EP3405301B1 - Method for rotary electromagnetic stirring of a molten metal during casting of a product having a wide cross-section and apparatus for implementing same - Google Patents

Description

The present invention relates to the casting of metals, steel in particular. It is particularly aimed at the casting of metal products with a large square, rectangular or round cross section such as thick oars and large square or round blooms. More precisely, it relates to the electromagnetic stirring which generates an axial rotational movement of the molten metal during casting.

It is recalled that the electromagnetic stirring of the molten metal during the continuous casting of steel has been used for a long time to improve the productivity of continuous casting machines and the quality of the cast products obtained.

One of the main uses of electromagnetic stirring, and in which the present invention is part, consists in creating rotary movements of the molten metal, either in the form of a circulation loop rotating around the casting axis, therefore in the plane of the cross section of the cast product (BF 7520225), or in a vertical plane parallel to the large faces of the cast product, in the form of multiple loops with axes of rotation perpendicular to the casting axis ( EP 0550785 , EP 0151648 ).

As is known, these movements are generated by moving magnetic fields produced by polyphase static electromagnetic inductors mounted on the casting machine around and in the immediate vicinity of the cast product, already at the level of the ingot mold, or below, in the stages. secondary or final cooling of the machine.

It will be recalled that an inductor of this type is essentially constituted by a succession of electric coils wound on a ferromagnetic body, coils which produce magnetic poles when they are traversed by an electric current supplied by a two-phase or three-phase power supply. Like the stator of an asynchronous motor, the inductor windings are electrically connected to the phases of the power supply to form a system with a pair of magnetic poles of opposite signs per phase (two-phase or three-phase bipolar motor). A mobile magnetic field is thus generated, which moves along the inductor. If it penetrates into an electrically conductive medium, as is the molten metal cast, this mobile field then generates a volume force (Lorentz force) which sets in motion (we say "which stirs") the molten metal according to the well-known principles of the rotary or linear asynchronous induction motor.

In the case of continuous casting of long products, i.e. round or square format (blooms or billets), as shown in the figures 1 joined, the electromagnetic stirring equipment used is conventionally constituted by an annular inductor (circular fig. la or square fig. 1b ) that surrounds the cast product. This inductor produces a magnetic field which passes right through the cast product perpendicular to the casting axis and which rotates around this axis. An axial rotational movement of the molten metal is thus created in the manner of an asynchronous electric motor whose rotor is the molten metal.

In the case of the continuous casting of an elongated rectangular format, therefore a slab, the usual practice this time consists in using a stirring equipment formed by inductors of rectilinear shape (we say "linear" as opposed to circular) which produce a sliding magnetic field, such as a two-phase or three-phase bipolar linear electric motor. These inductors, used singly or in pairs, are mounted parallel to a large face of the cast slab.

It should be noted that the term “pair of inductors” should be understood to mean a pair of electrically matched linear inductors, that is to say supplied by synchronous polyphase electric currents.

Used alone (see figures 2a and 2b ), a linear inductor with a sliding field always operates in tangential magnetic flux (we also say "longitudinal"). This means that it generates a thrust in the molten metal which decreases exponentially when we move away from it. As document BF 8210844 shows, if this thrust takes place in the secondary cooling stage of the casting machine and it is oriented perpendicular to the casting axis, therefore according to the width of the slab, the metal in stirred fusion forms a double circulation loop known as the “butterfly wing loop”

Used in pairs (or in double pairs), they are then mounted one opposite on the other, thus defining between them a rectangular air gap which the cast slab occupies.

In this case, as shown in the figure 3a illustrating the teaching of the document EP 0151648 (KSC), an equipment with a pair of linear inductors is mounted at the level of the mold at the rate of one inductor per face. Each inductor operates in tangential magnetic flux with opposite sliding directions of the two magnetic fields. This results in individual thrusts in the opposite direction on the molten metal in the immediate vicinity of the large walls of the mold, therefore a zero thrust in the middle zone of the slab, which leads to creating an axial rotary movement of the molten metal in its entire straight section.

The term “axial” is understood to mean “rotation around the casting axis or parallel to it. This meaning will be valid for the rest of the description.

Another known document, illustrated by the figure 3b , shows a pair of linear inductors used in flux crossing in the same direction of sliding of the magnetic fields, which generates a substantially constant thrust throughout the thickness of the cast slab.

In the category of electromagnetic stirring equipment acting, this time at the level of the secondary cooling stage, there are notably well-known devices widely used in the steel industry, such as stirring rolls or in -roll EMS). These are support rollers and guide the slab in the secondary cooling made hollow to receive a linear inductor (USP 3,882,923 ), or even two inductors aligned and coupled in the case of very wide slabs ( WO 2011/117479 A1 ). These stirring rollers, generally used in pairs, are installed either in parallel one above the other, and operate in tangential magnetic flows, or face to face on either side of the slab, and then operate in magnetic flux through. But, each time, they have the effect of pushing the molten metal horizontally along the width of the slab to create the double circulation loops in "butterfly wings" mentioned above. They can also be used in double pairs to create quadruple circulation loops, by reversing the direction of sliding of the fields on the two mounted inductors aligned on each large face of the cast slab ( WO 2011/117479 ).

On the other hand, in an ingot mold, as shown for example in the document EP 0550785 (NKK), one more commonly uses a brewing equipment formed by a battery of two pairs of polyphase linear inductors, that is to say four identical inductors. The inductors are mounted on the two large walls of the mold, with two inductors aligned per wall and placed on either side of the casting nozzle. They are electrically connected in magnetic flux crossing to generate a substantially constant thrust through the thickness of the slab, because we want to act on the jets of "fresh" metal coming out of the gills of the nozzle, or to accelerate them (sliding of the fields magnetic in the direction of the jets towards the outside of the mold), or to slow them down (sliding of the fields against the direction of the jets towards the inside of the mold).

Such operating processes make it possible to install or stabilize selected modes of circulation of the molten metal known as "double loop" (double roll) or "single loop" (single roll) in the vertical plane within the mold ( see documents EP 0550785 and EP 0151648 already cited).

It is now accepted, and the work of the applicant has largely contributed to it, that not only the productivity of a continuous casting machine, but also the metallurgical quality of the finished cast product, both in terms of microstructure and in terms of cleanliness. inclusion, of axial porosity or segregation, are closely linked to the circulating movements of the molten metal during its casting. The control of these movements turns out to be the key to the success of the quality and the productivity of continuous casting and it is precisely the practice of electromagnetic stirring of steel that allows such control.

