EP0214882B2 - Protective lining for the interior of a metallurgical vessel, and process for making the lining - Google Patents

Abstract

An internal lining for protecting the permanent refractory lining of a metallurgical vessel (1, 2) such as a tundish, casting ladle or slag pot has a base of refractory inorganic particles coated with a binder. The protective internal lining is constituted by at least two layers, namely an inner layer (3) which sinters throughout its mass under the action of heat of the molten metal contained in the metallurgical vessel, and a layer (4 or 5) which does not sinter at all or sinters only to a partial extent in order to remain friable even when the inner layer (3) has completely sintered.

Description

The present invention relates to a coating for protecting the interior of a metallurgical container intended to contain a liquid metal such as liquid steel.

The invention also relates to a method for producing such a protective coating.

The metallurgical container which it is desired to protect by means of a coating in accordance with the invention may be a ladle, a tundish or a slag tank.

These metallurgical vessels generally comprise an outer steel casing which is coated internally with a lining of refractory material such as bricks made of magnesia, alumina or silico-aluminous or of refractory cement.

At the end of casting, it is necessary to remove the residues remaining in the containers which have contained the liquid metal. These residues are very aggressive towards the inner lining of refractory material, so that it wears over time and must be replaced after a certain time of use, which constitutes an operation. complicated and expensive.

Many solutions have already been proposed to protect against wear, the refractory lining of metallurgical vessels.

French Patent 2,316,027 recommends the protection of all the interior parts of a liquid metal transfer container by the interposition between the permanent refractory lining and the liquid metal of sinterable elements, generally in the form of plates.

French patent 2,393,637 describes a similar protection, made with or without the use of prefabricated elements, refractory insulators sinterable in contact with liquid steel and made integral with the permanent refractory lining by application of a composition of substantially identical nature. to that of the aforementioned prefabricated elements.

French Patent 2,451,789 relates to the protection of the permanent refractory lining of a metallurgical container, comprising between this refractory lining and the coating coming into contact with liquid steel, a relatively compressible layer based on organic fibers and / or inorganic coated in a binder.

It was also recommended in the patent application of the German Federal Republic No. 2,010,743 to incorporate under the prefabricated elements and behind them non-agglomerated sand, in order to increase the coefficient of thermal insulation of the coating. wear coming into contact with liquid steel.

French patent 2,393,637 already cited above also describes the possibility of projecting or introducing using a mold leaving between itself and the wall to be coated, a uniform space into which the composition is introduced by tamping. and / or by blowing, by suction or by vibration.

All of these solutions have many disadvantages.

The protective coatings formed by the plates or prefabricated elements are relatively expensive and complicated to implement. In addition, these prefabricated plates or elements generally do not resist beyond five to six successive flows.

In some cases, these plates must be preheated to a temperature above 600 ° C to remove moisture and the organic compounds they contain, in order to avoid any pollution of the liquid metal by hydrogen.

During this preheating, the prefabricated plates or elements try to curve under the effect of heat, creating between the joints of these plates or elements, spaces in which the liquid metal can infiltrate which can thus reach the permanent refractory lining.

This situation is further aggravated when the space between the plates and the permanent refractory lining is filled with pulverulent material such as sand. In fact, this pulverulent material risks polluting the liquid metal by flowing through the spaces created between the curved plates under the effect of heat. In addition, by infiltrating these spaces, the liquid metal mixes with the pulverulent material creating a mass which strongly adheres to the permanent refractory lining which then becomes very difficult to clean.

The single-layer coatings produced by spraying, as described in French patent 2,393,637, obtained from a mixture of refractory inorganic particles and an inorganic or organic binder, do not have the aforementioned drawbacks concerning plates or the like. prefabricated elements.

These coatings must necessarily sinter in contact with the liquid metal, in order to avoid any risk of inorganic particles detaching from these coatings and polluting the liquid metal.

