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
  • 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
• • 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
  • B22D11/16—Controlling or regulating processes or operations
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/02—Use of electric or magnetic effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like
  • B22D41/50—Pouring-nozzles
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C9/00—Alloys based on copper

Definitions

• the invention relates to the continuous casting of metals, in particular steel, in the form of slabs, or any other similar elongated flat product.
• FIGS. 1A and 1B Attached at the end of this memo. These figures show the stabilized shape of the trajectories of the main currents in a vertical plane passing through the casting axis and parallel to the two large faces of an ingot mold for continuous casting of slabs.
• the "single loop" mode (fig. 1A) essentially translates, as can be seen, by the fact that the metal jets 1 direct as soon as they exit from the gills 2 of the nozzle 3 rather upwards in the direction of the free surface (or meniscus) 4 of the metal cast in the mold.
• each jet 1 is then generally reflected downwards in the direction of the extraction of the cast product represented by the thick vertical arrow in the middle of the figure.
• the precise mapping of speeds is much more complex.
• the real mapping is much more complex, but it is this global image in "butterfly wings" which marks the observer facing the screen of a modeller or in front of a model operating in "double loop” mode.
• the operator of the continuous casting machine generally does not have the means to know the stable flow mode of the metal within its ingot mold. Moreover, most often, it must be recognized that he does not care, since in any case, he could not and could not intervene on the cast format or on the extraction speed, which are imposed by the order book and material flow within the factory.
• the object of the present invention is to offer the operator of the continuous slab casting a simple and efficient tool, added to his machine without having to reconsider its design, to enable it to be assuredly in "double loop” mode without modifying the setting of the casting parameters in any way.
• the invention relates to a process for controlling the configuration of the flows of the metal cast in a mold for continuous casting of metal slabs or other similar flat product, in particular steel, using a submerged nozzle provided with side outlet openings facing the small faces of the mold, said configuration being able to be in “single loop” or “double loop” or “unstable” mode, a process characterized in that the works of sliding magnetic fields acting, in an ingot mold at the height of the nozzle, on the flows of liquid metal arriving in the ingot mold by the gills of the nozzle, said fields being produced by polyphase linear electromagnetic inductors arranged opposite at least one face of the ingot mold on either side of the nozzle so as to install or stabilize a configuration in "double loop” mode.
• magnetic fields sliding horizontally outward are used, in the direction going from the nozzle towards each small face, by means of inductors arranged facing at least one large face of the ingot mold on either side of the nozzle.
• the sliding magnetic fields are made to act during the entire casting operation.
• the sliding magnetic fields are made to act only if the configuration of the movements is not naturally already in "double loop” mode. Additionally, if the configuration is already naturally in mode
• double loop horizontally sliding magnetic fields are made to act by means of inductors arranged opposite at least one large face of the ingot mold on either side of the nozzle in accordance with the preferred embodiment variant explained below. before, but the said inductors are adjusted so that the fields produced by each of them all slide in the same direction so as to impart to the liquid metal in the ingot mold an overall movement of rotation around the casting axis.
• the invention also relates to an installation for implementing the method according to said preferred embodiment comprising at least one pair of linear electromagnetic inductors with sliding magnetic field, mounted facing at least one large face of the mold. and oriented to produce a field magnetic sliding horizontally, and a polyphase controlled electrical power supply connected to the inductors to make them each produce a magnetic field sliding in a direction going from the nozzle towards a small face of the mold.
• the invention makes use of a well-known and, if one may say, commercially available means, the mobile magnetic field produced by a linear polyphase static inductor , to act dynamically on the liquid metal within the ingot mold in order to establish a "double loop" flow mode, or to stabilize it if it is already naturally present.
• JMHD magnetohydrodynamics
• the aim was thus to promote a solidification structure of the equiaxial type from the mold, as well as the improvement of subcutaneous cleanliness by washing the solidification front with the ascending currents of liquid metal taking with them the gas bubbles formed in situ and non-metallic inclusions up to the meniscus where they are fixed by the covering slag which floats.
• the European Patent Application published under No. 0.151.648 describes the possible choices between vertical mixing of the metal in the mold at using vertically sliding magnetic fields from bottom to top to improve the surface cleanliness of the cast product, and horizontal stirring using horizontally movable fields to then improve subcutaneous inclusion cleanliness by a forehead washing effect solidification.
• KSC European Patent Application published under No. 0.151.648
• fields sliding horizontally inwards, in opposite directions from the jets coming from the nozzle, therefore from the small faces towards the nozzle would be favorable for obtaining an inclusive cleanliness situated deep under the skin. solidified.
