JP2007509752A - Electromagnetic stirring method for continuous casting of metal products having an elongated cross section - Google Patents

Abstract

The electromagnetic stirring in a continuous casting installation for slabs, in which the mould (1) is equipped with an immersed casting nozzle (4) with lateral outlet holes (5, 5') directed towards the small faces, is carried out with the aid of sliding magnetic fields generated by polyphase induction coils arranged in the proximity of the cast metal. With the primary aim of favoring liquid metal exchanges at the heart of the solidification well (6) between the secondary zone (2) and the mould, one forces the establishment of a longitudinal metal flow in the central region of the cast product along two opposed collinear currents (10a, 10b). An independent claim is also included for a metal product with a elongated straight section from a continuous casting installation using this method of electromagnetic stirring.

Description

  The present invention relates to continuous casting of metals, particularly steel. The present invention relates in particular to electromagnetic stirring of a flat product (ie, a product with an elongated cross-section) during casting, and more precisely establishes a specific distribution of flow in a metal liquid pool by an applied magnetic field. About that.

  It should be noted that the general expression “product with an elongated cross-section” should be understood as referring to a metal product whose width is at least twice the thickness, in particular slabs, thin slabs, thin slabs etc. .

  Magnetic stirring, which emerged in the field of continuous steel casting at the beginning of the 70s, has rapidly established its position as an almost indispensable tool for controlling the flow in a liquid pool undergoing solidification. The most commonly used principle is the well-known MHD (magnetohydrodynamics), which is generated by a multi-phase inductor placed closest to the cast product, more generally a plurality of multi-phase inductors. A liquid metal (molten metal) is driven and moved by the movable (rotating or moving) magnetic field. These inductors are properly positioned at the metallurgical height of the casting machine and are supplied with current at an adjustable frequency, thereby allowing various modes of agitation modes that can meet the requirements of metallurgists.

  In addition, due to continuous progress in elucidating the mechanism of metal solidification in continuous casting, due to the cyclic movement of liquid metal in relation to the general quality of the final solidified product (ie internal stability, surface cleanliness or lack of inclusions, solidification structure, etc.) The important role became particularly clear.

  In this regard, the motion applied to the molten metal during continuous casting can be roughly classified into two categories, depending on how the mold, or the underlying secondary cooling stage of the caster, is considered. .

  The motion imparted to the liquid metal by electromagnetic agitation in the mold at a level where the liquid portion of the cast metal is the majority is essentially configured to control the flow in this critical area. In fact, in this case, if a free surface of the cast metal is found, its internal cleanliness depends on the geometry of this surface. Furthermore, in this case, when the first solidification envelope occurs, its main importance is well known both in terms of both the surface quality of the final cast product and the control of the casting process itself.

  On the other hand, by stirring the metal in the liquid pool under the mold and hence in the secondary cooling zone (usually referred to as “secondary”), the first objective is to develop the maximum equiaxed solidification. Through the improvement of the internal metallurgical structure of the cast product, which is known to be suitable both for example for the microsegregation of alloying elements and for the absence of the central porosity of the cast product. Thus, electromagnetic stirrer is increasingly more frequent whenever it is necessary to produce a product that requires a non-porous internal structure, such as a thick plate to produce a boiler or thick welded pipe, for example. In addition, it is used for continuous casting of slabs.

  Here, in order to fully understand the present invention as described below, as shown in the attached FIG. 3 diagram obtained from FR72 / 20546, the casting product is large in the secondary cooling zone of the continuous slab caster. It should be noted that it is well known to use linear inductors 41, 41 'that are positioned opposite each other on both sides of the surface and generate a transverse magnetic field that moves across the width of the product. The aim is therefore to create a flow in the liquid metal that essentially develops as two adjacent loops rotating in opposite directions. These loops 42, 43 are established parallel to the large face and extend within the stage along the length of the cast product to both sides of the common transverse zone of the magnetic field drive action, each loop flowing one small Ascends along the surface and descends along the small surface on the opposite side. Such a movement form is usually referred to as a “butterfly wing” form.