• tout d'abord lorsque toute la masse du revêtement est frittée, ce revêtement possède un pouvoir d'isolation thermique notablement réduit, de sorte qu'on risque de refroidir le métal liquide,
• par ailleurs, lorsque toute la masse du revêtement est frittée, cette masse adhère au garnissage réfractaire permanent et ce dernier devient alors très difficile à nettoyer.

This sintering takes place gradually and after a certain period of contact between the liquid metal and the protective coating, the entire mass of the latter is sintered, which results in the following two drawbacks:

• first of all when the entire mass of the coating is sintered, this coating has a significantly reduced thermal insulation power, so that there is a risk of cooling the liquid metal,
• moreover, when the entire mass of the coating is sintered, this mass adheres to the permanent refractory lining and the latter then becomes very difficult to clean.

For these two reasons, it is avoided to wait until the coating is completely sintered, so that when the casting is finished, this coating can detach in one piece from the interior walls of the metallurgical container by simple inversion thereof.

Consequently, this coating can only be used for a few successive castings and must therefore be replaced frequently. This replacement is relatively expensive and causes an interruption of the casting which is also unfavorable from an economic point of view.

In French patent 2,338,100, it was proposed to place between the sinterable coating and the lining permanent refractory, a material for example based on paper, which can mimic the risks of adhesion between the sintered coating and the permanent refractory lining. However, this material is quickly charred under the effect of heat, so that it is in practice incapable of fulfilling the above-mentioned function.

The object of the present invention is to remedy the drawbacks of the aforementioned known solutions by creating a protective coating which is both inexpensive, easy to implement, which withstands many successive flows, which withstands temperatures without damage. high preheating, which allows to maintain a high power of thermal insulation during many successive castings and which avoids any risk of adhesion between the coating and the wall of the metallurgical container, thus considerably facilitating the cleaning thereof this at the end of casting.

According to the invention, the coating for protecting the interior of a metallurgical container intended to contain a liquid metal, this coating being based on refractory inorganic particles, coated in a binder, and comprising a layer whose composition and particle size inorganic refractory particles are such that this layer sintered throughout its mass, under the effect of the heat of the liquid metal contained in the metallurgical container and being characterized in that it comprises between the aforementioned layer and the wall of the container, a layer whose composition and particle size of the refractory inorganic particles are such that this layer does not sinter or only sinter partially, so as to remain brittle, even when the first layer is completely sintered.

The coating according to the invention thus comprises at least two separate layers. One of these two layers gradually sintered when it is in contact with the liquid metal. After a long period of contact, for example after ten successive flows, this layer is sintered throughout its mass.

The other layer does not sinter or sinter only partially, so as to remain brittle, even when the first layer is completely sintered. Thus, when this other layer is in contact with the permanent refractory lining, this layer does not adhere to this lining. Consequently, any risk of adhesion between the coating and this refractory lining is avoided, even when the first layer is completely sintered, so that cleaning at the end of casting of the interior of the metallurgical container is very easy and the refractory lining of this container is not likely to be damaged, neither during pouring, nor during cleaning.

It is also known that sintering of the coating is harmful with regard to its insulating properties. Since the second layer does not sinter or only partially sinter, this second layer continues to provide sufficient thermal insulation, even when the first layer is completely sintered and therefore itself has very low thermal insulation power.

It is thus possible, by virtue of the association of two layers, one sinterable and the other partially sinterable or non-sinterable, considerably extend the duration of use of the protective coating of a metallurgical container, which makes it possible to avoid too frequent and too long and consequently costly interruptions of the casting.

Thus, the duration of use of a two-layer coating, in accordance with the invention, is surprisingly significantly greater than that of a coating formed of a single layer, sinterable throughout its mass, of the same thickness as that of the two layers of the coating according to the invention.

