AT402922B - METHOD AND POWDER MIXTURE FOR REPAIRING OXIDE-BASED REFRACTORY BODIES - Google Patents

Description

AT 402 922 B

The present invention relates to a method for repairing refractory bodies based on oxide by a ceramic welding method.

Oxides of silicon, zirconium, aluminum and magnesium are used as industrial refractory oxides. In particular, oxides of aluminum and magnesium are e.g. Currently used in the metallurgical industry, where they are chosen for their resistance to high temperature, erosion and corrosion caused by materials such as molten metal, slag and dross.

Refractory materials based on magnesium oxide, otherwise known as basic refractory materials, can form the lining of a pan for the transport of molten steel. Such linings are rubbed off by the molten steel and slag. The lining erosion occurs particularly at the level of the liquid. There is therefore a need to repair such refractory oxide-based bodies from time to time.

It has been proposed to repair refractory bodies using a "ceramic sweat" technique. In this mode of operation, the refractory body to be repaired is kept at an elevated temperature and a powder mixture is sprayed on in the presence of oxygen, which powder mixture contains particles of a refractory material and fuel particles which react exothermically with the oxygen to form a refractory oxide form. This process builds up a refractory mass and adheres to the refractory at the repair point. The method of ceramic welding is described in British Patent Nos. GB 1,330,894 (Glaverbel) and GB 2,170,191 (Glaverbel). The fuel particles are particles whose composition and grain size distribution are such that they react exothermically with the oxygen while forming a refractory oxide and while releasing the heat necessary for the at least superficial melting of the spun refractory particles.

However, it has been found that when a powder mixture consisting of oxide particles and fuel particles is used to repair an oxide-based refractory body and in particular a refractory body based on refractory oxides such as magnesium oxide and aluminum oxide, the refractory mass obtained can be porous. If there is a clearly visible porosity, the repair compound is not suitable for certain applications, especially if the repair compound is subject to erosion or corrosion due to molten materials.

It is therefore an object of the present invention to provide a method for repairing oxide-based refractory bodies which enables the formation of a refractory repair mass with an acceptable porosity.

It has surprisingly been found that when the fuel particles are selected from particles of magnesium, aluminum, silicon and mixtures thereof, this goal can be achieved by including a specific amount of silicon carbide in the powder mixture. This is in contrast to the generally recognized principle of aligning the composition of the refractory repair compound to the composition of the surface to be repaired made of refractory material. Furthermore, 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 porosity of the mass is therefore surprising.

Without being bound by theory, it is believed that the additional silicon carbide particles introduce heat into the refractory repair compound and that, over time, the prolonged exposure to high temperatures causes the silicon carbide particles to decompose to form elemental carbon, which is known to that it provides the refractory repair compound with good resistance to slag corrosion.

Thus, according to a first aspect of the invention there is provided a method of repairing an oxide refractory body by hurling a powder mixture against a surface of said body at an elevated temperature and in the presence of oxygen, said powder mixture containing refractory oxide particles and fuel particles which are exothermic Reacting manner with the oxygen to form a refractory oxide, which is characterized in that the fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and in that the powder mixture additionally contains up to 10% by weight of silicon carbide particles.

The content of silicon carbide in this powder mixture is preferably at least 1% by weight. If too much silicon carbide is included, it has been found that the result may be that no repair mass is formed at all since the repair material flows away from the repair site. Without being bound by theory, one might expect this to be due to the retention of too much heat after the repair process, resulting in a low viscosity liquid phase. If too little silicon carbide is used, the beneficial effects of the invention will no longer be significantly obtained. 2nd

AT 402 922 B

The silicon carbide preferably has a small particle size, such as less than 200 µm. By "particle size", when this term is used here, it is to be understood that the material in question has such a particle size distribution that at least 90% by weight of the particles comply with the stated limits. "Average dimension," as used herein, means such a dimension that 50% by weight of the particles have a dimension smaller than this average.

The refractory oxide particles can contain at least one oxide from which the refractory body is formed. Thus, if the refractory oxide body is a body containing alumina, the refractory oxide particles may contain particles of alumina. If the refractory oxide body is a body containing magnesium oxide, the refractory oxide particles may contain particles of magnesium oxide.

