WO2021038163A1 - Induction furnace comprising an additional resonant circuit - Google Patents

Induction furnace comprising an additional resonant circuit Download PDF

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Publication number
WO2021038163A1
WO2021038163A1 PCT/FR2020/051492 FR2020051492W WO2021038163A1 WO 2021038163 A1 WO2021038163 A1 WO 2021038163A1 FR 2020051492 W FR2020051492 W FR 2020051492W WO 2021038163 A1 WO2021038163 A1 WO 2021038163A1
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WO
WIPO (PCT)
Prior art keywords
inductor
circuit
crucible
heating
induction furnace
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PCT/FR2020/051492
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French (fr)
Inventor
Patrice Brun
Emilien SAUVAGE
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Commissariat A L'energie Atomique Et Aux Energies Alternatives
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Application filed by Commissariat A L'energie Atomique Et Aux Energies Alternatives filed Critical Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority to JP2022513314A priority Critical patent/JP2022546446A/en
Priority to CN202080060804.4A priority patent/CN114303035A/en
Priority to KR1020227010613A priority patent/KR20220075219A/en
Publication of WO2021038163A1 publication Critical patent/WO2021038163A1/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
    • H05B6/22—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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the subject of the invention is an induction furnace comprising an additional resonant circuit.
  • the induction frequency is generally between 100 kHz and 1000 kHz depending on the size of the crucibles.
  • Induction furnaces are well known in the field of foundry or metallurgy, or that of the nuclear industry for the preparation of materials or the formation of homogeneous mixtures. They include a crucible in which the charge is maintained, and at least one inductor, the excitation of which produces currents in the charge, which cause it to heat and melt. This heating process is simple to implement and makes it possible to avoid any contact between the thermal energy source and the crucible.
  • the crucible typically comprises a side wall joined to a hearth which may be flat and which constitutes the bottom thereof. If it is made of an electrically conductive material, it is often sectorized, that is to say composed of portions extending over angular sectors and separated by electrically insulating spacers, in order to avoid the appearance of induced currents circulating in a loop around the load and the corresponding energy losses.
  • Some crucibles are made of a refractory material such as rammed earth or graphite. Their advantage is a high melting temperature, but certain charges, in particular composed of oxides, must be melted at even higher temperatures, or at least sufficient to corrode them physically or chemically.
  • a design which is also very widespread, and which the invention repeats, is then that of the cold crucible, equipped with a cooling circuit by water or another liquid and which extends into the crucible.
  • the crucible then remains much cooler than the core of the charge during the operation of the process, and it remains protected from corrosion or other physical or chemical attack by a solidified layer of the material of the charge which remains against it, than one can consider as constituting an internal wall of the crucible and which is called self-crucible.
  • These cold crucibles make it possible to melt at high temperature, beyond 1500 K, or even more than 3000 K for example, highly reactive materials, which can be metallic such as titanium, steel or alloys of various oxides such as glass, titanium oxide, rare earths or a mixture; or else poorly conductive materials such as silicon or enamels.
  • highly reactive materials which can be metallic such as titanium, steel or alloys of various oxides such as glass, titanium oxide, rare earths or a mixture; or else poorly conductive materials such as silicon or enamels.
  • the induction frequency it is also possible to act on the induction frequency to try to obtain this melting of the charge at the bottom of the crucible: if the inductor is placed around the side wall, which is the most usual, the distribution of the heating inside the crucible in the radial direction depends on the excitation frequency of the inductor: the greater it is, the more heating is localized in the wall; it is therefore possible to choose or adjust this excitation frequency to adjust the volume of the molten bath and, to a certain extent, the temperature distribution inside the crucible; but the lack of uniformity of temperatures in the molten bath may become unacceptable.
  • the electrical circuit and the cooling system are generally oversized, without this increasing the device being necessarily satisfactory.
  • the cold crucible is made of an electrically conductive material, such as copper or certain grades of stainless steel, in particular because of the increase in electrical losses in the structures, but they are present whatever the material constituting the crucible and the structure thereof.
  • a final drawback of the simplest induction furnaces, described so far, which will be mentioned here, is that they are poorly suited to varying load volumes, and therefore of different heights inside the crucible, if the height of the inductor is markedly different.
  • Document EP 1045 216 B1 describes an additional inductor, arranged around the casting zone below the hearth, around the plug allowing pouring out of the crucible, in addition to the main inductor surrounding the side wall of the crucible. It makes it possible to create additional induced currents around the pouring orifice passing through the hearth, to prevent the charge from solidifying there and to guarantee the casting when the stopper has been removed.
  • this device not necessarily suitable for melting materials with a very high melting point. Its effect is purely local for a limited time, so that the more general problem of lack of heating uniformity of the charge to be melted is not solved. The same would apply if there were, which has already been proposed, an uncooled metal tube between this lower inductor and the pouring orifice with the hope of obtaining greater heating thanks to the tube; the latter also risks being corroded quickly, especially at high temperature.
  • the more conventional inductor disposed around the side wall of the crucible is replaced by an inductor located under the hearth and the shape of which may be that of one or more spirals.
  • This design is only suitable for baths of low height compared to the diameter, and it can be associated with significant heat losses by convection at the free surface of the molten bath and by conduction on the side wall.
  • the power supplied remains heterogeneous, typically high above the inductive turns, but much lower near the side wall, and at the center of the crucible if the turns are absent.
  • This part is a static part made of material with high magnetic permeability, which therefore reduces the interactions between magnetic fields.
  • This drawbacks are reduced, and a better yield can be expected.
  • this magnetic flux concentrator must be cooled so that it maintains its performance, and this can be technologically difficult in certain cases. situations.
  • the concentrator must be placed in an area that is difficult to access, being able to impose a displacement of the inductors with respect to the load; Finally, it is vulnerable to irradiation in the case of radioactive charges.
  • Another drawback is that this device does not allow the heating power to be distributed between the two inductors.
  • the invention relates to an improved induction furnace, the most important aspect of which is that it makes it possible both to increase the heating efficiency of the molten charge and to adjust the heating distribution in the heated space according to the requirements. needs, thanks to a more favorable construction of two inductors, one of which is placed around the side wall of the crucible and the other under (or in) the hearth. Higher electrical efficiencies than those of the prior devices and methods are hoped for. Better casting ease is also expected thanks to better heating efficiency in the bottom of the crucible.
  • an induction furnace comprising a crucible with a side wall cooled by a circulation of fluid and a hearth placed under the side wall, a first electric induction heating circuit comprising a first inductor and an electric power generator, and a second electric induction heating circuit comprising a second inductor, one of the inductors being placed around the side wall, and the another under or in the floor, characterized in that the second circuit is devoid of an electric power generator but in electromagnetic coupling with the first circuit and provided with a device of electric capacitors with adjustable capacity, said device of electric capacitors being connected to the second inductor.
  • This double-circuit electric device exploits a phenomenon of electric resonance of the furnace, facilitated by the free electromagnetic interaction of the two circuits.
  • an inductor surrounding the side wall and an inductor assigned to the sole are excited by the same power source by being connected to one another, or by two different sources by being then separated from one another.
  • Another advantage of the invention is an ease of distributing the heating better, which it is in particular possible to make more important at the core and at the bottom, just above the hearth, to improve the process and possibly facilitate the casting. .
  • This heating distribution depends on the adjustment of the total capacity (adjustable during the melting), with moreover a very great sensitivity to the variations of this capacity, to the point that it is possible either to obtain a good uniformity of the temperatures. , or on the contrary to heat essentially either at the periphery, or at the heart, or at the bottom of the molten charge.
  • first inductor it will be common for the first inductor to be arranged around the side wall since it constitutes the main inductor, the second electrical circuit then being assigned to the sole.
  • the opposite arrangement may however be encountered without being open to criticism, in particular for crucibles with a large surface area and low height.
  • the bottom inductor of the crucible can form a spiral covered with an electrical insulator and very good thermal conductor: it is then possible and advantageous that the bottom hearth of the crucible is formed by said inductor itself, which simplifies the design of the crucible and improves the heating efficiency.
  • the induction furnace may comprise at least one additional circuit devoid of an electric power generator and comprising an inductor and a capacitor device having an adjustable total capacity, and in electromagnetic coupling with at least the first circuit; this additional circuit or these additional circuits therefore have the same properties as the second circuit mentioned. They can prove to be useful in the upper part of the furnace to improve the heating of the newly introduced quantities of the charge. They can then be placed above the top of the crucible, facing the inductor located on or in the hearth, and parallel to it.
  • the additional circuit or the additional circuits can then be advantageously equipped with a disconnector making it possible to open them at will.
