JP2000178075A - Castable refractory containing carbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon containing castable refractory having the ability to inhibit structure spalling even when it is repeatedly used while hating, improved resistance to thermal impact, thereby the formation of exfoliation and crack is prevented, improved in resistance to infiltration of slag by carbon, thereby softening and melting of the refractory by infiltration of the slug can be inhibited, and improved in durability, which refractory is produced by using alumina raw material as the main component of its aggregate and its matrix, and further, controlling components contained in the matrix. SOLUTION: In the castable refractory, alumina raw material is used as the main component of its aggregate having particle diameters more than 0.3 mm and of its matrix having particle diameters of <=0.3 mm. The castable refractory contains 2 to 8 wt.% alumina cement, 2 to 8 wt.% magnesia raw material, 0.3 to 2 wt.% amorphous silica raw material and 0.5 to 3 wt.%, expressed in terms of the residual carbon, of a carbonaceous raw material, as the components of the matrix.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the thermal shock resistance during repeated use of heating and cooling, which is a drawback of alumina-magnesia castable refractories widely used in molten steel ladle, tundish lining material and the like. The present invention relates to a carbon-containing castable refractory that can be expected to improve durability by preventing peeling and abrasion of carbon.

[0002]

2. Description of the Related Art Alumina-magnesia castable refractories are superior in corrosion resistance and infiltration resistance to conventional castable refractories such as high alumina and alumina-spinel castable refractories. Widely used for lining materials and mass block materials. In particular,
Even if compared with alumina-carbon, magnesia-carbon brick, etc., the same durability can be obtained as the lining material of the molten steel ladle, depending on the operating conditions, and it can be said that it is already a general material. .

[0003] Alumina having such excellent properties
Although it is a magnesia castable refractory, a siliceous material is added to the magnesia material to prevent digestion of the magnesia material, so that the siliceous material vitrifies the tissue. This vitrification causes shrinkage and increase in strength after cooling, so repeated heating and cooling causes structural spalling at the vitrification-non-vitrification boundary and lowers thermal shock resistance of the working surface. There was a problem that peeling occurred. .

To prevent the occurrence of the structural spalling and the reduction of the thermal shock resistance, an amorphous refractory lined in a molten steel metal container in which 3 to 15% by weight of aluminum hydroxide is added to an alumina-magnesia castable component (Japanese Patent Application Laid-Open No. 9-1997) 1
No. 2375) has been proposed, but this involves a dehydration reaction of aluminum hydroxide, which causes problems such as generation of cracks due to magnesia digestion and deterioration of corrosion resistance due to an increase in porosity.

[0005] Alumina-magnesia castable refractories have a small construction thickness, and when they are used for precast blocks such as immersion nozzles and tundish injection pipes for heating the entire surface, the immersion portion is softened and melted by slag infiltration. There was a risk of falling off.

[0006]

SUMMARY OF THE INVENTION The present invention provides a carbon castable refractory having an alumina raw material as a main component of an aggregate and a matrix, and a matrix component regulated, thereby preventing structural spalling during repeated use. Peeling and cracking are prevented by
At the same time, by improving the slag infiltration resistance of carbon, softening and melting due to slag infiltration can be prevented, and the durability is improved.

[0007]

According to the present invention, an alumina-based raw material is mainly composed of an aggregate having a particle size exceeding 0.3 mm and a matrix having a particle size of 0.3 mm or less.
8% by weight of alumina cement, 2 to 8% by weight of magnesia raw material, 0.3 to 2% by weight of amorphous silica raw material, and 0.5 to 3% by weight of carbonaceous raw material in terms of residual carbon content. And a carbon-containing castable refractory (claim 1) and an alumina raw material having a particle size of 0.3 mm.
And a main component of a matrix of 0.3 mm or less, and 2 to 8% by weight of alumina cement as a matrix component, 2 to 8% by weight of magnesia raw material,
To 2% by weight of an amorphous silica raw material and a residual carbon content of 0.5 to 3
A carbon-containing castable refractory (Claim 2) characterized in that the carbon-containing castable refractory further contains 0.5% to 5% by weight of an inorganic carbide material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention uses an alumina material as a main component of an aggregate and a matrix. The alumina raw material here is fused alumina, sintered alumina,
Synthetic raw materials such as calcined alumina are preferred. Natural materials such as bauxite have instability in quality, making it difficult to maintain certain properties. In the aggregate, the particle size of such an alumina-based raw material exceeds 0.3 mm. Particle size 0.3mm
The following matrix contains alumina cement, magnesia-based material, amorphous silica material, and carbon-based material in addition to the above-mentioned alumina-based material. The invention according to claim 2 further contains an inorganic carbide raw material.