  Depending on the length of the caster, the transverse zones 51, 52 of the magnetic field drive action can be enlarged as shown in the attached FIG. 4 excerpted from FR82 / 10844. In this case, the zones are paired in the opposite direction of rotation between the nearest adjacent loops, producing the maximum possible agitation volume for a given effective agitation power. Thus, a pattern flow, referred to as a “triple zero shape”, occurs, which is between three adjacent loops that rotate in pairs in opposite directions, ie between two transverse drive zones 51, 52. The central loop 60 is formed, and two outer loops 61 and 62 that rotate in the same direction on both sides of the central loop.

  Whatever implementation is adopted, this may also be an inductor (FR72 / 20547) placed behind the support roller in the secondary cooling zone of the caster, if between these rollers, or the actual This can be achieved by an inductor (FR72 / 20546) housed in the roller. The same is true for the means of implementing the invention described below.

  Historically, we found this type of movement based on a metal loop recirculation formed in a plane parallel to the large surface of the slab, unlike long products, in continuous casting of flat products. Appears to be due to the fact that the elongated shape of the cross section of the product does not easily contribute to the establishment of a stable rotational movement around the casting axis. The main reason is expected to be the large velocity gradient required at the product thickness, which is slightly over about 20 centimeters for the thickest product.

  However, the stepped loop shape of the type shown in FIGS. 3 and 4 deployed over the entire metallurgical length parallel to the large face of the product does not suffer from such disadvantages. It further has the advantage of ensuring an excellent heat exchange between the top and bottom regions of the caster. The hottest molten metal from the upper region is driven downward by forced convection by the downward flows 42a and 43b, while the upward flows 42b and 43b introduce microcrystals of solidified metal gathering at the bottom to the top, This facilitates the early deployment of very homogeneous equiaxed solidification from the right periphery to the center of the cast product. However, these loops 42, 43 cannot be deployed as strongly near the top as desired due to the risk of disturbing the free surface of the metal in the mold. At present, how much maintenance of the brittle hydrodynamic equilibrium of the flow in the mold prevailing at this level of the mold is necessary to obtain good quality of the surface, sub-coating and core of the cast product Or is known.

  In particular, the introduction of the cast metal through the top of the mold using a submerged nozzle with a lateral outlet opening in the narrow face of the mold has become a substantially common practice at the present time. Replacing the nozzle with a single axial discharge, so that it is actually only reserved for long products. The great advantage gained by in-mold flow is the high temperature emanating from each lateral hole 27, 27 'of the nozzle 26 due to the repulsion effect on the narrow surface of the mold, as shown in the diagram of FIG. 1 attached hereto. The fact is that the liquid metal jet naturally spreads in two parts. The main part 21 is directed downwards in the direction of drawing the cast product. The other portion 22 reflects upward and is necessary to prevent the cast metal solidification phenomenon at the meniscus near the free surface 23 of the metal in the mold (which often causes a sudden stop in the casting process). Provide a good enthalpy. The aim is therefore to create a circulating mode in the mold called “double roll” versus “single roll” mode.

  The latter mode shown in FIG. 6 is primarily the use of argon to prevent nozzle clogging from a casting tundish placed above the nozzle when discharged from the nozzle outlet. This is manifested by the phenomenon of the metal moving upwards toward the meniscus, resulting from the injection of. This initial rise continues to the surface flow to each narrow surface, and then to the downward flow along each narrow surface. Thus, a speed map is rapidly established in the mold and, due to the absence of the upper roll 22 to supply "hot" metal to the meniscus, the speed is generally directed downward in the direction of drawing the cast product.

  However, the “double roll” mode continues during casting only if casting conditions (casting speed, slab width, casting nozzle immersion depth, clogging argon flow rate, etc.) contribute to that mode. To do. Random movement in the “single roll” mode may appear during the actual process of casting if these conditions vary (in fact, it corresponds to the general case).

  Furthermore, the essential aspect of controlling the “double roll” flow in the mold is the maintenance of “symmetrical” recirculation motion in the mold at the meniscus on both sides of the nozzle. The reason for this is that the occurrence of “left-right” asymmetry is due to vibrations in the metal bath, which can result in unacceptable rolling of the surface that is perceived by workers standing on the casting platform. This means that care must be taken to ensure that the partial recirculation flow 22, 22 ', especially near the top, is stable over time to avoid the occurrence of "left-right" asymmetry. These upward circulations are the first solidification line formed near the meniscus boundary with respect to the cooled copper wall of the mold while being sufficiently thermally effective to transfer the desired heat to the meniscus. From the hydrodynamic point of view it is not excessive in order to avoid 25 excess agitation. The regularity of this line of the first solidification is in fact the upper part of the mold without the risk of breakout under the mold due to the local thinness of the slag scale or the thickness of the solidification envelope. It is to ensure uniformity in the formation of the first outer cover.

