, insbesondere Rohren oder Stangen, mit mehreren Induktoren, die mit Kondensatoren mehrere von einer gemeinsamen Wechselstromquelle gespeiste Einzelschwingkreise bilden, deren Stromversorgung mittels einer Regeleinrichtung in Abhängigkeit von einer Sollwertabweichung der Werkstücktemperatur einzeln und/oder gruppenweise ein- oder ausschaltbar sind, wobei die Regeleinrichtung das Einschalten der Stromversorgung eines oder mehrerer Einzelschwingkreise nur dann vornimmt, wenn die Spannung der Wechselstromquelle zumindest für den Schaltaugenblickverschwindet.The invention relates to a device for inductive heating of workpieces, in particular tubes or rods, with a plurality of inductors which, with capacitors, form a plurality of individual resonant circuits fed by a common alternating current source, the power supply thereof by means of a control device as a function of a setpoint deviation of the workpiece temperature individually and / or can be switched on or off in groups, the control device only switching on the power supply of one or more individual resonant circuits when the voltage of the AC power source disappears at least for the instant of switching.

Bei einer bekannten Einrichtung dieser Art (DE-OS 2 914277) wird die Wechselstromquelle von einem Dreiphasennetz gebildet, an dessen Phasen die Induktoren getrennt voneinander angeschlossen sind. Zur Begrenzung des Ein- und Ausschaltstromes erfolgt das Ein- und Ausschalten der einzelnen Induktoren vorzugsweise im Augenblick des Null-Durchganges der Spannung der entsprechenden Phase. Da entsprechend der Erwärmung des Werkstückes einzelne Induktoren ausgeschaltet werden können, ergibt sich für das Dreiphasennetz eine unsymmetrische Belastung.In a known device of this type (DE-OS 2 914277) the AC power source is formed by a three-phase network, to the phases of which the inductors are connected separately. To limit the switch-on and switch-off current, the individual inductors are preferably switched on and off at the moment the voltage of the corresponding phase passes zero. Since individual inductors can be switched off in accordance with the heating of the workpiece, there is an asymmetrical load for the three-phase network.

Eine solche unsymmetrische Belastung tritt jedoch dann nicht auf, wenn, wie aus der Praxis, z.B. aus DE-A1 3 040 820, bekannt, jedem Induktor ein eigener Generator zugeordnet ist. Eine solche Einrichtung bietet darüber hinaus die Möglichkeit, die Leistungszufuhr nicht nur durch Abschalten der Induktoren, sondern auch über den Generator zu regeln. Bei einer solchen Einrichtung wird jedoch der höhere Einrichtungsaufwand in Kauf genommen.However, such an asymmetrical load does not occur if, as in practice, e.g. known from DE-A1 3 040 820, each inductor is assigned its own generator. Such a device also offers the possibility of regulating the power supply not only by switching off the inductors, but also via the generator. With such a facility, however, the higher installation effort is accepted.

Der Erfindung liegt die Aufgabe zugrunde, eine Einrichtung der eingangs genannten Art zu schaffen, bei der bei guter Regelbarkeit der Leistungszufuhr zu den Induktoren schädliche Auswirkungen durch das Ein- und Ausschalten der Induktoren nicht auftreten.The invention has for its object to provide a device of the type mentioned, in which, with good controllability of the power supply to the inductors, there are no harmful effects from switching the inductors on and off.

Diese Aufgabe wird erfindungsgemäss dadurch gelöst, dass die Wechselstromquelle ein gesteuerter Parallel-Schwingkreis-Umrichter ist, dessen Gleichrichterventile dann von der eine Vorrichtung zur Einstellung des Steuerwinkels der Gleichrichterventile enthaltenden Regeleinrichtung in den Sperrzustand steuerbar sind, wenn ein Einzelschwingkreis zugeschaltet oder der letzte in Betrieb befindliche Einzelschwingkreis abgeschaltet werden soll, hingegen dann lediglich auf verminderte Ausgangsspannung der Wechselstromquelle steuerbar sind, wenn einer der eingeschalteten Einzelschwingkreise abgeschaltet werden soll, wobei die verminderte Ausgangsspannung annähernd der nach Abschalten des Einzelschwingkreises zu erwartenden verminderten Leistungsabgabe der Wechselstromquelle entspricht.This object is achieved according to the invention in that the alternating current source is a controlled parallel resonant circuit converter, the rectifier valves of which can then be controlled into the blocking state by the control device containing a device for adjusting the control angle of the rectifier valves when a single resonant circuit is switched on or the last one is in operation Individual resonant circuit is to be switched off, however, can only be controlled to a reduced output voltage of the AC source when one of the switched-on individual resonant circuits is to be switched off, the reduced output voltage approximately corresponding to the expected reduced power output of the AC source after the individual resonant circuit has been switched off.

