Unshaped refractories for molten aluminum

Abstract

To provide a highly functional amorphous refractory for molten aluminum which does not require the addition of a penetration inhibitor in the production of a refractory product, or can exhibit an excellent penetration inhibiting function even if the amount of the penetration inhibitor is reduced.SOLUTION: In an amorphous refractory for molten aluminum comprising a refractory main raw material and a refractory binder, the refractory main raw material is composed of dense ceramic granules having an apparent porosity of 7% or less and has a chemical composition consisting of 65 mass% or more of Al2O3, 0.06-35 mass% of MgO, and 5 mass% or less of other components as a whole. The refractory main raw material contains round particles having a rounded shape without corners and having a similar chemical composition and a circularity of 0.70 or more in an amount of 10-80 mass%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an amorphous refractory for molten aluminum, and particularly to an amorphous refractory suitably used for forming the inner surface (refractory surface) of a melting furnace, a holding furnace, a ladle, a runner, etc., which comes into contact with molten aluminum.

Background Art

[0002] Conventionally, in the melting and casting of aluminum and aluminum alloys, in the parts where molten aluminum (including molten aluminum alloy, the same hereinafter) directly contacts, the refractories used to make the contact surface a refractory surface are required to (a) prevent the growth of ghosts due to the adhesion and penetration of aluminum to the refractory, (b) prevent the contamination and component change of the molten metal, and further (c) have damage resistance to physical wear and thermal shock, and long life.

[0003] Here, the "ghost" in the above (a) refers to a deposit that forms and grows on the upper part of the molten aluminum surface when aluminum or volatile gas components that adhere to and penetrate the refractory react with air. The generation of such ghosts leads to metal loss and efficiency reduction. Further, when pieces of the ghosts mix into the molten metal, they become a cause of the generation of non-metallic inclusions. Therefore, physical removal of such ghosts is carried out, but at that time, the refractory is often damaged. Regarding the above (b), the refractory structure is decomposed by the highly reducing molten aluminum, and in the contamination of the molten metal by the generated free components, and in the generation of ghosts and alumina loss, there is an inherent risk of causing component change of the molten metal due to the concentration of specific components in the molten metal. Furthermore, regarding the long life in (c), the wear of the amorphous refractory handling molten aluminum is mainly due to chemical erosion by the above-mentioned molten aluminum, physical damage such as wear due to the flow of the molten metal, mechanical impact, and thermal shock based on rapid temperature rise and fall.

[0004] Therefore, conventional measures to suppress glare and improve the corrosion resistance of refractories have mainly involved reducing the wettability to molten aluminum and increasing the density of the refractories. Furthermore, to prevent wear against thermal shock, measures have been taken to improve the heat insulation and reduce the thermal expansion of refractories. For example, methods to reduce the wettability to molten aluminum include adding penetration inhibitors such as fluorine compounds, boron compounds, barium sulfate, and zircon (see Patent Documents 1-3), applying a surface coating to the refractory using such penetration inhibitors (see Patent Documents 4-5), and using materials that are not easily wetted by molten aluminum, such as graphite, silicon carbide, silicon nitride, and zircon, as the main material of the refractory (see Patent Documents 6-7).

[0005] On the other hand, densification of amorphous refractories is mainly achieved by adding dispersants such as sodium phosphate, polycarboxylic acid, and polyacrylic acid, and by performing the process with a low moisture content. This is because molten non-ferrous metals such as aluminum have relatively low surface tension and can penetrate even fine pores (see Non-Patent Documents 1-3), so by reducing the moisture content and porosity as much as possible, it is possible to suppress the penetration of such molten non-ferrous metals. In addition, some penetration inhibitors, such as barium sulfate, are designed to densify amorphous refractories and refine pores, thereby exhibiting an effect of suppressing the penetration of molten metals.

[0006] However, all of these conventional proposals are based on the idea of ​​imparting properties using additive components such as penetration inhibitors and dispersants, and there have been no reports of efforts to improve the properties of the alumina raw material itself, which is the main raw material for refractories and is used in many shapeless refractories for molten aluminum. Furthermore, fluorine compounds, which are often used as penetration inhibitors, are released into the atmosphere as gas or produce aluminum dross, which is industrial waste, when mixed with molten aluminum. These pose problems such as being harmful to human health and having a high environmental impact. For this reason, since defluorination is already being promoted in flux materials, which also frequently use fluorine compounds in the aluminum melting and smelting process, it is thought that defluorination will also be necessary in refractories in the future.

