Monomorphic fire-resistant composition and fire-resistant slurry, and fire-resistant film-forming product on which a fire-resistant coating is formed.

Abstract

The present invention provides an amorphous fire-resistant composition and fire-resistant slurry that can be used to form a fire-resistant coating on an object to be protected, as well as a fire-resistant film-formed object on which a fire-resistant coating has been formed. [Solution] A granular amorphous refractory composition mainly composed of refractory granules made of granular magnesia, alumina, silica, and manganese oxide, wherein the refractory granules contain 2% to 15% by mass of magnesia, 5% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

Description

Technical Field

[0001] The present invention relates to an amorphous refractory composition and a refractory slurry used for forming a refractory coating film on an object to be protected, and a refractory film formation in which a refractory coating film is formed on the object to be protected.

Background Art

[0002] Amorphous refractories are in great demand and widely used in steelworks etc. because they are superior to shaped refractories in terms of workability and ease of deformation. Conventionally, as amorphous refractories, alumina-spinel-based, magnesia-based, or those containing graphite have been mainly used. Each component constituting the refractory has its own characteristics. For example, alumina is excellent in heat resistance and molten steel resistance, and magnesia also has high molten steel resistance. On the other hand, graphite has poor molten steel resistance, but can impart slag penetration resistance and thermal shock resistance to the refractory. In addition, in order to complement the drawbacks of each component, a plurality of components are often combined.

[0003] An amorphous refractory containing magnesia and alumina generates spinel by firing, which causes densification of the structure and improves corrosion resistance. However, if spinel is excessively generated, the amorphous refractory is likely to crack, and when a layer using the amorphous refractory is formed on the surface of the object to be protected, the layer is likely to peel off from the object to be protected.

[0004] As a method for suppressing this, there is a method of combining alumina, which is large particles with a maximum particle size of about 3 to 5 mm, with fine particles of magnesia or alumina. By mixing large particles with fine particles, it becomes possible to reduce the firing shrinkage spinel and suppress the shrinkage due to firing. Furthermore, by forming a structure in which large particles and fine particles are mixed, the progress of cracks can be prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] While the aforementioned refractory materials have various drawbacks, technologies to overcome these drawbacks are disclosed, for example, in Patent Documents 1 to 4. Graphite-containing refractories have a problem in that, when exposed to high-temperature environments, the carbon inside gradually oxidizes and is emitted as carbon monoxide and carbon dioxide, leading to a decrease in their physical properties. To address this problem, a method of suppressing oxidation by applying a glass coating to the surface of the graphite-containing refractories is disclosed in Patent Document 3. However, carbon has poor wettability, making it difficult to apply a glass coating to graphite-containing refractories, but the addition of metal oxides is effective in this regard (see Patent Documents 1 and 2).

[0007] Furthermore, while magnesia-based refractories have excellent resistance to molten steel, if low-viscosity slag penetrates deep into the refractory and solidifies, it can cause structural spalling, leading to the refractory layer peeling away from the protected object. This is due to the large difference in thermal expansion coefficients between slag and magnesia. As a method to reduce the penetration of slag into magnesia-based refractories, a method of adding manganese oxide is disclosed, for example, in Patent Documents 3 and 4.

[0008] However, the conventional methods disclosed in Patent Documents 3 and 4 contain relatively large particle sizes of refractory granules, which means that when attempting to form a refractory layer on the surface of an object to be protected, there are limitations on the work area for forming the refractory layer, and the refractory layer becomes thick.

[0009] The present invention has been made in view of these circumstances, and aims to provide an amorphous fire-resistant composition and a fire-resistant slurry that can be used to form a fire-resistant coating on an object to be protected, as well as a fire-resistant film-forming product on which a fire-resistant coating has been formed on an object to be protected. [Means for solving the problem]

[0010] The first monolithic refractory composition according to the above-mentioned objective is a granular monolithic refractory composition mainly composed of refractory granules made of granular magnesia, alumina, silica, and manganese oxide, wherein the refractory granules contain 2% to 15% by mass of magnesia, 5% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

[0011] The second invention, which is in line with the above objective, is a refractory slurry obtained by mixing a granular amorphous refractory composition mainly composed of refractory granules made of granular magnesia, alumina, silica, and manganese oxide with a mixed liquid, wherein the refractory granules contain 2% to 15% by mass of magnesia, 5% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

