WO2002094477A1

WO2002094477A1 - Electromagnetic equipment for ingot mould head for continuous metal casting in elongated quadrangular formats

Info

Publication number: WO2002094477A1
Application number: PCT/FR2002/001735
Authority: WO
Inventors: Jean-Marie Galpin; Jean-Yves Lamant; Pascal Gardin
Original assignee: Usinor
Priority date: 2001-05-23
Filing date: 2002-05-23
Publication date: 2002-11-28
Also published as: FR2825040B1; FR2825040A1

Abstract

The invention concerns an electromagnetic equipment comprising an inductor (10) enclosing the ingot mould and placed at the meniscus (7) of the cast metal to generate an axial alternating current magnetic field, said field being associated with a transverse direct current magnetic field generated by an electromagnet (20) whereof the magnetic poles (21, 22), located behind the two large sides (3, 3') of the ingot mould, face each other on either side of the cast product at the level of the meniscus likewise. The inductor generating the axial alternating current magnetic field consists of two linear conductors (11, 11') mechanically independent of each other, and arranged each along the width of each large size (3, 3') of the ingot mould, between said large side and one of the poles (21, 22) of said electromagnet (20). Such an equipment, designed to stabilise a meniscus (7) in a marked convex shape, enables the width of the cast semi-finished products to be modified.

Description

ELECTROMAGNETIC EQUIPMENT FOR CONTINUOUS CASTING LINGOTIERE HEAD OF METALS IN LONG QUADRANGULAR FORMATS

The present invention relates to the continuous casting of metals, steel in particular, into semi-finished products of elongated quadrangular format, such as slabs. More particularly, the invention relates to the application of electromagnetic forces in the upper region of the mold, where the meniscus of the poured liquid metal is established.

By "elongated quadrangular" format is meant to qualify the semi-finished products (and, in an equivalent manner, the corresponding ingot molds) whose cross section,

10 elongated rectangular, has large sides (or large faces) at least three times longer than the other two sides (or small end faces). For convenience later, these elongated formats will be designated under the single term "slabs". By "meniscus" is conventionally designated the border area of the upper surface of the cast metal in contact with the cooled metal wall of the mold, generally

15 made of copper or a copper alloy, this upper surface being either left free or more generally covered with a slag.

It is now considered that in order to increase the productivity of continuous slab casting machines, it has become necessary to act simultaneously in the two directions of increasing the product casting speed, as well as

20 improvement of the skin quality and internal inclusiveness of the cast product.

Electromagnetic forces have been used for many years in continuous casting of steel in an attempt to increase the productivity of machines by improving the quality of the product and increasing the speed of casting.

25 We will mention in this regard the abundant literature published over the past twenty years on the subject of electromagnetic mixing of the metal cast within the mold using inductors placed behind the walls of cooled copper of the mold. A desired effect of stirring is a faster evacuation of the overheating of the cast metal, making possible an increase in the casting speed, as well as an improvement

30 of inclusive cleanliness by washing the solidification front with liquid metal set in motion.

A technique is also known, known as the "electromagnetic brake", which has been developing for a few years and which consists in subjecting the cast product to a continuous through magnetic field directed perpendicularly to the large faces of the

35 ingot mold, therefore orthogonal to the casting axis, and placed at a distance under the meniscus. This field, which thus "separates" the casting space of the ingot mold into two superimposed compartments, makes it possible to reduce in one of the compartments the hydrodynamic disturbances of the liquid metal present in the other, in particular those coming from the casting jet.

40 It will also be mentioned that, in the case of a continuous casting mold under load

(i.e. surmounted by a refractory weight containing metal kept in the state liquid) electromagnetic confinement attempts have been proposed. An axial alternating magnetic field is generated by an induction coil surrounding the product poured about twenty centimeters below the meniscus where the refractory-copper junction of the ingot mold is located. The aim is thus to create a vertical artificial meniscus by causing an electromagnetic necking at this location which moves the skin away from the metal poured from the copper wall of the ingot mold and thus in particular improving the skin quality by reducing, or even eliminating wrinkles. oscillations. However, one of the major difficulties linked to this type of technique resides in the geometric instability of such a confinement meniscus, an instability which is far too random to be compatible with the requirements of industrial practice.

