Pouring material for the tip of the blast furnace trough

Abstract

To provide a pourable material for the tip of a blast furnace trough that can suppress the occurrence of cracks at the tip of the blast furnace trough. [Solution] A pourable material for the tip of a blast furnace trough, comprising 1 to 7% by mass of andalusite with a particle size of 1 mm or more and less than 5 mm, 1 to 5% by mass of ultrafine silica powder with an average particle size of 1 μm or less, and 15 to 45% by mass of silicon carbide with a particle size of less than 1 mm, wherein the content of andalusite with a particle size of less than 1 mm is 3% by mass or less (including 0), the content of andalusite with a particle size of 5 mm or more is 3% by mass or less (including 0), and the content of the remaining other refractory materials with a particle size of 5 mm or more is 5% by mass or less (including 0).

Description

Technical Field

[0001] The present invention relates to a pouring material for the tip of a blast furnace trough.

Background Art

[0002] A blast furnace is equipment for producing hot metal by reducing raw materials such as iron ore and sintered ore with coke or the like. The hot metal produced in the blast furnace is separated into hot metal and slag in a main trough, and the hot metal passes through a hot metal trough and a hot metal pouring trough and is transported to a hot metal pretreatment process in a hot metal ladle or a hot metal mixer car. Further, the slag is transported from the slag trough through a slag pouring trough or directly to a granulation facility or a dry pit or the like. Here, in the present invention, the "blast furnace trough" is a general term for each trough through which the hot metal or slag produced in the blast furnace passes, and the "tip of the blast furnace trough" refers to the tip of each trough.

[0003] Normally, the blast furnace trough has a U-shape with upper release, and a shaped or unshaped refractory is lined inside the U-shaped iron skin. Further, since the hot metal temperature in the blast furnace trough is extremely high at around 1500°C and it is worn out by the high temperature and flow, repairs are frequently performed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the blast furnace trough structure described above, the iron shell deforms as its temperature rises as the inner lining material wears down, reaching temperatures of approximately 150°C to 300°C. Furthermore, because the blast furnace trough has an open top and a U-shape, the iron shell is more susceptible to deformation. The tip of the blast furnace trough is particularly close to subsequent troughs, molten iron ladles, and dry pits, making the iron shell at the tip especially vulnerable to radiant heat and resulting in greater deformation. This deformation of the blast furnace trough's iron shell causes cracks in the inner lining material. The tip of the blast furnace trough is particularly open on one side. Therefore, structurally, the restraining force of the iron shell and lining material is weaker, which exacerbates deformation and makes it more prone to cracking.

[0006] As a countermeasure, Patent Document 1 discloses that, regarding cracks on the end faces of the rising sections of large troughs and cracks at the ends of molten iron troughs, it is presumed that the iron shell expands during use, causing it to open outwards, and as a result the restraining force of the refractory material on the trough end surface, including the rising section, decreases, leading to cracks extending from the outer circumference to the inner surface. Therefore, it discloses installing a device to prevent the iron shell from opening at the rising section of large troughs and the ends of molten iron troughs. However, depending on the layout or shape of blast furnace troughs such as large troughs and molten iron troughs, it may not be possible to install a device to prevent the iron shell from opening.

[0007] The problem that this invention aims to solve is to provide a pourable material for the tip of a blast furnace trough that can suppress the occurrence of cracks at the tip of the blast furnace trough. [Means for solving the problem]

[0008] As a result of repeated testing and studies to solve the above problems, the inventors have found that the following means are effective. Specifically, the first means is to increase the strength of the construction body of the pourable material for the tip of the blast furnace trough, thereby suppressing crack generation due to stress caused by deformation of the steel shell, and the second means is to include expansive refractory aggregate in the refractory raw material mixture of the pourable material, thereby creating microspaces around the expansive refractory aggregate in the construction body and dispersing cracks. In other words, the technical idea of ​​the present invention is to suppress the occurrence of fatal cracks that lead to a decrease in service life by these means.

