Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/11—Treating the molten metal
  • B22D11/114—Treating the molten metal by using agitating or vibrating means
  • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields

Definitions

• the present invention relates to the continuous casting of metals, in particular steel. It relates more particularly to techniques consisting, using a magnetic field, in influencing the circulation of molten metal when it arrives in the continuous casting mold.
• Electromagnetic convection consists in causing a washing of the solidification front by a forced current of poured liquid metal, from bottom to top for example, which takes with it, towards the meniscus, non-metallic inclusions which would otherwise be trapped by this front .
• This current of liquid metal is created by a sliding magnetic field, generally produced by a multi-winding inductor of the polyphase linear motor stator type (bi or three-phase) arranged parallel and facing a large face of the slab in the mold. 2,358,222 and BF 2,358,223).
• An inductor of this type is conventionally made up of electrical windings, the conductors of which are shaped as evenly spaced parallel bars, or as coils of wires, housed in teeth of a
• SUBSTITUTE SHEET (RULE 26 magnetic yoke and mounted in pairs in series-opposition. Each winding is connected to a different phase of a polyphase electrical supply, namely, three-phase or two-phase, in 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 sliding magnetic field by coupling with a polyphase supply, is widely described in the electrotechnical literature.
• electrostatic braking in which the present invention is included, on the other hand consists of acting directly on the, or the jets of arrival of the metal in the 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 as flat as possible.
• the operation of such a brake follows the well-known principle of the eddy brake: when a moving liquid metal (more generally an electrically conductive fluid) passes through a static magnetic field, it undergoes a force from it Contrary, whose intensity depends on that of the field and the speed of the metal.
• An electromagnetic brake for a mold for continuous casting of slabs consisting essentially of two electromagnets with salient poles facing each other on either side of the large walls of the mold and of opposite polarity so as to create between the poles of crossing magnetic lines of force.
• the electromagnets are positioned in the upper part of the ingot mold in order to intercept the jet of metal as soon as it arrives in the ingot 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 entire width of the mold and to locate this bar in height at the lateral gills of outlet of the pouring nozzle to perform a braking action permanent throughout the propagation of the jet coming from each nozzle of the nozzle towards the small faces.
• the PCT document WO 96/26029 teaches to have, not one, but two magnetic bars per face, located at different height levels, one below the other on either side. outlet openings of the nozzle so as to form a magnetic confinement of the jet area to hydrodynamically isolate it from the rest of the volume of liquid metal present in the mold.
• the flow conditions of the liquid metal in the ingot mold can vary markedly from one casting to another, or even during the same casting, according to various parameters, such as the speed of casting, the depth of immersion of the nozzle, the shape of its gills giving the direction of the jet, the width of the mold, if the latter is of the variable width type, etc ... Therefore, if the it is desired to optimize the zones of action of the magnetic field in an ingot mold as a function of these parameters, this cannot be done without moving the inductor along the large faces of the ingot mold, which is impractical in practice.
• the object of the invention is to provide steelmakers with a means of easily and without delay modifying the zones of action of an electromagnetic brake in a continuous casting mold so as to be able to permanently adjust their location to the precise conditions of the casting to coming, or pouring in progress, simply by adjusting the parameters of the power supply, so without requiring any intervention on the machine. casting and in particular without having to modify the position of the inductor.
• the subject of the invention is an equipment for electromagnetic braking 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 a face of the product being cast, said inductor having two or three phase windings, equipment characterized in that said power supply consists of two, respectively three, elementary DC power supplies adjustable in current intensity each independently of the others, and in that each of said elementary power supplies is connected to one and only one of said phase windings of the inductor.
• the invention consists in associating an inductor of the "linear motor stator with sliding magnetic field" type -whose design and structure have been widely known for a long time and of which the use in continuous casting of slabs as a means of setting the molten metal in motion according to the height of the mold (see for example GB 1507444 and 1542316) -with a battery of individual direct current power supplies, independently adjustable of the others and each coupled with a winding of the inductor and it alone in order to create a static magnetic field which is adjustable in localization (and of course also in intensity) according to the height or the width of the large faces of the ingot mold (more generally besides on any chosen place of the metallurgical height, but where the product poured still contains a fair amount of liquid metal which is not solidified to the core) 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.
• 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 adjusting, as a function of the casting conditions, the position of the magnetic pole (s) of said inductor without displacement of the latter, an intensities I, electrical currents flowing through the windings of the inductor are adjusted.
• FIG. 2 schematically shows an electromagnetic braking equipment according to the invention in a two-winding embodiment similar to that of the two-phase mixing inductor known in Figure 1;
• FIG. 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 casting mold continuous steel slabs according to a first embodiment with height adjustment of the braking action;
• FIG. 4 shows a variant of the installation of Figure 3, according to which the structure of the braking inductor is partitioned along the width of the mold;
• FIGs 5a and 5b each illustrate an embodiment of the braking equipment according to the invention in a different embodiment of the inductor;
• FIG. 6 is a schematic view, in vertical cross section passing 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 shows 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 across the width ingot mold;
• FIG. 9 illustrates, seen schematically from above and in section along the plane A-A of Figure 8, a mode of adjustment of the braking equipment shown in Figure 8;
• FIG. 11 schematically shows an alternative embodiment of a power supply of the invention
• FIG. 12 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 the height of the mold.
