Refractory article and method for manufacturing the same

Abstract

To provide a refractory article capable of preventing large cracks from occurring during use and to provide a method for manufacturing the same.SOLUTION: A refractory material is provided in which a heat-burnable sheet or a space formed by burning the sheet is randomly included in a refractory material structure mainly composed of a refractory raw material. The refractory article is obtained by a method for manufacturing the refractory article, including a step of adding the heat-burnable sheet to a refractory raw material compound mainly composed of the refractory raw material and then mixing the resultant mixture. When a main length is defined as A, a maximum length in a plane of the sheet in a direction perpendicular to a direction of the main length A is defined as B, and a thickness is defined as C, the heat-burnable sheet satisfies C≤1 mm, C / A≤0.1, and 0.2≤B / A≤1.0.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a refractory material for use in a furnace or facility for processing or holding molten metal or high-temperature substances, and a method for manufacturing the same. [Background technology]

[0002] In such refractories, except for some products such as nozzles for continuous casting, it is almost impossible to suppress the occurrence of cracks with current material technology. Therefore, cracks will inevitably occur during use. If the cracks grow, the refractory cannot be used continuously and its life will be over. Therefore, suppressing the growth of cracks is useful for improving the durability of the refractory.

[0003] One of the known methods for suppressing crack propagation is to mix a defect-forming material into the refractory structure. In other words, it is considered that this defect-forming material functions as a stress concentration part in the refractory structure, and improves crack dispersion by making it easier for second and subsequent cracks to occur after the initial crack occurs. Therefore, it is considered that by mixing an appropriate amount of defect-forming material into the refractory structure, crack dispersion is improved, and as a result, it is possible to suppress the occurrence of large cracks (hereinafter referred to as "large cracks") that adversely affect the durability of the refractory.

[0004] As such a defect-forming member, that is, as a member that functions as a stress concentration portion in the refractory structure, Patent Document 1 discloses mixing in wood chips, and Patent Document 2 discloses mixing in wood powder having a particle size of 0.2 mm to 4 mm. However, the conventional method of mixing in these wood chips or wood powder is not sufficient to suppress the occurrence of large cracks. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-225195 A [Patent Document 2] Special Publication No. 62-21752 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a refractory material capable of suppressing the occurrence of large cracks during use, and a method for producing the same. [Means for solving the problem]

[0007] In order to solve the above problems, the inventors conducted extensive testing and research into the material and shape of a defect-forming component that functions as a stress concentration portion in the refractory structure, and discovered that it is effective to use a heat-dissipating material such as plastic as the material and to form the component in a thin sheet shape.

[0008] That is, according to one aspect of the present invention, the following refractory material is provided. A refractory, comprising: at least one of a thermally burnable sheet and a space formed by burning the sheet, which is randomly included in a refractory structure mainly made of a refractory raw material; The sheet is a refractory material in which, when a characteristic length is A, a maximum length within the plane of the sheet in a direction perpendicular to the direction defined by the characteristic length A is B, and a thickness is C, C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0 are satisfied.

[0009] According to another aspect of the present invention, there is provided the following method for producing a refractory material. A method for producing a refractory material, comprising the steps of adding a heat-burnable sheet to a refractory raw material mixture mainly composed of a refractory raw material, and mixing the mixture, wherein the sheet satisfies C≦1 mm, C / A≦0.1 and 0.2≦B / A≦1.0, where A is a characteristic length, B is a maximum length within the plane of the sheet in a direction perpendicular to the direction defining the characteristic length A, and C is a thickness. Effect of the Invention

[0010] According to the present invention, it is possible to provide a refractory capable of suppressing the occurrence of large cracks during use, and a method for producing the same. [Brief description of the drawings]

[0011] [Figure 1] An explanatory diagram showing the representative length A and maximum length B of the sheet used in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The refractory of the present invention is a refractory in which at least one of the thermally burnable sheet and the space formed by burning the sheet is randomly included in a refractory structure mainly composed of refractory raw materials. The manufacturing method of the refractory of the present invention is a refractory manufacturing method including a step of adding the thermally burnable sheet to a refractory raw material mixture mainly composed of refractory raw materials and mixing them. Here, the refractory is a general term for unshaped refractories and shaped refractories, and precast blocks are considered to be included in the unshaped refractories.

