EP0010041B1 - Process for the continuous casting of metals with stirring in the secundary cooling zone - Google Patents

Process for the continuous casting of metals with stirring in the secundary cooling zone Download PDF

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Publication number
EP0010041B1
EP0010041B1 EP79400695A EP79400695A EP0010041B1 EP 0010041 B1 EP0010041 B1 EP 0010041B1 EP 79400695 A EP79400695 A EP 79400695A EP 79400695 A EP79400695 A EP 79400695A EP 0010041 B1 EP0010041 B1 EP 0010041B1
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Prior art keywords
casting
metal
electromagnetic
entrainment
solidification
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German (de)
French (fr)
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EP0010041A1 (en
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Robert Alberny
Jacques Ruer
Jean-Pierre Birat
Roger Ventavoli
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Institut de Recherches de la Siderurgie Francaise IRSID
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Institut de Recherches de la Siderurgie Francaise IRSID
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/122—Accessories for subsequent treating or working cast stock in situ using magnetic fields

Definitions

  • the present invention relates to the continuous casting of molten metals, in particular steel. It relates more precisely to the operations of mixing the liquid metal, during solidification in the secondary cooling stage of the casting machine, in order to improve the metallurgical quality of the product obtained.
  • the invention relates in particular to the casting of products of elongated section, for example slabs.
  • the liquid interior part of the product is therefore substantially in the form of a cone, the base of which corresponds to the free surface of the metal in the mold and the top of which is located at the outlet of the cooling stage. secondary. It is customary to designate this cone by the expression “liquid well” or “solidification well”, and the distance separating the base from the top by "metallurgical height”.
  • the stirring in the secondary cooling stage of a continuous casting machine of products with elongated format, such as slabs can it be carried out by entraining the liquid metal in a horizontal translational movement, this is that is to say directed perpendicular to the pouring axis and propagating from one small face of the product to the other.
  • This stirring can also consist of a vertical entrainment of the molten metal extended over the entire width of the cast product (German patent n ° 2,720,391) or on its perimeter (French patents n ° 2,085,261 and n ° 2,104,863).
  • the applicant asked the question whether the improvement in metallurgical quality, resulting from an increased proportion of equiaxed solidification structure, was due to the mixing as such, in which case it can be estimated that this means is used to the best of its ability, or if this improvement depends quantitatively on the type of metal drive, that is to say on the directional characteristics of the forced convection movements that are created within the mass in merger, or its extension to most of the product.
  • the subject of the invention is a process for vertical or curved continuous casting of molten metals, in particular steel, for obtaining products of elongated cross section, such as slabs, process according to which, at by means of inductors, the molten metal is subjected during solidification in the stage of the secondary cooling of the casting machine to an electromagnetic stirring action exerted at least in the vicinity of the bottom of the solidification well, and electromagnetic stirring by driving the molten metal in a direction having at least one component along the casting axis, process characterized in that one locates the electromagnetic drive action of the metal along at least one large face of the poured product, in an area whose width represents only a portion of that of said face.
  • the present invention therefore consists, in its essential characteristics, of promoting vertical exchanges of molten material, therefore of stimulating a rise in the liquid metal from the bottom of the solidification well, more effectively than by the methods previously mentioned.
  • the latter by carrying out hori zontal of the liquid metal parallel to the large faces, certainly favoring an exchange of material between the regions located at the same level respectively in the vicinity of one and the other of the small faces but are hardly suitable for allowing an exchange between regions superimposed.
  • the map of the speeds of movements in a plane parallel to the large faces of the product reveals a horizontal motor drive corridor, that is to say subjected directly to the action of the magnetic field and which, for this reason, can be qualified as "driving zone” or “circulation zone” as opposed to the two more diffuse regions of recirculation which are established necessarily to ensure the return of the metal , on either side of the central corridor, in a shape reminiscent of that of butterfly wings.
  • the invention makes it possible to locate exactly where it is desired, the action of the electromagnetic fields and therefore to obtain the desired result.
  • the idea at the base of the present invention therefore consists in fetching these small crystals accumulated at the bottom of the well, and available in large quantities and in transporting them to higher levels of the metallurgical height where one is located. wants to see basalt growth stop in favor of an equiaxed structure.
  • the invention is basically an operation of seeding the most disadvantaged regions of the liquid well, with small equiaxial crystals coming from richer regions located at the bottom of the well.
  • liquid metal is not here as a role for itself but rather 'as a vehicle for collection and transport of solidification germs. Incidentally, it is true, this movement of liquid mass between the bottom of the solidification well and higher regions makes it possible to mix a hot metal with a cooler metal and therefore to homogenize the temperature, which in particular has the effect of reducing the overheating of the upper regions, therefore, to facilitate the growth of the solidification germs which are brought there.
  • the electromagnetic stirring in question here consists in subjecting the cast product to the action of a mobile magnetic field, which gives rise in liquid metal to convection movements directed and oriented in the direction of propagation. of the field.
  • the stirring of the metal is an effective means of controlling the solidification structure of the cast product
  • the mobile magnetic field constitutes, apart from a privileged implementation tool, since it allows the stirring to be controlled. itself, by conferring on the user the control of the driving of the metal, therefore the control of the convection movements which he wishes to develop there.
  • the poured metal already solidified is designated by 1, 2 the liquid well in the course of solidification, 3 the solidification front without distinguishing that relating to the large faces of the slab from that relating on the small faces, 4 the bottom of the solidification well, and at 5 the pouring axis which, moreover, merges with the axis of the slab.
  • the circulation loops of the liquid metal are represented by arrow lines in broken line of small thickness.
  • the motor area referenced X6 of the recirculation zone (s), referenced X7, X8 ... according to their number, where X denotes the number of the figure which represents them.
  • X indicates the number of the figure which shows them for the first time.
  • V B Vellocity vector of the magnetic induction field B
  • liquid metal well is shown in the figures by way of illustration without it being possible to assume quantitatively the actual relationships existing between the metallurgical height and the transverse dimensions of the cast product.
  • the bottom of the solidification well is in the form of a narrow and deep valley oriented parallel to the plane of the large faces and whose slopes are formed by the solidification fronts relating to these large faces.
  • the closure of the well that is to say the end of solidification, then occurs by gradual approximation of the two slopes, without any significant contribution from the solidification fronts of the small faces, unlike less asymmetrical formats, such as circles or squares , in which complete solidification results from an equivalent and simultaneous progression of the entire periphery.
  • the exchanges of materials between the bottom of the well 2 and the higher regions are favored by a configuration of the movements of the metal having a driving zone on a large face of the product which is, not uniformly spread over the width of the well, but limited to a specific portion thereof.
  • FIG. 1 A configuration of this type is illustrated in FIG. 1.
  • the speed map shows a vertical driving zone 16 located in the middle of a large face, followed by two recirculation zones 17 and 18 along the solidification front of each of the small faces, these two zones being arranged symmetrically on either side of the central direct drive zone. Circular movements are thus created roofs curling in planes parallel to the large faces.
  • planar movements being all the more easy as the available surface is more important, it is understood that, taking into account the format of the cast product, this mode of mixing, whose circulation loops occupy the half-width of the well, is more advantageous than the previously known stirring modes, the loops of which close according to the thickness of the liquid well.
  • the vertical driving zone 16, rising in the case of the figure, can be obtained by means of a magnetic field sliding vertically and whose action remains localized in the central region of the well.
  • the one-piece inductor 21 has a structure similar to that of a linear induction motor stator. It is constituted by a flat cylinder head 22 made of laminated sheets having, on its face facing the cast product, notches parallel to each other and perpendicular to the plane of the sheets. These notches are occupied by electrical conductors 23, generally copper bars.
  • the inductor is arranged, in accordance with the invention, facing one of the large faces of the slab and so that the conductive bars 23 are perpendicular to the casting axis 5. As shown in the figure, these bars are connected together in pairs in series so that the electric current flows there in opposite directions. Each bar is spaced from its partner by a number of notches equal to the number of phases of the power supply so as to constitute overall a well known nested type winding.
  • connection box 20 a polyphase, for example three-phase power supply, symbolically represented, at 24, in the figures, by the three phases R, S, T and neutral N, so as to generate a magnetic field sliding vertically along the axis 5.
  • a polyphase for example three-phase power supply, symbolically represented, at 24, in the figures, by the three phases R, S, T and neutral N, so as to generate a magnetic field sliding vertically along the axis 5.
  • this inductor is, as clearly shown in FIG. 2, that the length of the bars 23 is reduced so as to limit its action of electromagnetic mixing of the molten metal to the central zone of the liquid well 2.
  • the mixing mode illustrated in Figure 1 is obtained by a propagation Va of the field oriented from bottom to top. This direction of propagation is achieved by means of the connection mode of the inductor 21 to the power supply 24 as shown diagrammatically in FIG. 2.
  • the letter R, S or T representative of the phase to which it is connected, and possibly surmounted by a line R, S and T indicating the relative direction of the electric current flowing through it.
  • the bars marked R and R constitute a pair connected in series, connected, to the phase R of the supply and are respectively traversed by the same current flowing in opposite directions, for example from left to right for the bar R and from the right left for bar R.
  • the mode of circulation of the liquid metal illustrated in FIG. 1 is reversible, which can be obtained simply by reversing the direction of sliding of the magnetic field, by inversion of two phases of the electrical supply.
  • FIG 12 schematically showing on a circle the three phases R, S, T of the power supply offset from each other by 120 °, as well as their "inverses".
  • R, S, T by rotating vectors, constitutes a convenient means for quickly finding, from a given connection mode of the inductor, the sliding direction of the magnetic field which it creates. It suffices for this to remember that the field progresses as the maximum voltage on each phase, namely in the direction R ⁇ S ⁇ TR ... that is to say, as shown by the arrow in the figure, in the opposite direction from the trigonometric direction.
  • the induction device 31 is this time constituted by the association of several identical inducing units 32, for example six in number and each placed inside a roller tubular support 33.
  • each inductor unit is known and described in detail in the British patent No. 1,405,312 already cited. Recall that it consists of elementary coils 34 arranged side by side, "one after the other, around a common horizontal axis, so as to cover the entire width of the slab.
  • coils belonging to the same inductor unit can be mounted in parallel or in series.
  • reversing the direction of the electric current between two coils can be achieved by reversing either the direction of winding of the windings or the direction of connection.
  • a system similar to a plurality of sliding field inductors (three in the example considered) is thus constructed, each consisting of a vertical succession of coils, and arranged side by side parallel to the casting axis 5 and covering a portion the width of the solidification well 2.
  • inductor units 32 connected to the same phase of the power supply 24 can either be connected in series, as shown in the figure, or in parallel.
  • FIG. 4 Another alternative embodiment of planar movements parallel to the plane of the large faces consists, as shown in FIG. 4, this time in creating two vertical driving zones each located opposite the solidification fronts of the small faces of the product.
  • these two motor zones are oriented in opposite directions, a simple and relatively well organized circulatory regime is established around a perperdicular axis with large faces and passing through the median axis 5.
  • the movements become more complicated if the motor zones (76 and 76 ') are brought closer to axis 5, because recirculation zones 77 and 77' are thus confined in the narrow regions located between a motor zone and the forehead solidification of the nearest small face.
  • Such a drive mode can be obtained, as can be seen in the following two figures 5 and 6, or by means of vertically sliding magnetic fields, produced by inductors arranged facing at least one large face of the slab. and placed laterally on either side of the casting axis.
  • These inductors can be of the “monobloc” type (FIG. 5 ref. 51 and 51 ′) therefore arranged behind the support rollers, and of a design completely similar to the inductor seen previously with reference to FIG. 2, but connected to the power supply 24 so as to create two magnetic fields sliding vertically in opposite directions.
  • inductors can also be constituted by the inducing units 32 previously described, in which case, as shown in FIG. 6, only a few coils 34 per unit 32 will be activated, shifted towards the ends of the large face, facing the solidification front. small sides of the slab.
  • the offset of the coils to be activated will be limited, for example, to the two intermediate zones located halfway between the solidification fronts of the small faces and the middle of the large ones. faces.
  • another configuration of the movements of circulation of the liquid metal capable of ensuring the transport of the crystals between the bottom of the liquid well and the higher regions, consists in creating, as shown in FIG. 8, a motor zone 86 parallel to the large faces of the product, directed obliquely and oriented from the bottom up. There is thus formed on either side of the motor zone 86, a lower recirculation zone 87 and an upper recirculation zone 88.
  • the crystals coming from the lower region 87 penetrate through the lower end of the direct drive zone 86 and exit from it by the upper end, taking the easiest path, that is to say by engaging in the upper region 88.
  • the crystals travel a path a form of "S" passing from the lower half-loop to the opposite upper half-loop without having to make a sudden change of direction.
  • the desirable orientation for the motor area would be horizontal orientation, as is customary.
  • this increasing inclination correlatively disadvantages the possibilities of material exchange between the bottom of the well and the higher levels and therefore goes against the desired result.
  • This compromise is characterized by a metal entrainment parallel to the large faces and whose direction of propagation has a non-zero angle with the horizontal, and preferably between around 30 and 60 °.
  • the direction in which the metal is driven can no longer be reversible, as in the previous brewing modes, but necessarily oriented from bottom to top.
  • the system remains symmetrical with respect to the casting axis 5 as regards the direction of the drive.
  • the first variant is produced, in accordance with FIG. 9, by means of the monobloc inductor 21, already seen with reference to FIG. 2, but this time having an inclined orientation relative to the casting axis 5.
  • the advantage of this variant lies essentially in the fact that the inductor being independent of the constituent members of the casting machine, one is free to give it the desired inclination;
  • the second variant is produced, as shown in FIG. 10, by means of inductor units 32 housed in the support rollers 33.
  • each unit 32 has a functional autonomy and creates a horizontally sliding magnetic field ( ⁇ lt), along generators of the rollers.
  • ⁇ lt horizontally sliding magnetic field
  • the system according to the invention is however characterized by the fact that the inducting units have a phase shift between them, so that a succession of coils of the same rank, taken one after the other on units different, constitutes, as in the case of FIGS. 3 and 6, an inductor with a magnetic field sliding vertically from bottom to top
  • the combined effect of the horizontal displacement field with the field moving vertically upward identifies with the effect of a single field obliquely ropaging according to their result
  • the actual position of the inductor over the metallurgical height is not limited to that visible in the figures. The user can act on this position so that the movements caused reach the immediate vicinity of the bottom of the solidification well.
  • the setting in motion of the liquid metal at the bottom of the well depends not only on the height position of the inductor but also on its power, in other words the intensity of its electromagnetic action on the metal.

