Refractory and method for producing same

Abstract

The present invention provides: a refractory which is capable of suppressing the occurrence of a large crack during use; and a method for producing the same. A refractory according to the present invention randomly contains, in a refractory tissue that is mainly composed of a refractory starting material, at least one of a burnable and eliminable sheet and a space that is formed by burning and eliminating the sheet. The refractory is obtained by a method for producing a refractory, the method including a step for adding and mixing a burnable and eliminable sheet to a refractory starting material formulation that is mainly composed of a refractory starting material. With respect to the burnable and eliminable sheet, if A is the representative length, B is the maximum length in the plane of the sheet in a direction that is orthogonal to the definition direction of the representative length A, and C is the thickness, C ≤ 1 mm, C / A ≤ 0.1, and 0.2 ≤ B / A ≤ 1.0 are satisfied.

Description

Refractory and its manufacturing method

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

[0002] With the current material technology, it is virtually impossible to prevent cracks from occurring in such refractories, except for some products such as continuous casting nozzles. Therefore, cracks inevitably occur during use. If the cracks grow, the refractory cannot be used continuously and its lifespan is reached. Therefore, preventing crack growth is useful for improving the durability of refractories.

[0003] One known method for suppressing crack propagation is to incorporate a defect-inducing material into the refractory structure. This defect-inducing material functions as a stress concentration site in the refractory structure, and is thought to improve crack dispersion by facilitating the initiation of subsequent cracks after the initial crack. Therefore, by incorporating an appropriate amount of defect-inducing material into the refractory structure, crack dispersion is improved, and as a result, it is thought that the occurrence of large cracks (hereinafter referred to as "large cracks") that adversely affect the durability of the refractory can be suppressed.

[0004] As such defect-forming members, i.e., members that function as stress concentration portions in the refractory structure, Patent Document 1 discloses mixing in wood chips, and Patent Document 2 discloses mixing in wood powder with a particle size of 0.2 mm to 4 mm. However, these conventional methods of mixing in wood chips or wood powder were not sufficient to suppress the occurrence of large cracks.

[0005] Japanese Patent Application Laid-Open No. 2006-225195 Japanese Patent Publication No. 62-21752

[0006] The problem to be solved by 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.

[0007] In order to solve the above problems, the inventors conducted extensive testing and research into the material and shape of the defect-forming member 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 it in the form of a thin sheet.

[0008] That is, one aspect of the present invention provides the following refractory: A refractory in which at least one of a thermally burnable sheet and spaces formed by the burnout of said sheet is randomly included in a refractory structure mainly made of refractory raw materials, 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 said sheet in a direction perpendicular to the direction defining said characteristic length A, and C is a thickness.

[0009] According to another aspect of the present invention, there is provided the following method for producing a refractory material, comprising the step of adding a thermally burnable sheet to a refractory raw material composition mainly composed of refractory raw materials and mixing the sheet, wherein, when a characteristic length of the sheet is A, a maximum length within the plane of the sheet in a direction perpendicular to the direction defining the characteristic length A is B, and a thickness of the sheet is C, the relationships C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0 are satisfied.

[0010] According to the present invention, it is possible to provide a refractory that can suppress the occurrence of large cracks during use, and a method for producing the same.

[0011] An explanatory diagram showing the representative length A and maximum length B of the sheet used in the present invention.

