FI109421B - Method and powder mixture for repairing refractory bodies containing oxides - Google Patents

Description

109421

This invention relates to a method for repairing an oxide-containing refractory body by a ceramic welding process.

The oxides of silicon, zirconium, aluminum and magnesium are used as industrial refractory oxides. Aluminum and magnesium oxides are commonly used, particularly in the metallurgical industry, where they are selected because they withstand high temperatures, abrasion and corrosion caused by materials such as molten metal, slag and metal slag.

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Magnesium oxide refractory materials, also known as alkaline refractory materials, can form a sheath for transferring molten steel. Molten steel ·: ··: 20 and slag, harden such cladding in use. Ver. ·. houkseh wear occurs especially on the surface of the liquid • I ·. ·. level. Thus, it is necessary to repair such refractory bodies containing oxides from time to time.

• · · 25 It has been suggested to use "ceramic welding" to repair refractory parts. In this technique, the cor "· *: refractory body is maintained at elevated temperature and the powder blend is injected in the presence of oxygen, said powder blend comprising refractory mate, fuel particles reacting exothermically with oxygen; V. Refractory Oxide With this method, the refractory material builds and adheres to the refractory body at the point of repair. · Ceramic welding techniques are described in GB 5 1,330,894 (Glaverbel) and GB 2,170,191 (Glaverbel). size distribution is such that they react with oxygen in an exothermic manner to form a refractory oxide with Selma while releasing the heat necessary to melt at least the surface of the injected refractory particles. See, for example, DE 402029 and US 4,946,806.

However, it has been found that when a powder mixture composed of oxide particles and fuel particles is used to repair an oxide-containing refractory body, and especially when the refractory body to be repaired contains high-melting oxides such as magnesium oxide and alumina, the resultant molten may be. If it has a strong visible porosity, the repair compound will not be useful for certain applications, especially if the repair compound is exposed to wear or corrosion caused by molten materials.

It is therefore an object of the present invention to provide a successful; a method for repairing refractory bodies containing oxides * * · '·', which enables the production of a refractory mass having acceptable porosity.

Surprisingly, we have discovered that when the fuel particles are selected from magnesium, aluminum, and silicon, and their alloys, this object IV can be achieved by blending a certain amount of silicon carbide in the powder blend. This is contrary to the generally accepted principle of 109421 3, according to which the composition of the refractory repair mass 5 must be consistent with the composition of the surface of the refractory material to be repaired. In addition, silicon carbide has been considered an inert material in this ceramic welding process and is not wetted by the liquid phase formed during the reaction. For these reasons, the effect of silicon carbide on the porosity of the pulp is very surprising.

While not wishing to be bound by this theory, however, we consider it likely that the added SiC 15 particles will lead to heat in the refractory repair mass, and that the extended heating time at high temperatures will cause the SiC particles to decompose, producing an

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Thus, according to a first aspect of the present invention, there is provided a method of repairing an oxide-containing refractory body by spraying a powder blend against the surface of said body at elevated temperature and in the presence of oxygen, said powder blend consisting of refractory oxide particles and fuel particles react exothermically with oxygen to form · ;;; refractory oxide, characterized in that the fuel particles are selected from the group consisting of magnesium, aluminum, and silicon and their alloys,, and that the powder mixture further contains up to 10% by weight of silicon carbide particles.

The concentration of silicon carbide in said powder blend is preferably at least 1% by weight. If included; too much silicon carbide, we have found that the result may be that no repair mass 109421 4 is formed at all, since the repair material runs out of the 5 areas to be repaired. Without wishing to be bound by theory, it would be conceivable that this is because too much heat is retained as a result of a correction process resulting in a low viscosity of the liquid phase. If too little SiC is used, the advantages of the invention will no longer be substantially achieved.

The silicon carbide preferably has a small particle size, such as less than 200 µm. By "particle size" as used herein, it is meant that the material for which it has a particle size distribution such that at least 90% by weight of the particles have a size within the given limits. "Average diameter" as used herein denotes a diameter such that 50% by weight of the particles have a diameter smaller than this average.

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The refractory oxide particles may comprise at least one oxide from which the refractory body is formed.

·. Thus, when the refractory oxide body is an alumina containing body, the refractory oxide particle cassettes consist of alumina particles. Where the refractory oxide body is a magnesium oxide-containing ·· '· body, the refractory oxide particles consist of magnesium oxide particles.