Sintering is the physico-chemical phenomenon which makes it possible to create a bond between two inorganic particles. This sintering takes place at a temperature significantly lower than the melting temperature of these particles. This sintering is favored by the high pressure exerted by the liquid metal on the coating according to the invention, by the possible presence, within this coating of very fine particles, of fluxes (inorganic particles having a melting point lower than that other particles that are refractory) and by using the lowest possible binder content, so that the inorganic particles are arranged very close to each other.

According to another aspect of the invention, the method for producing the coating according to the invention consists in successively applying the different layers from a mud comprising the solid ingredients of the layer which it is desired to form, mixed with a liquid, for example ethylene glycol alcohol and / or water at a rate of 3 to 30% by weight of liquid, the density of this sludge varying according to the layer, between 0.8 and 3.5 kg / dm3, after which the different layers are dried. This drying is carried out at a temperature between 100 and 200 ° C to remove the free water. In certain cases, the different layers are preheated to a temperature between 600 and 1450 ° C. to remove the water of constitution and / or of crystallization to avoid any pollution of the liquid metal by hydrogen.

The mud is applied, preferably by spraying and / or spraying, but can also be carried out by other mechanical means such as: molding, injection, vibration, by gravity, trowelling or any other means of application. .

The process according to the invention is both very economical and is perfectly suited to the application of successive layers having different compositions.

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

The attached single figure shows, by way of nonlimiting example, in cross section, a coating according to the invention, with three superimposed layers, applied inside a tundish.

In the embodiment shown in the appended figure, the flow distributor intended to contain liquid steel, comprises an outer casing made of steel 1 comprising on its internal faces a permanent refractory lining composed of refractory bricks 2.

On this permanent refractory lining, a protective coating is applied in the form of mud, which, in the example shown, comprises three layers 3, 4, 5.

The outer layer 3 intended to come into contact with the liquid metal which is poured into the tundish, consists of a mixture of refractory inorganic particles, linked together by means of an organic and / or inorganic binder. The composition of these inorganic particles and their particle size are such that these particles can sinter, that is to say bind to each other to create a coherent mass, in contact with the liquid metal.

In contact with the liquid metal, this sintering is carried out very gradually and reaches the entire thickness of the layer 3, that is to say the entire mass of this layer, after a certain contact time which generally corresponds to several hours and several successive flows.

Of course, the greater the thickness of this layer 3, the longer will be the time at the end of which this layer is completely sintered in its mass. The thickness of this layer 3 is generally between 1 and 10 cm.

The intermediate layer 4 is also constituted by a mixture of inorganic particles linked together by means of an organic and / or inorganic binder. The composition and the grain size of these particles are such that these particles only partially sinter, so that this layer 4 remains brittle (or meringuable according to the expression used in steelmakers), even when the outer layer 3 is completely sintered in its mass. The thickness of this layer 4 is generally of the same order of magnitude as that of layer 3.

Layer 5 is in direct contact with the lining of refractory bricks 2. This layer 5 is also constituted by a mixture of refractory inorganic particles, linked together by an organic and inorganic binder. However, unlike the other layers 3 and 4, the layer 5 is not sinterable, so that after destruction under the effect of heat, of the organic and / or inorganic binder which ensures the initial cohesion of this layer , this layer 5 becomes powdery and no longer has any adhesion with the lining of refractory bricks 2.

• liant minéral (par exemple bore et/ou acide borique et/ou argile et/ou un ou plusieurs silicates et/ou ciment alumineux et/ou phosphatique et/ou magnésien) et/ou liant organique et/ou synthétique (par exemple une colle synthétique telle que résine phénolique)   0,3 à 15%
• particules inorganiques réfractaires sous forme de grains et'ou de fibres (par exemple chrome - magnésie et/ou magnésie et/ou silicate de magnésie et/ou silice et/ou alumine et/ou zircon et/ou zircone)   70 à 99,7%
• particules organiques et/ou matières carbonées en fibres et/ou en grains   0 à 28,7%
• composé tensio-actif   0 à 5%