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Abstract

1. A process for continuous, vertical or curvilinear casting of molten metals, steel in particular, to obtain cross-sectional elongated products such as slabs, whereby, by means of inductors, the molten metal, whilst solidifying in the secondary cooling stage of the casting machine, is subjected to electromagnetic agitation at least near the bottom (4) of the solidification well (2), such electromagnetic agitation being performed by entraining the molten metal in a direction of which at least one component is along the casting axis (5), said process being characterized in that the electromagnetic entrainment of the metal is located along, at least, one of the larger sides of the casting and within an area the width of which accounts for only a portion of the said side.

Description

La présente invention a trait à la coulée continue des métaux en fusion, notamment de l'acier. Elle se rapporte plus précisément aux opérations de brassage du métal liquide, en cours de solidification dans l'étage du refroidissement secondaire de la machine de coulée, afin d'améliorer la qualité métallurgique du produit obtenu. L'invention concerne en particulier la coulée de produits de section allongée, par exemple les brames.The present invention relates to the continuous casting of molten metals, in particular steel. It relates more precisely to the operations of mixing the liquid metal, during solidification in the secondary cooling stage of the casting machine, in order to improve the metallurgical quality of the product obtained. The invention relates in particular to the casting of products of elongated section, for example slabs.

On sait que la coulée continue des métaux consiste essentiellement. à verser de façon régulière et ininterrompue le métal en fusion dans un récipient sans fond énergiquement refroidi, appelé lingotière, à la base duquel on retire, de façon également continue, une barre à l'aide de moyens de guidage et d'extraction appropriés. La solidification progressive du produit depuis sa périphérie, s'effectue initialement en lingotière et se poursuit en-dessous de celle-ci, généralement sous l'effet de jets d'eau de refroidissement, jusqu'à solidification complète. La zone de refroidissement située en aval de la lingotière est habituellement dénommée: "étage de refroidissement secondaire".It is known that the continuous casting of metals consists essentially. pouring the molten metal in a regular and uninterrupted manner into an energetically cooled bottomless container, called an ingot mold, at the base of which a bar is removed, also continuously, using suitable guidance and extraction means. The progressive solidification of the product from its periphery, is initially carried out in an ingot mold and continues below it, generally under the effect of cooling water jets, until complete solidification. The cooling zone located downstream of the mold is usually called: "secondary cooling stage".

Au cours de la coulée, la partie intérieure liquide du produit se présente donc sensiblement sous la forme d'un cône dont la base correspond à la surface libre du métal en lingotière et dont le sommet se situe à la sortie de l'étage de refroidissement secondaire. On a coutume de désigner ce cône par l'expression "puits liquide" ou "puits de solidification", et la distance séparant la base du sommet par "hauteur métallurgique".During the casting, the liquid interior part of the product is therefore substantially in the form of a cone, the base of which corresponds to the free surface of the metal in the mold and the top of which is located at the outlet of the cooling stage. secondary. It is customary to designate this cone by the expression "liquid well" or "solidification well", and the distance separating the base from the top by "metallurgical height".

