EP0765702A1 - Immersion nozzle for introducing liquid metal into a continuous casting mould - Google Patents

Abstract

A nozzle (1) for introducing liquid metal into a continuous casting mould of the type incorporates a primary tubular part (2), one end of which is destined to be connected to a vessel containing the liquid metal and the other end (4) of which emerges into a secondary hollow part (6), of which at least a part (29) of the inner space (7) is oriented essentially perpendicular to the primary tubular part (2). The part (29) of the inner space (7) incorporates at each of its ends at least one orifice (10,11) destined to open out into the casting space of the mould. Characteristically it incorporates an obstacle placed in the path of the liquid metal inside the primary tubular part (2) or in its prolongation. The obstacle is made up of at least one perforated component designed to deviate the metal from its preferential trajectory inside the nozzle. The obstacle may take the form of a lozenge perforated with a multiplicity of holes or a hollow component, fitted with a bottom part, penetrating into the second part of the nozzle, the hollow component incorporating some openings in its lateral wall.

Description

The invention relates to the continuous casting of metals, in particular steel. More specifically, it relates to the tubes of refractory material called "nozzles" which, usually, are connected by their upper end to the container serving as a reservoir of liquid metal, and whose lower end plunges into the bath of liquid metal contained in the mold. where the solidification of the metal product should begin. The primary role of these nozzles is to protect the jet of liquid metal on its path between the container and the ingot mold from atmospheric oxidation. They also make it possible, thanks to appropriate configurations of their lower end, to favorably orient the flows of liquid metal in the ingot mold so that the solidification of the product takes place under the best possible conditions.

The casting can take place in an ingot mold which must give the product a very elongated rectangular section, which usually designates it by the expression "flat product". This is the case when, in the steel industry, steel is poured in the form of slabs, that is to say products having approximately 1 to 2 m in width and a thickness generally of the order of 20 cm, but which can descend up to a few cm on some recent installations called "thin slab casting machines". In these examples, the ingot mold is composed of fixed walls which are energetically cooled on their face which is not in contact with the metal. We are also experimenting with installations making it possible to obtain, directly by solidification of the liquid metal, steel strips a few mm thick. To do this, molds are used, the casting space of which is delimited on its long sides by a pair of internally cooled cylinders with parallel horizontal axes and rotating around these axes in opposite directions, and on its short sides by plates of closure (called side faces) of refractory material applied against the ends of the cylinders. The cylinders can also be replaced by cooled endless belts.

In these types of ingot mold, it is considered that it is preferable to orient the flows of the molten metal in a privileged manner in the direction of the short sides of the casting space. It is thus sought, in particular, to obtain a thermal homogenization of the metal so as to attenuate the variations in the solidified thickness along the perimeter of the mold. This thermal homogenization and the stirring of the liquid bath which it requires are particularly crucial in the case of the casting of thin strips, due to the use of the refractory side faces. Indeed, if we did not ensure a forced renewal of the metal surrounding these side faces, this metal would cool abnormally intense, and we would see undesirable solidifications of metal on the side faces.

To obtain the desired homogenization, two-part nozzles are sometimes used, in particular in casting between cylinders (see document JP-A-60021171). The first part is composed of a cylindrical tube, the upper end of which is connected to an orifice in the bottom of the distributor which constitutes the reserve of liquid steel supplying the ingot mold, an orifice which can be closed at will by the operator, partially or totally, thanks to a stopper or a drawer system ensuring the regulation of the metal flow. The cross-section of this orifice depends on the maximum metal flow which can flow inside the nozzle. The second part, fixed to the lower end of the preceding tube, for example by screwing, is intended to be immersed in the bath of liquid metal present in the ingot mold. It is composed of a hollow element inside which opens the lower orifice of the preceding cylindrical tube. The interior space of this hollow element has a generally elongated shape in its terminal part and is oriented substantially perpendicular to the tube. When the nozzle is in service, the hollow element is placed parallel to the long sides of the ingot mold, and the liquid metal flows into the ingot mold through two orifices made at each end of the elongated end portion of the hollow element, and called "gills".

