Dry coating material for tundish

Abstract

The present invention provides a dry coating material for a tundish, the dry coating material being capable of improving the strength of a constructed body and reducing a problem of odor generation. That is, the present invention provides a dry coating material for a tundish, the dry coating material containing a total of 3-15 mass% of a first binder that is one or more kinds selected from inorganic hydrate powders having a thermal decomposition initiation temperature of 40-300°C, and a total of 0.1-10 mass% of a second binder that is one or more kinds selected from powdered alkali silicates other than hydrates, powdered alkali sulfates other than hydrates, and powdered alkali phosphates other than hydrates, the content of a phenolic resin being 0.5 mass% or less (including 0), and the remainder being mainly a refractory raw material.

Description

Dry coating material for tundishes

[0001] The present invention relates to a dry coating material for a tundish.

[0002] In continuous steel casting, the tundish plays a role in distributing molten steel, uniformly regulating the temperature, and floating up deoxidation products. The refractory lining of the tundish is usually coated with a thin refractory coating, primarily made from basic refractory materials such as magnesia and dolomite, to prevent contamination of the molten steel and protect the lining. This coating is typically applied by spraying or troweling with the addition of water.

[0003] After application, the coating material is heated and dried before use. However, the water added to the coating material cannot be completely removed even by drying, leading to hydrogen pickup caused by the water, which leads to a deterioration in the quality of steel products. Furthermore, when the remaining thickness of the coating material becomes small due to wear and tear, it is dismantled and new coating is applied, but dismantling takes a considerable amount of time and effort because the coating material has burned onto the refractory lining, reducing the operating rate of the tundish.

[0004] In recent years, therefore, application methods using dry coating materials have been proposed (e.g., Patent Documents 1 and 2). In this method, a core is placed in a tundish with a refractory lining, and a dry coating material containing refractory raw materials and a binder is poured between the refractory lining and the core. After filling, the dry coating material is heated from the inside of the core with a gas burner or the like to harden it. Unlike spraying or troweling, this application method using dry coating materials does not add water, thereby eliminating the problems of hydrogen pickup and seizure mentioned above.

[0005] JP 2006-7317 A JP 2013-39597 A

[0006] Conventional dry coating materials use thermoplastic resins as binders to harden through heating and drying. However, because the heat is applied from the inside through the core, and the dry coating material itself has insulating properties, the backside of the coating is less likely to receive sufficient heat. Furthermore, due to the operating rate of the tundish, the heating time is often insufficient. As a result, dry coating materials are unable to receive sufficient heat during the heating and drying process after application, resulting in insufficient strength. Unlike refractory linings, dry coating materials are typically thin, typically about 30 to 100 mm thick. If the coating's strength is insufficient, it is prone to collapse due to the impact it receives during transport from the tundish.

[0007] Furthermore, phenolic resins are commonly used as thermoplastic resins in dry coating materials. However, when the amount of phenolic resin used is large, the amount of residual carbon increases due to carbonization of the resin, which causes problems with molten steel contamination due to carbon pickup, thereby reducing the effectiveness of dry coating materials in preventing molten steel contamination. Furthermore, thermal decomposition of the phenolic resin during heating generates a strong odor, which is undesirable for the working environment.

[0008] Therefore, the problem to be solved by the present invention is to provide a dry coating material for a tundish that can improve the strength of the applied body and reduce the problem of odor generation.

[0009] According to one aspect of the present invention, there is provided the following dry coating material for a tundish: the dry coating material for a tundish contains a total of 3 to 15 mass% of a first binder which is one or more inorganic hydrate powders having a thermal decomposition onset temperature of 40 to 300°C, and a total of 0.1 to 10 mass% of a second binder which is one or more alkali silicates other than hydrates, powdered alkali sulfates other than hydrates, and powdered alkali phosphates other than hydrates, and the content of a phenolic resin is 0.5 mass% or less (including 0), with the remainder being primarily a refractory raw material.

