EP1039979B1 - Electromagnetic braking device for a smelting metal in a continuous casting installation - Google Patents

Abstract

Both an apparatus and method are provided for electromagnetically braking a flow of molten metal during a continuous casting operation. The apparatus includes an electric electromagnetic inductor of the traveling-magnetic-field polyphase stator-type connected to a source of electrical power. The inductor is mounted on a casting plant opposite one face of the product being cast, and has two or three phase windings. The electrical power supply of the apparatus includes two or three elementary DC sources, each of which can be adjusted in terms of current intensity independent of one another. Each of the elementary electrical DC sources is connected to one, and only one of the phase windings of the inductor. The arrangement of the apparatus allows a flow of molten, ferromagnetic metal such as steel to be adjustably braked by merely adjusting the parameters of the source of electrical supply.

Description

The present invention relates to the continuous casting of metals, in particular steel. It relates more particularly to the techniques consisting, using a field magnetic, to influence the circulation of the molten metal upon its arrival in the continuous casting ingot mold.

We know that the incoming jet of molten metal into the ingot mold creates within this a hydrodynamic disturbance often at the origin of defects observed then on the rolled cast product. On the one hand, the jet carries with it deep into the heart product liquid being poured from non-metallic inclusions which then have trouble to be eliminated by natural decantation on the meniscus (free surface of the molten metal in the mold). This general phenomenon is even more marked on the casting machines of "curved" or "semi-curved" type, as is the case for casting large products section, in particular the slabs, in which the solidification front of the lower surface of the poured product then forms an obstacle to the rise of inclusions which accumulate at this place. On the other hand, the recirculations of liquid metal induced by the jet within the ingot mold translate among other things into a backwash which agitates the meniscus of randomly, all the more vigorously moreover when one sinks at high speed (i.e. above 1.5 m / min approximately to fix ideas). Such surface instabilities are responsible for irregularities in the solidification of the first skin of the cast product according to the around the mold that we know to be the cause of annoying or even unacceptable faults on the final product (blistering, exfoliation, etc.).

Faced with the problem posed by this hydrodynamic perturbation due to the jet, the steelmaker today has two response channels, each using the available tools magnetohydrodynamics suitable for the continuous casting of metals. One, rather "curative" aims to reduce the effects on the metallurgical quality of the product obtained: electromagnetic convection (or mixing). The other, of a preventive nature, works to counter this disturbance: electromagnetic braking.

Electromagnetic convection involves washing the forehead solidification by a forced current of molten liquid metal, from bottom to top for example, which takes with it, towards the meniscus, non-metallic inclusions which otherwise would be trapped by this front. This current of liquid metal is created by a magnetic field sliding, generally produced by a multi-winding inductor such as a motor stator linear polyphase (bi or three-phase) arranged parallel and opposite a large face of the slab in an ingot mold (BF 2 358 222 and BF 2 358 223). An inductor of this type is conventionally made up of electrical windings whose conductors feel conformed regularly spaced parallel bars, or in coils of wire, housed in teeth of a magnetic yoke and mounted in pairs in series-opposition. Each winding is connected to a different phase of a polyphase power supply, namely, three-phase or two-phase, according to a connection order ensuring the desired sliding of the magnetic field along the inductor in a direction perpendicular to the conductors. This type of multi-winding inductor, capable of producing a magnetic field sliding by coupling with a polyphase supply, is widely described in the electrotechnical literature.

The technique of "electromagnetic braking", in which the present invention, on the other hand, consists of acting directly on the or the metal arrival jets in mold. The aim is thus to limit the depth of penetration, as well as to attenuate the recirculation movements induced by the liquid metal and therefore to tend towards obtaining a meniscus without agitation, as calm and flat as possible. The functioning of such brake follows the well-known principle of eddy brake: when a liquid metal in movement (more generally an electrically conductive fluid) passes through a field static magnetic, it undergoes a contrarian force from it, the intensity of which depends on the field strength and the speed of the metal.