[0012] A third invention relating to the above-mentioned objective is a refractory film-forming object having a refractory coating film formed on its surface and a refractory film-forming object having the refractory coating film, wherein the refractory coating film is made of a refractory slurry obtained by mixing a granular amorphous refractory composition mainly composed of refractory granular materials composed of granular magnesia, alumina, silica, and manganese oxide with a mixed liquid, wherein the refractory granular materials contain 2% to 15% by mass of magnesia, 5% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide. [Effects of the Invention]

[0013] Since the amorphous fire-resistant composition according to the first invention is granular, it can be used as a material for forming a coating on the surface of an object to be protected. Furthermore, the main component of this amorphous refractory composition, the refractory granules, contains 2% to 15% by mass of magnesia, 5% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide. In this regard, the inventors of the present invention have confirmed through verification that even when an amorphous refractory composition with small particle sizes (for example, an average particle size of 3 mm or less) is used, the coating film formed using that amorphous refractory composition stably exhibits refractory properties.

[0014] Therefore, this amorphous fire-resistant composition is usable (suitable) for forming fire-resistant coatings on objects to be protected. The same applies to the fire-resistant slurry according to the second invention. Furthermore, the fire-resistant film-forming product according to the third invention is one in which the fire-resistant coating is formed on the surface of the object to be protected. [Brief explanation of the drawing]

[0015] [Figure 1] (A), (B), and (C) are photographs of test specimens taken from molten steel, respectively. [Modes for carrying out the invention]

[0016] Next, embodiments of the present invention will be described to facilitate understanding of the present invention. An amorphous refractory composition according to one embodiment of the present invention is a granular composition mainly composed of refractory granules (refractory microparticles) made up of granular (fine) magnesia, alumina, silica, and manganese oxide, respectively. A detailed description follows below.

[0017] In this embodiment, the monolithic refractory composition contains 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more, of refractory granular material, with the monolithic refractory composition being 100% by mass. The refractory granular material contains magnesia in an amount of 2% to 15% by mass, alumina in an amount of 5% to 25% by mass, silica in an amount of 60% to 80% by mass, and manganese oxide in an amount of 2% to 15% by mass, with the refractory granular material being 100% by mass.

[0018] The unshaped refractory composition can be produced by mixing granular magnesia raw material, granular alumina raw material, granular silica raw material, granular manganese oxide raw material, and other granular materials. The other granular materials may be omitted. That is, the unshaped refractory composition can be composed of only the granular magnesia raw material, granular alumina raw material, granular silica raw material, and granular manganese oxide raw material.

[0019] The mixing amounts of the magnesia raw material, alumina raw material, silica raw material, and manganese oxide raw material are adjusted according to the purity of each of the magnesia raw material, alumina raw material, silica raw material, and manganese oxide raw material. That is, the amounts of the respective raw materials are adjusted so as to satisfy the mass ratios of magnesia, alumina, silica, and manganese oxide in the refractory granular material described above.

[0020] The unshaped refractory composition can be used as a refractory slurry in which the unshaped refractory composition and a mixed liquid are mixed. The refractory slurry can be produced by mixing granular magnesia raw material, granular alumina raw material, granular silica raw material, granular manganese oxide raw material, other granular materials, and a mixed liquid. Needless to say, the refractory slurry can also be produced by adding and mixing the remaining substances to a mixture of some of the granular magnesia raw material, granular alumina raw material, granular silica raw material, granular manganese oxide raw material, other granular materials, and the mixed liquid.

[0021] In the refractory slurry, the mixed liquid mixed with the unshaped refractory composition is water, an aqueous dispersion, or the like. In this embodiment, the ratio of the mixed liquid to 100 parts by mass of the unshaped refractory composition is 10 parts by mass to 30 parts by mass. As long as a refractory coating film can be formed by applying the refractory slurry to the object to be protected, the ratio of the mixed liquid to the unshaped refractory composition is not limited to this range.

[0022] The fire-resistant slurry is applied to the surface of the object to be protected, forming a fire-resistant coating (fire-resistant layer) on the surface of the object. The fire-resistant slurry can be applied to the surface of the object to be protected by known coatings, such as spraying with an air sprayer or airless sprayer, or by coating with a brush, spatula, or roller.

[0023] From the viewpoint of workability in the process of applying the refractory slurry to the surface of the object to be protected, in this embodiment, the average particle size of the monolithic refractory composition is 3 mm or less. From the same viewpoint, the average particle size of the monolithic refractory composition is preferably 1 mm or less, and more preferably 800 μm or less. The average particle size here refers to the value calculated using a sieve specified in JIS-Z8801. Specifically, it is the value calculated by the following procedure.