[0007] Furthermore, in the case of amorphous refractories, even if the corrosion resistance to molten aluminum is improved when the main raw material is changed to a Si-based material, SiO2 will be generated in the parts located above the molten surface due to oxidation by air. This SiO2 is easily decomposed by molten aluminum, and therefore inherently has the problem of contamination with Si components, which are impurities. Moreover, in molten aluminum, an increase in Si components promotes penetration into the refractory, forming a blackened layer, also known as blackening. Since this altered layer has a higher expansion rate than the original refractory, it inherently has the problem of being a cause of damage due to structural spalling. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 59-169971 [Patent Document 2] Japanese Patent Application Publication No. Hei 1-192773 [Patent Document 3] Japanese Patent Publication No. 2006-182576 [Patent Document 4] Patent No. 4783660 [Patent Document 5] WO2013 / 111731 [Patent Document 6] Japanese Patent Publication No. 2000-344575 [Patent Document 7] Japanese Patent Publication No. 2019-210180 [Non-patent literature]

[0009] [Non-Patent Document 1] Toshio Komatsu, Hiroyuki Suzuki, Refractories, 44 (1992) 288-294 [Non-Patent Document 2] Masao Miyawaki, Yasuo Hongo, Refractories, 51 (1999) 303-309. [Non-Patent Document 3] Yosuke Tamura, Refractories, 70 (2018) 457-464 [Overview of the project] [Problems that the invention aims to solve]

[0010] As mentioned above, in the case of amorphous refractories for molten aluminum, there have been very few proposals focusing on improving the functionality of alumina, the main raw material that makes up the largest proportion of the compound. Currently, from a cost-effectiveness perspective, the mainstream approach is to improve functionality by adding penetration inhibitors and dispersants to high-alumina, low-cement castable materials. Thus, while there is a demand for improved penetration inhibition effects on refractory products with refractory surfaces that come into contact with molten aluminum in order to meet the demand for higher quality in aluminum products and reduce metal loss in order to compete on costs, there is also a conflicting situation where chemical substance regulations are becoming stricter in order to reduce environmental impact. In this context, improving the functionality of alumina, the main raw material for refractories, has become essential.

[0011] This invention was made against this backdrop, and its objective is to provide a highly functional amorphous refractory for molten aluminum that, by imparting penetration-inhibiting and moisture-reducing functions to the ceramic raw material itself, which is the main raw material for refractories, eliminates the need to add penetration inhibitors and dispersants during the manufacture of refractory products, or allows for the maintenance of equivalent densification and penetration-inhibiting functions even with reduced use of such agents. [Means for solving the problem]

[0012] Furthermore, in order to solve the above-mentioned problems, the present invention can be suitably implemented in various embodiments as listed below, and each embodiment described below can be adopted in any combination. It should be understood that the embodiments or technical features of the present invention are not limited in any way to those described below, and can be recognized based on the description of the entire specification and the inventive concept disclosed therein.

[0013] Therefore, the present invention aims to solve the aforementioned problems by providing an amorphous refractory for forming a refractory surface that comes into contact with molten aluminum, comprising at least a refractory main raw material and a refractory binder, wherein the refractory main raw material is composed of dense ceramic powder granules having an apparent porosity of 7% or less, and has an overall chemical composition consisting of 65% by mass or more of Al2O3, 0.06 to 35% by mass of MgO, and 5% by mass or less of other components, and further comprises 10 to 80% by mass of round particles having the above chemical composition and a roundness of 0.70 or more, exhibiting a round shape without corners.

[0014] Furthermore, according to one preferred embodiment of the amorphous refractory for molten aluminum in accordance with the present invention, the round particles are characterized in that they are mainly composed of particles with a particle size of 3-1 mm and / or particles with a particle size of 1 mm-45 μm.

[0015] Moreover, according to another preferred embodiment of the unshaped refractory for molten aluminum according to the present invention, the refractory main raw material contains particles having a particle size of less than 1 mm with the above chemical composition at a ratio of 40 to 95% by mass.

[0016] Furthermore, according to another preferred embodiment of the unshaped refractory for molten aluminum according to the present invention, the round particles are sintered particles having a round shape without corners, obtained by firing granulated products having the above chemical composition or crushed products thereof.

[0017] Furthermore, in the unshaped refractory for molten aluminum according to the present invention, preferably, the refractory main raw material is composed of a mixture of the round particles and crushed particles of a sintered body having the above chemical composition.

[0018] Also, according to another desirable embodiment of the unshaped refractory for molten aluminum according to the present invention, the refractory main raw material is contained at a ratio of 75 to 99% by mass.

[0019] In addition, in the present invention, preferably, the refractory binder is alumina cement.

[0020] And, according to another desirable embodiment of the unshaped refractory for molten aluminum according to the present invention, a penetration inhibitor is further contained, whereby a more excellent penetration inhibiting effect can be exhibited.