On sait que la coulée continue avec brassage du métal liquide en cours de solidification présente, par rapport à la coulée continue classique, l'avantage d'améliorer la qualité métallurgique des produits obtenus, puisqu'elle influe favorablement sur la propreté inclusion- naire et/ou sur la structure de solidification. A cet égard, il a été constaté que la mise en mouvement du métal liquide favorise la formation et la développement de la zone centrale de solidification de type "équiaxe" au détriment de la zone périphérique de solidification dendritique, dite de type "basaltique". Les résultats métallurgiques obtenus se caractérisent notamment par une réduction de la porosité centrale du produit et une diminution des macro- ségrégations en éléments d'alliage.It is known that continuous casting with stirring of the liquid metal in the course of solidification has, compared to conventional continuous casting, the advantage of improving the metallurgical quality of the products obtained, since it has a favorable influence on the cleanliness and inclusion. / or on the solidification structure. In this regard, it has been observed that the setting in motion of the liquid metal promotes the formation and the development of the central solidification zone of the "equiaxial" type to the detriment of the peripheral dendritic solidification zone, known as of the "basaltic" type. The metallurgical results obtained are characterized in particular by a reduction in the central porosity of the product and a reduction in macro-segregation in alloying elements.

Il est connu de mener les opérations de brassage en entraînant le métal liquide soit en rotation autour de l'axe de coulée, soit en translation, le choix du type d'entraînement dépendant de l'endroit sur la hauteur métallurgique où l'on souhaite brasser (lingotière ou étage de refroidissement secondaire) ainsi que du format du produit coulé.It is known to conduct brewing operations by driving the liquid metal either in rotation around the casting axis, or in translation, the choice of the type of drive depending on the location on the metallurgical height where it is desired. stir (ingot mold or secondary cooling stage) as well as the format of the cast product.

Ainsi, le brassage dans l'étage de refroidissement secondaire d'une machine de coulée continue de produits à format allongé, tels que les brames, peut-il s'effecteur en entraînant le métal liquide dans un mouvement de translation horizontal, c'est-à-dire dirigé perpendiculairement à l'axe de coulée et se propageant d'une petite face du produit à l'autre. (Brevet français n° 2.068.803, brevet anglais n° 1.405.312, brevet allemand n° 2.401.145). Ce brassage peut également consister en un entraînement vertical du métal en fusion étendu sur toute la largeur du produit coulé (Brevet allemand n° 2.720.391) ou sur son périmètre (Brevets français n° 2.085.261 et n° 2.104.863).Thus, the stirring in the secondary cooling stage of a continuous casting machine of products with elongated format, such as slabs, can it be carried out by entraining the liquid metal in a horizontal translational movement, this is that is to say directed perpendicular to the pouring axis and propagating from one small face of the product to the other. (French patent n ° 2,068,803, English patent n ° 1,405,312, German patent n ° 2,401,145). This stirring can also consist of a vertical entrainment of the molten metal extended over the entire width of the cast product (German patent n ° 2,720,391) or on its perimeter (French patents n ° 2,085,261 and n ° 2,104,863).

Face à une telle situation, le demandeur s'est posé la question de savoir si l'amélioration de qualité métallurgique, consécutive à une proportion accrue de structure de solidification équiaxe, était due au brassage en tant que tel, auquel cas on peut estimer que ce moyen est utilisé au mieux de ses capacités, ou si cette amélioration dépendait quantitativement du type d'entraînement du métal, c'est-à-dire des caractéristiques directionnelles des mouvements de convection forcée que l'on crée au sein de la masse en fusion, ou de son extension à la plus grande partie du produit.Faced with such a situation, the applicant asked the question whether the improvement in metallurgical quality, resulting from an increased proportion of equiaxed solidification structure, was due to the mixing as such, in which case it can be estimated that this means is used to the best of its ability, or if this improvement depends quantitatively on the type of metal drive, that is to say on the directional characteristics of the forced convection movements that are created within the mass in merger, or its extension to most of the product.

L'étude et l'expérience ont permis au demandeur de répondre à ces questions et ainsi de réaliser la présente invention dont le but, par rapport aux procédés connus, est d'améliorer encore la qualité métallurgique des produits obtenus grâce à une action plus efficace du brassage sur leur structure de solidification.The study and experience have enabled the applicant to answer these questions and thus realize the present invention, the aim of which, compared with known methods, is to further improve the metallurgical quality of the products obtained thanks to a more effective action. of brewing on their solidification structure.

A cet effet, l'invention a pour objet un procédé de coulée continue verticale ou courbe des métaux en fusion, notamment de l'acier, pour l'obtention de produits de section droite allongée, tels que des brames, procédé selon lequel, au moyen d'inducteurs, on soumet le métal en fusion en cours de solidification dans l'étage du refroidissement secondaire de la machine de coulée à une action de brassage électromagnétique s'exerçant au moins au voisinage du fond du puits de solidification, et on effectue de brassage électromagnétique en entraînant le métal en fusion dans une direction ayant au moins une composante selon l'axe de coulée, procédé caractérisé en ce que on localise l'action d'entraînement électromagnétique du métal le long d'au moins une grande face du produit coulé, dans une zone dont la largeur ne représente qu'une portion de celle de ladite face.To this end, the subject of the invention is a process for vertical or curved continuous casting of molten metals, in particular steel, for obtaining products of elongated cross section, such as slabs, process according to which, at by means of inductors, the molten metal is subjected during solidification in the stage of the secondary cooling of the casting machine to an electromagnetic stirring action exerted at least in the vicinity of the bottom of the solidification well, and electromagnetic stirring by driving the molten metal in a direction having at least one component along the casting axis, process characterized in that one locates the electromagnetic drive action of the metal along at least one large face of the poured product, in an area whose width represents only a portion of that of said face.

Comme on le comprend, la présente invention consiste donc, dans ses caractéristiques essentielles, à favoriser les échanges verticaux de matière en fusion, donc de stimuler une remontée du métal liquide depuis le bas du puits de solidification, de façon plus efficace que par les procédés précédemment évoqués. Ces derniers, en réalisant un entraînement horizontal du métal liquide parallèle aux grandes faces, favorisant certes un échange de matière entre les régions localisées à un même niveau respectivement au voisinage de l'une et de l'autre des petites faces mais ne sont guère appropriés à permettre un échange entre des régions superposées. En effet, comme l'indique le brevet français n° 2.068.803 déjà cité, la carte des vitesses des mouvements dans un plan parallèle aux grandes faces du produit laisse apparaitre un couloir horizontal d'entraînement moteur, c'est-à-dire soumis directement à l'action du champ magnétique et qui, de ce fait, peut être qualifié de "zone motrice" ou "zone de circulation" par opposition aux deux régions plus diffuses de recirculation qui s'établissent nécéssairement pour assurer le retour du métal, de part et d'autre du couloir central, selon une forme rappelant celle d'ailes de papillon. Une telle configuration, si elle procure un brassage de la masse liquide localisée respectivement dans l'une et l'autre des régions précitées, n'est guère appropriée à assurer un brassage de ces deux régions entre elles, donc en particulier la remontée du métal de la région la plus basse à la région supérieure, puisqu'il faudrait pour cela imposer au métal un changement brutal de recirculation à la sortie de couloir central.As can be understood, the present invention therefore consists, in its essential characteristics, of promoting vertical exchanges of molten material, therefore of stimulating a rise in the liquid metal from the bottom of the solidification well, more effectively than by the methods previously mentioned. The latter, by carrying out hori zontal of the liquid metal parallel to the large faces, certainly favoring an exchange of material between the regions located at the same level respectively in the vicinity of one and the other of the small faces but are hardly suitable for allowing an exchange between regions superimposed. Indeed, as indicated in the French patent n ° 2.068.803 already cited, the map of the speeds of movements in a plane parallel to the large faces of the product reveals a horizontal motor drive corridor, that is to say subjected directly to the action of the magnetic field and which, for this reason, can be qualified as "driving zone" or "circulation zone" as opposed to the two more diffuse regions of recirculation which are established necessarily to ensure the return of the metal , on either side of the central corridor, in a shape reminiscent of that of butterfly wings. Such a configuration, if it provides mixing of the liquid mass located respectively in one and the other of the aforementioned regions, is hardly suitable for ensuring mixing of these two regions together, therefore in particular the rise of the metal from the lowest region to the upper region, since it would be necessary to impose on the metal a sudden change in recirculation at the outlet of the central corridor.

D'autre part, par rapport aux procédés utilisant un brassage vertical connu, l'invention permet de localiser exactement où on le désire, l'action des champs électromagnétiques et donc d'obtenir le résultat souhaité.On the other hand, compared to the methods using a known vertical mixing, the invention makes it possible to locate exactly where it is desired, the action of the electromagnetic fields and therefore to obtain the desired result.

A première vue, il peut paraître suprenant que le simple fait de favoriser la remontée du métal depuis la région du fond du puit de solidification suffise a promouvoir la formation d'une large zone de structure de solidification équiaxe au sein du produit obtenu par coulée continue.At first glance, it may seem surprising that the simple fact of promoting the ascent of the metal from the region of the bottom of the solidification well is sufficient to promote the formation of a large area of equiaxed solidification structure within the product obtained by continuous casting. .

La longue expérience du demandeur ainsi que ses études récentes sur les mécanismes de solidification des produits de coulée continue lui ont permis de dégager les conclusions qui suivent:

  • Une première observation est que plus tôt commence la solidification équiaxe, plus importante est sa proportion dans le produit brut de coulée. Autrement dit, dans le cas de la coulée continue, cette proportion sera d'autant plus substantielle que la naissance "équiaxe" a lieu plus haut sur la hauteur métallurgique.
The applicant's long experience as well as its recent studies on the solidification mechanisms of continuous casting products have enabled it to draw the following conclusions:
  • A first observation is that the earlier the equiaxed solidification begins, the more important is its proportion in the gross product of casting. In other words, in the case of continuous casting, this proportion will be all the more substantial as the "equiaxial" birth takes place higher on the metallurgical height.