• the same elements are designated with identical references.
• the stirring inductor 1 shown in FIG. 1 has functions and effects on the flow of liquid metal completely different from those of the brake device of the invention, but it serves as a sort of framework for the constitution of this latest. He therefore presents with him close analogies of constitution. Also, a few reminders concerning it and concerning its operating mode will facilitate understanding of the invention.
• the main active part of this static inductor with sliding field consists of electrical conductors, here rectilinear copper bars 2, 3, 4 and 5, housed in regularly spaced parallel notches (or teeth) formed in a cylinder head magnetic 6. These bars are thus arranged parallel to each other by being regularly spaced from one another by a distance which makes it possible to define the pole pitch of the inductor.
• the inductor is of the two-phase stator type. It has for this purpose four conductive bars mounted electrically in pairs, in pairs in series-opposition, that is to say connected by their ends located on the same side of the inductor (on the 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 (on the left in the figure) are connected, in the order shown in the figure, to the terminals of a two-phase supply 7, the two phases 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, as those of the phase which supplies them, distinguishing the arrival ends , of the ends of return of the current whose letter is surmounted by a horizontal line, in accordance with the use.
• These windings, as can be seen, are here of the "nested" type, because the coupled bars forming a winding are not adjacent bars, but separated by a bar from the other winding.
• the bar 2 is connected to the bar 4 to form the winding A
• the bar 3 is connected to the bar 5 to form the other winding B.
• Similar arrangements are found in the case of an inductor of the type three-phase stator, the nesting of the three windings then being obtained, as we know, by a separation jump between coupled bars, not of one, but of two bars each belonging to one and the other of the two other windings.
• the inductor 1 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 N B in the figure), namely from top to bottom, and this, at speed (iela frequency of current) with which the intensity of the supply current reaches its maximum successively from bar 2 to bar 5.
• the small diagram "cartridge” on the left of the figure shows, using the trigonometric circle, the dynamic organization of the two phases which will make it possible to understand simply what has just been said if one traverses this circle clockwise.
• a mixing inductor of this kind can easily find its place within a casting mold cont inue de slabs for example, and numerous documents, in particular in the form of patent applications, describe such a use.
• the inductive device of FIG. 1 must be modified 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. It is therefore analogous to that produced by known electromagnetic braking devices in a continuous casting ingot mold, but its area of action can be adjusted in position over the height of the ingot mold (or over the width, depending on the mounting method adopted). without any intervention on the casting installation.
• this modification consists in replacing the two-phase power supply 7 by two direct current power supplies 8 and 9, individual and independent of each other, their only common point possibly being their neutral N, pooled for convenience.
• These power supplies are each provided with means for adjusting the intensity of the currents which they deliver.
• These adjustment means known by themselves and quite usual in this field, have therefore 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 condition as soon as each of the windings A and B of the inductor 1 is connected to one of its two elementary power supplies and to it alone. In the example illustrated in FIG. 2, the winding A is connected to the power supply 8, and the winding B is connected to the power supply 9.
• braking equipment of the invention is in fact also applicable under the ingot mold, therefore usable, more generally, on a continuous casting product, a steel slab for example, the interior is still in a very liquid state.
• FIG. 3 showing precisely the positioning 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.
• the two large opposite faces of the ingot mold can thus be equipped by two identical inductors arranged opposite one another on either side of the cast product and each extending 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 in relation to the other opposite, the braking effect can be promoted through the entire thickness of the product. sunk (field configuration called "crossing"), or locate it in the vicinity of the skin only (field configuration called "longitudinal").
• the molten metal is poured into the ingot mold by the nozzle 19, the lower end of which, provided with lateral outlet gills 21, 21 ′, plunges into the mass of molten steel during casting already present in the ingot mold.
• These lateral outlet openings 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 descending flow 28, responsible for the deep entrainment d 'non-metallic inclusions, and a rising flow 28' coming to agitate the meniscus 22. It is on these jets 27 and 27 'that the braking means according to the invention will act. In the example illustrated by FIG.
• the inductor 1 previously described is mounted opposite a large face 14 of the ingot mold with an orientation such that the conductive bars 2 to 5 are horizontal, the casting axis X being him vertical.
• the direct current which it delivers in the winding A forms a current loop located in the upper half of the inductor 1 (therefore of the mold) and in which the electric current flows through the conductive bar 2 from left to right, then the bar 4 from right to left.
• a stationary magnetic field Bu directed perpendicular to the plane of the winding, which in this case is also that of the figure.
• this inductor 1 is able to play a brake role acting on the flows of molten metal entering the ingot mold, like the known electromagnetic braking devices. But, now there is the decisive advantage of being able to adjust at any time over the height of the mold the location of the magnetic pole of the braking field, without having to move any part of the inductor, simply by acting on the adjustment power supplies.