We know an electromagnetic brake for continuous casting mold for slabs consisting essentially of two electromagnets with salient poles facing each other and other large walls of the mold and of opposite polarity so as to create between the poles of the crossing magnetic lines of force. The electromagnets are positioned in the upper part of the mold in order to intercept the metal jet as soon as it arrives in the mold. It should be noted that, strictly speaking, the liquid steel arriving in ingot mold and subject to such a field is not really slowed down, but rather redirected and distributed in the volume available nearby. Indeed, overall the metal flow flow, therefore the speed of flow of the product, are fortunately not changed by the brake. This in fact acts as a flow distributor giving greater homogeneity of the flow velocity map at the top of the mold. The term "braking" electromagnetic is therefore strictly unfit, but it will continue to be used in the suite for convenience to comply with common usage. A brake of this type is described for example in document EP-A-0 040 383, recommending the use of four electromagnets paired in pairs in pairs arranged opposite each other on the large faces of an ingot mold for continuous casting of slabs, a pair being placed on each side a pouring nozzle having two lateral outlets for the outlet of the supply jets directed towards the small faces of the mold.

PCT document WO 92/12814 proposes to reinforce the braking effect by replacing the two electromagnets on each large face with a magnetic bar making the whole width of the mold and to locate in height this bar at the level of the lateral outlet vents of the pouring nozzle in order to perform a braking action permanent throughout the propagation of the jet coming from each nozzle of the nozzle in direction of the small faces.

More recently, the PCT document WO 96/26029 teaches to have, not one, but two magnetic bars per side, located at high levels different, one below the other on either side of the nozzle outlet openings so as to form a magnetic confinement of the jet area to isolate it hydrodynamically from the rest of the volume of liquid metal present in the mold. However, as is known, the conditions for the flow of liquid metal in the ingot mold can vary markedly from one casting to another, even during the same casting, depending on various parameters, such as casting speed, immersion depth of the nozzle, the shape of its gills giving the direction of the jet, the width of the mold, if this is of the variable width type, etc ... Therefore, if we want to optimize the areas of action of the magnetic field in an ingot mold according to these parameters, this cannot be done without moving the inductor along the large faces of the mold, which is impracticable in practice.

The object of the invention is to provide steelmakers with a means for easily modifying and without delay the areas of action of an electromagnetic brake in the casting mold continues so that they can constantly adjust their location to the conditions precise details of the casting to come, or of the casting in progress, simply by adjusting the power supply parameters, therefore without requiring any intervention on the machine casting and in particular without having to modify the position of the inductor.

To this end, the invention relates to electromagnetic braking equipment of a molten metal within a continuously cast product, in particular a slab, comprising an electrical supply and, connected to said supply, at least one electromagnetic inductor of the “polyphase stator with sliding magnetic field” type intended to be mounted on the casting installation opposite one side of the product being casting, said inductor having two or three phase windings, characterized equipment in that said electrical supply consists of two, respectively three, elementary direct current power supplies adjustable in current intensity each independently of the others, and in that each of said electrical supplies elementary is connected to one and only one of said phase windings of the inductor.

As will no doubt have been understood, the invention consists in associating an inducer of type "linear motor stator with sliding magnetic field" -whose design and structure are widely known for a long time and which we also know well the use in continuous casting of slabs as a means of setting the molten metal in motion depending on the height of the mold (see for example GB 1507444 and 1542316) with a battery individual direct current power supplies, independently adjustable from one others and each coupled with a winding of the inductor and it alone to create a static magnetic field which is adjustable in location (and of course also in intensity) depending on the height or width of the large faces of the mold (more generally elsewhere on any chosen place of metallurgical height, but where the cast product still contains a fair amount of non-solidified liquid metal) by selectively activating the windings of the inductor by simply adjusting the operating parameters of these elementary power supplies, namely in fact the intensity of the electric currents they deliver. These settings can be made instantly, during casting itself even if desired, away from the casting machine, in any case safety for operators, and in a completely transparent manner, that is to say without risk disruption, even minimal, of the smooth running of the casting operation.