  Simply put, by casting with a submerged nozzle with a transverse outlet, it is a “double roll” type, either randomly or in any case not necessarily desirable, throughout any casting run. Alternatively, flow in either mold of “single roll” type, or unstable flow due to “left-right” asymmetry can be achieved.

  This is due in particular to these difficulties of flow control in the upper region of the continuous caster, where an electromagnetic stirrer system has recently been in the mold for the transverse jet exiting the nozzle. The effect of was revealed. As shown in the attached FIG. 2a, FIG. 2b-1, and FIG. 2b-2 excerpts from JP1533472, the horizontally moving magnetic field is large in the mold 32 facing the metal jet discharge path on both sides of the nozzle 31. Produced by multiphase linear inductors 30a, 30b and 30a ', 30b' arranged along the plane. By adjusting the direction of movement of the magnetic field, the flow of the metal jet is then decelerated (moving from a small surface in the direction of the nozzle, moving in the opposite direction of the magnetic field, FIG. 2b-1), or vice versa. The flow of the metal jet can be accelerated (common direction flow movement from nozzle to small surface, FIG. 2b-2). In principle, this is an adjustment of the amount of enthalpy delivered to the surface of the cast metal without excessively disturbing the in-mold flow mode that needs to be maintained as a priority, for example depending on the casting conditions. enable.

  Thus, referring to the prior art, if there is no contradiction, a cast product (e.g., a flat product) having an elongated cross-section will have a stirring of the metal in the mold on the one hand and the stirring in the secondary cooling zone on the other hand. Clearly show the distinctions that exist when in between.

  In particular, the object of the present invention is to overcome such disadvantageous conditions. In other words, the object of the present invention, applicable to the continuous casting of flat products, in particular slabs, is that between the secondary cooling zone and the mold due to the studied global stirring motion of the molten metal over the metallurgical length. In both directions it is to provide a proper exchange of the metal still in the liquid state. Therefore, this detracts from the specific cumulative advantageous effects on the agitation in the mold and the agitation in the secondary cooling zone, respectively, correspondingly if possible without disturbing the in-mold flow mode. Rather, it achieves thermal and chemical uniformity between the top and bottom of the pool of cast liquid metal.

  One supplementary object of the present invention is to help improve the metallurgical quality grade of steel, which is desirable for products with excellent internal qualities such as thick or thick welded pipes, ferritic stainless steel, or silicon electric steel. That is.

  Another supplemental object of the present invention is to change the flow in the secondary cooling zone so that the flow is accelerated or oppositely decelerated with respect to the metal entering the mold, or the "metal movement" in the mold. As a means of preventing the “left-right” asymmetry tendency, it can be used at the same level as the casting jet emitted from the nozzle.

  With these objectives in mind, the subject of the present invention is a method of electromagnetic stirring in the secondary cooling zone of a continuous casting plant for slabs or other similar flat products, where the casting plant mold is a narrow surface of the mold. A submerged nozzle with a transverse outlet directed towards the is provided, the stirring method being carried out by a moving magnetic field generated by a multiphase inductor placed near the cast metal, in the longitudinal direction The liquid metal flow is forcibly established in the secondary cooling zone, and the forced flow is confined locally as two collinear streams in two opposite directions within the central region of the cast product. Features.

  This naturally establishes a circulation of the entire liquid metal in the secondary cooling zone, which circulation has a “four-leaf clover” configuration with two upper lobes and two lower lobes, The lobe extends into the mold to the level of the jet discharged from the casting nozzle outlet.

  According to an embodiment of the present invention, these two longitudinally opposite collinear streams in the central part of the product moving away from each other extend into the mold to the level of the jet exiting the casting nozzle outlet. Two upper lobes are generated to flow and merge in the same direction as the jet to enhance the stream.

  According to another embodiment of the present invention, these two longitudinally opposite collinear streams gathering together in the central part of the product are within the mold to the level of the jet discharged from the outlet of the casting nozzle. Two upper lobes extending in the direction of the jets overlap in order to decelerate the stream.