Preferably, a major part of this powder mixture is formed from refractory oxide particles selected from magnesium oxide, aluminum oxide and mixtures thereof. These are the oxides in the presence of which the exothermic reaction is the most vigorous and therefore has a higher risk of leading to a highly porous repair material. Preferably, the refractory oxide particles are less than 2.5 mm in size, with virtually no particles larger than 4 mm in size.

The fuel particles are selected from particles of magnesium, aluminum, silicon and mixtures thereof. A mixture of aluminum and silicon is particularly advantageous. The fuel particles used in the mixture preferably have an average dimension of less than 50 µm.

The repair operation is generally carried out when the refractory body is hot. This enables the repair of eroded refractories while the device remains practically at its working temperature.

The elevated temperature can be over 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 releasing a refractory oxide and generating sufficient heat to form the oxide particles together with the combustion product of the fuel into the refractory repair mass that is the repair.

The invention also provides, according to a second aspect, a powder mixture for the repair of refractory bodies based on oxide, which mixture contains: 80 to 95% by weight of refractory particles comprising a refractory oxide and 5 to 20% by weight Fuel particles which react exothermically with the oxygen to form a refractory oxide, characterized in that these fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and in that these refractory particles up to 10% by weight, based on the total mixture , Comprise silicon carbide particles.

In order to obtain a homogeneous repair mass, an amount of at least 80% by weight of refractory particles, including the oxide particles, should be present in the powder mixture.

In a preferred embodiment, the mixture comprises: - 80 to 94% by weight of refractory oxide particles selected from particles of aluminum oxide, magnesium oxide and mixtures thereof, - 1 to 5% by weight of silicon carbide particles, and - 5 to 15% by weight Fuel particles.

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

A useful way of working to bring the powder mixture against a surface of the refractory body to be repaired is to spin the powder mixture together with an oxygen-containing gas. It is generally recommended to spin particles in the presence of a high concentration of oxygen, e.g. by using commercially available oxygen as a gas carrier. In this way, a repair mass is easily formed which adheres to the surface on which the particles are thrown. Because of the very high temperatures that the ceramic welding reaction can reach, it can penetrate slag that may be present on the surface of the refractory body to be treated and can soften or melt the surface in such a way that there is a good bond between the treated one Surface and the newly formed refractory repair compound is generated.

This procedure is conveniently carried out using a lance. A suitable lance for use in the method of the invention comprises one or more outlets for the delivery of the powder stream, optionally together with one or more outlets for additional gas. For repairs carried out in a hot environment, the gas streams can be discharged from a lance that is cooled by the fluid medium circulating through it. Such cooling can be easily achieved by providing a lance with a water jacket. Such lances are suitable for spraying powder in amounts of 30 to 500 kg per hour.

In order to facilitate the formation of a regular jet of powder, the refractory particles preferably comprise practically no particles larger than 4 mm, more preferably not larger than 2.5 mm.

The invention is particularly suitable for the repair or maintenance of steel ladles, since it can be carried out quickly at a high temperature between ladle batches, because the refractory bodies which form part of such steel ladles are particularly attacked by contact with molten metal and slag. The region that requires the greatest repair tends to be the line of the liquid surface.

The invention will now be described in more detail in the following non-limiting examples.

example 1

A refractory repair compound is formed on a wall of the magnesium oxide lining of a steel ladle. A mixture of refractory particles and fuel particles is thrown onto these bricks. The temperature of the wall is about 850 * C. The mixture is spun at a rate of 150 kg per hour in a stream of pure oxygen. The mixture has the following composition:

MgO 87% by weight SiC 5% by weight Si 4% by weight At 4% by weight

The MgO particles have a maximum dimension of about 2 mm. The silicon carbide particles have a particle size of 125 µm with an average dimension of 57 µm. The silicon particles and the aluminum particles have a maximum dimension below 45 µm.

