EP0765702B1 - 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 tubes made of refractory material called "nozzles" which, usually are connected by their upper end to the container used for liquid metal reservoir, the lower end of which dips into the metal bath liquid contained in the ingot mold where the solidification of the product must begin metallic. The primary role of these nozzles is to protect from oxidation atmospheric the jet of liquid metal on its path between the container and the mold. They also allow, thanks to appropriate configurations of their end lower, to favorably direct the flow of liquid metal in the 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 under slab shape, i.e. products about 1 to 2 m wide and a thickness generally of the order of 20 cm, but which can go down to a few cm on certain 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 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, we use ingot molds, the casting space is delimited on its long sides by a pair of cooled cylinders internally with parallel horizontal axes and rotating around these axes in a direction inverses, and on its short sides by closing plates (called lateral faces) made of refractory material applied against the ends of the cylinders. Cylinders can also be replaced by cooled endless belts.

In these types of ingot mold, it is considered preferable to orient the liquid metal flows favorably towards the short sides of casting space. We thus seek, in particular, to obtain a homogenization thermal of the metal so as to attenuate variations in the solidified thickness depending on the perimeter of the mold. This thermal homogenization and agitation of the bath liquid it requires are particularly crucial in the case of pouring 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 lateral faces, this metal would cool abnormally intensely, and we would see undesirable metal solidifications on the lateral faces.

To obtain the desired homogenization, it is sometimes used, in particular in casting between cylinders, two-part nozzles (see document JP-A-60021171). The first part is composed of a cylindrical tube whose upper end is connected to an opening in the bottom of the distributor which constitutes the reserve of liquid steel feeding the ingot mold, 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 section of this orifice depends on the flow maximum of metal that can flow inside the nozzle. The second part, fixed at the lower end of the previous tube, for example by screwing, is intended to be immersed in the bath of liquid metal present in the mold. She is composed a hollow element inside which opens the lower orifice of the cylindrical tube previous. 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 of the ends of the elongated end part of the hollow element, and called "hearing".

When a significant steel flow, for example of the order of 60 t / h, circulates at inside the nozzle, the speed of the metal in the tubular part easily reaches several meters per second. Under these conditions, we observe only a very filling partial of the section of the cylindrical part of the nozzle by the liquid metal. This improper filling has several disadvantages. First, by an "effect of ", it tends to favor the suction of outside air through the porosities of the refractory and any leaks in the connection between the nozzle and the distributor, this which deteriorates the quality of the 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 high 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 disadvantage that we mentioned. We can thus observe asymmetries in the flows which are established on the right and left portions of the ingot mold. This instability and this asymmetry cause waves to appear. the interior of the liquid metal bath in an ingot mold which permanently varies the level of its surface, which is very unfavorable to the regularity of the solidification of the product. These waves also cause the device detecting the level to react unduly. of the surface and the regulation of its position: it will seek to compensate for what it takes for variations in the average level of the metal when ordering modifications rapid and continuous opening of the stopper or the drawer. And these Continuous changes will, in fact, worsen 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 quieter and more fluid metal flow conditions in the mold regular than the nozzles usually used when pouring products metallurgical continuously.

To this end, the invention relates to a nozzle for the introduction of a metal liquid in a continuous metal casting ingot mold, 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 consisting of at least one perforated part intended to divert the metal from its preferential path inside the nozzle.

According to a first variant of the invention, said obstacle consists of at minus one patch 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 having openings on its side wall.

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

As will be understood, the invention consists in interposing on the course of the liquid metal an obstacle intended to impede its natural flow, by deviating brutally this flow of its theoretical preferential trajectory and by reducing locally the section of space available for the passage of metal. This has the effect, at equal metal flow, limit the speed of flow and improve filling of the interior space of the nozzle as a whole. This reduces variations erratic in the conditions of the flow of metal out of the nozzle, and the symmetry of the flows in the right and left halves of the mold and the regularity in time of these flows are significantly improved.

• la figure 1a 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 perforated pellets, which are themselves shown in plan view in FIGS. 1b, 1c and 1d ;
• Figure 2 which shows schematically, in longitudinal section, a second variant of the invention, where the obstacle is constituted by 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 the 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 graphite alumina, which here are assembled to each other by screwing the first into the second. The first part comprises a cylindrical or substantially cylindrical tube 2, of which the interior space 3 constitutes the path for the passage of the liquid metal. This tube 2 is normally intended to be held vertically. Its upper part no shown is intended to be connected to a container serving as a metal reservoir liquid, such as a continuous flow distributor, at an orifice through which the metal liquid can flow with a flow that the operator regulates by means of a stopper or of 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 example described and shown, externally has the shape of an inverted T. Interior space 7 of the hollow element 6, also in the form of an inverted T, thus comprises a portion cylindrical 8 extending the interior space 3 of the tube 2. The upper zone of this cylindrical portion 8 has a flare 9, the wall of which is threaded, so as to ability to screw the lower end 4 of the tube 2. The cylindrical portion 8 opens out in a tubular portion 10 which is substantially perpendicular thereto, of section approximately circular, oval or rectangular. Each end of this tubular portion 29 has an orifice 11, 11 'called "hearing", through which the metal liquid can flow out of the nozzle. During casting, these vents 10, 11 are intended to be permanently maintained under the surface of the filling liquid metal casting space.