[0024] For monolithic refractory compositions, a sieving process (vibration for 5 minutes) is performed using sieves with nominal mesh openings of 2800, 2000, 1400, 1000, 710, 500, 355, 250, 180, 125, 90, 63, and 45 μm as specified in JIS-Z8801, so that the monolithic refractory composition passes through the sieves in order from the largest mesh opening. Next, the mass of the monolithic refractory composition remaining in each sieve (that did not pass through the sieve) is measured (hereinafter referred to as the section mass), and the average particle size is calculated using the following formula 1.

[0025] (Average particle size)=Σwidi / Σwi...Equation 1

[0026] However, in Equation 1, wi is the segment mass and di is the segment representative diameter of the segment in question. For example, the representative diameter of the section of the amorphous refractory composition remaining on a 180 μm sieve is 215 μm = (250 + 180) / 2 μm. The above-described method for calculating the average particle size assumes that all amorphous refractory composition passes through a sieve with a nominal mesh size of 4000 μm, which is larger than the sieve with the largest mesh size of 2800 μm. If any amorphous refractory composition remains in the sieve with a nominal mesh size of 4000 μm, an additional sieve with an even larger nominal mesh size will be used to determine the average particle size.

[0027] There are no particular limitations on the shape of each component of an amorphous refractory composition (the same applies to refractory granular materials). For example, one or more of the components may be fibrous, or they may have a shape that cannot be defined as either fibrous or granular. Furthermore, in this embodiment, the objects to be protected are various sensors and components used by being immersed in molten steel, but this is not limited to these. For example, various sensors and components installed in locations where molten steel or other high-temperature objects may be scattered can be treated as objects to be protected.

[0028] By using the aforementioned mass ratios of magnesia, alumina, silica, and manganese oxide in refractory granules, a refractory slurry produced using an amorphous refractory composition with a small average particle size (e.g., an average particle size of 3 mm or less) can function as a refractory coating that stably protects the object being protected from high temperatures. This is based on facts verified through numerous experiments.

[0029] From various verifications conducted by the inventors, it was found that, from the viewpoint of the refractory slurry stably protecting the object to be protected from high-temperature materials, the proportion of magnesia to the total refractory granules is preferably 3% by mass or more (more preferably 5% by mass or more), the proportion of alumina to the total refractory granules is preferably 20% by mass or less (more preferably 15% by mass or less). Furthermore, the proportion of silica to the total refractory granules is preferably 70% by mass or more, and the proportion of manganese oxide to the total refractory granules is preferably 3% by mass or more and 9% by mass or less.

[0030] Next, we will individually explain the components of the refractory granules: magnesia, alumina, silica, and manganese oxide.

[0031] (Magnesia) In this embodiment, there are no particular restrictions on the magnesia. Commercially available electrofused magnesia, sintered magnesia, seawater magnesia, natural magnesia, etc., can be used as the magnesia. The reasons why the amorphous refractory composition contains magnesia, and why the proportion of magnesia to the total refractory granules is limited to a range of 2% by mass or more and 15% by mass or less, are as follows.

[0032] This is because, when a protected object coated with the relevant amorphous refractory composition is immersed in molten steel, the reaction between magnesia and alumina generates spinel, which densifies the refractory slurry (refractory coating) and improves the molten steel resistance of the refractory slurry. If the proportion of magnesia to the total refractory granules is less than 2% by mass, densification will be insufficient, and the molten steel resistance to molten steel and slag will decrease.

[0033] On the other hand, if the proportion exceeds 15% by mass, when the object to be protected coated with refractory slurry is immersed in molten steel or slag, excessive spinel is generated by the reaction of magnesia and alumina, causing cracks in the refractory slurry. This leads to significant peeling of the refractory slurry from the object to be protected. Therefore, if the proportion of magnesia to the total refractory granules exceeds 15% by mass, it leads to a decrease in the molten steel resistance and durability (the property of the refractory coating to be maintained for a long period of time in molten steel or slag, hereinafter the same) of the refractory slurry.

[0034] (alumina) In this embodiment, there are no particular restrictions on the alumina. For example, calcined alumina, electrofused alumina, sintered alumina, bauxite, shale, etc. can be used as alumina. The reason for limiting the proportion of alumina to the total refractory granules to a range of 5% by mass or more and 25% by mass or less is as follows:

[0035] If the proportion of alumina to the total refractory granules is less than 5% by mass, the amount of spinel formed decreases, resulting in reduced resistance to molten steel and reduced durability. In other words, maintaining a proportion of alumina to the total refractory granules at 5% by mass or more, in conjunction with maintaining a proportion of magnesia to the total refractory granules in the range of 2% to 15% by mass, enables the formation of an appropriate amount of spinel to ensure the resistance to molten steel and durability of the refractory slurry. On the other hand, if the proportion exceeds 25% by mass, the relative amounts of magnesia and silica decrease, which in turn reduces the resistance to melting and durability of the steel.

