CZ289860B6 - Method for repairing parts from oxide based refractory material and a powder mixture for making the same - Google Patents

Abstract

In the present invention there is disclosed a method for repairing parts from oxide based refractory material by spraying a powder mixture onto a surface of a respective part at elevated temperature and in the presence of oxygen. The powder mixture for making the process contains oxide particles and fuel particles that react in exothermic manner with each other under formation of a refractory oxide. The method is characterized in that the fuel particles are represented by particles of magnesium, aluminium, silicon particles and mixtures thereof, whereby in addition thereto the powder mixture also contains up to 10 percent by weight of silicon carbide, based on the mixture total weight. By employing the method it is possible, to repair parts of oxide based refractory material whereby a reparation material exhibiting acceptable porosity is formed.

Description

A method for repairing components of an oxidic refractory material and a powder mix for carrying out the method

Technical field

The invention relates to a method of repairing components of an oxidic refractory material by a method of welding a ceramic and a powder mixture for carrying out the method.

BACKGROUND OF THE INVENTION

In industrial practice, silicon, zirconia, aluminum and magnesium oxides are commonly used as refractory oxides. At present, aluminum and magnesium oxides are mainly used in the metallurgical industry for their excellent high temperature resistance and for their erosion and corrosion resistance to materials such as metals, slag and scale.

Magnesium oxide-based refractory materials, otherwise known as basic refractory materials, can be used as liner materials for ladle transport of molten steel. In practice, this lining is subject to considerable erosion by molten steel and slag. Lining erosion occurs especially in the region of the melt level. For this reason, it is sometimes necessary to repair these parts made of refractory oxides.

The so-called "ceramic welding" method has been developed to repair refractory materials. In this method, the refractory component to be repaired is kept heated at elevated temperature and a powder mixture is shot blasted in the presence of oxygen, the powder mixture containing refractory particles and fuel particles that react with the exothermic oxygen and form a refractory oxide. By this method, the refractory mass is welded on and adhered to the repaired place of the refractory component. The method of welding ceramics is described in United Kingdom Patent Nos. 1,330,894 (Applicant Glaverbel) and 2,170,191 (Applicant Glaverbel). The composition and granulometric distribution of the fuel particles are selected in such a way as to react exothermically with the oxygen to form a refractory oxide and to release the amount of heat necessary for at least the surface melting of the blasted refractory particles.

However, it has been found that when a powder mixture consisting of oxide particles and fuel particles is used to repair the refractory components, and in particular when the refractory component is made of high melting point oxides, such as e.g. magnesium oxide and alumina may result in the resulting refractory being porous. If the resulting refractory is highly porous, then the repaired material is not suitable for certain applications, especially if the material is exposed to the erosive and corrosive effects of the molten materials.

United Kingdom Patent No. 2,233,323 discloses a powder mix for ceramic welding repairs and a process using the mix. This mixture contains refractory oxide particles and fuel particles (silicon, magnesium, zirconium and aluminum, but this mixture differs from the present invention in that the mixture requires the use of "other particles of material whose composition and / or size are chosen to the incorporation of this material into the shot-blasting mixture resulted in a porosity in the resulting refractory mass. ”The aim of this measure is therefore to achieve a certain porosity (at least 30%) and this refractory mass of this type is suitable for thermal insulation. Several porosity-inducing materials, including carbonaceous material, are mentioned in this patent, the amount of such porosity-inducing particles being at least 10% by weight, but in the example, 20% by weight are mentioned.

-1 CZ 289860 B6

United Kingdom Patent No. 1,374,458 discloses a composition for making a refractory material comprising graphite, alumina, and silica carbide. The starting mixture comprises graphite, a carbon binder, silica, silicon carbide, and glass material. This starting material is burned in a reducing atmosphere to yield a carbon-containing refractory material.

The composition of this patent and the method of preparing the refractory material (i.e., not repairing) are quite different from the present invention since the process of the present invention is carried out in an oxidizing atmosphere, the material used being based on an oxides refractory material.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel method of repairing components of an oxidic refractory 15 in which acceptable porosity can be achieved with the refractory refractory.

BACKGROUND OF THE INVENTION The present invention relates to a method of repairing components of an oxidic refractory material by sputtering a powder mixture onto the surface of the component at elevated temperature and in the presence of 20 oxygen. characterized in that the fuel particles are selected from the group consisting of magnesium, aluminum, silicon particles and mixtures thereof, and the powder mixture further comprises up to 10% by weight of silicon carbide particles.

In a preferred embodiment of the process, the silicon carbide content of the powder mixture is at least 1% by weight.

According to another preferred embodiment, the silicon carbide has a particle size of less than 200 µm.

According to a further preferred embodiment said refractory oxide particles comprise at least one oxide of which the refractory component is formed. Preferably, said refractory material component is an aluminum oxide-containing component and a magnesium oxide-containing component. According to a further preferred embodiment said component to be repaired is part of a steel casting ladle.

The bulk of the powder mixture is preferably refractory oxide particles, which are magnesium oxide and alumina.