Advantages of the Invention

[0021] Thus, in the amorphous refractory for molten aluminum according to the present invention, round particles made of high-performance Al2O3-MgO ceramic containing a predetermined amount of MgO are used, and by substituting a portion of the conventional alumina raw material, the fluidity is advantageously improved, and the corrosion resistance to molten aluminum is effectively enhanced, thereby exhibiting the exceptional effects and properties listed below. (1) Because it is possible to simply substitute it with conventional alumina raw materials, the basic mix design is not compromised, and the improved fluidity effectively reduces the moisture content during construction, while also improving corrosion resistance to molten aluminum. (2) By reducing contamination of molten aluminum, metal loss can be reduced, improving product quality and productivity. (3) It becomes possible to reduce the amount of penetration inhibitors and dispersants added while maintaining the function of conventional monolithic refractories. [Brief explanation of the drawing]

[0022] [Figure 1] This is a micrograph of round particle A used in the example. [Figure 2] This is a micrograph of the round particle used in the example. [Figure 3] This is a micrograph of the crushed particle A used in the example. [Modes for carrying out the invention]

[0023] Incidentally, the amorphous refractory for molten aluminum according to the present invention has a major feature in that it can advantageously improve the penetration resistance of the amorphous refractory to molten aluminum and achieve densification through low-moisture construction by imparting a fluidity-enhancing effect to the raw material itself, as well as wettability to molten aluminum. The main raw material of the refractory used therein is composed of dense ceramic powder granules having an apparent porosity of 7% or less in terms of particle density, and has a chemical composition consisting of 65% by mass or more of Al2O3, 0.06 to 35% by mass of MgO, and 5% by mass or less of other components.

[0024] Here, the ceramic powder and granules that constitute the main raw material of such refractories must have a dense structure with an apparent porosity of 7% or less in order to reduce the amount of water absorbed during the construction of monolithic refractories and to suppress the penetration of molten aluminum into refractory products such as furnace walls and side walls formed using such monolithic refractories. Conversely, if the apparent porosity exceeds 7%, the amount of water absorbed by the pores in the ceramic powder and granules (aggregate) becomes too large, increasing the amount of water that needs to be added during mixing when constructing monolithic refractories, and as a result, causing an increase in the porosity of the refractory product and a decrease in corrosion resistance.

[0025] Furthermore, the present invention uses a high-performance ceramic raw material as the main raw material for refractories, which has an overall Al2O3-MgO system chemical composition consisting of 65% or more by mass of Al2O3, 0.06 to 35% by mass of MgO, and 5% or less by mass of other components. In such a chemical composition, when the MgO content is 1% by mass or less, the constituent minerals of the ceramic raw material become a single phase of corundum; when the MgO content is 1 to 20% by mass, two phases of corundum and spinel coexist; and when the MgO content is 20 to 35% by mass, it becomes a single phase of spinel. Here, spinel refers to Al2O3-MgO spinel. When the composition ratio of MgO increases and exceeds 35% by mass, periclase begins to crystallize in addition to spinel. Consequently, the resulting periclase readily undergoes hydration reactions, forming brucite and becoming brittle, making long-term storage difficult. This makes it unsuitable for amorphous refractories for molten aluminum, which are mixed with water for application and used for several months to several years. Therefore, in order to advantageously achieve the objectives of the present invention, the composition ratio of MgO in the main raw material of the refractory used in this invention needs to be 0.06 to 35% by mass. When MgO is added to Al2O3 in an amount that does not form spinel, the MgO functions as a sintering aid. Therefore, assuming densification and simple substitution with existing alumina raw materials, the most preferable composition ratio of MgO is about 0.06 to 1% by mass, which results in a single phase of corundum.

[0026] Furthermore, the main raw material for refractories having the chemical composition described above is composed of a single-composition Al2O3-MgO-based ceramic raw material. In addition, it is also possible to use a compound made by mixing such an Al2O3-MgO-based ceramic raw material with Al2O3-MgO-based ceramic raw materials of other compositions or ceramic raw materials with different component compositions. However, in the case of a compound made of two or more ceramic raw materials, the overall chemical composition must contain Al2O3 and MgO within the range defined in the present invention as described above. These ceramic raw materials are then sized to various particle sizes commonly used in the formulation of amorphous refractories, specifically 5-3 mm (coarse grain), 3-1 mm (medium grain), 1 mm-45 μm (fine grain), -45 μm (fine powder), etc., and blended in appropriate proportions to constitute the main raw material for refractories. In addition, depending on the size of the target refractory product, ceramic raw materials (particles) with particle sizes exceeding 5 mm may also be used as appropriate.

[0027] Furthermore, in the present invention, in a refractory main raw material having the specific chemical composition described above, 10 to 80% by mass, preferably 15 to 60% by mass, and more preferably 30 to 50% by mass, must consist of round particles with a circularity of 0.70 or higher, having the specific chemical composition; in other words, Al2O3-MgO-based ceramic particles exhibiting a rounded shape without corners, such as rice grains or marbles, as shown in the micrographs in Figures 1 and 2. This allows the raw material itself to be advantageously given functions to suppress penetration into molten aluminum and reduce moisture. It should be noted that, as long as such round particles are one of the constituent components of the refractory main raw material, they must, like other constituent components, be dense ceramic particles with an apparent porosity of 7% or less. Furthermore, if the proportion of such round particles is too low, it becomes difficult to fully exhibit the features of the present invention related to improved fluidity. On the other hand, if the proportion is too high, it can cause various problems during the construction of amorphous refractories, potentially adversely affecting the properties of the intended refractory product.