Of these, alumina cement is indispensable as a binder. The greater the content of the alumina component, the more excellent the corrosion resistance, but the content of the alumina component is preferably 70 to 80% by weight because the developing strength is reduced. The addition amount of alumina cement is required to be 2 to 8% by weight, and if it is less than 2% by weight, the strength at the time of demolding and the handling strength after drying with a precast block product are insufficient. Conversely, when the content is 8% by weight or more, there is no problem in strength at the time of handling, but the calcia component becomes excessive and the corrosion resistance is reduced.

The magnesia-based raw material causes a spinel reaction with volume expansion with the alumina-based raw material, which is a main raw material, and as a result, densifies the structure. Therefore, it is indispensable to obtain high corrosion resistance and high infiltration resistance. As this raw material, a synthetic raw material such as electrofused magnesia and sintered magnesia is desirable. If this is a natural magnesia raw material, the quality is not stable and it is difficult to maintain certain characteristics. The added amount of the magnesia raw material needs to be 2 to 8% by weight. If this is less than 2% by weight, not only densification is insufficient, but also corrosion resistance to basic slag cannot be expected. Conversely,
If it exceeds 8% by weight, it becomes difficult to cure the magnesia by hydration and to prevent cracking during drying.

An amorphous silica raw material is indispensable for preventing a hydration reaction of a magnesia raw material. The magnesia raw material becomes magnesium hydroxide by a hydration reaction with the kneading water, and cracks are easily generated during curing and drying of the molded article due to its volume expansion action. Therefore, if amorphous silica is present, the amorphous silica is strongly negatively charged by surface electrolysis in water, which is conversely adsorbed on the surface of the positively charged magnesia raw material to form magnesia particles. It is believed that the surface is coated with amorphous silica to prevent the hydration reaction of the magnesia raw material.

As an amorphous silica raw material, silica fume is generally used. In order to achieve a coating effect with a smaller amount of amorphous silica, the particle size should be as small as possible. The addition amount of the amorphous silica is 0.3 to 2% by weight. If this amount is less than 0.3% by weight, the effect of preventing the digestive reaction of the magnesia raw material becomes insufficient, and cracks are likely to occur during curing and drying. If it exceeds 2% by weight, the effect of preventing digestion is sufficient, but the corrosion resistance is reduced by vitrification, so that an improvement in durability cannot be expected.

The carbonaceous raw material is the most important raw material in the present invention, and is indispensable for preventing the alumina-carbonaceous castable refractory, which is a feature of the present invention, from cracking during repeated heating. According to the study of the inventors, the addition of the carbonaceous material suppresses the increase in strength and shrinkage after firing, and as a result, prevents structural spalling due to the suppression of vitrification of silica during repeated overheating, and improves thermal shock resistance. Was found to be achieved. Further, the addition of a carbonaceous material significantly improves the resistance to slag infiltration, and can prevent softening and melting wear due to slag infiltration, which could not be prevented when the wall thickness is small. Improvements in durability of such thin products can be expected.

The amount of the carbonaceous raw material added is as follows: when heated at 350 ° C. for one hour at which castable water can be removed,
0.5 to 3% by weight of the remaining coal is required. This is 0.5
If the amount is less than the weight percentage, the above-mentioned prevention of structural spalling and improvement in thermal shock resistance cannot be expected. On the other hand, if it exceeds 3% by weight, improvement in durability cannot be expected due to wear due to insufficient strength. That is, alumina
In order to maintain the characteristics of magnesia castables and exhibit the effects of preventing structural spalling and improving thermal shock resistance of the present invention, the above-mentioned amount is important. The carbonaceous raw material is desirably carbon black because of its high dispersibility in water and high residual carbon content. Since the inorganic carbide raw material has higher reactivity with oxygen than the carbonaceous material, it is effective as an antioxidant for the carbonaceous material. In addition, since the inorganic carbide raw material has a small decrease in corrosion resistance, the effect of the present invention is more stably exhibited by its addition.

In the case of a precast block product, it is possible to prevent oxidation of carbon during preheating by applying an antioxidant coating agent such as glaze on the surface in advance, but in the case of a lining material, a coating spraying equipment or the like is used. Is required, and the construction place is limited. In addition, in order to prevent variations in properties due to peeling of the coating agent, it is desirable to add an inorganic carbide raw material as a carbon antioxidant.

As the inorganic carbide raw material, silicon carbide, boron carbide, zirconium carbide and the like are effective. The added amount is 0.5 to 5% by weight. If it is less than 0.5% by weight, the effect of preventing oxidation of the carbonaceous raw material cannot be sufficiently obtained. On the other hand, if it exceeds 5% by weight, the antioxidant effect is high, but the lowering of the melting point lowers the corrosion resistance and makes it impossible to expect an improvement in the durability.