La seconde observation est que l'initiation et le développement d'une structure de solidification de type équiaxe est favorisée, d'une part par une faible surchauffe du bain métallique, d'autre part par la présence au sein de la masse en fusion de germes de solidification. Ces germes peuvent être notamment de petits cristaux qui se forment dans le bain ou qui proviennent plus généralement de têtes de dendrites cassées par les mouvements de convection de l'acier liquide contre le front de solidification. Or il est connu que le fond du puits de solidification est une région particulièrement riche en petits cristaux "équiaxes", soit qu'ils se forment en cet endroit car les conditions y sont plus favorables qu'ailleurs, soit qu'ils y descendent par gravité.The second observation is that the initiation and the development of a solidification structure of the equiaxial type is favored, on the one hand by a slight overheating of the metal bath, on the other hand by the presence within the molten mass of solidification germs. These germs can in particular be small crystals which form in the bath or which more generally come from dendrite heads broken by the convection movements of the liquid steel against the solidification front. However, it is known that the bottom of the solidification well is a region particularly rich in small "equiaxed" crystals, either because they are formed there because the conditions are more favorable than elsewhere, or because they descend there by gravity.

L'idée à la base de la présente invention consiste donc à aller chercher ces petits cristaux accumulés au fond du puits, et disponibles en grande quantité et à les transporter à des niveaux plus élevés de la hauteur métallurgique où l'on. souhaite voir s'interrompre une croissance basaltique au profit d'une structure équiaxe.The idea at the base of the present invention therefore consists in fetching these small crystals accumulated at the bottom of the well, and available in large quantities and in transporting them to higher levels of the metallurgical height where one is located. wants to see basalt growth stop in favor of an equiaxed structure.

On comprend donc que l'invention est fondamentalement une opération d'ensemencement des régions du puits liquide les plus défavorisées, par des petits cristaux équiaxes en provenance de régions plus riches situées au fond du puits.It is therefore understood that the invention is basically an operation of seeding the most disadvantaged regions of the liquid well, with small equiaxial crystals coming from richer regions located at the bottom of the well.

Il est apparu au demandeur que l'un des moyens les mieux adaptés pour effectuer le transport des cristaux était le métal liquide lui-même pour peu qu'on lui confère, comme l'enseigne la présente invention des mouvements de convection appropriés.It appeared to the applicant that one of the most suitable means for carrying out the transport of the crystals was the liquid metal itself, provided that it is given, as the present invention teaches, suitable convection movements.

Il doit donc être bien compris que le métal liquide n'a pas tant ici un rôle par lui-même mais plutôt en' tant que véhicule de ramassage et de transport des germes de solidification. Accessoirement, il est vrai, ce mouvement de masse liquide entre le bas du puits de solidification et des régions plus élevées permet de mélanger un métal chaud avec un métal plus froid donc d'homogénéiser la température, ce qui a notamment pour effet de réduire la surchauffe des régions supérieures, donc, de faciliter la croissance des germes de solidification qui y sont apportés.It should be understood that the liquid metal is not here as a role for itself but rather 'as a vehicle for collection and transport of solidification germs. Incidentally, it is true, this movement of liquid mass between the bottom of the solidification well and higher regions makes it possible to mix a hot metal with a cooler metal and therefore to homogenize the temperature, which in particular has the effect of reducing the overheating of the upper regions, therefore, to facilitate the growth of the solidification germs which are brought there.

Différents moyens pour entraîner le métal liquide dans le puits de solidification ont déjà été envisagés, au moins dans la littérature, parmi lesquels les moyens de nature électromagnétique semblent désormais devoir s'imposer dans la pratique.Various means for entraining the liquid metal in the solidification well have already been envisaged, at least in the literature, among which the means of electromagnetic nature now seem to have to prevail in practice.

On rappelle pour mémoire que le brassage électromagnétique dont il est question ici consiste à soumettre le produit coulé à l'action d'un champ magnétique mobile, qui donne naissance dans le métal liquide à des mouvements de convection dirigés et orientés dans le sens de propagation du champ.It will be recalled that the electromagnetic stirring in question here consists in subjecting the cast product to the action of a mobile magnetic field, which gives rise in liquid metal to convection movements directed and oriented in the direction of propagation. of the field.

Il apparait ainsi que, si le brassage du métal est un moyen efficace de contrôle de la structure de solidification du produit coulé, le champ magnétique mobile constitue pour ',a part un outil privilégié de mise en oeuvre puisqu'il permet le contrôle du brassage lui-même, en conférant à l'utilisateur la commande de l'entraînement du métal, donc la maîtrise des mouvements de convection qu'il souhaite y développer.It thus appears that, if the stirring of the metal is an effective means of controlling the solidification structure of the cast product, the mobile magnetic field constitutes, apart from a privileged implementation tool, since it allows the stirring to be controlled. itself, by conferring on the user the control of the driving of the metal, therefore the control of the convection movements which he wishes to develop there.

Dans la domaine de la coulée continue de produits à section droite de forme allongée, tels que des brames d'acier, des techniques assez récentes pour entraîner le métal liquide dans un mouvement de translation horizontal parallèle au plan des grandes faces consistent à soumettre le produit à l'action d'un champ magnétique glissant dont les caractéristiques directionnelles sont en tout point identiques à celles de l'entraînement direct du métal liquide que l'on veut provoquer. Un tel champ est généralement créé par un inducteur statique polyphasé, de conception similaire à celle d'un stator de moteur linéaire à induction et disposé soit derrière les rouleaux servant au guidage et à l'extraction de la brame, soit dans l'espace disponible entre deux rouleaux consécutifs (Brevet français n° 2.185.468) soit en substitution d'un ou plusieurs rouleaux (Brevet français n° 2.068.803 déjà cité) soit encore à l'intérieur même d'un ou plusieurs rouleaux, rendus tubulaires à cette fin (Brevet anglais n° 1.405.312 déjà cité).In the field of continuous casting of products of straight section of elongated shape, such as steel slabs, fairly recent techniques for entraining the liquid metal in a parallel horizontal translational movement. in the plane of the large faces consist in subjecting the product to the action of a sliding magnetic field whose directional characteristics are in all points identical to those of the direct entrainment of the liquid metal which it is desired to cause. Such a field is generally created by a polyphase static inductor, of a design similar to that of a linear induction motor stator and placed either behind the rollers used for guiding and extracting the slab, or in the space available. between two consecutive rolls (French patent n ° 2,185,468) either as a replacement for one or more rollers (French patent n ° 2,068,803 already mentioned) or even inside one or more rollers, made tubular with this end (English Patent No. 1,405,312 already cited).

Ce sont des dispositifs de ce type, dont on trouvera une description détaillée de leur structure dans les documents précités, qui peuvent être utilisés avec profit pour la mise en oeuvre de la présente invention.These are devices of this type, a detailed description of their structure will be found in the aforementioned documents, which can be used with advantage for the implementation of the present invention.

Toutefois, leur application doit bien entendu être adaptée en fonction de l'entraînement du métal liquide que l'on cherche à réaliser, conformément aux caractéristiques de la présente invention.However, their application must of course be adapted as a function of the entrainment of the liquid metal that one seeks to achieve, in accordance with the characteristics of the present invention.

Cette dernière sera bien comprise et d'autres aspects et avantages ressortiront plus clairement au vu de la description qui suit donnée en référence aux planches de dessins annexées sur lesquelles:

  • - les figures 1, 4, 7 et 8 montrent, en coupe longitudinale parallèle aux grandes faces, respectivement quatre variantes possibles du mode de brassage conforme à l'invention dans la région du fond du puits de solidification d'une brame coulée en continu,
  • -les figures 2 et 3 montrent chacune, vue de face, une variante de réalisation d'un inducteur pour obtenir le mode de brassage illustré sur la figure 1,
  • - les figures 5 et 6 montrent, chacune, vu de face, une variante de réalisation d'un inducteur pour obtenir le mode de brassage illustré sur la figure 4,
  • - les figures 9 et 10 montrent, chacune, vu de face, une variante de réalisation d'un inducteur pour obtenir le mode de brassage illustré sur la figure 8,
  • - la figure 11 montre une réalisation de l'inducteur équivalente à celle de la figure 10,
  • - la figure 12 est une représentation graphique commode des trois phases, R, S, T d'une alimentation électrigue triphasée ainsi que de leurs inverses R, S, T.
The latter will be well understood and other aspects and advantages will emerge more clearly in the light of the description which follows, given with reference to the accompanying drawing plates in which:
  • FIGS. 1, 4, 7 and 8 show, in longitudinal section parallel to the large faces, respectively four possible variants of the stirring mode according to the invention in the region of the bottom of the solidification well of a continuously cast slab,
  • FIGS. 2 and 3 each show, front view, an alternative embodiment of an inductor to obtain the mixing mode illustrated in FIG. 1,
  • FIGS. 5 and 6 show, each, seen from the front, an alternative embodiment of an inductor to obtain the mixing mode illustrated in FIG. 4,
  • FIGS. 9 and 10 each show, seen from the front, an alternative embodiment of an inductor to obtain the mixing mode illustrated in FIG. 8,
  • FIG. 11 shows an embodiment of the inductor equivalent to that of FIG. 10,
  • - Figure 12 is a convenient graphical representation of the three phases, R, S, T of a three-phase electrical supply as well as their inverses R, S, T.