[0009] This invention was conceived based on the above knowledge and technical ideas, and its gist is as follows. In terms of the proportion of 100% by mass of the refractory raw material mixture, Andalusite with a particle size of 1 mm or more and less than 5 mm, 1 to 7% by mass, 1 to 5% by mass of silica ultrafine powder with an average particle size of 1 μm or less. Each contains 15 to 45% by mass of silicon carbide with a particle size of less than 1 mm. Furthermore, the andalusite content with a particle size of less than 1 mm is 3% by mass or less (including 0). The andalusite content is 3% by mass or less (including 0) with a particle size of 5 mm or more. A pourable material for the tip of a blast furnace trough, wherein the content of the remaining refractory materials with a particle size of 5 mm or larger is 5% by mass or less (including 0). [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the occurrence of cracks at the tip of the blast furnace trough. [Modes for carrying out the invention]

[0011] The pourable material for the tip of a blast furnace trough according to the present invention (hereinafter simply referred to as "pourable material") contains andalusite with a particle size of 1 mm or more and less than 5 mm, silica ultrafine powder with an average particle size of 1 μm or less, and silicon carbide with a particle size of less than 1 mm as refractory raw materials. A detailed explanation follows below.

[0012] Andalusite with a particle size of 1 mm to less than 5 mm is a type of expansive refractory aggregate. As mentioned above, its primary purpose is to generate microspaces around the structure to disperse cracks, and it is used in a content of 1 to 7% by mass of 100% by mass of refractory raw materials. If the content of andalusite with a particle size of 1 mm to less than 5 mm is less than 1% by mass, the amount of microspaces generated is too small, and the effect of dispersing cracks is not achieved. As a result, crack formation cannot be suppressed, and the thermal spalling resistance decreases. On the other hand, if the content of andalusite with a particle size of 1 mm to less than 5 mm exceeds 7% by mass, the amount of microspaces generated becomes excessive, and the amount of SiO2 component derived from andalusite also increases, resulting in a decrease in corrosion resistance.

[0013] In this invention, the content of andalusite with a particle size of 5 mm or more is 3% by mass or less (including 0). Although andalusite with a particle size of 5 mm or more is a type of expansive refractory aggregate, excessive use of large aggregate particles with a particle size of 5 mm or more results in excessive residual expansion, and at the same time, the number of aggregate particles decreases, which reduces the number of locations where microspaces are generated. As a result, the effect of dispersing cracks is not obtained, and crack propagation accelerates, making it impossible to suppress crack initiation and reducing heat spalling resistance.

[0014] Furthermore, in this invention, the content of andalusite with a particle size of less than 1 mm is also limited to 3% by mass or less (including 0). If small particles with a particle size of less than 1 mm are used in excess, sintering is accelerated too much, resulting in excessive residual shrinkage and a decrease in corrosion resistance.

[0015] As described above, one of the technical features of the present invention is the use of andalusite with a particle size of 1 mm or more and less than 5 mm in a content of 1 to 7% by mass as an expandable refractory aggregate. However, from the viewpoint of generating microspaces more appropriately and dispersing cracks more effectively, it is preferable to use andalusite with a particle size of 1 mm or more and less than 3 mm in a content of 1 to 5% by mass as an expandable refractory aggregate. In this case, it is even more preferable that the content of andalusite with a particle size of 3 mm or more be 1% by mass or less (including 0).

[0016] In this invention, silica ultrafine powder with an average particle size of 1 μm or less (hereinafter simply referred to as "silica ultrafine powder") is used at a content of 1 to 5% by mass in 100% by mass of the refractory raw material, primarily for the purpose of increasing the strength of the constructed body of the pourable material. If the silica ultrafine powder content is less than 1% by mass, the increase in strength will be insufficient due to insufficient sintering. On the other hand, if the silica ultrafine powder content exceeds 5% by mass, sintering is promoted too much, resulting in excessive residual shrinkage and a decrease in corrosion resistance. The silica ultrafine powder content is preferably 2 to 4% by mass.

[0017] As described above, the present invention uses ultrafine silica powder primarily to increase the strength of the pourable material construction body. However, as mentioned above, if the content of ultrafine silica powder is high, there is a concern that corrosion resistance will decrease due to oversintering. Therefore, in the present invention, with the primary objective of suppressing the decrease in corrosion resistance, silicon carbide with a particle size of less than 1 mm is used at a content of 15 to 45% by mass in 100% by mass of the refractory material. If the content of silicon carbide with a particle size of less than 1 mm is less than 15% by mass, the effect of suppressing the decrease in corrosion resistance is insufficient. On the other hand, if the content of silicon carbide with a particle size of less than 1 mm exceeds 45% by mass, a large amount of water needs to be added during construction, and as a result, the structure of the construction body becomes porous and lacks strength. It is preferable that the content of silicon carbide with a particle size of less than 1 mm is 20 to 40% by mass. The reason why the particle size of silicon carbide is limited to less than 1 mm in the present invention is to increase the specific surface area of ​​the silicon carbide particles and thereby increase the effect of suppressing the decrease in corrosion resistance.

