EP0270418B1 - Float for retaining slags, and method for its use and manufacture - Google Patents

Description

The present invention relates to a slag retaining plug inside a metallurgical container. This plug is intended to close the pouring orifice of the container at the end of the pouring of the liquid metal contained in this container, but before the passage of the slag through this orifice.

The invention also relates to a method for the implementation of this plug.

It is known that, in a metallurgical container containing liquid metal, such as a converter, an oven, a ladle, a distributor, there is always a layer of slag which floats above the liquid metal. It is a constant concern of the metallurgist, during the pouring of the liquid metal, to prevent the passage of slag, likely to pollute the cast metal. To avoid this pollution, the metallurgist plugs the pouring orifice before the passage of the slag.

To plug the pouring orifice, a ball made of material denser than liquid metal such as copper is currently used in the case of liquid steel. This ball has a diameter greater than the inside diameter of the pouring orifice. It is thrown into the metallurgical container at the end of the casting, and because of its density, it sinks into the liquid metal, rolls on the bottom of the container and is placed on the pouring orifice by blocking it. Such a copper ball is expensive and delicate to use since it must not be thrown away too early, which would cause a loss of metal, or too late, which would allow slag to pass. Furthermore, the use of such a copper ball involves a risk of pollution of the liquid metal by copper.

To avoid slag entrainment at the end of the emptying of the converter, of the ladle or of the tundish, shutter valves, slide valves and massive floats have also been proposed. Due to the geometrical variation of the taphole during the successive spills of liquid metal, these massive floats, the diameter of which is constant, do not provide convincing results as to stopping the flow of slag.

A plug of refractory cement in the form of a funnel is also used, extended by a metal rod serving as a guide for such a plug. This plug is suspended from the curved end in the shape of an open ring of a tool; it is released above the pouring orifice at the moment deemed opportune to close off the pouring orifice. The use of such a stopper is delicate and painful because the operator is forced to stand very close to the metallurgical container, so that it is exposed to very intense heat.

Known from JAPANESE PATENT REPORTS, "Mechanical" section, week T24, summary no. 39 164 T, and JP-A-72 20 803, a slag retaining plug inside a metallurgical container, intended to automatically plug the pouring orifice of the container at the end of the pouring of the liquid metal contained in this container before the passage of the slag floating above the liquid metal, this plug comprising a substantially spherical outer casing, made of a refractory material , and a heavy core intended to give the stopper a specific mass such that it floats on the liquid metal by sinking sufficiently into the metal to plug the pouring orifice at the end of the pouring before the passage of the slag.

Such a plug is automatically driven towards the pouring orifice by the currents generated in the liquid metal, so that its use requires no personnel near the metallurgical container. Since the specific mass of the material making up this envelope is less than that of liquid metal, this material floats on the surface of the latter. Thanks to the heavy core, it is possible to adjust the depth of immersion of the stopper in the liquid metal and to determine the height of liquid metal and slag which will remain at the bottom of the metallurgical container when the stopper closes the pouring orifice.

Also known from EP-A-0 128 576 is a retaining plug constituted by a sphere of refractory material surrounded by a metallic envelope. The metal envelope is made up of two hemispherical steel half-shells. Pieces of scrap metal can be embedded in the refractory material to make the plug heavier and to ballast in its lower part.

The object of the invention is to remedy the drawbacks of known devices and to propose a slag retaining plug, effective, inexpensive and very simple to use, making it possible to plug the pouring orifice of a metallurgical container with the end of the pouring of the liquid metal contained in this container before the passage of the slag, without any risk of pollution of the metal.

According to the invention, this plug is characterized in that the envelope consists of two hollow semi-shells substantially of revolution, and in particular hemispherical, assembled using a refractory glue and made of a refractory thermal insulating material which is susceptible sinter at the temperatures prevailing in the container and which is composed of refractory inorganic particles embedded in a binder.

The hollow half-shells can be produced easily by molding and allow the heavy core to be placed easily.

Because the inorganic particles sinter in contact with the liquid metal, the outer envelope of the stopper according to the invention retains its mechanical cohesion while being slightly malleable for the entire duration of its stay in the liquid metal. The envelope does not require any cooking before use.