[0013] In the present invention, the shape of the sheet satisfies the conditions C≦1 mm, C / A≦0.1 and 0.2≦B / A≦1.0, where A is a characteristic length of the sheet, B is a maximum length within the plane of the sheet in a direction perpendicular to the direction defining the characteristic length A, and C is a thickness. Here, the characteristic length of a sheet refers to the length of the longest side (hereinafter referred to as the "longest side") when the planar shape of the sheet is a triangle as shown in Fig. 1(a), and refers to the length of the longest line segment in the plane of the sheet when the planar shape of the sheet is a polygon having four or more sides, an ellipse, a circle, or an irregular shape as shown in Fig. 1(b) to (e). Also, as shown in Fig. 1(a) to (e), the maximum length in the plane of the sheet in the direction perpendicular to the direction in which the characteristic length A is defined is B. The thickness C of the sheet is often constant, but if the thickness of the sheet varies, the average value of the thicknesses at multiple locations is taken as the thickness C of the sheet. The sheet is not limited to a single layer, and may be multi-layered, such as a bag-shaped sheet or a two-ply sheet. In this case, the multi-layer sheet is considered as one sheet, and the representative length A, maximum length B, and thickness C are evaluated.

[0014] In the present invention, the shape of the sheet satisfies the conditions C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0 as described above. These conditions were derived as a result of testing and research by the inventors, and the gist of the conditions is to limit the thickness to thin ones due to the conditions C≦1 mm and C / A≦0.1, and to exclude elongated shapes due to the condition 0.2≦B / A≦1.0. In other words, the gist is to exclude chunky and string-like shapes and to limit the shape to a thin sheet-like shape.

[0015] In the present invention, the characteristic length A of the sheet is preferably greater than 1 / 3 of the maximum grain size of the refractory raw material for the following reasons. The boundary between the aggregate and the matrix in the refractory structure forms a boundary layer, which acts as a potential defect and is considered to have a certain effect in suppressing large cracks. The size of the boundary layer is determined by the particle size of the refractory raw material, so the size of the potential defect depends on the maximum particle size of the refractory raw material. It is obviously not possible to directly calculate the size of the defect caused by the boundary layer when it is simplified to an ideal defect shape such as a penny-shaped crack. Considering the area of ​​the boundary layer projected onto a certain plane, the size is considered to be at most about the diameter of the particle, but in reality, only a part of the boundary layer on the outer periphery of the particle is perpendicular to the loading direction of the stress, so it is considered to be much smaller than the diameter. The coefficient of the maximum particle size of the refractory raw material, 1 / 3, was defined as this value, and was obtained by experimentally investigating the relationship between the maximum length of the defect-forming member and the particle size of the refractory raw material, and organizing the conditions under which cracks are reduced. Here, in the present invention, the "maximum particle size of the refractory raw material" refers to the maximum particle size of the refractory raw material excluding so-called large coarse particles having a particle size of more than 8 mm. This is because it is difficult to ensure uniformity of the large coarse particles in the refractory structure, and it is difficult to stably improve the defect density. For this reason, in the present invention, the large coarse particles are not included in the refractory raw material. In other words, in the present invention, the large coarse particles are added at a predetermined addition rate as necessary to 100% by mass of the refractory raw material, similar to the sheet.

[0016] On the other hand, the material of the sheet is not particularly limited as long as it is a material that is heat-burnable. Here, in the present invention, heat-burnable refers to the property of forming a space by carbonization, decomposition, vaporization, shrinkage, etc., with the temperature rise during production or use, and the heat-burnable material is selected from plastic, wood chips, paper, cloth, leather, etc. Among them, plastic is optimal from the viewpoint of mechanical properties such as high strength and low elastic modulus, relatively low softening temperature, and availability of sheet-shaped raw materials with small thickness. As plastic, that is, synthetic resin, any of thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, acrylonitrile-styrene, polymethyl methacrylic, polyvinyl alcohol, polyvinylidene chloride, polyethylene terephthalate, polyester, phenol, melamine, polyurethane, and epoxy, phenol, melamine, polyurethane, and epoxy may be used. A laminated sheet in which some of these are combined may also be used. In the present invention, the metal is not a material that can be burned off by heat.

