EP0901851B1 - Side wall for confining the casting space in a continuous roll caster installation for the production of metallic strips and casting installation equipped therewith - Google Patents

Abstract

A lateral face (11) is claimed for closing the casting space (6) of an installation for the continuous casting of metal strip. It has two internally cooled contra-rotating rolls (5, 5'), with horizontal axes, and the cylindrical lateral faces define a casting space (6). The width of the neck (7) determines the thickness of the strip. The lateral face (11) presents an active part (3) to rub against the sides (4) of the rolls (5, 5') during casting and faces the casting space (6). The dimensions of this active part (3) are such that its lower edge (12) is designed to be situated at a distance (d) equal to at least 1 mm above the neck (7) whilst the lateral face (7) is mounted on the casting installation. The continuous casting installation incorporating this lateral face is also claimed.

Description

The invention relates to the continuous casting of thin metal strips, made directly from liquid metal. More specifically, it concerns the obturation lateral of the casting space of the so-called "casting between cylinders" installations in particular with the casting of strips of steel or ferrous alloys.

In this type of installation, the application of which to the casting of steel strips of a few mm thick is being industrialized, the casting space is delimited on the one hand by the internally cooled cylindrical side surfaces of two cylinders close horizontal rotated in opposite directions around their axes, against which the liquid metal initiates its solidification, and on the other hand by plates of material refractory applied by elastic means against the flat ends of the cylinders (called "songs"). These plates close off the pouring space laterally, so that prevent liquid metal from leaking out of the installation. Their lower edge is located in below the "neck", ie the area where the surfaces of the cylinders are closest to one on the other, and whose width corresponds substantially to the desired thickness for the strip.

The side cover plates must be strongly preheated before casting, so that the liquid metal does not solidify against they during the filling of the mold (whose bottom, during the filling operation, is closed by a part called "mannequin", which is extracted from the casting space when begins the rotation of the cylinders and brings with it the beginning of the strip) and in the first moments of casting. But even if such a precaution is taken, the faces side constitute a thermally delicate point of the machine, in that they create inevitably in their vicinity an area where the extraction of heat from metal liquid is abnormally high. This is, in particular, the case near the cylinders which, as they are internally cooled by circulation of water, they tend to cool lateral faces in the vicinity of the areas where their contact takes place. It may result that the solidification of the steel on the edges of the cylinders takes place significantly faster than on the portions of the cylinders closer to their central areas, and this can be a source of problems. Indeed, normally the metal "skins" which solidify on each of the cylinders, the thickness of which at a given point gradually increases as measure of the rotation of the cylinder, must, to form the band, join either exactly at the level of the neck, or very slightly below this level. If this junction skin occurs too noticeably lower than the neck, the band may not be fairly solid at the outlet of the cylinders and cracking. It may also present internal porosities. Conversely, if the skins are joined upstream of the cervix, under the influence of particularly cold side faces, the thickness of the strip solidified at neck level is greater than the nominal width of the neck. It is then necessary to remove the cylinders from each other to prevent them from providing a rolling force on the strip then that they were not designed for that. This spacing of the cylinders is a source of faults on the tape, which are related to the changes it causes on the thickness and the mode of solidification of the product. Another consequence of the abnormal conditions of the solidification of the strip near the side faces is the strong pressure exerted by the metal being solidified on the lower part of the side faces. He is coming frequently this pressure is enough to move the side face back on at least part of its height, which can locally destroy the tightness of the contact side cylinders. Liquid metal can then escape out of the casting space.

The object of the invention is to propose a configuration of the casting installation making it possible to create conditions for solidifying the strip in the vicinity of the faces which are not likely to disturb the regularity of the casting process. It should also limit the phenomenon of receding side faces.

The subject of the invention is a side face for closing off the pouring space. of a continuous casting installation of metal strips of the type comprising two internally cooled counter-rotating cylinders with horizontal axes, the surfaces of which cylindrical sides define a casting space whose width at the neck determines the thickness of the strip, said lateral face having an active part intended to rub against the edges of the rolls during casting and facing said casting space, characterized in that the dimensions of said active part are such that its edge lower is intended to be located at a distance equal to at least 1 mm above the neck when the side face is mounted on the casting installation.

The invention also relates to an installation for continuously casting strips of the type comprising two internally cooled counter-rotating cylinders, with axes horizontal, whose cylindrical side surfaces define a pouring space whose width at the neck determines the thickness of the strip, and two lateral sides for closing its pouring space, characterized in that said lateral faces are of the type previously described.

As will be understood, according to the invention the active part of the lateral face is to say its part which is in contact either with the edges of the cylinders or with the liquid metal enclosed by the casting space, is interrupted not below the neck as it is usual, but on top of it. This leaves a free space on both sides of the pass where the metal is not in contact with any refractory material and therefore exerts no pressure on the side faces. Thus, the metal present in front of this free space cannot cause of the side faces, even if its solidified fraction is abnormally high. Else apart, this free space gives the possibility for solidified metal or in the process of solidification to extend towards the outside of the casting space, which limits the forces that must bear the edges of the cylinders.

