EP0603094A1 - Side wall for a continuous twin-roll casting machine - Google Patents

Abstract

The wall (5) includes a first vertical plate (11) made from refractory material which is placed in contact with the front ends of the rolls (1, 2), a second rigid plate (12) made from electrically conducting material, arranged against the first plate, and means for linking the two ends (16, 17) of this plate to a source (18) of electrical current, this second plate constituting an electrical heating resistance element for heating the first plate (11) in contact with the cast (poured) liquid metal. <IMAGE>

Description

The present invention relates to an installation for the continuous casting of metals between cylinders, and more particularly to a lateral closure wall of the casting space situated between the cylinders.

It is known that, in installations of this type, it is necessary to avoid premature solidification of the cast metal in contact with the lateral closure walls. To this end, it has already been proposed to heat these walls at high temperature to avoid or at least limit the cooling of the metal cast on contact with them.

For example, document JP-A-58 32 552 describes such a wall made of refractory material comprising a recess in which an electrical heating resistance is placed. Document JP-A-62 124 051 describes a wall comprising a first plate in contact with the cast metal and a second support plate, comprising on the side of the first plate, grooves in which are placed heating means.

The recesses or grooves in which the heating means are placed weaken the mechanical resistance of this type of wall.

Furthermore, making the grooves involves machining the support plate. The production of a recess in the refractory plate also involves machining or special molding which complicates the manufacture of the lateral closure wall.

Furthermore, the heat transmission from the resistor in contact with the cast metal takes place indirectly through a coating material cast around the electrical resistance, which impairs good heat transfer.

The object of the present invention is to solve the above problems, and to propose a lateral obturation wall comprising electric heating means, which is of simple construction, has good resistance. mechanical and ensures the best possible heat transfer between the heating element and the refractory plate in contact with the cast metal.

With these objectives in view, the subject of the invention is a lateral closure wall for a continuous casting installation between cylinders of thin metal strips, comprising a first vertical plate of refractory material, placed in contact with the front ends of the cylinders, and means for electrically heating said first plate, characterized in that the heating means comprise a second rigid plate of electroconductive material, disposed against the first plate, and means for connecting two ends of this plate to a current source electric.

Thanks to the invention, it is the entire second plate which serves as a heating resistor. In addition, this second plate being rigid ensures increased mechanical strength of the lateral closure wall. The thickness of this second plate may be sufficient for it in fact to constitute the essential means giving the mechanical resistance necessary for the closure wall.

As a result, the first refractory plate may have a reduced thickness since the forces to which the closure wall is subjected, are essentially supported by the second plate.

According to a preferred arrangement of the invention, the second plate includes offset notches produced alternately from a first edge of the plate and a second edge opposite the first, perpendicular to the plate.

Thanks to this arrangement, the length of the electrical circuit formed by the plate is considerably increased and simultaneously its section is reduced. As a result, a high power can be supplied by the resistance thus formed.

The notches can be made horizontally or vertically, and their spacing can vary from area to area. the other of the plate to locally adapt the quantity of thermal energy supplied.

Preferably, an insulating material is placed in these notches. The role of this insulator, for example mica sheets, is to avoid any contact between two parts of the plate located on either side of the same notch, and on the other hand to consolidate the second plate by strengthening its rigidity. .

The second plate can be made of graphite, or of an electroconductive refractory material in its mass, such as alloy magnesia.

According to another arrangement of the invention, the closure wall comprises an electrically insulating backplate for holding and pressing, in contact with the second plate, and on which pressure means act, to push the entire wall shutter against the cylinders.

The set of three plates is preferably placed in a box, which leaves the free face of the first refractory plate visible, supplied with an inert gas, such as nitrogen, to prevent oxidation of the electroconductive material.

Other characteristics and advantages will appear in the description which will be given by way of example of a lateral closure wall of a continuous casting installation between cylinders of thin steel strips.

• la figure 1 est une vue schématique d'une installation de coulée continue entre cylindres ;
• la figure 2 est une vue en perspective de la seconde plaque de la paroi d'obturation latérale conforme à l'invention ;
• la figure 3 est une vue en coupe de la paroi d'obturation selon la ligne III-III de la figure.

Reference is made to the appended drawings in which:

• Figure 1 is a schematic view of a continuous casting installation between cylinders;
• Figure 2 is a perspective view of the second plate of the side closure wall according to the invention;
• Figure 3 is a sectional view of the closure wall along line III-III of the figure.

The installation for casting between rolls shown in FIG. 1 conventionally comprises two rolls 1, 2, with horizontal and parallel axes, delimiting between them a pouring space 3 for the molten metal fed according to arrow 4.

The pouring space is closed on each side, towards the ends of the cylinders by lateral closing walls 5.

During casting, the cast metal 6 solidifies on contact with the cooled walls of the cylinders 1, 2, driven in rotation according to the arrows 7, 8, and is extracted downwards, in the form of a thin metal strip 9.

The lateral closure wall 5, according to the invention, shown in FIGS. 2 and 3, comprises a first plate 11 made of refractory material, placed against the front ends of the cylinders 1, 2.