The layers 3 and 4 respectively sinterable and partially sinterable preferably have the following weight composition:

• mineral binder (for example boron and / or boric acid and / or clay and / or one or more silicates and / or aluminous and / or phosphatic and / or magnesium cement) and / or organic and / or synthetic binder (for example an adhesive synthetic such as phenolic resin) 0.3 to 15%
• inorganic refractory particles in the form of grains and'or fibers (for example chromium - magnesia and / or magnesia and / or magnesia silicate and / or silica and / or alumina and / or zircon and / or zirconia) 70 to 99.7 %
• organic particles and / or carbonaceous materials in fibers and / or grains 0 to 28.7%
• surfactant compound 0 to 5%

The more or less sinterable nature of the layers 3 and 4 depends on the nature and composition of the refractory inorganic particles, on the particle size thereof, on the possible presence of fluxes such as iron oxide or carbonate of alkali or alkaline earth metals and binder content.

So that the layer 3 can sinter completely in contact with the liquid metal, a composition containing a large proportion of refractory inorganic particles will preferably be used. Thus, the proportion by weight of these will preferably be between 90 and 99.7%. The particle size of these particles is preferably between 0 and 4 mm, which implies that some of them are very fine, this fineness promoting sintering.

The intermediate layer 4 contains a proportion of refractory inorganic particles lower than that of the completely sinterable layer 3. This proportion is preferably between 75 and 95% by weight. The particle size of these particles is advantageously between 0 and 3 mm, preferably between 0.25 and 2.5 mm, so that very fine particles of particle size less than 0.5 mm are absent from this composition, so as to limit sintering. Thus, this layer 4 can only partially sinter while remaining brittle, that is to say brittle, even when the layer 3 is completely sintered in its mass.

Because this intermediate layer 4 only partially sintered, this intermediate layer retains its thermal insulation properties, so that it makes it possible to avoid cooling of the liquid metal, even when the outer layer 3 is completely sintered and thus has lost its initial thermal insulation properties.

The layer 5 adjacent to the refractory permanent lining 2 preferably contains between 65 and 96% by weight of refractory inorganic particles whose particle size is preferably between 0 and 5 mm. This layer 5, due to its lower content of refractory inorganic particles, and the fact that it is separated from the sinterable layer 3, by an intermediate layer 4, thermally insulating, does not sinter under the effect of heat, so that after destruction of the binder initially ensuring the cohesion of the layer, the latter loses all its cohesion and becomes pulverulent. Thus, after many successive castings, when it is considered that the coating according to the invention is sufficiently worn and that it is advisable to replace it with a new coating, since the layer 5 adjacent to the permanent refractory lining 2 is powdery , there is no adhesion between this refractory lining and the entire coating, so that the latter is very easily detached and in one piece from the refractory lining 2, by simply inverting the tundish.

Consequently, the coating according to the invention not only effectively protects the lining permanent refractory 2 but it makes it very easy to clean the interior of the distributor at the end of casting.

In accordance with the method according to the invention, in order to produce the three-layer coating 3, 4, 5 which has just been described, these layers are successively applied to the walls of the tundish, in the form of sludge containing the solid ingredients of these layers, mixed with a liquid for example such as water and / or oils, in a proportion of 3 to 30% by weight of liquid. An alcohol may also be suitable (for example: ethylene glycol).

The mud applied must be sufficiently pasty, so as to adhere to the walls of the tundish, or to the other layers, without sinking.

The density of the applied mud varies according to the layers 5, 4, 3, between 0.8 kg / dm3 and 3.5 kg / dm3, the outer layer 3 being denser than the intermediate layer 4 and the latter being itself even denser than the layer 5 adjacent to the refractory lining 2.

The layers 3, 4, 5 thus applied are then dried at a temperature of between 100 and 200 ° C., for example by buckling and / or by blowing hot air or by means of electric heating resistors, placed inside. of the tundish and attached to a cover closing the latter. This drying eliminates the free water from the mud which constitutes the different layers.