Thus, the subject of the invention is also a method of electromagnetic braking of a liquid metal within a continuously cast product, according to which a permanent magnetic field acting on the liquid metal is used to slow its flow, said field being created by multi-winding electromagnetic inductor braking equipment of the “polyphase stator with sliding magnetic field” type coupled to elementary direct current electrical supplies individually adjustable in accordance with the equipment defined above, characterized in that, with the aim of regulating, as a function of the casting conditions, the position of the magnetic pole (s) of said inductor without displacement of the latter, adjustment is made of the intensities I _i of the electric currents flowing through the windings of the inductor using a variable factor ϕ between 0 and π radians so that, at each instant, I ₁ = K cos ϕ and I ₂ = K s in ϕ in the case of an inductor with two windings, and I ₁ = K sin ϕ, I ₂ = K sin (ϕ + 2π / 3) and I ₃ = K sin (ϕ + 4π / 3) in the event of a inductor with three windings, K being a constant representative of the desired braking force at the location of the magnetic pole (s) of the inductor, and whose maximum value is limited by the maximum intensity of the electric current delivered by each supply elementary electric.

• la figure 1 représente schématiquement un inducteur électromagnétique biphasé de type connu pour brasser le métal coulé dans une lingotière de coulée continu et dont des éléments vont se retrouver dans l'équipement de freinage selon l'invention;
• la figure 2 représente schématiquement un équipement de freinage électromagnétique selon l'invention dans une forme de réalisation bi-enroulements analogue à celle de l'inducteur de brassage bi-phasé connu de la figure 1;
• la figure 3 représente un inducteur de l'équipement de freinage selon l'invention conforme à la figure 2 tel qu'il apparaít quand il est monté dans le corps d'une lingotière de coulée continue de brames d'acier selon un premier mode de réalisation à réglage en hauteur de l'action de freinage;
• la figure 4 représente une variante de l'installation de la figure 3, selon laquelle la structure de l'inducteur de freinage est partitionnée selon la largeur de la lingotière;
• les figures 5a et 5b illustrent chacune un mode de mise en oeuvre de l'équipement de freinage conforme à l'invention dans une forme différente de réalisation de l'inducteur;
• la figure 6 est une vue schématique, en coupe verticale transversale passant par l'axe de coulée X de la figure 3, de l'équipement selon la figure 3 illustrant un mode de réglage de cet équipement;
• la figure 7 est une vue analogue à la figure 6 mais illustrant un autre mode de réglage de l'équipement de freinage selon l'invention;
• la figure 8, à rapprocher de la figure 3, représente un équipement de freinage selon l'invention monté sur une lingotière de coulée continue de brames d'acier selon un second mode de réalisation à réglage de l'action de freinage sur la largeur de la lingotière;
• la figure 9 illustre, vu schématiquement de dessus et en coupe selon le plan A-A de la figure 8, un mode de réglage de l'équipement de freinage montré sur la figure 8;
• la figure 10 illustre, selon les mêmes dispositions que la figure 9, un autre mode de réglage de cet équipement;
• la figure 11 représente schématiquement une variante de réalisation d'une alimentation électrique de l'invention;
• la figure 12, à rapprocher des figures 8 et 4, représente un équipement de freinage selon l'invention monté sur une lingotière de coulée continue de brames d'acier selon un troisième mode de réalisation à réglage d'une action conjuguée de freinage sur la largeur et sur la hauteur de la lingotière.

The invention will be well understood, and other aspects and advantages will appear more clearly in the light of the description which follows, given solely by way of nonlimiting example of embodiment with reference to the sheets of attached drawings in which:

• FIG. 1 schematically represents a two-phase electromagnetic inductor of a type known for stirring the metal cast in a continuous casting mold and elements of which will be found in the braking equipment according to the invention;
• FIG. 2 schematically represents an electromagnetic braking device according to the invention in an embodiment with two windings similar to that of the two-phase mixing inductor known from FIG. 1;
• 3 shows an inductor of the braking equipment according to the invention according to Figure 2 as it appears when it is mounted in the body of a mold for continuous casting of steel slabs according to a first mode of realization with height adjustment of the braking action;
• FIG. 4 represents a variant of the installation of FIG. 3, according to which the structure of the braking inductor is partitioned along the width of the mold;
• Figures 5a and 5b each illustrate an embodiment of the braking equipment according to the invention in a different embodiment of the inductor;
• Figure 6 is a schematic view, in vertical cross section through the casting axis X of Figure 3, of the equipment according to Figure 3 illustrating a mode of adjustment of this equipment;
• Figure 7 is a view similar to Figure 6 but illustrating another mode of adjustment of the braking equipment according to the invention;
• FIG. 8, to be compared with FIG. 3, represents a braking equipment according to the invention mounted on a mold for continuous casting of steel slabs according to a second embodiment with adjustment of the braking action over the width of the ingot mold;
• FIG. 9 illustrates, seen schematically from above and in section along the plane AA of FIG. 8, a mode of adjustment of the braking equipment shown in FIG. 8;
• Figure 10 illustrates, according to the same arrangements as Figure 9, another mode of adjustment of this equipment;
• FIG. 11 schematically represents an alternative embodiment of a power supply of the invention;
• FIG. 12, to be compared with FIGS. 8 and 4, shows a braking equipment according to the invention mounted on a mold for continuous casting of steel slabs according to a third embodiment with adjustment of a combined braking action on the width and height of the mold.

In these figures, the same elements are designated with identical references.

The stirring inductor 1 shown in Figure 1 has functions and effects on the liquid metal flows completely different from those of the brake device invention, but it serves as a sort of framework for the constitution of the latter. he therefore presents with him close analogies of constitution. Also, a few reminders concerning and concerning its mode of operation will facilitate the understanding of the invention.

The main active part of this sliding field static inductor consists by electrical conductors, here rectilinear copper bars 2, 3, 4 and 5, housed in regularly spaced parallel notches (or teeth) in a cylinder head magnetic 6. These bars are thus arranged parallel to each other, being spaced apart regularly from each other by a distance which makes it possible to define the polar pitch of the inductor.

In the example considered, the inductor is of the two-phase stator type. It involves effect four conductive bars electrically mounted two by two, in pairs in series-opposition, that is to say connected by their ends located on the same side of the inductor (at right in the figure) so that the electric current flows there in opposite directions. Each pair of bars, 2-4 or 3-5, forms a winding whose free ends (at left in the figure) are connected, in the order shown in the figure, to the terminals of a two-phase power supply 7, the two phases of which are conventionally identified by the letters U, V, and the neutral by the letter N. These free ends are designated by the same letters, U or V, than those of the phase which feeds them, distinguishing the arrival ends, return ends of the current whose letter is surmounted by a horizontal line, according to usage. These windings, as we can see, are here of the "nested" type, because the coupled bars forming a winding are not neighboring bars, but separated by a bar from the other winding. Thus, bar 2 is connected to bar 4 to form winding A, and bar 3 is connected to bar 5 to form the other winding B. Similar provisions are found in the case of a stator type inductor three-phase, the interweaving of the three windings being obtained then, as we know, by a jump of separation between coupled bars, not of one, but of two bars belonging each to one of the other two windings.

When the inductor 1 is supplied by an alternating current supply, the electrical installation diagram of which is that shown in FIG. 1, the electric current flowing through the bars 2, 3, 4, 5 produces a magnetic field perpendicular to the plane of the figure and sliding from one bar to the next in the direction perpendicular to the orientation of the bars (represented by the arrow V _B in the figure), namely from top to bottom, and this, at speed (iela frequency of the current ) with which the intensity of the supply current reaches its maximum successively from bar 2 to bar 5. The small "cartridge" diagram on the left of the figure shows, using the trigonometric circle, the 'dynamic organization of the two phases which will make it easier to understand what has just been said if we go through this circle clockwise. A stirring inductor of this kind can easily find its place within an ingot mold for continuous casting of slabs for example, and numerous documents, in particular in the form of patent applications, describe such a use.

The invention, the description of which will now follow, agrees perfectly with what has just been said in terms of inductor structure, coupling of the conductors for forming windings or inductor integration on a casting machine keep on going.