[0028] Here, the circularity used as an indicator of the shape of the round particles in the present invention described above is calculated using the area (A) and circumference (L) of each particle from particle photographs taken with an optical microscope, using the known formula: Circularity = 4π × A / L 2 The circularity is calculated according to the formula, and the closer the value is to 1, the closer the particle is to a circle or sphere. However, when calculating this circularity, if the number of measured particles is too small, the circularity will fluctuate greatly due to the presence of particles with unusual shapes. Therefore, the average value of the circularity obtained from at least 20 randomly sampled particles is used as the circularity of round particles.

[0029] The round particles according to the present invention are blended with alumina raw materials, which have been conventionally used as amorphous refractory raw materials, to constitute the main refractory raw material in the present invention. Various known alumina raw materials can be appropriately used as the blending material, but in particular, in the present invention, angular crushed particles with fracture surfaces, as shown in Figure 3, obtained by crushing a sintered body having the above chemical composition, are advantageously used. Such crushed particles generally exhibit a roundness of 0.50 to 0.80.

[0030] Furthermore, in the present invention, round particles, which constitute a predetermined proportion of the main raw materials of the refractory material, can be used in various particle sizes adopted in the formulation of amorphous refractory materials. In particular, particles with a particle size of 3-1 mm, -1 mm, and especially particles with a particle size of 1 mm-45 μm are preferably used, and by using such fine particles such as medium grains, fine grains, and fine powders, the objectives of the present invention can be advantageously realized.

[0031] Furthermore, the round particles having the above-described chemical composition, which constitute the main raw material for refractories according to the present invention, can be advantageously obtained by using a round granule obtained by kneading calcined alumina, which is the main raw material, with a magnesium component additive and a binder, then forming it into a spherical shape or into a round shape without corners, drying it, and then firing it at a temperature of 1700°C or higher. Alternatively, a granule like a pellet can be formed by pressure molding, and then the obtained granule can be dried or, prior to drying, crushed using a mechanical crusher to form crushed granules of a predetermined size, and then the obtained crushed granules can be rotary-fired at a temperature of 1700°C or higher using a firing furnace such as a rotary kiln to produce round particles with a round shape without corners, such as grains of rice or marbles, and a circularity of 0.70 or higher.

[0032] The round particles (sintered particles) obtained in this way are usually sized to various particle sizes before use. Needless to say, when firing as described above, it is necessary to fire (sinter) the round particles thoroughly until the apparent porosity of the obtained round particles is 7% or less. Furthermore, as magnesium component additives to be blended into the calcined alumina, magnesium inorganic salts such as magnesium oxide and magnesium hydroxide, magnesium oxo salts such as magnesium sulfate and magnesium carbonate, and magnesium organic salts such as magnesium stearate and magnesium sulfonate can be used, and it is also acceptable if part of the binder contains magnesium components.

[0033] The round particles obtained in this manner have a dense sintered structure mainly composed of corundum and spinel mineral phases. In monolithic refractories made by blending a refractory binder such as alumina cement with a main raw material containing such round particles, the wettability to molten aluminum can be effectively reduced compared to when using general alumina raw materials. Furthermore, the improved fluidity of the monolithic refractories themselves effectively reduces the amount of water required during mixing. This allows for a reduction in the amount of penetration inhibitors and dispersants used conventionally, or even the elimination of such agents, while still ensuring the effect of suppressing or preventing the penetration of molten aluminum, and advantageously reducing the amount of water required during the construction of monolithic refractories.

[0034] Furthermore, round particles, which are high-performance ceramic raw materials having the specific chemical composition described above, are used as one of the components of the main refractory raw material in amorphous refractories. Other dense ceramic raw materials used in combination with such round particles include, as mentioned above, crushed sintered bodies (crushed particles) having the specific chemical composition, as well as known ceramic raw materials, such as aggregates or powders of alumina, graphite, silicon carbide, silicon nitride, zircon, mullite, chamotte, and fused silica, as long as they satisfy the specific chemical composition as a whole. In this case, in order to fully utilize the non-wetting properties to molten aluminum, which are a characteristic of the present invention, it is desirable to limit the use of Al2O3-SiO2-based raw materials such as mullite and chamotte, which undergo reductive decomposition by molten aluminum, to the smallest possible amount.

[0035] Furthermore, in the present invention, it is desirable that the refractory main raw material having the specific chemical composition described above as a whole consists of 40 to 95% by mass of fine powder with a particle size of less than 1 mm having the specific chemical composition, and in addition, it is desirable that 20 to 60% by mass of the refractory main raw material consists of fine powder with a particle size of 1 mm to 45 μm (less than 1 mm, 45 μm or more), and that 20 to 75% by mass of the refractory main raw material consists of fine powder with a particle size of -45 μm, in other words, less than 45 μm. By using a refractory main raw material containing ceramic particles with such a particle size configuration, the characteristics of the raw material itself can be advantageously exhibited, and the penetration resistance of the amorphous refractory to molten aluminum can be effectively improved.