For example, FR2893868 discloses a method of adjusting the electromagnetic stirring mode of the liquid metal to the height of a continuous casting mold, and corresponding equipment, in which method the inductors are mounted to slide vertically and pass, by translation, from a low functional position acting at the outlet openings of a nozzle, at a high functional action position acting at the level of the meniscus of the liquid metal in the ingot mold. When switching from one functional position to another, the connection of the inductors to the power supply is changed in order to reverse the direction of sliding of the magnetic field of only one of the two inductors of the same pair as well as that, among the two inductors of another pair, which is its symmetrical with respect to the casting axis. This document does not however disclose that the opposite poles of the inductor are connected to the same electrical phase and are maintained at the same polarity.

However, if the current good practice of electromagnetic mixing, as it has just been briefly mentioned, is quite suitable for controlling the movements of molten steel during casting, it is in fact only so. for cast products of common formats, and not for very large formats, i.e. those, to fix ideas, whose thickness (or diameter for the rounds) is of the order of a meter, or even more.

However, it turns out that a demand is now emerging from a certain global steel industry to cast, not only in ingots, but also in continuous or semi-continuous casting of such formats, both in rounds, squares, or rectangles, and that XXL formats will be designated hereinafter for convenience of language.

• Plus le format coulé augmente, plus la distribution de la température au sein du métal liquide devient inhomogène, et cette hétérogénéité thermique devient alors le problème principal pour couler des formats XXI.
• Un brassage en boucles multiples dans le plan vertical parallèle à l'axe de coulé semble a priori approprié. Mais, les modes de brassage conventionnels connus à flux magnétique traversant ne sont plus applicables aux formats XXL du fait de la grande dimension de la section droite du produit coulé. La raison est que le champ magnétique, qui doit traverser la grande distance entre les deux inducteurs, décroit alors fortement au centre du produit et que la poussée (force de Lorentz) au milieu de la brame devient alors trop faible pour générer un mouvement de brassage efficient sur toute l'épaisseur de la brame.
• Le même phénomène se produit dans les inducteurs annulaires pour produits ronds et carrés. La distance entre les pôles appariés devenant alors si grande pour les sections XXL, que le couple de rotation (forces de Lorentz) devient alors trop faible vers le centre du produit coulé. Le mouvement rotationnel du métal liquide reste alors concentré à la périphérie et ne se développe plus vers le centre du produit.
• Enfin, et même surtout, le mouvement rotationnel du métal en fusion autour de l'axe de coulée, qui reste pour l'essentiel limité à la région périphérique du produit XXL, ne parvient plus à uniformiser suffisamment la température au sein du métal en fusion, ni au niveau du front de solidification, ni au niveau du gradient de température entre l'intérieur et l'extérieur du produit coulé.

It turns out that such formats cannot be understood by extrapolation, to such large dimensions, from current calculation methods and existing knowledge. When studying these projects with CFD (computer fluid dynamics) simulations, the following problems actually arose:

• The more the cast format increases, the more the temperature distribution within the liquid metal becomes inhomogeneous, and this thermal heterogeneity then becomes the main problem for casting XXI formats.
• A mixing in multiple loops in the vertical plane parallel to the casting axis seems a priori appropriate. However, the known conventional stirring methods with a through magnetic flux are no longer applicable to XXL formats because of the large dimension of the cross section of the cast product. The reason is that the magnetic field, which must cross the great distance between the two inductors, then decreases sharply in the center of the product and that the thrust (Lorentz force) in the middle of the slab then becomes too weak to generate a stirring movement. efficient over the entire thickness of the slab.
• The same phenomenon occurs in annular inductors for round and square products. The distance between the paired poles then becomes so great for XXL sections, that the torque (Lorentz forces) then becomes too weak towards the center of the cast product. The rotational movement of the liquid metal then remains concentrated at the periphery and no longer develops towards the center of the product.
• Finally, and even above all, the rotational movement of the molten metal around the casting axis, which remains essentially limited to the peripheral region of the XXL product, no longer manages to sufficiently uniform the temperature within the molten metal. , neither at the level of the solidification front, nor at the level of the temperature gradient between the inside and the outside of the cast product.

The Applicant has discovered that these difficulties inherent in XXL formats could nevertheless be overcome by establishing an axial rotational stirring in "adjacent multi-loops", namely an organized plurality of axial rotary recirculation loops distributed side by side around the surrounding area. 'casting axis to achieve, above all, to homogenize the temperature well in planes perpendicular to the casting axis.

Thus, and with this main objective of thermal homogenization in view, the first object of the invention is a method of rotary electromagnetic stirring of the molten metal, during the casting of metal products in XXL format, of round, square or cross section. rectangular, in which a stirring equipment comprising linear polyphase inductors with a sliding magnetic field is used, and the molten metal is stirred in the form of a plurality of adjacent axially rotating circulation loops, distributed around the surrounding of the casting axis and occupying at best the entire cross section of the cast product.

The method is characterized in that said stirring is carried out by placing said polyphase linear inductors with a sliding magnetic field around the casting axis to form an air gap, in that the magnetic fields sliding in this air gap so that they slide in opposite directions on any two neighboring inductors, and in that the pairs of poles connected to the same electrical phase and located one opposite the other are adjusted to the same magnetic polarity on two separate paired inductors.

Another subject of the invention is equipment for electromagnetic stirring of metal products in XXL format. of round, square or rectangular section, equipment for carrying out the method according to claim 1 or 2 and comprising at least one pair of linear inductors with sliding magnetic field mounted symmetrically, facing each other with respect to a plane of symmetry (P) of the cast product, around the casting axis so as to define an air gap through which the product passes cast, at least one polyphase power supply provided with electrical connection means with said inductors, and means for adjusting the direction of sliding of the magnetic fields on each inductor, equipment characterized in that said connection means impose the same polarity on each pair of magnetic poles belonging to the same phase and placed symmetrically with respect to said plane (P) facing each other on two paired inductors.

In an alternative embodiment, the stirring equipment comprises at least two pairs of linear inductors with a sliding magnetic field, forming a set of at least four inductors arranged around the casting axis so as to define a air gap in which the cast product passes, equipment characterized in that said means for adjusting the direction of sliding of the magnetic fields are configured so that the magnetic fields of any two neighboring inductors slide in opposite directions.

