Method for manufacturing non-fired brick

Abstract

The present invention provides a method for manufacturing a non-fired brick whereby reductions in corrosion resistance and creep resistance due to the generation of low melting point substances can be suppressed, and sufficient strength can be exhibited. In the present invention, water is added to and mixed with a refractory raw material formulation containing 0.2-15 mass% of magnesia having a particle diameter of less than 75 μm and 0.3-10 mass% of silica having a particle diameter of less than 44 μm, with the remainder being mainly one or more of an alumina raw material, an alumina silica raw material, a silica raw material, and a spinel raw material, and the total content ratio of alkali metal phosphates and alkali metal silicates being less than 1 mass% (including 0), the total content ratio of the Na2O component and K2O component being 0.5 mass% or less (including 0), and the content ratio of the P2O5 component being 0.7 mass% or less (including 0). Thereafter, the mixture is press molded and then left standing at room temperature or heat treated at a temperature of 1000°C or less.

Description

Method for Producing Unfired Brick

[0001] The present invention relates to a method for producing unfired brick used in coke ovens, blast furnaces, hot blast stoves, CDQ, molten steel ladles, hot metal ladles, secondary refining furnaces and the like.

[0002] In coke ovens, blast furnaces, hot blast stoves, CDQ, molten steel ladles, hot metal ladles, secondary refining furnaces and the like, Al as a chemical component ２ O ３ component and / or SiO ２ component as main components (hereinafter referred to as "Al ２ O ３ / SiO ２ based fired brick") are used. Examples thereof include alumina brick, alumina-silica brick, clay brick, silica brick, alumina-magnesia brick, alumina-spinel brick, spinel brick and the like. Generally, these bricks are produced by kneading a refractory raw material composition containing one or more of alumina raw materials, alumina-silica raw materials, silica raw materials and spinel raw materials, then pressure-molding the mixture with a molding machine, and firing the molded product at a high temperature (for example, Patent Documents 1 to 3). However, Al ２ O ３ / SiO ２ based fired brick is fired at a high temperature for a long time in the production method, so there are problems of CO ２ gas emission and high energy cost.

[0003] For this reason, unfiring production of Al ２ O ３ / SiO ２ based fired brick has been studied for a long time. For example, in Patent Document 4, a siliceous precast block is produced by casting a monolithic refractory mainly composed of fused silica, removing the frame, and then drying. However, in such a method for producing a precast block by casting, it takes 12 to 24 hours from pouring the material into the molding frame to removing the frame, so there is a problem of poor molding efficiency.

[0004] On the other hand, among alumina-based and alumina-silica bricks, unfired bricks using alkali metal silicates or alkali metal phosphates as binders are known. For example, Patent Document 5 discloses a method for producing an unfired brick that uses an alumina raw material and a magnesia raw material containing 90 mass% or more of fine powder of 0.5 mm or less, and uses sodium silicate and potassium silicate as binders. However, when sodium silicate or potassium silicate is used as a binder as in Patent Document 5, the alkali metal oxide (Na ２ O component and K ２ O) in the binder easily reacts with other refractory raw materials to form low-melting-point substances, which causes problems of reduced corrosion resistance and creep resistance. Furthermore, when an alkali metal phosphate is used as a binder, the use of phosphate is not preferred because there is concern about the elution of phosphorus component (P ２ O ５ component) into molten steel.

[0005] On the other hand, Patent Document 6 discloses an alumina-based unfired brick in which 0.3 mass% of phosphate is added as a binder, but there is a problem that sufficient strength cannot be obtained because the amount of phosphate is too small.

[0006] Japanese Patent Publication Sho 53-13642 Japanese Unexamined Patent Publication 2017-65956 Japanese Unexamined Patent Publication 2016-64956 Japanese Patent No. 6823042 Japanese Unexamined Patent Publication 2007-145684 Japanese Unexamined Patent Publication Hei 8-109062

[0007] The problem to be solved by the present invention is to provide a method for producing an unfired brick that can suppress the reduction of corrosion resistance and creep resistance caused by the formation of low-melting-point substances, and can exhibit sufficient strength.

