EP0589811B1 - Side wall for a continuous cashing plkant for cashing metal between movable walls and apparatus - Google Patents

Abstract

The wall comprises a cooled plate (31) made from electrically conducting material, oriented in a vertical plane perpendicular to the movable walls, and an inductor (10) supplied with an alternating current and consisting of a spiral-wound conductor parallel to the plate and in direct proximity therewith, and such that at least one first angular sector (15, 16) of the spiral is located opposite a first zone (17, 18) coplanar with the plate and electrically insulated from a second zone (19) included in the plate and which is located opposite a second sector (14). The invention applies to the continuous casting of metals between movable walls, particularly between rolls. <IMAGE>

Description

The present invention relates to the continuous casting of metals, especially steel, between movable walls cooled, especially between cylinders. It concerns more precisely the lateral shutter walls of the space of casting defined between said walls.

In these installations, a long known problem date is to avoid premature solidification of the metal poured in contact with the lateral obturation walls, and limit the friction of said metal on said walls which are fixed.

In an attempt to resolve this problem, it has already been offered to heat either the side walls or the metal being close to them, so as to prevent, or at least delay its solidification.

Thus it has already been proposed, in document JP 62 77156, to heat the metal by induction, using U-shaped inductors arranged behind side walls in refractory material and generating in the cast metal eddy currents. Congestion constraints and current technological limitations prevent the implementation practical work of such solutions.

It has also been proposed in document FR 2670413, to similarly heat the metal, but using sufficiently thin cooled metal side walls so that the induced magnetic field acts directly on the cast metal. As soon as the wall thickness reaches or exceeds the penetration depth of the magnetic field, this heating mode is no longer effective.

The invention aims to solve the problems mentioned above, to allow inductive heating effective metal near the side walls, limit friction, and therefore wear, on said walls, and improve the seal between the movable walls and said side walls.

With these objectives in view, the invention relates to a lateral sealing wall of a casting installation continuous between movable walls comprising two movable walls cooled defining between them a limited casting space laterally by two of said lateral closure walls which adjoin the edges of said movable walls, characterized in that said lateral closure wall comprises a cooled plate of electrically conductive material, oriented along a vertical plane perpendicular to the walls mobile, and an inductor powered by a variable current, including alternative, and consisting of a conductor wound in spiral parallel to the plate and in close proximity to this, and such that at least a first angular sector of the spiral is located opposite a first coplanar zone with the plate and electrically isolated from a second area included in the plate and which faces a second spiral sector.

The invention also relates to a casting installation continuous between cylinders, characterized in that it comprises two walls as above, said cylinders constituting said movable walls.

The inventive idea underlying the present invention has been to use the basic principles of the so-called technique of "cold crucible" known for many years for the heating and induction melting of certain metals either with a very high melting point, which is to be avoided contact with a refractory crucible for reasons of purity of the molten metal. A "cold crucible" device is composed of a cylinder, usually made of copper, cooled by water circulation and radially segmented, surrounded by a solenoid which is coaxial with it and powered by a current at high frequency. By the effect of the induced magnetic field and eddy currents that develop in the cylinder and the metal to be melted, on the one hand the metal is heated and melted, and on the other hand the electromagnetic forces created tend to move molten metal away from the cylinder wall.

This cold crucible technique has already been the subject of many developments which respect the basic technique of the segmented cylinder surrounded by a solenoid generating a magnetic field oriented along the axis of the cylinder.

As will be easily understood, such a technique is not applicable as is in a pouring between movable walls, due to the configuration of this type of installation. The inventors therefore had to imagine an entirely original structure to find a solution to the problem of heating nearby cast metal side walls and decrease the friction of the metal on these walls.

Thanks to the invention, the metal is heated as in the technique of the cold crucible by the eddy currents which are developed by the inductor via the material plate electrically conductive, and electromagnetic forces resulting from the interaction of these eddy currents with the induced magnetic field tend to move the cast metal away of said plate, which therefore reduces friction. The principle of the invention will be more clearly explained in the description given below of an exemplary embodiment.

• la plaque est formée d'un seul élément et deux desdits premiers secteurs angulaires de la spirale, diamétralement opposés, sont situés face à des zones coplanaires avec la plaque et situées hors dudit élément ;
• la plaque est formée de plusieurs éléments juxtaposés isolés électriquement entre eux ;
• les éléments sont allongés selon une direction horizontale et juxtaposés verticalement ;
• les éléments sont allongés selon une direction verticale et juxtaposés horizontalement ;
• tous les éléments sont réalisés en un même matériau électriquement conducteur ;
• au moins un élément est réalisé en un matériau ayant des caractéristiques électromagnétiques différentes de celles des matériaux des autres éléments ;
• chaque élément est refroidi par circulation interne d'un fluide refroidissant.