The plug according to the invention can thus be produced quickly, simply and economically.

According to another embodiment of the invention, the insulating material in which is made

the envelope has a composition and a particle size such that its specific mass is between 0.5 and 2.9 kgldm ³ . This specific mass is much lower than that of liquid steel. The depth of immersion of the plug in liquid steel can thus be easily adjusted by means of the heavy core.

According to a preferred embodiment of the invention, the heavy core is made of metal and has the shape of a cube or a rectangular parallelepiped. The core is preferably placed in the center of the stopper and additional ballasting means are advantageously provided in one of the half-shells to lower the center of gravity of the stopper.

Thus, it is avoided that the plug rotates around itself under the effect of vortices generated in the liquid metal.

The method according to the invention consists in placing in a metallurgical container containing liquid metal a plug of the aforementioned kind and the lower part of which is immersed in the metal bath below the slag bed.

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

• la figure 1 est une vue générale en perspective d'un mode de réalisation d'un bouchon conforme à l'invention,
• la figure 2 est une vue en coupe suivant un plan diamétral du bouchon de la figure 1,
• la figure 3 est une vue en coupe verticale axiale d'un convertisseur en position relevée à l'intérieur duquel on a introduit un bouchon conforme à l'invention,
• la figure 4 est une vue en coupe verticale axiale du convertisseur de la figure 3 en position partiellement basculée pour permettre la coulée du métal dans une poche de coulée,
• la figure 5 est une vue en coupe verticale axiale analogue à la figure 4 montrant le convertisseur en position complètement basculée en fin de coulée au moment où le bouchon vient obturer l'orifice de coulée.

In the appended drawings given by way of nonlimiting examples:

• FIG. 1 is a general perspective view of an embodiment of a plug according to the invention,
• FIG. 2 is a sectional view along a diametrical plane of the plug of FIG. 1,
• FIG. 3 is a view in axial vertical section of a converter in the raised position inside which a plug according to the invention has been introduced,
• FIG. 4 is a view in axial vertical section of the converter of FIG. 3 in the partially tilted position to allow the metal to be poured into a ladle,
• Figure 5 is an axial vertical sectional view similar to Figure 4 showing the converter in the fully tilted position at the end of casting when the plug closes the pouring orifice.

In the embodiment shown in FIGS. 1 and 2, the substantially spherical plug 1 comprises a casing 2 consisting of two half-shells 3, 4, hollow, assembled using a refractory glue 5, surrounding a heavy core 6, for example made of metal, having the shape of a cube or of a rectangular parallelepiped of square section, and which can be a billet section.

The two hollow half-shells 3, 4 are made of a refractory thermal insulating material, composed of refractory inorganic particles, such as silica, and / or alumina, and / or magnesia, ..., and optionally organic and / or mineral fibers, the whole agglomerated using an organic and / or mineral and / or synthetic binder, capable of sintering at the temperature prevailing in the metallurgical container.

The composition of the material and the particle size of the constituents are adjusted so that sintering occurs in the case of steel metallurgy, between 800 ° C and 1500 ° C. The specific mass of this material can vary between 0.5 and 2.9 kg / dm ³ depending on the composition and the particle size of its constituents.

The diameter of the plug 1 is adapted to the diameter of the pouring orifice of the metallurgical container which must be closed, taking into account possible wear of the refractory lining which surrounds this pouring orifice.

The dimensions and the nature of the core 6 are adapted to the diameter and to the composition of the casing 2 so that the specific mass of the plug 1 is such that it floats on the liquid metal while sinking sufficiently into the metal to plug the orifice of the tap hole at the end of the pouring before the slag passes through it.

Thus, in the case of steel metallurgy, the specific mass of the plug 1 is advantageously between 3 and 6.5 kg / dm ³ , and is preferably equal to or greater than 3.8 kg / dm ³ . The core 6 is advantageously made of steel.