1. (a) Ainsi, sont voisins, au sens de l'invention, deux inducteurs qui se suivent l'un l'autre directement, c'est à dire sans inducteur analogue intermédiaire ou intercalaire, sur l'entour de l'axe de coulée, quelque soit le sens de rotation choisi autour de cet axe pour passer d'un inducteur à l'autre.
2. (b) Pour répondre à cette seconde interrogation, il faut d'abord prendre en considération la convention selon laquelle les phases électriques sont nommées dans un ordre immuable et déterminé dans le temps, car données ainsi par le réseau de distribution de l'énergie électrique: U puis V (en retard de 90°) pour une alimentation biphasée ou U puis V (en retard de 120°) puis W (en retard de 240°) pour une alimentation triphasée. Dès lors, le sens de glissement du champ magnétique le long de l'inducteur qui le produit dépendra du séquençage choisi pour l'ordre de connexion des phases sur les bobinages de l'inducteur.

Before going any further, it is important to provide more details and clarifications on certain terms and expressions used above: (a) what should be understood by "neighboring inductors" (b) how to conveniently define "the direction of sliding" d 'a magnetic field of the inductor, and (c) how to unambiguously understand what it means in practice to slip "in the same direction" or "in opposite directions" on two neighboring inductors.

1. (a) Thus, are neighbors, within the meaning of the invention, two inductors which follow each other directly, that is to say without a similar intermediate or intermediate inductor, around the casting axis , whatever the direction of rotation chosen around this axis to switch from one inductor to another.
2. (b) To answer this second question, it is first necessary to take into consideration the convention according to which the electrical phases are named in an immutable order and determined in time, because thus given by the electrical energy distribution network : U then V (delayed by 90 °) for a two-phase supply or U then V (delayed by 120 °) then W (delayed by 240 °) for a three-phase supply. Therefore, the direction of sliding of the magnetic field along the inductor which produces it will depend on the chosen sequencing. for the phase connection order on the inductor windings.

Thus, for example for the case of a rotary inductor, the magnetic field will rotate according to the U. V sequencing for a two-phase inductor ( fig. 1b ) and U, V, W for a three-phase inductor ( fig. 1a ), i.e. clockwise. For the case of a three-phase linear inductor of the figure 2a . the magnetic field will also slide according to the U, V. W sequencing, that is to say from left to right in the figure. And, it will slide from right to left, as shown in the figure 2b , if the sequencing has been changed by permutation of two phases between them (V and W in the example considered) without changing the North or South magnetic polarity of each pole.

Also, it is agreed, within the framework of the invention, to always place the phase U on the pole of the inductor located at one of its two ends. Therefore, if the succession of phases in time is in a sequential order U, V, W, the direction of the sliding of the magnetic field is always given by the sequencing of the magnetic poles U, V, W, this sequencing being given by the electrical connections between the inductor windings and the power supply.
(c) To compare the direction of sliding of the magnetic fields between several inductors installed on a casting machine, it suffices to consider the direction of sliding of the field of each one by traversing them one after the other around the axis of casting. As a result, the fields of the two inductors shown on the fig. 3a slide in the same direction, according to the definition of the invention, whereas, seen from above in the figure, it looks like they slide in the opposite direction. It also follows that the fields of the two inductors shown on the fig. 3b slide in the opposite direction according to the definition of the invention, whereas, seen from above in the figure, it looks like they slide in the same direction.

1. 1) S'ils sont disposés en parallèle, l'un en regard de l'autre, deux inducteurs linéaires (i.e. dont les pôles magnétiques sont alignés entre eux), produisent des champs magnétiques glissant en sens opposés si l'un peut se transformer en l'autre par une opération de symétrie par rapport à un plan parallèle à la ligne des pôles de l'inducteur. Sinon, ils produisent des champs qui glissent dans le même sens.
2. 2) S'ils sont disposés alignés l'un à la suite de l'autre, deux inducteurs linéaires produisent des champs magnétiques glissant dans le même sens, si l'un peut se transformer en l'autre par une opération de translation parallèle à sa ligne des pôles. Sinon, ils produisent des champs qui glissent en sens contraire.

We will now present, in a more geometric language, another comparative definition of the sliding directions of magnetic fields, more general than the previous one, ie independently of the casting machine for which the "stirring equipment" is intended. The reader will choose the one that suits him best.

1. 1) If they are arranged in parallel, one opposite the other, two linear inductors (ie whose magnetic poles are aligned with each other), produce magnetic fields sliding in opposite directions if one can transform in the other by an operation of symmetry with respect to a plane parallel to the line of the poles of the inductor. Otherwise, they produce fields that slide in the same direction.
2. 2) If they are arranged aligned one after the other, two linear inductors produce magnetic fields sliding in the same direction, if one can be transformed into the other by a translation operation parallel to its pole line. Otherwise, they produce fields that slide in the opposite direction.

In the description of the prior art of the electromagnetic stirring in continuous casting of standard format steel products which was made at the beginning of this specification, it has been seen that, except for the case shown in the figure 3a , the inductors are used in magnetic coupling with through-flow, and this, both in circular configuration (rotating field applied to blooms of round or square section) as in linear configuration by pair of inductors (sliding fields applied to rectangular products such as slabs). This means that the poles of the same phase which face each other on two inductors facing each other are of opposite polarities.

It is quite different in the case of the invention where it is the same polarity which is imposed on the poles of the same phase which face each other on two paired inductors. Here, expressed simply, to which must answer a determining characteristic of an equipment which produces a tangential magnetic flux, whatever the size of its air gap.

The invention will be well understood and other aspects and advantages will emerge more clearly in view of the following description given with reference to the sheets of the appended figures.

In these figures, the letters U, V and W represent the three electrical phases of the three-phase power supply phase-shifted by 120 °. They also designate, consequently, the phase windings on the inductors connected to this power supply, and the additional letters U *, V *, W * designate the phase windings on the inductors wound in the opposite direction of the windings. U, V, W so that the electric current flows in it in an opposite direction.

• les figures 1, 2 et 3 sont des schémas de principe électromagnétique qui se rapportent à l'art antérieur cité dans l'introduction du présent mémoire. Pour cette raison, elles ont toutes été regroupées sur une planche unique;
• les figures 4a et 4b sont deux variantes d'un même schéma de principe de fonctionnement d'un équipement de brassage élémentaire selon l'invention, i.e. à une paire d'inducteurs linéaires à flux tangentiel, de forme rectiligne, en situation de travail sur une coulée de brames XXL;
• la figure 5 est un schéma de principe analogue à ceux des figures 4, mais dans le cas d'inducteurs linéaires de forme arquée pour la coulée d'un bloom XXL de forme circulaire;
• les figures 6a et 6b montrent deux variantes d'un même schéma de principe de fonctionnement d'un équipement de brassage standard selon l'invention, i.e. à deux paires d'inducteurs linéaires à flux tangentiel (soit un ensemble de quatre inducteurs), de forme rectiligne, en situation de travail sur une coulée de brames XXL
• la figure 7 est un schéma de principe de fonctionnement d'un équipement de brassage standard selon l'invention, i.e. à deux paires d'inducteurs linéaires à flux tangentiel de forme arquée, en situation de travail sur une coulée de blooms XXL ronds;
• la figure 8 est un schéma analogue à celui de la figure 1 mais avec des inducteurs linéaires rectilignes utilisés pour la coulée de blooms XXL carrés;
• et la figure 9 montre schématiquement un équipement de brassage complet tel qu'utilisé au niveau d'une lingotière de coulée continue de brames XXL dotée d'une busette immergée à quatre ouïes latérales.

