FR2713108A1 - Process and mixture of powders for the repair of oxide-based refractory bodies - Google Patents

Abstract

The invention relates to a method for repairing refractory bodies based on oxides and a mixture of powders which can be used for this purpose. The repair is carried out by spraying a mixture of refractory powder and combustible powder in the presence of oxygen. The combustible particles react exothermically with oxygen and form a refractory oxide. These particles are chosen from magnesium, aluminum and silicon. The mixture contains up to 10% by weight of silicon carbide particles. The invention is particularly suitable for the hot repair of ladles for liquid steel.

Description

Process and mixture of powders for the repair of refractory bodies with

  The present invention relates to a method of repairing a

  refractory body based on oxides by a ceramic welding process.

  The oxides of silicon, zirconium, aluminum and magnesium are refractory oxides customary in the industry. In particular, aluminum and magnesium oxides are commonly used in the metallurgical industry, where they are chosen for their resistance to high temperatures, erosion and corrosion by materials such as metal, slag and

melted slag.

  Magnesium oxide refractories, otherwise known as basic refractories, can form the lining of molten steel transport pouches. Such packings wear in contact with melted root and slag. Erosion of the lining occurs mainly at the surface of the liquid. It is therefore necessary to

  repair from time to time such refractory bodies based on oxides.

  It has been proposed to repair refractory bodies by using a technique of "ceramic welding". In this technique, the refractory body to be repaired is kept at a high temperature, and a mixture of powders is sprayed in the presence of oxygen, said powder mixture comprising particles of refractory material and combustible particles which react exothermically with oxygen to form a refractory oxide. By this method, a refractory mass is formed and adhered to the refractory body at the place to be repaired. The ceramic welding technique is illustrated in British Patent Nos. 1,330,894 (Glaverbel) and GB 2,170,191 (Glaverbel). The combustible particles are particles whose composition and particle size are such that they react exothermically with oxygen by forming a refractory oxide and releasing the necessary heat

  to melt, at least superficially, the projected refractory particles.

  However, when a mixture of powders consisting of oxide particles and combustible particles is used to repair an oxide-based refractory body, and in particular a refractory body based on oxides with a high melting point such as With magnesium oxide and aluminum oxide, the resulting refractory mass may be porous. If there is significant apparent porosity, the repair mass will not be useful for some applications, especially if the repair mass is to be subjected to

  erosion or corrosion by molten materials.

  One of the objects of the present invention therefore consists in providing a method of repairing oxide-based refractory bodies which allows the

  forming a refractory repair mass having acceptable porosity.

  It has surprisingly been found that when the combustible particles are selected from magnesium, aluminum, silicon, and mixtures thereof, this objective can be achieved by incorporating a specific amount of silicon carbide into the powder mixture. This is contrary to the generally accepted principle of harmonizing the composition of the refractory repair material with the composition of the surface of the refractory material being repaired. In addition, silicon carbide is considered an inert material in the ceramic welding process and is not wetted by the liquid phase that forms during the reaction. The effect of silicon carbide on the

  The porosity of the mass is therefore surprising.

  Without wishing to be bound by any theory, we believe that the additional particles of silicon carbide lead the heat into the refractory repair mass and that prolonged exposure to high temperatures causes a decomposition of the silicon carbide particles generating carbon. elementary, which is known to confer to the mass

  refractory repair a good resistance to corrosion by the slag.

  Accordingly, the present invention, in its first aspect, relates to a method of repairing a refractory body based on oxides by high temperature spraying and in the presence of oxygen of a mixture of powders on a surface of said body, said mixture of powders comprising refractory oxide particles and combustible particles which react exothermically with oxygen to form a refractory oxide, characterized in that the combustible particles are selected from magnesium, aluminum, silicon and mixtures thereof and in that the powder mixture further contains up to 10% by weight of silicon carbide particles. The silicon carbide content of said powder mixture is preferably at least 1% by weight. Including an excessively high silicon carbide content may result in an absence of repair mass formation because the repair material flows out of the site to be repaired. Without wishing to be bound by theory, it can be assumed that this is due to too much heat retention after the repair process, leading to a low viscosity liquid phase. If one uses too little silicon carbide, the advantages of

  the invention are no longer obtained at a significant level.

  Preferably, the size of the silicon carbide particles is small, for example less than 200 μm. The term "particle size" as used herein means that the material of interest has a particle size distribution such that at least 90% by weight of the particles is within the given limits. The term "average size" as used herein means a dimension such that 50% by weight of the particles has a dimension smaller than

this average.