[0017]

Examples (Examples 1 to 5) Each raw material having the compounding ratio shown in Table 1 was subjected to a fluidity test by flow value measurement according to JIS R-5201, and was equivalent to a conventional alumina-magnesia castable refractory. A test piece of castable refractory was prepared with the added water exhibiting the fluidity. Physical properties of this castable refractory were evaluated as follows.

Evaluation of physical properties (sample size, 40 × 40 × 160
mm) It was dried at 110 ° C. for 2 hours, baked at 1500 ° C. for 3 hours, and the bulk density and the bending strength were compared. The firing was performed in a carbon breathe.

Evaluation of thermal shock resistance (sample size, 40 × 40 ×
160mm) In a spalling electric furnace in which the base plate reciprocates in two chambers where the temperature can be set individually, holding at 500 to 1500 ° C for 1 hour is repeated 5 times, and after the test, the sample is cut and crack growth is visually observed. confirmed. The degree of crack growth was evaluated on a three-point scale. ◎ indicates no cracks, は indicates slight cracks, and × indicates many cracks. Further, in order to compare the degree of structural deterioration, the strength of the sample repeatedly fired under the above conditions was also measured.

Evaluation of corrosion resistance and slag erosion resistance (sample size, φ20 × 160 mm) Immerse in a molten steel temperature of 1600 ° C. for 60 minutes by a dielectric furnace dipping method, cut the sample after cooling, and determine the amount of wear and slag infiltration. It was measured. The index of Example 1 was set to 100, and the amount of slag infiltration of other Examples was shown by numerical values. In this case, the smaller the numerical value, the higher the corrosion resistance. In addition, the erosion agent used synthetic slag, and the composition of this slag is shown in Table 4.

Oxidation resistance evaluation (sample size, 40 × 40 × 4
0 mm) The sample was heated to 1200 ° C. (heated in 8 hours and held for 3 hours) in an electric furnace. This was allowed to cool naturally and then cut, and the thickness of the oxide layer was measured. The thickness of the oxidized layer in Example 1 was indexed as 100, and the amount of slag infiltration in other examples was shown by numerical values. In this case, the smaller the value, the higher the oxidation resistance. The results are shown in Table 1.

Comparative Examples 1 to 12 Comparative Examples 1 to 12 are shown in Tables 1 to 3. Among the comparative examples, Comparative Examples 10 to 12 are obtained by adding aluminum hydroxide to a conventional alumina-magnesia castable refractory.

The preparation of the raw materials and test pieces used here and the evaluation of the physical properties of the castable refractories were performed in the same manner as in the examples.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

As is clear from Table 1, it can be seen that all of the embodiments of the present invention improve the spalling resistance during repeated heating. Regarding the corrosion resistance, when immersed in the slag for a long time, the softening and melting phenomenon as seen in the prior art is not observed, and the improvement of the durability can be clearly confirmed.

Further, an immersion nozzle (inner diameter 40 mm, length 3
In the actual machine test of 60 mm), when a test product (surface coating of an antioxidant coating agent) manufactured using the composition of Example 2 was used, a large crack reduction and a large cracking were obtained as compared with the conventional alumina-magnesia castable refractory. The improvement of corrosion resistance was confirmed.

[0030]

According to the castable refractory containing carbon of the present invention, the spalling of the refractory is prevented by the prevention of structural spalling and the improvement of the thermal shock resistance during repeated use, and as a result, the refractory The product can be expected to have improved durability. Further, the effect of improving the slag infiltration resistance of carbon in the refractory can prevent softening and melting due to slag infiltration when the wall is thin, and improvement in durability can be expected in this aspect as well.

Claims (2)

[Claims] An alumina-based raw material is mainly composed of an aggregate having a particle size of more than 0.3 mm and a matrix having a particle size of 0.3 mm or less, and 2 to 8% by weight of an alumina cement as a matrix component; Magnesia material, 0.3 to 2% by weight of amorphous silica material, and 0.5 to 3% by weight of residual carbon
A castable refractory containing carbon, characterized by containing: 2. An alumina-based raw material comprising an aggregate having a particle size of more than 0.3 mm and a matrix having a size of 0.3 mm or less, 2 to 8% by weight of alumina cement as a matrix component, and 2 to 8% by weight of Magnesia material, 0.3 to 2% by weight of amorphous silica material, and 0.5 to 3% by weight of residual carbon
A castable refractory containing carbon, characterized in that the castable refractory further comprises 0.5 to 5% by weight of an inorganic carbide material.