It may be advantageous to provide additional ballasting means 7 in the half-shell 4 so as to lower the center of gravity of the plug 1 and to permanently maintain this half-shell 4 in the low position. The plug 1 can thus be prevented from rolling on itself. These additional ballasting means 7 may advantageously consist of sections of metal bars, embedded in the mass of the half-shell 4 or, on the contrary, at least for part of them, welded to the core 6, for example at the underside of the latter so as to exert a maximum return torque. The assembly plane of the two half-shells 3, 4 is thus maintained in all circumstances in a horizontal position.

FIGS. 3, 4 and 5 represent a converter 8, comprising, in a known manner, an outer steel casing 9, a refractory lining 10, a tap hole 11 opening out inside the refractory lining 10 through a pouring orifice 14.

The converter 8 is shown in Figure 3 in the raised position. The converter 8 contains liquid metal 12 ready to be poured and surmounted by a layer of slag 13. A cap 1 for retaining slag 13, according to the invention, has been introduced inside the converter and floats on the metal liquid 12 by partially sinking into the metal.

As soon as the plug 1 is inserted inside the converter 8, due to the ambient temperature, the insulating material situated on the periphery of the two hollow half-spheres 3, 4 begins to sinter. This sintering continues inside the plug 1 as the temperature increases within the plug 1.

Thanks to this sintering, the cohesion of the material is maintained, despite the decomposition of the binder. In addition, it has been observed that the liquid metal does not wet the surface of the stopper and the slag 13 does not become fixed thereon. Therefore, the behavior of plug 1 until the end of casting is not likely to be disturbed by undesirable adhesions of metal or slag liable to modify the depth of immersion of the plug.

To pour the liquid metal 12 from the converter 8 into a second metallurgical container constituted in the example of FIG. 4 by a ladle 15, the converter 8 is rocked in a known manner according to the arrow so that the liquid metal 12 s' flows through the tap hole 11 into the ladle 15 as shown in Figure 4.

The upper level 16 of the metal is always maintained clearly above the level of the pouring orifice 14. The plug 1 floats on the liquid metal 12 by sinking slightly into the metal so that the lower part of the shell 4 is below the upper level 16 of the metal.

At the end of the pouring of the liquid metal 12, the converter 8 being in the fully tilted position shown in FIG. 5, the upper level 16 of the liquid metal 12 is always located above the level of the pouring orifice 14. On the other hand, the plug 1, partially driven by the metal 12 flowing through the tap hole 11, has permanently remained in position above the pouring orifice 14. At a certain moment, the shell 4, the lower part is below the slag bed 13 closes the pouring orifice 14 and stops the flow of metal 12 shortly before the slag 13 passes.

It is important to give the plug 1 a specific mass and a diameter appropriate to the geometry of the converter, to that of the pouring orifice and also to the presumed thickness of the layer of slag so that, during the sealing of the pouring orifice 14 through the shell 4, not only can no slag pass, but also that there remains in the converter the quantity of metal 12 just sufficient to ensure automatic capping.

The composite structure of the plug 1 provided by the invention makes it easy to respond to such specifications.

Thus, provision has been made to produce, for an internal diameter of tap hole of 200 mm, a spherical plug 1 with a diameter equal to 235 mm containing a steel core 6 in the form of a rectangular parallelepiped of height 160 mm and of square section of 130 mm side, mass 19.5 kg, the two hemispherical half-shells 3, 4 being produced by press or by accelerated filtration by pressure or by vacuum using a material as described above. specific mass of approximately 1.6 kg / dm ^3, ie a mass of 6.5 kg for a volume of approximately 4 dm ³ , the lower half-shell 4 being more weighted by means of sections 7 of a bar 25 mm diameter steel representing a total length of 130 mm and a total mass of 0.5 kg. At least one of these sections can be welded to the underside of the core 6.

The stopper thus produced has a mass of 26.5 kg for a total volume of 6.8 dm ³ , or a specific mass of approximately 3.8 kg / dm ³ .

The use of the plug according to the invention is particularly convenient. Indeed, it is enough to throw it in the metallurgical container and it does not then require any monitoring therefore no permanent presence of personnel near the metallurgical container exposed to intense and painful heat.

The material of the stopper has a certain sintering rate. It therefore sintered from its surface and therefore became refractory on the surface, but not at its core. After use, the stopper disintegrates and therefore does not interfere with subsequent operations.