  The refractory oxide particles may comprise at least one oxide of which the refractory body is constituted. Therefore, when the refractory body is a body containing aluminum oxide, the refractory oxide particles may comprise alumina particles. When the refractory body is a body containing magnesium oxide, the refractory oxide particles

  may include particles of magnesia.

  Preferably, most of said powder mixture is formed of refractory oxide particles selected from magnesia, alumina and mixtures thereof. These are the oxides in the presence of which the exothermic reaction is the most intense and therefore presents a greater risk of producing a very porous repair mass. Preferably, the refractory oxide particles have a dimension of less than 2.5 mm, with substantially

  no particle with a dimension greater than 4 mm.

  The combustible particles are selected from magnesium, aluminum, silicon and mixtures thereof. A mixture of aluminum and silicon is particularly advantageous. The combustible particles used in the

  mixture preferably have an average size of less than 50 pmn.

  The repair operation is generally carried out when the refractory body is hot. This makes possible the repair of eroded refractory bodies while the equipment remains substantially at its disposal.

working temperature.

  The high temperature may be greater than 600 C, measured on the surface of the refractory body to be repaired. At this temperature, the fuel particles burn in the presence of oxygen to release a refractory oxide and generate heat sufficient for the oxide particles, together with the fuel combustion product, to form the refractory mass that constitutes the repair. The invention also relates, in its second aspect, to a

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  powder mixture for the repair of oxide-based refractory bodies, said mixture comprising: from 80% to 95% by weight of refractory particles comprising a refractory oxide; and from 5% to 20% by weight of combustible particles which react exothermically with oxygen to form a refractory oxide, characterized in that the combustible particles are selected from magnesium, aluminum, silicon and mixtures thereof and in that the refractory particles contain up to 10% by weight (calculated with respect to the total of

  mixture) of silicon carbide particles.

  To obtain a homogeneous repair mass, an amount of at least 80% by weight of refractory particles, comprising the particles

  of oxide, must be present in the powder mixture.

  In a preferred embodiment, the mixture comprises: from 80% to 94% by weight of refractory oxide particles selected from alumina, magnesia particles and mixtures thereof; from 1% to 5% by weight of silicon carbide particles; and

  from 5% to 15% by weight of combustible particles.

  Preferably, the refractory particles in the powder mixture, including the silicon carbide particles, have a size of at least 10 pfm. If particles that are too small are used, there is a risk that they

  be lost during the reaction.

  An easy technique for bringing the mixture of powders to a surface of the refractory body to be repaired is to spray the powder mixture with an oxygen-containing gas. In general, it is recommended to spray the particles in the presence of a high oxygen concentration, for example by using commercial grade oxygen as a carrier gas. In this way, the repair mass is easily formed and adheres to the surface on which the particles are projected. Because of the very high temperatures that the ceramic welding reaction achieves, it can penetrate the slag that may be on the surface of the refractory body to be treated, and it can soften or melt the surface in such a way that a good liaison is established between the

  treated surface and the newly formed repair refractory mass.

  This method is advantageously implemented by means of a lance. A lance suitable for carrying out the method of rinsing comprises one or more openings (s) for the powder stream, optionally with one or more ports (s) for additional gas. For repairs performed in a hot environment, the gas streams can be discharged by a

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  lance cooled by fluid circulation. Such cooling can be easily achieved by providing the lance with a water jacket. Such spears are suitable for spraying powder at flow rates ranging from 30 to 500 kg / hour. In order to facilitate the formation of a regular stream of powder, the refractory particles preferably comprise substantially no particles whose size is greater than 4 mm, preferably no

particles greater than 2.5 mm.

  The invention is particularly suitable for the repair or maintenance of molten steel bags because it can be used quickly, at a high temperature, between the bag loads. The refractory bodies forming part of such pockets are particularly stressed by contact with molten metal or slag. The area requiring repairs

  more important is at the level of the liquid surface.