The letters N and S denote the north or south polarity of the poles when the electrical phase which supplies them is at the maximum current intensity. As it is the phase windings which generate the magnetic poles on an inductor, it will be seen in the figures that, by convention, a phase winding U, V, or W is always associated with a pole of polarity N, while winding U *, V * or W * will always be associated with a pole of polarity S.

• the figures 1, 2 and 3 are electromagnetic block diagrams which relate to the prior art cited in the introduction to this specification. For this reason, they have all been grouped together on a single board;
• the figures 4a and 4b are two variants of the same operating principle diagram of an elementary stirring equipment according to the invention, ie to a pair of linear inductors with tangential flow, of rectilinear shape, in a working situation on a casting of XXL slabs ;
• the figure 5 is a block diagram similar to those of figures 4 , but in the case of linear inductors of arcuate shape for the casting of an XXL bloom of circular shape;
• the figures 6a and 6b show two variants of the same operating principle diagram of a standard brewing equipment according to the invention, ie with two pairs of linear inductors with tangential flow (i.e. a set of four inductors), of rectilinear shape, in situation working on an XXL slab casting
• the figure 7 is a block diagram of the operation of a standard brewing equipment according to the invention, ie with two pairs of linear inductors with tangential flow of arcuate shape, in a working situation on a casting of round XXL blooms;
• the figure 8 is a diagram similar to that of the figure 1 but with rectilinear linear inductors used for casting XXL square blooms;
• and the figure 9 schematically shows a complete brewing equipment as used in an XXL continuous casting ingot mold with a submerged nozzle with four side openings.

In all of these figures, the same elements are represented by identical numerical references.

As has already been seen, FIG. La is the functional diagram of a known three-phase annular inductor with a rotating magnetic field. This type of inductor, with a pair of poles per phase, annular in shape with a circular base, is usually used for the continuous casting of long products in round format (blooms, billets), whether at the level of the mold or, below. , in the area of secondary cooling of the casting machine. It presents here an additional educational interest, useful for the presentation of the invention, which is to serve as a phase circle for a three-phase system. On this circle, U, V and W denote the three phases of a balanced three-phase power supply. It follows that, in time, the maximum intensity of electric current passes, with a regular speed which depends on its frequency of the current, from phase U to phase V then to phase W, and so on. On an inductor with a rotating field, as shown diagrammatically here, the pairs of paired magnetic poles of each phase are excited by windings wound in opposite directions so as to present magnetic polarities of opposite signs (N or S). Thus, the marking U, V, W, U *, V * and W * points to the physical positions of the magnetic poles on the inductor at the moment when they are each, in turn, in full phase (ie with a maximum intensity of the electric current in the associated winding).

The sequence, taken in this order, namely U, W *, V, U *, W, V * (and again U ....), represents, in space, the ordered physical succession of the poles on l 'inductor thus configured. The same sequence, but taken over time, therefore shows that the displacement of the magnetic field from one pole of the inductor to the next develops clockwise v. This results in a field rotating around the longitudinal axis of the inductor, which here merges with the axis of the casting. We see that if we switch two phases between them, for example V and W, without changing anything in the magnetic polarities, we realize the sequence U, V *, W, U *, V, W *, which then expresses the fact that the magnetic field reverses its direction of displacement on the inductor to rotate counterclockwise.

The figure 1b illustrates the functional diagram of an inductor with two pairs of poles per phase, but two-phase this time and of annular shape with square base for the casting of long products of square format. If necessary, we will know how to use it, in the same way as with the figure 1a , to find on such a circle of phases the attributes specific to a two-phase system. We will easily realize that, in this case, we will be able to reverse the direction of rotation of the magnetic field indifferently, by switching the phases U and V (ie putting V in advance of 90 ° on U), or by reversing the direction of the current in the windings of one phase.

In any case, the same arrangements prevail if the moving field inductor is linear instead of being annular. Indeed, if by thought we unroll the three-phase inductor of figure la after having cut it for example between the poles U and V *, one obtains the functional diagram of a three-phase linear inductor with sliding field, such as that illustrated on the figures 2 .

In view of the phase circle of the three-phase system, it is immediately understood that the magnetic field produced by this linear inductor 1 slides, on the figure 2a , from its left end to its right end (arrow v). Thus, like any linear inductor taken in isolation in space, inductor 1 naturally generates in the cast metal product, here a slab 2, a magnetic induction flux of the "tangential" type, ie a flux whose main property is to generate a Lorentz thrust, the intensity of which decreases rapidly as one moves away from the inductor.

Always by thought, if, without changing anything in the polar signs of the poles, one simply permutes two phases between them, for example V and W (U remaining on the pole at the left end of the inductor), the direction of sliding of the field is reversed on the inductor thus reconfigured.

This is verified for a three phase supply. In the case of a two-phase power supply, we can easily verify using the circle of the four-pole phases U, V, U * and V *, that the magnetic field changes direction of sliding by simply reversing the polar sign, ie the polarity, of the two poles coupled on the same phase.

The figures 3 illustrate what happens when a matched identical inductor 3 is brought closer to inductor 1 to place them in parallel, on either side of a plane of symmetry P which is the main plane of symmetry of the cast rectangular slab 2.

The case of figure 3b is that of the usual classical configuration: the magnetic poles opposite each side of the plane of symmetry P are at the same phase, but of opposite polarities. Everything then takes place as if such a pair of inductors 1, 3 produced a "piston" magnetic field sliding from their left end to their right end (arrow v or v '), in a way like the bars of a mobile ladder whose fixed slides are the inductors themselves. Thus, like any pair of inductors matched and configured for use on a casting machine, the brewing equipment of the figure 3b generates a sliding induction flux of the "through" type. It results in particular that the Lorenz thrust produced on the molten metal is, this time, of almost constant intensity through the entire thickness of the cast slab, as shown by the associated vignette at the bottom of the figure.