In certain cases, it is advisable to remove from the layers 3, 4, 5 all the organic constituents and all the water of constitution and of crystallization of these layers, in order to avoid any risk of pollution of the liquid metal by hydrogen. . For this purpose, the layers 3, 4, 5 are preheated to a temperature equal to at least 600 ° C., this temperature possibly reaching 1450 ° C.

At these high temperatures, the inorganic and / or organic binders which decompose the initial cohesion of the layers 3, 4, 5 are decomposed. This heating at high temperature has the effect of partially sintering the outer layer 3. This partial sintering makes it possible to restore the cohesion of the entire coating. This cohesion makes it possible to prevent, when the liquid metal is poured into the tundish, that the inorganic particles detach from the coating to pollute the liquid metal.

Compared to an applied coating, monolayer and sinterable, conventional, having a composition similar to that of the outer layer 3 of the coating according to the invention, the latter has, for the same total thickness, the following main unexpected technical advantages .

Its duration of use is considerably longer, since the sintering practically does not continue beyond the outer layer 3 and therefore cannot reach the permanent refractory lining 2.

On the other hand, since the intermediate layer 4 only sintered partially and that the layer 5 adjacent to the permanent refractory lining 2 does not sinter, these layers 4 and 5 provide excellent thermal insulation, thus avoiding any cooling. liquid metal during its stay in the tundish.

Furthermore, since the layer 5 adjacent to the permanent refractory lining 2 does not sinter and becomes powdery, this layer 5 has no adhesion with respect to this lining, so that at the end of casting, the removal coating is very easy and there is no risk of damaging the refractory lining by trying to remove by means of tools such as jackhammers, the solidified masses adhering to this permanent refractory lining.

In a simplified embodiment of the invention, one of the layers 4 or 5 can be omitted, so as to imitate the number of layers at least 2.

When the sinterable outer layer 3 is separated from the permanent refractory lining 2 by the non-sinterable layer 5, there is also no risk of obtaining adhesion between this layer 5 and the refractory lining 2. However, the thermal insulation power provided by these two layers will be worse than in the case of a three-layer coating.

When the sinterable outer layer 3 is separated from the permanent refractory lining 2 by the layer 4 sintering only partially and therefore remaining brittle, there is at most the risk of obtaining a slight adhesion between this layer 4 and the refractory lining 2.

Furthermore, in the case of a three-layer coating, it is possible to place the non-sinterable layer 5 between the sinterable layer 3 and the partially sinterable layer 4.

In addition, in the case where it is possible to tolerate a slight pollution of the liquid metal by inorganic particles coming from the coating, the layers 3 and 4 can be inverted, that is to say by placing the sinterable layer 3 between the non-sinterable layer 5 and the partially sinterable layer 4.

On the other hand, the process according to the invention makes it possible to apply to the area of the slag 6 floating on the liquid metal, an additional thickness 7 of the sinterable layer 3. This additional thickness 7 may have the same composition as the layer 3 so as to sinter at the same time as this. This additional thickness 7 makes it possible to reinforce the protection provided by the coating according to the invention, in the most vulnerable zone of the flow distributor, namely the zone of slag.

This additional thickness 7 may also have a composition different from that of the layer 3 so as to provide increased protection against slag. The composition of the layer forming this additional thickness 7 can thus contain highly refractory particles such as zircon and / or zirconia and / or carbon, and / or silicon carbide.

The thickness of the coating can, of course, also be increased in other places in the tundish and in part in the impact zone of the casting jet which is poured from the tundish placed above the tundish. casting.

Experience shows that it is also possible to apply the different layers using a trowel or by molding.