  The invention will now be further described in the following nonlimiting examples:

EXAMPLE 1

  A refractory repair mass is formed on a magnesium oxide lining wall of a molten steel ladle. These bricks are sprayed with a mixture of refractory particles and combustible particles. The temperature of the wall is about 850 ° C. The mixture is sprayed at a rate of 150 kg / hour in a stream of pure oxygen. The mixture has the following composition: MgO 87% by weight SiC 5% Si 4%

AI 4%

  The MgO particles have a maximum dimension of about 2 mm. The silicon carbide particles have a size of 125 pons, with an average dimension of 57 μm. The silicon and aluminum particles have

  a maximum dimension of less than 45 μm

  EXAMPLE 1A (Comparative) For comparison, the same repair is carried out in the same manner as in Example 1, but using a mixture of powders of the following composition: MgO 92% by weight Si 4%

AI 4%

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  The apparent specific gravity and apparent porosity (ie open porosity) of the refractory repair masses formed in Examples 1 and 1A are measured and the following results are obtained: Example n Specific mass Porosity (%) in kg / dm3 1 2.9 about 8% 1A 2- 2.4 about 20% In a variant of example 1, refractory containing aluminum oxide is repaired in a similar manner, but replacing in the mixture of powders magnesia particles by the same amount of

  alumina particles of the same particle size.

EXEMP LES 2 à 4

  Refractory repair bodies are formed on a lining wall of magnesium oxide, a ladle for molten steel. These bricks are sprayed with a mixture of refractory particles and combustible particles. The temperature of the wall is about 850 C. The mixture is sprayed at a rate of 60 kg / hour in a stream of pure oxygen. The mixtures have the following compositions (by weight): Example n 2 3 4 If 4% 4% 4% Ai 4% 4% 4% SiC 2% 5% 10% MgO 90% 87% 82% MgO particles have a maximum dimension of about 2 mm. The silicon carbide particles have a dimension of 125 μm, with an average dimension of 57 μm. The silicon and aluminum particles have

  a maximum dimension of less than 45 μm

  The apparent specific gravity and apparent porosity (ie open porosity) of the refractory repair masses formed in Examples 1 and 1A are measured and the following results are obtained: Example n Specific mass Porosity (%) in kg / dm3

2 2.6 14%

3 2.7 10%

4 2.9 8%

EXAMPLE 5

  A powder for ceramic welding has the following composition (by weight): Alumina 87% Silicon carbide 5% Aluminum 6% Magnesium 2% The alumina used is fused alumina. Alumina has a nominal maximum dimension of 700 μm, the silicon carbide has the same particle size as in example 1, the aluminum particles have a maximum dimension of less than 45 μm and the magnesium particles have a

  maximum dimension less than 75 μm.

  The above powder mixture can be used in a manner analogous to that described in Example 1, to repair a Corhart (TM) Zac refractory block (composition: alumina / zirconia / zircon) located in a pool of melting furnace. glass below the level of the surface of the melt, after the oven has been partially emptied to give access to the place of repair.

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Claims (9)

  A method of repairing an oxide-based refractory body by spraying at high temperature and in the presence of oxygen a mixture of powders on a surface of said body, said powder mixture comprising oxide particles refractory and combustible particles which react exothermically with oxygen to form a refractory oxide, characterized in that the combustible particles are selected from magnesium, aluminum, silicon and mixtures thereof and in that the powder mixture contains additionally up to 10% by weight of silicon carbide particles. 2. Method according to claim 1, characterized in that the silicon carbide content of said mixture of powders is at least 1% by weight.   3. Method according to one of claims 1 or 2, characterized in that   that the size of the silicon carbide particles is less than 200 lum.   4. Method according to one of claims 1 to 3, characterized in that   that the refractory oxide particles comprise at least one oxide of which is constituted the refractory body.   5. Method according to rune of claims 1 to 4, characterized in that   that the said refractory body is selected from the bodies containing roxide   of aluminum and bodies containing magnesium oxide.   6. Method according to rune of claims 1 to 5, characterized in that   that most of said powder mixture is formed of particles   refractory oxide selected from magnesia, alumina and mixtures thereof.   7. Method according to one of claims 1 to 6, characterized in that   that said refractory body to be repaired is part of a ladle for molten steel.   8. Mixture of powders for the repair of refractory bodies based on oxides, said mixture comprising: - from 80% to 95% by weight of refractory particles comprising a refractory oxide; and from 5% to 20% by weight of combustible particles which react exothermically with oxygen to form a refractory oxide, characterized in that the combustible particles are selected from magnesium, aluminum, silicon and mixtures thereof and that the refractory particles contain up to 10% by weight (calculated on the total of   mixture) of silicon carbide particles. 9 2713108   9. Mixture of powders according to claim 8, characterized in that it comprises: from 80% to 94% by weight of refractory oxide particles chosen from particles of alumina and magnesia and their mixtures; from 1% to 5% by weight of silicon carbide particles; and   from 5% to 15% by weight of combustible particles.