To make the electromagnetic braking equipment according to the invention, as shown in Figure 2, the inductive device of Figure 1 must be modified from so that it produces, no longer a moving magnetic field, but a stationary field permanent located in a chosen location of the inductor, but changeable at will. This static field will therefore be produced from a DC power supply. he is therefore analogous to that produced by known electromagnetic braking devices in a continuous casting mold, but its working range can be adjusted in position on the mold height (or width, depending on the mounting method adopted) without no intervention on the casting installation.

As seen in Figure 2, this modification consists in replacing the two-phase supply 7 by two direct current supplies 8 and 9, individual and independent of each other, their only common point being their neutral N, set common for convenience. These power supplies are each provided with means of adjustment of the intensity of the currents they deliver. These adjustment means, known by themselves and quite usual in this area, so have been simply illustrated by the respective elements 10 and 11 in the figures. The inductor 1 has not undergone any modification; the connections between conductors defining the windings A and B remain unchanged.

The equipment according to the invention is in working order as soon as each of the windings A and B of inductor 1 is connected to one of its two power supplies elementary and alone. In the example illustrated in FIG. 2, the winding A is connected to supply 8, and winding B is connected to supply 9.

Applied to a continuous casting mold, such equipment then produces the effect of braking sought to reduce the penetration depth of the jet and its effects undesirable on the internal quality of the cast product obtained after complete solidification. We note also that the braking equipment of the invention is in fact applicable also under the mold, therefore usable, more generally, on a product of continuous casting, for example a steel slab, the interior of which is still in good condition liquid.

At this stage of the presentation, reference should be made to Figure 3 showing precisely the installation of the inductor of the braking equipment according to the invention on a large face of a mold 12 for continuous casting of steel slabs 13. Of course, the two large opposite faces of the mold can be equipped with two inductors identical arranged opposite one another on either side of the cast product and extending each over substantially the entire width of the mold. The rest of the presentation will show that, depending on the choice of polarities on one of the inductors compared to the other in vis-à-vis, we can promote the braking effect through the entire thickness of the product sunk (configuration of field called "crossing"), or locate it near the skin only (so-called “longitudinal” field configuration).

An ingot mold for continuous casting of slabs is essentially constituted, as we know, by an assembly of four vertical plates, in copper or copper alloy, two large plates 14 and 15, called "large faces", supplemented by two plates in end 16 and 17 closing the ends, called "small faces". These plates define between they a bottomless pouring space for molten metal 18 coming in from above using a nozzle 19 mounted in the bottom of a distributor 20 placed above. energetically cooled externally by vigorous circulation of water to ensure the heat extraction necessary for the formation of a skin of solidified metal in contact with them thick enough to allow the extraction of the product poured into good operating conditions. The molten metal is poured into the mold by the nozzle 19, of which the lower end, provided with lateral outlet openings 21, 21 ', plunges into the mass of molten steel during casting already present in the mold. These outlet gills side each deliver a jet of molten metal 27 and 27 'directed towards the small faces of the ingot mold, and in the vicinity of which there is a separation between a main flow descendant 28, responsible for the in-depth training of non-metallic inclusions, and a rising flow 28 'coming to agitate the meniscus 22. It is on these jets 27 and 27' that go act the braking means according to the invention.

In the example illustrated by FIG. 3, the inductor 1 previously described is mounted opposite a large face 14 of the mold with an orientation such that the bars conductive 2 to 5 are horizontal, the pouring axis X being vertical. In these conditions, if we also refer again to Figure 2 to consider only for the moment the supply 8, the direct current which it delivers in the winding A (its intensity being adjusted by its adjustment means 10) forms a current loop located in the upper half of inductor 1 (therefore of the mold) and in which the current electric crosses the busbar 2 from left to right, then the bar 4 from right to left. A field is thus created in the area defined by the area of this current loop magnetic Bu stationary, directed perpendicular to the plane of the winding, which the occurrence is also that of the figure. We understand that is thus formed in the part high of the mold, and along its entire width, a magnetic field stationary Bu perpendicular to the direction of flow X and perpendicular to the plane of distribution of the propagation speeds of the metal jets 27, 27 ′ and the intensity of which maximum is at the center of winding A, i.e. at the height of the passive bar 3 of winding B. If, we now consider in the same way only power supply 9 and winding B which it supplies with current, a field is obtained magnetic Bv identical to the previous field Bu, but the maximum of which is located this times at the level of passive bar 4 of winding A.