According to specific provisions of the invention:

• the plate is formed from a single element and two of said first angular sectors of the spiral, which are diametrically opposite, are situated opposite coplanar zones with the plate and situated outside said element;
• the plate is formed of several juxtaposed elements electrically insulated from each other;
• the elements are elongated in a horizontal direction and juxtaposed vertically;
• the elements are elongated in a vertical direction and juxtaposed horizontally;
• all the elements are made of the same electrically conductive material;
• at least one element is made of a material having electromagnetic characteristics different from those of the materials of the other elements;
• each element is cooled by internal circulation of a cooling fluid.

Other characteristics and advantages will appear in the description which will be made of several variants of the invention, in the case of a casting installation continuous between cylinders of thin steel products.

• la figure 1 est une vue schématique en perspective de l'installation de coulée entre cylindres ;
• la figure 2 est une vue frontale selon la flèche F1 de la figure 1 montrant la disposition générale d'une paroi d'obturation latérale conforme l'invention ;
• la figure 3 est une représentation didactique en coupe selon la ligne III-III de la figure 2 montrant les courants, champ magnétique et forces agissant dans l'installation selon l'invention ;
• la figure 4 est une représentation en vue de dessus de la figure 3 .
• la figure 5 est une représentation similaire dans le cas d'une plaque d'obturation en plusieurs éléments verticaux ;
• la figure 6 est une vue en perspective d'une première variante de la paroi d'obturation latérale selon l'invention ;
• la figure 7 est une vue en coupe verticale de la paroi, où l'inducteur n'a pas été représenté ;
• la figure 8 est une vue frontale d'une deuxième variante de la paroi d'obturation latérale ;
• la figure 9 est une vue simplifiée d'une troisième variante, et
• la figure 10 est une vue schématique de dessus d'une quatrième variante.

Reference is made to the appended drawings in which:

• Figure 1 is a schematic perspective view of the casting installation between cylinders;
• Figure 2 is a front view along arrow F1 of Figure 1 showing the general arrangement of a side closure wall according to the invention;
• Figure 3 is a didactic sectional representation along line III-III of Figure 2 showing the currents, magnetic field and forces acting in the installation according to the invention;
• FIG. 4 is a view from above of FIG. 3.
• Figure 5 is a similar representation in the case of a cover plate in several vertical elements;
• Figure 6 is a perspective view of a first variant of the lateral closure wall according to the invention;
• Figure 7 is a vertical sectional view of the wall, where the inductor has not been shown;
• Figure 8 is a front view of a second variant of the lateral closure wall;
• FIG. 9 is a simplified view of a third variant, and
• Figure 10 is a schematic top view of a fourth variant.

The steel casting installation shown in Figure 1 has two movable walls here formed by the two cylinders 1 and 2 with parallel and horizontal axes. Of in a conventional manner and known per se, the cylinders 1, 2 are internally cooled and rotated in direction opposite. Two lateral closing walls 3 and 4 are arranged against the front faces of the cylinders, and therefore oriented along vertical planes, such as the P plane, perpendicular to the cylindrical walls of the cylinders. These lateral obturation walls define with the walls of the cylinders, in the area above the level of their axes, a casting space 5.

During casting, molten steel 6 is poured (according to arrow F ₂ ) into the casting space 5, where it gradually solidifies on contact with the cooled walls of the cylinders, forming skins of solidified steel. By the rotation of the cylinders, the solidified skins are driven downwards and meet at the neck between the cylinders to form the thin product 7 continuously extracted.

FIG. 2 shows the closure wall side 3 which has a plate 31 made of material electrically conductive, such as copper or an alloy of copper, trapezoidal, with lateral edges adjoin the front ends of the cylinders. An inductor 10 formed of a conductor 11 wound in a spiral 12 plane is placed parallel to plate 31, and in close proximity to this one. The inductor 10 is supplied by a source 13 of alternating current, for example from 50 Hz to 500 KHz, and high intensity. Inductors shaped in this way are commonly called "Pancake".

In the arrangement of Figure 2, the spiral 12 has a trapezoidal shape, and is arranged relative to the plate 31 so that the horizontal parts 14 of the conductor are facing plate 31, while the lateral parts obliques 15, 16 project laterally from said plate. In other words, we can assimilate the spiral of form trapezoidal inductor to a spiral shape circular, and said horizontal portions 14, and lateral obliques 15, 16 to angular sectors of this spiral. So, the angular sectors 15, 16, diametrically opposite, are located in front of zones 17, 18 (framed on Figure 2 by dashed lines, which do not have here physical reality) coplanar with plate 31, and located out of said plate, and therefore implicitly electrically isolated from it. In addition the angular sectors corresponding to the horizontal parts 14 of the conductor, is face zone 19 defined here by the surface of the plate 31.