An advance towards a solution to such a problem is described in the French Patent Application in the name of the Applicant published under the number 99-14816. Schematically, this involves, in a conventional continuous casting ingot mold (without counterweight), superimposing on the axial alternating magnetic field a transverse continuous magnetic field passing right through the cast product perpendicular to the casting axis at the meniscus of the continuous casting mold. The axial alternating field retains its function of confining the meniscus by necking by pushing the liquid metal from the walls of the mold, while the orthogonal continuous field added has the function of damping the disturbances of the meniscus due to this alternating field, as well as to stabilize what is customary to call the line of first solidification that the cast metal draws by its meniscus on the inner periphery of the mold.

The effects of the superposition of an axial alternating magnetic field and a transverse continuous magnetic field on the deformation of the meniscus in the mold (formation of a dome) and on the damping of the level fluctuations of this meniscus were tested and measured on a scale, 1/3 scale, operating with mercury. The results obtained showed that the dome height could reach 20 to 30 mm depending on the frequency values (250, 1500 and 20000 Hz) and the strength of the continuous field used, and that the rate of damping of the meniscus level fluctuations was included in 50 and 100% depending on the location of the measuring point on the meniscus. It has thus been observed that the transverse continuous magnetic field applied to the meniscus greatly reduces the following movements:

1- the electromagnetic stirring resulting from the presence of the axial alternating magnetic field used to locally form and stabilize the meniscus. This mixing forms swirls of horizontal axes located near the faces of the mold in the convex part of the meniscus, have velocity components perpendicular to the continuous magnetic field which undergo effective braking. At the meniscus, the main speed component of the metal, due to the ingot mold being fed by the submerged nozzle, is perpendicular to the magnetic field applied and therefore also undergoes a braking effect, 2- movements associated with deformations of the liquid-dairy steel interface, such as progressive or stationary waves which affect the stability of the meniscus and the first solidification line.

The alternating magnetic field is generated by a conductor inductor completely surrounding the ingot mold and placed high in the meniscus region. The orthogonal continuous field is itself generated by an electromagnet, the poles of which, placed along the large faces of the mold face each other on either side of the product cast at the level of the meniscus also. Figure 1 given at the end of this thesis schematically shows such equipment mounted in the upper part of a mold for continuous casting of slabs within the cooling circuit thereof.

Equipment of this type is, however, relatively complex from a technological point of view and not very easy to install on the upper part of a continuous casting ingot mold, in principle not intended to receive it. In addition, it is frozen in its realization once and for all and can therefore only be used for a given mold of single format in cross section, while semi-finished products in elongated formats of varied and multiple dimensions are usually continuously cast. The primary object of the present invention is to propose an answer making it possible to resolve such handicaps and aims in particular to propose modular equipment according to the size of the cast products.

To this end, the subject of the invention is an electromagnetic equipment for the mold ingot head for continuously casting metals in elongated quadrangular formats, such as slabs, comprising an inductor surrounding the ingot mold and placed at the meniscus to generate an alternating magnetic field. axial, said field being associated with a transverse continuous magnetic field created by an electromagnet, the poles of which, placed behind the two large faces of the mold, face each other on either side of the product poured at the level of the meniscus also, equipment characterized in that the inductor generating the axial alternating magnetic field consists of two linear conductors, mechanically independent of each other, and each housed on one of the large faces of the mold according to the width of these ci, between the cast product and a pole of said electromagnet.

According to an alternative embodiment, these two conductors are electrically connected in series with one another by their end situated in the vicinity of the same small face of the ingot mold, their other end being each connected to one of the opposite terminals of an electrical supply. alternating current.

According to another alternative embodiment, the two conductors are electrically independent of each other, each having its two ends ^* connected to the two opposite terminals of an electrical supply so that the electric current flows in the same direction at same time in each of the two conductors.

In accordance with a preferred embodiment, each linear conductor is a bar formed by assembling, in a parallel bundle, a plurality of tubular metallic elements, of copper or aluminum, cooled by internal circulation of a cooling fluid (of preferably water), said bar being rigidly fixed in the water box of the large faces of the mold at the level of the meniscus of the cast product.