  • Figure 1 a general view of the induction furnace
  • Figure 2 a view of the side inductor
  • Figure 3 a view of the bottom inductor
  • Figure 4 a diagram of the electrical circuit
  • FIG. 5 an embodiment of the capacitor bank
  • Figure 7 a first state of heating
  • Figure 9 a second state of heating
  • Figure 11 a third state of heating
  • Figure 13 another embodiment of the crucible
  • Figure 14 a third embodiment of the crucible; Figure 15 the sole of this third mode;
  • Figure 16 a section of the sole of the first mode.
  • This induction furnace embodiment comprises a side wall 1 or cylindrical shell composed of adjacent vertical copper or stainless steel tubes 2 and connected by electrically insulating spacers for prevent the appearance of induced circular currents in the side wall 1.
  • the tubes 2 are traversed by a cooling liquid such as water, according to known arrangements.
  • a cooling circuit 12 can circulate the liquid alternately upwards and downwards with connections between tubes 2 alternately at the upper end and the lower end.
  • Another possible construction, among others still, would be that of US-6,996,153-B2, where each tube is cooled independently by a circuit making a vertical return flow.
  • a lateral inductor 3 surrounds the lateral wall 1. It is here with a single turn and composed of parallel strands 4 and superimposed in height and each making a single turn of the crucible. Their ends are joined by two vertical connections 5 and 6, which moreover provide both the electrical connection to an alternating electric power generator and the hydraulic connection, the strands 4 also being cooled by the circulation of the cooling liquid, connected to the cooling circuit 13. Other arrangements of the lateral inductor, in particular with successive helical turns, would still be possible.
  • the crucible is completed by a hearth 8 composed mainly of an auxiliary inductor 7 in the form of a spiral ( Figures 3 and 16).
  • the auxiliary inductor 7 is also a tube cooled by water, and its ends 9 and 10 also lead to a cooling circuit 14.
  • the turns 31 of the spiral are joined by an electrical insulator 32 insulating spacer electric and very good conductor of the heat which separates them while giving a continuous structure to the sole 8.
  • the auxiliary inductor 7 is covered on its upper face by a thin insulating layer 33 of electricity and a good conductor of electricity. heat, composed of alumina for example.
  • Such a design makes it possible to eliminate the hearth conventionally used and to retain the charge of the crucible directly by the auxiliary inductor 7.
  • the cooling of the hearth 8 and of the side pair 1 also causes the formation of the auto-crucible, that is to say that a layer of the filler in contact with them remains solid and protects them from corrosion.
  • a pouring plug 11 is arranged in the center of the spiral. It is cooled by a conventional device, not shown here.
  • the cooling circuits 12, 13 and 14 of the side wall 1, of the main inductor 3 and of the auxiliary inductor 7 are only shown diagrammatically here, being in accordance with the embodiments already known and each being able to include in particular a pump and a heat exchanger. heat.
  • the electrical device is depicted in FIG. 4.
  • the main inductor 3 is connected to the terminals of an electric power generator 15 of alternating current.
  • a capacitor bank 16 is also connected to the terminals of the power generator 15, in parallel with the main inductor 3.
  • the assembly forms a main electrical circuit 18 closed.
  • This main electrical circuit 18 has a resistance due above all to the resistances of the structure of the crucible, of the load contained therein and of the main inductor 3.
  • the auxiliary inductor 7 forms with an adjustable bank of capacitors 17 an electrical circuit.
  • auxiliary 19 closed which is physically separate from the power generator 15 and without its own power generator.
  • This auxiliary electric circuit 19 has a resistance mainly due to the auxiliary inductor 7.
  • the proximity of the inductors 3 and 7 means that an electromagnetic coupling appears between the electric circuits 18 and 19 in operation, despite the absence of a generator. power in the auxiliary electric circuit 19.
  • This coupling varies in particular as a function of the power injected and the load in the crucible, and also of an adjustment of the total capacity of the capacitor bank 17, which is composed of individual capacitors, which can be connected to the auxiliary electric circuit 19 or be separated therefrom by switches 21.
  • the individual capacitors 20 can be placed in parallel as shown in FIG. 5, or otherwise.
  • the capacitor bank 17 could be replaced by an adjustable capacitor 22, the effect of which would be identical.
  • the invention is based on the electromagnetic coupling between the electric circuits 18 and 19 by the inductors 3 and 7, to adjust the currents induced by these and act on the distribution of the heating in the load contained in the crucible, in particular in order to homogenize its temperature during a melting and stirring process, or (among other possibilities) to increase the heating at the bottom in order to release the pouring plug 11 and facilitate pouring.
  • the first line represents the operation of a device where the auxiliary circuit 19 would be open.
  • the voltages at the terminals of the main inductor 3 and the current flowing therein are high, the voltage at the terminals of the auxiliary inductor 7 is low, the heating is therefore carried out mainly by the main inductor 3, but with losses large in the side wall 1 and relatively low efficiency.
  • This mode of operation is analogous to known conditions and is neither representative of the invention, nor normally sought.
  • Figures 7 and 8 which show the temperature distribution in the molten charge in perspective from above and in perspective from below (light shades of color signifying greater local heating) illustrate significant heating at the periphery, here lower at the center, the load therefore being there much colder, and above all heating by the very low power generator 15 just above the hearth.
  • the choice of a different excitation frequency can vary the distribution of the heating in the radial direction, but the heating will remain low anyway at the bottom of the crucible, and temperature homogeneity will not be achieved.
  • the following lines of the table illustrate the effect of increasing capacities of the capacitor bank 17 or of the adjustable capacitor 22.
  • the electromagnetic resonance increases, the voltage across the main inductor 3 and the intensity of the current decrease, while the voltage at the terminals of the auxiliary inductor 7 and the intensity of the current which passes through it increases.
  • the losses in the side wall 1 decrease sharply and more and more, and the losses in the auxiliary inductor 7 increase while remaining at much lower values, which means that the efficiency of the furnace is much greater and reaches a maximum. 85% at a capacitance value estimated here at 69.45 nF.
  • FIG. 13 illustrates the use of a second auxiliary electric circuit 23, comprising an inductor 24 and a capacitor 25 placed across the terminals of the inductor 24 by closing the circuit.
  • the capacitor 25 may or may not be adjustable.
  • the inductor 24 is placed above the top of the crucible, similar in shape to that of the auxiliary electrical circuit 19 and facing it.
  • the second auxiliary electric circuit 23 does not have an electric generator.
  • the second auxiliary circuit 26 can be deactivated by opening a disconnector 26.
  • Figures 14 and 15 illustrate an embodiment where the sole, then bearing the reference 27, is composed of water boxes 28 in sectors of circles joined by curved tubes 29 for circulating coolant from a water box 28 to the next one.
  • the extremities 30 of the cooling circuit also serve as a connection to an adjustable capacitor bank as in the previous embodiment.
  • the device is otherwise identical to the previous one, and the operation is similar; but this embodiment is not preferred since the electromagnetic coupling for the benefit of the auxiliary circuit would be much less good.
  • the inducers can be of any known kind.
  • the auxiliary inductor mainly envisaged is in the form of a spiral, but a single coil inductor, formed of several concentric strands arranged in parallel or of a single strand, would be possible and should give good results.
  • the main inductor considered here, with several parallel strands and with a single turn, could reciprocally be replaced by a helical inductor with several turns.
  • the total capacities at which it is possible to adjust the capacitor bank 17 must be chosen to allow different operating modes corresponding to the heating distributions that one wishes to obtain, such as good homogeneity in most of the volume, and sufficient heating. concentrate at the bottom of the crucible to allow pouring. It will generally be indicated that the state of maximum resonance of the circuit can be reached in order to be able to send the maximum power into the auxiliary circuit 19. The state corresponding to the highest efficiency may be preferred during most of the process, without this being essential since the efficiency remains improved in a range of large values of the total capacity of the capacitor bank 17.
  • auxiliary circuits in electromagnetic coupling with the main circuit, composed of an inductor and a capacitor and devoid of own electric generator, could be added again if necessary at various places of the crucible.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Crucibles And Fluidized-Bed Furnaces (AREA)
  • Furnace Details (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • General Induction Heating (AREA)

Abstract

A crucible comprises at least two electric induction heating circuits, one of which is positioned around the side wall, and the other under or in the bottom of the crucible. One of the circuits (18) comprises an electric power generator (15) connected to an inductor (3), and the other circuit (19) is devoid of an electric power generator, but is electromagnetically coupled to the former and made up of an auxiliary inductor (7) and capacitors (17) having a fully adjustable capacity. It is possible to modify the coupling conditions, the respective powers passing through the two inductors (3, 7) and the distribution of the temperature build-up to homogenise the heating, or to concentrate it at the bottom of the crucible. Good heating performance can be expected.

Description

Description Description
Titre : Four à induction comprenant un circuit résonant additionnelTitle: Induction furnace including an additional resonant circuit
L'invention a pour sujet un four à induction comprenant un circuit résonant additionnel. The subject of the invention is an induction furnace comprising an additional resonant circuit.