[0012] The refractory of the present invention is a refractory in which at least one of a thermally burnable sheet and spaces formed by the burnt-out sheet is randomly included in a refractory structure mainly composed of refractory raw materials. The method for producing a refractory of the present invention is a refractory production method comprising the step of adding a thermally burnable sheet to a refractory raw material composition mainly composed of refractory raw materials and mixing the mixture. Here, the term "refractory" collectively refers to monolithic refractories and monolithic refractories, and precast blocks are considered to be included in monolithic 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 the representative length of the sheet, B is the maximum in-plane length of the sheet in a direction perpendicular to the direction defining the representative length A, and C is the thickness. Here, the representative length of the sheet refers to the length of the longest side (hereinafter referred to as the "longest side") when the planar shape of the sheet is triangular as shown in FIG. 1A. When the planar shape of the sheet is a polygon with more than one side, an ellipse, a circle, or an irregular shape as shown in FIGS. 1B to 1E, the representative length refers to the length of the longest line segment in the plane of the sheet. Also, as shown in FIGS. 1A to 1E, the maximum in-plane length of the sheet in a direction perpendicular to the direction defining the representative length A is B. While the thickness C of a sheet is often constant, if the thickness of the sheet varies, the average value of thicknesses at multiple locations is taken as the sheet thickness C. Furthermore, the sheet is not limited to a single layer, and may be a multi-layer sheet 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 above-mentioned conditions of C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0. These conditions were derived from the results of tests and research by the inventors, and the gist of them is to limit the thickness to only thin shapes due to the conditions of C≦1 mm and C / A≦0.1, and to exclude elongated shapes due to the condition of 0.2≦B / A≦1.0. In other words, the gist is to exclude chunky and string-like shapes and limit the shape to a thin sheet.

[0015] In the present invention, the characteristic length A of the sheet is preferably greater than one-third of the maximum particle size of the refractory raw material. The reason for this is as follows: A boundary layer forms at the boundary between the aggregate and the matrix in the refractory structure. This boundary layer acts as a latent defect and is believed to have a certain effect in suppressing large cracks. Because the size of the boundary layer is determined by the particle size of the refractory raw material, the size of the latent defect depends on the maximum particle size of the refractory raw material. Naturally, the size of a boundary layer defect, when simplified to an ideal defect shape such as a penny-shaped crack, cannot be directly calculated. Considering the area of ​​the boundary layer projected onto a certain plane, the size is considered to be at most approximately the diameter of the particle. However, in reality, only a portion of the boundary layer around the particle periphery is perpendicular to the stress loading direction, so the size is considered to be significantly smaller than the diameter. The coefficient of one-third of the maximum particle size of the refractory raw material, defined as the coefficient of the maximum particle size of the refractory raw material, was obtained by experimentally investigating the relationship between the maximum length of the defect-forming component and the particle size of the refractory raw material and identifying the conditions for reducing cracks. 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 exceeding 8 mm. This is because it is difficult to ensure uniformity of the large coarse particles within the refractory structure, making it 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 needed to 100% by mass of the refractory raw material, similar to the case of the sheet.

[0016] On the other hand, the material of the sheet is not particularly limited as long as it is a thermally burnable material. In this invention, thermally burnable refers to the property of forming voids by carbonization, decomposition, vaporization, shrinkage, etc., as the temperature rises during production or use. Thermally burnable materials are selected from plastics, wood chips, paper, cloth, leather, etc. Among these, plastics are optimal from the viewpoints of mechanical properties such as high strength and low elastic modulus, a relatively low softening temperature, and the availability of thin sheet-shaped raw materials. Examples of plastics, i.e., synthetic resins, include thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, acrylonitrile-styrene, polymethyl methacrylic, polyvinyl alcohol, polyvinylidene chloride, polyethylene terephthalate, and polyester, and thermosetting resins such as phenol, melamine, polyurethane, and epoxy. Laminated sheets combining several of these may also be used. Note that, in this invention, metals are not considered to be thermally burnable materials.

[0017] In the present invention, the addition rate of the sheet does not need to be particularly limited and may be appropriately determined based on technical common sense, etc. For example, in the case of monolithic refractories, the sheet may be added at an addition rate of 0.03 mass% or more but less than 3 mass%, preferably 0.1 mass% or more but 2.5 mass% or less, relative to 100 mass% of the refractory raw materials. Furthermore, in the case of monolithic refractories, the sheet may be added at an addition rate of 0.03 mass% or more but less than 0.6 mass%, preferably 0.1 mass% or more but 0.3 mass% or less, relative to 100 mass% of the refractory raw materials. Since the production process of monolithic refractories includes a step of adding and mixing the sheet to the refractory raw material blend and then a step of molding, the upper limit of the addition rate of the sheet is preferably lower than that of monolithic refractories in terms of suppressing springback during molding. However, this point may also be appropriately determined based on technical common sense, etc.