[0008] According to one aspect of the present invention, the following method for producing an unfired brick is provided. The brick contains 0.2 mass% to 15 mass% of magnesia with a particle size of less than 75 μm, and 0.3 mass% to 10 mass% of silica with a particle size of less than 44 μm. The remainder mainly contains one or more selected from the group consisting of an alumina raw material, an alumina-silica raw material, a silica raw material and a spinel raw material. Furthermore, the total content of alkali metal phosphate and alkali metal silicate is 1 mass% or less (including 0), and Na ２ O component and K２ The total content of component O is 0.5% by mass or less (including 0), and P ２ O ５ A method for producing unfired bricks, comprising adding water to a refractory raw material mixture having a component content of 0.7% by mass or less (including 0), kneading the mixture, press molding it, and then leaving it at room temperature or heat-treating it at a temperature of 1000°C or less. In addition, according to another aspect of the present invention, the following method for producing unfired bricks is provided: containing 0.2% by mass or more and 5% by mass of magnesia with a particle size of less than 75 μm, 10% by mass or less of magnesia with a particle size of 75 μm or more (excluding 0), and 0.3% by mass or more and 10% by mass of silica with a particle size of less than 44 μm, with the remainder mainly consisting of alumina raw materials, and having a total content of alkali metal phosphates and alkali metal silicates of 1% by mass or less (including 0), and Na ２ O component and K ２ The total content of component O is 0.5% by mass or less (including 0), and P ２ O ５ A method for producing unfired bricks, comprising adding water to a refractory raw material mixture having a component content of 0.7% by mass or less (including 0), kneading the mixture, press molding it, and then leaving it at room temperature or heat-treating it at a temperature of 1000°C or less.

[0009] In the manufacturing method of the present invention, although the details will be described later, magnesium silicate hydrate is formed as a binder, so that the decrease in corrosion resistance and creep resistance due to the formation of low-melting-point materials can be suppressed, and an unfired brick that can exhibit sufficient strength can be obtained.

[0010] The inventors have discovered that by adding water to a refractory raw material mixture containing magnesia powder and silica powder, kneading it, and then press-molding it, leaving it at room temperature or heat-treating it at a temperature of 1000°C or lower, an unfired brick with sufficient corrosion resistance, creep resistance, and strength can be obtained. The mechanism is thought to be as follows: Magnesia powder and silica powder form a gel-like magnesium silicate hydrate in the presence of water, so even by leaving it at room temperature, the moisture content in the brick decreases, and it functions as a binder in the matrix of the brick. Subsequently, even if the temperature of the brick rises due to heat treatment and the magnesium silicate hydrate dehydrates, it forms an amorphous magnesium silicate bond, thus maintaining strength. Furthermore, when heated, the amorphous magnesium silicate becomes forsterite, which suppresses the decrease in strength until the usage temperature. Moreover, forsterite has a high melting point and is stable during use without forming low-melting-point substances with other raw materials, and hardly adversely affects creep resistance or corrosion resistance.

[0011] In one aspect of the present invention, magnesia fine powder is used as a magnesia component for producing magnesium silicate hydrate in a content of 0.2% to 15% by mass in 100% by mass of the refractory raw material formulation. Since the smaller the particle size of the magnesia fine powder, the easier it is to form hydrate in the presence of water, specifically, a particle size of less than 75 μm is used. That is, in one aspect of the present invention, the refractory raw material formulation contains 0.2% to 15% by mass of magnesia fine powder, which is magnesia with a particle size of less than 75 μm. If the magnesia fine powder content is less than 0.2% by mass, the connective tissue in the brick structure is insufficient, resulting in low strength. If it exceeds 15% by mass, the amount of reaction products (secondary spinel, enstatite, etc.) and low-melting-point compounds (cordierite, etc.) with different volumes from the surrounding raw materials increases. In alumina-silica and silica-based materials, a decrease in creep resistance becomes a problem, and in alumina and spinel-based materials, residual expansion increases, making cracking more likely during use.

[0012] As the content of magnesia fine powder increases, residual expansion increases, for example, in alumina. On the other hand, magnesia raw material is a refractory material that is effective in ensuring corrosion resistance. Therefore, in another aspect of the present invention, the upper limit of the content of magnesia fine powder is reduced to 5% by mass from the viewpoint of reducing residual expansion and further improving volume stability, and magnesia with a particle size of 75 μm or more is included at a content of 10% by mass or less (excluding 0) from the viewpoint of ensuring corrosion resistance.

