LU87757A1 - PROCESS FOR APPLYING A PROTECTIVE COATING COMPRISING AT LEAST TWO LAYERS ON THE INTERNAL FACES OF A METALLURGICAL CONTAINER - Google Patents

Description

CLAIM OF THE PRIORITY of the patent application / utility model Brief Description filed in support of an application for

PATENT OF INVENTION at

Luxembourg in the name of: DAÜSSAN ET COMPAGNIE (Société en Nom Collectif) 29-33, Route de Rombas F-57140 WOIPPY France for: "Process for applying a protective coating comprising at least two layers on the inner faces of a metallurgical container "

The present invention relates to a method for creating on the internal faces of a metallurgical container for transferring liquid metal a protective coating comprising at least two layers. The present invention also relates to a coating obtained by the implementation of this method.

Numerous methods are known for applying a protective coating of the aforementioned type. In its French patent No. 2,585,273, the applicant has for example described a protective coating based on refractory inorganic particles coated in a binder, and which comprises at least two layers: a layer which sintered throughout its mass in contact with the liquid metal, and a layer that does not or only partially sinter. These layers are applied successively in the form of sludge comprising the solid ingredients of the layer to be formed mixed with a liquid such as water. After spraying, the different layers are dried at a temperature between 100 and 200 ° C to remove the free water, and can be preheated to a temperature between 600 ° and 1450 ° C to remove the water of constitution and / or the water of crystallization of the two layers.

This process gives full satisfaction to its users. In particular, the second layer does not adhere to the permanent coating (or the metal envelope) of the container, so that the protective coating comes off and falls off by itself if the container is turned over, which can be then replenish immediately without wasting time. This method however has the drawback of requiring very substantial drying of said two layers and of the permanent coating.

Furthermore, EP-A-0064863 describes a process according to which a protective coating is formed in a single layer: according to this process, a substantially dry mixture is poured, comprising refractory particles and a thermosetting resin, between the inner wall of the container to be coated and the outer wall of a core, then the mixture is heated to harden the resin, finally the core is removed.

The container is immobilized during the heating time necessary to harden the resin, and there can only be a single layer which is liable to become attached to the permanent coating if it is allowed to sinter completely. If the permanent coating wears out, an additional amount of the mixture is used which is lost.

Finally, according to US-A-4 372 544, a one-piece protective coating is prepared in the container to be protected, prepared in advance and deposited on support plates. No immobilization of the container is necessary. On the other hand, the coating in one piece must be resistant, and therefore thick, heavy and expensive, in order to be handled.

It would be the same if the coating consisted of a few pieces assembled inside the container to be protected.

The object of the present invention is to remedy the drawbacks of known methods, and to propose a method of the aforementioned type which makes it possible to carry out easily, quickly and with reduced immobilization of the container to be protected as well as very short drying of its coating. protection and its permanent coating, an inexpensive protective coating which has sufficient resistance to withstand erosion by liquid metal, which does not risk sticking to the walls of the container, this process being very flexible and making it possible to adjust the thickness of the coating depending on the intended conditions of use.

According to the invention, the method of the aforementioned type is characterized by the following steps: A / A core which can be heated is introduced into the metallurgical container to be protected, the outer walls of said core creating a molding space with the inner faces of said container . B / A material composed of inorganic particles resistant to the temperature prevailing during the transfer of liquid metal is introduced into the space thus created, said particles being pre-coated with a curable binder and / or mixed with a curable binder, said material being dry or practically dry (for example a liquid content such as water less than 10%). C / After hardening of said material on the walls of the container or on its permanent coating, said core is extracted from the container, leaving a first protective layer in place. D / On the hardened material which has sufficient cohesion, a second layer is applied, implemented by a spraying process in the wet phase, which has a wetting rate greater than 5%, which rate is preferably between 8 and 30%, this second layer being composed of a pulverulent product resistant to temperature prevailing during the decanting of liquid metal, said pulverulent product being able to be mixed with an inorganic and / or organic binder, and being able to comprise a wetting agent and / or cellulose. E / The interior faces of the metallurgical vessel are heated using known heating means (for example, using gas burners, electric resistances or a microwave generator) so as to eliminate any trace of moisture or water of crystallization.