[0010] Here, the thermal decomposition onset temperature refers to the temperature at which water of crystallization begins to be released by thermal decomposition of an inorganic hydrate, and is the temperature at which weight begins to decrease in a TG curve obtained by measurement using a thermogravimetric differential thermal analyzer (TG-DTA).

[0011] The dry coating material for a tundish of the present invention can improve the strength of the applied body and reduce the problem of odor generation.

[0012] One of the technical features of the dry coating material for tundishes of the present invention (hereinafter simply referred to as "dry coating material") is the use of a first binder, which is one or more types selected from inorganic hydrate powders having a thermal decomposition onset temperature of 40 to 300°C, in combination with a second binder, which is one or more types selected from powdered alkali silicates other than hydrates, powdered alkali sulfates other than hydrates, and powdered alkali phosphates other than hydrates. In other words, in the dry coating material of the present invention, the second binder, which is one or more types selected from powdered alkali silicates other than hydrates, powdered alkali sulfates other than hydrates, and powdered alkali phosphates other than hydrates, dissolves in the crystallization water released by the thermal decomposition of the first binder, which is one or more types selected from inorganic hydrate powders having a thermal decomposition onset temperature of 40 to 300°C, and hardens as dehydration and polymerization proceed. This improves the strength of the applied structure.

[0013] In the dry coating material of the present invention, the first binder is one or more inorganic hydrate powders having a thermal decomposition onset temperature of 40 to 300°C. With inorganic hydrates having a thermal decomposition onset temperature lower than 40°C, decomposition may begin in high-temperature environments, such as summer, potentially solidifying the material before application. On the other hand, with inorganic hydrates having a thermal decomposition onset temperature higher than 300°C, heating at high temperatures is required, raising concerns about deformation of the core. Furthermore, because the core temperature does not decrease in a short time, a long waiting time is required before the core can be removed, i.e., before the core can be removed from the frame. From the perspective of reducing waiting time, it is preferable that the thermal decomposition onset temperature of the inorganic hydrate used as the first binder is 40 to 200°C.

[0014] The inorganic hydrate used as the first binder in the dry coating material of the present invention is not particularly limited as long as it has a thermal decomposition initiation temperature of 40 to 300°C and acts as a binder. For example, silicates, phosphates, and sulfates that are commonly used as binders for monolithic refractories and have a thermal decomposition initiation temperature of 40 to 300°C can be used. Specific examples include Na ２ SiO ３ ・4H ２ O, Na ２ SiO ３ ・5H ２ O, Na ２ SiO ３ ・6H ２ O, Na ２ SiO ３ ・9H ２ O, Na ３ P.O. ４ ・12H ２ O, Na ３ P.O. ４ ・6H ２ O, Na ３ P.O. ４ ・7H ２ O, MgSO ４ ・7H ２ O, and K.H. ２ P.O. ４ ・3H ２ O.

[0015] In the dry coating material of the present invention, the content of the first binder is 3 to 15% by mass. If the content of the first binder is less than 3% by mass, the amount of crystal water released by thermal decomposition is insufficient, making it impossible to obtain sufficient strength of the applied body. On the other hand, if the content of the first binder is more than 15% by mass, the amount of crystal water released by thermal decomposition is excessive, reducing the density of the structure and making it impossible to obtain sufficient strength of the applied body. From the perspective of improving the strength of the applied body, the content of the first binder is preferably 5 to 10% by mass.

[0016] In the dry coating material of the present invention, the content of the second binder is 0.1 to 10% by mass. If the content of the second binder is less than 0.1% by mass, the bonding ability is insufficient, making it impossible to obtain sufficient strength for the applied structure. Furthermore, if the content of the second binder is more than 10% by mass, a large amount of low-melting-point substances is produced, which reduces the ease of core removal, i.e., the ease of frame removal, and also reduces corrosion resistance. From these perspectives, the content of the second binder is preferably 1 to 5% by mass.