Elle concerne les fours à creuset froid à chauffage par induction électromagnétique destinés à faire fondre, notamment, au moins un matériau conducteur électrique tel qu'un oxyde ou des mélanges d'oxyde, ou de tels mélanges avec des proportions de métaux allant jusqu'à environ 30% massiques, ces mélanges étant représentatifs des coriums fondus. Elle s'applique aussi en particulier aux fours utilisés dans l'industrie verrière, l'élaboration des émaux ou tout matériau de haute pureté élaboré à haute température, de par exemple 1200 K à plus de 3000 K. La fréquence d'induction est généralement comprise entre 100 kHz et 1000 kHz selon la taille des creusets. It relates to cold crucible furnaces with electromagnetic induction heating intended to melt, in particular, at least one electrically conductive material such as an oxide or mixtures of oxides, or such mixtures with proportions of metals ranging up to approximately 30% by mass, these mixtures being representative of molten corium. It also applies in particular to furnaces used in the glass industry, the production of enamels or any high purity material produced at high temperature, for example from 1200 K to more than 3000 K. The induction frequency is generally between 100 kHz and 1000 kHz depending on the size of the crucibles.
Elle doit améliorer les fours à creuset froid en permettant en particulier une meilleure homogénéité de la température de la charge, avec la conséquence possible d'une diminution de l'épaisseur de la croûte sur la sole au fond du creuset, sans impliquer une surchauffe importante du bain liquide du ou des matériaux en fusion ni produire des courants induits, qui seraient néfastes en pouvant perturber les pièces constituant le circuit électrique du ou des inducteurs, notamment les générateurs de courant. Les avantages obtenus sont associés à un meilleur rendement et une meilleure homogénéité thermique ; ils permettent de simplifier l'installation, d'améliorer le brassage du bain liquide par convection et de faciliter la coulée du liquide à travers la sole par gravité. It must improve cold crucible furnaces by allowing in particular a better homogeneity of the temperature of the charge, with the possible consequence of a reduction in the thickness of the crust on the hearth at the bottom of the crucible, without involving significant overheating. of the liquid bath of the molten material (s) or produce induced currents, which would be harmful by being able to disturb the parts constituting the electrical circuit of the inductor (s), in particular the current generators. The advantages obtained are associated with better efficiency and better thermal homogeneity; they make it possible to simplify the installation, to improve the stirring of the liquid bath by convection and to facilitate the flow of the liquid through the hearth by gravity.
Les fours à induction sont bien connus dans le domaine de la fonderie ou de la métallurgie, ou celui de l'industrie nucléaire pour l'élaboration de matériaux ou la formation de mélanges homogènes. Ils comprennent un creuset dans lequel la charge est maintenue, et au moins un inducteur, dont l'excitation produit des courants dans la charge, qui amènent son chauffage et sa fusion. Ce procédé de chauffage est simple à mettre en œuvre et permet d'éviter tout contact entre la source d'énergie thermique et le creuset. Induction furnaces are well known in the field of foundry or metallurgy, or that of the nuclear industry for the preparation of materials or the formation of homogeneous mixtures. They include a crucible in which the charge is maintained, and at least one inductor, the excitation of which produces currents in the charge, which cause it to heat and melt. This heating process is simple to implement and makes it possible to avoid any contact between the thermal energy source and the crucible.
Le creuset comprend typiquement une paroi latérale jointe à une sole pouvant être plate et qui en constitue le fond. S'il est en matériau conducteur de l'électricité, il est souvent sectorisé, c'est-à-dire composé de portions s'étendant sur des secteurs angulaires et séparées par des intercalaires isolants électriques, afin d'y éviter l'apparition de courants induits circulant en boucle autour de la charge et les pertes d'énergie correspondantes. The crucible typically comprises a side wall joined to a hearth which may be flat and which constitutes the bottom thereof. If it is made of an electrically conductive material, it is often sectorized, that is to say composed of portions extending over angular sectors and separated by electrically insulating spacers, in order to avoid the appearance of induced currents circulating in a loop around the load and the corresponding energy losses.
Certains creusets sont construits en un matériau réfractaire tel le pisé ou le graphite. Leur avantage est une température de fusion élevée, mais certaines charges, notamment composées d'oxydes, doivent être fondues à des températures plus élevées encore, ou du moins suffisantes pour les corroder physiquement ou chimiquement. Some crucibles are made of a refractory material such as rammed earth or graphite. Their advantage is a high melting temperature, but certain charges, in particular composed of oxides, must be melted at even higher temperatures, or at least sufficient to corrode them physically or chemically.
Une conception également très répandue, et que reprend l'invention, est alors celle du creuset froid, équipé d'un circuit de refroidissement par l'eau ou un autre liquide et qui s'étend dans le creuset. Le creuset reste alors beaucoup plus froid que le cœur de la charge pendant le fonctionnement du procédé, et il reste protégé de la corrosion ou d'autres attaques physiques ou chimiques par une couche solidifiée du matériau de la charge qui subsiste contre lui, qu'on peut considérer comme constituant une paroi interne du creuset et qui est appelée auto-creuset. Ces creusets froids permettent de fondre à haute température, au-delà de 1500 K, voire plus de 3000 K par exemple, des matériaux hautement réactifs, qui peuvent être métalliques comme le titane, l'acier ou des alliages divers composés d'oxydes comme le verre, l'oxyde de titane, des terres rares ou un mélange ; ou encore des matériaux peu conducteurs tels que silicium ou les émaux. A design which is also very widespread, and which the invention repeats, is then that of the cold crucible, equipped with a cooling circuit by water or another liquid and which extends into the crucible. The crucible then remains much cooler than the core of the charge during the operation of the process, and it remains protected from corrosion or other physical or chemical attack by a solidified layer of the material of the charge which remains against it, than one can consider as constituting an internal wall of the crucible and which is called self-crucible. These cold crucibles make it possible to melt at high temperature, beyond 1500 K, or even more than 3000 K for example, highly reactive materials, which can be metallic such as titanium, steel or alloys of various oxides such as glass, titanium oxide, rare earths or a mixture; or else poorly conductive materials such as silicon or enamels.
On observe toutefois des défauts d'homogénéité du chauffage dans le creuset. La portion la plus chaude de la charge tend à remonter vers la surface libre par convection. Or les courants induits responsables de réchauffement tendent à se concentrer dans les portions les plus conductrices de l'électricité, qui correspondent aux portions chaudes pour les charges d'oxydes notamment. La conséquence de cette convection, renforcée éventuellement par le chauffage hétérogène et par une diminution de l'induction électromagnétique près de la sole si elle est métallique, est que la charge est plus difficile à chauffer au fond du creuset, que sa température y reste moins élevée, et que normalement la couche solidifiée est beaucoup plus épaisse sur le dessus de la sole (parfois quelques dizaines de millimètres, au lieu de quelques millimètres en vis-à-vis de la paroi latérale du creuset). Cette difficulté plus grande à procéder à la fusion, associée à des pertes électriques importantes dans les structures refroidies, est dommageable en soi et peut affecter la qualité du procédé. Elle est encore plus gênante quand il est prévu d'évacuer la charge fondue par le fond du creuset, en descellant un bouchon au centre de la sole, plutôt que par un retournement du creuset, délicat à réaliser et souvent exclu. La croûte solidifiée peut en effet empêcher la coulée quand le bouchon a été retiré. Il est envisageable d'augmenter la puissance pour faire fondre cette croûte de fond du creuset et concentrer le chauffage au centre ; mais le risque existe que réchauffement devienne excessif ailleurs, en augmentant la volatilité de certains oxydes et modifiant ainsi la composition de la charge à fondre, en fondant la couche de charge solidifiée qui couvrait la paroi latérale ou en endommageant certaines structures du creuset, comme les isolants entre secteurs. Les pertes thermiques peuvent aussi être multipliées par un facteur pouvant être de 1,5 ou 2, dans des procédés déjà caractérisés par des rendements faibles, où les pertes par rayonnement à la surface libre du bain, conduction sur les parois du creuset, et convection avec l'atmosphère environnante sont importantes. However, there are homogeneity defects in the heating in the crucible. The hottest portion of the load tends to rise towards the free surface by convection. Now, the induced currents responsible for heating tend to concentrate in the most electrically conductive portions, which correspond to the hot portions for the oxide charges in particular. The consequence of this convection, possibly reinforced by heterogeneous heating and by a decrease in electromagnetic induction near the hearth if it is metallic, is that the charge is more difficult to heat at the bottom of the crucible, that its temperature remains less there. high, and that normally the solidified layer is much thicker on the top of the hearth (sometimes a few tens of millimeters, instead of a few millimeters opposite the side wall of the crucible). This greater difficulty in proceeding with the merger, associated with significant electrical losses in cooled structures, is damaging in itself and can affect the quality of the process. It is even more troublesome when it is planned to evacuate the molten charge through the bottom of the crucible, by unsealing a stopper in the center of the hearth, rather than by turning the crucible, which is difficult to perform and often excluded. The solidified crust can in fact prevent pouring when the stopper has been removed. It is conceivable to increase the power to melt this bottom crust of the crucible and concentrate the heating in the center; but there is a risk that heating will become excessive elsewhere, increasing the volatility of certain oxides and thereby altering the composition of the charge to be melted, melting the solidified charge layer which covered the side wall or damaging certain crucible structures, such as insulators between sectors. The thermal losses can also be multiplied by a factor which can be 1.5 or 2, in processes already characterized by low yields, where the losses by radiation at the free surface of the bath, conduction on the walls of the crucible, and convection with the surrounding atmosphere are important.