• a precise location of the magnetic pole of the braking field at the top of the ingot mold can indeed be optimal under certain casting conditions, and prove to be less well suited than another if, from a casting to the following or even during casting, the casting parameters are modified, such as the immersion depth of the nozzle 19, the level of the meniscus 22 in the mold, the casting speed, etc. We are then led to want to change the position of this pole on the height of the 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 the power supply.
• the braking inductor according to the invention may concern only a fraction of this width. For example, only the central part, or only the lateral parts on either side of the nozzle 19, can be concerned, or, as already said with reference to FIG. 4, the entire width, but by successive independent action zones using several juxtaposed inductors. It is then possible to adjust the intensity of the braking action at the magnetic pole differently depending on the width of the slab cast simply by using electric supply currents with intensities different in each inductive module thus formed. Similarly, it is possible to position the magnetic braking 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 to the width of the cast product.
• 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 ...
• an inductor 1 or the braking equipment according to the invention can be mounted opposite each of the large faces of the ingot mold. It is then possible, by playing on the polarities of the active windings at the same time on either 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 in which the inductor 1 has been designated by the index "a" to distinguish it from the inductor paired on the other face of the ingot mold and referenced under the index " b ".
• Magnetic fields of the same orientation on the two inductors facing each other will reinforce each other 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. core of the metal and will consequently concentrate their braking action on the periphery of the cast metal, necessarily taking a configuration of the "longitudinal field” type (fig. 7).
• the inductor la 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.
• two such inductors the t and the, with vertical conductors placed on a large face of the ingot mold on either side of the nozzle 19 we have all latitude to precisely adjust the position of the magnetic braking poles to the desired distance from each of the outlet openings 21 and 21 'of the nozzle.
• FIG. 9 shows the mode of adjustment of an equipment with two pairs of inductors of this type ensuring a braking effect along the entire thickness of the cast product 13.
• the principle of such an adjustment is extremely simple. In the active windings which face each other, it suffices that the electric current passes in the same direction in the conductors opposite one another on each side of the cast product. Under these conditions, in fact, the magnetic fields produced by these windings in the molten liquid metal add up; the force lines cross the product well perpendicular to its wall without deviating from their initial trajectory taken at the level of the inductors. We are then in a configuration known as "through field" which provides a braking effect depending on the thickness of the cast product and therefore in particular in the center.
• Figure 10 shows this same equipment but adjusted on the contrary to maximize the braking action in skin of the cast product. To this end, it suffices, as can be seen, 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 in opposition.
• inductors can be used juxtaposed along the width of the large face of the mold and having between them orientations different from their electrical conductors.
• three inductors are placed side by side, one in the central position in the region of the pouring nozzle 19, the other two, la and lb, in the lateral position on either side. other of the central inductor.
• 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 in height the location of its magnetic braking pole at the place of arrival of the metal cast in ingot mold.
• the conductors of the lateral inductors are oriented vertically so as to be able to adjust, according to the width of the large face, the location of their magnetic braking pole in the vicinity of the small faces of the mold.
• these relative arrangements can be reversed in order to be able to make a height adjustment in the vicinity of the small faces and a width adjustment in the vicinity of the arrival of the metal in the mold.
• Each phase U, N, W of the power supply (three-phase in the example considered) is constructed according to this mode.
• the inverter ensures compliance with the phase shifts between the phases produced by the group 30 and all the phases of the power supply are made available for use by means of a connection box 33 provided with a common neutral ⁇ .
• putting such an electrical supply into operation to supply the windings of the braking device shown diagrammatically at 34, at the rate of one phase per winding consists in setting the inverter 28 at zero frequency, by carrying out such adjustments at selected times so that the intensities of the currents in each phase are at those times those which it is desired to obtain in the windings connected to these phases.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Continuous Casting (AREA)
• Braking Arrangements (AREA)

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• 1997
  • 1997-12-17 FR FR9715984A patent/FR2772294B1/fr not_active Expired - Fee Related
• 1998
  • 1998-12-01 ES ES98958286T patent/ES2186242T3/es not_active Expired - Lifetime
  • 1998-12-01 AU AU14381/99A patent/AU735023B2/en not_active Ceased
  • 1998-12-01 DE DE69809288T patent/DE69809288T2/de not_active Expired - Lifetime
  • 1998-12-01 CA CA002312876A patent/CA2312876C/fr not_active Expired - Fee Related
  • 1998-12-01 WO PCT/FR1998/002577 patent/WO1999030856A1/fr not_active Ceased
  • 1998-12-01 AT AT98958286T patent/ATE227181T1/de active
  • 1998-12-01 EP EP98958286A patent/EP1039979B1/de not_active Expired - Lifetime
  • 1998-12-01 JP JP2000538821A patent/JP3725028B2/ja not_active Expired - Fee Related
  • 1998-12-01 KR KR1020007006726A patent/KR100586665B1/ko not_active Expired - Fee Related
  • 1998-12-01 RU RU2000118818/02A patent/RU2212977C2/ru not_active IP Right Cessation
  • 1998-12-01 CN CN98812345A patent/CN1112264C/zh not_active Expired - Fee Related
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  • 1998-12-04 US US09/205,714 patent/US6164365A/en not_active Expired - Lifetime

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