[0017] Among the second binders, examples of powdered alkali silicates other than hydrates include sodium silicate, potassium silicate, and calcium silicate. Examples of alkali sulfates other than hydrates include sodium sulfate, potassium sulfate, calcium sulfate, and magnesium sulfate. Examples of alkali phosphates other than hydrates include sodium hexametaphosphate, sodium pyrophosphate, sodium tetrapolyphosphate, sodium tripolyphosphate, sodium ultraphosphate, potassium phosphate, lithium phosphate, calcium phosphate, magnesium phosphate, and aluminum phosphate.

[0018] In the present invention, the content of phenolic resin, which has been used as a binder in conventional dry coating materials, is limited to 0.5% by mass or less (including 0). As the phenolic resin content increases, the residual carbon component increases due to resin carbonization, causing problems with molten steel contamination due to carbon pickup, and the effectiveness of dry coating materials in preventing molten steel contamination is impaired. In addition, phenolic resin generates a strong odor due to thermal decomposition during heating, which is undesirable for the working environment. From these perspectives, the lower the phenolic resin content, the better, with 0 being most preferable. When phenolic resin is used, it should be in powder or flake form.

[0019] In the dry coating material of the present invention, the remainder, other than the first binder, second binder, and phenolic resin, is primarily refractory raw materials, similar to conventional dry coating materials. Examples include magnesia, magnesite, dolomite, calcia, alumina, silica, and combinations thereof. From the viewpoint of preventing molten steel contamination, it is preferable to primarily use basic refractory raw materials such as magnesia, magnesite, dolomite, and calcia. Furthermore, recycled refractories primarily composed of these basic materials may also be used. The particle size may be, for example, a maximum of 1 to 4 mm, and may be appropriately adjusted to coarse, medium, or fine particles.

[0020] In the dry coating material of the present invention, the balance may contain organic short fibers, organic wetting agents, organic hardening agents, etc., as needed. Specific examples of organic short fibers include vinylon fibers, polyethylene fibers, polypropylene fibers, cellulose, and cotton waste. Specific examples of organic wetting agents include coal and petroleum oils, vegetable oils, and animal oils. Specific examples of organic hardening agents include lactams, acetanilides, and alkylphenols. However, in the dry coating material of the present invention, the balance is primarily a fire-resistant raw material. Here, "primarily" refers to a content of 70% by mass or more relative to the remainder (100% by mass).

[0021] The application of the dry coating material of the present invention is similar to the application of conventional dry coating materials, and is carried out on tundishes newly lined with refractory or on used tundishes. For used tundishes, the dry coating material is applied after removing any remaining dry coating material. Specifically, a core is placed inside the tundish, and the dry coating material of the present invention is poured into the gap between the refractory lining and the core to fill it. During filling, it is preferable to apply vibrations using a vibrator attached to the core, as in conventional methods, to improve the packing rate of the dry coating material. The preferred thickness of the dry coating material is 20 to 60 mm. Next, the core is heated from the inside with a gas burner or the like to a surface temperature of approximately 400°C, hardened, and then the core is removed.

[0022] Examples of the present invention and comparative examples are shown below. Various tests were carried out using dry coating materials with the compositions shown in Table 1. In each example, the refractory raw material was magnesia. The particle size was 4.0 mm or less in terms of JIS sieve opening. The thermal decomposition starting temperature of the inorganic hydrate used as the first binder was 1.0 mm. ２ SiO ３ ・9H ２ O is 40°C, Na ３ P.O. ４ ・6H ２ O at 60°C, MgSO ４ ・7H ２ O is 70°C.

[0023]