[0013] In this invention, light-calcined magnesia can also be used as magnesia powder. Light-calcined magnesia is obtained by calcining magnesite, magnesium hydroxide, etc., at a relatively low temperature, for example, 1400°C or lower, usually 1000 to 1400°C, and is generally called activated magnesia or calcined magnesia, with an average particle size of 1 μm or less. Because this light-calcined magnesia has a large specific surface area and high activity, it dissolves more easily in water compared to sintered magnesia and electrofused magnesia, so that magnesium silicate bonds develop well in the brick structure and the strength of the brick can be increased. This light-calcined magnesia can be used in a content of 0.2% to 5% by mass in 100% by mass of the refractory raw material blend.

[0014] Furthermore, in this invention, as a silica component for producing magnesium silicate hydrate, silica fine powder with a particle size of less than 44 μm is used in a content of 0.3% to 10% by mass in 100% by mass of the refractory raw material formulation. If the silica fine powder content is less than 0.3% by mass, the bonding strength of the brick structure becomes insufficient, and if it exceeds 10% by mass, the corrosion resistance and creep resistance decrease.

[0015] As silica fine powder, silica flower, fused silica, silica sol, silica brick scraps, or silica fine powder can be used. Note that since silica sol is in liquid form, its content is SiO ２The amount shall be converted to the following. In addition, in the case of silica flower, due to its high reactivity, its content can be 0.3% by mass or more and 2.5% by mass or less. Furthermore, in this invention, silica flower refers to fine silica particles with an average particle size of 10 μm or less, and is a general term for silica fume, fumed silica, and white carbon. Silica fume is a by-product obtained by collecting exhaust gas generated during the refining process of ferrosilicon, metallic silicon, electrofused zirconia, etc., and is relatively inexpensive to obtain. Fumed silica is produced by hydrolyzing silicon compounds, including silicon tetrachloride, in an oxygen and hydrogen flame. White carbon is obtained by decomposition of sodium silicate using acid or alkali. These silica flowers are easily soluble in alkaline water in which some magnesia fine powder is dissolved, so magnesium silicate bonds develop well in the brick structure, which can increase the strength of the brick.

[0016] In one embodiment of the present invention, the composition of raw materials other than magnesia fine powder and silica fine powder contained in the refractory raw material formulation, i.e., the composition of the remaining raw materials in the refractory raw material formulation, mainly consists of one or more of alumina raw materials, alumina silica raw materials, silica raw materials, and spinel raw materials. In another embodiment of the present invention, the composition of raw materials other than magnesia fine powder, magnesia with a particle size of 75 μm or more, and silica fine powder contained in the refractory raw material formulation, i.e., the composition of the remaining raw materials in the refractory raw material formulation, mainly consists of alumina raw materials. As alumina raw materials, one or more of electrofused alumina, sintered alumina, calcined alumina, bauxite, and banket can be used. As alumina silica raw materials, one or more of mullite, sillimanite, andalusite, kyanite, pyrophyllite, chamotte, and clay can be used. As silica raw materials, one or more of fused silica and silica can be used. As spinel raw materials, Al ２ O ３ The content of is 60-90% by mass, and the content of MgO is 10-40% by mass, Al ２ O ３ Products containing a total of 95% by mass or more of MgO can be used.

[0017] In one embodiment of the present invention, the remainder of the refractory raw material mixture may contain one or more of the following as refractory raw materials other than the alumina raw material, alumina silica raw material, silica raw material, and spinel raw material, in a content of 5% by mass or less in proportion to 100% by mass of the refractory raw material mixture: metal powder, silicon carbide, graphite, carbon black, zirconia, glass powder, zircon, and boron carbide. Thus, in one embodiment of the present invention, the raw material composition other than magnesia fine powder and silica fine powder contained in the refractory raw material mixture, that is, the raw material composition of the remainder of the refractory raw material mixture, is mainly one or more of the alumina raw material, alumina silica raw material, silica raw material, and spinel raw material, and therefore the unfired brick according to the present invention has Al as its chemical component. ２ O ３ Components and / or SiO ２ This results in an unfired brick with the alumina as the main component. In other embodiments of the present invention, the remainder of the refractory raw material mixture may also contain one or more of the following as refractory raw materials other than the alumina raw material mentioned above, in a content of 5% by mass or less in proportion to 100% by mass of the refractory raw material mixture: metal powder, silicon carbide, graphite, carbon black, zirconia, glass powder, zircon, and boron carbide. Thus, in other embodiments of the present invention, the raw material composition other than magnesia fine powder, magnesia with a particle size of 75 μm or more, and silica fine powder contained in the refractory raw material mixture, that is, the raw material composition of the remainder of the refractory raw material mixture, is primarily alumina raw material, and therefore the unfired brick according to the present invention has Al as its chemical component. ２ O ３ It becomes an unfired brick with the main component being the element.