On peut aussi agir sur la fréquence d'induction pour tenter d'obtenir cette fusion de la charge au fond du creuset : si l'inducteur est disposé autour de la paroi latérale, ce qui est le plus habituel, la répartition de l'échauffement à l'intérieur du creuset dans la direction radiale dépend de la fréquence d'excitation de l'inducteur : plus elle est importante, plus réchauffement est localisé en paroi ; il est donc possible de choisir ou d'ajuster cette fréquence d'excitation pour régler le volume du bain fondu et, dans une certaine mesure, la répartition des températures à l'intérieur du creuset ; mais le manque d'homogénéité des températures dans le bain fondu peut devenir inacceptable. En pratique, on surdimensionne en général le circuit électrique ainsi que le système de refroidissement, sans que cet alourdissement du dispositif soit forcément satisfaisant. It is also possible to act on the induction frequency to try to obtain this melting of the charge at the bottom of the crucible: if the inductor is placed around the side wall, which is the most usual, the distribution of the heating inside the crucible in the radial direction depends on the excitation frequency of the inductor: the greater it is, the more heating is localized in the wall; it is therefore possible to choose or adjust this excitation frequency to adjust the volume of the molten bath and, to a certain extent, the temperature distribution inside the crucible; but the lack of uniformity of temperatures in the molten bath may become unacceptable. In practice, the electrical circuit and the cooling system are generally oversized, without this increasing the device being necessarily satisfactory.
Ces défauts sont particulièrement marqués dans le cas courant où le creuset froid est en matériau conducteur de l'électricité, comme le cuivre ou certaines nuances d'acier inoxydables, notamment à cause de l'augmentation des pertes électriques dans les structures, mais ils sont présents quels que soient le matériau constituant le creuset et la structure de celui-ci. Un dernier inconvénient des fours à induction les plus simples, décrits jusqu'à présent, qu'on mentionnera ici, est qu'ils sont mal adaptés à des volumes de charge variables, donc de hauteurs différentes à l'intérieur du creuset, si la hauteur de l'inducteur est nettement différente. These defects are particularly marked in the common case where the cold crucible is made of an electrically conductive material, such as copper or certain grades of stainless steel, in particular because of the increase in electrical losses in the structures, but they are present whatever the material constituting the crucible and the structure thereof. A final drawback of the simplest induction furnaces, described so far, which will be mentioned here, is that they are poorly suited to varying load volumes, and therefore of different heights inside the crucible, if the height of the inductor is markedly different.
L'art antérieur illustrant de tels fours à induction est abondant. On s'appesantira maintenant sur certaines conceptions particulières, supposées améliorer l'homogénéité du chauffage. The prior art illustrating such induction furnaces is abundant. We will now dwell on certain particular designs, supposed to improve the homogeneity of the heating.
Le document EP 1045 216 B1 décrit un inducteur supplémentaire, disposé autour de la zone de coulée au-dessous de la sole, autour du bouchon permettant la coulée hors du creuset, en plus de l'inducteur principal entourant la paroi latérale du creuset. Il permet de créer des courants induits supplémentaires autour de l'orifice de coulée traversant la sole, d'y empêcher la solidification de la charge et de garantir la coulée quand le bouchon a été retiré. Il subsiste cependant des difficultés de mise en œuvre, ce dispositif ne convenant pas forcément à la fusion de matériaux à point de fusion très élevé. Son effet est purement local pendant un temps limité, si bien que le problème plus général de manque d'homogénéité de chauffage de la charge à fondre n'est pas résolu. Il en irait de même si on disposait, ce qui a déjà été proposé, un tube métallique non refroidi entre cet inducteur inférieur et l'orifice de coulée avec l'espoir d'obtenir un chauffage plus important grâce au tube ; ce dernier risque d'ailleurs d'être corrodé rapidement, surtout à haute température. Document EP 1045 216 B1 describes an additional inductor, arranged around the casting zone below the hearth, around the plug allowing pouring out of the crucible, in addition to the main inductor surrounding the side wall of the crucible. It makes it possible to create additional induced currents around the pouring orifice passing through the hearth, to prevent the charge from solidifying there and to guarantee the casting when the stopper has been removed. However, there are still implementation difficulties, this device not necessarily suitable for melting materials with a very high melting point. Its effect is purely local for a limited time, so that the more general problem of lack of heating uniformity of the charge to be melted is not solved. The same would apply if there were, which has already been proposed, an uncooled metal tube between this lower inductor and the pouring orifice with the hope of obtaining greater heating thanks to the tube; the latter also risks being corroded quickly, especially at high temperature.
Dans certaines conceptions comme celle du document US 6 185 243 Bl, l'inducteur plus classique disposé autour de la paroi latérale du creuset est remplacé par un inducteur situé sous la sole et dont la forme peut être celle d'une ou plusieurs spirales. Cette conception convient seulement pour des bains de faible hauteur par rapport au diamètre, et elle peut être associée à des pertes thermiques importantes par convection à la surface libre du bain fondu et par conduction sur la paroi latérale. La puissance fournie reste hétérogène, typiquement importante au-dessus des spires inductrices, mais beaucoup plus faible près de la paroi latérale, et au centre du creuset si les spires y sont absentes. Il a encore été proposé de disposer un inducteur unique s'étendant à la fois autour de la paroi latérale et sous la sole (US-1645526- A), ou deux inducteurs séparés commandés chacun par une source de puissance (US 4 609425, JP 10 253 260, US 4687 646). Les possibilités d'une meilleure égalité de chauffage de la charge sont toutefois contrariées par des antagonismes de champs électriques produits par les deux inducteurs ou partie d'inducteur, qui perturbent leur fonctionnement et peuvent même endommager l'électronique de commande. Un perfectionnement à ces conceptions a été enfin proposé dans le document WO 2017/093165 Al, dans lequel une pièce appelée concentrateur à flux magnétique est placée à la jonction de la paroi latérale et de la sole en séparant ainsi les deux inducteurs. Cette pièce est une pièce statique en matière à perméabilité magnétique élevée, qui réduit donc les interactions entre les champs magnétiques. Les inconvénients précédents sont réduits, et un rendement meilleur peut être espéré. Il faut malheureusement, notamment pour la plage de fonctionnement envisagée ici (celle qui concerne la fréquence d'excitation de la source de puissance), refroidir ce concentrateur à flux magnétique pour qu'il maintienne ses performances, et cela peut être technologiquement difficile dans certaines situations. Le concentrateur doit être placé dans une zone difficile d'accès, en pouvant imposer un déplacement des inducteurs par rapport à la charge ; il est enfin vulnérable aux irradiations dans le cas de charges radioactives. Un inconvénient d'un autre ordre est que ce dispositif ne permet pas de répartir la puissance de chauffage entre les deux inducteurs. In certain designs such as that of document US Pat. No. 6,185,243 B1, the more conventional inductor disposed around the side wall of the crucible is replaced by an inductor located under the hearth and the shape of which may be that of one or more spirals. This design is only suitable for baths of low height compared to the diameter, and it can be associated with significant heat losses by convection at the free surface of the molten bath and by conduction on the side wall. The power supplied remains heterogeneous, typically high above the inductive turns, but much lower near the side wall, and at the center of the crucible if the turns are absent. It has also been proposed to have a single inductor extending both around the side wall and under the sole (US-1645526-A), or two separate inductors each controlled by a power source (US Pat. No. 4,609425, JP 10,253,260, US 4,687,646). The possibilities of a better equal heating of the load are however thwarted by antagonisms of electric fields produced by the two inductors or part of the inductor, which disturb their operation and can even damage the control electronics. An improvement to these designs has finally been proposed in document WO 2017/093165 A1, in which a part called a magnetic flux concentrator is placed at the junction of the side wall and the sole, thus separating the two inductors. This part is a static part made of material with high magnetic permeability, which therefore reduces the interactions between magnetic fields. The foregoing drawbacks are reduced, and a better yield can be expected. Unfortunately, especially for the operating range considered here (that which concerns the excitation frequency of the power source), this magnetic flux concentrator must be cooled so that it maintains its performance, and this can be technologically difficult in certain cases. situations. The concentrator must be placed in an area that is difficult to access, being able to impose a displacement of the inductors with respect to the load; Finally, it is vulnerable to irradiation in the case of radioactive charges. Another drawback is that this device does not allow the heating power to be distributed between the two inductors.