[0036] Furthermore, the monolithic refractory material according to the present invention is formulated with the main refractory raw materials described above, along with a refractory binder, such as a known binder such as alumina cement, hydraulic alumina, phosphate, silicate, silica sol, or resin, to bind them together. The amount of this refractory binder used is similar to that used in conventional monolithic refractory materials, and is generally used in a proportion of about 1 to 30% by mass of the monolithic refractory material.

[0037] Incidentally, the monolithic refractories according to the present invention can exhibit an excellent penetration inhibitory effect on molten aluminum without using conventional penetration inhibitors. However, by using such a penetration inhibitor in combination, it is possible to further improve the penetration inhibitory effect on molten aluminum. There are no particular restrictions on the penetration inhibitor, and it is possible to use the same ones as in the past. This is because the melting point of aluminum is about 660°C, and the operating temperature of an aluminum melting furnace is at most about 1000°C. Therefore, corundum and spinel, which constitute the main refractory raw materials of the monolithic refractories according to the present invention, are stable against penetration inhibitors such as calcium fluoride, aluminum borate, barium sulfate, and zircon, and their respective effects are not impaired. The amount of such penetration inhibitor used is the same as in the past, for example, in a proportion of about 1 to 20% by mass of the monolithic refractories.

[0038] Furthermore, while the addition of a dispersant to the monolithic refractory according to the present invention is not mandatory but optional, if one is added, known dispersants such as sodium phosphate, polycarboxylic acid, and polyacrylic acid can be appropriately selected. In addition, it goes without saying that various known additives can be blended in as needed to improve the properties of the monolithic refractory.

[0039] As described above, the amorphous refractory for molten aluminum according to the present invention contains a refractory main raw material and a refractory binder having the specific chemical composition described above as essential components, and is further composed of various known additives such as penetration inhibitors and dispersants as needed. The content ratio of such refractory main raw material in the amorphous refractory is appropriately selected within a range that can achieve the objectives of the present invention, but is generally set to be within the range of 75 to 99% by mass. This is because if the content ratio of the refractory main raw material in the amorphous refractory becomes too low, it becomes difficult to use it as an amorphous refractory, and problems such as difficulty in effectively exhibiting the features of the present invention tend to occur. [Examples]

[0040] The present invention will be further clarified below by showing several embodiments and comparing them with comparative examples. However, it goes without saying that the present invention is not limited in any way by the descriptions of such embodiments and comparative examples. Furthermore, it should be understood that, in addition to the embodiments below and the above specific descriptions, various changes, modifications, and improvements can be made to the present invention based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention.

[0041] First, various refractory raw materials (ceramic particles) shown in Table 1 below were prepared as the main refractory raw materials for amorphous refractories. Crushed particles A and B were produced by adding a predetermined amount of magnesium component (magnesium oxide) and a binder to calcined alumina, kneading the mixture, granulating it into pellets, drying the resulting granules, firing them at a temperature of 1700°C or higher to form a sintered body, and then mechanically crushing the sintered body.

[0042] Furthermore, round particles A, B, C, and D are each obtained by calcination in the same manner as the crushed particles A and B described above. Among these, round particles B and C are produced by granulating the same raw materials as crushed particles A or B into a round or spherical shape, drying the resulting round / spherical granules, and then rotating and calcining them in a rotary kiln. Round particles A and D are produced by granulating the same raw materials as crushed particles A into a pellet shape, drying the resulting granules, mechanically crushing them, and then rotating and calcining the resulting crushed material in a rotary kiln.

[0043] These crushed and round particles are then sized and used as refractory raw materials of their respective particle sizes. To clarify the particle shapes of the obtained round particles A and B, and the crushed particle A, micrographs of them are shown in Figures 1, 2, and 3, respectively. The tabular alumina prepared as a refractory raw material is a commercially available sintered alumina material, and commercially available electrofused alumina is used, but all of these are crushed particles.

[0044] For each refractory raw material, its main mineral phase was identified using an X-ray diffractometer, while the content ratios of Al2O3, MgO, and SiO2 were measured using an X-ray fluorescence analyzer. Furthermore, the apparent porosity was measured in accordance with JIS-R-2205. In addition, the circularity of the refractory raw materials used was calculated using the area and circumference of individual particles from particle photographs taken with an optical microscope for particles with a particle size of 1 mm to 0.5 mm, according to the calculation formula shown in the main text. The average value of 50 randomly sampled particles was then calculated and defined as the circularity (1-0.5 mm particles). These measurement results are shown in Table 1 below. Note that SiO2 in the chemical composition is one of the other components besides Al2O3 and MgO. Of course, it goes without saying that such other components include not only SiO2 but also other impurity components.