[0018] As described above, the present invention contains andalusite, silicon carbide, and silica ultrafine powder in the refractory raw material mixture. In the present invention, the remainder of the refractory raw material mixture contains one or more other refractory raw materials selected from alumina, bauxite, mullite, chamotte, spinel, magnesia, zircon, zirconia, titania, graphite, carbon, etc. The particle sizes of these other refractory raw materials are adjusted as appropriate, but in the present invention, the content of other refractory raw materials with a particle size of 5 mm or more is set to 5% by mass or less (including 0). If the content of other refractory raw materials with a particle size of 5 mm or more exceeds 5% by mass, the amount of thermal expansion due to the thermal expansion of the other refractory raw materials becomes too large, resulting in a decrease in thermal spalling resistance. Here, "other refractory materials" refers to refractory materials of a different type from andalusite, silicon carbide, and silica; that is, refractory materials of a type other than andalusite, silicon carbide, and silica, regardless of particle size. Examples of other refractory materials are as described above. For example, alumina can be fused alumina or sintered alumina. Blown alumina can be white alumina or brown alumina. When using alumina as another refractory material, brown alumina is preferable from a price and other perspective. Furthermore, since brown alumina has a higher coefficient of thermal expansion than white alumina, it is particularly beneficial to limit the content of brown alumina with a particle size of 5 mm or more to 5% by mass or less (including 0).

[0019] In the present invention, the remainder of the refractory raw material mixture may contain a binder. While alumina cement is most commonly used as the binder, other known binders may also be used. In other words, the type and content of the binder may be the same as those of conventionally used pourable materials.

[0020] In the present invention, various additives such as dispersants and explosion inhibitors can be appropriately added to the refractory raw material formulation. The dispersant imparts fluidity during the construction of the pouring material. Specific examples include inorganic salts such as sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, acidic sodium hexametaphosphate, sodium borate, sodium carbonate, polymetaphosphates, etc., and sodium citrate, sodium tartrate, sodium polyacrylate, sodium sulfonate, polycarboxylates, β-naphthalenesulfonates, naphthalenesulfonic acid, etc. Specific examples of the explosion prevention agent are organic fibers, organic foaming agents, metallic aluminum, etc. Specific examples of the organic fibers are polymer organic fibers such as vinylon (including polyvinyl alcohol), rayon, polyester, nylon, polypropylene, polyethylene, etc. These additives are added based on 100% by mass of the refractory raw material formulation. The addition rate may be the same as that of a general pouring material.

[0021] In addition, the particle size referred to in the present invention is the size of the sieve mesh when the refractory raw material particles are sieved and separated. For example, andalusite with a particle size of less than 5 mm means andalusite that passes through a sieve with a sieve mesh of 5 mm, and andalusite with a particle size of 1 mm or more means andalusite that does not pass through a sieve with a sieve mesh of 1 mm. Also, the average particle size referred to in the present invention means the particle size when the relationship between the particle size measured by a laser diffraction scattering type particle size distribution meter and the mass ratio is plotted on a graph and the mass integration ratio reaches 50%.

Examples

[0022] Tables 1 to 4 show the formulations of the refractory raw materials and the evaluation results of the examples and comparative examples of the present invention. In Tables 1 to 4, brown alumina was used as the alumina. A predetermined amount of water and a dispersant were added to the refractory raw material of each example and kneaded, and then cast into a mold of a predetermined shape to produce a cured body of a predetermined shape. After the cured body was cured, the one dried by heat treatment at 110°C for 24 h was used as a test piece, and evaluations of the residual linear change rate, bending strength, apparent porosity, corrosion resistance, and heat spalling resistance were carried out. The evaluation methods for each evaluation item are as follows.

[0023] <Percentage change of remaining wire> In accordance with JIS R 2554, the specimen dimensions after drying were used as a reference, and measurements were taken after holding the specimens at 1450°C for 3 hours. This residual linear change rate is an indicator of volumetric stability at hot temperatures. A residual linear change rate of 0.05% or more and less than 0.5% was evaluated as ○ (Excellent), -0.05% or more and less than 0.05% as △ (Good), and 0.5% or more or less than -0.05% as × (Poor). In Tables 1 to 3, a residual linear change rate of 0.5% or more is indicated as × (H), and less than -0.05% is indicated as × (L).