Preferably, the bulk of said powder mixture is formed of refractory oxide particles selected from the group consisting of magnesium oxide and alumina, and mixtures thereof. These are the oxides, ;;; in the presence of which the exothermic reaction is most intense, and therefore there is a greater risk that the reaction will result in a very porous correction mass of ≤ 5,109,421. Preferably, the refractory oxide particles have a size of less than 2.5 mm and such that substantially none of the particles have a size greater than 4 mm.

The fuel particles are selected from the group consisting of 10 magnesium, aluminum and silicon particles and their alloys. A mixture of aluminum and silicon is particularly preferred. The fuel particles used in the blend preferably have an average diameter of less than 50 µm.

15 The remedy is usually performed when the refractory is hot. This makes it possible to repair refractory pieces while maintaining substantially the equipment at its working temperature.

20 The elevated temperature may be above 600 © C as measured on the surface of the refractory object to be repaired. At this temperature, the fuel particles burn in the presence of oxygen to produce a refractory oxide and to generate sufficient heat to cause the oxide particles, together with the 25 combustion products of the fuel, to form a refractory repair mass as a material for repair.

In accordance with another aspect of the invention, this invention relates to; kee powder mixture for repairing refractory bodies containing oxides, said mixture comprising: * 1 1 · ”1: 80% to 95% by weight of refractory particles which» · ·

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»1 •» 109421 6 j consist of refractory oxide; and 5 5 to 20% by weight of fuel particles reacting exothermically with oxygen to form a refractory oxide, characterized in that said fuel particles are selected from the group consisting of magnesium, aluminum and silicon and their alloys, and that said refractory particles contain 10% to weight, based on the total alloy, of silicon carbide particles.

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

In a preferred embodiment, the composition comprises: 80% to 94% by weight of refractory oxide particles selected from the group consisting of alumina and 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.

Preferably, the powder mixture has refractory particles, including silicon carbide particles, of at least 10 µm in size. If particles that are too small in size are used, there is a risk that they may get caught ;;; wasted during the reaction.

A useful method of applying a powder blend to a surface of a refractory body to be repaired 40 109421 is by spraying a blend of powder 5 with an oxygen-containing gas. In general, it is recommended that the particles be sprayed in the presence of a high concentration of oxygen, for example, using commercial grade oxygen as the gas carrier. In this way, a helical paste is formed which adheres to the surface where the particles are sprayed. Due to the very high temperature that the ceramic welding reaction can achieve, it can penetrate through the surface of the refractory body to be treated and possibly soften or melt the surface so as to provide a good connection between the surface to be treated and the newly formed refractory repair mass. .

This method is conveniently carried out using a suitable blow pipe. The blowing tube suitable for use in the method has one or more outlet ports for discharge of the powder stream and an option. One or more exhaust ports for additional gas.

• # · | tWhen repairing in a hot environment, can. 25 gas streams spray from a blowing pipe which is cooled by a · ·; fluid through it. Such cooling: can be easily achieved by providing a blowing tube with a water jacket. Such blow pipes are suitable. ”· · For use in spraying powder at speeds from 30 ° C to 500 kg / h.

t * »| · In order to facilitate the formation of a regular powder jet, it is preferable that the refractory particles do not * in particular, it contains particles having a size greater than,,; and, preferably, not greater than 2.5 mm.

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The present invention is particularly useful in repairing and maintaining molten steel buckets because it can be performed quickly, at high temperatures and between bucket refills, while refractory bodies forming part of such buckets are particularly stressed by contact with molten metal and die. . The area requiring the greatest correction tends to be the boundary of the liquid surface.

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The invention is further illustrated by the following non-limiting embodiments.

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Example 1

A refractory repair compound is formed on the wall of a mild steel bucket containing magnesium oxide.

20 A mixture of refractory particles and fuel particles is injected onto these bricks. The wall temperature is approximately 850 ° C. The mixture is injected at · speed. 150 kg / h for pure oxygen flow. The mixture has the following composition:. 25

MgO 87% by weight ··· · SiC 5% ···: Si 4% v: Al · 4% 30

The maximum diameter of MgO particles is approximately 2 mm. Silicon 1: The carbide particles have a particle size of 125 µm, with an average diameter of 57 µm. • with silicon particles and alumina; mine particles have a maximum diameter of less than 45 µm.