As will be understood, the invention resides in the fact that, as a counterpoint to the known technology based on the principle of a rigid inductor completely surrounding the ingot mold, the vertical alternating field is generated only on the large faces of the mold. If necessary, this field can be oriented and concentrated towards the small faces using added magnetic yokes taking place on each small face of the ingot mold in line with the linear conductors. The alternating field is then produced using two independent conducting bars each housed in a notch provided for this purpose on the cold wall of each large face of the mold. The invention will be well understood and other aspects and advantages will appear more clearly in the light of the description which follows, given by way of example of embodiment, with reference to the plates of attached drawings in which:

- Figure 1 is a block diagram based on a vertical sectional view of the upper part of a slab ingot mold equipped with an electromagnetic device according to the prior art coming from document FR-A-9914816 already mentioned in the part introductory ^" to this memo;

- Figure 2 is a 3D representation in elevation, oblique view from above and partially cut away in the foreground, of a mold similar to that of Figure 1, but in the case of equipment according to the invention. - Figure 3 is a schematic view showing from above the relative arrangement of the two conductive bars electrically connected by one of their ends according to an alternative embodiment of the invention;

- Figures 4a and 4b shows in detail, viewed respectively in cross section and in longitudinal section, the constitution of the linear inductors according to the invention in a preferred embodiment;

- Figure 4 is a 3D representation viewed obliquely from above and partially cut away from one end of the mold showing the connection at the end of the current bars.

In these figures, the same elements are designated by identical references. In itself. referring again to FIG. 1 schematically illustrating the state of the known technique closest to the invention, it can be seen that the active part 1 of the ingot mold, namely its central part, the only one shown in this figure, is formed of two large opposite flat faces 3, 3 'and two small equally flat end faces of which only the small face 4 in the background is shown in the figure. These elements, joined at the end at a right angle in a leaktight manner, define between them a casting space 5 of elongated quadrangular shape for the casting of steel slabs. In this casting space, the molten metal will be introduced from above by a submerged vertical nozzle 8, mounted in the bottom of a not shown distributor placed at a distance above. The cast product, solidified only at the periphery in the mold, will be continuously extracted from the mold down in the direction of casting symbolized by the axis casting A. It is moreover in this direction that the mold will be animated during the entire casting operation with a vertical oscillation movement 6 of small amplitude necessary for the quality of the sliding contact between the skin of the cast product and the inner wall of the mold. 7 shows the meniscus of the molten metal kept level within the mold throughout the casting.

The walls of the ingot mold, conventionally made of copper or a copper alloy, are vigorously cooled by vigorous circulation of a coolant, generally treated water, along their outer surface (cold face). This cooling water circulates against the walls from a lower introduction chamber to an upper evacuation chamber.

By focusing momentarily on the more complete representation of the mold shown in Figure 2, we see that the upper water chamber 28 occupies most of the height of the mold, the lower water chamber 29 serving primarily to distribute the 'arrival of water at the base of the mold uniformly according to the width of the large faces. An outer jacket 27, constituted by a thick steel counter-plate and laterally provided with inlets and outlets 32 of cooling water, remotely doubles the copper walls of the ingot mold to define these water chambers. The assembly is completed by an upper cover 30 and by a lower bottom plate 31 mounted leaktight at the ends of the mold. These generalities recalled, we will now endeavor to describe the electromagnetic equipment mounted at the level of the upper water chamber in the meniscus holding zone 7 on which it must act.

Firstly, reference will again be made to the known technology illustrated by the diagram in FIG. 1. The continuous magnetic field, directed orthogonally to the pouring axis A and crossing the large faces 3 of the mold at the meniscus , is generated by an electromagnet 20. Each of its two constituent coils 20a and 20b, with opposite polarities, is of oblong shape so as to extend over all or almost all of the width of the large faces 3, 3 'of the ingot mold. Each coil receives a rectilinear soft iron magnetic core 24, the free ends of which are preferably end caps of vertically laminated structure. This lamination makes it possible to avoid excessive heating of the pole pieces by the Joule effect of the induced currents formed by the alternating axial magnetic field which will be discussed later. These free ends form magnetic poles 21 and 22 which establish between them the transverse magnetic field (horizontal in the figure) in which the meniscus 7 of the cast steel is placed. Thus, the poles 21, 22 are placed along the large walls 3 and 3 'of the mold and face each other on either side of the cast product, at the height of the meniscus. These two poles are connected to the steel frame 23 of the mold to form a cylinder head for closing the magnetic circuit, as described in the aforementioned French patent application and which can be referred to for additional information on the production of the electromagnet, if desired.

