EP0065514B1 - Thermally insulating casting tube for metallurgic container - Google Patents

Abstract

A heat insulating casting tube is disposed between the outlet orifice of a first metallurgical vessel and a second metallurgical vessel. One end of the casting tube has a removable and substantially leaktight engagement about a casting nozzle or an adapter forming an extension of the nozzle of the first vessel. The casting tube is formed of a material sinterable under the action of the heat of the liquid metal as it flows in the tube. A ring of refractory material is disposed on the tube end engaged on and surrounding the lateral surface of the casting nozzle or adapter. The internal surface of this ring is shaped as the lateral surface of the casting nozzle or adapter and has a substantially leaktight engagement with that lateral surface. The height of the ring is such that its bottom edge is located above the zone in which the liquid metal which is poured into the tube would be liable to come into contact with the internal surface of the tube.

Description

The present invention relates to a thermally insulating pouring tube intended to be placed between the pouring orifice of a first metallurgical container such as a ladle and a second metallurgical container such as a tundish.

Known pouring tubes are produced in different categories of materials.

In one of these categories, the tube material is highly refractory such as silica, magnesia, zirconia, and isostatically pressed carbon.

These materials have the advantage of having remarkable mechanical and heat resistance, so that the tubes produced in such materials have a very long service life.

The disadvantages of these materials are numerous, however.

Firstly, because of their poor thermal insulating power and / or to prevent them from bursting, these tubes require long and costly preheating before casting the liquid metal, to limit the risks of solidification of this metal in contact with their wall, this solidification being able to generate a complete sealing of these tubes.

Secondarily, these tubes are heavy, therefore difficult to handle and are very expensive.

To remedy the aforementioned drawbacks, the applicant has described in its French patent No. 2 333 599 a pouring tube made of thermal insulating material constituted by refractory inorganic particles (silica, alumina, magnesia) possibly added with mineral or organic fibers, these particles and fibers being coated in an organic or inorganic binder.

Due to the remarkable insulating properties of this material, such tubes require no preheating. In addition, these tubes are light and therefore easy to handle and inexpensive.

During the casting of the liquid steel, the organic constituents of material of these tubes decompose but the cohesion of the tubes is maintained due to the sintering of the inorganic particles, under the effect of the heat given off when the liquid metal passes through it. inside the tube.

The decomposition of organic constituents and the sintering of inorganic particles give the material a porous structure with a high power of thermal insulation. The Applicant has noted, however, that at the upper end of these tubes by which they are engaged in the nozzle of the ladle, the aforementioned sintering did not take place because the material of the tube is not at this location, not in direct contact with the jet of liquid metal.

Therefore, at this end, the material tends to crumble quickly, so that at the end of casting, the seal is no longer formed between the pouring tube and the pouring nozzle on which its end is engaged.

This leakage then risks allowing the introduction of air inside the tube, by suction effect, which is likely to form inclusions of oxides within the metal. As a result, such pouring tubes generally become unusable after a single casting operation.

The finding of this drawback is the basis of the present invention.

French Patent 1,551,363 describes a conventional refractory material pouring nozzle, that is to say practically free of organic material. At the top of this nozzle and on the internal surface of the latter is inserted a ring of refractory material harder than the refractory material of the nozzle. The role of this hard ring is to limit the wear caused at the entry of the nozzle, by the passage of liquid metal. Such a ring of refractory material, if it was placed inside a tube of insulating and sinterable material, as described in French Patent No. 2,333,599, on the one hand would not solve the problem the crumbling of the material of the tube in the part which surrounds the nozzle and the other by risking causing the solidification of the metal in contact with this ring.

The object of this invention is therefore to overcome this drawback, by creating a pouring tube having all the advantages of the tubes described in French patent n ° 2 333 599, while having a considerably prolonged life.