The inventors have realized that the cooling conditions of the steel at the inside of the mold, with the usual casting parameters, was such that from a level which can be a few cm above the neck, the solidification of the metal on the edges of the casting space, although not yet complete, is already sufficiently advanced so that there is no significant leakage of liquid metal to the outside of the machine, even if the metal is no longer retained by the side faces. They deduced that the removal of the lower part of the lateral faces of the prior art was possible. This suppression makes the casting machine more tolerant of slight deviations in the process of solidification of the strip. Indeed, with the invention, a thickness of the skins solidified on the edges of the cylinders slightly larger than expected in the last mm or cm preceding the collar no longer causes the side faces to recede and the risk of loss sealing in the upper levels of the casting space associated with them. Else apart, the excessively solidified parts of the strip can extend laterally if the cylinders exert on them a compressive force, which makes significantly less likely the need to spread the cylinders to minimize the stresses they undergo.

The invention thus provides greater stability of the casting conditions, which will in the sense of better overall tape quality and higher reliability of the casting installation.

• la figure 1 qui schématise vue de face (figure 1a) et de profil (figure 1b) en coupe selon Ib-Ib une face latérale de coulée continue entre cylindres selon l'art antérieur;
• la figure 2 qui schématise vue de face (figure 2a) et de profil (figure 2b) en coupe selon IIb-IIb une face latérale de coulée continue entre cylindres selon l'invention.

The invention will be better understood on reading the description which follows, given with reference to the following appended figures:

• Figure 1 which shows schematically front view (Figure 1a) and profile (Figure 1b) in section along Ib-Ib a side face of continuous casting between cylinders according to the prior art;
• Figure 2 which shows schematically front view (Figure 2a) and profile (Figure 2b) in section along IIb-IIb a side face of continuous casting between cylinders according to the invention.

The side face 1 according to the prior art shown schematically in Figure 1 includes a support plate 2, in which the active part 3 of the face is embedded lateral 1, ie its portion intended, during casting, to come into contact with the edges 4 cylinders 5, 5 ′ (of which only the contours have been shown in dotted lines in FIG. 1a), of liquid steel which will contain the casting space 6 of the machine and, below the level from the neck 7 where the cylinders 4, 4 ′ are as close as possible to each other, from the solidified strip. of the means (not shown) known in themselves ensure the application of the side face 1 against the edges 4 of the cylinders 5, 5 '. They allow, thanks to springs or cylinders, temporary withdrawals from the side face 1 in the event of metal infiltration between its active part 3 and the edge 4 of a cylinder 5, 5 ′, or of excessive force exerted by the strip during solidification on its lower part. Reference may be made, in particular, to document EP-A-0 698,433 for the description of an example (non-limiting) of such means. The part active 3 is, in the example shown, divided into two portions. Portion 8 in double arc of circle which, when the side face 1 is mounted on the machine, constitutes the area of contact with the edges 4 of the cylinders 5, 5 ′, the immediate vicinity of this contact zone and the area surrounding the neck 7, is constructed of a first refractory material. Its quality essential is a high hardness so that it resists friction as well as possible edges 4 of the cylinders 5, 5 'and (around the neck 7) of the strip being solidified or already solidified. It is, for example, made of SiAlON® or boron nitride. She may be consisting of a single piece or of several adjoining pieces that are integral with each other. Its lower edge 9 is located below the level of the neck 7, so as to produce a total lateral closure of the pouring space 6. The remaining portion 10 of the active part 3 is made of a refractory material having a high insulating power, such as silica or alumina. The active part 3 of the side face 1 is projecting relative to the support plate 2 with a thickness equal to at least its maximum tolerable wear during casting, by example 10 mm. During the casting, the portions of the active part 3 which are in contact edges 4 of cylinders 5, 5 'wear mainly by friction, with for consequence that, little by little, the other portions of the active part 3, which wear only at one more moderate speed because they are only in contact with steel, liquid or being solidification, penetrate slightly inside the casting space 5. As a variant, the whole active part 3 of the side face 1 can be constituted by a single part.