If both power supplies flow at the same time in their respective windings, the Bu and Bv fields are present simultaneously and the existence an overlap zone between bars 2 and 3 due to the fact that here the windings A and B are nested, so these fields add up in this region. The maximum magnetic induction, therefore maximum braking effect, is then obtained at the heart of this central zone if the supply currents are of the same intensity. However, this maximum will be reached at the center of winding A if individual supply 9 is left inactive (see fig.5a), or in the center of winding B if the individual power supply 8 is left inactive (see fig.5b), or in an infinite number of possible locations between these two extreme positions, simply by adjusting, using the adjustment means 10 and 11, a voluntary imbalance of the currents between the two power supplies 8 and 9 then active jointly (fig. 2). We agree here, for the sake of simplicity, to call "pole magnetic "location of the space (in this case, one of the large faces of the ingot mold a braking inductor) where the magnetic braking field is maximum.

Thus, this inductor 1 is able to play a brake role acting on the flows of molten metal entering the ingot mold, like known devices electromagnetic braking. But now we have the decisive advantage of ability to adjust the location of the pole at any time over the height of the mold magnetic brake field, without having to move any part of the inductor, simply by acting on the adjustment of the power supplies.

As already said, a precise location of the magnetic pole of the braking field at the top of the mold can indeed be optimal under certain conditions and be less suitable than another if, from one pour to the next or to the even during casting, we change casting parameters, such as the depth immersion of the nozzle 19, the level of the meniscus 22 in the mold, the speed of casting, etc ... We are then led to want to modify the position of this pole on the height of the ingot mold. As we have just seen, thanks to the device of the invention, this becomes very easy since it suffices to act on the adjustment of the electrical operating parameters of food.

As shown in Figure 4, it is possible to "style" the large faces of the ingot mold, no longer by a single inductor making the whole width, but by three functionally equivalent inductors 1a, 1b, 1c, arranged side by side along the width large faces of the mold, and thus be able to modulate the braking actions electromagnetic on the differently cast metal in central position and on the sides of large faces.

It will be understood that instead of covering the entire width of the mold, the braking inductor according to the invention may concern only a fraction of this width. For example, only the central part can be concerned, or only the lateral parts on either side of the nozzle 19, or again, as already said with reference to FIG. 4, the entire width but by independent successive action areas using several inducers juxtaposed. It is then possible to adjust the intensity of the action of braking at the magnetic pole differently depending on the width of the slab being cast simply by using electrical supply currents with intensities different in each inductive module thus formed. Likewise, it is possible to position the magnetic brake pole on different height levels depending on whether one is in the center or rather on the sides of the large face of the mold. Likewise again, it thus becomes possible in a mold with variable format to adapt the zone of action of the magnetic braking field across the width of the product being poured.

In general, if we call “K” a chosen constant, representative of the desired braking force at the location of the magnetic pole of each inductor, the maximum value of which is limited by the maximum intensity of the electric current delivered by elementary power supplies 8, 9 ..., one can, by intervention on the adjustment means 10, 11 ..., adjust the location of this magnetic pole where desired by simply varying between 0 and π radians a parameter setting ϕ which functionally links the elementary power supplies together so that the intensities I _i of current passing through the windings are established according to the relationships: I ₁ = K cos ϕ and I ₂ = K sin ϕ in the case of a equipment with two elementary power supplies (two separate windings per inductor), or according to the relationship I ₁ = K sin ϕ, I ₂ = K sin (ϕ + 2π / 3) and I ₃ = K sin (ϕ + 4π / 3) in case of equipment with three power supplies tional (ie having three distinct windings per inductor).

