JP2009139021A - Construction method for monolithic refractory - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction method for obtaining monolithic refractor having excellent spalling resistance without special additive in the monolithic refractory using alumina cement as a binder. <P>SOLUTION: This construction method includes a series of processing steps of mixing monolithic material containing alumina cement, casting, curing, drying and heating the same. In the construction method for the monolithic refractory, the above curing after casting is performed at a temperature of 35 to 80°C for 24 hours or longer or preferably while covering with an air-tight sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for constructing an irregular refractory, and particularly to a method for forming a lining refractory such as a molten metal holding container by pouring construction.

  Conventionally, as a refractory used for the lining of a molten metal holding container such as a ladle, an amorphous refractory (such as a casting material) has been used. However, in recent years, as the demand for high-grade steel has increased, the ladle usage conditions have become severe, such as the temperature of the ladle receiving steel increased and the secondary refining treatment ratio increased. The product has insufficient corrosion resistance and spall resistance.

  The corrosion resistance of the irregular shaped material is generally governed by the chemical composition of the refractory. Corrosion resistance is improved by adding magnesia or chromia to the most commonly used alumina material as the amorphous refractory. For example, it has been proposed to blend magnesia spinel clinker with fine powder of alumina amorphous refractory (Patent Document 1).

On the other hand, in order to improve the spall resistance of the alumina amorphous refractory material, by adding silica (CaO), chromia (Cr ₂ O ₃ ) or the like, or by adding unstabilized zirconia, There is a proposal to improve the spall property (Patent Document 2).

  In addition, Patent Document 3 proposes a method for improving the spall resistance by suppressing sintering by adding organic fibers.

  Furthermore, Patent Document 4 proposes to suppress the progress of cracks and improve the spall resistance by forming coarse grains.

  However, the technique disclosed in Patent Document 2 is economically disadvantageous because zirconia is expensive. Further, the technique of Patent Document 3 has a problem in that the addition of organic fibers reduces the fluidity during kneading, leading to an increase in the amount of added water, resulting in an increase in porosity and loss of corrosion resistance. Further, Patent Document 4 has a restriction that the case where coarse grains can be added is limited to a case where the construction thickness is sufficiently large with respect to the coarse grains.

In any case, these conventional techniques require at least some additives from the viewpoint of improving the spall resistance, and in this respect, the material cost is excessive. Further, although these conventional techniques can improve the spall resistance, the corrosion resistance may be reduced, and it has not necessarily been a proposal for a desirable amorphous refractory.
Japanese Patent Application Laid-Open No. 64-87577 JP-A-5-51266 JP-A-2-225379 JP-A-8-2975

  As described above, conventional refractories for casting construction, especially refractories containing alumina cement as a binder, add various additives to improve corrosion resistance and spall resistance. However, the use of this additive has a problem that it is less effective or, on the contrary, obstructs other properties.

  Therefore, an object of the present invention is to propose a construction method capable of making an amorphous refractory having good spall resistance without the use of a special additive.

  While examining each of the above-mentioned problems of the prior art, the inventor developed the present invention according to the following summary configuration as an effective construction method particularly for improving the spall resistance of the irregular refractory. I arrived.

  That is, the present invention is a construction method comprising a series of treatment steps of kneading, pouring, curing, drying, and heating an alumina cement-containing amorphous material, and the curing performed after pouring is performed at a temperature of 35 to 80 ° C. It is the construction method of the amorphous refractory characterized by the process hold | maintained for more than time.

  In the present invention, at the time of the curing treatment, it may be more preferable to cover the surface of the casting material with a vapor-impermeable airtight sheet and to perform the curing treatment in a steam saturated atmosphere.

  According to this invention concerning said structure, the spall resistance of the amorphous refractory containing an alumina cement can be improved by devising the curing method at the time of construction. Therefore, according to the present invention, no special additive is used, which is economically advantageous.

  Moreover, according to this invention, when employ | adopting an airtight sheet | seat or the curing process in a steam saturated atmosphere, there exists an effect which suppresses the explosion at the time of drying performed after that.

  The inventor has found that when an amorphous refractory with alumina cement as a binder is actually used in a ladle or the like, even if the same material is used under the same operating conditions, there is a large difference in its life. I found out. As a result of investigating the cause, it was found that the construction conditions, especially the curing conditions, had a great influence. While investigating the cause in more detail, the inventor found out that the anti-sball resistance can be improved by introducing microcracks (microcracks) in advance into the irregular refractory.

In general, it is known that a hardened body of alumina cement generates microcracks at a high curing temperature and causes a decrease in strength. That is, the strength of alumina cement increases at 20 ° C. as the amount of CAH ₁₀ and C ₂ AH ₈ increases, but at 40 ° C., the strength decreases as CAH ₁₀ decreases and C ₃ AH ₆ increases. Cracks occur and the strength decreases.