When a large steel flow, for example of the order of 60 t / h, circulates inside the nozzle, the speed of the metal in the tubular part easily reaches several meters per second. Under these conditions, only a very partial filling of the section of the cylindrical part of the nozzle is observed with liquid metal. This poor filling has several drawbacks. Firstly, by a "trumpet effect", it tends to favor the suction of outside air by the porosities of the refractory and any leaks in the connection between the nozzle and the distributor, which deteriorates the quality metal. On the other hand, especially when the device closing the bottom of the distributor is only partially open, the flow of metal is swirling and irregular. This leads to a strong instability of the metal currents leaving the gills, instability which is further increased when a neutral gas is blown into the nozzle to alleviate the first drawback which has been mentioned. One can thus observe asymmetries in the flows which are established on the right and left portions of the mold. This instability and this asymmetry cause the appearance of waves inside the bath of liquid metal in the mold which permanently vary the level of its surface, which is very unfavorable to the regularity of the solidification of the product. These waves also unduly react the device ensuring the detection of the surface level and the regulation of its position: it will seek to compensate for what it takes for variations in the average level of the metal by commanding rapid and continuous changes in the degree opening the distaff or drawer. And these incessant modifications will, in fact, aggravate the instabilities of the metal level. Finally, the high speeds of the liquid metal in the nozzle favor the wear of the refractory materials which constitute it, in particular at the point of impact of the jet on the bottom of the horizontal hollow element.

The object of the invention is to provide metallurgists with nozzles which ensure conditions for the flow of metal in the ingot mold quieter and more regular than the nozzles usually used during the continuous casting of metallurgical products.

To this end, the subject of the invention is a nozzle for the introduction of a liquid metal into a mold for the continuous casting of metals, of the type comprising a first tubular part, one end of which is intended to be connected to a container containing said liquid metal, and the other end of which opens into a second hollow part, at least a portion of the interior space of which is oriented substantially perpendicular to said first tubular part, said portion comprising at each of its ends at least one orifice intended to open into the casting space of said ingot mold, characterized in that it comprises an obstacle placed on the path of the liquid metal inside said first tubular part or in its extension, said obstacle being constituted by at least one perforated part intended to deflect the metal from its preferential path inside the nozzle.

According to a first variant of the invention, said obstacle consists of at least one pellet perforated by a multiplicity of holes.

According to a second variant of the invention, said obstacle consists of a hollow part, provided with a bottom, penetrating into the interior space of said second part of the nozzle, said hollow part comprising openings on its side wall.

In one embodiment of the invention, the interior space of the entire nozzle has the general shape of a T.

As will be understood, the invention consists in interposing on the path of the liquid metal an obstacle intended to impede its natural flow, by abruptly deviating this flow from its theoretical preferential trajectory and by locally reducing the section of the space available for the passage of metal. This has the effect, at an equal metal flow rate, of limiting the speed of the flow and of improving the filling of the interior space of the nozzle as a whole. The erratic variations in the conditions of the flow of the metal out of the nozzle are thus attenuated, and the symmetry of the flows in the right and left halves of the mold and the regularity over time of these flows are notably improved.

• la figure la qui schématise, vue en coupe longitudinale, une première variante de l'invention, où l'obstacle est constitué par un empilement de pastilles perforées, qui sont elle-mêmes représentées en vue de dessus sur les figures 1b, 1c et 1d;
• la figure 2 qui schématise, vue en coupe longitudinale, une seconde variante de l'invention, où l'obstacle est constitué par une pièce creuse prolongeant la première partie tubulaire de la busette et orientant le métal vers les parois latérales de la deuxième partie de la busette.