  According to one particular embodiment of the method, the position of the longitudinal flow in the secondary cooling zone moves laterally towards one or the other of the narrow faces of the cast product, and the “left and right” of the metal movement in the mold. ”Prevents asymmetry tendencies.

  According to one method of implementation, the longitudinal metal flow in the central region of the cast product is caused by two collinear magnetic fields moving longitudinally in the central region that move together or move further apart. It is generated as a collinear stream in the opposite direction.

  According to a preferred implementation, the longitudinal metal flow in the central region of the cast product is produced as two collinear streams in two opposite directions by a collinear moving magnetic field that moves transversely across the width of the cast product. Move closer to the center from the edge of the product or move further away from the center of the cast product to the edge.

  According to another preferred embodiment, the moving magnetic field is generated by a multiphase linear inductor placed opposite the large face of the cast product.

  According to another embodiment, the inductor is supplied with various strengths of current and in various ways changes the effect on the two opposite collinear metal streams generated by the moving magnetic field generated by the inductor. .

  It should be noted that the term “collinear” as applied to magnetic field movement or metal flow refers to two collinear vectors as opposed to two parallel vectors, where the magnetic field or metal stream does not move parallel to each other. It should be understood that this means moving along the same line.

  As will be appreciated, the present invention consists in principle of creating a “stirring intersection” having two transverse branches and two longitudinal branches in the secondary cooling zone. A transverse branch (or a horizontal branch if the casting axis is assumed to be vertical) is deployed across the width of the cast product, and the two longitudinal (or vertical) branches are within the central region of the cast product ( Usually developed in the axial region).

  In practice, this “stirring intersection” in the secondary cooling zone of the casting machine develops the recirculation flow in the four-leaf shaped liquid pool and then creates the overall form of movement that reaches the mold area As a result, the above-mentioned object intended by the present invention is achieved.

  The invention will be more clearly understood and other aspects will become apparent from the description given with reference to the accompanying drawings.

  1 to 4 show typical examples of the prior art studied above.

  5 to 9 are diagrams specific to the present invention.

  Recall from FIG. 1 to FIG. 4 that it has helped explain the prior art made at the beginning of the specification. Accordingly, these figures will not be referenced again in the following description.

  In FIGS. 5-9, which show the agitation mode within the secondary cooling zone specific to the present invention in these two modes of operation (metal streams that divide or collect in the center), the moving magnetic fields are linear inductors that generate them. Similarly, it is represented by a thick vertical arrow or a thick horizontal arrow. The generated convection motion itself is indicated by a main path in the form of a line with arrows indicating the direction of circulation of movement over the entire transport path. The solid line represents the active convection zone, and thus the circulation zone that is affected by the moving magnetic field. The dashed line represents the passive convection zone, in other words, the intensive recirculation zone required for the active zone to close the moving loop.

  In these drawings, identical elements are denoted by identical reference numerals. Where necessary, periodic reference numerals have not been shown so as to make the main elements of the invention shown in these figures clearer so as not to unnecessarily burden certain drawings. .

  Each drawing shows a continuous slab mold 1 and a secondary cooling zone 2 of the casting machine below it, here intentionally omitting the support roll in order not to unnecessarily reduce the clarity of the figure. ing. Since the figure is in a plane parallel to the large face of the mold, only the narrow faces are indicated by 3 and 3 ', which determine the narrow sides 18, 18' of the cast product 6. The large surface is not drawn in the drawing because it lies in the plane of the drawing. Furthermore, for the sake of clarity, reference numeral 6 denotes either the cast slab itself or the core still in the liquid state, more commonly referred to as the “liquid pool”.

  A soaked nozzle 4 centered on the casting axis A (here, corresponding to the longitudinal axis of the cast product as usual) is a tundish (not shown) placed on the nozzle. To supply molten metal to the mold. This nozzle comprises transverse outlets 5 and 5 'that are directed to one or the other of the narrow surfaces 3 and 3', respectively. The size of the cast product is determined by the inner dimension of the mold that defines the casting space. Molten metal enters this casting space in the form of jets 7, 7 ′ which are discharged from the outlet of the nozzle 4, usually along a substantially horizontal average direction, or slightly inclined downward. In this way, the cast product is from the top (at the same level as the meniscus 8) from the lower casting machine, along the vertical path in a plane perpendicular to the figure or along the curved path, usually 1 m. It progresses at a drawing speed (casting speed) of about / min. As the casting progresses, the casting product gradually solidifies from the periphery to the center by extracting the internal heat, and then the secondary cooling zone that receives the effect of the water spray rail on the mold 1 that contacts the copper wall that has been cooled first. Enter 2.