Such a transfer reaction liberates a large amount of water as shown in the following formula, but this transfer is also considered to occur only in the presence of water.
3CAH ₁₀ → C ₃ AH ₆ + 2AH ₃ + 18H
As described above, when CAH ₁₀ is transferred to C ₃ AH ₆ which is a stable crystal, C ₃ AH ₆ and AH _{3 have} a higher specific gravity than CAH ₁₀ , so that voids, that is, microcracks are generated around the cement hydrate. It occurs and the strength decreases. As described above, the transition generation of C ₃ AH ₆ causes micro cracks, but the spall resistance of the irregular refractory is conversely improved.

Therefore, in the present invention, an amorphous material containing 1 to 20 mass% (inner number) of alumina cement is kneaded and used. In the case of a casting material, it is cured at 35-80 ° C. immediately after the casting is finished. When an amorphous refractory using alumina cement is cured, CAH ₁₀ is mainly produced on the low temperature side, and CAH ₁₀ is produced on the high temperature side at 30 ° C., and then transferred to C ₃ AH ₆ . Further, in the vicinity of 30 ° C., there is a problem that these low temperature type and high temperature type reaction becomes a branch point, and as a result of the interaction, the reaction is delayed and the condensation is delayed. In the present invention, the reason for curing the alumina cement-containing amorphous material at 35 to 80 ° C. is to intentionally generate C ₃ AH ₆ which is a cement hydrate and generate the microcracks. When the curing temperature is 30 ° C. or lower, no transition occurs in the high-temperature C ₃ AH _6, and in the range of 30 to 35 ° C., there is a problem that the setting is delayed. On the other hand, when the curing temperature exceeds 80 ° C., there are problems such as large cracks occurring during curing and evaporation of moisture being unavoidable.

In the present invention, the curing time is 24 hours or longer in order to reliably transfer CAH ₁₀ to C ₃ AH ₆ . Due to this transition, microcracks (microcracks) are generated in the cement hydrate, and, of course, a decrease in strength as a hardened cement body is also observed. However, the macro cracks remain after drying and firing, and at least contribute greatly to the improvement of the spall resistance. In this regard, if the curing time is less than 24 hours, the above-mentioned transfer does not proceed sufficiently and the effect of improving the spall resistance is reduced. On the other hand, when the time exceeds 100 hours, the transition is completed, and the effect of improving the spall resistance is saturated.
In addition, even if it is cured at 35 ° C. or lower for about 24 hours and then cured at 35 ° C. or higher, the same transition occurs, but the effect of improving the spall resistance is small.

Next, since the curing described above is performed at 35 ° C. or higher, free water in the amorphous refractory evaporates with time. However, as described above, the transition from CAH ₁₀ to C ₃ AH ₆ requires the presence of moisture. Therefore, in the present invention, in consideration of the fact that when the moisture evaporates from the surface of the molded body due to the influence of the high temperature at the time of curing, the surface reaction does not proceed, the surface portion of the cast amorphous material It was decided to suppress water evaporation.

  In order to suppress such moisture and steam, as a preferred embodiment of the present invention, the surface of the cast amorphous refractory is made of various kinds of concrete such as a steam-impermeable sheet, that is, an airtight sheet, for example, a blue sheet. It is recommended to cover with a curing sheet for heating or a heating curing sheet with a heater. Another method is to perform the curing treatment in a steam saturated atmosphere. In any case, it is desirable to prevent or suppress moisture evaporation from the surface of the cast amorphous refractory.

In the present invention, the alumina cement-containing amorphous refractory contains, as an aggregate, at least one of Al ₂ O ₃ , SiO ₂ , and MgO as a main component, and, if necessary, Cr ₂ O ₃ , ZrO ₂ An amorphous refractory containing SiC, SiC, C, or the like can be used.

For example, the following (a) to (d) are used.
(A) An alumina spinel amorphous refractory comprising at least 60 mass% of spinel clinker, 10 to 35 mass% of alumina clinker, and 3 to 10 mass% of alumina cement.
(B) An organic short fiber having a length of 0.5 to 20 mm in a composition of 100 mass% mainly composed of 40 to 90 mass% of alumina, _{2 to} 50 mass% of MgO · Al ₂ O ₃ spinel and _{2 to} 25 mass% of alumina cement. Alumina spinel amorphous refractory containing 0.01 to 0.5 mass% of outer shell.
(C) Magnesia 2 to 20 mass%, alumina cement 1 to 15 mass%, the balance being 100 mass% of the main component of alumina, 0.05 to 3 mass% of amorphous silica ultrafine powder and particle size 10 An amorphous refractory containing 10 to 40 mass% of alumina super coarse particles of 50 mm.
(D) Spinel clinker having a particle size exceeding 1 mm: 5-30 mass%, magnesia clinker having a particle size of 1 mm or less: 5-15 mass%, unstable zirconia clinker having a particle size of 1 mm or less: 5-10 mass%, An alumina spinel amorphous refractory comprising the balance of alumina clinker with an Al ₂ O ₃ content of 90 mass% or more and ultrafine silica powder with a particle size of 10 μm or less.
(E) Alumina-silica refractory material composed of magnesia: 7 mass%, silica: 0.8 mass%, alumina cement: 2 mass%, and the remaining alumina.