[0018] In this invention, since magnesium silicate hydrate functions as a binder, alkali metal phosphates and alkali metal silicates do not need to be included as binders as in conventional unfired bricks, and therefore do not need to be used, although they can be used as auxiliary binders. However, in this case, the total content should be 1% by mass or less, preferably 0.2% by mass or less. If the total content exceeds 1% by mass, corrosion resistance and creep resistance will decrease. In the case of alkali metal phosphates, there is a concern that the phosphoric acid component will dissolve into the molten steel. Here, alkali metal silicates are sodium silicate and potassium silicate, and alkali metal phosphates are sodium phosphate and potassium phosphate. Thus, in this invention, it is basically not necessary to use conventional alkali metal silicates and alkali metal phosphates as binders, so the Na in the refractory raw material composition is not required. ２ O component and K ２ The total content of component O can be 0.5% by mass or less (including 0), and P ２ O ５ The content of the component can be 0.7% by mass or less (including 0). This suppresses a decrease in corrosion resistance and creep resistance, as well as suppresses the leaching of phosphorus components into the molten steel. ２ O component and K ２ Component O and P ２ O ５ The components are contained in the binders, such as alkali metal silicates and alkali metal phosphates, as well as in refractory raw materials such as alumina raw materials. The content in the refractory raw material formulation is the sum of the content derived from the binders and the content derived from the refractory raw materials. Furthermore, in this invention, it is basically unnecessary to use organic binders that are used in conventional unfired bricks, such as pitch, phenolic resin, molasses, pulp waste liquid, dextrin, methylcellulose, lignin sulfonates, and polyvinyl alcohol. However, they may be used as an auxiliary to supplement the strength after molding if the content is 1.5% by mass or less, more preferably 1% by mass or less. Note that the content of organic binders containing solvents is given as solid content.

[0019] In the method for producing unfired bricks of the present invention, water is added to the above-mentioned refractory raw material mixture and kneaded, followed by press molding. The amount of water added should be appropriate depending on the raw material composition, etc., in order to generate magnesium silicate hydrate as a binder and to ensure the moldability of the clay, but specifically, it can be added at an addition rate of 0.5% to 8% by mass per 100% by mass of the refractory raw material mixture. At this time, organic solvents such as ethylene glycol or methanol that are compatible with water may be used in combination with water. After press molding, magnesium silicate hydrate is generated, and by removing some of the moisture, sufficient handling strength can be obtained. Therefore, sufficient strength for handling the bricks can be obtained even by leaving them at room temperature. Here, room temperature refers to the temperature inside the brick manufacturing plant, specifically between 25°C and 60°C. The time to leave them should be adjusted according to the size and temperature of the bricks, for example, between 12 hours and 120 hours is sufficient. Furthermore, depending on the intended use and conditions of the bricks (e.g., preheating temperature and time), if the factory temperature is below 25°C, or if it is desired to complete the product quickly, heat treatment can be performed by selecting appropriate temperature conditions within the temperature range of 60°C to 1000°C.

[0020] Here, the particle size as used in this invention refers to the size of the sieve mesh when refractory raw material particles are separated by sieving. For example, magnesia with a particle size of less than 75 μm refers to magnesia that passes through a sieve with a mesh size of 75 μm, and magnesia with a particle size of 75 μm or more refers to magnesia that does not pass through a sieve with a mesh size of 75 μm. Furthermore, the average particle size as used in this invention refers to the volume-average particle size corresponding to the median cumulative value (D50) of the cumulative curve measured by a laser diffraction scattering particle size distribution analyzer.

[0021] Tables 1 to 4 show the composition of the refractory raw material formulations in the examples and comparative examples of the present invention, and the evaluation results of the obtained bricks. Note that the brick materials differ in Tables 1 to 4: Table 1 shows alumina-silica unfired bricks, Table 2 shows silica-based unfired bricks, Table 3 shows spinel-based unfired bricks, and Table 4 shows alumina-based unfired bricks.