  The metallurgical length (or liquid pool depth) has traditionally been between the level of the free surface of the cast metal in the mold (or meniscus) and the level of the bottom of the liquid pool below the secondary cooling zone. Defined as a dimensional difference along the vertical direction, at the level of the bottom of the liquid pool below the secondary cooling zone, the finished solidification front matches, which progresses across each large surface of the cast product as solidification progresses To do.

  A point P, which is arbitrarily placed about 3 to 4 m below the meniscus 8 along the longitudinal axis of the cast product (corresponding to the casting axis A) and thus in the secondary cooling zone 2, is the “stirring intersection” 9 And represents a specific generation of the present invention. This agitating intersection 9 is an intersection having four branches and is collinear in pairs, ie two longitudinal (here vertical) branches 10a, 10b, aligned with the casting axis A The pairs 11a and 11b form a pair and develop across the entire width of the cast product. In each of the two branches of any pair, the liquid metal stream circulates in opposite directions in pairs. Furthermore, the circulation of the streams in one pair is in the opposite direction to the circulation of the other pair of streams.

  Due to the inevitable “finite” dimensional characteristics of the cast product, these branches are joined together by a recirculation loop, as is evident in the figure, and deployed in a four-leaf clover shape in the plane of the large face of the cast product. Form an overall flow. Each leaf constitutes a lobe L1, L2, L3, L4, the two L1 and L4 above the lobe extending to the same mold level as the discharge jets 7, 7 '.

  Thus, in the agitation mode shown in FIGS. 5 and 8, the vertical branches of the pair are “branched” convection types. The metal streams move away from the center P from each other. One branch 10a flows toward the mold 1 above it, and the other branch 10b flows downward in the direction of drawing out the cast product and into the liquid pool toward the closing point. In the horizontal pair 11a, 11b, the metal convection is thus “convergent”. The metal streams flow towards each other in the direction of the center of confluence P and from the small face of the cast product towards the longitudinal axis A.

  As mentioned above, the metal streams forming these branches are generated by a moving magnetic field, which is itself generated by a linear inductor placed in the immediate vicinity of the cast product facing these large surfaces (preferably both sides). . Of course, two pairs of branches need not necessarily be actuated simultaneously by a magnetic field. For example, only one of the vertical branches 10a, 10b and the other branches 11a, 11b can be actuated because the center P acts as a flow passage node that maintains the mass flow rate and travel, and of course then the reaction Makes it a recirculation site, and vice versa.

  However, in this first agitation mode of the present invention, it is important that the vertical branches 10a and 10b flow away from each other as shown in FIGS. In the upper lobes L1 and L4 close to the mold, the metal rises along the center and falls along the narrow surface. The opposite is true for the lower lobes L2 and L3.

  Under these conditions, the practice of the present invention has been found to maximize the exchange of metallic material between the bottom and top of the liquid pool. First, metal circulation in either lobe occurs in a direction of rotation opposite to that established in the two nearest adjacent lobes. Secondly, because the forces of the casting jets 7 and 7 'are then systematically enhanced by the central flux 10a which then rises in the same direction, recirculation loops L5 and L6 in the mold next to the meniscus 8 Will be strengthened. Thus, the “double roll” modes L5, L1, L4 and L6 appearing in the mold are thereby further stabilized.

  Thus, any liquid metal elements (conceptually separated at any point along the metallurgical length) must be re-dropped before the liquid metal is initially in the secondary cooling zone. If a continuous up or down flow at least once in the mold is randomly followed by a high probability and the liquid metal is initially selected to be in the mold, the reverse It will be easily understood. It will be appreciated that the entire liquid metal element will inevitably undergo a downward average movement in the direction of withdrawal with an average speed equal to the casting speed. In other words, this implementation of the present invention maximizes the exchange of molten metal material between the hot zone of the mold and the cold zone of the secondary cooling zone and stabilizes the “double roll” mode within the mold. Do this by strengthening the appropriate, known means.