Claims (12)

1. Use of a covering for protecting the interior of a casting distributor or casting ladle for holding a liquid metal, the covering being based on refractory inorganic particles embedded in a binder, the covering comprising a layer (3) of refractory inorganic particles having a composition and size such that the layer is sintered all the way through by the heat of the liquid metal in the distributor or ladle, and comprising a layer (4 or 5) between the said layer (3) and the vessel wall and having a composition and size of refractory inorganic particles different from those of the said layer (3) and such that it is not or is only partially sintered and thus remains friable and heat-insulating even when the first layer (3) has completely sintered.
2. Use according to claim 1, characterised in that the said covering is applied to the interior of a metallurgical vessel whose wall has a permanent lining (2) of refractory material.
3. Use according to claim 1 or 2, characterised in that the covering comprises the following three layers:

   - a layer (3) adapted to come into direct contact with the liquid metal and to be sintered all the way through in contact with the liquid metal, the layer covering

   - a layer (4) which sinters only partially and remains friable even when the preceding layer has sintered all the way through, and

   - a layer (5) in direct contact with the refractory lining and non-sinterable and becoming pulverulent under the action of heat.
4. Use according to claim 1 or 2, characterised in that the covering comprises the following three layers:

   - a layer adapted to come into direct contact with the liquid metal and adapted to be sintered all the way through in contact with the liquid metal and covering:

   - a non-sinterable layer which becomes pulverulent under the action of heat, and

   - a layer in direct contact with the refractory lining and sintering only partially and remaining friable even when the sinterable layer has sintered all the way through.
5. Use according to any of claims 1 to 4, characterised in that the sinterable layer (3) or the partially sinterable layer (4) has the following composition by weight:

   - a mineral binder (e.g. clay and/or silicate and/or aluminous and/or phosphate and/or magnesia cement) and/or an organic binder (e.g. synthetic glue)   0.3 to 15%;

   - refractory inorganic particles in the form of grains and/or fibres (e.g. magnesia, chromium-magnesia and/or silicate of magnesia and/or silica and/or alumina and/or zircon and/or zirconium dioxide)   70 to 99.7%;

   - organic particles and/or carbonaceous material in fibres and/or grains   0 to 28% and

   - a surface-active compound   0 to 5%.
6. Use according to any of claims 2 to 5, characterised in that the sinterable layer (3) adapted to come in contact with the liquid metal contains from 70 to 99.7% by weight of refractory inorganic particles having a size preferably between 0 and 4 mm.
7. Use according to any of claims 2 to 6, characterised in that the layer (4) which is partly sinterable but remains friable contains from 75 to 95% by weight of refractory inorganic particles having a size preferably between 0.25 and 2.5 mm.
8. Use according to any of claims 3 to 7, characterised in that the non-sinterable layer (5) which becomes pulverulent contains from 65 to 96% by weight of refractory inorganic particles having a size between 0 and 5 mm.
9. Use according to any of claims 1 to 8, characterised in that, at the zone of the slag (6) floating on the liquid metal, the covering has an extra thick portion (7) of the layer adapted to be sintered completely in contact with the liquid metal.
10. Use according to any of claims 1 to 8, characterised in that, at the zone of the slag (6) floating on the liquid metal, the covering has an extra thick portion (7) in the form of a layer applied to the layer (3) adapted to become completely sintered in contact with the liquid metal, the extra thick layer containing inorganic particles which are resistant to slag.
11. Use according to any of claims 1 to 10, characterised in that the various layers (5, 4, 3) are successively applied in the form of sludge comprising the solid components of the layer to be formed and mixed with a liquid such as water in a proportion of 3 to 30% by weight of liquid, the density of the sludge varying from 0.8 to 3.5 kg/dm³, after which the various layers (5, 4, 3) are dried at a temperature between 100 and 200°C to eliminate the free water.
12. Use according to claim 11, characterised in that the various layers (5, 4, 3) are preheated to a temperature between 600 and 1450°C to eliminate the water of formation and/or of crystallisation.

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