The present invention also includes a powder composition for repairing components of oxidic refractory materials comprising:

80 to 95% by weight of particles of a refractory material containing a refractory oxide, and

- 5% to 20% by weight of fuel particles which react exothermically with oxygen to form 45 refractory oxide, characterized in that the fuel particles are selected from the group consisting of magnesium, aluminum, silicon and mixtures thereof, said fraction of refractory particles % of the material comprises silicon carbide particles in an amount of up to 10% by weight based on the total weight of the composition.

Preferably, the powder composition comprises:

- 80% to 94% by weight of refractory oxide particles selected from the group consisting of aluminum oxide, magnesium oxide particles and mixtures thereof,

1% to 5% by weight of silicon carbide particles, and

-2GB 289860 B6

- 5% to 15% by weight of said fuel particles.

It has surprisingly been found that if the fuel particles are particles of magnesium, aluminum, silicon, and mixtures thereof, this can be achieved by adding some silicon carbide to the powder mixture. This finding is contrary to the generally accepted principle that the composition of the refractory repair material should be adapted as much as possible to the surface composition of the refractory material to be repaired. In addition, silicon carbide behaves as an inert material in this ceramic welding process and does not wet the liquid phase formed during the reaction. The effect of silicon carbide on the porosity of the material is therefore quite surprising.

According to the present invention, it is believed, but without being limited by theory, that the added silicon carbide particles distribute heat in the refractory repair mass and that the prolonged exposure to high temperatures causes the decomposition of the silicon carbide particles to form elemental carbon by which is known to impart good slag corrosion resistance to the refractory repair material.

The silicon carbide content of the powder mixture is preferably at least 1% by weight. According to the present invention, it has been found that if too much silicon carbide is added, the result may be that no repair material is formed at all, since all the repair material will drain from the repair site. In view of the above phenomenon, it is believed, without being limited by theory, that this may be due to the retention of excessive heat by the repair process, resulting in a low viscosity liquid phase. Conversely, if too little silicon carbide is used, the beneficial effects of the process of the invention are not achieved to a significant extent.

The silicon carbide particles are usually small, less than 200 µm. By "particle size" as used herein is meant that the material in question has a particle size distribution such that at least 90% by weight of the particles comply with the given values. As used herein, the term "average size" refers to a size where 50% by weight of said particles are smaller than a given diameter.

The refractory oxide particles in the repair mass comprise at least one of the oxides of which the refractory material is formed. Thus, in the case where the refractory oxide material is an alumina-containing material, the refractory oxide particles in the repair material should also contain alumina particles. If the refractory oxidic material contains magnesium oxide, the refractory oxide particles in the repair material should contain magnesium oxide particles.

The bulk of the powder mixture is preferably refractory oxide particles selected from the group consisting of magnesium, aluminum oxides and mixtures thereof. These oxides are oxides in which the exothermic reaction is the most vivid and therefore there is a greater risk that the result will be a highly porous repair mass. The refractory oxide particles preferably have a size below 2.5 millimeters, with substantially no particles larger than 4 millimeters.

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

The material repair process is generally carried out with hot refractory material. This allows the erosion of the damaged refractory body to be repaired under the condition that the device remains substantially at its operating temperature.

-3GB 289860 B6

The elevated temperature may be greater than 600 ° C measured at the surface of the refractory body being repaired. At this temperature, and in the presence of oxygen, the fuel particles burn to form a refractory oxide, releasing sufficient heat to cause the particles of oxidic material to form together with the combustion product into the refractory repair mass.

In preparing a homogeneous repair mass, the powder mixture should contain at least 80% by weight of the refractory particles including the oxide particles.

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

A suitable method of applying the powder composition of the invention to the surface of the refractory 15 component to be repaired is to spray the powder composition together with the oxygen-containing gas. In general, it is recommended to carry out the blasting of the particles in the presence of high concentration oxygen, for example, it is appropriate to use oxygen of conventional industrial quality as carrier gas. In this method, the repair mass is easily formed and adheres to the surface onto which the particles are shot. Since very high temperatures can be reached in the ceramic welding reaction, slag penetrates into the surface of the refractory material, which may be present on the surface of the refractory component to be repaired, thereby softening or melting the surface to such an extent that creates a good connection between the repaired surface and the newly formed refractory repair mass.

This process can preferably be carried out with an oxygen burner. A suitable burner for use in the process of the present invention is provided with one or more outlets for conducting the powder stream, optionally also together with one or more outlets for conducting the auxiliary gas. For hot repairs, the gas streams can be passed from a circulating liquid-cooled burner. This method of cooling with a cooling jacket. These burners are suitable for 30 shot blasting in a flow rate of 30 to 500 kilograms / hour.

In order to facilitate the formation of a regular powder stream, it is preferred that the refractory particles essentially contain no particles larger than 4 millimeters, most preferably no more than 2.5 millimeters.

The process according to the invention is particularly suitable for repairing or maintaining steel casting ladles, since the repair can be carried out quickly at high temperature between two ladle batches, where the refractory parts forming part of the ladles are partially damaged by contact with the molten metal and slag. Area 40 around the melt level requires major repairs.