[0018] The above-mentioned sheet addition rate refers to the addition rate of a sheet whose material is heat-burnable and whose shape satisfies C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0 (hereinafter referred to as "standard sheet"). In other words, the refractory material of the present invention may contain a heat-burnable sheet whose shape does not satisfy C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.0 (hereinafter referred to as "non-standard sheet"). Non-standard sheets are unavoidably generated during the production of standard sheets. In this case, they are added to the refractory raw material together with the standard sheets. Furthermore, when waste plastic sheets are used as the raw material for standard sheets, metal pieces or other impurities may be mixed in. In this case, the metal pieces or other impurities are added to the refractory raw material together with the standard sheets. In either case, the above-mentioned sheet addition rate refers to the addition rate of standard sheets.

[0019] Because the present invention achieves the desired effect by changing the shape of the refractory structure, the refractory material is not particularly limited, and any material commonly used for refractories may be used, such as alumina, alumina-silica, alumina-magnesia, alumina-silicon carbide-carbon, alumina-spinel, alumina-spinel-carbon, magnesia, or magnesia-carbon. The refractory raw material is also not particularly limited, and commonly used refractory raw materials, such as alumina raw materials, silica raw materials, alumina-silica raw materials, magnesia raw materials, spinel raw materials, mullite raw materials, silicon carbide raw materials, and carbon raw materials, can be used depending on the refractory material. In the present invention, binders for monolithic refractories, such as alumina cement, magnesia cement, Portland cement, silicates, and phosphates, are considered to be included in the refractory raw material. Meanwhile, in the present invention, organic binders for monolithic refractories, such as phenolic resins, are not considered to be included in the refractory raw material, and are added at a predetermined addition rate relative to 100% by mass of the refractory raw material, as with the sheet described above. In the present invention, additives such as dispersants and organic fibers are not included in the refractory raw material, and are added at a predetermined addition rate relative to 100% by mass of the refractory raw material, similar to the above-mentioned sheet. The addition rates of the organic binder and additives are determined within the scope of common technical knowledge.

[0020] The method for producing a refractory of the present invention includes a step of adding a heat-burnable sheet (standard sheet) to a refractory raw material composition mainly composed of refractory raw materials and mixing them. In the case of a shaped refractory, the mixing step is followed by a molding step as described above. In the case of an unshaped refractory, the construction can typically be performed by pouring. In this case, construction is carried out through a step of kneading the unshaped refractory of the present invention with water, a pouring step, a curing step, and a drying step. The construction conditions for each of these steps are determined within the scope of common technical knowledge. Note that the construction of the unshaped refractory of the present invention is not limited to pouring, and can also be performed by spraying or patching.

[0021] Example A: Example of Monolithic Refractory (Part 1) Table 1 shows the raw material composition of a monolithic refractory that is an example of the present invention, and the crack index of the applied body in a thermal shock test. Table 2 shows the raw material composition of a monolithic refractory that is a comparative example of the present invention, and the crack index of the applied body in a thermal shock test. In Tables 1 and 2, defect-forming components, excluding ropes, are expressed in the format of material - thickness - representative length A x maximum length B (mm) (planar shape of sheet). In the shape parameter columns of 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 below.

[0022]

[0023]

[0024] The monolithic refractories of each example shown in Tables 1 and 2 were all alumina-silica based, with 100% by mass of refractory raw material consisting of 78% by mass of chamotte aggregate, 10% by mass of alumina fine powder, 7% by mass of ultrafine siliceous powder, and 5% by mass of alumina cement. The maximum particle size Pmax of the refractory raw materials in Examples 1 to 16 and Comparative Examples 1 to 4 was 5 mm, while the maximum particle size Pmax of the refractory raw materials in Examples 17 to 19 was 8 mm. Although not shown in Tables 1 and 2, each example contained additives, such as a dispersant at 0.2% by mass and organic fiber at 0.05 to 0.1% by mass. No large coarse particles were added.