[0017] In the present invention, the addition rate of the sheet does not particularly need to be limited and may be appropriately determined based on common general knowledge in the art and the like. For example, in the case of monolithic refractories, it can be added at an addition rate of 0.03% by mass or more and less than 3% by mass, preferably 0.1% by mass or more and 2.5% by mass or less, based on 100% by mass of the refractory raw material. In the case of shaped refractories, it can be added at an addition rate of 0.03% by mass or more and less than 0.6% by mass, preferably 0.1% by mass or more and 0.3% by mass or less, based on 100% by mass of the refractory raw material. In the case of shaped refractories, since the manufacturing process includes a step of adding and mixing the sheet to the refractory raw material blend and then a forming step, from the viewpoint of suppressing springback during forming, the upper limit of the addition rate of the sheet is preferably lower than that in the case of monolithic refractories, but this point may also be appropriately determined based on common general knowledge in the art and the like.

[0018] Note that the above-mentioned addition rate of the sheet refers to the addition rate of a sheet whose material is thermally volatilizable and whose shape satisfies C ≤ 1 mm, C / A ≤ 0.1 and 0.2 ≤ B / A ≤ 1.0 (hereinafter referred to as "sheet within specifications"). In other words, the refractory of the present invention may contain a thermally volatilizable sheet whose shape does not satisfy C ≤ 1 mm, C / A ≤ 0.1 and 0.2 ≤ B / A ≤ 1.0 (hereinafter referred to as "sheet outside specifications"). Sheets outside specifications may unavoidably occur during the production stage of sheets within specifications, and in this case, they will be added to the refractory raw material together with the sheets within specifications. Also, when using a waste plastic sheet as the material for the sheet within specifications, metal pieces and the like may be mixed in as impurities, and in this case, the metal pieces and the like will be added to the refractory raw material together with the sheet within specifications. In any case, the above-mentioned addition rate of the sheet refers to the addition rate of the sheet within specifications.

[0019] Since the present invention obtains the desired effect by the shape change of the refractory structure, the material of the refractory is not particularly limited, and any material generally used as a refractory may be used, such as alumina-based, alumina-silica-based, alumina-magnesia-based, alumina-silicon carbide-carbon-based, alumina-spinel-based, alumina-spinel-carbon-based, magnesia-based, magnesia-carbon-based, etc. Also, the refractory raw material is not particularly limited, and depending on the material of the refractory, alumina raw material, silica raw material, alumina-silica raw material, magnesia raw material, spinel raw material, mullite raw material, silicon carbide raw material, carbon raw material, etc., those generally used as refractory raw materials can be used. In the present invention, binders for monolithic refractories such as alumina cement, magnesia cement, Portland cement, silicates, phosphates, etc. are included in the refractory raw materials. On the other hand, in the present invention, organic binders for shaped refractories such as phenolic resins are not included in the refractory raw materials, and are added at a predetermined addition rate with respect to 100% by mass of the refractory raw materials in the same manner as the above-mentioned sheet. Also, in the present invention, additives such as dispersants and organic fibers are not included in the refractory raw materials, and are added at a predetermined addition rate with respect to 100% by mass of the refractory raw materials in the same manner as the above-mentioned sheet. The addition rates of the organic binder and the additive are determined within the scope of common general technical knowledge.

[0020] The manufacturing method of the refractory of the present invention includes a step of adding and mixing a thermally burnable sheet (sheet within specifications) to a refractory raw material mixture mainly composed of refractory raw materials. In the case of shaped refractories, as described above, it includes a forming step after the mixing step. Also, in the case of monolithic refractories, the construction can typically be a casting construction. In this case, the monolithic refractory of the present invention is constructed through a kneading step, a casting step, a curing step, and a drying step with water. The construction conditions for each of these steps are determined within the scope of common general technical knowledge. Note that the construction of the monolithic refractory of the present invention is not limited to casting construction, and can also be spraying construction, patching construction, etc.

Examples

[0021] <Example A: Example of monolithic refractory (Part 1)> Table 1 shows the raw material composition of the monolithic refractory which is an example of the present invention, and the crack index of its constructed body by the thermal shock test. Table 2 shows the raw material composition of the monolithic refractory which is a comparative example of the present invention, and the crack index of its constructed body by the thermal shock test. In Tables 1 and 2, the defect forming members are represented in the form of material - thickness - representative length A × maximum length B (mm) (plane shape of the sheet), except for the rope. Also, in the columns of the shape parameters in Tables 1 and 2, A, B, and C are the above - mentioned representative length A, maximum length B, and thickness C respectively, and Pmax is the maximum particle size of the refractory raw material. These notations are the same in Tables 3 to 7 described later.