According to the invention, the thermally insulating pouring tube intended to be placed between the pouring orifice of a first metallurgical container and a second metallurgical container, one end of the pouring tube being intended to be engaged in a removable manner and substantially sealed on the pouring nozzle or on an adapter extending the nozzle of the first container, this pouring tube being made of a material consisting of inorganic particles optionally added with fibers, coated in a binder, these inorganic particles being sinterable under the effect of the heat of the liquid metal passing through this tube, is characterized in that the end of the tube intended to be engaged on the pouring nozzle comprises a ring of refractory material practically free of organic matter, the internal surface of this ring being intended to come into direct contact with the pouring nozzle or with the adapter extending the nozzle, the height of this ring being sufficient sufficiently weak so that the lower part of the internal surface of the ring cannot come into contact with the liquid metal passing through this tube.

This refractory ring thus mechanically strengthens the part of the pouring tube which does not undergo the sintering effect indicated in the introduction to this description.

Thanks to this refractory ring, the seal between the tube and the pouring nozzle remains excellent even after several successive casting operations.

In addition, this refractory ring does not reduce insulating properties of the pouring tube and does not entail any risk of solidification of the liquid metal, since this ring does not come into direct contact with this metal.

According to an advantageous version of the invention, the height of the aforementioned refractory ring is at least equal to the distance over which the end of the tube is intended to be engaged on the pouring nozzle of the first metallurgical container.

The tightness between the pouring tube and the nozzle are thus maintained under excellent conditions.

According to a preferred version of the invention, the pouring tube is produced by molding and the ring of refractory material is fixed to the material of the wall of the tube, during this molding.

The fixing of the refractory ring to the tube can thus be carried out without any additional difficulty.

Since the end of the pouring tube opposite the pouring nozzle is generally intended to immerse in the liquid metal which is poured into the second metallurgical vessel, it is advantageous that this end of the pouring tube also includes a refractory ring.

Thus, this end of the pouring tube is not liable to wear out by melting on contact with the liquid metal, and therefore, the life of this tube is further extended.

Other features and advantages of the invention will appear in the description below.

• - la figure 1 est une vue en coupe longitudinale partielle, du fond d'une poche de coulée et d'un répartiteur de coulée placé sous cette dernière, un tube de coulée conforme à l'invention étant disposé sous la busette de sortie de la poche de coulée,
• - la figure 2 est une vue en coupe longitudinale partielle, à grand échelle, montrant l'extrémité supérieure du tube de coulée, engagée sur la busette de coulée, ainsi que le jet de métal liquide passant dans ce tube.
• - les figures 3 à 7 sont des vues en coupe longitudinale partielle, montrant diverses variantes de l'invention,
• -la figure 8 est une vue en coupe longitudinale de l'extrémité inférieure d'une version avantageuse du tube de coulée conforme à l'invention, plongeant dans le métal liquide contenu dans le répartiteur de coulée,
• - la figure 9 est une vue en coupe longitudinale d'un tube de coulée engagé sur un adaptateur pour busette à tiroir et la figure 10 est une autre variante en coupe longitudinale.

In the appended drawings, given by way of nonlimiting examples:

• - Figure 1 is a partial longitudinal sectional view of the bottom of a ladle and a tundish located under the latter, a pouring tube according to the invention being disposed under the outlet nozzle of the ladle,
• - Figure 2 is a partial longitudinal sectional view, on a large scale, showing the upper end of the pouring tube, engaged on the pouring nozzle, as well as the jet of liquid metal passing through this tube.
• FIGS. 3 to 7 are views in partial longitudinal section, showing various variants of the invention,
• FIG. 8 is a view in longitudinal section of the lower end of an advantageous version of the pouring tube according to the invention, immersed in the liquid metal contained in the pouring distributor,
• - Figure 9 is a longitudinal sectional view of a pouring tube engaged on an adapter for nozzle with drawer and Figure 10 is another variant in longitudinal section.

In the embodiment according to FIG. 1, the bottom 2 of the ladle 1 includes a pouring nozzle 3 made of a highly refractory material such as silica, magnesia, refractory brick or zirconia.