[0045] [Table 1]

[0046] Next, using the various refractory raw materials prepared in this manner, various amorphous refractories shown in Tables 2 and 3 below were prepared in various particle size compositions. Specifically, in Examples 1 to 4, crushed particle material A with an MgO content of 0.08 mass% was used as the main refractory raw material, along with round particle A with a circularity of 0.84 and a similar MgO content. In Example 5, crushed particle material A with an MgO content of 0.08 mass% was used as the main refractory raw material, along with round particle D with a circularity of 0.73 and a similar MgO content. Furthermore, in Examples 6 and 7, round particle B with a circularity of 0.88 and a similar MgO content, close to spherical, was used along with crushed particle material A. In Example 8, crushed particle material B with an MgO content of 25.7 mass% was used along with round particle C with a circularity of 0.86 and a similar MgO content. In these examples, round particles A to D are used in the medium-sized portion (3-1 mm) and the fine-sized portion (1 mm-45 μm), respectively, to form a mixed powder that constitutes the main raw material for refractories. In Table 2, the symbols A, B, I, Ro, Ha, and Ni in parentheses to the right of the numbers for each particle size of the main raw material indicate the crushed particles or round particles used for each particle size.

[0047] On the other hand, in Comparative Examples 1 and 2, only crushed particles A or B were used as the main raw material for the refractory material, respectively. In Comparative Examples 3 and 4, only tabular alumina (sintered alumina) material or commercially available electrofused alumina material containing almost no MgO (Tr) was used as the main raw material for the refractory material. The mixing ratios of the coarse grain portion (5-3 mm), the medium grain portion (3-1 mm), the fine grain portion (1 mm-45 μm), and the fine powder portion (-45 μm) were all adjusted to a ratio of 10:20:30:25, similar to the example.

[0048] Incidentally, the refractory main raw materials prepared in the examples and comparative examples have a particle size composition consisting of a coarse particle portion of 5-3 mm, a medium particle portion of 3-1 mm, a fine particle portion of 1 mm-45 μm, and a fine powder portion of -45 μm, as shown in Tables 2 and 3 below. In this context, the coarse particle size of "5-3 mm" means that, in the classification of ceramic particles, the particles are large enough to pass through a 5 mm mesh but not a 3 mm mesh. Similarly, the medium particle size of "3-1 mm" means that the particles pass through a 3 mm mesh but not a 1 mm mesh, the fine particle size of "1 mm-45 μm" means that the particles pass through a 1 mm mesh but not a 45 μm mesh, and the fine powder of "-45 μm" means that the particles are large enough to pass through a 45 μm mesh.

[0049] Furthermore, each of the amorphous refractories related to the examples and comparative examples shown in Tables 2 and 3 below contains, in addition to the main raw material, commercially available calcined alumina, high-alumina cement as a hardening agent (refractory binder), and a dispersant (sodium phosphate), each in the proportions shown in the table below.

[0050] Furthermore, in evaluating all the compound compositions of the monolithic refractories used in the examples and comparative examples, test specimens were prepared assuming similar workability. Specifically, as an indicator of workability, the amount of added water was adjusted so that the tap flow was approximately 160-170 mm, the mixing time was 5 minutes, and the casting process was completed within 10 minutes. The flow value was measured in accordance with JIS-R-2521, and the free flow value was defined as the average of the diameter of the maximum diameter and its perpendicular direction 1 minute after removing the flow cone. Immediately after measuring this free flow value, the tap flow value was measured as the average of the diameter of the maximum diameter and its perpendicular direction after dropping the flow stand 10 times over approximately 30 seconds. Two types of test specimens were prepared: a rectangular parallelepiped shape for physical property / strength testing and a crucible shape for erosion testing. Specifically, the rectangular prism shape was made with dimensions of 40mm x 40mm x 160mm, while the crucible shape had dimensions of 85mm outer diameter, 65mm upper inner diameter, 60mm bottom inner diameter, 60mm height, and 10mm bottom thickness. Furthermore, each test specimen was prepared by casting each amorphous refractory material into a mold of the respective shape with vibrations of approximately 3G, curing at room temperature for 24 hours, removing the mold, and then drying in a 110°C dryer for another 24 hours. After that, the rectangular prism samples were fired at a temperature of 850°C for 72 hours.

[0051] For each amorphous refractory in the examples and comparative examples, the fluidity was evaluated by comprehensively considering the added water and tap flow values. The one with the highest fluidity was evaluated as "++++", and as the fluidity decreased, it was evaluated as "+++", "++", and "+". Specifically, the added moisture content was categorized into less than 6%, 6-7%, and 7% or more, and the tap flow value was categorized into less than 150 mm, 150-160 mm, 160-170 mm, and 170 mm or more. Then, the added moisture content was less than 6% and the tap flow value was 160-170 mm, which was categorized as "++++", the added moisture content was less than 6% and the tap flow value was 150-160 mm, or the added moisture content was 6-7% and the tap flow value was 160-170 mm and 170 mm or more, which was categorized as "++", the added moisture content was 6-7% and the tap flow value was 150-160 mm, or the added moisture content was 7% or more and the tap flow value was 160-170 mm and 170 mm or more, which was categorized as "++", and the added moisture content was 7% or more and the tap flow value was 150-160 mm, or the tap flow value was less than 150 mm, which was categorized as "+". In this case, the "+" category was judged to be poor flowability.