L'invention concerne un four à induction perfectionné, dont l'aspect le plus important est qu'il permet à la fois d'augmenter l'efficacité de chauffage de la charge fondue et de régler la répartition de chauffage dans le volume chauffé selon les besoins, grâce à une construction plus favorable de deux inducteurs dont l'un est placé autour de la paroi latérale du creuset et l'autre sous (ou dans) la sole. Des rendements électriques supérieurs à ceux des dispositifs et procédés antérieurs sont espérés. Une meilleure facilité de coulée est aussi attendue grâce à une meilleure efficacité de chauffage dans le fond du creuset. The invention relates to an improved induction furnace, the most important aspect of which is that it makes it possible both to increase the heating efficiency of the molten charge and to adjust the heating distribution in the heated space according to the requirements. needs, thanks to a more favorable construction of two inductors, one of which is placed around the side wall of the crucible and the other under (or in) the hearth. Higher electrical efficiencies than those of the prior devices and methods are hoped for. Better casting ease is also expected thanks to better heating efficiency in the bottom of the crucible.
Elle concerne précisément un four à induction, comprenant un creuset à paroi latérale refroidie par une circulation de fluide et une sole placée sous la paroi latérale, un premier circuit électrique de chauffage par induction comprenant un premier inducteur et un générateur de puissance électrique, et un deuxième circuit électrique de chauffage par induction, comprenant un deuxième inducteur, l'un des inducteurs étant placé autour de la paroi latérale, et l'autre sous ou dans la sole, caractérisé en ce que le deuxième circuit est dépourvu de générateur de puissance électrique mais en couplage électromagnétique avec le premier circuit et pourvu d'un dispositif de condensateurs électriques à capacité réglable, ledit dispositif de condensateurs électriques étant relié au deuxième inducteur. It relates specifically to an induction furnace, comprising a crucible with a side wall cooled by a circulation of fluid and a hearth placed under the side wall, a first electric induction heating circuit comprising a first inductor and an electric power generator, and a second electric induction heating circuit comprising a second inductor, one of the inductors being placed around the side wall, and the another under or in the floor, characterized in that the second circuit is devoid of an electric power generator but in electromagnetic coupling with the first circuit and provided with a device of electric capacitors with adjustable capacity, said device of electric capacitors being connected to the second inductor.
Ce dispositif électrique à double circuit exploite un phénomène de résonance électrique du four, facilité par l'interaction électromagnétique libre des deux circuits. Contrairement aux dispositifs connus dans lesquels un inducteur entourant la paroi latérale et un inducteur affecté à la sole sont excités par une même source de puissance en étant reliés l'un à l'autre, ou par deux sources différentes en étant alors séparés l'un de l'autre, on n'observe aucun antagonisme des champs magnétiques d'induction à leur jonction et aucune perturbation sur les circuits électriques. Il en résulte un meilleur rendement électrique et des pertes réduites. This double-circuit electric device exploits a phenomenon of electric resonance of the furnace, facilitated by the free electromagnetic interaction of the two circuits. Unlike the known devices in which an inductor surrounding the side wall and an inductor assigned to the sole are excited by the same power source by being connected to one another, or by two different sources by being then separated from one another. on the other hand, there is no antagonism of the magnetic induction fields at their junction and no disturbance on the electrical circuits. This results in better electrical efficiency and reduced losses.
Un autre avantage de l'invention est une facilité de mieux répartir le chauffage, qu'il est en particulier possible de rendre plus important à cœur et au fond, juste au-dessus de la sole, pour améliorer le procédé et faciliter éventuellement la coulée. Cette répartition du chauffage dépend du réglage de la capacité totale (ajustable au cours de la fusion), avec d'ailleurs une très grande sensibilité aux variations de cette capacité, au point qu'il est possible soit d'obtenir une bonne uniformité des températures, soit au contraire de chauffer essentiellement soit à la périphérie, soit au cœur, soit au fond de la charge fondue. Another advantage of the invention is an ease of distributing the heating better, which it is in particular possible to make more important at the core and at the bottom, just above the hearth, to improve the process and possibly facilitate the casting. . This heating distribution depends on the adjustment of the total capacity (adjustable during the melting), with moreover a very great sensitivity to the variations of this capacity, to the point that it is possible either to obtain a good uniformity of the temperatures. , or on the contrary to heat essentially either at the periphery, or at the heart, or at the bottom of the molten charge.
Il sera courant que le premier inducteur soit disposé autour de la paroi latérale puisqu'il constitue l'inducteur principal, le second circuit électrique étant alors affecté à la sole. La disposition inverse peut toutefois être rencontrée sans qu'elle soit critiquable, notamment pour les creusets à grande surface et faible hauteur. It will be common for the first inductor to be arranged around the side wall since it constitutes the main inductor, the second electrical circuit then being assigned to the sole. The opposite arrangement may however be encountered without being open to criticism, in particular for crucibles with a large surface area and low height.
L'inducteur de fond du creuset peut former une spirale couverte d'un isolant électrique et très bon conducteurthermique : il est alors possible et avantageux que la sole de fond du creuset soit constituée par ledit inducteur lui-même, ce qui simplifie la conception du creuset et améliore le rendement du chauffage. The bottom inductor of the crucible can form a spiral covered with an electrical insulator and very good thermal conductor: it is then possible and advantageous that the bottom hearth of the crucible is formed by said inductor itself, which simplifies the design of the crucible and improves the heating efficiency.
Le four à induction peut comprendre au moins un circuit supplémentaire dépourvu de générateur de puissance électrique et comprenant un inducteur et un dispositif de condensateurs ayant une capacité totale réglable, et en couplage électromagnétique avec au moins le premier circuit ; ce circuit supplémentaire ou ces circuits supplémentaires ont donc les mêmes propriétés que le deuxième circuit mentionné. Ils peuvent se révéler utiles en partie haute du four pour améliorer le chauffage des quantités nouvellement introduites de la charge. On peut alors les placer au- dessus du sommet du creuset, face à l'inducteur situé sur ou dans la sole, et parallèlement à lui. The induction furnace may comprise at least one additional circuit devoid of an electric power generator and comprising an inductor and a capacitor device having an adjustable total capacity, and in electromagnetic coupling with at least the first circuit; this additional circuit or these additional circuits therefore have the same properties as the second circuit mentioned. They can prove to be useful in the upper part of the furnace to improve the heating of the newly introduced quantities of the charge. They can then be placed above the top of the crucible, facing the inductor located on or in the hearth, and parallel to it.
Le circuit supplémentaire ou les circuits supplémentaires peuvent alors être avantageusement équipés d'un sectionneur permettant de les ouvrir à volonté. The additional circuit or the additional circuits can then be advantageously equipped with a disconnector making it possible to open them at will.
L'invention sera maintenant décrite dans différents aspects, caractéristiques et avantages au moyen des figures suivantes qui en représentent certaines réalisations particulières, purement illustratives : The invention will now be described in various aspects, characteristics and advantages by means of the following figures which represent certain particular embodiments thereof, purely illustrative:
Figure 1 une vue générale du four à induction ; Figure 1 a general view of the induction furnace;
Figure 2 une vue de l'inducteur latéral ; Figure 2 a view of the side inductor;
Figure 3 une vue de l'inducteur de fond ; Figure 3 a view of the bottom inductor;
Figure 4 un schéma du circuit électrique ; Figure 4 a diagram of the electrical circuit;
Figure 5 une réalisation de la batterie de condensateurs ; Figure 5 an embodiment of the capacitor bank;
Figure 6 une autre réalisation ; Figure 6 another embodiment;
Figure 7 un premier état de chauffage ; Figure 7 a first state of heating;
Figure 8 le même, en vue de dessous ; Figure 8 the same, seen from below;
Figure 9 un deuxième état de chauffage ; Figure 9 a second state of heating;
Figure 10 le même, en vue de dessous ; Figure 10 the same, seen from below;
Figure 11 un troisième état de chauffage ; Figure 11 a third state of heating;
Figure 12 le même, en vue de dessous ; Figure 12 the same, seen from below;
Figure 13 un autre mode de réalisation du creuset ; Figure 13 another embodiment of the crucible;
Figure 14 un troisième mode de réalisation du creuset ; Figure 15 la sole de ce troisième mode ; Figure 14 a third embodiment of the crucible; Figure 15 the sole of this third mode;
Figure 16 une coupe de la sole du premier mode. Figure 16 a section of the sole of the first mode.