This pouring nozzle 3 is arranged above a pouring distributor 4. Around this nozzle 3, is engaged in a removable manner, the upper end 5a of a pouring tube 5, slightly frustoconical whose lower end is intended to be immersed in the liquid metal which is introduced into the tundish 4.

The removable fastening means of the pouring tube 5 to the nozzle 3 are not shown. These means can be of the kind described in French patents No. 2,333,599 and No. 2,409,809.

The pouring tube 5 comprises an outer protective sleeve 6 made of metal sheet, for example of steel, which surrounds an inner wall 7 made of a thermally insulating and light material. This material consists of inorganic particles (silica, alumina, magnesia), added with inorganic fibers, coated in an organic binder such as a synthetic resin or an inorganic binder. The composition of this material is such that the inorganic particles sinter under the effect of the heat given off by the molten metal which is poured into the tube, which makes it possible to maintain the cohesion and the insulating properties of this material, despite the decomposition of the organic components of it.

According to the invention, the end 5a of the tube 5 engaged on the pouring nozzle 3 comprises a ring 8 of refractory material, the internal surface 8a of this ring being in direct contact with the casting nozzle 3.

The refractory material of the ring 8 is of the same nature as that of the nozzle 3. It can be, for example, silica, magnesia, refractory brick, isostatically pressed carbon or chamotte. These materials all have the advantage of having excellent mechanical and thermal resistance. In addition, they have a very high dimensional stability, so that it is possible to obtain a very precise adjustment of the ring 8 on the nozzle 3.

In the embodiment according to FIGS. 1 and 2, the height of the refractory ring 8 is greater than the distance over which the end 5a of the tube 5 is engaged on the pouring nozzle 3.

In addition, the thickness of the wall of the refractory ring 8 is substantially equal to the thickness of the wall 7 of the tube 5, so that the inner 8a and outer surfaces of the ring 8 are located substantially in the extension inner 7a and outer surfaces of the wall 7 of the tube 5.

The thermally insulating wall 7 is obtained by molding in a mold, the outer wall of which is formed by the sheet 6. This molding makes it possible to obtain direct adhesion of the material of the wall 7 to the sheet 6. In addition, the direct connection between the material of the wall 7 and the refractory ring 8 can also be obtained during this molding. We can nevertheless provide other means of fixing the ring 8 to the sheet 6 and / or to the insulating wall 7, such as screws, cement or glue.

In the alternative embodiment of FIG. 3, the contact surface between the refractory ring 9 and the insulating material constituting the wall 7 of the pouring tube comprises an annular recess 10. The ring 9 is thus fitted onto the wall 7, which improves the mechanical connection between this wall 7 and the ring 9 obtained during molding. In addition, this annular step 10 makes it possible to maintain a certain thermal insulation in the part 7b of the wall 7.

In the version represented in FIG. 4, the thickness of the wall of the ring 11 is less than that of the wall 7 of the tube, the internal surface 11 a of this ring 11 being arranged substantially in the extension of the internal surface 7a of the wall 7. This ring 11 is thus entirely embedded in an annular recess 7c formed at the end of the tube. This arrangement is favorable as regards the solidity of the fixing of the ring 11 to the wall 7 and the thermal insulation at the level of the ring 11 in the part 7d.

In the embodiment of Figure 5, the refractory ring 12 has an inner diameter smaller than the inner diameter of the tube and the outer surface 12a of this ring is arranged in the extension of the inner surface 7a of the tube. The fixing of this ring 12 in the tube is ensured by the fitting which results from the taper of the outer surface 12a of the ring 12 and of the inner surface 7a of the tube. This fixing can possibly be reinforced by gluing or other suitable mechanical means.

In the variant of FIG. 6, the refractory ring 13 has an outside diameter greater than the inside diameter of the tube and this ring is a part embedded in an annular shoulder 13a formed in the wall 7.