Der Einsatz eines Parallel-Schwingkreis-Umrichters gewährleistet neben einer komfortablen Regelung der Leistungszufuhr auch, dass bei einem speisenden Dreiphasennetz das Netz nicht unsymmetrisch belastet wird. Durch die erfindungsgemässen Massnahmen wird auch verhindert, dass sich das Ein- und Ausschalten der einzelnen Induktoren schädlich auf den Parallel-Schwingkreis-Umrichter, z.B. in Form von Überspannungen oder durch Kippung, auswirkt. Beim Erwärmen von Werkstücken wird angestrebt, das über die Erwärmungsstrecke zu transportierende Werkstück mit einem bestimmten Temperaturgradienten zu fahren, so dass das am Ausgang der Erwärmungsstrecke ankommende Werkstück gerade die für die nachfolgende Verarbeitung optimale Temperatur hat. Durch das Ein-und Ausschalten der einzelnen Schwingkreise lässt sich im quasi-stationären Zustand mit der Einrichtung das Hauptpatentes der gewünschte Temperaturgradient erreichen. Der Einsatz des Parallelschwingkreisumrichters gewährleistet neben einer komfortablen Regelung der Leistungszufuhr auch, dass bei einem speisenden Dreiphasennetz das Netz nicht unsymmetrisch belastet wird. Ausserdem wird verhindert, dass sich das Ein- und Ausschalten der einzelnen Induktoren schädlich auf den Parallelschwingkreisumrichter, zum Beispiel in Form von Überspannungen oder Kippungen, auswirkt.The use of a parallel resonant circuit converter ensures, in addition to convenient control of the power supply, that the network is not loaded asymmetrically in a three-phase supply system. The measures according to the invention also prevent the switching on and off of the individual inductors from being harmful to the parallel resonant circuit converter, e.g. in the form of overvoltages or by tipping. When heating workpieces, the aim is to move the workpiece to be transported over the heating section with a certain temperature gradient, so that the workpiece arriving at the exit of the heating section has the optimum temperature for subsequent processing. By switching the individual resonant circuits on and off, the main patent can achieve the desired temperature gradient in the quasi-stationary state with the device. In addition to convenient control of the power supply, the use of the parallel resonant circuit converter also ensures that the network is not loaded asymmetrically in a three-phase supply system. In addition, it is prevented that the switching on and off of the individual inductors has a detrimental effect on the parallel resonant circuit converter, for example in the form of overvoltages or tipping.

Solange die Erwärmung im quasi-stationären Zustand erfolgt, d.h. nach Erreichen des vorgegebenen Temperaturgradienten, bleiben die Impedanzen der den einzelnen Abschnitten der Erwärmungsstücke zugeordneten Schwingkreise konstant. Wenn jedoch ein Werkstück mit über seine Länge zunächst gleichmässiger Temperatur unterschiedlich stark in den einzelnen Abschnitten erwärmt werden soll, um den gewünschten Temperaturgradienten zu erreichen, dann ändern sich während der Erwärmung die Impedanzen der einzelnen Schwingkreise. Das führt dazu, dass bei unveränderter Ausgangsspannung des Umrichters dieser wegen zu hoher Stromaufnahme der Schwingkreise überlastet wird.As long as the heating takes place in the quasi-stationary state, i.e. after reaching the predetermined temperature gradient, the impedances of the resonant circuits assigned to the individual sections of the heating pieces remain constant. However, if a workpiece with a temperature that is initially uniform over its length is to be heated to different degrees in the individual sections in order to achieve the desired temperature gradient, then the impedances of the individual resonant circuits change during the heating. This means that if the converter output voltage remains unchanged, it will be overloaded due to the high current consumption of the resonant circuits.