The case of figure 3a is also known, although less common than that seen above: the magnetic poles opposite each side of the main plane of symmetry P of the slab 2 are again of reverse magnetic polarities, but the phase correspondence on the two inductors 1 and 3 opposite is random, so it is no longer respected. Despite appearances, the two magnetic fields slide in the same direction (see the comparative definition according to the invention above). The magnetic fluxes produced are of the "tangential" type and the Lorentz thrusts, which are then exerted in a sensitive manner only at the periphery of the cast slab 2, are opposed and therefore cooperate to achieve an overall axial rotary stirring of the molten metal. , as shown in the associated thumbnail at the bottom of the figure.

The figures which follow all relate to the invention.

The figures 4 and 5 relate to a brewing equipment that can be qualified as elementary in the sense that it comprises a single pair of linear inductors, while the following figures relate to a brewing equipment with four linear inductors, that we can qualify as standard or majority key because this configuration with two pairs of inductors is widely used.

The basic brewing equipment shown on the figure 4a thus comprises a pair of rectilinear linear three-phase inductors 1 and 3. The two inductors are placed parallel to each other, face to face and at a distance so as to define between them an air gap for the passage of a cast product 2 of rectangular XXL format , therefore a slab (or even a square bloom). In other words, the two inductors 1 and 3 are symmetrical to each other with respect to the main plane of symmetry P of the XXL cast product.

The wiring of this equipment to a three-phase power supply is not visible in the figure, but the equipment is presented in its functional electrical configuration ready to perform a stirring action from magnetic fields sliding in opposite directions (cf. . the two arrows v oriented from left to right in the figure). This configuration, of the "tangential magnetic flux" (or longitudinal) type, differs from those of the prior art. through flow shown on figure 3b , or even with longitudinal flow shown on the figure 3a , by the fact that, this time, the magnetic poles which face each other on the two paired inductors are constantly, not only connected to the same phase of the three-phase power supply, but kept at the same magnetic polarity S or N. In other words , a polarity reverser of the magnetic poles (which will be admitted to be integrated into the power supply not shown) was requested for each of the three phases on the inductor 3 with respect to the inductor 1 in its configuration of the figure 3b .

We recall here the locating convention, very convenient in practice, which arbitrarily consists in always applying, in three-phase as in two-phase, the phase U on the pole located at one of the ends on a sliding field inductor, rather than on a pole having two neighbors. Thus, for the pair of linear inductors exemplified on figure 4a , we see that the phase U is applied to the pole at the left end of each of the two inductors. It is thus easy to see that the field therefore slides from this end to the other end, therefore from left to right in the figure, while respecting the sequencing of the three phases of the power supply recalled clockwise on the circle. of three-phase phases of the figure 1a .

It is the same in the case of the figure 4b , where, after permutation of phases V and W, we see that, from the end pole U, the sequencing of the three phases being U, V *, W, U *, V, W *, on each inductor 1 and 3, their magnetic field therefore slides from -.-, right to left in the figure (anti-clockwise on the phase circle), each generating in the molten metal cast a tangential magnetic induction flux.

As can be seen on the associated thumbnails, whether in one direction of sliding of the magnetic fields or in the other, the action of such a stirring mode results in Lorentz thrusts on the molten metal located in edge of the slab and which propagate over the entire width thereof. This results in a setting in motion of the molten metal in these places according to two parallel active branches in the same direction 4 and 5, completed by a common median branch 6, which, for its part, is passive because it corresponds to the return metal flow. in an area where the Lorentz thrusts - are zero (or - almost zero). The whole results in the formation of two adjacent axial circulation loops in counter-rotation mutual 7 and 8, identical, well formed and stable and which concern the entire cross section of the XXL cast slab occupied by the molten metal.

A similar situation is found in the case of casting an XXL bloom of round format as shown on the figure 5 . In this figure, an XXL bloom 9 of round format being poured is surrounded by a stirring equipment 10 formed this time by two identical linear inductors 11 and 12, of arcuate shape in a semicircle which abut at their ends 15, each then being the symmetrical of the other with respect to the plane of symmetry P of the bloom 9 passing through the casting axis A. Their salient magnetic poles 13, 14 are turned inward to define a closed air gap 16 of size adjusted to the template of the round bloom 9. As can be seen, from their end pole U, the sequencing of the phases on each inductor 11, 12 is of the type U, W *, V, U *, W, V *, This expresses that the sliding magnetic field that they each produce progresses from one pole to the next in that order. In other words, the two magnetic fields, slide in opposite directions, that of the inductor 11 progressing in the clockwise direction shown by the arrow V11, that of the paired inductor 12 progressing in the anti-clockwise direction shown by the arrow V12 .

It is important to note, as the figure 5 , that the symmetry by the axial plane P is also respected for the magnetic polarity N or S of each pair of poles 13-14 located opposite one another each on separate inductors. It is under such a characteristic of electrical wiring of the paired inductors 11 and 12 that the production of a tangential magnetic flux is guaranteed on each inductor.

It is for this reason that the stirring action is then expressed by Lorentz thrusts on the molten metal located at the periphery of the XXL bloom 9. These thrusts develop identically in two active branches 17, 18 in semicircle each according to the sequencing of the phases on the poles of their respective inductor and which cooperate with each other to form a common median branch 19 of passive return of the metal flux in the plane P, where the Lorentz thrusts are zero.

The assembly results in the formation of two adjacent axial circulation loops in mutual counter-rotation 20 and 21 which are identical, well formed and stable, and the addition of which concerns the entire cross section occupied by the molten metal cast.

We will now consider the mixing mode in adjacent axial multi-loops according to the invention taken at a higher rank than that described hitherto, namely a mode implementing, no longer two, but four loops, or even more. Beforehand, it is advisable to refer to the figure 9 , because it allows first of all to specify the technological means of the invention.

This figure relates to an ingot mold for the continuous casting of XXL steel slabs, equipped with a submerged casting nozzle with four lateral outlet openings to ensure a sufficient inflow of molten metal compatible with the requirements imposed by the production of products cast in such imposing sizes.

As can be seen, the electromagnetic mixing equipment comprises a polyphase power supply 22 followed by a phase switch 23 which manages the sliding directions of the magnetic fields on each of the four linear inductors 24a, 24b, 25a, 25b connected in downstream. As shown in wiring lines 26 and 27, the four inductors are grouped into two pairs (24 and 25). Each pair of matched inductors 24a, 24b and 25a, 25b is connected to the phase switch 23 separately from the other, but they are both synchronously connected to the common polyphase supply 22.

Polyphase power supplies of this type are commercially available. They make it possible to transform the current, supplied by the electrical energy distribution network (50 or 60Hz), into a low-frequency current (say between 2 and 10hz) suitable for the electromagnetic mixing of molten metals. Here, moreover, the power supply 22 will incorporate current inverters to enable the N / S polarity of the magnetic poles generated by the coils of the inductors to be reversed.