In the embodiment of FIG. 7, the refractory ring 14 has at the upper part of its internal surface an annular widening 14a, receiving the free end of the nozzle 3. This arrangement improves the seal between the upper part of the tube and the nozzle 3. In addition, the shoulder 14b constitutes a stop which ensures perfect axial positioning of the tube relative to the nozzle while avoiding any risk of relative entanglement between the nozzle and the ring 14.

The above-mentioned embodiments have in common the following technical advantages:

First, taking into account the mechanical properties of the refractory material constituting the rings 8, 9, 11, 12, 13 and 14, it is possible to obtain a very precise adjustment between the inner surface of these rings and the outer surface of the nozzle 3.

On the other hand, taking into account the high abrasion resistance of these rings, a perfect seal between them and the nozzle 3 is maintained even after several successive positions of the tubes on the nozzle.

During casting, the rings according to the invention undergo no chemical transformation. In addition, since these rings are generally made of a refractory material of the same kind as that of the nozzle 3, these rings undergo thermal expansion comparable to that of the nozzle 3, so that no play is formed between these rings and the nozzle. The junction thus remains perfectly sealed and any possible introduction of air inside the tube and any risk of oxidation of the liquid metal are avoided.

During casting, the diameter of the jet of liquid metal 15 (see FIG. 2) which flows from the nozzle 3 is braked due to the gradual narrowing of the internal diameter of the tube 5, which results in a widening of the jet 15 to its upper part 15a. The contact between the jet of liquid metal 15 and the wall 7 of the tube 5 causes sintering of the material constituting this wall. This sintering maintains the mechanical cohesion of this material during casting. This sintering does not, however, take place in the zone 16b of the wall 7 close to the nozzle 3, because the latter is not in direct contact with the metal jet 15, as can be seen in FIG. 2. This zone 16b thus tends to crumble due to the decomposition of the binder under the effect of heat. Thus, in the absence of the refractory ring 8, at the end of casting, the zone 16b of the wall 7 of the tube 5 would be completely decomposed and this would necessarily result in a significant annular clearance between the upper part of the wall 7 of the tube and the nozzle 3. This play would thus allow the introduction of air inside the tube and consequently, the oxidation of the liquid metal, so that this tube would no longer be usable for a new casting.

In the case of the invention, the decomposition of the zone 16b of the wall 7 of the tube 5 does not cause any drawback, because the ring 8 ensures at the end of casting, as at the beginning of it, a perfect seal between the nozzle 3 and the tube 5.

In addition, at the end of casting, the part of the wall 7 located below the zone 16b remains perfectly coherent retains a high thermal insulation power due to the porous structure obtained by sintering.

Thus, the tube according to the invention remains usable for several successive castings.

When the end of the tube 5 is intended to immerse in the liquid metal, which is poured into the tundish 4, the outer sheet 6 melts in contact with the liquid metal and the same applies to the material of the wall 7 of the tube. This can also prevent the reuse of the pouring tube 5.

To remedy this problem, it is advantageous to provide the free end of the tube 5 with another ring 16 of refractory material resistant to contact with liquid metal 17, as indicated in FIG. 8.

The height of this ring 16 corresponds at least to the depth of immersion of the end of the pouring tube in the metal 17 contained in the tundish.

In the embodiment shown, the thickness of the wall of this ring 16 is substantially equal to the thickness of the wall 7 of the tube, plus that of the sheet 6. This sheet 6 completely covers the wall 7 of the tube and stops at the level of the ring 16 to avoid any direct contact with the liquid metal 17.

The ring 16 can be fixed to the wall 7 of the tube 5 during the molding of this wall, as in the case of the upper rings shown in FIGS. 1 to 7. The fixing of this ring 16 to the wall 7 is improved when the contact surface of this attachment has an annular recess 16a as shown in FIG. 8.

Thanks to the refractory ring 16, the end of the tube 5 does not risk being damaged in contact with the liquid metal 17, and therefore, this tube can be reused for several successive castings.

Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to these.

Thus the invention can also be applied to the case where an adapter 18 is interposed between a short nozzle 19, and the pouring tube 5, as indicated in FIG. 9. This nozzle 19 is part of the drawer 20 of a system of 'opening and closing called "drawer nozzle" of the orifice of a ladle. In this case, the adapter 18 of refractory material has at its upper part an annular cavity 21 which receives the end of the nozzle 19. The frustoconical lower end 18a of the adapter 18 is fitted in a sealed manner in the interior surface 11 a of a refractory ring 11.

In this embodiment the refractory ring 11 plays. the same role vis-à-vis the adapter 18 as vis-à-vis the casting nozzle 3 in the case of the previous embodiments.

This adapter 18 is necessary in all cases where the pouring nozzle is too short. This adapter 18 sometimes also acts as a box for collecting the gases intended to be blown into the liquid steel.

In addition, the shape and method of attachment of the upper refractory ring can be changed to suit all possible shapes of nozzles, provided that the inner surface of the ring is in direct contact with the outer surface of the nozzle.

Likewise, the shape and the method of fixing the lower ring 16 can be modified provided that the liquid metal contained in the tundish does not come into direct contact with the insulating wall 7 and with the outer sheet 6.

For ease of assembly and to prevent the lower ring from deteriorating during transport, it can be incorporated into the sheet 6. The molten steel coming into contact with the sheet 6 melts the latter over the entire depth immersion in the steel bath. Therefore, it is advantageous to incorporate this ring high enough in the outer sheet 6 so that the lower part of this non-molten sheet can hold the ring in place.

Of course, the pouring tube according to the invention can be used for other metallurgical vessels than the ladles and the tundish.

On the other hand, it is advantageous for the outer sheet 6 of the pouring tube 5 to include an annular bead 22 projecting outwards (see FIG. 2) defining an empty annular space 23 between the sheet and the thermally insulating inner wall 7 . This bead 22 serves to maintain, by means of a support 24, the tube 5 in abutment against the external surface of the nozzle 3.

In the embodiment shown in Figure 2, the empty annular space 23 communicates with a horizontal tube 25 connected to a source of non-oxidizing or inert gas such as argon. This bead 22 is preferably arranged opposite the non-sinterable zone 16b adjacent to the ring 8 of the wall 7, which remains porous. Thus, the gas introduced into the annular space 19 diffuses through the wall 7, in a regular manner, all around the latter and penetrates inside the tube 7, providing the liquid metal with additional protection against the 'oxidation.

In the embodiment of Figure 10, the outer sheet 6 has at its upper part a second annular bead, constituted by a winding 26 from the edge of the sheet inward. This winding 26 is supported on the adjacent end of the insulating wall 7. This winding 26 defines an annular duct communicating with an inlet pipe 28 of inert gas such as argon. The winding 26 has a series of openings 27 directed radially towards the axis of the tube 5.

The advantage of this arrangement is as follows: since the ring 8 is made of hard refractory material, this material is liable to flake when it is brought too suddenly into contact with the refractory and hard material of the same kind than the nozzle 3 or the extension 19. The scales thus formed can generate air inlets inside the pouring tube 5, by suction (Venturi effect). The winding 26 provided with openings 27 makes it possible to produce jets of argon or other inert gas all around the nozzle 3, thereby avoiding any penetration of air inside the tube 5.