Der Erfindung liegt die weitere Aufgabe zugrunde, ein Verfahren zum induktiven Erwärmen von Werkstücken, die über eine von mehreren Induktoren gebildete Erwärmungsstrecketransportiert werden, zu schaffen, das die Aufheizung eines Werkstückes in kürzester Zeit und bei minimalem Ausschuss ermöglicht.It is another object of the invention to provide a method for inductively heating workpieces which are transported over a heating path formed by a plurality of inductors, which enables the heating of a workpiece in a very short time and with minimal waste.

Diese Aufgabe wird unter Verwendung der erfindungsgemässen Einrichtung dadurch gelöst, dass die Energiezufuhr zu den den einzelnen Abschnitten der Erwärmungsstrecke zugeordneten Schwingkreisen in Abhängigkeit von der Grösse der Temperaturabweichung von einer vorgegebenen Temperaturkurve über die Erwärmungsstrecke derart erfolgt, dass durch Steuerung der Einschaltdauer, des Einschaltzeitpunktes und der Einschaltfolge des bzw. der Schwingkreise dem bzw. den Schwingkreisen mit der grössten Sollwertabweichung mehr Energie zugeführt wird als dem bzw. den Schwingkreisen mit kleinerer Sollwertabweichung, wobei die Summe der den Schwingkreisen zugeführten Energie möglichst auf Nennleistung des Umrichters gehalten wird.This object is achieved using the device according to the invention in that the energy supply to the resonant circuits assigned to the individual sections of the heating section takes place in dependence on the size of the temperature deviation from a predetermined temperature curve over the heating section in such a way that by controlling the on-time, the on-time and the Switch-on sequence of the oscillating circuit (s) to which the oscillating circuit (s) with the greatest setpoint deviation is supplied more energy than the oscillating circuit (s) with smaller setpoint deviation, the sum of the Energy supplied to resonant circuits is kept to the nominal power of the converter if possible.

Mit dem erfindungsgemässen Verfahren ist es möglich, den Umrichter während der gesamten Aufheizphase praktisch mit Nennleistung zu betreiben, denn durch die verschiedenen Möglichkeiten der Steuerung der Energiezufuhr zu den einzelnen Schwingkreisen lässt sich aus den Einzelimpedanzen der Schwingkreise immer eine Gesamtimpedanz zusammenstellen, die einen Betrieb des Umrichters mit voller Ausgangsspannung ermöglicht, so dass Schwingungsrückwirkungen auf das Netz minimal sind und sich ein maximaler Netz-cos ergibt. Da es mit dem erfindungsgemässen Verfahren möglich ist, das Werkstück im stationären Zustand entsprechend der vorgegebenen Temperaturkurve aufzuheizen, fällt praktisch kein Ausschuss mehr an. Ferner ist es mit dem Verfahren möglich, bei Betriebsunterbrechung das nicht weitertransportierte Werkstück mit dem vorgegebenen Temperaturgradienten über die Erwärmungsstrecke warmzuhalten. Um am Ende der Aufheizphase des Werkstücks zu einem schleifenden Temperaturübergang in den einzelnen Abschnitten des Werkstükkes zu kommen, beginnt der Transport des Werkstückes bei einer vorgegebenen Temperatur.With the method according to the invention, it is possible to operate the converter practically at nominal power during the entire heating-up phase, because the various possibilities for controlling the energy supply to the individual resonant circuits always allow the individual impedances of the resonant circuits to be used to compile a total impedance that enables the converter to operate with full output voltage, so that vibration effects on the network are minimal and there is a maximum network cos. Since it is possible with the method according to the invention to heat the workpiece in the stationary state in accordance with the predefined temperature curve, there is practically no longer any scrap. Furthermore, the method makes it possible to keep the workpiece which has not been transported further warm with the predetermined temperature gradient over the heating path when the operation is interrupted. In order to achieve a sliding temperature transition in the individual sections of the workpiece at the end of the heating-up phase of the workpiece, the workpiece is transported at a predetermined temperature.