Toutes les figures sont des schémas dépouillés au maximum de manière à faire mieux ressortir l'essentiel utile à la bonne compréhension des moyens de l'invention.All the figures are diagrams stripped to the maximum so as to better highlight the essentials useful for a good understanding of the means of the invention.

Sur toutes les figures montrant la brame en cours de solidification, on a désigné par 1 le métal coulé déjà solidifié, 2 le puits liquide en cours de solidification, 3 le front de solidification sans distinguer celui relatif aux grandes faces de la brame de celui relatif aux petites faces, 4 le fond du puits de solidification, et en 5 l'axe de coulée qui se confond d'ailleurs avec l'axe de la brame.In all the figures showing the slab in the course of solidification, the poured metal already solidified is designated by 1, 2 the liquid well in the course of solidification, 3 the solidification front without distinguishing that relating to the large faces of the slab from that relating on the small faces, 4 the bottom of the solidification well, and at 5 the pouring axis which, moreover, merges with the axis of the slab.

Sur les figures illustrant un mode de brassage, les boucles de circulation du métal liquide sont représentées par des lignes fléchées en trait discontinu de faible épaisseur. On a distingué dans ces boucles, la zone motrice, référencée X6 de la ou des zones de recirculation, référencées X7, X8 ... selon leur nombre, où X désigne le numéro de la figure qui les représente.In the figures illustrating a method of stirring, the circulation loops of the liquid metal are represented by arrow lines in broken line of small thickness. We distinguished in these loops, the motor area, referenced X6 of the recirculation zone (s), referenced X7, X8 ... according to their number, where X denotes the number of the figure which represents them.

Lorsque plusieurs figures représentent les mêmes boucles, X désigne le numéro de la figure qui les montre pour la première fois.When several figures represent the same loops, X indicates the number of the figure which shows them for the first time.

Le même principe de notation a été adopté pour les autres éléments représentés.The same scoring principle was adopted for the other elements represented.

Les figures indiquent le sens du déplacement du champ magnétique glissant par des droites fléchées en traits continus de faible épaisseur, désignés par la notation VB (vecteur Vitesse du champ d'induction magnétique B).The figures indicate the direction of movement of the sliding magnetic field by straight lines arrowed in continuous thin lines, designated by the notation V B (Velocity vector of the magnetic induction field B).

Il doit être compris que le puits de métal liquide se trouve représenté sur les figures à titre d'illustration sans qu'il puisse être présumé quantitativement des rapports réels existants entre la hauteur métallurgique et les dimensions transversales du produit coulé.It should be understood that the liquid metal well is shown in the figures by way of illustration without it being possible to assume quantitatively the actual relationships existing between the metallurgical height and the transverse dimensions of the cast product.

Il est à noter que, dans le cas des formats à section allongée tels que les brames, le fond du puits de solidification se présente sous la forme d'une vallée étroite et profonde orientée paral- lélément au plan des grandes faces et dont les versants sont constitués par les fronts de solidification relatifs à ces grandes faces. La fermeture du puits, c'est-à-dire la fin de la solidification intervient alors par rapprochement progressif des deux versants, sans contribution sensible des fronts de solidification des petites faces, contrairement aux formats moins dissymétriques, tels que les ronds ou les carrés, dans lesquels la solidification complète résulte d'une progression équivalente et simultanée de toute la périphérie.It should be noted that, in the case of formats with an elongated section such as slabs, the bottom of the solidification well is in the form of a narrow and deep valley oriented parallel to the plane of the large faces and whose slopes are formed by the solidification fronts relating to these large faces. The closure of the well, that is to say the end of solidification, then occurs by gradual approximation of the two slopes, without any significant contribution from the solidification fronts of the small faces, unlike less asymmetrical formats, such as circles or squares , in which complete solidification results from an equivalent and simultaneous progression of the entire periphery.

Conformément à l'invention, les échanges de matières entre le fond du puits 2 et les régions plus élevées, sont favorisées par une configuration des mouvements du métal présentant une zone motrice sur une grande face du produit qui soit, non pas uniformement étendue sur la largeur du puits, mais limitée à une portion déterminée de celle-ci.In accordance with the invention, the exchanges of materials between the bottom of the well 2 and the higher regions, are favored by a configuration of the movements of the metal having a driving zone on a large face of the product which is, not uniformly spread over the width of the well, but limited to a specific portion thereof.

Une configuration de ce type est illustrée sur la figure 1. La carte des vitesses montre une zone motrice verticale 16 localisée au milieu d'une grande face, suivie de deux zones de recirculation 17 et 18 le long du front de solidification de chacune des petites faces, ces deux zones étant disposées symétriquement de part et d'autre de la zone centrale d'entraînement direct. Il se crée ainsi des mouvements circulatoires se bouclant dans des plans parallèles aux grandes faces.A configuration of this type is illustrated in FIG. 1. The speed map shows a vertical driving zone 16 located in the middle of a large face, followed by two recirculation zones 17 and 18 along the solidification front of each of the small faces, these two zones being arranged symmetrically on either side of the central direct drive zone. Circular movements are thus created roofs curling in planes parallel to the large faces.

L'organisation de mouvements plans étant d'autant plus aisée que la surface disponible est plus importante, on comprend que, compte tenu du format du produit coulé, ce mode de brassage, dont les boucles de circulation occupent la demi-largeur du puits, est plus avantageux que les modes de brassage antérieurement connus dont les boucles se referment selon l'épaisseur du puits liquide.The organization of planar movements being all the more easy as the available surface is more important, it is understood that, taking into account the format of the cast product, this mode of mixing, whose circulation loops occupy the half-width of the well, is more advantageous than the previously known stirring modes, the loops of which close according to the thickness of the liquid well.

La zone motrice verticale 16, remontante dans le cas de la figure, peut être obtenue au moyen d'un champ magnétique glissant verticalement et dont l'action demeure localisée dans la région centrale du puits.The vertical driving zone 16, rising in the case of the figure, can be obtained by means of a magnetic field sliding vertically and whose action remains localized in the central region of the well.

Un tel champ magnétique peut être créé par des inducteurs statiques polyphasés de type connu dont deux exemples sont donnés ici en référence aux deux figures suivantes:

  • un inducteur monobloc 21 (figure 2) placé derrière les rouleaux de soutien (non représentés pour ne pas surcharger le schéma) ou un ensemble inductif 31 (figure 3) constitué par l'association fonctionnelle de plusieurs inducteurs unitaires identiques 32 structurellement indépendants les uns des autres, et placés chacun à l'intérieur des rouleaux de soutien tubulaires 33.
Such a magnetic field can be created by polyphase static inductors of known type, two examples of which are given here with reference to the following two figures:
  • a monobloc inductor 21 (FIG. 2) placed behind the support rollers (not shown so as not to overload the diagram) or an inductive assembly 31 (FIG. 3) constituted by the functional association of several identical unitary inductors 32 structurally independent from each others, and each placed inside the tubular support rollers 33.

On rappelle que l'inducteur monobloc 21 (figure 2) présente une structure similaire à celle d'un stator de moteur linéaire à induction. Il est constitué par une culasse plane 22 en tôles feuilletées présentant, sur sa face tournée vers le produit coulé, des encoches parallèles entre elles et perpendiculaires au plan des tôles. Ces encoches sont occupées par des conducteurs électriques 23, généralement des barres de cuivre. L'inducteur est disposé, conformément à l'invention, en regard de l'une des grandes faces de la brame et de manière que les barres conductrices 23 soient perpendiculaires à l'axe de coulée 5. Comme le montre la figure, ces barres sont reliées entre elles par paires en série de sorte que la courant électrique y circule dans des sens opposés. Chaque barre est distante de sa partenaire d'un nombre d'encoches égal au nombre de phases de l'alimentation électrique de manière à constituer globalement un enroulement de type imbriqué bien connu.It will be recalled that the one-piece inductor 21 (FIG. 2) has a structure similar to that of a linear induction motor stator. It is constituted by a flat cylinder head 22 made of laminated sheets having, on its face facing the cast product, notches parallel to each other and perpendicular to the plane of the sheets. These notches are occupied by electrical conductors 23, generally copper bars. The inductor is arranged, in accordance with the invention, facing one of the large faces of the slab and so that the conductive bars 23 are perpendicular to the casting axis 5. As shown in the figure, these bars are connected together in pairs in series so that the electric current flows there in opposite directions. Each bar is spaced from its partner by a number of notches equal to the number of phases of the power supply so as to constitute overall a well known nested type winding.