Example 1A (comparison)

For comparison, the same repair was carried out in the same manner as described in Example 1, but using a powder mixture of the following composition:

MgO 92% by weight Si 4% by weight At 4% by weight

The apparent density and surface porosity (i.e. the open porosity) of the refractory repair compositions formed in Examples 1 and 1A were measured and the results were as follows:

Example No.Density kg / dm3 porosity (%) 1 2.9 about 8% 1A 2 - 2.4 about 20%

In a modification of Example 1, a refractory body containing aluminum oxide can be repaired in a corresponding manner, but the magnesium oxide particles in the powder mixture being replaced by the same amounts of aluminum oxide particles of the same grain size.

Examples 2 to 4

Refractory repair compounds are formed on a wall of the magnesium oxide-based lining of a steel ladle. Mixtures of refractory particles and particles of fuel are added to this 4

Claims (9)

AT 402 922 B flung brick. The temperature of the wall is around 850 * C. The mixtures are spun at a rate of 60 kg per hour in a stream of pure oxygen. The mixtures had the following compositions (% by weight): Example No. 2 3 4 Si 4% 4% 4% At 4% 4% 4% SiC 2% 5% 10% MgO 90% 87% 82% The MgO particles have a maximum dimension of about 2 mm. The silicon carbide particles have a particle size of 125 µm with an average dimension of 57 µm. The silicon particles and the aluminum particles have a maximum dimension below 45 µm. The apparent density and surface porosity (ie open porosity) of the refractory repair compositions formed in Examples 2 to 4 were measured and the results were as follows: Example No. Density kg / dm1 2 porosity (%) 2 2.6 14% 3 2.7 10 % 4 2.9 8% Example 5 A ceramic welding powder has the following composition (% by weight): aluminum oxide 87% silicon carbide 5% aluminum 6% magnesium 2% The aluminum oxide used was an electrical aluminum oxide. The alumina had a nominal maximum grain size of 700 µm, the silicon carbide had the same grain as that given in Example 1 above, the aluminum particles had a maximum dimension below 45 µm and the magnesium particles had a maximum dimension of 75 µm. The above powder mixture, as described in Example 1, can be used to repair a Corhart (Trade Mark) Zac refractory block (composition: alumina / zircon / zirconia) in a glass furnace below the level of the work surface of the melt after the tub has been partially emptied Give access to the repair center. 1. A method for repairing a refractory oxide-based body by spinning a powder mixture against a surface of this body at an elevated temperature and in the presence of oxygen, said powder mixture containing refractory oxide particles and fuel particles which exothermic with the oxygen to form a refractory Oxides react, characterized in that the fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and in that the powder mixture additionally contains up to 10% by weight of silicon carbide particles. 5 1 Method according to claim 1, characterized in that the content of silicon carbide in this 2 powder mixture is at least 1 wt .-%. AT 402 922 B 3. The method according to claim 1 or 2, characterized in that the silicon carbide has a particle size of less than 200 microns. 4. The method according to any one of the preceding claims, characterized in that the refractory oxide particles contain at least one oxide from which the refractory body is formed. 5. The method according to any one of the preceding claims, characterized in that the refractory oxide body is selected from aluminum oxide-containing bodies and magnesium oxide-containing bodies. 6. The method according to any one of the preceding claims, characterized in that a main part of the powder mixture is formed from refractory oxide particles which are selected from magnesium oxide, aluminum oxide and mixtures thereof. 7. The method according to any one of the preceding claims, characterized in that the refractory body to be repaired is part of a steel ladle. 8. Powder mixture for the repair of refractory bodies based on oxide, the mixture comprising: - 80 to 95% by weight of refractory particles which contain a refractory oxide, and - 5 to 20% by weight of fuel particles which are exothermic react with oxygen to form a refractory oxide, characterized in that these fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and in that the refractory particles comprise up to 10% by weight, based on the total mixture, of silicon carbide particles. 9. Powder mixture according to claim 8, characterized in that there are - 80 to 94% by weight of refractory particles selected from particles of aluminum oxide, magnesium oxide and mixtures thereof, - 1 to 5% by weight of silicon carbide particles, and - 5 to 15% by weight .-% contains fuel particles. 6