Sollte es bei einer vorgegebenen Anzahl von Schwingkreisen nicht möglich sein, aus den Schwingkreisen eine Gesamtimpedanz zusammenzustellen, bei der der Umrichter mit voller Ausgangsspannung betrieben werden kann, ohne dass es zu einer Überlastung des Umrichters kommt, dann sieht eine Ausgestaltung der Erfindung vor, auch die Ausgangsspannung des Umrichters derart zu steuern, dass der Nennstrom des Umrichters nicht überschritten wird.If it is not possible for a predetermined number of resonant circuits to put together a total impedance from the resonant circuits, at which the converter can be operated with full output voltage without the converter being overloaded, then an embodiment of the invention provides, including that Control the output voltage of the converter in such a way that the nominal current of the converter is not exceeded.

Im folgenden wird die Erfindung anhand einer ein Ausführungsbeispiel darstellenden Zeichnung näher erläutert.The invention is explained in more detail below with the aid of a drawing representing an exemplary embodiment.

Im einzelnen zeigen

  • Fig. 1 eine Einrichtung zum induktiven Erwärmen von Werkstücken und
  • Fig. 2 ein Diagramm mit dem Temperaturgradienten, aufgetragen über die Erwärmungsstrekke.
Show in detail
  • Fig. 1 shows a device for inductive heating of workpieces and
  • Fig. 2 is a diagram with the temperature gradient, plotted over the heating route.

Bei der in Fig. 1 dargestellten Einrichtung speist ein drehstromgespeister Umrichter U für eine Mittelfrequenzspannung mehrere parallelgeschaltete Schwingkreise, die jeweils aus einer Parallelschaltung eines Kondensators C1, C2, Cn und eines Induktors L1, L2, Ln bestehen. In der Stromversorgungsleitung eines jeden Schwingkreises C1, L1, C2, L2, Cn, Ln, ist ein elektronischer Schalter Sl, SZ, Sn angeordnet. Die Induktoren L1, L2, Ln, sind als Ringspulen ausgebildet und umschliessen ein zu erwärmendes, stabförmiges Werkstück W.In the device shown in FIG. 1, a three-phase-fed converter U for a medium-frequency voltage feeds a plurality of resonant circuits connected in parallel, each consisting of a capacitor C 1 , C 2 , C n and an inductor L 1 , L 2 , L n connected in parallel. An electronic switch S 1 , S Z , S n is arranged in the power supply line of each resonant circuit C 1 , L 1 , C 2 , L 2 , C n , L n . The inductors L 1 , L 2 , L n are designed as ring coils and enclose a rod-shaped workpiece W to be heated.

Jedem Induktor LI, L2, Ln ist ein Temperaturfühler F1, F2, Fn für die Werkstücktemperatur im Bereich des jeweiligen Induktors zugeordnet. Die Temperaturfühler F1, F2, Fn liefern die Isttemperatur an eine Vergleichsstufe V, der auch die Sollwerte von Einstellgliedern G1, G2, Gn zugeführt werden. Bei einer Soll-Istabweichung liefert die Vergleichsstufe V ein Stellsignal an ein Entscheidungsglied E, das eine Einrichtung GW zur Einstellung des Gleichrichter-Steuerwinkels a ansteuert. Der Einrichtung GW wird zur Kontrolle die Mittelfrequenzspannung des Umrichters U zugeführt.A temperature sensor F 1 , F 2 , F n for the workpiece temperature in the area of the respective inductor is assigned to each inductor L I , L 2 , L n . The temperature sensors F 1 , F 2 , F n supply the actual temperature to a comparison stage V, to which the setpoints of setting elements G 1 , G 2 , G n are also supplied. In the event of a target-actual deviation, the comparison stage V supplies an actuating signal to a decision element E, which controls a device GW for setting the rectifier control angle a. The medium frequency voltage of the converter U is fed to the device GW for control purposes.