[0024] The test methods for the various tests are as follows. <Odor> Odor was evaluated by sensory assessment of the degree of odor generated when a predetermined amount of dry coating material was applied to bricks heated to 300°C. A three-level evaluation was conducted, with ○ (excellent) indicating almost no odor, △ (good) indicating a slight odor, and × (poor) indicating an odor. A rating of ○ (excellent) or △ (good) was deemed acceptable. <Frame Removal> Frame removal was evaluated by filling a metal frame with the dry coating material, which had inner dimensions of 40 x 40 x 160 mm and was intended to accommodate a core, and leaving the frame in an atmosphere at 300°C for three hours. The frame was then lightly struck with a plastic hammer to remove it. A rating of ○ (excellent) was deemed acceptable if the frame came off after 0 to 5 light strikes, △ (good) if the frame came off after 6 to 10 light strikes, and × (poor) if the frame came off after 11 or more light strikes. A rating of ○ (excellent) or △ (good) was deemed acceptable. <Flexural Strength> Flexural strength was measured in accordance with the provisions of JIS R 1601 using test pieces that had been filled with the dry coating material into a metal frame and then heated at 300°C, as in the above-mentioned test for ease of frame removal. The flexural strength was evaluated on a three-level scale: ○ (excellent) for 1.0 MPa or more, △ (good) for 0.5 to less than 1.0 MPa, and × (poor) for less than 0.5 MPa, with ○ (excellent) or △ (good) being considered a pass. <Apparent Porosity> Apparent porosity was measured in accordance with the provisions of JIS R 2205 using test pieces that had been filled with the dry coating material into a metal frame and then heated at 300°C, as in the above-mentioned test for ease of frame removal. The apparent porosity was evaluated on a three-level scale: ○ (excellent) for 10 to less than 30%, △ (good) for 30 to less than 40%, and × (poor) for 40% or more, with ○ (excellent) or △ (good) being considered a pass. <Overall Evaluation> The overall evaluation was made on a three-point scale based on the evaluation results of odor, ease of removal from the frame, bending strength, and apparent porosity. Specifically, a sample with all evaluation results of ◯ was rated as ◯ (excellent), a sample with at least one evaluation result of △ and no evaluation result of × was △ (good), a sample with at least one evaluation result of × was △ (poor), and a sample with ○ (excellent) or △ (good) was rated as passing.

[0025] As the test results in Table 1 show, all of the dry coating materials according to the examples passed the odor evaluation. As a result, the problem of odor generation is resolved, making it possible to improve the construction environment. All of the dry coating materials according to the examples passed the evaluation of form removal. As a result, the core can be removed from the form without the applied structure collapsing. All of the dry coating materials according to the examples have sufficient strength and density when heated and dried at 300°C. This can also be confirmed by measurements of bending strength and apparent porosity. As a result, the applied structure strength can be obtained without waiting for sufficient heating or long drying times, making it possible to heat and dry in the short time required for dry coating materials.

[0026] Comparative Example 1 does not contain the first binder. Comparative Example 2 contains the first binder, but the content is below the lower limit specified in the present invention. On the other hand, Comparative Example 3 has a first binder content above the upper limit specified in the present invention. The dry coating materials according to Comparative Examples 1 to 3 do not exhibit sufficient strength and density in measurements of bending strength and apparent porosity.

[0027] Comparative Example 4 does not contain a second binder. Comparative Example 5 contains a second binder, but the content is below the lower limit specified in the present invention. The dry coating materials of Comparative Examples 4 and 5 do not achieve sufficient strength in the bending strength measurement. On the other hand, the content of the second binder of Comparative Example 6 exceeds the upper limit specified in the present invention. The dry coating material of Comparative Example 6 was evaluated as having poor frame removal properties.

[0028] In Comparative Example 7, the content of the phenol resin exceeds the upper limit specified in the present invention. The dry coating material according to Comparative Example 7 was evaluated as poor in odor.

Claims

1. A dry coating material for tundishes, comprising a total of 3 to 15 mass% of a first binder, which is one or more inorganic hydrate powders having a thermal decomposition onset temperature of 40 to 300°C, and a total of 0.1 to 10 mass% of a second binder, which is one or more powdered alkali silicates other than hydrates, powdered alkali sulfates other than hydrates, and powdered alkali phosphates other than hydrates, and the content of phenolic resin is 0.5 mass% or less (including 0), with the remainder being primarily refractory raw materials.

2. A dry coating material for a tundish as described in claim 1, wherein the content of the first binder is 5 to 10 mass % in total, and the content of the second binder is 1 to 5 mass % in total.

3. A dry coating material for a tundish according to claim 1 or 2, wherein the inorganic hydrate has a thermal decomposition starting temperature of 40 to 200°C.

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