The drying time of the protective layers and of the permanent coating is limited to the drying of the layer produced during step D, which will be very short, having only the quantity of liquid provided by the second layer, that projected, to eliminate.

Considering that it takes about a tonne of product to produce a protective coating for a medium-sized container, in the case where this coating is sprayed using a machine of the screw pump type , that is to say a wet transfer machine whose product to be sprayed is hydrated before the spray nozzle, we will have to remove by drying about 300 liters of a liquid such as water, this type of machine requiring around thirty percent of mixing liquid. Since the coating, which is the subject of this patent, consists of two parts, that produced during steps B and C which contains little or no mixing liquid and which represents 2/3 of said coating, and that produced during steps D and E equivalent to the remaining 1/3, the value of one third of the mixing liquid of the example cited above, or approximately 100 liters, should be eliminated.

Another advantage which results from the present invention lies in the fact that, thanks to the first protective layer of the container produced during the execution of steps from A to C which becomes very resistant, it is also possible during the execution of step D use a rotor machine, known as a dry transfer machine, the pulverulent product of which is wetted at the outlet of the spray nozzle, this spraying process requires only 10% of mixing water approximately 30 liters of water , or ten times less than when projecting a conventional coating with a machine of the screw pump type. This represents a huge advantage, especially for countries like Japan which have very high cost energy, or for countries which do not have large quantities of water.

The layer formed of inorganic particles coated or mixed with a binder remains integral with the wall of the metallurgical vessel or its permanent coating after the execution of step C. It is thus possible to use for step B a much less expensive pulverulent product. than that used for step D. We can therefore compensate, with the layer used for step B, inexpensively for some wear of a possible permanent refractory lining, and / or irregularities in shape due to deformation of the metallurgical envelope of the container. It is therefore possible to use a single core for several containers of substantially identical shapes.

According to an interesting version of the invention, a pulverulent product which does not sinter or which only sintered slightly at the prevailing temperature is used to form the layer resulting from step B when the metallurgical container is filled with liquid metal, so to remain brittle even when said layer is completely sintered.

Thus the powdery product does not risk attaching to the wall or to the permanent coating of the metallurgical container. Then simply invert the container to drop the protective coating after use.

According to an advantageous version of the invention, a heating mold is used to form the layer resulting from step B, it suffices however to do without it, that the walls of the container or of its permanent coating are brought to around 200 at 300 ° C to obtain rapid hardening of many types of binders, in particular thermosetting resins, very easy to use. Provided that the pulverulent product is slightly damp, a hydraulic binder such as cement and / or a chemical binder such as for example a powdered silicate can usefully be used.

According to an interesting version of the invention, said layer B, having a thickness of two to three centimeters, is used to form said inorganic particles chosen from the group preferably comprising inexpensive particles, for example silica, alumina, dolomite, carbonaceous materials. and their mixtures, without renouncing the more expensive particles such as magnesia, chromium-magnesia, zircon, zirconia and their mixtures if certain technical necessities so require, the particle size and composition of all these particles being chosen so that said layer does not sinter, or only sits partially throughout its mass.

According to an advantageous version of the invention, to use the layer resulting from stage D, that which comes into contact with the liquid steel, more noble inorganic particles chosen from the group comprising for example magnesia, chromium-magnesia, or all the magnesium silicates, zircon, zirconia, carbonaceous materials and their mixtures, without in certain cases renouncing silica, alumina, dolomite and / or alkaline earth hydroxides and their mixtures, the particle size and the composition of these particles being chosen so that said whole sintered layer is in contact with the liquid metal having previously removed the free water at a temperature between 100 and 200 ° C., or again by preheating after spraying in order to eliminate between 600 ° C and 1450 ° C the water of constitution and / or the water of crystallization and / or in order to proceed to the decarbonation of the dolomite and / or the alkaline-earth hydroxides. Such sintering gives said layer the cohesion necessary to resist the erosion of the liquid metal. It is known, in this area, that it generally suffices for this to have a thickness of one to three centimeters.

According to another aspect of the invention, the coating according to the invention for protecting the interior of a metallurgical container for transferring liquid metal is characterized in that it is obtained by means of the method according to the invention.