Die beschriebene Einrichtung arbeitet auf folgende Weise: Nach Schliessen der Schalter S1, S2, Sn wird der Umrichter U eingeschaltet, so dass die Erwärmung des Werkstücks W beginnt. Sobald die von einem Temperaturfühler F1 festgestellte Temperatur mit der am Einstellglied G1 eingestellten Soll-Temperatur übereinstimmt, gibt die Vergleichsstufe V ein Stellsignal an das Entscheidungsglied E ab, das feststellt, ob nach Abschaltung des Induktors L1 mindestens noch ein Induktor L2, Ln eingeschaltet ist. Sofern das der Fall ist, gibt das Entscheidungsglied E an die Einrichtung GW zur Einstellung des Gleichrichter-Steuerwinkels ein Stellsignal zur Verminderung des Mittelfrequenzspannung des Umrichters U, die der erwarteten verminderten Leistungsaufnahme des Induktors L, entspricht. Sobald die Mittelfrequenzspannung entsprechend vermindert ist, gibt das Entscheidungsglied E ein Stellsignal an den Schalter S1, der die Stromzufuhr zum Schwingkreis C1, L1 unterbricht.The device described works in the following way: After closing the switches S 1 , S 2 , S n , the converter U is switched on, so that the workpiece W begins to heat up. As soon as the temperature determined by a temperature sensor F 1 matches the target temperature set on the setting element G 1 , the comparison stage V emits an actuating signal to the decision element E, which determines whether at least one inductor L 2 is still present after the inductor L 1 has been switched off. L n is switched on. If this is the case, the decision element E gives the device GW for setting the rectifier control angle an actuating signal for reducing the medium-frequency voltage of the converter U, which corresponds to the expected reduced power consumption of the inductor L. As soon as the medium frequency voltage is reduced accordingly, the decision element E sends an actuating signal to the switch S 1 , which interrupts the current supply to the resonant circuit C 1 , L 1 .

Sollte dagegen das Entscheidungsglied E feststellen, dass nach Unterbrechung der Stromzufuhr zum Schwingkreis L1, C1 kein weiterer Schwingkreis mehr am Umrichter U angeschlossen ist, wird die Mittelfrequenzspannung nicht weiter erniedrigt, sondern der Umrichter U abgeschaltet. Die Abschaltung des Umrichters U ist auch jedesmal erforderlich, wenn ein weiterer Schwingkreis zugeschaltet wird.If, on the other hand, the decision element E determines that after the power supply to the resonant circuit L 1 , C 1 has been interrupted, no further resonant circuit is connected to the converter U, the medium-frequency voltage is not reduced further, but the converter U is switched off. Switching off the converter U is also necessary every time a further resonant circuit is switched on.