[0022]

Table 1

[0023]

Table 2

[0024] The materials of the monolithic refractories in each example shown in Tables 1 and 2 are all alumina - silica based. The breakdown of 100% by mass of the refractory raw materials is 78% by mass of chamotte aggregate, 10% by mass of alumina fine powder, 7% by mass of silica ultra - fine powder, and 5% by mass of alumina cement. And the maximum particle size Pmax of the refractory raw materials in Examples 1 to 16 and Comparative Examples 1 to 4 is 5 mm, and the maximum particle size Pmax of the refractory raw materials in Examples 17 to 19 is 8 mm. Also, although not shown in Tables 1 and 2, in each example, as additives, a dispersant was added at a rate of 0.2% by mass and organic fibers were added at an addition rate of 0.05 - 0.1% by mass. On the other hand, no large coarse grains were added.

[0025] Regarding the monolithic refractories of these examples, the crack index of their constructed bodies by the thermal shock test was obtained as follows. The size of the constructed body (hereinafter referred to as "specimen") subjected to the thermal shock test was 230×114×65 mm. For each example, water was added to the monolithic refractory of each example and kneaded with a mixer, then poured into a mold corresponding to the size of the specimen, and then cured at room temperature. After curing, the mold was removed, dried under the conditions of 110°C×24 h, and then fired under the conditions of 1000°C×3 h. A random pattern was applied to the 230×114 mm surface of the fired specimen with a heat-resistant paint, and then the initial image used for image processing was taken. In the thermal shock test, the specimen was placed in the opening of an electric furnace preheated to a predetermined temperature (1500°C in this test) so that one 114×65 mm surface of the specimen was heated, held for 10 minutes, then the specimen was removed from the electric furnace and cooled naturally. After sufficient cooling, the post-test image of the specimen was taken. By processing the initial image and the post-test image by the digital image correlation method, the displacement amounts of a large number of points on the specimen surface can be measured. Using these measured values, the crack index was calculated. That is, when measuring the strain on the surface of the specimen after the thermal shock test by the digital image correlation method, the increase in crack width is detected as an increase in the apparent strain amount. This method can perform multi-point measurement of about 10,000 points, for example. When the apparent strains of each evaluation point on the specimen surface are added together and divided by the number of evaluation points, the average strain amount per evaluation point is obtained. However, in the case of a large crack width or a long crack, this value increases. Since this value can comprehensively represent the degree of cracking with respect to the crack width and length, it was used as the crack index for evaluation. Note that the strain is obtained by dividing the difference in the movement amounts of an observation point on the specimen surface and its adjacent point by the initial length. Also, a cut-off amount corresponding to the noise level of the test is provided as necessary.

[0026] The smaller the crack index obtained in the above manner, the more the occurrence of large cracks can be suppressed during use. In Tables 1 and 2, the crack indices of the monolithic refractories of each example are shown, and the ratio of the crack index (hereinafter referred to as "crack index ratio") with the crack index of Comparative Example 1, which is the base material without the addition of a defect-forming member, set to 100 is also shown. In this test, a crack index ratio of 80 or less was set as the passing level. It is preferable that this crack index ratio is 60 or less, and more preferably 40 or less.

[0027] In Table 1, in Examples 1 to 19, a within-specification sheet was added in the range of 0.03% by mass or more and less than 3% by mass with respect to 100% by mass of the refractory raw material, and the crack index ratio was 80 or less, obtaining good results. Among them, in Examples 2 to 8 where the addition rate of the within-specification sheet was within the preferable range, that is, in the range of 0.1% by mass or more and 2.5% by mass or less, the crack index ratio was 40 or less, obtaining particularly good results. Example 17 was obtained by adding a within-specification sheet in the range of 0.03% by mass or more and less than 3% by mass with respect to 100% by mass of the refractory raw material. Even though Pmax was 8 mm, the crack index ratio was 80 or less, obtaining good results. Example 18 was obtained by adding a within-specification sheet in the range of 0.1% by mass or more and 2.5% by mass or less with respect to 100% by mass of the refractory raw material. Even though Pmax was 8 mm, the crack index ratio was 40 or less, obtaining particularly good results. Example 19 was obtained by adding a within-specification sheet in the range of 0.1% by mass or more and 2.5% by mass or less with respect to 100% by mass of the refractory raw material, and the representative length A was smaller than 1 / 3 of Pmax. Even though the representative length A was smaller than 1 / 3 of Pmax, the crack index ratio was 80 or less, obtaining good results.