[0024] <Bending strength> In accordance with JIS R 2553, the test specimens were dried as described above and then fired at 1450°C for 3 hours before measurement. After firing at 1450°C, the bending strength was evaluated as follows: ○ (Excellent) if it was 6 MPa or higher, △ (Good) if it was between 3 MPa and 6 MPa, and × (Poor) if it was less than 3 MPa.

[0025] <Apparent porosity> In accordance with JIS R 2205, the dried test specimens were fired at 1450°C for 3 hours before measurement. The apparent porosity after firing at 1450°C was evaluated as follows: less than 19% was rated as ○ (Excellent), 19% or more but less than 22% was rated as △ (Good), and 22% or more was rated as × (Poor).

[0026] <Corrosion resistance> A slag rotation erosion test was conducted on the dried specimens using blast furnace slag at 1650°C for 6 hours, and the amount of erosion and penetration was measured. A erosion and penetration amount (total of erosion and penetration) of less than 7 mm was evaluated as ○ (excellent), 7 mm or more but less than 11 mm as △ (good), and 11 mm or more as × (poor). Note that the erosion and penetration amount is an indicator of corrosion resistance, and a smaller amount of erosion and penetration indicates higher corrosion resistance.

[0027] <Heat-resistant spalling> The dried test specimens were fired at 1450°C for 3 hours and allowed to air cool naturally. Afterward, they were placed in a furnace maintained at 1450°C, removed after 30 minutes, and forced-air cooled using a fan. This process was repeated five times, and the rate of reduction in elastic modulus before and after the test was compared for evaluation. A reduction in elastic modulus of less than 65% was rated as ○ (Excellent), 65% to less than 75% as △ (Good), and 75% or more as × (Poor). The rate of reduction in elastic modulus is an indicator of heat spalling resistance; a lower rate indicates higher heat spalling resistance.

[0028] <Overall Rating> A score of ◎ (Excellent) was given when all evaluation results were ○, a score of ○ (Good) was given when at least one evaluation result was △ and there were no evaluation results of ×, and a score of × (Poor) was given when at least one evaluation result was ×. A score of ◎ (Excellent) or ○ (Good) was considered a passing grade.

[0029] [Table 1]

[0030] [Table 2]

[0031] [Table 3]

[0032] [Table 4]

[0033] In Table 1, Examples 1 to 3 are examples with different andalusite content, ranging in size from 1 mm to less than 5 mm in particle size. However, all examples fall within the scope of the present invention, and good evaluation results were obtained in all aspects of evaluation, including residual linear change rate, bending strength, apparent porosity, corrosion resistance, and heat spalling resistance. In contrast, Comparative Example 1 is an example that does not contain andalusite, and as residual shrinkage increased, the evaluation of residual linear change rate and heat spalling resistance was × (poor). Therefore, there is a problem of cracks occurring due to excessive sintering shrinkage and decreased heat spalling resistance. On the other hand, Comparative Example 2 is an example in which the content of andalusite with a particle size of 1 mm or more and less than 5 mm exceeds the upper limit of the present invention, and as residual expansion increased, the evaluation of residual linear change rate was × (poor). In addition, the evaluation of corrosion resistance was × (poor). Therefore, there is a problem of cracks occurring due to excessive residual expansion. Furthermore, there is a problem of insufficient residual thickness of the construction body during operation due to insufficient corrosion resistance.

[0034] In Table 1, Examples 4 to 7 are examples with different andalusite content (particle size between 1 mm and 3 mm), but all are within the scope of the present invention, and good evaluation results were obtained in all evaluations. In particular, Examples 4 to 6, in which the andalusite content (particle size between 1 mm and 3 mm) is within the preferred range (1 to 5% by mass), received an overall evaluation of ◎ (excellent), and obtained particularly good evaluation results.

[0035] In Table 1, Example 8 is an example where the andalusite content is 3% by mass and has a particle size of 5 mm or more, but it is within the scope of the present invention, and good evaluation results were obtained in all evaluations. In contrast, Comparative Example 3 is an example where the content of andalusite with a particle size of 5 mm or more exceeds the upper limit of the present invention, resulting in increased residual expansion. Consequently, the evaluation of residual linear change rate and heat spalling resistance was marked as × (poor). Therefore, there is a problem of crack formation due to excessive residual expansion and decreased heat spalling resistance.