Un mode de réalisation va être décrit au moyen des figures 1 à 3. Cette réalisation de four à induction comprend une paroi latérale 1 ou virole cylindrique composée de tubes 2 de cuivre ou inox verticaux adjacents et reliés par des intercalaires isolant de l'électricité pour empêcher l'apparition de courants induits circulaires dans la paroi latérale 1. Les tubes 2 sont parcourus par un liquide de refroidissement tel que l'eau, suivant des dispositions connues. Un circuit de refroidissement 12 peut faire circuler le liquide alternativement vers le haut et vers le bas avec des raccords entre tubes 2 alternativement à l'extrémité supérieure et l'extrémité inférieure. Une autre construction possible, parmi d'autres encore, serait celle de US - 6 996 153 - B2, où chaque tube est refroidi indépendamment par un circuit faisant un aller et retour vertical. One embodiment will be described by means of Figures 1 to 3. This induction furnace embodiment comprises a side wall 1 or cylindrical shell composed of adjacent vertical copper or stainless steel tubes 2 and connected by electrically insulating spacers for prevent the appearance of induced circular currents in the side wall 1. The tubes 2 are traversed by a cooling liquid such as water, according to known arrangements. A cooling circuit 12 can circulate the liquid alternately upwards and downwards with connections between tubes 2 alternately at the upper end and the lower end. Another possible construction, among others still, would be that of US-6,996,153-B2, where each tube is cooled independently by a circuit making a vertical return flow.
Un inducteur latéral 3 entoure la paroi latérale 1. Il est ici à spire unique et composé de brins 4 parallèles et superposés en hauteur et faisant chacun un tour unique du creuset. Leurs extrémités sont réunies par deux raccordements verticaux 5 et 6, qui assurent d'ailleurs aussi bien le raccordement électrique à un générateur de puissance électrique alternative que le raccordement hydraulique, les brins 4 étant eux aussi refroidis par la circulation du liquide de refroidissement, connectés au circuit de refroidissement 13. D'autres agencements de l'inducteur latéral, notamment à spires successives en hélice, seraient encore possibles. A lateral inductor 3 surrounds the lateral wall 1. It is here with a single turn and composed of parallel strands 4 and superimposed in height and each making a single turn of the crucible. Their ends are joined by two vertical connections 5 and 6, which moreover provide both the electrical connection to an alternating electric power generator and the hydraulic connection, the strands 4 also being cooled by the circulation of the cooling liquid, connected to the cooling circuit 13. Other arrangements of the lateral inductor, in particular with successive helical turns, would still be possible.
Le creuset est complété par une sole 8 composé principalement d'un inducteur auxiliaire 7 en forme de spirale (figures 3 et 16). L'inducteur auxiliaire 7 est lui aussi un tube refroidi par de l'eau, et ses extrémités 9 et 10 mènent aussi à un circuit de refroidissement 14. Les spires 31 de la spirale sont jointes par un isolant de l'électricité 32 intercalaire isolant électrique et très bon conducteur de la chaleur qui les sépare tout en donnant une structure continue à la sole 8. De plus, l'inducteur auxiliaire 7 est recouvert à sa face supérieure par une couche mince isolante 33 de l'électricité et bonne conductrice de la chaleur, composée d'alumine par exemple. Une telle conception permet de supprimer la sole classiquement utilisée et de retenir la charge du creuset directement par l'inducteur auxiliaire 7. Le refroidissement de la sole 8 et de la paire latérale 1 amène aussi la formation de l'auto-creuset, c'est-à-dire qu'une couche de la charge à leur contact reste solide et les protège de la corrosion. The crucible is completed by a hearth 8 composed mainly of an auxiliary inductor 7 in the form of a spiral (Figures 3 and 16). The auxiliary inductor 7 is also a tube cooled by water, and its ends 9 and 10 also lead to a cooling circuit 14. The turns 31 of the spiral are joined by an electrical insulator 32 insulating spacer electric and very good conductor of the heat which separates them while giving a continuous structure to the sole 8. In addition, the auxiliary inductor 7 is covered on its upper face by a thin insulating layer 33 of electricity and a good conductor of electricity. heat, composed of alumina for example. Such a design makes it possible to eliminate the hearth conventionally used and to retain the charge of the crucible directly by the auxiliary inductor 7. The cooling of the hearth 8 and of the side pair 1 also causes the formation of the auto-crucible, that is to say that a layer of the filler in contact with them remains solid and protects them from corrosion.
Un bouchon de coulée 11 est disposé au centre de la spirale. Il est refroidi par un dispositif classique, non représenté ici. Les circuits de refroidissement 12, 13 et 14 de la paroi latérale 1, de l'inducteur principal 3 et de l'inducteur auxiliaire 7 sont seulement schématisés ici, étant conformes aux réalisations déjà connues et pouvant comprendre chacun notamment une pompe et un échangeur de chaleur. A pouring plug 11 is arranged in the center of the spiral. It is cooled by a conventional device, not shown here. The cooling circuits 12, 13 and 14 of the side wall 1, of the main inductor 3 and of the auxiliary inductor 7 are only shown diagrammatically here, being in accordance with the embodiments already known and each being able to include in particular a pump and a heat exchanger. heat.
Le dispositif électrique est décrit à la figure 4. L'inducteur principal 3 est relié aux bornes d'un générateur de puissance 15 électrique de courant alternatif. Une batterie de condensateurs 16 est également reliée aux bornes du générateur de puissance 15, en parallèle à l'inducteur principal 3. L'ensemble forme un circuit électrique principal 18 fermé. Ce circuit électrique principal 18 possède une résistance due surtout aux résistances de la structure du creuset, de la charge contenue dans celui-ci et de l'inducteur principal 3. L'inducteur auxiliaire 7 forme avec une batterie réglable de condensateurs 17 un circuit électrique auxiliaire 19 fermé, qui est matériellement séparé du générateur de puissance 15 et dépourvu de générateur de puissance propre. Ce circuit électrique auxiliaire 19 possède une résistance due surtout à l'inducteur auxiliaire 7. La proximité des inducteurs 3 et 7 fait qu'un couplage électromagnétique apparaît entre les circuits électriques 18 et 19 en fonctionnement, malgré l'absence d'un générateur de puissance dans le circuit électrique auxiliaire 19. Ce couplage varie notamment en fonction de la puissance injectée et de la charge dans le creuset, et aussi d'un réglage de la capacité totale de la batterie de condensateurs 17, qui est composée de condensateurs individuels, qui peuvent être branchés au circuit électrique auxiliaire 19 ou en être séparés par des interrupteurs 21. Les condensateurs individuels 20 peuvent être placés en parallèle comme il est représenté à la figure 5, ou autrement. En variante (figure 6), la batterie de condensateurs 17 pourrait être remplacée par un condensateur réglable 22 dont l'effet serait identique. The electrical device is depicted in FIG. 4. The main inductor 3 is connected to the terminals of an electric power generator 15 of alternating current. A capacitor bank 16 is also connected to the terminals of the power generator 15, in parallel with the main inductor 3. The assembly forms a main electrical circuit 18 closed. This main electrical circuit 18 has a resistance due above all to the resistances of the structure of the crucible, of the load contained therein and of the main inductor 3. The auxiliary inductor 7 forms with an adjustable bank of capacitors 17 an electrical circuit. auxiliary 19 closed, which is physically separate from the power generator 15 and without its own power generator. This auxiliary electric circuit 19 has a resistance mainly due to the auxiliary inductor 7. The proximity of the inductors 3 and 7 means that an electromagnetic coupling appears between the electric circuits 18 and 19 in operation, despite the absence of a generator. power in the auxiliary electric circuit 19. This coupling varies in particular as a function of the power injected and the load in the crucible, and also of an adjustment of the total capacity of the capacitor bank 17, which is composed of individual capacitors, which can be connected to the auxiliary electric circuit 19 or be separated therefrom by switches 21. The individual capacitors 20 can be placed in parallel as shown in FIG. 5, or otherwise. As a variant (FIG. 6), the capacitor bank 17 could be replaced by an adjustable capacitor 22, the effect of which would be identical.
L'invention est fondée sur le couplage électromagnétique entre les circuits électriques 18 et 19 par les inducteurs 3 et 7, pour ajuster les courants induits par ceux-ci et agir sur la répartition du chauffage dans la charge contenue dans le creuset, afin notamment d'homogénéiser sa température pendant un processus de fusion et de brassage, ou (entre autres possibilités) d'augmenter le chauffage au fond afin de dégager le bouchon de coulée 11 et faciliter une coulée. The invention is based on the electromagnetic coupling between the electric circuits 18 and 19 by the inductors 3 and 7, to adjust the currents induced by these and act on the distribution of the heating in the load contained in the crucible, in particular in order to homogenize its temperature during a melting and stirring process, or (among other possibilities) to increase the heating at the bottom in order to release the pouring plug 11 and facilitate pouring.