It will be recognized that a person skilled in the art is not tempted to produce a protective coating for a container intended to receive liquid metal, comprising at least two layers, the second layer of which is sprayed wet on a first layer previously dried. Other features and advantages of the invention will become apparent in the description below.

In the accompanying drawings given by way of nonlimiting examples: - Figure 1 is a cross-sectional view of a flow distributor showing the formation of the first coating layer, - Figure 2 is a view similar to Figure 1 showing the formation of the second layer of the coating.

As shown in FIGS. 1 and 2, the process for applying a protective coating to the interior faces (4, 5, 6) of the metallurgical container (1) for transferring liquid metal, comprises the following steps: A / A core (9) possibly heated using handling rings (10) in the metallurgical container (1) to be protected which creates a molding space with the internal faces (4, 5, 6) of said container, and with the outer faces (14, 15, 16) of the core (9). B / An inorganic material pre-coated with a curable binder and / or mixed with a curable binder is introduced into the space thus created by means of a tube (11) (see FIG. 1). C / After hardening of said material on the interior walls of the container (1) or on its permanent coating (3), the core (9) is extracted from the container (1), leaving a first protective layer (7) in place. D / On the first protective layer (7) which has sufficient cohesion, a second layer (8) is applied using a wet phase spraying process (12, 13} (see FIG. 2}. E / The inner faces (17, 18, 19) of the metallurgical vessel are heated using known heating means (not shown).

Of course, the invention is not limited to the embodiments described and numerous modifications can be made to them without departing from the scope of the invention.

Claims (8)

1. Method for applying to the inner faces (4, 5, 6) of a metallurgical container (1) for transferring liquid metal a protective coating, comprising at least two layers (7, 8), characterized by the following steps : A / An optionally heating core (9) is introduced, using the handling rings (10) into the metallurgical container (1) to be protected which creates a molding space with the interior faces (4, 5, 6) of said container, and with the outer faces (14, 15, 16) of the core (9), B / An inorganic material pre-coated with a hardenable binder and / or mixed with a hardenable binder is introduced into the space thus created of a tube (11), C / After hardening of said material on the interior walls of the container (2) or on its permanent coating (3), the core (9) is extracted from the container (1), leaving a first protective layer (7), D / On is projected onto the first protective layer ection (7) which has sufficient cohesion, a second layer (8) implemented by a wet phase spraying process (12, 13), E / The inner faces (17, 18, 19) of the metallurgical vessel are heated using known heating means. 2. Method according to claim 1, characterized in that inorganic particles chosen from the group comprising silica, alumina, dolomite, carbonaceous materials, such as, for example, coke and / or are used to form said layer (7) cellulose, magnesium silicate, zircon, zirconia and their mixtures, the particle size and composition of these particles being chosen so that said layer (7) does not sinter or only sintered superficially so as to always remain brittle. 3. Method according to one of claims 1 or 2, characterized in that a thermosetting binder is preferably used to form said layer (7), said binder being able to pre-coat and / or be mixed with the inorganic particles which compose it. 4. Method according to one of claims 1 to 3, characterized in that one uses to form said layer (8) particles in grains and / or powder chosen, preferably, from the group comprising magnesia, chromium- magnesia, zircon, zirconia, dolomite, silica, alumina, carbonaceous materials, molding agent, organic binder, inorganic binder and their mixtures, the particle size and composition of these particles being chosen so that said layer (8) sintered throughout its mass on contact with liquid metal. 5. Method according to claims 1 to 3, characterized in that the metal carcass (2) and / or its permanent coating (3) is preheated or that a heating mold (9) is used. 6. Method according to claims 1 to 5, characterized in that, at the time of the introduction of the core (9) into the metallurgical container (1), the position or the dimensions of the core (9) in the container are adjusted ( 1) to adjust the thickness of said layer (7). 7. Coating for protecting the interior of a container (1) for transferring liquid metal, characterized in that it is obtained by means of the process according to any one of claims 1 to 6. 8. Coating according to claim 7, characterized in that it is applied inside a metallurgical container (1) comprising a permanent lining (3) whose refractory material can be in a state of wear even advanced .