[0052] Furthermore, the bulk density and apparent porosity were measured using rectangular parallelepiped samples fired at 850°C, in accordance with JIS-R-2205, and the compressive strength was measured using the same rectangular parallelepiped samples fired at 850°C, in accordance with JIS-R-2553.

[0053] Furthermore, the penetration resistance was evaluated using a crucible erosion test with molten aluminum. Specifically, molten aluminum alloy (AC2B) was poured into a dry crucible-shaped sample (molded body), held in an electric furnace at 850°C for 72 hours, then allowed to cool naturally. After being cut in half lengthwise with a diamond cutter, the penetration of the aluminum alloy into the cross-section and the adhesion between the aluminum alloy and the crucible sample were observed and evaluated. The highest penetration resistance was assigned a rating of "++++", and as the penetration resistance decreased, it was assigned "+++", "++", and "+". More specifically, a sample was evaluated as "++++" if no penetration of the aluminum alloy was observed in the divided cross-section of the crucible-shaped sample, the crucible-shaped sample and the aluminum alloy could be easily separated without applying any particular force, and no traces of penetration or blackened oxide film were observed on the contact surface between the crucible-shaped sample and the aluminum alloy after separation, especially on the crucible-shaped sample side. Furthermore, if no penetration of the aluminum alloy was observed in the cross-section, and the crucible-shaped sample and the aluminum alloy could be easily separated without applying any particular force, but a trace of penetration of several mm or the adhesion of a blackened oxide film was observed on the contact surface between the crucible-shaped sample and the aluminum alloy after separation, particularly on the crucible-shaped sample side, it was evaluated as "+++". If the aluminum alloy had partially penetrated into the divided cross-section of the crucible-shaped sample, making separation of the crucible-shaped sample and the aluminum alloy difficult, it was evaluated as "++". In addition, if penetration of the aluminum alloy was confirmed to the divided cross-section and even the back surface of the crucible-shaped sample, and the formation of a ghost-like substance was observed on the top of the crucible-shaped sample, it was evaluated as "+". Here, the "++" and "+" classifications were judged as poor penetration resistance.

[0054] The free flow value, tap flow value, fluidity, bulk density, apparent porosity, compressive strength, and permeability resistance of various amorphous refractories shown in the examples and comparative examples were evaluated according to the measurement or evaluation methods described above. The results are shown in Tables 2 and 3 below.

[0055] [Table 2]

[0056] [Table 3]

[0057] As is clear from the comparison of the results in Tables 2 and 3, Examples 1 to 8 employ refractory formulations using ceramic aggregate made from sintered products produced by a similar manufacturing method. In these examples, round or spherical particles having the chemical composition defined in the present invention are used, resulting in improved fluidity and a tendency for the required amount of added water to decrease. The circularity of round particles A, C, and D used in these examples was 0.84, 0.86, and 0.73, respectively, while the round particle B, which is considered a spherical particle, had a circularity of 0.88. Micrographs of round particles A and B used in these examples are shown in Figures 1 and 2. Of these, round particle A shown in Figure 1 differs from the spherical round particle shown in Figure 2 in that it is somewhat flattened and has a large aspect ratio, exhibiting a somewhat distorted particle size. In addition, the addition of any of the round particles A, B, C, and D improved fluidity, and improvements in moisture content and densification properties were confirmed. For example, in the sample of Example 2, in which the particles with a particle size of 1 mm-45 μm in the formulation were replaced with round particle A, the required amount of added water decreased from 6.2% to 5.5%, a relative decrease of 11%, even though the chemical composition and particle size composition of the formulation were the same as in Comparative Example 1. Furthermore, a reduction in oxide film adhesion was confirmed in terms of resistance to penetration, indicating superior properties in terms of fluidity and resistance to penetration, while also having equivalent properties such as compressive strength.

[0058] In Example 4, the entire amount of crushed particles A (3-1 mm and 1 mm-45 μm) and slightly more than half of the -45 μm particles were replaced with round particles A (3-1 mm and 1 mm-45 μm), increasing the proportion of round particles in the main raw material formulation to approximately 76%. This resulted in the highest fluidity among the examples, and the required amount of added water decreased from 6.2% to 4.4% compared to Comparative Example 1, a relative decrease of 29%. Furthermore, in Examples 6 and 7, which used round particles B (spherical particles with higher circularity), an improvement in fluidity, lower moisture content, and densification tended to occur with increasing usage ratio. Moreover, in Example 8, which used round particles C (spinel phase), a similar reduction in moisture content and densification effect can be confirmed even with round particles of the spinel phase, which is a different mineral phase from the corundum phase in round particles A, B, and D.