  Specifically, such an exchange provides a better overheating heat without the risk of disturbing the flow mode in the mold, and instead by enhancing the stability of the “left-right” symmetry of movement on both sides of the nozzle. Contributes to the removal and initiation of early and sufficient equiaxed solidification of the metal, and there is any local mode, ie “double roll” (see FIG. 5) or “single roll” (see FIG. 6) Also contributes to doing so, thus suppressing the inherent random tendency to transition from one mode to the other.

  As described above, the branches 10 and 11 of the stirring intersection 9 are generated by the action applied to these points by the moving magnetic field. These magnetic force lines are perpendicular to the surface of the cast product or at least have a major normal component to maximize electromagnetic coupling with the liquid metal.

  It is well known that such a magnetic field can be easily generated by a conventional multiphase linear inductor.

  FIG. 7a shows a first embodiment of the present invention, where two collinear inductors 12 and 13 are arranged horizontally at the same vertical level on the casting machine on both sides of the casting axis (collinear inductor), and It is mounted in the opposite direction and generates a collinear magnetic field that moves transversely from the small side 18, 18 'towards the center over the entire width of the cast product.

  Advantageously, these inductors are arranged such that each inductor generates a moving magnetic field in the active convection branch (11a or 11b) having a length slightly shorter than half of the half width of the cast slab 6. Is done.

  In this case, the driving force for stirring is given by the transverse branches 11a and 11b where the stirring intersections gather, and then the flows 10a and 10b separated in the longitudinal direction are obtained after passing through the junction P.

  FIG. 7b shows a second type of implementation of the invention that is similar to the embodiment described above with respect to the effect obtained. According to this second embodiment, the linear inductors 14 and 15 mounted in the same line but in the opposite direction are arranged vertically along the casting axis. In this way, the vertical branches 10a and 10b (which is exactly the basis of the invention that this vertical branch is present in the secondary cooling zone) are then actuated directly and the upper inductor 14 is Then, a magnetic field is generated that moves toward the top of the casting machine in the direction of the mold, and the lower inductor 15 generates a magnetic field that moves downward toward the bottom of the pool.

  FIG. 8 illustrates a preferred embodiment of the present invention. This consists of converting the upper edge of the upper recirculation lobes L1 and L4 (strengthening the casting jets 7 and 7 ') into an active convection zone. To do this, two additional linear inductors 16, 17 that generate a horizontally moving magnetic field are added to the pair of inductors already present in the secondary cooling zone in order to generate the agitation intersection 9. . These two inductors are arranged on the same line on both sides of the nozzle 4 at the same level as the metal jets 7 and 7 ′ emitted from the discharge ports 5 and 5 ′, and from the nozzle to the narrow surfaces 3 and 3 ′ of the mold 1. And move in parallel with the jet. In this way, the effect of gathering between the jet and the central flow rising from the bottom is thus further enhanced, so that the local “double roll” mode in the mold is enhanced as well.

  FIG. 9 is similar to FIG. 5 but is fundamentally distinguished by the fact that the metal circulation direction in each of the four branches of the intersection 9 is reversed. Thus, FIG. 9 shows a second main embodiment of the present invention, which consists of generating opposite longitudinal collinear streams 20a, 20b in the central part of the casting 6, These streams gather together towards point P to provide a total circulation of liquid metal. This total circulation of the liquid metal extends through the mold 1 by the flow rising along the small side surfaces 18, 18 ′ to the same level as the metal jets 7, 7 ′ discharged from the nozzle outlets 5, 5 ′. They decelerate them as counterflow.

  Overall, there is again an agitation configuration in the secondary cooling zone consisting of four lobes L1 to L4, and the loop of that lobe therefore rotates in the opposite direction as the first implementation loop. However, due to the opposite direction effect of the upper lobes L1 and L4 on the jets 7 and 7 ′, the flow back to the bottom of the metal in the central part of the liquid pool is hardly countered and limited, instead the first It is more diffused and dispersed in the cast product than in the variant.

  It will be appreciated that these two main modes of operation are actually only two different and complementary aspects of the same invention and can appear together when implementing a stirring method. I will. In fact, from a dynamic point of view, it is possible to slow or accelerate the flow of the casting jets 7, 7 'as required by acting on local agitation in the secondary cooling zone away from these jets. As described above, for example, by reversing the polarity of the inductor that generates the magnetic field, it is easy to change the moving direction of the acting magnetic field.