Ces barres sont reliées, de façon également connue, par l'intermédiaire d'une boîte de connexion 20, à une alimentation électrique polyphasée, par exemple triphasée, représentée symboliquement, en 24, sur les figures, par les trois phases R, S, T et le neutre N, de mainère à générer un champ magnétique glissant verticalement le long de l'axe 5.These bars are connected, also in a known manner, via a connection box 20, to a polyphase, for example three-phase power supply, symbolically represented, at 24, in the figures, by the three phases R, S, T and neutral N, so as to generate a magnetic field sliding vertically along the axis 5.

L'une des caractéristiques de cet inducteur est, comme le montre clairement la figure 2, que la longueur des barres 23 est réduite de mainère à limiter son action de brassage électromagnétique du métal fondu à la zone centrale du puits liquide 2.One of the characteristics of this inductor is, as clearly shown in FIG. 2, that the length of the bars 23 is reduced so as to limit its action of electromagnetic mixing of the molten metal to the central zone of the liquid well 2.

De ce fait, le mode de brassage illustré sur la figure 1 est obtenu par une propagation Va du champ orientée de bas en haut. Ce sens de propagation est réalisé grâce au mode de connexion de l'inducteur 21 à l'alimentation électrique 24 tel qu'il est schematiquement montré sur la figure 2. De plus, on a porté sur chaque barre 23 la lettre R, S ou T représentative de la phase à laquelle elle est reliée, et éventuellement surmontée d'un trait R, S et T indiquant le sens relatif du courant électrique qui la traverse. Ainsi les barres marquées R et R constituent une paire montée en série, reliée, à la phase R de l'alimentation et sont respectivement parcourues par le même courant circulant en sens opposés, par exemple de gauche à droite pour la barre R et de droite à gauche pour la barre R.Therefore, the mixing mode illustrated in Figure 1 is obtained by a propagation Va of the field oriented from bottom to top. This direction of propagation is achieved by means of the connection mode of the inductor 21 to the power supply 24 as shown diagrammatically in FIG. 2. In addition, the letter R, S or T representative of the phase to which it is connected, and possibly surmounted by a line R, S and T indicating the relative direction of the electric current flowing through it. Thus the bars marked R and R constitute a pair connected in series, connected, to the phase R of the supply and are respectively traversed by the same current flowing in opposite directions, for example from left to right for the bar R and from the right left for bar R.

Il est à noter que le mode de circulation du métal liquide illustré sur la figure 1 est réversible, ce qui peut être obtenu simplement en inversant le sens de glissement du champ magnétique, par inversion de deux phases de l'alimentation électrique.It should be noted that the mode of circulation of the liquid metal illustrated in FIG. 1 is reversible, which can be obtained simply by reversing the direction of sliding of the magnetic field, by inversion of two phases of the electrical supply.

A cet égard, la figure 12, représentant schématiquement sur un cercle les trois phases R, S, T de l'alimentation électrique décalées les unes des autres de 120°, ainsi que leurs "inverses". R, S, T, par des vecteurs tournants, constitue un moyen commode pour retrouver rapidement, à partir d'un mode de connexion donné de l'inducteur, le sens de glissement du champ magnétique qu'il créé. Il suffit pour cela de se souvenir que le champ progresse comme le maximum de tension sur chaque phase, à savoir dans le sens R→S→T­R ... c'est-à-dire, comme le montre la fléche de la figure, dans le sens contraire du sens trigonométrique.In this regard, Figure 12, schematically showing on a circle the three phases R, S, T of the power supply offset from each other by 120 °, as well as their "inverses". R, S, T, by rotating vectors, constitutes a convenient means for quickly finding, from a given connection mode of the inductor, the sliding direction of the magnetic field which it creates. It suffices for this to remember that the field progresses as the maximum voltage on each phase, namely in the direction R → S → TR ... that is to say, as shown by the arrow in the figure, in the opposite direction from the trigonometric direction.

Il est clair que le mode de brassage du métal de la figure 1 peut être encore obtenu en plaçant l'inducteur 21 en regard de l'autre grande face de la brame. De même, on peut intensifier l'action d'entraînement du métal en plaçant un inducteur en regard de chacune des grandes faces.It is clear that the mode of mixing the metal of FIG. 1 can still be obtained by placing the inductor 21 opposite the other large face of the slab. Likewise, the metal driving action can be intensified by placing an inductor opposite each of the large faces.

En se reportant à présent à la figure 3, on voit que le dispositif à induction 31 est cette fois constitué par l'association de plusieurs unités inductrices identiques 32, par exemple au nombre de six et placées chacune à l'intérieur d'un rouleau de soutien tubulaire 33.Referring now to FIG. 3, it can be seen that the induction device 31 is this time constituted by the association of several identical inducing units 32, for example six in number and each placed inside a roller tubular support 33.

La technologie de chaque unité inductrice est connue et décrite en détail dans le brevet anglais n° 1.405.312 déjà cité. On rappelle qu'elle est constituée de bobines élémentaires 34 disposées côte à côte, le" unes à la suite des autres, autour d'un axe commun horizontal, de manière à couvrir la totalité de la largeur de la brame.The technology of each inductor unit is known and described in detail in the British patent No. 1,405,312 already cited. Recall that it consists of elementary coils 34 arranged side by side, "one after the other, around a common horizontal axis, so as to cover the entire width of the slab.

Dans la pratique habituelle, le montage des bobines ainsi que leur connexion à une alimentation électrique polyphasée sont réalisés de manière à créer un champ magnétique glissant horizontalement selon les génératrices du rouleau en se propageant d'une bobine à la suivante. Ici, il s'agit de créer un champ magnétique glissant, non plus horizontalement, mais verticalement d'une unité inductrice à la suivante, et dont l'action se manifeste sélectivement sur une portion seulement de la largeur du puits liquide 2.In usual practice, the assembly of the coils as well as their connection to a polyphase electrical supply are carried out so as to create a magnetic field sliding horizontally along the generatrices of the roller by propagating from one coil to the next. Here, it's a question of creating a sliding magnetic field, no longer horizontally, but vertically from one inducing unit to the next, and whose action is selectively manifested over only a portion of the width of the liquid well 2.

Une première réalisation, illustrée sur la figure 3, consiste:

  • - à brancher chaque unité inductrice 32 à une phase déterminée de l'alimentation électrique 24,
  • - à réaliser les connexions internes des bobines 34 de manière que le courant électrique circule dans des sens opposés dans deux bobines immédiatement voisines appartenant à une même unité inductrice ainsi que dans deux bobines de même rang, appartenant chacune respectivement à des unités inductrices 32 distinctes et immédiatement voisines,
  • - et à n'activer, sur chaque unité 32, que les bobines localisées en regard de la région centrale du puits 2, c'est-à-dire ges grandes faces du produit coulé.
A first embodiment, illustrated in FIG. 3, consists:
  • - to connect each inductor unit 32 to a determined phase of the electrical supply 24,
  • to make the internal connections of the coils 34 so that the electric current flows in opposite directions in two immediately adjacent coils belonging to the same inductor unit as well as in two coils of the same rank, each belonging respectively to separate inductor units 32 and immediately neighbors,
  • - And to activate, on each unit 32, that the coils located opposite the central region of the well 2, that is to say ges large faces of the cast product.

Il est à noter que les bobines appartenant à une même unité inductrice peuvent être montées en parallèle ou en série.It should be noted that the coils belonging to the same inductor unit can be mounted in parallel or in series.

Par ailleurs, l'inversion du sens du courant électrique entre deux bobines peut être réalisée par inversion, soit du sens d'enroulement des bobinages, soit du sens de connexion.Furthermore, reversing the direction of the electric current between two coils can be achieved by reversing either the direction of winding of the windings or the direction of connection.

Ainsi, si on respecte le montage des bobines et le mode de connexion de l'inducteur tels que le montre la figure 3, on crée un champ magnétique glissant verticalement de bas en haut, parallèlement à l'axe de coulée 5, et qui se propage d'une bobine donnée sur une unité inductrice à son homologue de même rang sur l'unité inductrice suivante, et ainsi de suite.Thus, if we respect the assembly of the coils and the connection mode of the inductor as shown in Figure 3, we create a magnetic field sliding vertically from bottom to top, parallel to the casting axis 5, and which is propagates a given coil on one inductor to its counterpart of the same rank on the next inductor, and so on.

On construit ainsi un système analogue à une pluralité d'inducteurs à champ glissant (trois dans l'exemple considéré), constitués chacun par une succession verticale de bobines, et disposés côte à côte parallélement à l'axe de coulée 5 et couvrant une partie de la largeur de puits de solidification 2.A system similar to a plurality of sliding field inductors (three in the example considered) is thus constructed, each consisting of a vertical succession of coils, and arranged side by side parallel to the casting axis 5 and covering a portion the width of the solidification well 2.

Il est rappelé que les unités inductrices 32 reliées à une même phase de l'alimentation électrique 24 peuvent indifféremment être montées en série, comme le montre la figure, ou en parallèle.It is recalled that the inductor units 32 connected to the same phase of the power supply 24 can either be connected in series, as shown in the figure, or in parallel.