  As the above-mentioned alumina cement, 1 to 5 kinds of JIS R 2511 and alumina cement having an alumina content of about 90% can be used although not in the JIS standard.

  The above-mentioned amorphous refractory is added to water, kneaded with a universal kneader, mortar mixer, etc., applied to the target construction site, subjected to the curing treatment described above, and then required by a method in accordance with conventional ordinary methods. Depending on the temperature, it is deframed, heated to a temperature of 100 to 500 ° C. and dried, and then heated and fired to the use temperature (about 1200 to 1700 ° C.) to obtain an amorphous refractory for use. .

An amorphous refractory consisting of 7 mass% MgO-0.8 mass%, SiO ₂ -2 mass% alumina cement-remainder alumina was prepared. Using a universal kneader, 4 mass% of water was added and kneaded for 5 minutes, and poured into a normal mold and a test mold of (35 × 35 × 160) mm.
As an example, the curing temperature was 40 ° C., and curing was performed in a sealed plastic bag. Further, as a comparative example, curing was performed at a temperature of 20 ° C. in a laboratory. After these curing, it was dried at 110 ° C. for 1 day, and was fired in an atmospheric furnace at 1100 ° C. or 1500 ° C. for 3 hours.

  Using a (35 × 35 × 160) mm test piece, the bending strength and elastic modulus after curing and after drying were measured. Also. The parallel-shaped test piece was fired at 1100 ° C. for 3 hours and subjected to a spalling resistance test. In the spalling resistance test, heating was carried out for 15 minutes in an electric furnace maintained at 1350 ° C. according to the JIS R2657 fireproof brick spalling test method, and then single-sided water cooling for 5 minutes and air cooling for 10 minutes were repeated. From the photograph of the heated surface taken during air cooling, the area ratio remaining without being peeled off was determined, and the number of times the remaining was below 90% was taken as the number of peeling. However, the maximum number of repetitions was 10.

  FIG. 1 and FIG. 2 show the relationship between the bending strength and the elastic modulus after curing and drying, and the number of curing days. When curing at 40 ° C., the curing intensity decreases as the number of days of curing passes. The elastic modulus slightly decreases as the number of days of curing at 40 ° C. passes. About the intensity | strength after drying, it became intensity | strength about twice as much as after curing in any case. On the other hand, the elastic modulus after drying is not different from that after curing. This phenomenon indicates that 40 ° C. curing produces microcracks (microcracks) and has the effect of reducing the strength and elastic modulus after curing and after drying. Moreover, when it hardened | cured at 40 degreeC, even if it dried, it turned out that an elastic modulus does not increase and it is preferable from a viewpoint of spall resistance.

  3 and 4 show changes in strength and elastic modulus after firing in Comparative Example 1 and Inventive Example 1. FIG. About the intensity | strength and elastic modulus after curing, it can be estimated that the relationship between a comparative example and the example of this invention is maintained after drying and baking, and the structure | tissue form is also maintained.

  FIG. 5 shows the effect of curing conditions on the number of peelings as a measure of sparing resistance. When cured at 40 ° C. (Invention Examples 1 to 4), 60 ° C. (Invention Example 5), and 80 ° C. (Invention Example 6) for one day or more in accordance with the present invention, none of them are peeled even by 10 thermal shocks. Although excellent spall resistance was obtained, when it was cured at 20 ° C. (Comparative Example 1) and when it was cured for half a day (Comparative Example 2), it was inferior in spall resistance and the effect of the present invention was clearly Appeared. These spall resistances are considered to be related to the aforementioned change in mechanical properties.

  The construction method of the present invention, especially the curing technique, is an effective method for improving the spall resistance of an amorphous refractory mainly containing alumina cement, and is economical because no special additive is used. Although it is used for lining of molten metal containers used in the industry, it can also be applied as a refractory construction method for lining refractories for storage containers of other materials such as other molten metal containers and glass.

It is a graph which shows the change of the bending strength and elastic modulus after curing and drying. It is a graph which shows the change of the bending strength and elastic modulus after curing and drying. It is a graph which shows the change of the intensity | strength after baking according to curing conditions, and an elasticity modulus. It is a graph which shows the change of the intensity | strength after baking according to curing conditions, and an elasticity modulus. It is the graph which showed the influence of the curing condition on the frequency | count of peeling which is a measure of sparing resistance.

Claims (3)

In the construction method consisting of a series of processing steps of kneading, casting, curing, drying and heating the amorphous cement-containing amorphous material, the curing to be performed after the casting is maintained at a temperature of 35 to 80 ° C. for 24 hours or more. A method for constructing an irregular refractory, characterized by being. The construction method of the amorphous refractory according to claim 1, wherein the surface of the casting material is covered with an airtight sheet during the curing process. The construction method for an amorphous refractory according to claim 1, wherein the curing treatment is performed in a steam saturated atmosphere.

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