In another arrangement shown diagrammatically in FIG. 9, the plate 31 is formed of two elements 32 ', 33' juxtaposed, and the center of the spiral 12 'is located at the interface between the two elements 32 ', 33'. A first angular sector of the spiral, formed by its half upper is located opposite a first zone constituted here from the surface of element 32 ', which is insulated electrically of a second zone, constituted here of the surface of the element 33 ′, which faces the second angular sector of the spiral formed by its half superior.

As we will understand better later, the interest of the arrangement of the inductor according to the invention is avoid looping the eddy currents generated in the plate 31 when the inductor is supplied, in a plane parallel to those of the plate and the inductor.

Next to Figures 3 to 5 we will now describe the operating principle of the wall shutter according to the invention.

The currents, fields and forces flowing or acting in the plane of the sheet by arrows, and by circles when they are perpendicular to the plane of the sheet. The fields or currents directed from front to back of the sheet are represented by a circle containing a cross, and those directed inversely by a circle containing a point.

The diagram in Figure 3 shows these currents, fields and forces in a vertical section along line III-III of Figure 2; the diagram in Figure 4 shows them in a horizontal section at line IV-IV in figure 3, in the case of a one-piece plate 31 such as that of the Figure 2; the diagram in Figure 5 is similar to that of Figure 4, but in the case where the plate 31 is formed of several vertically elongated and joined elements, and electrically isolated from each other.

In a simplified manner, it can be said that the current I ₁ flowing in the conductor 11 generates a magnetic field B ₁ whose penetration depth in the plate 31 is small. This field B ₁ creates in the skin thickness of the plate induced currents I ₂ which loop horizontally. The currents I ₂ generate a field B ₂ which penetrates into the skin thickness of the steel 6 contained in the casting space and in turn generates there induced currents I ₃ . These currents on the one hand cause the steel to heat up and thus prevent premature solidification of the steel near the plate 31, and on the other hand, by interaction with the field B ₂ , create directed forces F _R towards the middle of the casting space, which tend to move the solidified metal film 6 'away from said plate, thereby reducing the friction of the metal poured onto this plate. Thus, the two objectives of the invention, which are to limit the solidification of the steel near the lateral obturation wall and to limit the friction against this wall, are achieved.

In addition, in the contact zone between the plate 31 and the edges 1 ′, 2 ′ of the cylinders, the currents I ₂ generate, in a similar manner to what has been explained above, induced currents I ₄ , generating their turn in the steel located in the corners of the casting space of the currents I ₃ ′, which circulate according to the arrows indicated in FIG. 4, which also tend to repel the steel cast from the wall of the cylinders. The composition of the forces exerted leads to a resultant F _R 'which tends to push back the steel from the joint between the cylinders 1, 2 and the side wall, and therefore improves the sealing by preventing infiltration of liquid metal into this joint.

The explanations given above in the case of a plate 31 formed of a single element also apply to the case represented in FIG. 5 where the plate is formed of three elements 31 ', 31'',31''' , the only difference being that the currents I ₂ loop in each element instead of looping in the entire section of the plate.

It will also be easily understood that the explanations above, taking into account fields, currents and forces in the upper half of the device apply to the bottom half with a simple reversal of the direction of currents and fields.

We will also understand that the induced currents and forces in cast steel can only exist thanks to the fact that the currents induced in the plate 31 or in each element 31 ', 31' ', 31' '' of plates circulate according to a plan perpendicular to the general plane of the plate. That is why no coil of the inductor is entirely facing the same plate element. If this were the case, the induced currents would loop in the surface area of this element located opposite the inductor, parallel to the plane of the plate and on the one hand would not reach the area surface of the element located on the side of the cast steel, and on the other hand would only create a heating of said element.

It should also be noted that the induced currents I ₂ , I ₃ , I ₃ ', I ₄ circulate near the surfaces of the different materials because the frequency of the inductor current I ₁ is such that the penetration depth of the induced fields is weak. The frequency must therefore be high enough, depending on the material of which the plate 31 is made, so as not to have too deep a penetration depth of the field B ₁ in the plate 31. Furthermore, if the penetration depth of the field B ₂ in the cast steel is small, the repulsion forces F _R are strong, but the stirring effect of the liquid steel can be weak or even almost zero.

For example for a plate 31, or elements of plate, copper, the inductor current could be 50 Hz at 500 kHz, which corresponds to penetration depths in copper from 9.2 mm to 0.09 mm respectively.

The frequency will therefore be chosen mainly in depending on the desired effect in the steel, taking into account that the total thickness of the copper plate is largely greater than the depth of penetration indicated above.

