SI9400425A - A method and powder mixture for repairing oxide based refractory bodies - Google Patents

Description

The present invention relates to a method for repairing an oxide-based refractory body by a ceramic welding process.

Silicon, zirconium, aluminum and magnesium oxides are used as industrial refractory oxides. In particular, aluminum and magnesium oxides are now used in the metallurgical industry, where they are selected for their resistance to high temperature, erosion and corrosion by materials such as molten metal, slag and foam.

Magnesium oxide-based refractory materials, otherwise known as basic refractory materials, can form a casting pan for molten steel. Such linings become torn off due to molten steel and slag when used. Lining erosion occurs especially at the fluid level. Thus, from time to time, such oxide-based refractory bodies need to be repaired.

They suggested repairing refractory bodies using a ceramic welding technique. In this technique, they maintain the refractory body to be repaired at an elevated temperature and the powder mixture is sprayed in the presence of oxygen, the powder mixture comprising particles of refractory material and fuel particles which react exothermically with oxygen to form refractory oxide. According to this method, the refractory mass develops and adheres to the refractory body at the point of repair. Ceramic welding techniques are shown in BG 1,330,894 (Glaverbel) and GB 2,170,191 (Glaverbel). Fuel particles are particles that are of such composition and granulometry that they react exothermically with oxygen to form a refractory oxide and to release the heat required to melt, at least superficially, the refractory injected particles.

However, they have found that when a powder mixture consisting of oxide particles and fuel particles can be used to repair a refractory oxide-based body, in particular a refractory oxide body with high melting point, as magnesium oxide, the resulting refractory mass is porous. In the case of significant apparent porosity, the repair mass is not usable for certain applications, especially if the repair mass is subject to erosion or corrosion by molten materials.

Therefore, it is an object of the present invention to provide a process for the repair of oxide-based refractory bodies that allows the formation of refractory refractory mass with acceptable porosity.

It has been surprisingly discovered that this purpose can be achieved by incorporating a specific amount of silicon carbide into the powder mixture when the fuel particles are selected from magnesium, aluminum, silicon particles and mixtures thereof. This is contrary to the generally accepted principle of matching the composition of the refractory with the surface of the refractory being repaired. Furthermore, silicon carbide is considered to be an inert material in this ceramic welding process and is not wetted by the liquid phase produced during the reaction. The effect of silicon carbide on the porosity of the mass is therefore somewhat surprising.

Although we do not wish to be bound by the theory that additional silicon carbide particles transfer heat to the refractory mass and, after a long time, cause prolonged exposure to high temperatures, the decomposition of silicon carbide particles produces a carbon known to provide refractory repellent mass good resistance to slag corrosion.

Thus, the first aspect of the invention is a method for repairing a refractory oxide-based body by spraying a powder mixture against the surface of said body at elevated temperature and in the presence of oxygen, wherein said powder mixture comprises refractory oxide particles and fuel particles that react exothermically with oxygen, to form a refractory oxide, characterized in that the fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and that the powder mixture further comprises up to 10% by weight of silicon carbide particles.

The level of silicon carbide in the powder mixture is preferably at least 1% by weight. If too much silicon carbide is included, we have found that it may not be possible to form a repair mass at all because the repair material drains from the repair site. Without wishing to be bound by theory, it can be expected that this may be due to the retention of too much heat after the reparation process, leading to a liquid phase with low viscosity. If too little silicon carbide is used, the advantages of the invention are not achieved to a significant extent.

Silicon carbide preferably has a small particle size of less than 200 μτη. With the particle size as used herein, it is considered that the material in question has a particle size distribution such that at least 90% by weight of the particles meet the given limits. The average dimension as used here indicates that it has a dimension of 50% by weight. particles smaller than this average.

Refractory oxide particles may comprise at least one oxide of which the refractory body is made. Thus, refractory oxide particles, where the refractory oxide body is a body containing alumina, may comprise alumina particles. When a refractory oxide body is a body containing magnesium oxide, the refractory oxide particles may comprise magnesium particles.