[0059] Furthermore, among Examples 1 to 8, Example 8, which used crushed particles B and round particles C with a high MgO content, demonstrated remarkably excellent resistance to penetration. Examples 1 to 7, which used crushed particles A and round particles I, II, and D with a low MgO content, also exhibited sufficient resistance to penetration. However, in Comparative Examples 3 and 4, which used corundum-based tabular alumina and electrofused alumina containing almost no MgO, it was observed that the molten aluminum reached the back of the crucible-shaped sample in a penetration test lasting only 72 hours. From this, it can be seen that the resistance to penetration by molten aluminum varies greatly depending on the presence or absence of MgO in the main raw material of the refractory.

[0060] In contrast, Comparative Examples 1 to 4 all use crushed particles as the main raw material for refractories, and therefore require a larger amount of added water compared to the refractory raw material formulations used in Examples 1 to 8, resulting in insufficient fluidity. Furthermore, the crushed particles A and B used in Comparative Examples 1 and 2, unlike the tabular alumina and electrofused alumina used in Comparative Examples 3 and 4, contain a predetermined amount of MgO, and thus their resistance to penetration by molten aluminum is improved. In addition, a micrograph of crushed particle A is shown in Figure 3, where it is clearly revealed that the particle has a fractured surface and an angular shape with sharp corners.

[0061] Furthermore, the characteristics of the penetration resistance of the monolithic refractories according to the present invention can be advantageously improved by using a penetration inhibitor in combination. The results of Examples 9 to 11 and Comparative Examples 5 to 7 shown in Table 4 below are based on the compound composition of the monolithic refractories in Example 1 and Comparative Example 1, respectively, and clarify the evaluation of refractories when barium sulfate (BaSO4) is added externally at a concentration of 2 to 10% as a penetration inhibitor.

[0062] [Table 4]

[0063] As is clear from the results in Table 4, in Examples 9 to 11, the further addition of the penetration inhibitor (barium sulfate) improved the resistance to penetration of molten aluminum alloy compared to the results of Example 1 in Table 2. Furthermore, the resistance to penetration improved with increasing amounts of the penetration inhibitor, and excellent resistance to penetration was obtained with an addition of 5% or more. Moreover, Examples 9 to 11, which used round particles A with a particle size of 1 mm to 45 μm, showed higher resistance to penetration compared to Comparative Examples 5 to 8, which used only crushed particles A, even with the same amount of penetration inhibitor added. This also suggests that by mixing round particles as aggregate in monolithic refractories, monolithic refractories with superior resistance to penetration can be obtained with less penetration inhibitor.

[0064] Furthermore, the evaluation results for the amorphous refractories obtained by changing the amount of dispersant used in Example 3 and Comparative Example 1 from 0.1% externally to 0.05% externally are shown in Table 5 below as Example 12 and Comparative Example 8, respectively. Table 5 also shows the evaluation results for the refractories of Example 3 and Comparative Example 1.

[0065] [Table 5]

[0066] As is clear from the results in Table 5, even when the amount of dispersant used is reduced by half, it is possible to prepare an amorphous refractory material with excellent properties in terms of both fluidity and penetration resistance, as shown in the results of Example 12. In contrast, in the case of an amorphous refractory material that does not contain round particles according to the present invention, it was found that reducing the amount of dispersant resulted in a significant deterioration of fluidity, as shown in the results of Comparative Example 8, making it unsuitable for practical use.

Claims

1. An amorphous refractory material for forming a fire-resistant surface that comes into contact with molten aluminum, comprising at least a refractory main material and a refractory binder, The main raw material of the refractory is composed of dense ceramic powder granules having an apparent porosity of 7% or less, and Al 2 O 3 An amorphous refractory for molten aluminum, characterized in that it has a chemical composition consisting of 65% by mass or more of , 0.06 to 35% by mass of MgO, and 5% by mass or less of other components, and the main raw material of the refractory contains 10 to 80% by mass of round particles having the above chemical composition and a circularity of 0.70 or more, which have a round shape without corners.

2. The amorphous refractory for molten aluminum according to claim 1, characterized in that the round particles are mainly composed of particles with a particle size of 3-1 mm and / or particles with a particle size of 1 mm-45 μm.

3. The amorphous refractory for molten aluminum according to claim 1, characterized in that the main raw material of the refractory contains particles with a particle size of less than 1 mm having the chemical composition in a proportion of 40 to 95% by mass.

4. The amorphous refractory for molten aluminum according to claim 1, characterized in that the round particles are sintered particles having a rounded shape without corners, obtained by firing a granule or crushed material that gives the chemical composition.

5. The amorphous refractory for molten aluminum according to claim 1, characterized in that the main raw material of the refractory is composed of a mixture of round particles and crushed particles of a sintered body having the chemical composition.

6. The amorphous refractory for molten aluminum according to claim 1, characterized in that the aforementioned refractory main raw material is contained in a proportion of 75 to 99% by mass.

7. The amorphous refractory material for molten aluminum according to claim 1, characterized in that the refractory binder is alumina cement.

8. An amorphous refractory for molten aluminum according to any one of claims 1 to 7, characterized in that it further contains a penetration inhibitor.

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