It is further specified that, in the case of a plate made up of several elements, these elements can be made of different materials having different electroconductive characteristics. This particular arrangement makes it possible to adapt the intensity of the currents and the forces as a function of the location of the elements in the plate with respect to the casting space. For example, a judicious choice, in the plate represented in FIG. 5, of the material of the elements 31 ', 31''' which are located near the walls of the cylinders, allows, by using a single inductor traversed by the current I ₁ , to create greater repulsion forces, or preferential reheating, in the corners of the casting space than towards the middle of the side wall where the element 31 '' acts, made of another material, the choice of materials being based on the value of their respective penetration depths, and their electrical conductivities.

FIG. 6 shows a side wall according to the invention, in the variant where the plate 31 is formed of three elements 32, 33, 34 elongated in a direction vertical and juxtaposed horizontally, a thin film 35 in electrically insulating material being placed between two adjacent elements. Each element has a conduit longitudinal center 36 (only that of element 32 has been shown in the figure so as not to overload it). The three conduits 36 open down into a channel of distribution 37 (Figure 7) connected by piping 38 to a supply circuit, not shown, with a cooling, for example water. Likewise the pipes 36 open up into a collector 39 connected to a outlet piping 40.

The distribution channel 37 is arranged in a housing lower 41 and the collector is arranged in a housing upper 42, these two housings used to maintain the assembly of elements 32, 33, 34, as well as positioning of the entire plate with respect to cylinders 1, 2, and to the fixing on the installation. These housings 41, 42 are electrically insulated from elements 32, 33, 34 of the plate.

The inductor 10 is a flat inductor of the "Pancake" type, kept at a short distance from the plate, so as to have the highest possible proportion of induced magnetic field in said plate, while being electrically isolated from the latter. The lateral parts of the inductor protrude from the plate 31. These lateral parts could also, especially if we increase the number of elements juxtaposed, be located facing the elements located on the edges of the plate, in which case the induced currents would circulate in the area of these side walls either horizontally as in the other elements, but vertically.

Figure 8 shows another alternative embodiment in which the plate 31 consists of four elements horizontal 45 juxtaposed vertically, two boxes side 46, 47 ensuring the same function as the housings 41, 42 of the previous variant. The inductor here overflows with the plate up and down. We will easily understand that in this variant the induced currents flow in substantially vertical planes, currents and forces induced in the cast metal are deduced from the explanations previous by simple transposition.

Other execution variants are possible while remaining within the scope of the present invention. for example the number of components of the plate 31 can be amended. The plate 31 may constitute only part of the obturation side wall, for example by being placed at the level of the neck between the movable walls and surmounted by a another plate of refractory material. Or again, like shown schematically in Figure 10, the plate as well that the inductor may be slightly concave in their part in contact with the liquid metal 6, which allows concentrating the power injected into said metal.

Claims (12)

1. Side closure wall of a plant for continuous casting between moving walls, comprising two cooled moving walls (1, 2) which between them define a casting space (5) bounded laterally by two of the said side closure walls (3) which adjoin the edges of the said moving walls, characterized in that the said side closure wall comprises a cooled plate (31) made of an electrically conductive material, oriented in a vertical plane perpendicular to the moving walls, and an inductor (10) which is supplied with a variable current and consists of a conductor wound in a spiral parallel to the plate and in direct proximity to the latter, and such that at least one first angular sector (15, 16) of the spiral lies opposite a first region (17, 18) which is coplanar with the plate and electrically insulated from a second region (19), the latter being included in the plate and lying opposite a second sector (14) of the spiral.
2. Wall according to Claim 1, characterized in that the plate (31) is formed from a single element and two (15, 16) of the said first angular sectors of the spiral, which are diametrically opposed, lie opposite regions coplanar with the plate and lying outside the said element.
3. Wall according to Claim 1, characterized in that the plate is formed from several juxtaposed elements (32, 33, 34) which are electrically insulated from one another.
4. Wall according to Claim 3, characterized in that the elements are elongate in a horizontal direction and are juxtaposed vertically.
5. Wall according to Claim 3, characterized in that the elements are elongate in a vertical direction and are juxtaposed horizontally.
6. Wall according to Claim 3, characterized in that all the elements are made of the same electrically conductive material.
7. Wall according to Claim 3, characterized in that at least one element is made of a material having electrical conductivity characteristics different from those of the materials of the other elements.
8. Wall according to either of Claims 2 and 3, characterized in that each element is cooled by the internal circulation of a coolant.
9. Wall according to Claim 1, characterized in that the plate (31) is made of copper or a copper alloy.
10. Wall according to Claim 1, characterized in that the frequency of the inductor current is from 50 Hz to 500 kHz.
11. Wall according to Claim 1, characterized in that the plate 31 and the inductor 10 are concave.
12. Twin-roll continuous casting plant, characterized in that it comprises two walls according to one of the preceding claims, the said rolls constituting the said moving walls.

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