It will also be noted that an inductor 1 or 1 'of the braking equipment according to the invention can be mounted opposite each of the large faces of the mold. It is then possible, by playing on the polarities of the active windings at the same time, and on the other side of the cast slab, to reinforce the braking action in the center of the cast product, or to concentrate it in the vicinity of the skin. These provisions are the subject of Figures 6 and 7 on which inductor 1 has been designated by the index "a" to distinguish it from the inductor matched on the other side of the mold and referenced under the index "b". The fields the same orientation on the two inductors facing each other will strengthen mutually in the "through" direction and therefore will reinforce the braking action in the core of the cast metal (fig. 6), while opposite magnetic fields will contradict each other in the heart of the metal and will consequently concentrate their braking action at the periphery of the cast metal necessarily taking a "field" configuration longitudinal "(fig. 7).

It goes without saying that the invention is not limited to the embodiments exemplified above, but extends to many variants or equivalents as long as its definition given in the appended claims.

Thus, as shown in Figure 8, the inductor 1a ₁ can be mounted in a mold with its conductive bars 2 ... 5 oriented parallel to the casting axis X, that is to say vertically, instead of horizontally. At a given height level, it is then possible to modify the location of the braking action of the magnetic field over the half-width of the cast product with the desired precision along the propagation of the metal jet 27 coming from the hearing 21 of the casting nozzle 19. By then implementing two such inductors 1a ₁ and 1a ₂ with vertical conductors placed on a large face of the ingot mold on either side of the nozzle 19, there is any latitude to adjust with precision the position of the magnetic braking poles at the desired distance from each of the outlet openings 21 and 21 'of the nozzle. In addition, the possibilities are further enlarged by having two other similar inductors on the other large face of the mold, since it is then possible, as we have already seen before, to concentrate the action of the field at a chosen location in the thickness of the product: at the core rather than at the periphery, or vice versa.

Figure 9 shows the setting mode of equipment with two pairs of inductors of this type ensuring a braking effect along the entire thickness of the cast product 13. As as we can see, the principle of such an adjustment is extremely simple. In active windings facing each other, it suffices that the electric current flows in the same direction in the conductors facing each other on each side of the cast product. In these conditions indeed, the magnetic fields produced by these windings in the metal poured liquid add up; the main lines cross the product well perpendicular to its wall without deviating from their initial trajectory taken at the level of inducers. We are then in a so-called "through field" configuration which provides a braking effect depending on the thickness of the product poured and therefore in particular in the center. It is understood that it may be advantageous in this case to preferably activate the . windings closest to the outlets 21 and 21 'of the nozzle 19, since the jets 27 and 27 'are rather powerful and tightened at the outlet of the nozzle, while they are more diffuse and flourish as they progress towards the small faces of the mold.

Figure 10 shows this same equipment but adjusted on the contrary to maximize the skin braking action of the cast product. To this end, it suffices, as we see, to reverse the direction of the current in one of the two active windings facing each other, so that the magnetic fields produced by these two windings are opposed. We are then in a "longitudinal field" type configuration: induction magnetic is minimal in the center of the product, because its lines of force are strongly deflected 90 ° in the central median plane of the product from their initial direction taken at the level of the inductors. As only the component of the field perpendicular to the jet stream lines 27,27 'acts on the latter, the braking effect will then be maximum against the solidification front of the metal poured in places located precisely opposite the activated windings of inductors.

As a variant, as shown in FIG. 12, inductors can be used juxtaposed along the width of the large face of the mold and having between them different orientations of their conductors, electric. In the example shown on this figure, we have side by side three inductors, one 1c in a central position in the region of the pouring nozzle 19, the other two, 1a and 1b, in the lateral position on either side of the central inductor 1c. The conductors of the latter are oriented horizontally, that is to say perpendicular to the casting axis X, in order to be able to adjust the height of the location of its magnetic braking pole at the place of arrival of the cast metal in an ingot mold. The conductors of the lateral inductors, on the other hand, are oriented vertically to be able to adjust according to the width of the large face the location of their magnetic braking pole near the small faces of the mold. Of course, these relative provisions can be reversed in order to be able to adjust in height in the vicinity of the small faces and a width adjustment in the vicinity of the arrival of the metal in ingot mold.