Furthermore, according to this known technology, also visible in this figure 1, the alternating axial magnetic field (frequency between about 0.1 and 100 kHz) is itself generated by an inductor 10 formed by continuous wired electric conductor wound in turns completely surrounding the ingot mold and placed at the meniscus 7 of the poured liquid metal, therefore in the air gap of the electromagnet 20.

In accordance with the technology according to the invention on the other hand, the inductor with alternating axial magnetic field, visible first of all on the overall view of FIG. 2 to which we are now going, is formed essentially, no longer by a winding of encircling turns, but by two rectilinear bars 11 and 11 'each equipping a large face of the mold. Each bar is oriented horizontally so as to be able to extend over the width of the large face which receives it. Its installation is carried out by partial engagement in a recess 26 of corresponding shape specially machined for this purpose in the usual metal counterplate 36. This is firmly applied against the large face 3 (or 3 ') associated in order to delimit between them watertight pipes for cooling water circulation. As shown in the figure, the blocking in position of the bar 11 (and 11 ') can advantageously be done by coming into abutment bearing on the pole face 25 of the pole 21 (or 22) of the electromagnet. This pole face 25 is consequently shaped in the form of a "" to come to marry the bar 11 while also coming to apply against the jacket 36, which has the effect of maximizing the electromagnetic efficiency of the electromagnet 20.

As will be noted, the coils 20a and 20b of this electromagnet are offset at a distance behind the peripheral mantle 27 outside the upper water chamber 28. The magnetic core 24 channeling the lines of force of the magnetic field produced by these coils up to the added laminated poles 21, 22 (silicon steel sheet) here is a pole piece shaped as an "S", the other end of which extends beyond the coil associated with it as far as the cylinder head 23 of the magnetic circuit surrounding the ingot mold and which in this case also serves as a support frame for the ingot mold. The assembly of the different parts constituting each pole piece ensures the assembly and disassembly of the electromagnet on the mold as well as the adjustment in the casting position of the large faces of the mold.

We now consider again the means of the invention for producing the axial variable magnetic field.

The linear inductors 11 and 11 ′ can be supplied electrically independently, each having its two ends connected to the two opposite terminals of a power supply so that the electric current flows in opposite directions at the same time in each of the two conductors. As shown in the diagram in Figure 3, however, they can also be switched on. In the latter case, the electrical connection between the two inductors can be done very simply by flexible connections 33 associated with connectors 35 mounted at the end of the bars 11, 11 ', located in the vicinity of the same small face of the mold, their the other end being each connected to one of the opposite terminals of an alternating current power supply. Preferably, the connection between the bars 11 and 11 ′ will be made by a semi-rigid circuit integrated in the frame of the continuous casting machine, as will be seen with reference to FIGS. 5 and 4a

The primary purpose of this technological solution is, as already pointed out, to allow changes in width of the mold during casting (or at a standstill of course), while limiting the losses of electrical energy by increasing reactive power.

The integration of the inductor bars 11, 11 'in the water box 28 of the large faces of the ingot mold also makes it possible to bring them closer to the casting space 5. This has the effect of increasing the maximum intensity of the magnetic field axial available in the mold with constant electrical power.

In the case of the use of complementary magnetic yokes 34, 34 ', intended to ensure a minimum of alternating field in the area of the small faces 4, 4' of the mold), these can be integrated or not in the box with water from said small faces. In any case, they will be positioned in line with the linear conductors 11 and 11 ′, as shown in FIG. 3 and their shape is defined so as to obtain the best possible deviation of the alternating field towards the interior of the small faces. The truncated and widened "V" shape shown in Figure 3 is generally well suited in this regard. These cylinder heads will be cooled either by the water circulating in the water box (if they are integrated into it) or by a specific water circuit. ) from the mold to the right of the linear conductors (11, 11 ').

As shown in FIGS. 4a and Ab, the current bars 11, 11 ′ can advantageously be formed by a parallel bundle 40 of tubular conductors 41 internally cooled by circulation of a cooling fluid, for example water. This beam can be embedded in an insulating resin matrix 42 which will ensure mechanical cohesion. At each end, a drilled manifold block 43, for entering / leaving the water, is provided ensuring the interface with the pipes 44 for supplying and leaving the water.