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

• FIG. 1a which schematically shows, in longitudinal section, a first variant of the invention, where the obstacle consists of a stack of pellets perforated, which are themselves shown in top view in Figures 1b, 1c and 1d;
• FIG. 2 which schematically shows, in longitudinal section, a second variant of the invention, where the obstacle consists of a hollow part extending the first tubular part of the nozzle and orienting the metal towards the side walls of the second part of the nozzle.

In a first example of implementation of the invention, shown in FIGS. 1a-1d, the nozzle 1 is formed, as in the previously cited prior art, of two main parts made of a refractory material such as alumina graphite, which are assembled here to each other by screwing the first into the second. The first part comprises a cylindrical or substantially cylindrical tube 2, the interior space 3 of which constitutes the path for the passage of liquid metal. This tube 2 is normally intended to be held vertically. Its upper part, not shown, is intended to be connected to a container serving as a liquid metal reservoir, such as a continuous casting distributor, at the level of an orifice through which the liquid metal can flow with a flow rate that the operator adjusts by means of a stopper or a drawer device. The lower end 4 of the tube 2 has a thread 5 on its outer wall, and this thread 5 makes it possible to assemble it to the second part of the nozzle 1. This second part is composed of a hollow element 6 which, in the The example described and shown, has the external shape of an inverted T. The interior space 7 of the hollow element 6, also in the shape of an inverted T, thus comprises a cylindrical portion 8 extending the interior space 3 of the tube 2. The upper region of this cylindrical portion 8 comprises a flare 9 whose wall is threaded, so as to be able to screw the lower end 4 of the tube 2. The cylindrical portion 8 opens into a tubular portion 10 which is substantially perpendicular to it, of approximately circular, oval or rectangular section. Each end of this tubular portion 29 has an orifice 11, 11 ′ called "hearing", through which the liquid metal can flow out of the nozzle. During casting, these vents 10, 11 are intended to be kept permanently under the surface of the liquid metal filling the casting space.

According to the invention, the cylindrical portion 8 of the interior space 7 of the hollow element 6 comprises, inside the flare 9 and under the thread of its wall, a housing 12, in which, prior to the 'assembly of the two parts 2, 6 of the nozzle 1, one can place a stack of three pellets of refractory material: an upper pad 13, an intermediate pad 14 and a bottom pad 15. The respective dimensions of the housing 12 and the pads 13 , 14, 15 are chosen so that, after assembly of the nozzle 1, the lower end of the tube 2 abuts against the upper pad 13. The upper pad 13 has a certain number of perforations 16, distributed over the portion of its surface intended to be located directly above the interior space 3 of the tube 2. The intermediate patch 14 comprises a single perforation 17 of shape, for example, square or circular, d opening at least equal to that of the interior space 3 of the tube 2. Its role is, in fact, that of a spacer used to separate the upper 13 and lower 15 pellets. This also includes a certain number of perforations 18, which can be different in number and in size of the perforations 16 of the upper pad 13. But it is important, for obtaining the desired results, that the perforations 16 and 18 are substantially offset from one another, of so that a fraction as small as possible of the liquid metal has the theoretical possibility of crossing the obstacle constituted by all of the pellets 13, 14, 15 without hitting them. For a better obstacle efficiency, it is also preferable that the upper pellet 13 does not have a perforation in its center, where the probability of the presence of liquid metal is the greatest, so as to slow down the casting jet also as early as possible.

In general, the total cross-section of the orifices of a given pellet should not be less than the cross-section of the outlet port of the distributor, in order to guarantee that it will always be possible to flow with a maximum metal flow rate as high as 'in the absence of obstacles.