In FIG. 2 which represents a lateral face 11 according to the invention mounted on the casting installation, the elements common with those of FIG. 1 are designated by the same references. According to the invention, for the reasons which have been said, the lower edge 12 of the active part 3 of the lateral face 11 which ensures contact with the cylinders 5, 5 'and closes the lower part of the casting space 6 is no longer located under the neck 7, but at a distance "d" above it. This distance "d" can be very small, up to 1 mm, if we usually manage to regulate skin growth with great precision solidified on the edges of cylinders 5, 5 ', and if the proportion of solid matter present in the metal not yet fully solidified in this region of the casting space 6 is likely to go very quickly from 0 to 100%. These parameters depend, in particular, of the casting shade. The grades of steel most loaded with carbon and elements of various alloys, such as stainless steels, have solidification intervals (the gap between liquidus and solidus temperatures) wider than those of steel grades ordinary or iron-nickel alloys, and this makes it more difficult to control their conditions solidification. Above all, this wide solidification interval implies that one begins to observe a significant level of solid matter in the vicinity of the lateral face 11 at relatively high levels of casting space 6. For these steels with a wide range of solidification, it is therefore necessary to provide a distance "d" greater than for the grades to narrow solidification interval which solidifies quickly when temperature is reached of liquidus. In practice, a distance "d" of between 10 and 40 mm is suitable for the most common grades of stainless steel, cast in the form of strips 3 mm thick with 1500 mm diameter cylinders and casting speeds of around 1 m / min. The optimal choice of distance "d" also depends on the pressure ferrostatic reigning in the lower part of the casting space, therefore of the geometry of the casting installation and the nominal level of the surface of the liquid steel present in casting space. Good results have thus been obtained with a distance "d" of 1 to 7 mm on a machine fitted with 600 mm diameter cylinders, when casting steels low-alloy carbon and iron-silicon alloys.

Preferably, in order to reduce the mechanical stresses exerted on it and could cause its rapid and uncontrolled degradation, the lower edge 12 of the part active 3 of the side face 11 which faces the casting space 6 does not have a sharp angle, but a rounded 13 whose radius of curvature can, for example, be of the order of 10 to 20 mm. The same function can be ensured by bevelling the lower edge 12, according to a inclined plane, for example, at 45 °.

It is also possible to provide the possibility of cooling the edge of the strip by projection of a fluid (water, nitrogen or liquid argon ...) between the lower edge of the part active 3 of the side face 11 and the neck 7. This cooling can be achieved so permanent, to ensure that the edge of the strip is always sufficiently solidified to prevent it from tearing while letting out liquid metal. It can also be performed only when the initiation of such a tear in the shore is observed, or when the monitoring the casting parameters makes one suspect the risk of the appearance of such a tear. As means for supplying cooling fluid to the edge of the strip, it is possible to use, for example, one or more conduits 14 passing through the support plate 2 and opening into the space 15 between the support plate 2, the edges 4 of the cylinders 5, 5 'and the neck 7. But one can imagine other means of supplying fluid, which would be possibly independent of the lateral face 11, such as one or more sprinklers which would arranged under the lateral face 11 and oriented towards the edge of the strip.

An indicator of the effectiveness of the invention is the number of setbacks from the lateral face that we observe during casting. It was thus found that this number could be divided by three on the whole of a casting, compared to the use of descending side faces down to the neck. The improvement is even more noticeable when we consider the first minutes of casting, during which the operation of the casting machine is not always perfectly stabilized. These observations were made during the steel casting austenitic stainless steel type SUS 304 cast in 3 mm thick strips, with a distance "d" equal to 25 mm and a cylinder diameter of 1500 mm.

The adaptation of such lateral faces to an already existing casting installation can, if necessary, make some modifications to the manikin, so that that the entire pouring space 6 is closed laterally during filling, before the start of casting.

It goes without saying that the application of the invention is not limited to the configuration precise from the side which has just been given as an example, but is applicable to any other configuration which allows an interruption of the active part above the neck.

Of course, the invention is applicable not only to casting between cylinders of strips of steel and other ferrous alloys, but of any other metal liable to be cast by this method.

Claims (6)

1. Side wall (11) for confining the casting space (6) of a continuous roll caster installation of the two-roll type, for the production of metallic strips, comprising two contra-rotating, internally cooled and horizontally oriented rollers (5, 5'), the cylindrical side walls of which define a casting space (6), whose neck size (7) determines the thickness of the strip, said side wall (11) showing an active part (3) meant for rubbing against the edges (4) of the cylinders (5, 5') during casting and facing said casting space (6), characterised in that the dimensions of said active part (3) are such that, during operation, its lower edge (12) is situated at a distance (d) equal to at least 1 mm above the neck (7), if the side wall (11) is fitted to the caster installation.
2. Side wall according to claim 1, characterised in that said lower edge (12) shows a rounding (13) facing the casting space (6).
3. Side wall according to claim 1 or 2, characterised in that said lower edge (12) shows a bevelling facing the casting space (6).
4. Side wall according to one of the claims 1 to 3, characterised in that said active part (3) is fixed on a supporting plate (2), and in that said supporting plate (2) comprises at least one conduit (14) which traverses it and leads to the space (15) comprised between the supporting plate (2), the edges (4) of the cylinders (5, 5') and the neck (7), said conduit (14) being connectable to injection means for the injection of a cooling medium.
5. Continuous roll caster installation of the two-roll type, for the production of metallic strips, comprising two contra-rotating, internally cooled and horizontally oriented rollers (5, 5'), the cylindrical side walls of which define a casting space (6), whose neck size (7) determines the thickness of the strip, and comprising two side walls for confining its casting space, characterised in that said side walls are of type according to one of the claims 1 to 4.
6. Installation according to claim 5, characterised in that it comprises means to project a coolant onto the section of the strip above the neck (7).

Images