In the embodiment presented, the current bar 11 thus formed is kept fixed in its housing 26 machined in the plywood 36 by virtue of the magnetic pole 21 of the electromagnet which is just screwed onto the plywood using studs 37 and the pole face 25 of which has been profiled in "L" shape to cover the part of the bar 11 protruding from the housing 26. The ply plate 36 is it rigidly assembled to the copper plate 3 constituting the large face of the ingot mold using tie rods engaged in lashing tips 39 incorporated in the plate 3.

As shown in Figures 4a and 5, the copper block 43, 43 'also serves of electrical connection end of bars 11 and 11 '. To this end, it offers a flat front face 45 on which the tubular conductors 41 are welded at their end. The face 45 is perforated in correspondence in order to present a calibrated orifice opposite each tube 41. Thus, the coolant is channeled inside the drilled block towards the bent collectors of which only the horizontal branch 44, 44 'is visible in FIG. 4a, the vertical branch extending vertically from the base of the block 43, 43 ′ not having been shown. The drilled block 43, 43 ′ has, opposite its front face 45, a U-shaped projection slightly bent towards the outside of the ingot mold and forming an easel 46, 46 ′. In this easel, is housed the flat end of copper bars 48, 48 ', the assembly being carried out using transverse tightening bolts 49, 49'. These bars 48, 48 ′ have a return function making it possible to connect the drilled block 43, 43 ′ to a vertical bus 50, 50 ′ also made of copper. A copper plate 51 bridges the two buses 50 and 50 ', thus completing the rigid electrical circuit which connects the two current bars 11 and 11' by their ends situated in the vicinity of the small face 4 of the mold. Similar easel blocks are mounted at the other end of the bars 11 and 11 ′, therefore in the vicinity of the other small face 4 ′ (and of its plywood 54), in order to ensure the electrical connection with the arrival and departure of current from a power supply not shown. It will be noted that the return bars 48, 48 ′ and the associated vertical buses 50, 50 ′ are also cooled by an internal circulation of water, the inlet / outlet pipes 52, 53 of which are mounted on the chassis 23 itself. the ingot mold. It will also be noted that the steel counterplates 54 of the small faces 4, 4 ′ can act as complementary magnetic yokes 34.

It goes without saying that the invention cannot be limited to the exemplary embodiments described above, but that it extends to multiple variants or equivalents insofar as its definition is respected as given by the appended claims.

Claims

1) Electromagnetic equipment for ingot mold head for continuous casting of metals in elongated quadrangular formats, such as slabs, comprising an inductor (10) surrounding the ingot mold and placed at the meniscus (7) of the cast metal to generate an alternating magnetic field axial, said field being associated with a transverse continuous magnetic field created by an electromagnet (20) whose magnetic poles (21, 22), placed behind the two large faces (3, 3 ') of the mold, face each other on both sides of the product poured at the level of said meniscus also, equipment characterized in that said inductor generating the axial alternating magnetic field consists of two linear conductors (11, 11 '), mechanically independent of one another , and each arranged along the width of each large face (3, 3 ') of the mold, between said large face and one of the poles (21, 22) of said electromagnet (20).

2) Equipment according to claim 1 characterized in that said two conductors (11, 11 ') are electrically connected in series with one another by their end using connectors (35) located in the vicinity of the same small face (4) of the mold, their other end being each connected to one of the opposite terminals of an alternating current power supply.

3) Equipment according to claim 1 characterized in that said two conductors (11, 11 ') are electrically independent of each other, each having its two ends connected to the two opposite terminals of an electrical supply so that the electric current flows in the same direction at the same time in each of the two conductors.

4) Equipment according to claim 1 characterized in that it further comprises complementary magnetic yokes (34, 34 ') in the vicinity of each small face (4, 4') of the mold in line with the linear conductors (11, 11 ').

5) Equipment according to claim 1 characterized in that each linear conductor (11, 11 ') is formed by a bar produced by an assembly (40), in parallel beam, of a plurality of tubular conductors (41) cooled by circulation internal coolant.

6) Equipment according to claims 2 and 5, characterized in that said end connectors (35) are rigid and constituted by drilled blocks (43,44) mounted on the ends of each bar (11, 11 ') and connected to buses (50, 50 ') by connecting bars (48, 48'), said buses being bridged together by a connecting strip (51)