Les effets obtenus peuvent être ceux du tableau 1 donné ci-dessous : The effects obtained can be those of Table 1 given below:
Tableau 1
Figure imgf000013_0001
Table 1
Figure imgf000013_0001
La première ligne représente le fonctionnement d'un dispositif où le circuit auxiliaire 19 serait ouvert. Les tensions aux bornes de l'inducteur principal 3 et le courant qui y circule sont importants, la tension aux bornes de l'inducteur auxiliaire 7 est faible, le chauffage s'effectue donc essentiellement par l'inducteur principal 3, mais avec des pertes importantes dans la paroi latérale 1 et un rendement relativement faible. Ce mode de fonctionnement est analogue aux conditions connues et n'est ni représentatif de l'invention, ni recherché normalement. Les figures 7 et 8, qui représentent la répartition des températures dans la charge fondue en perspective de dessus et en perspective de dessous (les nuances claires de couleur signifiant un chauffage local plus important) illustrent un chauffage important à la périphérie, ici plus faible au centre, la charge étant donc là beaucoup plus froide, et surtout un chauffage par le générateur de puissance 15 très faible juste au-dessus de la sole. Le choix d'une fréquence d'excitation différente peut faire varier la répartition du chauffage dans la direction radiale, mais le chauffage restera de toute façon faible au fond du creuset, et l'homogénéité des températures ne sera pas atteinte. The first line represents the operation of a device where the auxiliary circuit 19 would be open. The voltages at the terminals of the main inductor 3 and the current flowing therein are high, the voltage at the terminals of the auxiliary inductor 7 is low, the heating is therefore carried out mainly by the main inductor 3, but with losses large in the side wall 1 and relatively low efficiency. This mode of operation is analogous to known conditions and is neither representative of the invention, nor normally sought. Figures 7 and 8, which show the temperature distribution in the molten charge in perspective from above and in perspective from below (light shades of color signifying greater local heating) illustrate significant heating at the periphery, here lower at the center, the load therefore being there much colder, and above all heating by the very low power generator 15 just above the hearth. The choice of a different excitation frequency can vary the distribution of the heating in the radial direction, but the heating will remain low anyway at the bottom of the crucible, and temperature homogeneity will not be achieved.
Les lignes suivantes du tableau illustrent l'effet de capacités croissantes de la batterie de condensateurs 17 ou du condensateur réglable 22. La résonance électromagnétique se renforce, la tension aux bornes de l'inducteur principal 3 et l'intensité du courant décroissent, alors que la tension aux bornes de l'inducteur auxiliaire 7 et l'intensité du courant qui y passe croissent. Les pertes dans la paroi latérale 1 diminuent fortement et de plus en plus, et les pertes dans l'inducteur auxiliaire 7 croissent tout en restant à des valeurs bien inférieures, ce qui fait que le rendement du four est beaucoup plus important et atteint un maximum de 85% à une valeur de capacité estimée ici à 69,45 nF. Les diamètres typiques de répartition de réchauffement dans la charge sont alors ceux des figures 9 et 10, encore en perspective de dessus et de dessous respectivement : une homogénéité excellente du chauffage est obtenue dans la charge, et on observe cette fois que le fond du creuset est chauffé, en étant presque à la même température que les portions situées au-dessus. En augmentant encore la capacité de la batterie de condensateurs 17 ou du condensateur réglable 22, le chauffage du fond du creuset peut être accentué au détriment du reste : les figures 11 et 12 illustrent l'état obtenu à la capacité de 90 nF, qui correspond expérimentalement dans ce cas à une résonance électrique maximale, où la tension aux bornes de l'inducteur principal 3 et l'intensité du courant sont minimales, alors que la tension aux bornes de l'inducteur auxiliaire 7 et le courant qui y circule sont maximales. Le sommet de la charge est très peu chauffé, et le chauffage se concentre au fond du creuset comme le montre la figure 12. Le maintien de cet état de capacité totale importante de la batterie 17 et de résonance maximale, où le circuit électrique auxiliaire 19 travaille le plus en fournissant une puissance maximale, permet de concentrer le chauffage près du circuit électrique auxiliaire 19, c'est-à-dire ici au fond du creuset, et de favoriser la fusion de la croûte solide tandis que le brassage du bain fondu se poursuit. La coulée par gravité peut alors être obtenue en ouvrant le bouchon 11. The following lines of the table illustrate the effect of increasing capacities of the capacitor bank 17 or of the adjustable capacitor 22. The electromagnetic resonance increases, the voltage across the main inductor 3 and the intensity of the current decrease, while the voltage at the terminals of the auxiliary inductor 7 and the intensity of the current which passes through it increases. The losses in the side wall 1 decrease sharply and more and more, and the losses in the auxiliary inductor 7 increase while remaining at much lower values, which means that the efficiency of the furnace is much greater and reaches a maximum. 85% at a capacitance value estimated here at 69.45 nF. The typical heating distribution diameters in the load are then those of Figures 9 and 10, still in perspective from above and below respectively: excellent heating homogeneity is obtained in the load, and this time we observe that the bottom of the crucible is heated, being almost at the same temperature as the portions above. By further increasing the capacity of the capacitor bank 17 or of the adjustable capacitor 22, the heating of the crucible bottom can be accentuated to the detriment of the rest: figures 11 and 12 illustrate the state obtained at the capacitance of 90 nF, which corresponds experimentally in this case at maximum electrical resonance, where the voltage across the terminals of the main inductor 3 and the intensity of the current are minimum, while the voltage across the terminals of the auxiliary inductor 7 and the current flowing there are maximum . The top of the load is heated very little, and the heating is concentrated at the bottom of the crucible as shown in Figure 12. Maintaining this state of large total capacity of the battery 17 and maximum resonance, where the auxiliary electrical circuit 19 works the most by providing maximum power, allows the heating to be concentrated near the auxiliary electrical circuit 19, that is to say here at the bottom of the crucible, and to promote the melting of the solid crust while the stirring of the molten bath continues. Gravity casting can then be obtained by opening the stopper 11.
La figure 13 illustre l'utilisation d'un deuxième circuit électrique auxiliaire 23, comprenant un inducteur 24 et un condensateur 25 placé aux bornes de l'inducteur 24 en fermant le circuit. Le condensateur 25 peut être réglable ou non. L'inducteur 24 est placé au-dessus du sommet du creuset, de forme analogue à celle du circuit électrique auxiliaire 19 et lui faisant face. Le deuxième circuit électrique auxiliaire 23 est dépourvu de générateur électrique. Il travaille aussi en couplage électromagnétique résonant avec le circuit principal 18 et permet, avec un réglage ou un choix judicieux de la capacité du condensateur 25, d'instaurer un chauffage supplémentaire du creuset à sa partie supérieure, ce qui peut être utile soit pour un préchauffage d'une portion de charge nouvellement introduite dans le creuset, notamment dans des procédés à introduction progressive de la charge, ou encore pour des procédés où le volume de la charge est plus important et s'élève jusqu'à sa hauteur. Le deuxième circuit auxiliaire 26 peut être désactivé en ouvrant un sectionneur 26. FIG. 13 illustrates the use of a second auxiliary electric circuit 23, comprising an inductor 24 and a capacitor 25 placed across the terminals of the inductor 24 by closing the circuit. The capacitor 25 may or may not be adjustable. The inductor 24 is placed above the top of the crucible, similar in shape to that of the auxiliary electrical circuit 19 and facing it. The second auxiliary electric circuit 23 does not have an electric generator. It also works in resonant electromagnetic coupling with the main circuit 18 and makes it possible, with a judicious adjustment or choice of the capacity of the capacitor 25, to establish an additional heating of the crucible at its upper part, which can be useful either for a preheating of a portion of the charge newly introduced into the crucible, in particular in processes with progressive introduction of the charge, or again for processes where the volume of the charge is greater and rises to its height. The second auxiliary circuit 26 can be deactivated by opening a disconnector 26.
L'invention peut être mise en œuvre de bien d'autres façons. Les figures 14 et 15 illustrent un mode de réalisation où la sole, portant alors la référence 27, est composée de boîtes à eau 28 en secteurs de cercles joints par des tubes incurvés 29 de circulation de liquide de refroidissement d'une boîte à eau 28 à la suivante. Les extrémités 30 du circuit de refroidissement servent aussi de branchement à une batterie de condensateurs réglable comme dans la réalisation précédente. Le dispositif est par ailleurs identique au précédent, et le fonctionnement est analogue ; mais ce mode de réalisation n'est pas préféré puisque le couplage électromagnétique au profit du circuit auxiliaire serait beaucoup moins bon. The invention can be implemented in many other ways. Figures 14 and 15 illustrate an embodiment where the sole, then bearing the reference 27, is composed of water boxes 28 in sectors of circles joined by curved tubes 29 for circulating coolant from a water box 28 to the next one. The extremities 30 of the cooling circuit also serve as a connection to an adjustable capacitor bank as in the previous embodiment. The device is otherwise identical to the previous one, and the operation is similar; but this embodiment is not preferred since the electromagnetic coupling for the benefit of the auxiliary circuit would be much less good.