Preferably, the main portion of this powder mixture is formed by particles of refractory oxides selected from magnesium, alumina and mixtures thereof. These are oxides in the presence of which the exothermic reaction is most vigorous, and therefore there is a higher risk of obtaining a highly porous repair mass. Preferably, the oxide refractory particles have a particle size of less than 2.5 mm, with substantially no particles larger than 4 mm in size.

Fuel particles are selected from magnesium, aluminum, silicon particles and mixtures thereof. Particularly preferred is a mixture of aluminum and silicon. The fuel particles used in the mixture preferably have an average dimension of less than 50 μτη.

Reparations are generally performed when the refractory body is hot. This makes it possible to repair eroded refractory bodies while maintaining the equipment essentially at its operating temperature.

The elevated temperature may be above 600 ° C as measured on the surface of the refractory body to be repaired. At this temperature, the fuel particles will burn in the presence of oxygen, releasing the refractory oxide and generating enough heat to cause the oxide particles, together with the fuel burning product, to form into a refractory refractory mass that forms the reparation.

The invention also provides, in accordance with its second aspect, a powder mixture for the repair of oxide-based refractory bodies, the composition comprising

- from 80 to 95% by weight of refractory particles comprising refractory oxide; and

- from 5 to 20% by weight of fuel particles which exothermically react with oxygen to form a refractory oxide, characterized in that these fuel particles are selected from magnesium, aluminum, silicon particles and mixtures thereof, and that these refractory particles include up to 10% by weight - based on the total mixture - of silicon carbide particles.

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

In a preferred embodiment, the mixture is of scale

- from 80 to 94% by weight of refractory oxide particles selected from alumina, magnesium particles and mixtures thereof;

- from 1 to 5% by weight of silicon carbide particles; and

- from 5 to 15% by weight of these fuel particles.

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

A useful technique for storing the powder mixture against the surface of the refractory body to be repaired is to spray the powder mixture together with gas containing oxygen. It is generally recommended to perform particle injection in the presence of high oxygen concentration, e.g. using market-grade oxygen as a gas carrier. In this way, a repair mass is easily formed which adheres to the surface on which the particles are sprayed. Due to the very high temperatures that can be attained in the ceramic welding reaction, it can penetrate the slag, which may be present on the surface of the refractory body being machined, and may soften or stiffen the surface so as to create a good bond between the treated surface and the new the resulting refractory.

This procedure is advantageously performed using a spear. A suitable spear for use in the process of the invention comprises one or more openings for the discharge of the powder stream, optionally together with one or more openings for the additional gas. For reparations made in hot environments, gas streams can be discharged from the spear, which is cooled by the fluid circulating through it. Such cooling can be easily achieved by providing a spear with a water jacket. Such spears are suitable for powder spraying at speeds of 30 to 500 kg / h.

To facilitate the formation of a regular powder jet, the refractory particles preferably do not substantially contain particles larger than 4 mm, most preferably not greater than 2.5 mm.

The invention is particularly useful for repairing or maintaining molten steel casting pans because it can be quickly carried out at high temperature between casting batch bins, while refractory bodies forming part of such casting pans are particularly affected by contact with molten metal and slag. The area requiring maximum reparation is aligned with the liquid surface line.

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

EXAMPLE 1

A refractory refractive mass is formed on the wall of the lining - based on magnesium oxide - a casting pan for molten steel. A mixture of refractory particles and fuel particles is sprayed onto these bricks. The wall temperature is about 850 ° C. The mixture was injected at a rate of 150 kg / h into a stream of pure oxygen. The mixture has the following composition:

MgO 87% by weight

SiC 5% by weight

Si 4 wt.%

Al 4 wt.%

MgO particles have a maximum dimension of about 2 mm. Silicon carbide particles have a particle size of 125 μτη with an average dimension of 57 μτη. Silicon particles and aluminum particles have a maximum dimension below 45 μτη.