  Thus, it is clear that the main advantage of the present invention is that it guarantees a good top / bottom exchange in the liquid pool, while at the same time acting remotely on the casting jet in the mold and the components are generally widely marketed. It can be done with a simple and uncomplicated configuration of the electromagnetic stirrer.

  As will be appreciated, the present invention, in summary, takes advantage of currently available electromagnetic stirring means to cut into two parallel strands in the longitudinal direction of the cast product within the secondary cooling zone, and within each strand. Forming a “butterfly wing” type stirring form. By doing this, an overall flow system is created in a secondary cooling zone of four lobes, whose core is a “stirring intersection” 9 with a center P.

  Preferably, for obvious reasons of symmetry, this division into two strands is made along the longitudinal axis of the cast product, since the median width of the cast product, ie the longitudinal axis generally coincides with the cast axis.

  Still, for example, the current intensity supplied to the inductors 12 and 13 is adjusted to be different so that the center position of the center P is directed toward one narrow surface 5 or laterally toward the other narrow surface 5 ′. In order to obtain a greater selection effect with respect to the movement in the mold on one side of the nozzle and therefore on the other side of the nozzle, the agitation force between the two lateral branches 11a, 11b is unbalanced. It is enough.

  Similarly, similar imbalances in the vertical branches 10a, 10b result in upward or downward movement from the center P of the agitation intersection without having to change the position of this apparatus in the caster using a given agitation device. Can be made.

  Obviously, if it is desired to be able to use both of these options to adjust the position of the center P of the agitation intersection, the four inductors 10a, 10b, 11a, 11b can be operated from four inductors so that they can be electromagnetically actuated. It is necessary to provide a secondary cooling zone for the device.

  Whatever the mode of implementation, the present invention does not appreciably interfere with certain advantageous effects for each of the stirring in the mold and in the secondary cooling zone, and without disturbing the local flow mode in the mold. In fact, stabilizing provides total agitation of the metal over a metallurgical length that can ensure both thermal and chemical uniformity between the top and bottom of the liquid pool.

  Needless to say, the present invention is not limited to the examples described above, but extends to many embodiments or equivalents, given their provisions given in the claims.

  Thus, for example, a conventionally used linear inductor has a planar structure, but this structure is just one desirable configuration. In addition, a curved inductor can be suitable to better match the shape of the slab surface at the point where the inductor is placed along the metallurgical length.

For the continuous casting of the slab through a submerged nozzle with a transverse outlet opening towards the narrow surface, for the continuous casting of the slab, in schematic form as a vertical central part parallel to the large face of the mold FIG. 2 is a standard diagram showing a known map of the circulation of liquid metal entering a mold. A straight line that is placed on either side of the nozzle on each large face of the mold and that generates a moving magnetic field that moves horizontally in pairs in opposite directions across the same large face (opposite to the metal ejection jet where the magnetic field is applied) FIG. 2 is a perspective view of a known in-mold electromagnetic stirring mode for continuous casting of a slab having a submerged nozzle with a transverse outlet (see FIG. 1) with a multiphase inductor. A straight line that is placed on either side of the nozzle on each large face of the mold and that generates a moving magnetic field that moves horizontally in pairs in opposite directions across the same large face (opposite to the metal ejection jet where the magnetic field is applied) FIG. 2 is a cross-sectional view of a known in-mold electromagnetic stirring mode for continuous casting of a slab having a submerged nozzle with a transverse outlet (see FIG. 1) by a multiphase inductor. A straight line that is placed on either side of the nozzle on each large face of the mold and that generates a moving magnetic field that moves horizontally in pairs in the opposite direction across the same large face (in the same direction as the metal ejection jet to which the magnetic field is applied) FIG. 2 is a cross-sectional view of a known in-mold electromagnetic stirring mode for continuous casting of a slab having a submerged nozzle with a transverse outlet (see FIG. 1) by a multiphase inductor. FIG. 6 is a simplified perspective view showing the slab during continuous casting so that the slab can be seen in the secondary cooling zone of the caster. This zone is horizontally opposed to each other on both sides of the cast product over the entire width of the cast product and to generate an electromagnetic stirring mode of the “rose fly wing” shape known, for example, from the aforementioned FR-7220546. It has a pair of linear inductors that generate a moving magnetic field. FIG. 4 is a view similar to FIG. 3 but illustrating a “triple roll” electromagnetic agitation mode generated, for example, by implementing the teachings of FR-8210844 described above. FIG. 2 is an overall view seen in an axially perpendicular part parallel to the large face of the mold for continuous casting of slabs, said mold having a submerged nozzle with a transverse outlet opening towards a narrow face Showing the principle of a four-leaf clover-shaped overall agitation in a secondary cooling zone according to one of the implementations of the present invention, wherein the opposite longitudinal streams move away from each other; FIG. 5 is a diagram showing a map of the circulating movement of the liquid metal generated by stirring in this zone under the mold. FIG. 6 is a similar view to FIG. 5, but in this case the in-mold flow mode is no longer a “double roll” type but a “single roll” type. FIG. 6 is a diagram showing a means for realizing a four-leaf clover-shaped stirring by a linear inductor having a magnetic field moving in the horizontal direction based on the repetition of FIG. 5. FIG. 7a shows another embodiment that is similar to FIG. 7a but implements the present invention, where a linear inductor with a magnetic field moving in the vertical direction is used. FIG. 5 shows a preferred embodiment of the present invention based on the repetition of FIG. 5, in which a complementary inductor flow in a “double roll” mode is generated by a linear inductor that generates a horizontally moving magnetic field. The moving magnetic field directly acts on the metal jet emitted from the casting nozzle outlet. Fig. 3 shows another implementation of the invention, which consists of producing streams in the central part of the cast product that are opposite to the longitudinal direction of the metal, and these streams collect no longer branching.