[0036] (silica) In this embodiment, silica not only improves resistance to molten steel, but also allows the refractory coating itself to become a uniform and dense film through vitrification. By bringing the refractory coating into contact with high-temperature materials such as molten steel together with the object to be protected, the silica melts into glass through sintering, softens, and also plays a role in absorbing expansion.

[0037] In this embodiment, there are no particular limitations on the type of silica that can be used, but it is preferable to use crystalline silica. The reason for setting the silica content of the refractory granules within the range of 60% to 80% by mass is as follows: If the content is less than 60% by mass, the vitrification of silica does not progress easily, reducing the resistance to molten steel and durability. Similarly, if the content exceeds 80% by mass, vitrification does not occur easily, and the refractory coating becomes brittle.

[0038] (Manganese oxide) In this embodiment, there are no particular limitations on the manganese oxide that can be used; any form of manganese oxide, such as MnO, Mn3O4, Mn2O3, MnO2, etc., can be employed. The added manganese oxide is partially absorbed into the magnesia when the refractory coating is immersed in molten steel or slag, resulting in the absorption of Mg into the magnesia. x Mn 1―x It can either dissolve as oxygen or combine to form Mg2MnO4, contributing to the sintering of refractory granular materials.

[0039] Furthermore, the remainder exists in the matrix as Mn3O4 and other manganese oxides. Because the slag reacts little with the magnesia-based material, it tends to penetrate into the refractory coating. However, when this happens, the Mn3O4 and other manganese oxides present in the matrix dissolve into the slag penetrating the refractory coating, increasing its viscosity and preventing further penetration of the slag into the coating. In addition, manganese reacts with the slag components and other refractory granular materials to clog pores, densifying the refractory coating and helping to prevent slag penetration.

[0040] In this embodiment, the ratio of manganese oxide to the total refractory granules is set to a range of 2% by mass or more and 15% by mass or less for the following reasons. If the ratio is less than 2% by mass, the refractory effect of the refractory coating decreases. On the other hand, if the ratio exceeds 15% by mass, the durability of the refractory coating decreases and it becomes more prone to peeling off the protected object, which is undesirable.

[0041] Furthermore, amorphous refractory compositions may contain materials other than refractory granules (other granular materials as described above). These materials include, for example, additives that promote the hardening of refractory granules and prevent the refractory coating from peeling off the protected object, and additives that prevent cracks from forming in the refractory coating when it hardens. Specifically, additives that promote hardening include hydroxides such as calcium hydroxide, sodium hydroxide, and potassium hydroxide; alkali aluminates such as sodium aluminate, potassium aluminate, and calcium aluminate; alkali silicates such as sodium silicate, potassium silicate, and lithium silicate; and inorganic salts such as carbonates, phosphoric acid, phosphates, nitric acid, nitrates, hydrochloric acid, and chlorides. For crack prevention, inorganic fibers such as alumina fibers, or organic fibers such as carbon fibers and cellulose can be used.

[0042] From the above explanation, the refractory slurry obtained by mixing a granular amorphous refractory composition containing refractory granules with a mixed liquid has the following proportions relative to the refractory granules: magnesia 2% to 15% by mass, alumina 5% to 25% by mass, silica 60% to 80% by mass, and manganese oxide 2% to 15% by mass.

[0043] Furthermore, a protected object with a fire-resistant coating formed on its surface and an object having such a fire-resistant coating are defined as a fire-resistant film-forming object. This fire-resistant film-forming object consists of a fire-resistant slurry obtained by mixing a granular amorphous fire-resistant composition containing fire-resistant granules with a mixed liquid, and the proportions of magnesia, alumina, silica, and manganese oxide relative to the fire-resistant granules are as described above. Furthermore, by setting the average thickness of the fire-resistant coating to 3 mm or less, the range of objects that can be protected with the fire-resistant coating is broadened. In other words, a fire-resistant coating can be applied to a wide variety of objects. [Examples]

[0044] Next, we will describe the experiments conducted to confirm the effects of the present invention. First, granular materials (granular magnesia raw material, alumina raw material, silica raw material, and manganese oxide raw material, respectively) were mixed to prepare several amorphous refractory compositions with different component compositions. The following products were used as the magnesia raw material, alumina raw material, silica raw material, and manganese oxide raw material. Magnesia raw material: Magnesium oxide, manufactured by Kanto Chemical Co., Ltd., 25018-01 Alumina raw material: Aluminum oxide (α-type) manufactured by Kanto Chemical Co., Ltd. 01173-01 Silica raw material: Silicon dioxide (quartz type) manufactured by Kanto Chemical Co., Ltd. 37974-00 Manganese oxide raw material: Manganese(IV) oxide 25063-01, manufactured by Kanto Chemical Co., Ltd.