[0036] In Table 1, Example 9 is an example where the andalusite content is 3% by mass and has a particle size of less than 1 mm, but it is within the scope of the present invention, and good evaluation results were obtained in all evaluations. In contrast, Comparative Example 4 is an example where the content of andalusite with a particle size of less than 1 mm exceeds the upper limit of the present invention, resulting in increased residual shrinkage and a negative (×) evaluation of the residual linear change rate. Furthermore, the evaluation of corrosion resistance was also negative (×). Therefore, there is a problem of crack formation due to excessive residual shrinkage. Moreover, there is a problem of insufficient residual thickness of the construction body during operation due to insufficient corrosion resistance.

[0037] In Table 2, Examples 10 to 13 show different silicon carbide content levels (less than 1 mm in particle size), but all are within the scope of the present invention and good evaluation results were obtained in all evaluations. In particular, Examples 11 and 12, in which the silicon carbide content level (less than 1 mm in particle size) is within the preferred range (20-40% by mass), received an overall evaluation of ◎ (excellent) and obtained particularly good evaluation results. In contrast, Comparative Example 5 is an example where the content of silicon carbide particles with a particle size of less than 1 mm falls below the lower limit of the present invention, and the evaluation of corrosion resistance was × (poor). Therefore, there is a problem in that insufficient corrosion resistance leads to insufficient remaining thickness of the construction body during operation. On the other hand, Comparative Example 6 is an example where the content of silicon carbide particles with a particle size of less than 1 mm exceeds the upper limit of the present invention, and the evaluation of bending strength was × (poor). Therefore, there is a problem in that insufficient strength leads to increased abrasion damage to molten iron and slag.

[0038] In Table 2, Examples 14 to 17 represent examples with different silica ultrafine powder content, but all are within the scope of the present invention, and good evaluation results were obtained in all evaluations. In particular, Examples 15 and 16, in which the silica ultrafine powder content is within the preferred range (2-4% by mass), received an overall evaluation of ◎ (excellent), showing particularly good evaluation results. In contrast, Comparative Example 7 is an example that does not contain silica ultrafine powder, and the evaluation of bending strength and apparent porosity was × (poor). Therefore, there is a problem that wear loss against molten iron and slag will be large due to insufficient strength and structural density. On the other hand, Comparative Example 8 is an example in which the silica ultrafine powder content exceeds the upper limit of the present invention, and the evaluation of corrosion resistance was × (poor). Therefore, there is a problem that insufficient corrosion resistance will result in insufficient remaining thickness of the construction body during operation.

[0039] In Table 3, Examples 18 and 19 show examples with different content rates of alumina (other refractory raw materials) with a particle size of 5 mm or larger, but both are within the scope of the present invention, and good evaluation results were obtained in all evaluations. In contrast, Comparative Example 9 is an example where the alumina content with a particle size of 5 mm or more exceeds the upper limit of the present invention, resulting in increased residual expansion. Consequently, the evaluation of residual linear change rate and heat spalling resistance was negative (×). Therefore, there is a problem of crack formation due to excessive residual expansion and decreased heat spalling resistance.

[0040] Each example shown in Table 4 is an example in which the raw material composition of other refractory materials has been changed. All of them are within the scope of the present invention, and good evaluation results were obtained in all evaluations.

Claims

1. In proportion to 100% by mass of the refractory raw material mixture, Andalusite with a particle size of 1 mm or more and less than 5 mm, 1 to 7% by mass, 1 to 5% by mass of silica ultrafine powder with an average particle size of 1 μm or less, Each contains 15 to 45% by mass of silicon carbide with a particle size of less than 1 mm. Furthermore, the andalusite content with a particle size of less than 1 mm is 3% by mass or less (including 0). The andalusite content with a particle size of 5 mm or more is 3% by mass or less (including 0). A pourable material for the tip of a blast furnace trough, wherein the content of materials with a particle size of 5 mm or larger among the remaining refractory materials is 5% by mass or less (including 0).

2. The pourable material for the tip of a blast furnace trough according to claim 1, wherein the content of silica ultrafine powder with an average particle size of 1 μm or less is 2 to 4% by mass.

3. The pourable material for the tip of a blast furnace trough according to claim 1, wherein the content of silicon carbide particles with a particle size of less than 1 mm is 20 to 40% by mass.

4. A pourable material for the tip of a blast furnace trough according to any one of claims 1 to 3, wherein the andalusite content is 1 to 5% by mass, with a particle size of 1 mm or more and less than 3 mm.

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