Claims (16)

1. Heat-insulating casting tube (5) to be placed between the casting outlet of a first metallurgical vessel (1) and a second metallurgical vessel (4), one of the ends (5a) of the casting tube being intended to be engaged in a removable and substantially leak-tight manner on the casting nozzle (3) or on an adapter (18) forming an extension of the nozzle (19) of the first vessel (1), this casting tube being formed of material consisting of inorganic particles to which fibers may be added and which are embedded in a binder, these inorganic particles being sinterable under the action of the heat of the liquid metal as it flows within this tube, characterized in that the tube end (5a) to be engaged on the casting nozzle (3) is provided with a ring (8, 9, 11, 12, 13, 14) of refractory material which is practically free of organic material, the internal surface of this ring being intended to come into direct contact with the casting nozzle (3) or with the adapter (18) which forms an extension of the nozzle (19) the height of this ring being sufficiently small to ensure that the lower portion of the internal surface of the ring cannot come into contact with the liquid metal which flows within this tube. 2. Casting tube in accordance with claim 1, characterized in that the height of the ring (8, 9, 11, 12, 13, 14) of refractory material is at least equal to the distance over which the said end (5a) of the tube (5) is intended to be engaged on the said casting nozzle.

3. Casting tube in accordance with either of claims 1 or 2, the tube being formed by moulding, characterized in that the ring (8, 9, 11, 12, 13, 14) of refractory material is attached to the material of the wall (7) of the tube (5) during the moulding of this latter.

4. Casting tube in accordance with any one of claims 1 to 3, characterized in that the thickness of the wall of the refractory ring (8, 9, 11) is substantially equal to the thickness of the wall (7), the internal and external surfaces of the ring being substantially coextensive with the internal and external surfaces of the wall (7) of the tube.

5. Casting tube in accordance with claim 4, characterised in that the contact surface between the-refractory ring (9) and the wall (7) of the tube has at least one stepped annular recess (10).

6. Casting tube in accordance with any one of claims 1 to 3, characterized in that the thickness of the refractory ring (11) is smaller than that of the wall (7) of the tube, the internal surface (11 a) of this ring being substantially coextensive with the internal surface (7a) of the tube.

7. Casting tube in accordance with any one of claims 1 to 3, characterized in that the internal diameter of the refractory ring (12, 13) is smaller than the internal diameter of the tube.

8. Casting tube in accordance with claim 7, characterized in that the external surface (12a) of the ring (12) is coextensive with the internal surface (7a) of the tube.

9. Casting tube in accordance with claim 7, characterized in that the external diameter of the refractory ring (13) is greater than the internal diameter of the tube and that this ring is partially sunk within an annular recess (13a) formed in the wall (7) of the tube.

10. Casting tube in accordance with any one of claims 1 to 9, characterized in that the refractory ring (14) is provided at the top portion of its internal surface with an annular enlargement (14a) for receiving the free end of the casting tube (3).

11. Casting tube in accordance with any one of claims 1 to 10, the end of this tube opposite to the nozzle (3) of the first vessel (1) being intended to dip into the liquid metal (17) which is poured into the second vessel (4), characterized in that the said tube end is also provided with a refractory ring (16).

12. Casting tube in accordance with claim 11, characterized in that the height of the ring (16) is at least equal to the depth of immersion of the tube (5) in the liquid metal (17) contained within the second casting vessel (4).

13. Casting tube in accordance with either of claims 11 or 12, characterized in that the thickness of the ring (16) is substantially equal to the thickness of the wall (7) of the tube (5).

14. Casting tube in accordance with any one of claims 1 to 13 and comprising a protective outer sheet-metal sleeve, characterized in that this sheet-metal sleeve is provided with an annular bulge (22) which projects outwards and defines an empty annular space (23) between this sheet-metal sleeve and the internal wall (7) of the tube, this space being intended to communicate with a pipe (28) connected to a source of non-oxidizing or inert gas.

15. Casting tube in accordance with claim 14, characterized in that the said annular bulge (18) is adjacent to the refractory ring (8).

16. Casting tube in accordance with either of claims 14 or 15, characterized in that the external sheet-metal sleeve (6) is provided at the top with an annular bulge constituted by a rolled-in edge (26) of the sheet-metal sleeve, this rolled-in edge being applied against the adjacent end of the wall (7) of the tube and intended to define within its interior an annular duct which communicates with a pipe (28) for the admission of inert gas, this rolled-in edge (26) being provided with a series of openings (27) directed radially towards the axis of the tube.

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