[0025] For each of these monolithic refractories, the crack index of the applied body was determined by a thermal shock test as follows. The size of the applied body (hereinafter referred to as "sample") subjected to the thermal shock test was 230 x 114 x 65 mm. Each sample was prepared by adding water to the monolithic refractory of each example and mixing it in a mixer. The mixture was then poured into a mold corresponding to the sample size and cured at room temperature. After hardening, the mold was removed, dried at 110°C for 24 hours, and then fired at 1000°C for 3 hours. A random pattern was applied to the 230 x 114 mm surface of the fired sample using heat-resistant paint, and an initial image was taken for image processing. The thermal shock test was performed by placing the sample in the opening of an electric furnace preheated to a predetermined temperature (1500°C in this test) so that one 114 x 65 mm surface of the sample was heated. After holding for 10 minutes, the sample was removed from the electric furnace and allowed to cool naturally. After sufficient cooling, post-test images of the sample were taken. By processing the initial and post-test images using digital image correlation, the displacements at numerous points on the sample surface could be measured. These measurements were used to calculate the crack index. Specifically, when measuring the strain on the sample surface after a thermal shock test using digital image correlation, an increase in crack width is detected as an increase in apparent strain. This method allows for multi-point measurements, for example, on the order of 10,000 points. Adding the apparent strains at each evaluation point on the sample surface and dividing by the number of evaluation points yields the average strain per evaluation point. This value increases for larger crack widths and longer cracks. Since this value can comprehensively express the extent of the crack in terms of both width and length, it was used as the crack index for evaluation. The strain was calculated by dividing the difference in the displacement between the observation point and its neighboring point on the sample surface by the initial length. A cutoff value was also set, as necessary, depending on the noise level of the test.

[0026] The smaller the crack index determined in the above manner, the more the occurrence of large cracks during use can be suppressed. Tables 1 and 2 show the crack index of each example of monolithic refractory, as well as the ratio of the crack index (hereinafter referred to as "crack index ratio"), with the crack index of Comparative Example 1, which is a base material without any defect-forming material added, being 100. In this test, a crack index ratio of 80 or less was considered to be the pass level. This crack index ratio is preferably 60 or less, and more preferably 40 or less.

[0027] In Table 1, Examples 1 to 19 all contain standard sheet added in a range of 0.03% by mass or more but less than 3% by mass relative to 100% by mass of refractory raw material, and good results were obtained with a crack index ratio of 80 or less. Among these, Examples 2 to 8, in which the standard sheet addition rate was within the preferred range, i.e., 0.1% by mass or more but less than 2.5% by mass, contained a crack index ratio of 40 or less, which was particularly good results. Example 17 contains standard sheet added in a range of 0.03% by mass or more but less than 3% by mass relative to 100% by mass of refractory raw material, and even when Pmax was 8 mm, it contained a good result with a crack index ratio of 80 or less. Example 18 contains standard sheet added in a range of 0.1% by mass or more but less than 2.5% by mass relative to 100% by mass of refractory raw material, and even when Pmax was 8 mm, it contained a particularly good result with a crack index ratio of 40 or less. In Example 19, the standard sheet was added in a range of 0.1 mass % to 2.5 mass % relative to 100 mass % of the refractory raw material, and the characteristic length A was smaller than 1 / 3 of Pmax. Even though the characteristic length A was smaller than 1 / 3 of Pmax, the crack index ratio was 80 or less, and good results were obtained.