DETAILED DESCRIPTION OF THE INVENTION

The process of repairing the refractory oxide material components of the present invention and the powder composition for carrying out the process will be explained in more detail in the following examples, which are illustrative only and not limiting.

Example 1

According to this example, a refractory repair mass was formed on the lining of the wall of the casting ladle made of magnesium oxide-based material. A mixture of refractory and fuel particles was shot blasted onto this brick lining. The wall temperature was about

-4GB 289860 B6

850 ° C. The mixture was jetted at a rate of 150 kg / h into a stream of pure oxygen. The composition had the following composition:

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

The maximum MgO particle size was approximately 2 millimeters. The silicon carbide particle size was 125 µm with an average size of 57 µm. The silicon and aluminum particles had a maximum dimension of less than 45 µm.

Example 1A (comparative)

For comparison, the same correction was carried out in the same manner as described in Example 1, except that a powder mixture of the following composition was used:

MgO 92% by weight

Si 4% by weight

Al 4% by weight

The apparent density and apparent porosity (i.e., open porosity) values of the refractory repair materials produced in Examples 1 and 1A are shown in the following table.

Example # Density (kg / dm ³ ) Porosity (%) 1 2.9 about 8 1A 2-2,4 about 20

By modifying the procedure of Example 1, the alumina-containing refractory material can be similarly repaired, but provided that the magnesium oxide particles in the powder mixture are replaced by an equal amount of aluminum oxide particles of the same granulometric composition.

Examples 2 to 4

A refractory repair mass was formed on the lining of the wall of the steel casting pan, which was made of magnesium oxide-based material. Mixtures of refractory and fuel particles were shot blasted onto this brick lining. The wall temperature reached about 850 ° C. The mixture was shot blasted at a rate of 60 kg / h into a stream of pure oxygen. The compositions had the following composition (% by weight):

2 Example # 3 4 Si 4% 4% 4% Al 4% 4% 4% SiC 2% 5% 10% MgO 90% 87% 82%

The maximum MgO particle size was approximately 2 millimeters. The particle size of the silicon carbide was 125 µm, with an average size of 57 µm. The silicon and aluminum particles had a maximum dimension of less than 45 µm.

-5GB 289860 B6

The apparent apparent density and apparent porosity (i.e., open porosity) of the refractory repair materials produced in Examples 2 to 4 are shown in the following table.

Example # Density (kg / dm ^J ) Porosity (%) 2 2.6 14 3 2.7 10 4 2.9 8

Example 5

In this example, a ceramic welding powder having the following composition (% by weight) was used:

aluminum oxide (A1 ₂ O ₃ ) 87% silicon carbide 5% aluminium 6% magnesium 2%

The alumina used was of the type of fused alumina. The alumina had a nominal maximum grain size of 700 µm, the silicon carbide had the same particle size distribution as described in Example 1 above, the aluminum particles had a maximum dimension of less than 45 µm and the magnesium particles had a maximum dimension of 75 µm.

The above powder mixture can be used for the same purpose as in Example 1 to repair a Corhart Zac refractory block (trade mark) (composition: alumina / zirconium / zirconia) in a glass melting tank furnace at a location below the working height of the melt after the bath was partially deleted to allow access to the repaired site.

PATENT CLAIMS

Claims (9)

A method of repairing components of an oxidic refractory material by blasting a powder mixture onto the surface of said component at elevated temperature and in the presence of oxygen, said powder mixture comprising refractory oxide particles and fuel particles that react exothermically with an oxides to form a refractory oxide, wherein said fuel particles are selected from the group consisting of magnesium, aluminum, silicon particles, and mixtures thereof, and the powder mixture further comprises up to 10% by weight of silicon carbide particles. The method of claim 1, wherein the silicon carbide content of said powder mixture is at least 1% by weight. The method of claim 1 or 2, wherein the silicon carbide has a particle size of less than 200 µm. Method according to any one of the preceding claims, characterized in that said refractory oxide particles comprise at least one oxide of which the refractory component is formed. The method of any one of the preceding claims, wherein said refractory material component is an aluminum oxide-containing component and a magnesium oxide-containing component. -6GB 289860 B6 A process according to any one of the preceding claims, characterized in that the bulk of said powder mixture is formed of refractory oxide particles and said oxides are magnesium oxide and alumina. Method according to any one of the preceding claims, characterized in that said component to be repaired is part of a steel casting ladle. 8. Powder mix for the repair of components made of oxidic refractory materials, comprising: 80 to 95% by weight of particles of a refractory material containing a refractory oxide, and - 5% to 20% by weight of fuel particles which react exothermically with oxygen to form a refractory oxide, characterized in that the fuel particles are selected from magnesium, aluminum, silicon and mixtures thereof, said fraction of refractory material particles comprising carbide particles % of silicon in an amount of up to 10% by weight, based on the total weight of the mixture. Powder composition according to claim 8, characterized in that it comprises: - 80% to 94% by weight of refractory oxide particles selected from the group consisting of aluminum oxide, magnesium oxide particles and mixtures thereof, 1% to 5% by weight of silicon carbide particles, and - 5% to 15% by weight of said fuel particles.