[0022] First, let's explain the refractory materials used in Tables 1-4. As alumina raw materials, electrofused alumina, sintered alumina, and calcined alumina are, respectively, Al ２ O ３ We used materials with a content of 98% by mass or more. Andalusite was used as the raw material for alumina silica. ２ O ３ Content is 60% by mass, SiO ２ Sintered mullite contains 37% by mass. ２ O ３ Content is 71% by mass, SiO ２ Chamotte contains 27% by mass. ２ O ３ Content is 33% by mass, SiO ２ Clay with an alcohol content of 64% by mass is called Al ２ O ３ Content is 40% by mass, SiO ２ Each product used contained 45% by mass of silica. As a silica raw material, fused silica was SiO ２ When the content is 99% by mass, silica is SiO ２ Each material used had a content of 98% by mass. The spinel raw material had a MgO content of 22% by mass and Al ２ O ３ Electrofused spinel with a content of 73% by mass was used. For magnesia fine powder, sintered magnesia with an MgO content of 98% by mass or more was used for magnesia with a particle size of less than 75 μm, and light-calcined magnesia with an MgO content of 98% by mass or more was used. Furthermore, for magnesia with a particle size of 75 μm or more, electrofused magnesia with an MgO content of 98% by mass or more was used. For silica fine powder, silica and SiO with a particle size of less than 44 μm were used. ２ Silica flower with a content of 98% by mass was used. Sodium phosphate was used as an alkali metal phosphate. ２ O ５ Sodium metaphosphate with a content of 65% by mass was used. As an alkali metal silicate, sodium silicate is Na ２ Sodium metasilicate with an O content of 30% by mass was used.

[0023] Unfired bricks were produced by adding water at a rate of 3% by mass to the refractory raw material formulations of each example listed in Tables 1 to 4, kneading the mixture, and then forming it into a shape of 230 × 114 × 100 mm using an oil press. The bricks were then heat-treated at 250°C for 5 hours. In addition, for some examples, bricks were prepared by leaving them at room temperature (25°C for 120 hours) and by varying the heat treatment temperature. Samples for physical property measurement were cut from these bricks, and their bending strength at room temperature was measured. For those heat-treated at 250°C, the corrosion resistance, residual expansion resistance, and creep resistance were evaluated.

[0024] The bending strength at room temperature was measured using a three-point bending test. Specifically, a 20 x 20 x 80 mm strip sample was prepared, and the bending strength was measured at a span of 50 mm and a pressing rate of 1.65 kN / s. Corrosion resistance was evaluated for both spinel and alumina materials, assuming their use as lining material for molten metal containers. Residual expansion resistance was also evaluated for both spinel and alumina materials. On the other hand, since alumina-silica and silica materials are often used in applications that do not come into contact with molten iron or molten steel, a load softening test was performed to evaluate their creep resistance.

[0025] Corrosion resistance was evaluated by a rotary erosion test. In the rotary erosion test, the inner surface of a drum with a horizontal rotation axis was lined with the test brick, slag was added, and the surface of the brick was eroded by heating. The heat source was an oxygen-propane burner, the test temperature was 1700°C, and the slag composition was CaO: 30 mass%, SiO ２ :30% by mass, Al ２ O ３ :20% by mass, FeO+Fe ２ O ３ The slag content was set to 20% by mass, and the discharge and addition of slag was repeated 10 times at 30-minute intervals. After the test, the amount of erosion (mm) was determined from the difference in thickness (mm) before and after the test at the most eroded part of each brick. Then, the erosion index was calculated, with the amount of erosion (mm) of the brick in "Comparative Example 11" listed in Table 3 set to 100. A smaller value for this erosion index indicates better corrosion resistance.

[0026] Residual expansion properties were evaluated using 20 x 20 x 80 mm strip samples. These were heat-treated at 1400°C for 5 hours in an air atmosphere, and the dimensions of the longer strips were compared before and after heat treatment. A dimensional change rate of less than 0.5% after heat treatment was rated as ○ (good), 0.5% to less than 1.0% as △ (acceptable), and 1.0% or more as × (poor).