The four linear inductors exemplified here are rectilinear in shape, because they are dedicated to the mixing of an XXL 2 slab. For this purpose, they are mounted, using suitable fasteners not shown, on the two large walls. 28 and 29 of a continuous casting mold 30 provided with an immersed nozzle 31 on the casting axis A. The assembly is carried out so that two paired inductors are placed symmetrically one opposite the other, of on either side of the vertical main plane of symmetry P of the slab 2 It follows that each large wall 28 and 29 of the mold is thus equipped with two unpaired aligned inductors (eg 24a and 25a on the wall 28) and arranged symmetrically to each other on either side of the secondary plane of symmetry Q of the slab, orthogonal on the main plane P and secant on the casting axis A.

Note that according to an alternative embodiment of the brewing equipment, the fixing members can be adapted to mounting the inductors, no longer at the level of the mold, but below, in the secondary cooling of the casting machine, without what has just been said to be changed.

To simplify, as we have already done for the miniature figures, we no longer show the physical position of the magnetic poles, but only, using arrows, the direction of sliding of the magnetic fields produced by the inductors. Remember that it is important that the magnetic poles of the same phase face each other on two inductors of the same pair and that they constantly have the same N or S polarity. It is on this condition that the magnetic induction fluxes , which act on the molten metal, will be tangential flows, thus respecting an essential functional characteristic of the brewing equipment of the invention.

Of course, as long as the inductors are not supplied with electric current, the natural configuration of the hydrodynamics of the molten metal remains prevalent, namely an unstable meniscus, weakly agitated with disparate and random wavelets, except in the vicinity of the gills of the metal. the nozzle 31 through which exit the jets of hot metal feeding the mold. It is different as soon as the invention is implemented. This is what we now see on this same figure 9 , considering the four inductors activated to each produce a sliding magnetic field.

In accordance with the invention, and with the convention adopted to define the directions of sliding of the magnetic fields between them, the fields slide in opposite directions on any two neighboring inductors. This is obviously the case with the two unpaired inductors 24a and 25a (or 24b and 25b) mounted on the same large wall 28 (respectively 29) of the mold 30, on either side of the secondary plane of symmetry Q This is also the case for the two neighboring inductors of the same pair (24a and 24b, or 25a and 25b) mounted symmetrically facing each other, on either side of the main plane of symmetry P.

The inductors of pair 24 reproduce the electromagnetic configuration of the paired inductors shown on the diagram. figure 4a . The magnetic fields produced both slide from left to right in the figure, ie in opposite directions on their respective inductors. It can be seen that the same is true for the two paired inductors forming the pair 25 and which, for their part, reproduce the configuration of the two paired inductors of the figure 4b . In this case, therefore, the magnetic fields slide opposite those of the first pair of inductors, i.e. from right to left on this figure 4b .

Thus, the magnetic fields slide in pairs in opposite directions with the two jets of "fresh" molten metal emerging from the nozzle 31 in the direction of the small faces 32 and 33 of the mold. The “tangential” induction flows, which thus progress over the half-widths of each large wall 28 and 29 of the ingot mold, significantly modify the configuration of the movements of the molten cast metal therein. In essence, the unstable natural agitation of the meniscus in the absence of mixing gives way to a configuration of circulatory movements in four adjacent loops 34, 35, 36 and 37, in axial rotation parallel to the casting axis A. These loops are organized side by side, in mutual counter-rotation, around the casting axis A to each occupy a quarter of the cross section of the cast product so that all the stirring movements occupy the best possible way. surface of the meniscus of the cast metal in its entirety, or almost all of it.

In fact, everything happens as if the two jets of the nozzle parallel to the large walls 28 and 29 of the mold are reinforced by a pushing action of the magnetic fluxes, while the other two jets, perpendicular to the plane of these large walls , they are thwarted, or even disappear almost completely, by a braking action of these magnetic fluxes. It is understood that if the sliding directions of the four magnetic fields are reversed, the hydrodynamic figure of the mixing in four adjacent circulatory loops 34 to 37 is preserved. Simply, the direction of axial rotation of each loop would be reversed so that, this time, it is the jets of the nozzle directed towards the small walls 32 and 33 of the mold which will be thwarted, and the two others directed towards the large walls. 28 and 29 which will be reinforced.

We will now be able to continue the description of the invention by approaching the figure 6 which show in detail the configurations electromagnetic elements of the four polyphase linear inductors with sliding magnetic field for XXL slabs of the figure 9 , assumption made that it is still a question here of three-phase inductors.

We find on the figure 6a the four identical rectilinear linear inductors grouped together in two electrically synchronous pairs. A first pair is formed by the two paired inductors 24a and 24b mounted one opposite the other, on either side of the main plane of symmetry P of the slab 2, over a half width thereof ( the left in the figure). The second pair is formed by the pair of matched inductors 25a and 25b mounted in a similar fashion to those of the previous pair, but on the other half width of the slab (the straight part in the figure). Thus, each large face of the slab 2 is provided with two aligned inductors, but not paired, namely the two inductors 24a, 25a for one of the large faces and the two inductors 24b, 25b for the other. It is recalled that these pairs of unpaired aligned inductors are therefore symmetrical to each other with respect to the secondary plane of symmetry Q of the slab, intersecting at right angles with the main plane P on the casting axis A .

As can be seen, the four adjacent oblong axial circulation loops 34, 35, 36 and 37, stirring the molten metal of the slab 2, are distributed evenly around the casting axis A (and in the cited order) in mutual counter-rotation between two neighboring loops and each time defining between them a common passive return branch of the molten metal.

These four stable and well-formed circulatory loops are achieved using the tangential flow electromagnetic configuration shown on figure 6a and according to which the magnetic fields on two neighboring inductors, aligned 24a and 25a, or paired 24a and 24b, slide in opposite directions. In this case, the magnetic fields on two aligned inductors slide by "approaching" one another (we will say, that they converge), so that the large passive branches of the metal return from the oblong loops of the stirring transport this molten metal from the A axis towards the small laces, of the slab, while the small branches bring back the metal from the large faces towards the casting axis.