Une autre variante de réalisation de mouvements plans parallèles au plan des grandes faces consiste, comme le montre la figure 4, à créer cette fois deux zones motrices verticales localisées chacune en regard des fronts de solidification des petites faces du produit. Lorsque ces deux zones motrices sont orientées en sens inverses, il s'établit un régime circulatoire simple et relativement bien organisé autour d'un axe perperdiculaire aux grandes faces et passant par l'axe médian 5. Cependant, comme le montre la figure 7, les mouvements se compliquent si l'on rapproche les zones motrices (76 et 76') de l'axe 5, car il se crée alors des zones de recirculation 77 et 77' confinées dans les régions étroites situées entre une zone motrice et le front de solidification de la petite face la plus voisine.Another alternative embodiment of planar movements parallel to the plane of the large faces consists, as shown in FIG. 4, this time in creating two vertical driving zones each located opposite the solidification fronts of the small faces of the product. When these two motor zones are oriented in opposite directions, a simple and relatively well organized circulatory regime is established around a perperdicular axis with large faces and passing through the median axis 5. However, as shown in FIG. 7, the movements become more complicated if the motor zones (76 and 76 ') are brought closer to axis 5, because recirculation zones 77 and 77' are thus confined in the narrow regions located between a motor zone and the forehead solidification of the nearest small face.

Bien entendu, le sens de l'entraînement est reversible. En pratique, il est même conseillé de l'inverser périodiquement afin d'égaliser les possibilités d'ensemencement entre les fronts des petites faces.Of course, the direction of training is reversible. In practice, it is even advisable to invert it periodically in order to equalize the possibilities of seeding between the fronts of the small faces.

Un tel mode d'entraînement peut être obtenu, ainsi qu'on le voit sur les deux figures suivantes 5 et 6, ou moyen de champs magnétiques glissant verticalement, produits par des inducteurs disposés en regard d'au moins une grande face de la brame et placés latéralement de part et d'autre de l'axe de coulée. Ces inducteurs peuvent être du type "monobloc" (figure 5 réf. 51 et 51') donc disposés derrière les rouleaux de soutien, et de conception tout à fait analogue à l'inducteur vu précédemment en référence à la figure 2, mais connectés à l'alimentation 24 de manière à créer deux champs magnétiques glissant verticalement dans des sens opposés.Such a drive mode can be obtained, as can be seen in the following two figures 5 and 6, or by means of vertically sliding magnetic fields, produced by inductors arranged facing at least one large face of the slab. and placed laterally on either side of the casting axis. These inductors can be of the “monobloc” type (FIG. 5 ref. 51 and 51 ′) therefore arranged behind the support rollers, and of a design completely similar to the inductor seen previously with reference to FIG. 2, but connected to the power supply 24 so as to create two magnetic fields sliding vertically in opposite directions.

Ces inducteurs peuvent également être constitués par les unités inductrices 32 précédemment décrites, auquel cas, comme le montre la figure 6, ne seront activées que quelques bobines 34 par unité 32, décalées vers les extrémités de la grande face, en regard du front de solidification des petites faces de la brame.These inductors can also be constituted by the inducing units 32 previously described, in which case, as shown in FIG. 6, only a few coils 34 per unit 32 will be activated, shifted towards the ends of the large face, facing the solidification front. small sides of the slab.

Bien entendu, si l'on recherche la configuration du mouvement illustrée sur la figure 7, le décalage des bobines à activer sera limité par exemple aux deux zones intermédiaires suituées à mi-distance entre les fronts de solidification des petites faces et le milieu des grandes faces.Of course, if the configuration of the movement illustrated in FIG. 7 is sought, the offset of the coils to be activated will be limited, for example, to the two intermediate zones located halfway between the solidification fronts of the small faces and the middle of the large ones. faces.

Conformément à l'invention, une autre configuration des mouvements de circulation du métal liquide, apte à assurer le transport des cristaux entre le fond du puits liquide et les régions plus élevées, consiste à créer comme le montre la figure 8, une zone motrice 86 parallèle aux grandes faces du produit, dirigée obliquement et orientée du bas vers le haut. Il se forme ainsi de part et d'autre de la zone motrice 86, une zone de recirculation inférieure 87 et une zone de recirculation supérieure 88. De cette façon, les cristaux en provenance de la région inférieure 87 pénétrent par l'extrémité basse de la zone d'entraînement direct 86 et en ressortent par l'extrémité haute, en empruntant le chemin le plus facile, c'est-à-dire en s'engageant dans la région supérieure 88. Ainsi les cristaux parcourent un trajet un forme de "S" en passant de la demi-boucle inférieure à la demi-boucle supérieure opposée sans avoir à opérer un changement brutal de direction.According to the invention, another configuration of the movements of circulation of the liquid metal, capable of ensuring the transport of the crystals between the bottom of the liquid well and the higher regions, consists in creating, as shown in FIG. 8, a motor zone 86 parallel to the large faces of the product, directed obliquely and oriented from the bottom up. There is thus formed on either side of the motor zone 86, a lower recirculation zone 87 and an upper recirculation zone 88. In this way, the crystals coming from the lower region 87 penetrate through the lower end of the direct drive zone 86 and exit from it by the upper end, taking the easiest path, that is to say by engaging in the upper region 88. Thus the crystals travel a path a form of "S" passing from the lower half-loop to the opposite upper half-loop without having to make a sudden change of direction.

Cette solution est inspirée par les considérations précédemment exposées relatives à l'importance de la surface offerte pour assurer la recirculation du métal.This solution is inspired by the considerations set out above relating to the size of the surface offered to ensure the recirculation of the metal.

Il est clair que plus la zone motrice 86 se rapproche de l'horizontale, plus la surface disponible à la recirculation du métal est grande puisqu'elle peut s'étendre verticalement sans être limitée par les fronts de solidification.It is clear that the closer the driving zone 86 is to the horizontal, the greater the surface available for recirculation of the metal. since it can extend vertically without being limited by the solidification fronts.

A cet égard, l'orientation souhaitable pour la zone motrice serait l'orientation horizontale, comme cela se pratique habituellement. Cependant, cette inclinaison croissante défavorise corrélativement les possibilités d'échanges de matières entre le fond du puits et les niveaux plus élevés et va donc à l'encontre du résultat recherché. Il existe ainsi un compromis entre la facilité avec laquelle s'organisent les mouvements du métal liquide et la facilité avec laquelle ces mouvements assurent la remontée des matières. Les travaux du demandeur ont révélé que ce compromis se caractérise par un entraînement du métal parallèlement aux grandes faces et dont la direction de propagation présente un angle non nul avec l'horizontale, et de préférence compris entre 30 et 60° environ. Par ailleurs, il est clair que, pour assurer l'efficacité des échanges, le sens d'entraînement du métal ne peut plus être reversible, comme dans les modes de brassage précédents, mais nécessairement orienté de bas en haut. Par contre, bien entendu, le système demeure symétrique par rapport à l'axe de coulée 5 en ce qui concerne la direction de l'entraînement.In this regard, the desirable orientation for the motor area would be horizontal orientation, as is customary. However, this increasing inclination correlatively disadvantages the possibilities of material exchange between the bottom of the well and the higher levels and therefore goes against the desired result. There is thus a compromise between the ease with which the movements of the liquid metal are organized and the ease with which these movements ensure the ascent of the materials. The work of the applicant has revealed that this compromise is characterized by a metal entrainment parallel to the large faces and whose direction of propagation has a non-zero angle with the horizontal, and preferably between around 30 and 60 °. Furthermore, it is clear that, in order to ensure the efficiency of the exchanges, the direction in which the metal is driven can no longer be reversible, as in the previous brewing modes, but necessarily oriented from bottom to top. On the other hand, of course, the system remains symmetrical with respect to the casting axis 5 as regards the direction of the drive.

Cet entraînement oblique du métal peut être obtenu par au moins deux manières distinctes d'opérer:

  • 1 °) au moyen d'un champ magnétique glissant lui-même obliquement dans la direction souhaitée,
  • 2°) au moyen de deux champs mobiles distincts se propageant dans deux directions différentes mais déterminées de manière que leur résultante soit oblique car le métal liquide, sous l'effet de leurs actions conjuguées, se comporte comme s'il était soumis à un champ unique glissant selon cette résultante.
This oblique metal entrainment can be obtained by at least two distinct ways of operating:
  • 1 °) by means of a magnetic field sliding itself obliquely in the desired direction,
  • 2) by means of two distinct mobile fields propagating in two different directions but determined so that their result is oblique because the liquid metal, under the effect of their combined actions, behaves as if it were subjected to a field unique sliding according to this result.