[0028] In Table 2, Comparative Example 1 is a base material to which the above-mentioned defect-forming member was not added. Comparative Example 2 is an example in which a non-standard sheet was used, with the shape parameter B / A outside the specifications of the present invention, and Comparative Example 3 is an example in which a non-standard sheet was used, with the shape parameter C / A outside the specifications of the present invention. In both cases, the crack index ratio was greater than 80 and did not reach the pass level. Comparative Example 4 is an example in which a PP rope was added as a defect-forming member. The shape was a long, thin rope, and both the shape parameters B / A and C / A outside the specifications of the present invention, so no crack reduction effect was obtained.

[0029] Table 3 shows the raw material composition of the monolithic refractory material according to another embodiment of the present invention, and the crack index of the applied body in a thermal shock test, together with a comparative example.

[0030]

[0031] In Tables 1 and 2 above, the monolithic refractories were made of alumina-silica. However, the monolithic refractories in each example shown in Table 3 were made of alumina-magnesia. The breakdown of 100% by mass of refractory raw material was 63% by mass of alumina aggregate, 22% by mass of alumina fine powder, 7% by mass of magnesia fine powder, 1% by mass of ultrafine silica powder, and 7% by mass of alumina cement. The maximum particle size Pmax of the refractory raw material was 8 mm. Although not shown in Table 3, additives were added in the amounts of 0.1% by mass of dispersant and 0.2% by mass of organic fiber in each example. The crack index was calculated as described above. The crack index ratio was calculated by setting the crack index of Comparative Example 6, which is the base material in Table 3 to which no defect-forming material was added, at 100.

[0032] In Table 3, Examples 20 to 23 all used standard sheets at an addition rate of 0.1 mass% relative to 100 mass% of the refractory raw material, and good results were obtained with crack index ratios of 40 or less. On the other hand, Comparative Example 5 is an example in which a non-standard sheet with a shape parameter C / A outside the specifications of the present invention was used, and the crack index ratio was greater than 80, which did not reach the pass level.

[0033] Table 4 shows the raw material composition of the monolithic refractory material which is yet another example of the present invention, and the crack index of the applied body in a thermal shock test, together with a comparative example.

[0034]

[0035] The material of the monolithic refractory of each example shown in Table 4 is alumina-silica, as in Tables 1 and 2 above. The breakdown of 100% by mass of refractory raw material is 70% by mass of chamotte aggregate, 10% by mass of alumina aggregate, 10% by mass of alumina fine powder, 5% by mass of ultrafine siliceous powder, and 5% by mass of alumina cement. The maximum particle size Pmax of the refractory raw material is 5 mm. Although not shown in Table 4, each example contained additives such as 0.2% by mass of dispersant and 0.1% by mass of organic fiber. The crack index was calculated as described above. The crack index ratio was calculated by setting the crack index of Comparative Example 7, which is the base material in Table 4 without the defect-forming material, to 100.

[0036] In Table 4, Examples 24 to 26 all contain standard sheets added at a rate of 0.1 mass% relative to 100 mass% of the refractory raw material, and the crack index ratio was 40 or less, resulting in favorable results. In Table 4, sheets with a thickness C of 0.01 to 0.03 mm, which is thinner than those in Table 1, were used, and it was confirmed that the effect of crack dispersion could be obtained even with such thin sheets.

[0037] As described above, the samples of the monolithic refractories shown in Tables 1 to 4 that were subjected to the thermal shock test were fired under the conditions of 1000°C x 3 hours. Therefore, the thermally burnable sheet contained in the monolithic refractory before firing was almost completely burned away, and as a result, the spaces formed by the burned-away sheet were randomly contained in the refractory structure.