[0028] In Table 2, Comparative Example 1 is a base material to which the above-described defect-forming member was not added. Comparative Example 2 is an example using an out-of-specification sheet where the shape parameter B / A and Comparative Example 3 is an example using an out-of-specification sheet where C / A is outside the standard of the present invention. In both cases, the crack index ratio was greater than 80 and did not reach the passing level. Comparative Example 4 is an example in which a PP rope was added as a defect-forming member. The shape is an elongated shape like a rope, and both the shape parameters B / A and C / A are outside the standard of the present invention, and the effect of reducing cracks was not obtained.

[0029] Table 3 shows the raw material formulation of the unshaped refractory, which is another example of the present invention, and the crack index by the thermal shock test of its construction body together with the comparative examples.

[0030]

Table 3

[0031] In Tables 1 and 2 above, the material of the monolithic refractory was alumina-silica, but the material of the monolithic refractory in each example shown in Table 3 is alumina-magnesia. The breakdown of 100% by mass of the refractory raw materials is as follows: 63% by mass of alumina aggregate, 22% by mass of alumina fine powder, 7% by mass of magnesia fine powder, 1% by mass of silica ultrafine powder, and 7% by mass of alumina cement. And the maximum particle size Pmax of the refractory raw materials is 8 mm. Also, although not shown in Table 3, in each example, as additives, a dispersant was added at an addition rate of 0.1% by mass and organic fibers were added at an addition rate of 0.2% by mass. The crack index was determined in the manner described above. Also, the crack index ratio was determined with the crack index of Comparative Example 6, which is the base material without the defect-forming member added in Table 3, taken as 100.

[0032] In Table 3, Examples 20 to 23 were all those in which a within-specification sheet was added at an addition rate of 0.1% by mass based on 100% by mass of the refractory raw materials, and the crack index ratio was 40 or less, obtaining good results. On the other hand, Comparative Example 5 is an example in which an out-of-specification sheet with C / A outside the specifications of the present invention among the shape parameters was used, and the crack index ratio was greater than 80 and did not reach the passing level.

[0033] Table 4 shows the raw material formulation of the monolithic refractory, which is still another example of the present invention, and the crack index of the constructed body by the thermal shock test together with the comparative examples.

[0034]

Table 4

[0035] The materials of the monolithic refractories in each example shown in Table 4 are alumina-silica, similar to those in Table 1 and Table 2 mentioned above. The breakdown of 100% by mass of the refractory raw materials is as follows: 70% by mass of chamotte aggregate, 10% by mass of alumina aggregate, 10% by mass of alumina fine powder, 5% by mass of silica ultra-fine powder, and 5% by mass of alumina cement. And the maximum particle size Pmax of the refractory raw materials is 5 mm. Although not shown in Table 4, in each example, as additives, a dispersant was added at an addition rate of 0.2% by mass and organic fiber was added at an addition rate of 0.1% by mass. The crack index was determined in the manner described above. Also, the crack index ratio was determined with the crack index of Comparative Example 7, which is the base material without the defect-forming member added in Table 4, taken as 100.

[0036] In Table 4, in Examples 24 to 26, a standard sheet was added at an addition rate of 0.1% by mass based on 100% by mass of the refractory raw materials, and the crack index ratio was 40 or less, obtaining good results. In Table 4, a sheet with a thickness C of 0.01 to 0.03 mm, which is thinner than that in Table 1, was used, and it was confirmed that such a thin sheet can also achieve the effect of crack dispersion.

[0037] As described above, in the monolithic refractories shown in Tables 1 to 4, the samples subjected to the thermal shock test were fired under the conditions of 1000 °C × 3 h. Therefore, the thermally volatile sheets contained in the unshaped refractory before firing were almost completely burned out, and as a result, the spaces formed by the burning out of the sheets were randomly included in the refractory structure.