Claims (10)

A method of electromagnetic stirring in a secondary cooling zone in a plant for continuous casting of elongated cross-section metal products, wherein the mold comprises an immersed casting nozzle with a transverse outlet directed towards the narrow face of the mold The stirring method is performed by a moving magnetic field generated by a multiphase inductor disposed near the cast metal,
For the purpose of facilitating the exchange of liquid metal in the liquid pool (6) between the secondary cooling zone (2) and the mold (1), a longitudinal metal flow is introduced into the secondary cooling zone. Forcedly established, the longitudinal metal flow is confined locally as two opposite collinear streams (10a, 10b, or 20a, 20b) in the central region of the cast product As a “four-leaf clover” configuration with a lobe and two lower lobes, it provides liquid metal circulation, the upper lobes (L1, L4) being the outlets of the immersed casting nozzle (4) ( 5. Stirring method, characterized in that it extends into the mold to the level of the jet (7,7 ') exiting from 5,5').   The longitudinally opposite collinear streams (10a, 10b) moving away from each other in the central region of the cast product are jets (7, 7) from the outlet (5, 5 ') of the casting nozzle (4). , 7 '), the two upper lobes (L1, L4) extending into the mold to the level are generated to flow and merge in the same direction as the jet to strengthen the stream, The stirring method according to claim 1.   The longitudinally opposite, collinear streams (20a, 20b) of the central region of the cast product that gather together are jets (7, 7) emitted from the discharge ports (5, 5 ') of the casting nozzle (4). The two upper lobes (L1, L4) extending into the mold to the level of ') are generated to overlap in a flow opposite to the jet to decelerate the stream. 2. The stirring method according to 1.   2. Stirring method according to claim 1, characterized in that the position of the longitudinal flow in the secondary cooling zone is moved laterally towards one or the other of the small sides of the cast product.   The longitudinal metal flow is generated as two collinear streams in two opposite directions by a collinear moving magnetic field moving longitudinally in the central region, moving together or moving further apart. The stirring method according to claim 2 and 3.   The longitudinal metal flow moves transversely across the entire width of the cast product moving closer together from the end of the cast product towards the center or moving further away from the center of the cast product towards the end. 4. Stirring method according to claims 2 and 3, characterized in that it is generated as a collinear stream in two opposite directions by a collinear magnetic field.   The stirring method according to any one of claims 1 to 6, characterized in that the moving magnetic field is generated by a multiphase linear inductor arranged opposite to a large surface of a cast product.   The stirring method according to claim 7, wherein the multiphase linear inductor is supplied with currents of various strengths.   Another moving magnetic field is also used, which acts directly on the metal jet (7, 7 ') emitted from the outlet (5, 5') of the casting nozzle (4) in the mold (1). The stirring method according to any one of claims 1 to 8.   A flat metal product obtained from a continuous casting plant, wherein the secondary cooling zone is in the position of electromagnetic stirring operation as claimed in claim 1.

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