[0027] Creep resistance was evaluated by measuring the load softening point. The load softening point was measured in accordance with JIS R2209 under a load of 0.2 MPa. The difference in the T2 value of each example and comparative example brick compared to the 2% softening point temperature (T2) of the brick of the reference example was judged as follows: ○ (Good) if less than 100°C, △ (Acceptable) if 100°C or more and less than 200°C, and × (Poor) if 200°C or more. Here, Example 1 was used as the reference for Examples 1 to 7 and Comparative Examples 1 to 3, Example 8 was used as the reference for Examples 8 to 12 and Comparative Examples 4 to 5, Example 13 was used as the reference for Examples 13 to 20 and Comparative Examples 6 to 8, and Example 21 was used as the reference for Examples 21 to 25 and Comparative Examples 9 to 10.

[0028]

[0029]

[0030]

[0031]

[0032] In Table 1, Examples 1 to 7 show cases where the content of magnesia fine powder in the refractory raw material formulation differs in alumina silicate unfired bricks, but these fall within the scope of the present invention, exhibiting sufficient strength and excellent creep resistance. On the other hand, Comparative Example 1 does not contain magnesia fine powder, resulting in insufficient strength after heat treatment. Comparative Example 3 has a magnesia fine powder content exceeding the upper limit of the present invention, resulting in poor creep resistance. Furthermore, Comparative Example 2 shows differences in the sodium silicate content and Na content in the refractory raw material formulation. ２ O component and K ２ Total content of component O (Na ２ O+K ２The content of O) exceeded the upper limit of the present invention, and compared to Examples 3 and 4, which were within the range of the present invention, the creep resistance was inferior.

[0033] In Table 1, Examples 8 to 12 show that while the silica fine powder content in the refractory raw material formulation differs in alumina-silica unfired bricks, it remains within the scope of the present invention, exhibiting sufficient strength and excellent creep resistance. On the other hand, Comparative Example 4 did not contain silica, resulting in insufficient strength after heat treatment. Comparative Example 5 exceeded the upper limit of the present invention in silica fine powder content, resulting in poor creep resistance. In Examples 8 to 10, heat treatment was performed at different temperatures, but sufficient strength was obtained in all cases.

[0034] In Table 2, Examples 13 to 20 show that while the content of magnesia fine powder in the refractory raw material formulation differs in siliceous unfired bricks, they are within the scope of the present invention, exhibiting sufficient strength and excellent creep resistance. On the other hand, Comparative Example 6 did not contain magnesia fine powder, resulting in insufficient strength after heat treatment. Comparative Example 8 exceeded the upper limit of the present invention in terms of magnesia fine powder content, resulting in poor creep resistance. Furthermore, Comparative Example 7 showed differences in the content of sodium silicate and Na in the refractory raw material formulation. ２ O component and K ２ Total content of component O (Na ２ O+K ２ O) exceeds the upper limit of the present invention, and when these content levels are compared with Examples 15 and 16, which are within the scope of the present invention, the creep resistance is inferior.

[0035] In Table 2, Examples 21 to 25 show cases where the silica fine powder content in the refractory raw material formulation differs in siliceous unfired bricks, but they are within the scope of the present invention, exhibiting sufficient strength and excellent creep resistance. On the other hand, Comparative Example 9 does not contain silica fine powder, resulting in insufficient strength after heat treatment. Comparative Example 10 has a silica fine powder content exceeding the upper limit of the present invention, resulting in poor creep resistance. Furthermore, although heat treatment was performed at different temperatures in Examples 21 to 23, sufficient strength was obtained in all cases.

[0036] In Table 3, Examples 26 to 32 show different content levels of magnesia fine powder in the refractory raw material formulation for spinel-based unfired bricks, but they are within the scope of the present invention, exhibiting sufficient strength, excellent corrosion resistance, and good residual expansion. On the other hand, Comparative Example 11 did not contain magnesia, resulting in insufficient strength after heat treatment. Comparative Example 13 exceeded the upper limit of the present invention in terms of magnesia fine powder content, resulting in increased residual expansion. Furthermore, Comparative Example 12 showed differences in the sodium phosphate content and P in the refractory raw material formulation. ２ O ５ The concentration of the components exceeded the upper limit of the present invention, resulting in inferior corrosion resistance compared to Examples 27 and 28, which fall within the scope of the present invention.