[0045] Subsequently, water was added to each monolithic refractory composition and mixed until it became muddy, producing multiple refractory slurries. The average particle size of each component constituting the monolithic refractory composition (i.e., the average particle size of the granular monolithic refractory composition) was 1 mm or less. Next, for each refractory slurry, an alumina brick with a square cross-section (30 mm per side) and a length of 200 mm was prepared. The refractory slurry was then applied with a brush to a predetermined area including one end of the longitudinal direction of the corresponding alumina brick, forming a refractory coating with a thickness of approximately 3 mm in that area.

[0046] Subsequently, the alumina bricks with the refractory coating were subjected to a 300°C heat drying process for 5 hours to prepare test specimens. Then, after immersing most of each test specimen, including the area where the refractory coating was formed, in molten steel for 10 minutes, the test specimen was removed from the molten steel, and its appearance was visually observed to evaluate the refractory coating. The molten steel used was cast iron equivalent to FC250, melted in a high-frequency induction furnace, at a temperature of approximately 1520°C to 1560°C.

[0047] The evaluation was based on three levels: A, B, and C, as shown below. A: There are no cracks in the fire-resistant coating, and there is no peeling or leaching of the fire-resistant coating. B: There is only slight peeling or leaching of the fire-resistant coating. C: The entire or majority of the fire-resistant coating is peeling or leaching.

[0048] The evaluation results are shown in Tables 1, 2, and 3.

[0049] [Table 1]

[0050] [Table 2]

[0051] [Table 3]

[0052] Regarding the proportions of refractory granules and additives shown in Tables 1 to 3, the mass percentages for magnesia, alumina, silica, manganese oxide, and potassium carbonate each represent the proportion of each component relative to the sum of magnesia, alumina, silica, manganese oxide, and potassium carbonate, which is 100% by mass. In contrast, the mass percentages for alumina fibers and potassium silicate represent the external addition relative to the sum of magnesia, alumina, silica, manganese oxide, and potassium carbonate.

[0053] Furthermore, the appearance of the test specimens of Example 5, Example 3, and Comparative Example 5, which were removed from the molten steel, is shown in Figures 1(A), (B), and (C), respectively.

[0054] Although embodiments of the present invention have been described above, the present invention is not limited to the above-described forms, and any changes to the conditions, etc., that do not depart from the gist of the invention are all within the scope of application of the present invention. For example, the average particle size of the amorphous refractory composition may exceed 1 mm.

Claims

1. A granular amorphous refractory composition mainly composed of refractory granules made from granular magnesia, alumina, silica, and manganese oxide, respectively, The aforementioned refractory granular material is characterized by containing 2% to 15% by mass of magnesia, 10% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

2. The amorphous refractory composition according to claim 1, characterized in that the refractory granular material contains 70% by mass or more of silica.

3. The amorphous refractory composition according to claim 1, characterized in that the refractory granular material contains 3% by mass or more and 9% by mass or less of manganese oxide.

4. An amorphous refractory composition according to any one of claims 1 to 3, characterized in that the average particle size is 1 mm or less.

5. A refractory slurry is obtained by mixing a granular amorphous refractory composition, which mainly consists of refractory granules composed of granular magnesia, alumina, silica, and manganese oxide, with a mixed liquid. The refractory granular material is characterized by containing 2% to 15% by mass of magnesia, 10% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

6. A protected object having a fire-resistant coating formed on its surface, and a fire-resistant film-forming object having the said fire-resistant coating, The aforementioned fire-resistant coating consists of a fire-resistant slurry obtained by mixing a granular amorphous fire-resistant composition, which mainly comprises fire-resistant granules composed of granular magnesia, alumina, silica, and manganese oxide, with a mixed liquid. The refractory granular material is characterized by containing 2% to 15% by mass of magnesia, 10% to 25% by mass of alumina, 60% to 80% by mass of silica, and 2% to 15% by mass of manganese oxide.

7. The fire-resistant coating product according to claim 6, characterized in that the average thickness of the fire-resistant coating is 3 mm or less.

Images