• this operating mode of magnetic fields sliding horizontally outward and acting in height at the gills of the nozzle on the incoming metal jets is like a preferred variant of what the invention proposes to do systematically during the entire casting, but, in this case, to impose a stable mode of circulation in "double loop" convection movements of the molten metal within the ingot mold.
• FIG. 2 is a statistical graph established from a compilation of real data and making it possible to determine as a function of the casting parameters that are the casting speed on the abscissa and the width of the slab casting on the ordinate, the operating domains naturally stable in "single loop” -domain S- and in "double loop” -domain D-.
• Triangles are “single loop” type events; the diamonds are “double loop” type events.
• the data corresponding to naturally unstable events, randomly switching from an S to D mode or from D to S have not been carried.
• FIG. 3 is a general schematic view of what an ingot mold for continuous casting of slabs equipped with the means of the invention
• - Figure 4 is a view similar to that of Figure 3 but showing a little more detail the technology of linear inductors sliding field usable
• - Figure 5 is a block diagram, showing seen from above the ingot mold the mode of action of the sliding field inductors implemented according to the invention
• FIG. 6 shows, coming from a computer simulation by calculation model, three pairs of diagrams A, B, C, arranged one above the other, and each representing the characteristics of the convection movements within a slab ingot mold with different values of the intensity of the sliding magnetic fields applied in accordance with the invention.
• the same elements are designated with identical reference numbers.
• FIGS. 1A and 1B have already served to illustrate the definitions given in the introductory part of this memo of what is to be understood under the terms of "single loop” and “double loop” in the context of the invention.
• the domains S and D corresponding respectively to the two types of stable natural recirculation “Single loop and” Double loop ", are separated by a double P line in broken lines slightly oblique with respect to This dividing line P makes it easy to see that the natural "double loop” recirculation mode, domain D, is rather reserved for high casting speeds, say greater than 1.4 m / min, and whatever the width of the casting strip, while below about 1.2 m / min, we are almost always in the S domain of the "single loop".
• the dotted line of general hyperbolic appearance R represents a reference flow with a constant metal flow rate of 4.6 tonnes / min, (product between the casting section and the casting speed if it is assumed that the level in meniscus height hardly fluctuates around a fixed value during casting).
• the separation line P translates to the left, widening the area of the "double loop" when the immersion depth of the nozzle increases or, if an argon bubbling is used to avoid the risks of clogging of the nozzle (flows of low or very low carbon grades calmed with aluminum for example), when the flow of argon decreases.
• the implementation of the invention consists in fact in making the line P disappear by translating it to the left until it is ousted from the diagram.
• an ingot mold 18 can be seen for the casting of steel slabs 9 consisting essentially of two pairs of plates of copper, or of copper alloy, vigorously cooled by circulation of cooling water: a pair of large plates facing each other at a distance defining the thickness of the slab: these are the large faces; and a pair of small plates, mounted in a leaktight manner at the end of the large plates in order to ensure the continuity of the internal periphery of the mold which defines the casting space.
• These lateral closing plates of the pouring space are the small faces.
• the ingot mold is supplied with fresh metal by a submerged nozzle 3 centered on the casting axis A and the upper end of which is tightly connected to the opening made in the bottom of a distributor not shown.
• a submerged nozzle 3 centered on the casting axis A and the upper end of which is tightly connected to the opening made in the bottom of a distributor not shown.
• the free lower end of the nozzle is provided with lateral outlet holes, diametrically opposed, and plunges into the mold at an adjusted depth (about forty centimeters below the upper edge copper plates), with an angular orientation adjusted so that each hole is turned opposite a small face 5 of the mold.
• the means for implementing the invention are clearly visible in the working position in FIG. 3. They consist of an electromagnetic unit 10 connected to a polyphase electrical supply 11, preferably three-phase.
• the power supply 11 has thyristors in order to be able to vary the frequency of the current by acting on the thumb wheel 12 on the front panel.
• Another knob 13 allows him to adjust the intensity of the current.
• the electromagnetic unit is formed by four linear inductors, preferably identical, of the flat stator type of an asynchronous motor.
• linear inductors are grouped in pairs, a pair of inductors 14.14 '(and 15.15') per large face of the ingot mold.
• the two inductors of the same pair, for example the pair 14, 14 ′, are mounted on the same large face, but on either side of the nozzle 3 in a preferably symmetrical relative position.
• These two inductors 14, 14 ′ can be independent of each other mechanically and electrically.
• each inductor is of the "salient magnetic pole” type therefore wound, or of the "distributed pole” type, are themselves polyphase and compatible in this respect with power supply 11 so that each can be connected to the terminals of this power supply in an adequate sequential phase order ensuring the sliding of the field in the desired "outward" direction.