[0037] In Table 3, Examples 33 to 37 show different silica fine powder content in the refractory raw material formulation of spinel-based unfired bricks, but all fall within the scope of the present invention, exhibiting sufficient strength, excellent corrosion resistance, and good residual expansion. On the other hand, Comparative Example 14 did not contain silica fine powder, resulting in insufficient strength after heat treatment. Comparative Example 15 exceeded the upper limit of the present invention in silica fine powder content, resulting in poor corrosion resistance. Furthermore, although heat treatment was performed at different temperatures in Examples 33 to 35, sufficient strength was obtained in all cases.

[0038] In Table 4, Examples 38 to 43 show cases where the content of magnesia fine powder in the refractory raw material formulation differs in alumina-based unfired bricks, but these fall within the scope of the present invention, exhibiting sufficient strength, excellent corrosion resistance, and good residual expansion. On the other hand, Comparative Example 16 did not contain magnesia fine powder, resulting in insufficient strength after heat treatment. Comparative Example 19 exceeded the upper limit of the present invention in terms of magnesia fine powder content, resulting in increased residual expansion. Furthermore, Comparative Example 18 showed differences in the content of sodium phosphate in the refractory raw material formulation and P ２ O ５ The component content exceeded the upper limit of the present invention, resulting in inferior corrosion resistance compared to Examples 40 and 41, which were within the scope of the present invention. Furthermore, Comparative Example 17, which did not contain silica fine powder but contained 0.3% by mass of sodium phosphate, showed insufficient strength.

[0039] In Table 4, Examples 44 to 47 show that although the silica fine powder content in the refractory raw material formulation differs in the alumina-based unfired bricks, they are within the scope of the present invention, exhibiting sufficient strength, excellent corrosion resistance, and good residual expansion. On the other hand, Comparative Example 20 did not contain silica fine powder, resulting in insufficient strength after heat treatment. Comparative Example 21 had a silica fine powder content exceeding the upper limit of the present invention, resulting in poor corrosion resistance. Furthermore, although heat treatment was performed at different temperatures in Examples 44 to 46, sufficient strength was obtained in all cases.

[0040] In Table 4, Examples 48 and 49 are cases in which alumina-based unfired bricks contain magnesia with a particle size of 75 μm or more in the refractory raw material formulation. These examples are within the scope of the present invention and exhibit superior residual expansion compared to Examples 39 and 42, which have a similar magnesia raw material content, as well as sufficient strength and corrosion resistance.

Claims

1. Contains 0.2% to 15% by mass of magnesia with a particle size of less than 75 μm and 0.3% to 10% by mass of silica with a particle size of less than 44 μm, with the remainder mainly containing one or more of alumina raw materials, alumina silica raw materials, silica raw materials, and spinel raw materials, and the total content of alkali metal phosphates and alkali metal silicates is 1% by mass or less (including 0), and Na ２ O component and K ２ The total content of component O is 0.5% by mass or less (including 0), and P ２ O ５ A method for producing unfired bricks, comprising adding water to a refractory raw material mixture having a component content of 0.7% by mass or less (including 0), kneading the mixture, press molding it, and then leaving it at room temperature or heat-treating it at a temperature of 1000°C or less.

2. A method for producing unfired bricks according to claim 1, wherein light-fired magnesia is used as the magnesia with a particle size of less than 75 μm.

3. A method for producing unfired bricks according to claim 1 or claim 2, wherein silica flower is used as silica with a particle size of less than 44 μm.

4. Contains 0.2% to 5% by mass of magnesia with a particle size of less than 75 μm, 10% to 10% by mass (excluding 0) of magnesia with a particle size of 75 μm or more, and 0.3% to 10% by mass of silica with a particle size of less than 44 μm, with the remainder mainly consisting of alumina raw materials, and the total content of alkali metal phosphates and alkali metal silicates is 1% by mass or less (including 0), and Na ２ O component and K ２ The total content of component O is 0.5% by mass or less (including 0), and P ２ O ５ A method for producing unfired bricks, comprising adding water to a refractory raw material mixture having a component content of 0.7% by mass or less (including 0), kneading the mixture, press molding it, and then leaving it at room temperature or heat-treating it at a temperature of 1000°C or less.

5. The method for producing unfired bricks according to claim 4, wherein light-fired magnesia is used as the magnesia with a particle size of less than 75 μm.

6. A method for producing unfired bricks according to claim 4 or claim 5, wherein silica flower is used as silica with a particle size of less than 44 μm.

Images