Zur Durchführung des erfindungsgemässen Verfahrens wird die Vergleichsstufe zu einer programmierten Steuer- und Regeleinrichtung ausgebaut. In Abhängigkeit von dem Temperaturwert in den einzelnen Abschnitten der Erwärmungsstrecke kann die Vergleichsstufe V die lmpedanz der zugehörigen Schwingkreise bestimmen und unter Berücksichtigung der Soll-Istwertabweichung der Temperatur die Energiezufuhr zu den einzelnen Schwingkreisen derart steuern, dass der Umrichter ohne Überlastung mit maximaler Ausgangsspannung betrieben werden kann. Wird von einem in der Erwärmungsstrecke über seine Länge gleichmässig kalten Werkstück ausgegangen, dann sind die Ausgangsimpedanzen aller Schwingkreise gleich. Bei gleichzeitigem Einschalten der drei Schwingkreise ist deshalb die Energiezufuhr zu allen Schwingkreisen gleich. Da die Impedanz mit zunehmender Erwärmung des Werkstücks in den einzelnen Abschnitten sinkt, ist es zur Aufrechterhaltung einer im wesentlichen konstanten Gesamtimpedanz erforderlich, den einen oder anderen Schwingkreis abzuschalten, der weniger Energie für die Erreichung der Soll-Temperatur benötigt als die anderen Schwingkreise, im vorliegenden Fall also der dem Abschnitt zugeordnete Schwingkreis. Die Abschaltung dieses Schwingkreises erfolgt aber nicht erst dann, wenn die Soll-Temperatur erreicht ist, sondern vorher, um durch Einschalten dieses Schwingkreises auch beim weitern Aufheizen noch die Möglichkeit zu haben, über ihn die Gesamtimpedanz zu verändern. Durch Verschachteln der Einschaltzeiten der einzelnen Schwingkreise, deren Einschaltdauer und deren Einschaltfolge lässt sich erreichen, dass in kürzester Zeit im stationären Zustand die im Ausführungsbeispiel gezeichnete Soll-Temperaturkurve (Fig. 2) über die Erwärmungsstrecke erhalten wird. Der Temperaturausgleich an den Grenzen der einzelnen Abschnitte, aber auch innerhalb der einzelnen Abschnitte wird dadurch begünstigt, dass nach Erreichen einer vorgegebenen Temperatur der Transport des Werkstückes beginnt. Das nach dem erfindungsgemässen Verfahren erwärmte Werkstück verlässt dann mit einem minimalen Ausschuss mit optimaler Temperatur für die weitere Bearbeitung die Erwärmungsstrecke. Anschliessend braucht dann nur noch für den quasi-stationären Zustand der eingestellten Temperaturkurve Energie den einzelnen Abschnitten zugeführt werden.To carry out the method according to the invention, the comparison stage is expanded to a programmed control and regulating device. Depending on the temperature value in the individual sections of the heating section, the comparison stage V can determine the impedance of the associated resonant circuits and, taking into account the setpoint / actual value deviation of the temperature, control the energy supply to the individual resonant circuits in such a way that the converter can be operated with maximum output voltage without overloading . If a workpiece that is uniformly cold over its length is assumed in the heating section, the output impedances of all resonant circuits are the same. When the three resonant circuits are switched on at the same time, the energy supply to all resonant circuits is the same. Since the impedance decreases with increasing heating of the workpiece in the individual sections, in order to maintain a substantially constant overall impedance, it is necessary to switch off one or the other resonant circuit that requires less energy to reach the target temperature than the other resonant circuits, in the present case So the case resonant circuit assigned to the section. However, this resonant circuit is not switched off only when the target temperature has been reached, but beforehand, so that by switching on this resonant circuit, even when it is heated further, it is still possible to change the overall impedance via it. By nesting the switch-on times of the individual resonant circuits, their switch-on duration and their switch-on sequence, it can be achieved that the target temperature curve (FIG. 2) drawn in the exemplary embodiment is obtained over the heating section in the shortest possible time in the stationary state. The temperature compensation at the borders of the individual sections, but also within the individual sections, is favored in that the transport of the workpiece begins after a predetermined temperature has been reached. The workpiece heated by the method according to the invention then leaves the heating section with a minimal scrap at the optimum temperature for further processing. Subsequently, energy only needs to be supplied to the individual sections for the quasi-stationary state of the set temperature curve.

Claims (4)