According to the invention, the cylindrical portion 8 of the interior space 7 of the element hollow 6 has, 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, a stack of three pellets of refractory material can be placed: a upper pad 13, an intermediate pad 14 and a lower pad 15. The respective dimensions of the housing 12 and the pads 13, 14, 15 are chosen such that so that, after assembly of the nozzle 1, the lower end of the tube 2 comes in abutment 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 at plumb with the interior space 3 of the tube 2. The intermediate patch 14 has a single perforation 17 of shape, for example, square or circular, opening at less 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. also has a number of perforations 18, which may be different in number and in size of the perforations 16 of the upper patch 13. But it is important, for obtaining the desired results, that the perforations 16 and 18 are noticeably offset from each other, so that a fraction as small as possible of the liquid metal has the theoretical possibility of cross the obstacle constituted by all the pellets 13, 14, 15 without hitting them. For a better obstacle efficiency, it is also preferable that the tablet upper 13 does not have a perforation in its center, where the probability of presence of liquid metal is most important, so as to slow down the pouring jet as early as possible.

In general, the total section of the orifices of a given patch should not not be less than the cross section of the distributor outlet, to ensure that we can always sink with a maximum metal flow as high as in the absence obstacle.

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 for 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 hitting violently the small sides of the mold and disturb the conditions of solidification. 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 holes leak 20 ensure a regular supply of hot metal to the lower part of the casting space, directly above the nozzle 1: here again, this goes in the direction of better control of 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 by 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 formed by 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, when pouring 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 for braking the flow of 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 regular metal exit speed and fairly substantially uniform over the entire section of the openings 11, 11 ′, for the same metal flow rate of 60 t / h. This provides satisfactory stability of the metal level in the mold when the flow rate of the metal passing through the nozzle 1 is not changed.

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 excessively chemically attacked by the metal.

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

In a second example of implementation of the invention, shown in the Figure 2 (on which the elements common to those of Figure la are identified by the same reference signs), the obstacle inserted in the nozzle 1 is constituted by a tubular part 21, provided with a bottom 22 at one of its ends. At its end open, this tubular part 21 has a shoulder 23 which can be inserted in the housing 12 formed in the hollow element 6 and which contained the pellets 13, 14, 15 in the example of implementation of the preceding 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 the number of six distributed in three levels over the height of the tubular piece 21, and are shaped approximately oval. 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 absorption of energy which is added to that undergone inside the tubular part 21. Similarly, for 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 vents 11, 11 '.

By way of example, a tubular piece 21, the interior space 28 of which would have a length of 84 mm, diameter of 30 mm, perforations 25, 26, 27 of 10x20 mm, have an influence on the speed and regularity of metal flows substantially comparable to that of the pellets 13, 14, 15 of the obstacle described and shown in Figures 1a to 1d, if it was inserted into an identical nozzle 1.

Of course, the examples described above are not limiting. We could, for example, imagine inserting the obstacle inside the tube 2, and not not just 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 can fulfill the same functions.

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

Claims (8)

1. Nozzle (1) for introducing a liquid metal into a mould for continuous casting of metals, of the type comprising a tubular first part (2), one end of which is intended to be connected to a receptacle enclosing the said liquid metal, and the other end (4) of which opens into a hollow second part (6) in which at least one portion (29) of the internal space (7) is oriented substantially perpendicularly to the said tubular first part (2), the said portion (29) comprising at each of its ends at least one orifice (10, 11) intended to open into the casting space of the said mould, characterized in that it comprises an obstacle placed in the path of the liquid metal inside the said tubular first part (2) or in its extension, the said obstacle consisting of at least one perforated component intended to divert the metal from its preferential trajectory inside the nozzle.
2. Nozzle according to Claim 1, characterized in that the said obstacle consists of at least one disc perforated with a multiplicity of holes.
3. Nozzle according to Claim 1, characterized in that the said obstacle consists of a plurality of discs (13, 15) perforated with a multiplicity of holes (16, 18) and separated from each other by other discs (14) perforated with a single hole (17) of section approaching the internal section of the said tubular first part (2).
4. Nozzle according to Claim 1, characterized in that the said obstacle consists of a tubular component (21) provided with a bottom (22), intended to receive the liquid metal inside it, the said tubular component (21) comprising perforations (25, 26, 27) in its side wall (24), the said perforations (25, 26, 27) permitting the metal to pass into the internal space (7) of the said second part (6) of the nozzle (1).
5. Nozzle according to Claim 4, characterized in that the said perforations (25, 26, 27) are oriented towards the inner wall of the said second part (6) of the nozzle (1).
6. Nozzle according to one of Claims 1 to 5, characterized in that the said first part (2) and the said second part (6) of the nozzle (1) are assembled by screwing the first part (2) into the second part (6) and in that the said obstacle is inserted into a housing (12) arranged in the internal wall of the said second part (6).
7. Nozzle according to one of Claims 1 to 6, characterized in that the said portion (29) of the internal space (7) of the second part (6) which is oriented substantially perpendicularly to the first part (2) has an elongate shape, giving the internal space of the whole of the nozzle the general form of a T.
8. Nozzle according to one of Claims 1 to 7, characterized in that the bottom (19) of the hollow member (6) comprises at least one leakage hole (20).

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