[0038] Example B: Example of Monolithic Refractory (Part 2) An evaluation test of the monolithic refractory was conducted using a model tundish similar to that of an actual furnace. The steel shell of the model tundish was rectangular with external dimensions of approximately 1000 mm x 800 mm and a height of approximately 600 mm. Y-shaped studs similar to those in an actual furnace were attached to the upper longitudinal direction. The monolithic refractory was poured into the inside of the steel shell using a core. In the test, the monolithic refractory of Example 20 shown in Table 3 and the monolithic refractory of Comparative Example 6, which was configured without the defect-forming component, were installed on the left and right sides. The hardening of the monolithic refractory was confirmed the day after installation, and after several days of curing, it was dried at a maximum temperature of 300°C. After drying, it was cooled to room temperature and cracks were confirmed, and the crack width was measured. As a result, the maximum crack width of the monolithic refractory of Example 20 was 63% of that of the monolithic refractory of Comparative Example 6, confirming that the crack reduction effect can be achieved even under relatively low temperature conditions such as drying. Many measurement examples are known for the results of thermogravimetry of the polyethylene used as the defect-forming member in Example 20, but it did not show any significant weight loss at 300°C, and it is thought that it did not result in sufficient burnout. However, the reason why a sufficient crack reduction effect was obtained is thought to be that the elastic modulus of the polyethylene randomly contained in the refractory structure is lower than that of the refractory itself, so that stress concentration occurs at room temperature, just like in voids, although to a different degree, and that the polyethylene softens and shrinks with increasing temperature, making stress concentration even more likely to occur, which leads to crack reduction.

[0039] Meanwhile, a high-temperature heating test was also conducted. In the high-temperature heating test, an oxygen-propane burner and a lid were set on top of the model tundish, and the inside of the model tundish was heated by the burner. The furnace temperature was maintained at a maximum of 1,550°C for 5 hours. After the burner was stopped, the refractory was cooled to room temperature and checked for cracks. The width of cracks occurring at major locations on the inner surface of the refractory was measured using a crack scale. As a result, the maximum crack width of the monolithic refractory of Example 20 was 38% of that of Comparative Example 6, confirming that the crack reduction effect could be obtained even under conditions that were somewhat similar to those of an actual furnace in terms of temperature, mechanical restraint by the steel shell, and size.

[0040] <Example C: Example of a standard refractory> Table 5 shows the raw material composition of a standard refractory, which is another example of the present invention, and the crack index ratio of the standard refractory (brick) obtained from that raw material composition in a thermal shock test, along with a comparative example.

[0041]

[0042] In Table 5, the materials of Examples 27-31 and Comparative Example 8 were magnesia-based, while the materials of Example 32 and Comparative Example 9 were magnesia-carbon-based. The maximum particle size Pmax of the refractory raw material was 5 mm. An appropriate amount of phenolic resin was added as an organic binder to the raw material blend of each example, and the mixture was kneaded. The mixture was then formed into a shape of 230 x 114 x 65 mm using an oil press, and then heat-treated at a maximum temperature of 250°C for 5 hours to obtain a sample for thermal shock testing. The crack index ratios obtained from the thermal shock test were determined as described above. Specifically, the crack index of the magnesia-based material of Examples 27-31 was calculated relative to the crack index of Comparative Example 8, which is a magnesia-based material without the addition of a defect-forming material, set to 100. The crack index of the magnesia-carbon-based material of Example 32 was calculated relative to the crack index of Comparative Example 9, which is a magnesia-carbon-based material without the addition of a defect-forming material, set to 100. In both the magnesia materials of Examples 27 to 31 and the magnesia-carbon material of Example 32, the crack index ratio was 80 or less, and good results were obtained.

[0043] Table 6 shows the raw material blend of a shaped refractory which is yet another embodiment of the present invention, and the elastic modulus reduction index of the shaped refractory (brick) obtained from that raw material blend in a thermal shock test, together with comparative examples.