> t 9 5 109421

Example IA (Comparative)

For comparison, the same correction was made in the same manner as described in Example 1, but using a powder mixture having the following composition: 10 MgO 92% by weight

Si 4% AI 4%

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

Example No Density kg / dm Porosity (%) 20 --------------------------------------- ----------- 1 2.9 about 8% IA 2-2.4 about 20% * ·

In the variation of Example 1, the refractory body containing the alumina is corrected in the same way, but in the same way the magnesium oxide particles of the powder mixture are replaced by: a number of alumina particles having the same particle size distribution.

* * *, · »· •« v 30 Examples 2 .....- ... 4 I ·

Refractory repair compounds are formed on the wall of a mild steel bucket containing magnesium oxide.

* f · ·· ;; Mixtures of refractory particles and fuel particles 35 are injected onto these bricks. The wall temperature is approximately 850 ° C. The mixtures are injected at a rate of 60 kg / h into a stream of pure oxygen. The compositions had the following compositions (by weight): 10 109421

Example No; 2_3_4___ 5 Si 4% 4% 4% AI 4% 4% 4%

SiC 2% 5% 10%

MgO 90% 87% 82% 10 The MgO particles have a maximum diameter of approximately 2 mm. The SiC particles have a particle size of 125 µm and an average diameter of 57 µm. The maximum diameter of silicon particles and aluminum particles is less than 45 µm.

15 The apparent density and apparent porosity (i.e., open porosity) of refractory repair masses formed in Examples 2-4 were measured and the results were as follows: 20 Example No Density kg / dm Porosity (%) 2 2.6 14% 3 2.7 10% * · 4 2.9 8 % i · · t 25 • · · »

Example 5 The composition of the ceramic welding powder is as follows (% by weight% 4; lift): · 30: Aluminum oxide 87%

SiC 5%

Aluminum 6%

Magnesium 2% 35 i The alumina used was electric cast aluminum oxide.

* ί 109421 li

The alumina had a nominal maximum particle size of 5,700 µm, silicon carbide had the same particle size distribution as in Example 1 above, aluminum particles had a maximum diameter of less than 45 µm and magnesium particles had a maximum diameter of 75 µm.

The powder mixture described above is used in the manner described in Example 1 for repairing a Corhart (trademark) Zac refractory ingot (composition: alumina / zirconia / zirconium silicate) in a glass melting furnace below the working surface level in the melt after 15 minutes from the bottom. emptied so that the point to be repaired is accessed.

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Claims (9)

A method of repairing oxide-based refractory by spraying a powder mixture against the surface of said piece under elevated temperature and in the presence of oxygen, said powder mixture comprising refractory oxide particles and fuel particles which react in an exothermic manner with oxygen during formation of a refractory oxide, characterized in that the fuel particles are selected from a group consisting of magnesium, aluminum and silicon and mixtures thereof, and that the powder mixture further contains up to 10% of its weight of silicon carbide particles. 10 The method of claim 1, wherein the silicon carbide content of said powder mixture is at least f% by weight. The method of claims 1 and 2, wherein the particle size of the silicon carbide is less than 200 µm. 4. The method as claimed in the preceding claims, wherein said refractory oxide particles comprise at least one oxide, of which the refractory has: "formed! 20 •, |. 5. The method as claimed in the preceding claims, wherein said refractory oxide piece is selected from a group to which include aluminum containing:. oxide and pieces containing magnesium oxide. 6. A solid heist method according to the claims of the foregoing, wherein the main part of said powder mixture consists of oxide particles selected from a group which. * ·: Includes magnesium oxide and alumina and mixtures thereof. *. /. t The method as claimed in the preceding claims, wherein said repaired refractory piece is part of a molten metal bucket. ► * *. ,. 8. Powder blend for repair of oxide-based refractories, wherein: said mixture comprises: by weight 80% - 95% refractory particles consisting of refractory oxide; and, by weight, 5% to 20% of fuel particles which react in an exothermic manner with oxygen to form a refractory oxide, characterized by said fuel fuel particle pickling acid group, to which belongs magnesium, aluminum and silicon, and mixtures thereof, and in said refractory particles. contains silicon carbide particles up to 10% by weight calculated on the total bond. The powder mixture according to claim 8, comprising: by weight 80% - 94% refractory oxide particles selected from a group formed of alumina and magnesium oxide particles and mixtures thereof; by weight 1% - 5% silicon carbide particles; and by weight 5% -15% of said fuel particles. «• a» 1 t <'«1 • ·« I I • · * 1 1 (* 1 1 I 1 ♦ ♦ k