[0038] <Example B: Examples of Monolithic Refractories (Part 2)> Regarding the monolithic refractory, an evaluation test was carried out using a model tundish close to the actual furnace. The iron skin of the model tundish is a rectangle with an outer dimension of about 1000 mm × 800 mm and a height of about 600 mm, and Y-shaped studs similar to those of the actual furnace are attached to the upper part in the longitudinal direction. For construction, the monolithic refractory was poured into the inside of the iron skin using a core. In the test, the monolithic refractory of Example 20 shown in Table 3 and the monolithic refractory of Comparative Example 6 having a configuration excluding the defect forming member were spread out left and right. Curing was confirmed on the day after the construction of the monolithic refractory, and after several days of curing, it was dried under the condition of a maximum temperature of 300 °C. After drying was completed and it was cooled to room temperature, cracks were confirmed and the crack width was measured. As a result, the maximum value of the crack width of the monolithic refractory of Example 20 was 63% of that of the monolithic refractory of Comparative Example 6, and it was confirmed that a crack reduction effect can be obtained even under temperature conditions with a relatively low degree of drying. Although many measurement cases are known for the thermogravimetric measurement results of polyethylene used as the defect forming member in Example 20, it does not show a significant weight loss at 300 °C and is considered not to reach sufficient burnout. However, the sufficient crack reduction effect was obtained because the elastic modulus of polyethylene randomly contained in the refractory structure is lower than that of the refractory, and although the degree is different, it causes stress concentration even at room temperature in the same way as voids, and also because the softening and shrinkage of polyethylene due to temperature rise make it easier to cause stress concentration, which is considered to lead to crack reduction.

[0039] On the other hand, a high-temperature heating test was also carried out. In the high-temperature heating test, an oxygen-propane burner and a lid were set on the upper part of the model tundish, and the inside of the model tundish was heated by the burner. The furnace temperature was kept at a maximum of 1550 °C for 5 h. After the burner was stopped, it was cooled to room temperature and cracks were confirmed. As a result of measuring the crack width at the main locations generated on the inner surface of the refractory using a crack scale, the maximum value of the crack width of the monolithic refractory of Example 20 was 38% of that of Comparative Example 6, and it was confirmed that a crack reduction effect can be obtained even under conditions approaching the actual furnace to a certain extent with respect to temperature, mechanical restraint by the iron skin, and size.

[0040] <Example C: Example of shaped refractory> Table 5 shows the raw material compositions of shaped refractories, which are other examples of the present invention, and the crack index ratios of the shaped refractories (bricks) obtained from the raw material compositions, together with comparative examples, in the thermal shock test.

[0041]

Table 5

[0042] In Table 5, the materials of Examples 27 to 31 and Comparative Example 8 are magnesia-based, the materials of Example 32 and Comparative Example 9 are magnesia-carbon-based, and the maximum particle size Pmax of the refractory raw materials is 5 mm in all cases. An appropriate amount of phenolic resin was added as an organic binder to the raw material compositions of each example and kneaded. After molding into a shape of 230×114×65 mm by an oil press, a heat treatment was performed by holding at a maximum temperature of 250°C for 5 hours to obtain samples for the thermal shock test. The crack index ratio in the thermal shock test was determined in the above-mentioned manner. Specifically, for the magnesia-based materials of Examples 27 to 31, the crack index of Comparative Example 8, which is a magnesia-based base material without adding a defect-forming member, was taken as 100 for calculation. For the magnesia-carbon-based material of Example 32, the crack index of Comparative Example 9, which is a magnesia-carbon-based base material without adding a defect-forming member, was taken as 100 for calculation. In both the magnesia-based materials of Examples 27 to 31 and the magnesia-carbon-based material of Example 32, the crack index ratio was 80 or less, and good results were obtained.

[0043] Table 6 shows the raw material compositions of shaped refractories, which are still other examples of the present invention, and the elastic modulus reduction index of the shaped refractories (bricks) obtained from the raw material compositions, together with comparative examples, in the thermal shock test.