[0044]

[0045] The shaped refractories of each example shown in Table 6 were made of magnesia-carbon material, with varying graphite contents, and the maximum particle size Pmax of the refractory raw material was 5 mm. The magnesia-carbon shaped refractories shown in Table 6 had higher graphite contents and superior thermal shock resistance compared to the magnesia-carbon shaped refractories shown in Table 5. Therefore, a thermal shock test was conducted on the magnesia-carbon shaped refractories shown in Table 6 as follows, and the elastic modulus reduction index was determined. Specifically, using a 40 × 40 × 190 mm sample, the thermal shock test consisted of immersing the sample in 1600°C molten iron for 90 seconds and then water-cooling for 30 seconds, and the elastic modulus reduction index was calculated from the elastic modulus measured before and after the test. The elastic modulus reduction index for each example was calculated by comparing it with the elastic modulus reduction index of the comparative example. The smaller this index, the less likely the elastic modulus reduction occurs compared to the base material, i.e., the greater the improvement in thermal shock resistance. The correspondence between each Example and its corresponding Comparative Example is as follows. Specifically, the base material of Example 33 was Comparative Example 10, the base material of Example 34 was Comparative Example 11, and the base material of Example 35 was Comparative Example 12, depending on the graphite content. Table 6 reveals that Examples 33-35 exhibit improved thermal shock resistance compared to their respective base materials (Comparative Examples 10-12). This confirms that improved thermal shock resistance, i.e., crack reduction, can be achieved even with magnesia-carbon shaped refractories (bricks) with high graphite content. The samples of the shaped refractories shown in Tables 5 and 6 subjected to thermal shock testing were heat-treated at a maximum temperature of 250°C for 5 hours. The sheet material was polyethylene, polypropylene, or high-density polyethylene, as shown in the table. Thermogravimetric analysis of these materials revealed no significant weight loss at 250°C. Therefore, in the samples before heating, the sheet was barely burned and randomly incorporated into the refractory structure.

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

[0047]

[0048] The shaped refractories in each example shown in Table 7 were made of alumina or alumina-silica, and the maximum particle size Pmax of the refractory raw material was 3 mm. After molding into a shape of 230 × 114 × 65 mm using an oil press, they were subjected to a heat treatment at a maximum temperature of 250 °C for 5 hours, followed by firing at 1600 °C for 5 hours to obtain samples for thermal shock testing. The crack index ratios from the thermal shock tests were determined as described above. Specifically, for Example 36, the crack index was calculated based on the crack index of Comparative Example 13, which is a base material containing no defect-forming material; for Example 37, the crack index was calculated based on the crack index of Comparative Example 14, which is a base material containing no defect-forming material; and for Example 38, the crack index was calculated based on the crack index of Comparative Example 15, which is a base material containing no defect-forming material. In all of Examples 36 to 38, the crack index ratio was 60 or less, indicating favorable results. This confirms that crack reduction effects can be achieved even with shaped refractories made of different materials. In addition, among the shaped refractories shown in Table 7, the samples subjected to the thermal shock test were those that had been fired at 1600°C for 5 hours. Therefore, the thermally burnable sheet contained in the molded body before firing was almost completely burned away, and as a result, the spaces formed by the burned-away sheet were randomly contained in the refractory structure.

Claims

1. A refractory in which at least one of a thermally burnable sheet and spaces formed by the burning of said sheet is randomly included in a refractory structure mainly made of refractory raw materials, wherein the sheet has a characteristic length A, a maximum length within the plane of the sheet in a direction perpendicular to the direction defined by the characteristic length A B, and a thickness C, satisfying C≦1 mm, C / A≦0.1, and 0.2≦B / A≦1.

0.

2. The refractory material according to claim 1, wherein the characteristic length A is greater than 1 / 3 of the maximum particle size of the refractory raw material.

3. A method for producing a refractory material, comprising the step of adding and mixing a heat-burnable sheet with a refractory raw material composition mainly composed of refractory raw materials, wherein the sheet satisfies C≦1 mm, C / A≦0.1 and 0.2≦B / A≦1.0, where A is a representative length, B is a maximum length within the plane of the sheet in a direction perpendicular to the direction defined by the representative length A, and C is a thickness.

4. The method for producing a refractory material according to claim 3, wherein the characteristic length A is greater than 1 / 3 of the maximum particle size of the refractory raw material.

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