In addition, by the expression "elementary direct current power supplies" used throughout the description to qualify one of the essential characteristics of the invention, it is necessary to hear not only an addition of unitary power supplies structurally independent, as considered so far with reference to the preceding figures, but another single polyphase supply with two or three phases and adjustable frequency, which is set at zero frequency to obtain a direct current. Power supplies polyphase electrics of this type are well known. They are commonly used to activate electric motors with rotating or sliding magnetic field. As the shown in Figure 11, they are of the inverter type 28 with adjustable chopping threshold. This inverter is conventionally supplied with rectified current by a rectifier 29 mounted at the output of a rotating group 30 by means of a transformer for adapting the voltage 31 and a switch 32.

Each phase U, V, W of the power supply (three-phase in the example considered) is built according to this mode. The inverter ensures compliance with the phase shifts between the phases produced by group 30 and all phases of feeding are made available to use by means of a connection box 33 provided with a common neutral N.

According to the invention, the putting into operation of such an electrical supply to supply the windings of the braking device shown diagrammatically at 34, at the rate of a phase by winding, consists in setting the inverter 28 to zero frequency, proceeding to such settings at selected times so that the intensities of the currents in each phase are at these moments those which one wishes to obtain in the windings connected to these phases.

Claims (9)

1. Electromagnetic braking device for a molten metal within a continuously cast product, comprising an electric power supply and, connected to said supply, at least one electromagnetic inductor (1) of type polyphased stator with sliding magnetic field, intended to be mounted on the casting installation opposite to one side of the product in casting, said inductor having at least two phase windings (A, B), device characterised in that said electric power supply (29) consists of elementary direct current power supplies (8, 9), each one independently from each other controllable in current intensity, and in that each of said elementary power supplies is connected to one and only one of said phase windings (A, B) of the inductor.
2. Device according to claim 1, characterised in that said electromagnetic inductor (1) is mounted at the mould level (12) of the casting installation.
3. Device according to claim 1 or 2, characterised in that it comprises at least two electromagnetic inductors (1) mounted on the casting installation, facing one another, on both sides of the product in casting.
4. Device according to claim 1, 2 or 3, characterised in that it comprises at least two inductors (1a, 1b) placed side by side along the width or the length of one side of the product in casting.
5. Device according to any of claims 1 to 4, characterised in that it comprises at least one inductor (1) mounted on the casting installation, its conductors (2, ... 5) being orientated perpendicularly to the casting axis (X).
6. Device according to any of claims 1 to 4, characterised in that it comprises at least one inductor (1) mounted on the casting installation, its conductors (2, ... 5) being orientated parallel to the casting axis (X).
7. Device according to claim 4, characterised in that it comprises at least three inductors mounted on the casting installation, its conductors being oriented according to different directions of the inductors.
8. Device according to claim 1, characterised in that the elementary electric power supplies (8, 9) are composed of a single polyphase power supply, the current of which is adjustable in frequency and controlled to value zero.
9. Method for electromagnetic braking of a molten metal within a continuously cast product, according to which a permanent magnetic field acting on the molten metal to brake its flow is used, said field being created by a braking device corresponding to claim 1, with pluri-winding electromagnetic inductor (1) of type polyphased stator with sliding magnetic field, characterised in that, in order to control the position of the magnetic pole or poles of said inductor (1), in function of the casting conditions and without moving the inductor itself, the elementary electric power supplies (8, 9) for the windings of the inductor (1) being direct current supplies and being individually controllable, one carries out, with the help of a factor ϕ, variable between 0 and π radians, a control of the intensities I_i of the electric currents flowing through the windings (2, ... 5) of the inductor, such that at any instant the currents are I₁ = K cos ϕ and I₂ = K sin ϕ in case of an inductor (1) with two windings (A, B) and I₁ = K sin ϕ, I₂ = K sin (ϕ + 2π/3) and I₃ = K sin (ϕ + 4π/3) in case of an inductor (1) with three windings, K being a representative constant of the desired braking force at the place of the magnetic pole or poles of the inductor (1), and the maximum value of which is limited by the maximum electrical current each of the elementary electric power supplies (8, 9) is able to deliver.

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