EXAMPLE IA (Comparative)

For comparison, the same reparation is carried out in the same manner as described in Example 1, but using a powder mixture with the following composition:

MgO 92% by weight

Si 4 wt.%

Al 4 wt.%

The apparent density and apparent porosity (i.e., open porosity) of the refractory refractory masses generated in cases 1 and IA are measured, and the results are as follows:

Density

Example no. kg / dm ³ porosity (%)

2.9 about 8%

IA 2-2.4 about 20%

In the modification of Example 1, a refractory material containing aluminum oxide can be repaired in a similar manner, except that the magnesium particles in the powder mixture are replaced by the same amount of alumina particles by the same granulometry.

EXAMPLES 2 to 4

Refractory refractories are formed on the wall of the lining - based on magnesium oxide - in a molten steel casting pan. Mixtures of refractory and fuel particles are sprayed onto these bricks. The wall temperature is about 850 ° C. The mixture was injected at a rate of 60 kg / h into a stream of pure oxygen. The mixtures have the following mass compositions:

Example no. 2 3 4 Si 4% 4% 4% Al 4% 4% 4% SiC 2% 5% 10% MgO 90% 87% 82%

MgO particles have a maximum dimension of about 2 mm. Silicon carbide particles have a particle size of 125 μτη with an average dimension of 57 μτη. Silicon particles and aluminum particles have a maximum dimension below 45 μτη. Measure the apparent density and apparent porosity (i.e., the open porosity) of the refractory refractories formed in Examples 2-4, and the results are as follows:

Density

Example no. kg / dm ³ porosity (%) 2 2.6 14% 3 2.7 10% 4 2.9 8%

EXAMPLE 5

Powder for ceramic welding has the following composition (wt.%):

Alumina 87% silicon carbide 5% aluminum 6% magnesium 2%

The alumina used is electrocorundum. The alumina has a nominal maximum grain size of 700 μτη, silicon carbide has the same granulometry as given in Example 1 above, aluminum particles have a maximum dimension below 45 μτη and magnesium particles have a maximum dimension of 75 μτη.

The above powder mixture can be used as described in Example 1 for Corhart reparation (trademark) Zac refractory block (composition: alumina / zirconium / zirconium) in a glass melting bath furnace below the level of the working surface of the melt after the tub has been partially exhausted to gain access to the reparation site.

Claims (9)

PATENT APPLICATIONS A method for repairing a refractory oxide-based body by spraying a powder mixture against the surface of said body at elevated temperature and in the presence of oxygen, wherein said powder mixture comprises refractory oxide particles and fuel particles that react exothermically with oxygen to form a refractory oxide , characterized in that the fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and that the powder mixture additionally contains up to 10% by weight of silicon carbide particles. Process according to claim 1, characterized in that the content of silicon carbide in this powder mixture is at least 1% by weight. Process according to claim 1 or 2, characterized in that the silicon carbide has a particle size below 200 μτη. A method according to any one of the preceding claims, characterized in that the refractory oxide particles comprise at least one oxide from which the refractory body is. Method according to any one of the preceding claims, characterized in that the body is selected from refractory oxides from bodies containing aluminum oxide and bodies containing magnesium oxide. Process according to any one of the preceding claims, characterized in that the main portion of this powder mixture is of refractory oxide particles selected from magnesium, alumina and mixtures thereof. Method according to any one of the preceding claims, characterized in that the refractory body to be repaired is part of a molten steel pan. 8. Powder mixture for the repair of oxide-based refractory bodies, the mixture comprising - from 80 to 95% by weight of refractory particles comprising refractory oxide; and - from 5 to 20% by weight of fuel particles which react exothermically with oxygen to form a refractory oxide, characterized in that these fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, and that these refractory particles include up to 10 wt. .% - based on the whole mixture - silicon carbide particles. Powder composition according to claim 8, characterized in that it comprises: - from 80 to 94% by weight of refractory oxide particles selected from alumina, magnesium particles and mixtures thereof; - from 1 to 5% by weight of silicon carbide particles; and - from 5 to 15% by weight of these fuel particles. 24504-xii-94-mn