1. Arrangement for heating workpieces (W), especially tubes or rods, by induction, using a plurality of inductors (L1, L2, Ln) which with capacitors (C1, C2, C3) form a plurality of individual resonant circuits (L1, C1; L2, C2, Ln, Cn) powered by a common a.c. source, the current supply to said resonant circuits being adapted to be connected and disconnected individually and/or in groups by a controlling system (V, E) in response to a deviation in the temperature of the workpiece, said controlling system (V, E) only connecting the supply of current to one or more individual resonant circuits if the voltage from the a.c. source disappears at least for the switching instant, characterised in that the a.c. source is a controlled anti-resonant circuit converter (U) the rectifier valves of which can be moved into the blocking state by the controlling system (V, E) containing a device (GW) for setting the delay angle of the rectifier valves whenever an individual resonant circuit (LI, CI; L2, C2; Ln, Cn) is to be connected or the last individual resonant circuit in operation is to be disconnected, but which, however, can only be operated to give a reduced outpt voltage from the a.c. source if one of the connected individual resonant circuits is to be disconnected, said reduced output voltage corresponding roughly to the reduced power output of the a.c. source expected after the individual resonant circuit is disconnected.
2. Method for heating by induction workpieces (W) transferred along a heating line formed by a plurality of inductors (L1, L2, Ln) using an arrangement in accordance with Claim 1, characterised in that the supply of power to the individual sections of the resonant circuits (L1, CI; L2, C2; Ln, Cn) associated to the heating line depends on the magnitude of the temperature deviation from a preset temperature curve along the heating line such that by controlling the duration of current, the time of connection and the sequence in which the resonant circuit or circuits are connected, more power is fed to the resonant circuit or circuits exhibiting the largest deviation than to the resonant circuit or circuits exhibiting a smaller deviation, the sum of the power supplied to the resonant circuits being kept as close as possible to the rated output of the converter (U).
3. Method in accordance with Claim 2, characterised in that the transfer of the workpiece (W) begins once a preset temperature is reached.
4. Method in accordance with Claim 2 or 3, characterised in that the output voltage of the converter (U) is controlled such that its rated current is not exceeded.
EP84102925A 1983-11-26 1984-03-16 Arrangement and method for heating by induction with several inductor workpieces, in particular tubes and rods Expired EP0143144B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT84102925T ATE35760T1 (en) 1983-11-26 1984-03-16 DEVICE AND PROCESS FOR INDUCTION HEATING OF WORKPIECES, ESPECIALLY TUBES OR RODS, WITH SEVERAL INDUCTORS.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19833342889 DE3342889A1 (en) 1983-11-26 1983-11-26 METHOD FOR INDUCTIVE HEATING OF WORKPIECES
DE3342889 1983-11-26

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EP0143144A2 EP0143144A2 (en) 1985-06-05
EP0143144A3 EP0143144A3 (en) 1985-07-03
EP0143144B1 true EP0143144B1 (en) 1988-07-13

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AT (1) ATE35760T1 (en)
DE (2) DE3342889A1 (en)
ES (1) ES8502308A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3815686A1 (en) * 1988-05-07 1989-11-16 Licentia Gmbh Parboil method in particular in domestic induction-cooking appliances
DE4032683C3 (en) * 1990-10-15 1996-06-13 Santrade Ltd Device for forming drops
DE4038560A1 (en) * 1990-12-04 1992-06-11 Licentia Gmbh Power control of microwave and induction heating cooker - involves microprocessor limiting load on inverter by switching of microwave oscillator and regulation of induction energy
EP1280381A3 (en) * 2001-07-25 2005-12-21 I. A. S. Induktions- Anlagen + Service GmbH & Co. KG Inductive heating device and process of billets with a billets heating coil

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Publication number Priority date Publication date Assignee Title
US3008025A (en) * 1958-08-09 1961-11-07 Deutsche Edelstahlwerke Ag Method of progressively induction heating metal strip and an apparatus for performing the same
DE1192343B (en) * 1962-03-27 1965-05-06 Siemens Ag Device for inductive heating of, in particular, rod-shaped workpieces
SE408518B (en) * 1974-05-17 1979-06-11 Matsushita Electric Ind Co Ltd INDUCTION HEATING DEVICE
DE2622825A1 (en) * 1976-05-21 1977-12-01 Siemens Ag Continuous induction heating of wire - where electronic circuit provides accurate heating despite variations in inlet temp. of wire
AT368824B (en) * 1978-04-11 1982-11-10 Vertina Anstalt DEVICE FOR INDUCTIVE HEATING OF ROD-SHAPED WORKPIECES
DE3040820C2 (en) * 1980-10-30 1983-06-01 Aeg-Elotherm Gmbh, 5630 Remscheid Device for inductive heating of a workpiece by means of several inductors
DE3220142C2 (en) * 1982-05-28 1984-04-26 Aeg-Elotherm Gmbh, 5630 Remscheid Device for inductive heating of workpieces, in particular tubes or rods, with several inductors

Also Published As

Publication number Publication date
EP0143144A2 (en) 1985-06-05
ES532148A0 (en) 1985-01-01
ATE35760T1 (en) 1988-07-15
DE3342889C2 (en) 1987-04-23
EP0143144A3 (en) 1985-07-03
DE3342889A1 (en) 1985-06-05
DE3472747D1 (en) 1988-08-18
ES8502308A1 (en) 1985-01-01

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