This first plate, which must be heated, is made of an electrically insulating material, for example vitreous silica.

A second plate 12 is placed against the first plate 11. The second plate 12 is made of electrically conductive material, for example graphite, and has a relatively large thickness, of several tens of millimeters, for example of the order of 20 mm, of so as to constitute a rigid solid block having good mechanical resistance in particular to compression and to bending.

The general shape of the second plate 12 is substantially trapezoidal, and corresponds substantially to the shape of a section of the casting space 3 in a vertical plane perpendicular to the axes of the cylinders.

Parallel notches 13 are made in the second plate 12, horizontally and over its entire thickness. These stepped notches are produced for example by a saw cut alternately from one 14 and the other 15 edge of the plate, so as to constitute a set of strips 20 superimposed and connected by their ends alternately on one edge and on the other of the plate 12, thus forming an electrical heating resistance, the ends 16, 17 of which are connected to a source of electricity 18.

ou ρ est la résistivité d'un matériau de la seconde plaque, et le rapport $$\frac{\text{l}}{\text{s}}$$

est sensiblement égal à $$\frac{{\text{Σ d}}_{\text{i}}}{\text{L.e}}$$

où d_i est la longueur de chaque lamelle, L étant l'épaisseur de la plaque 12 et donc la largeur de chaque lamelle, et e étant l'écartement entre deux rainures et donc l'épaisseur de chaque lamelle. A titre d'exemple, une plaque de graphite de 25 mm d'épaisseur ayant une hauteur de 300 mm pour une surface de 300 cm² a été usinée pour y réaliser des rainures de 3 mm de large, espacées d'environ 6 mm, formant ainsi une suite de lamelles de longueur totale 1885 mm et de section moyenne 150 mm². La puissance dissipée est de l'ordre de 10 000 W.The notches can be regularly spaced by a distance e . In this case, the electrical resistance R of the second plate can be expressed in the form R = ρ $$\frac{\text{l}}{\text{s}}$$

where ρ is the resistivity of a material of the second plate, and the ratio $$\frac{\text{l}}{\text{s}}$$

is substantially equal to $$\frac{{\text{Σ d}}_{\text{i}}}{\text{The}}$$

where d _i is the length of each strip, L being the thickness of the plate 12 and therefore the width of each strip, and e being the spacing between two grooves and therefore the thickness of each strip. For example, a 25 mm thick graphite plate having a height of 300 mm for an area of 300 cm² was machined to make grooves 3 mm wide, spaced about 6 mm apart, forming thus a series of slats with a total length of 1885 mm and an average section of 150 mm². The dissipated power is of the order of 10 000 W.

An insulating material such as mica sheets 19 is placed in each notch 13 to avoid any risk of short circuit or arcing between two neighboring lamellae, and to reinforce the plate 12.

A third rear plate 21 is pressed against the second plate 12 by pressure means, such as springs 22, which also serve to press the whole of the lateral closure wall against the cylinders.

A box 23 surrounds the lateral closure wall 5 while being tightly connected to the first and third plates 11, 21. This box is supplied by a conduit 24 with inert gas, for example nitrogen, intended to avoid the oxidation of graphite.

The invention is not limited to the arrangements described above by way of example. In particular, the notches can be made vertically. Their spacing, and therefore the thickness e of the slats 20, may also vary so as to locally adapt the thermal energy supplied by the plate 12, for example to heat more strongly in the upper part of the lateral obturation wall than towards the bottom of it.

The first plate 1 may also be formed by a refractory lining of the second plate, produced by casting or projection of this material on said second plate.

Claims (9)

1) Lateral closure wall (5) for a continuous casting installation between cylinders of thin metal strips, comprising a first vertical plate (11) of refractory material, placed in contact with the front ends of the cylinders (1,2), and means for electrically heating said first plate, characterized in that the heating means comprise a second rigid plate (12) made of electrically conductive material, disposed against the first plate, and means for connecting two ends (16,17) from this plate to a source (18) of electric current. 2) wall according to claim 1, characterized in that the second plate (12) comprises notches (13) offset produced alternately from a first edge (14) of the plate and a second edge (15) opposite the first, perpendicular to the plate. 3) wall according to claim 2, characterized in that the notches (13) are made vertically. 4) wall according to claim 2, characterized in that the spacing (e) between the notches is variable. 5) wall according to claim 2, characterized in that an insulating material (19) is placed in the notches (13). 6) wall according to claim 1, characterized in that the electroconductive material is graphite or an electroconductive refractory material in its mass. 7) wall according to claims 1 to 6, characterized in that it comprises a rear plate (21) electrically insulating holding and pressure, in contact with the second plate (12), and on which act pressure means (22), for pushing the entire closure wall against the cylinders. 8) wall according to one of claims 1 to 7, characterized in that the set of three plates is preferably placed in a box (23), which leaves apparent the free face of the first refractory plate (11), supplied by an inert gas. 9) Installation for continuous casting between cylinders, characterized in that it comprises two lateral closure walls according to one of claims 1 to 8.

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