• the field itself, generated by this inductor is generally perpendicular to the plane of this face.
• it is the component perpendicular to this face which is the only active in the production of useful energy in the form of a metal driving force in the direction of the sliding of the field. It is therefore advantageous, in order to maximize the energy efficiency of the operation, to have inductors whose lines of force of the fields produced are orthogonal to the plane of the faces and which they thus propagate as far as possible inside. metal to be poured.
• a second pair of inductors is added, such as 15.15 'facing each other on the other large face of the ingot mold.
• the power supply 11 then supplies these inductors added in phase opposition with respect to the inductors 14, 14 'facing taken in this order, so that the fields produced by two inductors facing each other on the two faces opposite of the ingot mold, in this case 14 and 15, or 14 'and 15', are in the same direction and therefore add up, at any point in the space of the gap thus formed, to constitute a magnetic field passing through the product poured right through, and the advantage of which is known with respect to a longitudinal field since the intensity at the center of the product is hardly lower than in the vicinity of the inductors.
• FIG. 4 makes it possible to offer a slightly more detailed view of a technological embodiment of the inductors. They are mounted, as can be seen, in the upper cooling water chamber 16 of the mold (drawn in thin lines) in order to benefit from the cooling effect, but also to be able to bring the polar active faces 17 closer together. cast metal.
• each inductor • carries visible ribs 19, 19 ', 20, intended to ensure the fastenings and alignments necessary between them and to adjust their height position by taking in corresponding support grooves in the supporting frame of the casting machine (not shown).
• FIG. 6 which we now refer clearly illustrates the benefit derived from this control.
• Each diagram A, B, or C presents, in its window on the left, the trajectories of the convection current lines of the metal chosen arbitrarily in the right half-space of casting of an ingot mold with slabs, contained on the abscissa L between the casting axis A and the small end face 5, and developing over the height h of the mold from the meniscus 4 (ordinate 0) to a depth of 70 cm.
• the associated graph on the right gives the corresponding values of the speed "s" of the metal on the ordinate at the meniscus 4 on the median measurement line which connects the outlet port 2 of the nozzle to the small opposite end face 5 placed on the abscissa.
• This speed is counted algebraically, with a positive sign when the direction of the currents goes from the nozzle to the small face and therefore negatively in the opposite direction.
• each couple is representative of a different value of the intensity of the magnetic field acting.
• Torque B is associated with an average magnetic field intensity value, corresponding to an excitation current of inductive windings with effective intensity i of 250 A.
• Couple C illustrates the situation when the applied magnetic field is produced at an intensity of current i of 450 A.
• diagram B shows that nothing happens significantly different from the previous situation. Note, however, on the velocity diagram a slight decrease in the positive speed peak (region of the meniscus to the right of the point of inversion M), therefore a slight displacement of this point M towards the small face 5, which expresses in made a start in favor of establishing the desired "double loop” circulation mode.
• This "double loop" mode is in fact fully obtained with an intensity of the excitation current of the inductors of 450 A eff., As shown in diagram C. In fact, the reversal point has this time completely disappeared to make room for a profile of negative values along the meniscus.
• the very principle of the operation of polyphase plane inductors with sliding field is that of the asynchronous motor: it is the speed differential between the sliding magnetic field and the current of liquid metal, on which it acts to entrain it in its displacement, which precisely determines the driving force of the metal.
• the implementation of the invention will have the advantage of stabilizing it, regularizing it, even moderating it if necessary . It is indeed enough for that to intervene on the adjustment of the excitation current frequency.
• the sliding speed of the mobile magnetic field that it generates is indeed, as we know, proportional to the frequency of the field's pulsation, therefore of the electric current which produces it by traversing the inductor windings. Consequently, the invention will allow the need to automatically calm an overly vigorous meniscus recirculation loop, by choosing a frequency of the excitation current such that the speed of movement of the fields is lower than that of the metal current at the meniscus.
• the intensity of the magnetic field is regulated by the choice of the intensity of the exciting current; its sliding speed is adjusted via the frequency of this current; and the direction of the sliding of the field is adjusted by an ad hoc connection of the windings of the inductor to the phases of the electrical supply.
• Figure 2 constitutes in this respect a precious graphic aid which will easily allow the operator to know straight away if it is naturally located, or if it is likely to be already located, in a single or double configuration. loop.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Continuous Casting (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Casting Support Devices, Ladles, And Melt Control Thereby (AREA)
• Engine Equipment That Uses Special Cycles (AREA)

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• 2002
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