Optionally, as is already known, the bottom 19 of the hollow element 6 is equipped with perforations 20 called "leak holes". These leakage holes 20 have the usual functions of deflecting part of the metal flows towards the lower part of the mold. This deviation limits the flow rate and the exit speed of the metal at the gills 11, 11 ′ and thus prevents the metal from violently striking the short sides of the ingot mold and disturbing the solidification conditions there. In the case of casting between cylinders, this also makes it possible to avoid excessive deterioration of the refractory side faces. On the other hand, these leakage holes 20 ensure a regular supply of hot metal to the lower part of the pouring space, directly above the nozzle 1: here again, this goes in the direction of better control. solidification conditions. The use of obstacles according to the invention makes it possible to take full advantage of the advantages provided by the leakage holes 20, insofar as these leakage holes 20 are all the more effective as the flows inside the nozzle 1, and in particular in the hollow element 6, are more regular. This allows, in particular, to attenuate the preferential flow of the metal through the leakage holes 20 which are closest to the axis of the nozzle.

• la pastille supérieure 13 possède huit perforations 16 de diamètre 13 mm, réparties en deux rangées de trois perforations séparées par une rangée de deux perforations;
• la pastille intermédiaire 14 possède une perforation unique 17 ayant une section carrée de 60 mm de côté, ou une section circulaire de 60 mm de diamètre;
• la pastille inférieure 15 possède cinq perforations 18 de diamètre 19 mm, à savoir une perforation centrale entourée par quatre perforations disposées en carré.

By way of example, it is possible to propose, for a nozzle 1 whose internal diameter of the tube 2 is 60 mm, and whose openings 11, 11 ′ of the hollow element have a circular section and a diameter of 30 mm, to use an obstacle made up of three pellets 13, 14, 15 with an outside diameter of 100 mm and a thickness of 25 mm, having the following characteristics:

• the upper pad 13 has eight perforations 16 of diameter 13 mm, distributed in two rows of three perforations separated by a row of two perforations;
• the intermediate patch 14 has a single perforation 17 having a square section of 60 mm on the side, or a circular section of 60 mm in diameter;
• the lower pad 15 has five perforations 18 of diameter 19 mm, namely a central perforation surrounded by four perforations arranged in a square.

In this example, during the casting of liquid steel, if the metal crosses the nozzle 1 with a flow rate of 60 t / h, in the absence of an obstacle it only partially fills the interior space of the tube 2. But the obstacle which has just been described is sufficient to slow the flow of the liquid steel so as to reduce its speed to approximately 1 m / s, and to obtain a good filling of the tube 2, as well as a speed regular and fairly substantially uniform output of the metal over the entire section of the openings 11, 11 ′, for this same metal flow rate of 60 t / h. This provides satisfactory stability of the level of the metal in the ingot mold when the flow rate of the metal passing through the nozzle 1 is not modified.

The pellets must be made of a refractory material such as zirconia, in any case compatible with the nature of the cast metal to prevent them from being attacked chemically by the metal in an excessive manner.

Of course, the precise type of obstacle with pellets which has just been described is only a nonlimiting example. One can imagine, in particular to use only one perforated tablet if this is sufficient to obtain an acceptable result under usual casting conditions, or on the contrary to use more than three tablets to accentuate the braking effect. of the casting jet. Likewise, the presence of an intermediate patch 14 with a large single perforation 17, therefore only serving as a spacer between two pellets 13, 15 with small multiple perforations, is not strictly speaking compulsory. However, it makes it possible to limit the wear of the lower pad 15, by avoiding an exclusive concentration of the metal flows on the solid areas of this pad which face the perforations of the upper pad 13.