• sur l'inducteur 24a, la séquence des phases soit la suivante: U, W*, V, U*, W, V* depuis le pôle de phase U 38 (choisi par convention à l'extrémité de l'inducteur,) situé ici au bord de brame afin que le champ magnétique produit glisse depuis ce bord vers le centre de face;
• sur son inducteur apparié 24b, la séquence des phases soit également U, W*, V, U*, W. V* depuis le pôle d'extrémité de phase U 39 choisi en position terminale au même bord de brame afin que le champ magnétique produit glisse depuis ce bord vers le centre de face, donc en sens opposé à celui de l'inducteur voisin apparié 24a;
• sur l'inducteur 25a, aligné avec l'inducteur 24a sur la même grande face de la brame, mais non apparié à lui, la séquence des phases soit également la suivante: U, W*, V, U*, W, V* depuis le pôle d'extrémité de phase U 40 choisi lui aussi en position terminale en bord de brame, mais à l'autre l'extrémité de celle afin que le champ magnétique produit glisse depuis ce bord vers le centre de face, donc dans un sens opposé à celui de son voisin 24a;
• et sur son inducteur apparié 25b, la séquence des phases soit là encore U, W*, V, U*, W, V* depuis le pôle d'extrémité de phase U 41 choisi en position terminale en même bord de brame afin que le champ magnétique mobile glisse depuis ce bord vers le centre de face, donc en sens opposé à celui de l'inducteur voisin apparié 25a;

This electromagnetic configuration is obtained by wiring: from the inductors to their three-phase power supply so that

• on inductor 24a, the phase sequence is as follows: U, W *, V, U *, W, V * from the phase pole U 38 (chosen by convention at the end of the inductor,) located here at the edge of the slab so that the magnetic field produced slides from this edge towards the face center;
• on its matched inductor 24b, the phase sequence is also U, W *, V, U *, W. V * from the phase end pole U 39 chosen in the terminal position at the same edge of the slab so that the magnetic field product slides from this edge towards the center of the face, therefore in the opposite direction to that of the neighboring paired inductor 24a;
• on inductor 25a, aligned with inductor 24a on the same large face of the slab, but not matched to it, the phase sequence is also as follows: U, W *, V, U *, W, V * from the phase end pole U 40 also chosen in the terminal position at the edge of the slab, but at the other end of that so that the magnetic field produced slides from this edge towards the face center, therefore in a direction opposite to that of its neighbor 24a;
• and on its matched inductor 25b, the phase sequence is again U, W *, V, U *, W, V * from the phase end pole U 41 chosen in the terminal position on the same edge of the slab so that the mobile magnetic field slides from this edge towards the center of the face, therefore in the opposite direction to that of the neighboring paired inductor 25a;

The figure 6b illustrates a situation quite similar in substance to that of the figure 6a . Simply, the phase switch 23 has been activated to swap phases V and W on each of the four inductors, all other things being equal. As a result, the magnetic fields on two aligned inductors slide this time "away" from each other (we will say that they diverge), leaving the direction of axial rotation of each of the four loops of metal flow is reversed with respect to the electromagnetic configuration of the brewing equipment of the figure 6a previous.

Whatever electromagnetic configuration is chosen, it is important, as shown by the two figures 6 , that, not only do the magnetic fields slide in opposite directions on any two neighboring inductors (for example on the opposite paired inductors 24a, 24b, and on the unpaired aligned inductors 24a, 25a), but that in addition, in order to to work in longitudinal magnetic induction flux, the magnetic poles at the same phase facing on two neighboring inductors, paired or not, have the same N or S polarity.

This characteristic relating to the magnetic polarity of the poles appears immediately at the sight on the figures 6 as regards the paired inductors, for example 24a and 24b. It is less immediate with regard to unpaired inducers, for example 24a and 25a. This is due to the fact that these rectilinear inductors are aligned, the example considered relating to the casting of a slab, therefore to a cast product of rectangular cross section. But it will also appear on the figures 7 and 8 following, which relate to the casting of long XXL products, the four linear sliding field inductors, constituting the equipment according to the invention, show an air gap, this time closed, which entirely envelops the product cast on its periphery.

The figure 7 shows a circular-shaped brewing equipment mounted around an XXL round bloom 71 in the secondary cooling stage of a continuous casting machine. It is composed of four identical three-phase bipolar linear inductors 72a, 72b, 73a, 73b of arcuate shape in a quarter of a circle, assembled contiguously one after the other, each covering an angular sector of 90 ° of the cast product.

The pairs of inductors 72a, 72b and 73a, 73b, arranged symmetrically with respect to the principal plane of symmetry P of the bloom, each form a pair. The two pairs (72 and 73) are symmetrical with respect to the secondary plane of symmetry Q, which in this case, due to the high order of symmetry of the cast XXL bloom, is equivalent to the plane P.

For clarity, the magnetic poles are not shown. But, the arched arrows on each inductor show the direction of slip of the magnetic fields produced by each of them. As we can see, the fields slide in opposite directions on any two neighboring inductors. If necessary, the reader will be able to reconstruct the sequencing of the electrical phases on each inductor for this purpose, using the phase circle. He will take care, however, to keep the same magnetic polarity on the poles connected to the same phase and placed opposite each other on two paired inductors, thus guaranteeing opposite sliding directions of the two magnetic fields. It will also take care that the pairs of poles at the same phase closest to two unpaired inductors (therefore between inductors 72a and 73b on the one hand, and between the inductors 72b and 73a on the other hand) are of the same magnetic polarity. It is this second characteristic which guarantees an electromagnetic configuration with tangential flow for sliding magnetic fields.

By such an electromagnetic configuration of the equipment of the invention, a mixing configuration of the molten metal is then created in the form of four adjacent loops 74, 75, 76, 77 in axial rotation, stable and regularly distributed over the surrounded by the axis, of casting A, in mutual counter-rotation between two neighbors and occupying at best the entire cross section of the XXL cast product.

A completely equivalent situation is found in the case of the casting of a square XXL bloom, as can be seen on the figure 8 . In this case, the linear inductors 82a, 82b, 83a and 83b, of rectilinear shape, are mounted around the square bloom 81 at the rate of one inductor per side. The pairs of paired inductors (82a, 82b, and 83a, 83b) are symmetrical with respect to any diagonal plane P, of symmetry of the cast product. The two pairs of inductors 82, 83 are they symmetrical to each other with respect to the other diagonal plane of symmetry Q. On any two neighboring inductors, the magnetic fields slide in opposite directions. The stirring loops which are then formed, 84, 85, 86 and 87, are there of generally triangular shape, stable and well formed, regularly distributed around the Taxe this flow A, in mutual counter rotation and occupying at best the entire cross section of the XXL cast product.

1. 1) des sens de glissement opposés des champs magnétiques sur inducteurs voisins;
2. 2) une même polarité N ou S des pôles, mis sous une même phase électrique et placés symétriquement sur deux inducteurs appariés en regard l'un de l'autre par rapport au plan principal de symétrie du produit coulé impliquant un flux magnétique tangentiel, c'est-à-dire une force de Lorentz élevée à la périphérie du produit coulé et nulle au centre, et
3. 3) des dimensions XXL du produit coulé, qui fait que le métal en fusion est entraîné pour former un ensemble de boucles de circulation adjacentes multiples, en rotation axiale en sens opposé deux à deux dans un plan perpendiculaire à Taxe de coule (à savoir dans une section droite du produit coulé).