La première variante est réalisée, conformément à la figure 9, au moyen de l'inducteur monobloc 21, déjà vu en référence à la figure 2, mais présentant cette fois une orientation inclinée par rapport à l'axe de coulée 5. L'avantage de cette variante réside essentiellement dans le fait que l'inducteur étant indépendant des organes constitutifs de la machine de coulée, on est libre de lui donner l'inclinaison souhaitée;The first variant is produced, in accordance with FIG. 9, by means of the monobloc inductor 21, already seen with reference to FIG. 2, but this time having an inclined orientation relative to the casting axis 5. The advantage of this variant lies essentially in the fact that the inductor being independent of the constituent members of the casting machine, one is free to give it the desired inclination;

La seconde variante est réalisée, comme le montre la figure 10, au moyen d'unités inductrices 32 logées dans les rouleaux de soutien 33. Ici, chaque unité 32 présente un autonomie fonctionnelle et crée un champ magnétique glissant horizontalement (Àlt), le long des génératrices des rouleaux. Pour ce faire, chaque unité 32 n'est plus, comme dans les cas précédents, connectée à une phase unique de l'alimentation électrique 24, mais aux trois phases simultanément et la cablage interne des bobines élémentaires 34, ainsi que les sens d'enroulements, sont réalisés selon la schéma de la pratique habituelle.The second variant is produced, as shown in FIG. 10, by means of inductor units 32 housed in the support rollers 33. Here, each unit 32 has a functional autonomy and creates a horizontally sliding magnetic field (Àlt), along generators of the rollers. To do this, each unit 32 is no longer, as in the previous cases, connected to a single phase of the electrical supply 24, but to the three phases simultaneously and the internal wiring of the elementary coils 34, as well as the directions of windings, are made according to the scheme of usual practice.

Le système selon l'invention se caractérise cependant par le fait que les unités inductrices présentent entre elles un décalage de phase, de façon qu'une succession de bobines de même rang, prises à la suite l'une de l'autre sur des unités différentes, constitue, comme dans le cas des figures 3 et 6, un inducteur à champ magnétique glissant verticalement de bas en haut

Figure imgb0001
L'effet combiné du champ à déplacement horizontal
Figure imgb0002
avec le champ à déplacement vertical remontant
Figure imgb0003
s'identifie avec l'effet d'un champ unique se ropageant obliquement selon leur résultante
Figure imgb0004
 The system according to the invention is however characterized by the fact that the inducting units have a phase shift between them, so that a succession of coils of the same rank, taken one after the other on units different, constitutes, as in the case of FIGS. 3 and 6, an inductor with a magnetic field sliding vertically from bottom to top
Figure imgb0001
 The combined effect of the horizontal displacement field
Figure imgb0002
 with the field moving vertically upward
Figure imgb0003
 identifies with the effect of a single field obliquely ropaging according to their result
Figure imgb0004

Bien entendu, comme le montre la figure 11 suivante, le sens d'orientation du champ à déplacement horizontal est réversible. Cette réversibilité, opérée périodiquement en cours de coulée, est d'ailleurs conseillée car elle permet de remédier à la dissymétrie du mode de brassage en égalisant les apports de matières en provenance du fond du puits sur les fronts de solidification des petites faces de la brame.Of course, as shown in the following figure 11, the direction of orientation of the field with horizontal displacement is reversible. This reversibility, operated periodically during casting, is moreover advised because it makes it possible to remedy the asymmetry of the brewing mode by equalizing the contributions of materials coming from the bottom of the well on the fronts of solidification of the small faces of the slab. .

C'est là un avantage appréciable de cette variante par rapport à celle représentée sur la figure 9.This is an appreciable advantage of this variant compared to that shown in FIG. 9.

La présente invention ne saurait bien entendu se limiter aux exemples décrits. Ainsi, ce qui a été dit à propos des inducteurs placés dans les rouleaux de maintien est également applicable au cas où l'on dispose les inducteurs entre les rouleaux ou à la place de certains rouleaux.The present invention cannot of course be limited to the examples described. Thus, what has been said about the inductors placed in the retaining rollers is also applicable in the case where the inductors are placed between the rollers or in place of certain rollers.

Par ailleurs, la position réelle de l'inducteur sur la hauteur métallurgique n'est pas limitée à celle visible sur les figures. L'utilisateur pourra agir sur cette position pour que les mouvements provoqués parviennent bien jusqu'au voisinage immédiat du fond du puits de solidification.Furthermore, the actual position of the inductor over the metallurgical height is not limited to that visible in the figures. The user can act on this position so that the movements caused reach the immediate vicinity of the bottom of the solidification well.

Pour un inducteur donné, la mise en mouvement du métal liquide au fond du puits dépend non seulement de la position en hauteur de l'inducteur mais également de sa puissance, autrement dit de l'intensité de son action électromagnétique sur le métal.For a given inductor, the setting in motion of the liquid metal at the bottom of the well depends not only on the height position of the inductor but also on its power, in other words the intensity of its electromagnetic action on the metal.

Il va de soi que plus cette action est faible, plus l'inducteur doit être placé bas sur la machine de coulée. Corrélativement, les régions supérieures, alimentées en métal liquide chargé en cristaux équiaxes en provenance de fond, se situeront à des niveaux plus bas et la proportion de structure de solidification équiaxe dans le produit coulé sera d'autant réduite.It goes without saying that the weaker this action, the lower the inductor must be placed on the casting machine. Correlatively, the upper regions, supplied with liquid metal charged with equiaxial crystals coming from the bottom, will be located at lower levels and the proportion of equiaxed solidification structure in the cast product will be correspondingly reduced.

Si l'on souhaite une proportion "équiaxe" accrue, il faut pouvoir ensemencer en cristaux des régions de niveaux plus élevés, donc remonter l'inducteur vers le haut de la machine de coulée et, par conséquent, augmenter sa puissance de brassage.If an increased "equiaxial" proportion is desired, it is necessary to be able to seed regions of higher levels with crystals, therefore raise the inductor to the top of the casting machine and, consequently, increase its stirring power.

Claims (8)

1) A process for continuous, vertical or curvilinear casting of molten metals, steel in particular, to obtain cross-sectional elongated products such as slabs, whereby, by means of inductors, the molten metal, whilst solidifying in the secondary cooling stage of the casting machine, is subjected to electromagnetic agitation at least near the bottom (4) of the solidification well (2), such electromagnetic agitation being performed by entraining the molten metal in a direction of which at least one component is along the casting axis (5), said process being characterized in that the electromagnetic entrainment of the metal is located along, at least, one of the larger sides of the casting and within an area the width of which accounts for only a portion of the said side.
2) A process, according to claim 1, characterized in that the electromagnetic entrainment of the metal is located in the median area (16) of the larger sides of the casting.
3) A process, according to claim 1, characterized in that the electromagnetic entrainment of the metal is located in areas (46, 46') near the side edges of the larger sides of the casting.
4) A process, according to claim 1, characterized in that the electromagnetic entrainment of the metal in areas (76, 76') is located in areas (76, 76') between the median longitudinal axis and the side edges of the larger sides of the casting.
5) A process according to claim 1, characterized in that the electromagnetic entrainment of the metal occurs in a direction parallel to the larger sides of the casting and at an angle approximately 30 to 60° from the casting axis.
6) A process, according to any one of the above claims, characterized in that the electromagnetic entrainment of the metal is derived from a drifting magnetic field generated by at least one single-piece polyphase inductor (21, or 51, 51').
7) A process, according to any claim 1 to 5, characterized in that the electromagnetic entrainment of the metal is derived from a drifting magnetic field generated by at least one polyphase static inductor (31) consisting along the casting axis, of successive induction units (32) elongated in shape and extending throughout the width of the larger sides of the casting, each such unit consisting of elementary co-axial side by side coils (34), and in that the only coils energized are those located in areas of the larger side of the product that correspond with the area or areas in which the electromagnetic entrainment of the metal is to be located.
8) A process, according to claim 7, characterized in that the inductive units (32) are arranged within the supporting rollers (33) of the secondary cooling stage of the casting machine.
EP79400695A 1978-10-05 1979-10-01 Process for the continuous casting of metals with stirring in the secundary cooling zone Expired EP0010041B1 (en)

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AT79400695T ATE1884T1 (en) 1978-10-05 1979-10-01 PROCESS FOR CONTINUOUS CASTING OF METALS, WITH STIRRING IN THE SECONDARY COOLING ZONE.

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FR7828726A FR2437900A1 (en) 1978-10-05 1978-10-05 CONTINUOUS CASTING PROCESS FOR METALS WITH BREWING IN THE SECONDARY COOLING AREA
FR7828726 1978-10-05

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SE8202431L (en) * 1982-04-19 1983-10-20 Asea Ab MOVING STRING
FR2528739B1 (en) * 1982-06-18 1985-08-02 Siderurgie Fse Inst Rech METHOD AND PLANT FOR ELECTROMAGNETIC BREWING OF METAL SLABS, ESPECIALLY STEEL, CONTINUOUSLY CAST
AT379976B (en) * 1984-04-06 1986-03-25 Voest Alpine Ag STIRRING DEVICE ON A CONTINUOUS CASTING SYSTEM
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CN106925762B (en) * 2015-12-29 2019-11-15 北京有色金属研究总院 A kind of device and method of high shear strong electromagnetic stirring melt processing
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US3693697A (en) * 1970-08-20 1972-09-26 Republic Steel Corp Controlled solidification of case structures by controlled circulating flow of molten metal in the solidifying ingot
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US3882923A (en) 1972-06-08 1975-05-13 Siderurgie Fse Inst Rech Apparatus for magnetic stirring of continuous castings
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DE2964155D1 (en) 1983-01-05

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