In a second example of implementation of the invention, represented in FIG. 2 (in which the elements common to those of FIG. 1a are identified by the same reference signs), the obstacle inserted in the nozzle 1 is constituted by a tubular piece 21, provided with a bottom 22 at one of its ends. At its open end, this tubular part 21 has a shoulder 23 which can be inserted into the housing 12 formed in the hollow element 6 and which contained the pellets 13, 14, 15 in the example of implementation of the previous invention. On its side wall 24, the tubular part 21 has perforations 25, 26, 27 which allow the metal liquid to pass from the interior space 28 of the tubular part 21 to the interior space 7 of the hollow element 6, after having lost a large part of its potential energy. In the example shown in Figure 2, these perforations 25, 26, 27 are six in number distributed in three levels over the height of the tubular part 21, and are of approximately oval shape. They preferentially make it possible to orient the liquid metal on the side wall of the cylindrical portion 8 of the interior space 7 of the hollow element 6. In this way, the impact of the metal against this side wall provides energy absorption which is added to that undergone inside the tubular part 21. Likewise, to obtain a residence time of the metal in the nozzle 1 as long and uniform as possible, it is preferable that, as shown, the orientation of these perforations is perpendicular to the orientation of the openings 11, 11 '.

By way of example, a tubular piece 21, the interior space 28 of which would be 84 mm long, 30 mm in diameter, perforations 25, 26, 27 of 10 × 20 mm, would have on the speed and regularity of the flows of metal, an influence substantially comparable to that of the pellets 13, 14, 15 of the obstacle described and shown in FIGS. 1a to 1d, if it were inserted in an identical nozzle 1.

Of course, the examples described above are not limiting. One could, for example, imagine inserting the obstacle inside the tube 2, and not simply in its extension. One could also insert into the nozzle 1 a plurality of obstacles similar to those which have been described, or different in their form but which can fulfill the same functions.

The invention is not limited in its application to the field of continuous casting of flat steel products (slabs, thin slabs, thin strips), even if it finds a preferred application there. It can be applied to many other examples of continuous casting nozzles of all metals in all formats, for which it is desired to obtain a slowing of the flows providing better filling of the nozzle and, therefore, greater stability of the flows of the metal. liquid coming out.

Claims (8)

Nozzle (1) for the introduction of a liquid metal into a mold for the continuous casting of metals, of the type comprising a first tubular part (2), one end of which is intended to be connected to a receptacle containing said liquid metal, and the other end (4) of which opens into a second hollow part (6), at least one portion (29) of the interior space (7) of which is oriented substantially perpendicular to said first tubular part (2), said portion ( 29) comprising at each of its ends at least one orifice (10, 11) intended to open into the casting space of said ingot mold, characterized in that it comprises an obstacle placed on the path of the liquid metal inside of said first tubular part (2) or in its extension, said obstacle being constituted by at least one perforated piece intended to deflect the metal from its preferential path inside the nozzle. Nozzle according to claim 1, characterized in that said obstacle consists of at least one patch perforated by a multiplicity of holes. Nozzle according to claim 1, characterized in that said obstacle consists of a plurality of pellets (13, 15) perforated by a multiplicity of holes (16, 18), and separated from each other by other pellets (14) perforated by a single section hole (17) approaching the interior section of said first tubular part (2). Nozzle according to claim 1, characterized in that said obstacle consists of a tubular part (21), provided with a bottom (22), intended to receive the liquid metal inside, said tubular part (21) comprising perforations (25, 26, 27) on its side wall (24), said perforations (25, 26, 27) allowing the passage of the metal into the interior space (7) of said second part (6) of the nozzle (1) . Nozzle according to claim 4, characterized in that said perforations (25, 26, 27) are oriented towards the internal wall of said second part (6) of the nozzle (1). Nozzle according to one of claims 1 to 5, characterized in that said first part (2) and said second part (6) of the nozzle (1) are assembled by screwing the first part (2) into the second part ( 6), and in that said obstacle is inserted in a housing (12) formed in the interior wall of said second part (6). Nozzle according to one of claims 1 to 6, characterized in that said portion (29) of the interior space (7) of the second part (6) which is oriented substantially perpendicular to the first part (2) has an elongated shape, giving the interior space of the entire nozzle the general shape of a T. Nozzle according to one of claims 1 to 7, characterized in that the bottom (19) of the hollow element (6) comprises at least one leakage hole (20).

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