Il serait encore possible de placer l'inducteur auxiliaire au-dessous d'une sole réfractaire et inerte électriquement, comme dans des dispositifs connus, au prix encore d'une diminution du rendement. It would still be possible to place the auxiliary inductor below a refractory and electrically inert hearth, as in known devices, at the cost of a further reduction in efficiency.
Les inducteurs peuvent être de tout genre connu. L'inducteur auxiliaire envisagé principalement est en forme de spirale, mais un inducteur à spire unique, formé de plusieurs brins concentriques disposés en parallèle ou d'un seul brin, serait envisageable et devrait donner de bons résultats. L'inducteur principal envisagé ici, à plusieurs brins parallèles et à spire unique, pourrait réciproquement être remplacé par un inducteur en hélice à plusieurs spires. The inducers can be of any known kind. The auxiliary inductor mainly envisaged is in the form of a spiral, but a single coil inductor, formed of several concentric strands arranged in parallel or of a single strand, would be possible and should give good results. The main inductor considered here, with several parallel strands and with a single turn, could reciprocally be replaced by a helical inductor with several turns.
Les capacités totales auxquelles il est possible de régler la batterie de condensateurs 17 devront être choisies pour permettre différents modes de fonctionnement correspondant aux répartitions de chauffage qu'on souhaite obtenir, comme une bonne homogénéité dans la plus grande partie du volume, et un chauffage suffisamment concentré au fond du creuset pour permettre la coulée. Il sera généralement indiqué que l'état de résonance maximale du circuit puisse être atteint afin de pouvoir envoyer le maximum de puissance dans le circuit auxiliaire 19. L'état correspondant au rendement le plus élevé pourra être préféré pendant la plus grande partie du procédé, sans que cela soit indispensable puisque le rendement reste amélioré dans une gamme de valeurs importantes de la capacité totale de la batterie de condensateurs 17. The total capacities at which it is possible to adjust the capacitor bank 17 must be chosen to allow different operating modes corresponding to the heating distributions that one wishes to obtain, such as good homogeneity in most of the volume, and sufficient heating. concentrate at the bottom of the crucible to allow pouring. It will generally be indicated that the state of maximum resonance of the circuit can be reached in order to be able to send the maximum power into the auxiliary circuit 19. The state corresponding to the highest efficiency may be preferred during most of the process, without this being essential since the efficiency remains improved in a range of large values of the total capacity of the capacitor bank 17.
Les positions de l'inducteur principal (relié au générateur de puissance électrique) et de l'inducteur auxiliaire (équipé du condensateur réglable) pourraient être interverties, sans changement de la structure du creuset et de l'agencement des circuits électriques que représentent les figures 1 à 4 notamment. The positions of the main inductor (connected to the electric power generator) and of the auxiliary inductor (equipped with the adjustable capacitor) could be reversed, without changing the structure of the crucible and the arrangement of the electrical circuits shown in the figures. 1 to 4 in particular.
D'autres circuits auxiliaires, en couplage électromagnétique avec le circuit principal, composés d'un inducteur et d'un condensateur et dépourvus de générateur électrique propre, pourraient être ajoutés encore en cas de besoin à divers endroits du creuset. Other auxiliary circuits, in electromagnetic coupling with the main circuit, composed of an inductor and a capacitor and devoid of own electric generator, could be added again if necessary at various places of the crucible.

Claims

Revendications Claims
1. Four à induction, comprenant un creuset (1, 8) à paroi latérale (1) refroidie par une circulation de fluide et une sole (8) placée sous la paroi latérale (1), un premier circuit électrique (18) de chauffage par induction comprenant un premier inducteur (3) et un générateur de puissance (15) électrique, et un deuxième circuit électrique (19) de chauffage par induction, comprenant un deuxième inducteur (7), l'un des inducteurs étant placé autour de la paroi latérale, et l'autre sous ou dans la sole, caractérisé en ce que le deuxième circuit (19) est dépourvu de générateur de puissance électrique mais en couplage électromagnétique avec le premier circuit (18) et pourvu d'un dispositif (17) de condensateurs électriques à capacité réglable, ledit dispositif de condensateurs électriques étant relié au deuxième inducteur (7). 1. Induction furnace, comprising a crucible (1, 8) with a side wall (1) cooled by a circulation of fluid and a hearth (8) placed under the side wall (1), a first electrical circuit (18) for heating by induction comprising a first inductor (3) and an electric power generator (15), and a second electric circuit (19) for induction heating, comprising a second inductor (7), one of the inductors being placed around the side wall, and the other under or in the sole, characterized in that the second circuit (19) is devoid of an electric power generator but in electromagnetic coupling with the first circuit (18) and provided with a device (17) adjustable capacitance electric capacitors, said electric capacitor device being connected to the second inductor (7).
2. Four à induction selon la revendication 1, caractérisé en ce que la sole (8) est constituée par un desdits inducteurs (7), qui est en forme de spirale composée de spires (31) jointes par un isolant électrique (32). 2. Induction furnace according to claim 1, characterized in that the sole (8) is constituted by one of said inductors (7), which is in the form of a spiral composed of turns (31) joined by an electrical insulator (32).
3. Four à induction selon l'une quelconque des revendications 1 ou 2, caractérisé en ce que le dispositif de condensateurs électriques comprend un condensateur à capacité variable (22). 3. Induction furnace according to any one of claims 1 or 2, characterized in that the electric capacitor device comprises a variable capacity capacitor (22).
4. Four à induction selon l'une quelconque des revendications 1 ou 2, caractérisé en ce que le dispositif de condensateur électrique comprend des condensateurs (20) reliés au deuxième circuit (19) par des sectionneurs (21). 4. Induction furnace according to any one of claims 1 or 2, characterized in that the electric capacitor device comprises capacitors (20) connected to the second circuit (19) by disconnectors (21).
5. Four à induction selon l'une quelconque des revendications 1 à 4, caractérisé en ce que le premier inducteur (3) est placé autour de la paroi latérale (2). 5. Induction furnace according to any one of claims 1 to 4, characterized in that the first inductor (3) is placed around the side wall (2).
6. Four à induction selon l'une quelconque des revendications 1 à 4, caractérisé en ce que le premier inducteur est placé sous ou dans la sole. 6. Induction furnace according to any one of claims 1 to 4, characterized in that the first inductor is placed under or in the hearth.
7. Four à induction selon l'une quelconque des revendications 1 à 6, caractérisé en ce qu'il comprend au moins un circuit électrique supplémentaire (23) de chauffage par induction, dépourvu de générateur de puissance électrique et comprenant un inducteur (24) et un dispositif de condensateurs ayant une capacité totale réglable, et en couplage électromagnétique avec au moins le premier circuit (18). 7. Induction furnace according to any one of claims 1 to 6, characterized in that it comprises at least one additional electric circuit (23) for induction heating, without an electric power generator and comprising an inductor (24) and a capacitor device having an adjustable total capacity, and in electromagnetic coupling with at least the first circuit (18).
8. Four à induction selon la revendication 7, caractérisé en ce qu'au moins un dit circuit électrique supplémentaire est équipé d'un sectionneur (26) permettant de l'ouvrir. 8. Induction furnace according to claim 7, characterized in that at least one said additional electrical circuit is equipped with a disconnector (26) allowing it to be opened.
9. Four à induction selon l'une quelconque des revendications 7 ou 8, caractérisé en ce que l'inducteur de l'au moins un circuit supplémentaire est placé au- dessus du creuset et face au deuxième circuit électrique. 9. Induction furnace according to any one of claims 7 or 8, characterized in that the inductor of the at least one additional circuit is placed above the crucible and facing the second electrical circuit.
10. Four à induction selon l'une quelconque des revendications 1 à 9, caractérisé en ce que la capacité totale du dispositif de condensateurs du deuxième circuit est réglable à un état de résonance électrique maximale du four. 10. Induction furnace according to any one of claims 1 to 9, characterized in that the total capacity of the capacitor device of the second circuit is adjustable to a state of maximum electrical resonance of the furnace.
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FR3100421A1 (en) 2021-03-05
FR3100421B1 (en) 2021-09-10
CN114303035A (en) 2022-04-08
KR20220075219A (en) 2022-06-07

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