Having reached the end of the description, it may be useful to underline again all the essential characteristics of the invention, namely:

1. 1) opposite sliding directions of the magnetic fields on neighboring inductors;
2. 2) the same N or S polarity of the poles, placed under the same electrical phase and placed symmetrically on two inductors paired opposite each other with respect to the main plane of symmetry of the cast product involving a tangential magnetic flux, c 'i.e. a Lorentz force high at the periphery of the cast product and zero at the center, and
3. 3) XXL dimensions of the cast product, which causes the molten metal to be driven to form a set of multiple adjacent circulation loops, axially rotated in opposite directions two by two in a plane perpendicular to the axis flow (i.e. in a straight section of the poured product).

The main reason why the present invention consists in generating multiple loops of axial circulation of the molten metal in a plane perpendicular to the casting axis, is the homogenization of the temperature in this plane. In fact, unlike traditional sized cast formats, the long distances specific to the sections of XXL formats cause considerable temperature differences within the molten metal, both radially and in the tangential direction of the cast product. This is true for the liquid metal within the mold and at the meniscus, as it is for the metal below, under the mold, in the secondary cooling of the casting machine.

But, there is another reason which militates in favor of a mixing in multiple adjacent axial rotational loops, namely the stabilization of the convection movements of the molten metal at the level of the ingot mold meniscus. Indeed, these large XXL formats are usually cast in an ingot mold with an immersed nozzle with four outlet openings oriented, not downwards as for traditional formats, but horizontally, or even upwards, to bring more enthalpy to the meniscus. . The four jets of liquid metal entering the mold could ideally create a natural flow in eight recirculating loops at the meniscus. However, in reality, the flow of liquid metal is never symmetrical, nor stable. The loops in a way compete with each other, overlap, cancel each other out, are reversed and create fluctuations at the meniscus, which contribute to deteriorating the good lubrication at this location on the wall of the mold, and to drag towards the low in the molten metal the powder of cover which covers it in ingot mold.

The use of two pairs of inductors as illustrated above, for the casting of an XXL format, whether of rectangular, square or round section, will transform the naturally unstable movement into four controlled and stable loops.

• soit augmenter ("aspirer") le débit des jets de la busette qui se dirigent vers les petites faces de la lingotière et donc freiner les jets qui se dirigent vers les grandes faces,
• soit augmenter le débit vers les grandes faces et freiner le débit vers les petites faces.

In addition, in casting XXL slabs depending on the choice of the direction of the sliding of the magnetic fields, we can:

• either increase ("suck") the flow rate of the jets of the nozzle which move towards the small faces of the mold and therefore slow down the jets which move towards the large faces,
• either increase the flow towards the large faces and slow down the flow towards the small faces.

This possibility offered by the implementation of the invention of being able to somehow "regulate" the flow of "fresh" metal entering the mold, and therefore the speed of the jets of the nozzle, is still applicable, of course, with a equipment with three pairs of inductors. When it is for example the casting of a round XXL bloom, six axial recirculation loops are then generated in an ingot mold provided with a submerged nozzle with six outlet openings offset by 60 ° when these six openings are located in the principal plane of symmetry P and the two secondary planes of symmetry Q.

It goes without saying that the invention cannot be limited to the examples described, but that it extends to multiples or equivalents in so far as its definition given by the appended claims is respected.

In particular, the power supply to the inductors can be chosen as two-phase, instead of three-phase. It is easy to realize then, simply by constructing the circle of phases only for the U and V phases shifted at 90 °, that swapping these two phases between them, or inverting the magnetic polarities on two poles of the same phase, produces an inversion. of the direction of displacement of the magnetic field in an equivalent manner. Adding these two operations, whatever the order, would therefore allow the need to keep the direction of displacement of the magnetic field, while assigning a given phase to the pole of its choice on the inductor.

Likewise again, it may be advantageous to produce the mixing equipment of the invention with a magnetic core common to several inductors.

Claims (3)

1. A method for the rotary electromagnetic stirring of molten metal during the casting of XXL-format metallic products of round, square or rectangular cross-section, wherein a stirring equipment (10) comprising sliding magnetic field linear polyphase inductors (1, 3, 11, 12, 24a, 24b, 25a, 25b), and the molten metal is stirred in the form of a plurality of adjacent axial rotary circulation loops (34, 35, 36, 37), distributed around the casting axis (A) and occupying at the best the entire cross-section of the cast product, a process characterized in that the said stirring is carried out by arranging the said sliding linear polyphase magnetic field inductors (1, 3, 11, 12, 24a, 24b, 25a), 25b) around the casting axis (A) to form an air gap (16), in that the sliding magnetic fields in this air gap (16) are adjusted so icthat they slide in opposite directions on any two adjacent inductors (24a, 24b ; 25a, 25b), and in that the pairs of poles connected to the same electrical phase and located opposite each other on two separate paired inductors (24a, 24b; 25a, 25b) are set to the same magnetic polarity.
2. Equipment for the electromagnetic stirring of XXL-format metallic products, of round, square or rectangular cross-section, equipment for carrying out the process according to claim 1 and comprising at least one pair of sliding magnetic field linear inductors (1, 3, 11, 12, 24a, 24b, 25a, 25b), mounted symmetrically opposite each other, with respect to a plane of symmetry (P) of the cast product, on the circumference of the casting axis (A) so as to define an air gap (16) through which the cast product passes, at least one polyphase power supply (22) provided with electrical connection means (26, 27) with said inductors (1, 3, 11, 12, 24a, 24b, 25a, 25b), and means for adjusting the sliding direction of the magnetic fields on each inductor, equipment characterized in that said connection means (26, 27) impose the same polarity to each pair of magnetic poles belonging to the same phase and placed symmetrically with respect to said plane (P) facing each other on two paired inductors (24a, 24b ; 25a, 25b).
3. Electromagnetic stirring equipment according to claim 2, comprising at least two pairs of sliding magnetic field linear inductors (24a, 24b; 25a, 25b), forming an assembly of at least four inductors arranged on the periphery of the casting axis (A) so as to define an air gap (16) through which the cast product passes, equipment characterized in that said means for adjusting the direction of sliding of the magnetic fields are configured so that the magnetic fields of any two neighbouring inductors (24a, 24b; 25a, 25b) slide in opposite directions.

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