[0044]

Table 6

[0045] The materials of the shaped refractories in each example shown in Table 6 are magnesia-carbon-based, with the graphite content varied, and the maximum particle size Pmax of the refractory raw materials is 5 mm. The magnesia-carbon shaped refractory shown in Table 6 has a higher graphite content and better thermal shock resistance compared to the magnesia-carbon shaped refractory shown in Table 5. Therefore, for the magnesia-carbon shaped refractory shown in Table 6, a thermal shock test was conducted and an elastic modulus reduction index was obtained as follows. That is, using a 40×40×190 mm sample, after immersing it in hot metal at 1600°C for 90 seconds, the thermal shock of 30-second water cooling was repeated 3 times, and the elastic modulus reduction rate was obtained from the elastic modulus measured before and after the test. Then, for each example, the ratio to the elastic modulus reduction rate of the comparative example used as a base was taken as the elastic modulus reduction index. The smaller this index, the less likely it is to cause a reduction in the elastic modulus rate with respect to the base material, that is, the higher the improvement effect of thermal shock resistance. The correspondence between each example and its base comparative example is as follows. That is, according to the graphite content, the base material of Example 33 is Comparative Example 10, the base material of Example 34 is Comparative Example 11, and the base material of Example 35 is Comparative Example 12. From Table 6, it can be seen that in Examples 33 to 35, the thermal shock resistance is improved for each base material (Comparative Examples 10 to 12). That is, it was confirmed that even in a magnesia-carbon shaped refractory (brick) with a high graphite content, an improvement effect of thermal shock resistance, that is, a crack reduction effect, can be obtained. In addition, for the shaped refractories shown in Tables 5 and 6, the samples used for the thermal shock test were heat-treated at a maximum temperature of 250°C for 5 hours. The material of the sheet is any one of polyethylene, polypropylene, and high-density polyethylene as described in the table, and it has been found from these thermogravimetric measurement results that there is no significant weight loss at 250°C. Therefore, in the sample before heating, the sheet is randomly contained in the refractory structure with almost no burning loss.

[0046] Table 7 shows the raw material composition of the shaped refractory, which is still another example of the present invention, and the crack index ratio of the shaped refractory (brick) obtained from the raw material composition by a thermal shock test together with a comparative example.

[0047]

Table 7

[0048] The materials of the shaped refractories in each example shown in Table 7 are alumina-based or alumina-silica-based, and the maximum particle size Pmax of the refractory raw materials is 3 mm. After being formed into a shape of 230×114×65 mm by an oil press, heat treatment was carried out by holding at a maximum temperature of 250°C for 5 hours, and then firing at 1600°C×5 h was carried out to obtain samples for the thermal shock test. The crack index ratio by the thermal shock test was determined in the above-mentioned manner. Specifically, for Example 36, the crack index of Comparative Example 13, which is the base material without the defect-forming member, was taken as 100 for determination; for Example 37, the crack index of Comparative Example 14, which is the base material without the defect-forming member, was taken as 100 for determination; and for Example 38, the crack index of Comparative Example 15, which is the base material without the defect-forming member, was taken as 100 for determination. In any of Examples 36 to 38, the crack index ratio was 60 or less, and good results were obtained. That is, it was confirmed that the crack reduction effect can be obtained even in shaped refractories with different materials. In addition, in the shaped refractories shown in Table 7, the samples subjected to the thermal shock test were those fired at 1600°C×5 h. Therefore, the thermally volatilizable sheet contained in the green body before firing was almost completely volatilized, and as a result, the spaces formed by the volatilization of the sheet were randomly included in the refractory structure.

Claims

Claim 1 A refractory in which at least one of a heat-loss sheet and a space formed by burning out the sheet is randomly included in a refractory structure mainly composed of a refractory raw material, wherein the sheet satisfies C ≤ 1 mm, C / A ≤ 0.1, and 0.2 ≤ B / A ≤ 1.0 when the representative length is A, the maximum length in the plane of the sheet in a direction orthogonal to the defined direction of the representative length A is B, and the thickness is C. Claim 2 The refractory according to claim 1, wherein the representative length A is greater than 1 / 3 of the maximum particle size of the refractory raw material. Claim 3 A method for manufacturing a refractory, comprising a step of adding and mixing a heat-loss sheet to a refractory raw material mixture mainly composed of a refractory raw material, wherein the sheet satisfies C ≤ 1 mm, C / A ≤ 0.1, and 0.2 ≤ B / A ≤ 1.0 when the representative length is A, the maximum length in the plane of the sheet in a direction orthogonal to the defined direction of the representative length A is B, and the thickness is C. Claim 4 The method for manufacturing a refractory according to claim 3, wherein the representative length A is greater than 1 / 3 of the maximum particle size of the refractory raw material.

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