Of course, the use of the plug according to the invention is not limited to the example described. Such a plug can obviously be used in metallurgical vessels other than converters such as ladles and continuous casting distributors. Such a plug can also be used in the metallurgy of metals other than steel, such as aluminum, copper and their alloys, the specific mass of the plug being in this case adapted to that of the liquid metal considered, and the composition of the insulating material of the envelope and the nature of the constituents being adapted so that the sintering takes place at a temperature substantially lower than the temperatures prevailing inside the metallurgical vessels concerned.

Likewise, the shape and composition of the core 6 and additional ballasting means 7 can be modified without departing from the scope of the present invention. In particular, the core 6 can be offset relative to the center of the plug, which eliminates the need for additional ballasting means 7. The shells 3 and 4 can also have different shapes and / or uneven volumes. One can also use sections 7 of bar of square or rectangular section and no longer round, or use for the lower half-shell 4 a material composed of inorganic particles denser than those of the upper half-shell 3 or on the contrary have a half upper shell more dense than the lower.

The manufacturing process by accelerated filtration allows, if desired, to manufacture the plug in one piece while incorporating the ballast mass inside the mold beforehand.

The method of manufacturing by accelerated filtration of the sludge to constitute the plug also makes it possible to manufacture with a substantially central recess by incorporating therein a product of the "hard wax" type used in foundry, or using a polystyrene element, by example on which liquid steel will be cast in the steelworks in order to ballast on the spot and inexpensively said plug.

Claims (10)

1. Plug (1) for retaining slags (13) inside a metallurgical vessel (8), intended automatically to plug the tap orifice (14) of the vessel (8) at the end of the pouring of the liquid metal (12) contained in this vessel (8) before the slags (13) floating on the top of the liquid metal (12) pass through, this plug comprising a substantially spherical outer casing (2) made of a refractory material, and a heavy core (6) which is intended to give the plug (1) a density such that it floats on the liquid metal (12), sinking sufficiently into the metal (12) to plug the tap orifice (14) at the end of the pouring before the slags (13) pass through, characterized in that the casing (2) consists of two hollow half-shells, substantially rotational symmetrical, and in particular hemispherical (3, 4), assembled with the use of a refractory adhesive (5) and made of a refractory thermally insulating material which is able to sinter at the temperatures prevailing in the vessel (8) and which is composed of refractory inorganic particles embedded in a binder.

2. Plug according to Claim 1, characterized in that the insulating material of which the casing (2) is made has a composition and a particle size such that its density is substantially included between 0.5 and 2.9 kg/dm³.

3. Plug according to any one of the preceding claims, characterized in that the heavy core (6) is of metal and has the shape of a cube or of a parallelepiped.

4. Plug according to Claim 3, characterized in that the core (6) is arranged in the centre of the plug (1) and that supplementary ballasting means (7) are provided in one (4) of the half-shells (3, 4) to lower the centre of gravity of the plug (1).

5. Plug according to Claim 4, characterized in that the supplementary ballasting means (7) consist of one or more sections of metal bars.

6. Plug according to any one of the preceding claims, which is usable in metallurgical vessels containing liquid steel, characterized in that the specific mass of the plug (1) is included between 3 and 6.5 kg/dm³ and in that the insulating material constituting the casing (2) has a composition such that the sintering occurs between 800°C and 1,500°C;

7. Plug according to Claim 6, characterized in that the specific mass of the plug (1) is substantially equal to 3.8 kg/d_m ³.

8. Procedure for the closing, at the end of pouring, of a metallurgical vessel containing liquid metal with slags on the top, consisting in placing in the said vessel a floating plug according to one of Claims 1 to 7, the bottom part of which is immersed in the bath of metal beneath the bed of the slags.

9. Procedure for making a plug according to one of Claims 1 to 7, consisting inmaking it in one or more elements either by pressing, or by pressure and/or vacuum accelerated filtration of the slurries of which it is composed.

10. Procedure for making a plug according to Claim 9, consisting in incorporating the ballasting mass or masses during or after its production, in the form of a solid and/or a liquid.

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