Refractory

Abstract

To provide a refractory that can be used in an electric furnace for rock wool production, and is less likely to undergo wall thinning and structural embrittlement.SOLUTION: A refractory used for a member for supplying an inert gas in an electric furnace for rock wool production comprises: 65 wt.% or more and 80 wt.% or less of graphite raw material; 10 wt.% or more and 25 wt.% or less of silicon carbide raw material; and 10 wt.% or less of clay raw material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a refractory used for a member for supplying an inert gas in an electric furnace for manufacturing rock wool.

Background Art

[0002] The production of rock wool is carried out by supplying molten slag produced as a by-product from a blast furnace as a main raw material into an electric furnace, heating the molten slag with electric power from an electrode, and further supplying a predetermined auxiliary raw material to the electric furnace to adjust the slag components and temperature to produce molten slag for rock wool.

[0003] As a method for shortening the time for dissolving an auxiliary raw material in molten slag stored in an electric furnace, a gas bubbling method is known. In this method, an inert gas such as nitrogen is blown into the molten slag using a lance pipe made of a refractory to stir the molten slag.

[0004] As a constituent material of the lance pipe, those containing 90% or more of natural graphite have been used so far, which has almost the same composition as the graphite electrode used in an electric furnace. Graphite is known to impart corrosion resistance to molten slag and is used as a constituent material for lance pipes, electrodes, etc. in an electric furnace.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In conventional lance pipes, the portion of the lance pipe located in the gas phase within the electric furnace is prone to thinning and structural embrittlement due to the oxidation reaction of graphite, and the portion of the lance pipe near the molten metal-gas phase interface experiences even greater thinning due to wear caused by molten metal flow.

[0007] The present invention has been made in view of the above circumstances, and its purpose is to provide a refractory material that can be used in electric furnaces for rock wool production and is less prone to thinning and structural embrittlement. [Means for solving the problem]

[0008] The refractory material according to the present invention is a refractory material used for a component that supplies inert gas in an electric furnace for rock wool manufacturing, Graphite raw material of 65% to 80% by weight, silicon carbide raw material of 10% to 25% by weight, and 10% by weight or less (Except for 0% by weight) The key point is that it contains clay raw materials.

[0009] In the refractory material according to the present invention, it is preferable that the graphite raw material is 67% by weight or more and 72% by weight or less, and the silicon carbide raw material is 18% by weight or more and 23% by weight or less.

[0010] The refractory material according to the present invention is a refractory material used for a component that supplies inert gas in an electric furnace for rock wool manufacturing, Graphite raw material containing 65% to 80% by weight, 10% or more by weight Silicon carbide raw material, alumina raw material, and less than 10% by weight. (Except for 0% by weight) It contains clay raw materials, and the total of the silicon carbide raw material and the alumina raw material is 10% by weight. more The key point is that it must be 25% by weight or less.

[0011] In the refractory material according to the present invention, it is preferable that the weight ratio of the silicon carbide raw material to the alumina raw material is in the range of 1:5 to 5:1.

[0012] In the refractory material according to the present invention, it is preferable to further contain 10% by weight or less of a metallic silicon raw material.

[0013] In the refractory material according to the present invention, it is preferable that the particle size of more than half of the silicon carbide raw material is 1.0 mm or larger. [Effects of the Invention]

[0014] The refractory material according to the present invention contains graphite raw material and therefore possesses corrosion resistance to molten slag. By setting the content of graphite to 65% to 80% by weight, the corrosion resistance effect can be maintained within an acceptable range. Furthermore, by including 10% to 25% by weight of silicon carbide raw material, a silicon dioxide (SiO2) film is formed on the surface by the oxidation reaction of the silicon carbide raw material, thereby suppressing the oxidation reaction of the graphite raw material. As a result, the refractory material has both oxidation resistance and corrosion resistance. For example, when the present invention is applied to lance pipes and used in electric furnaces for rock wool production, thinning and structural embrittlement are less likely to occur, and it can be used for a longer period than conventional lance pipes.

[0015] Furthermore, in the refractory material according to the present invention, if corrosion resistance is prioritized over oxidation resistance, the corrosion resistance can be improved by including alumina raw material in addition to silicon carbide raw material, compared to the case where only graphite raw material and silicon carbide raw material are used. Although alumina raw material has a lower antioxidant effect than silicon carbide raw material, the presence of alumina reduces the contact area between carbon, the main component of the lance pipe, and the outside air, thus improving oxidation resistance compared to the case where only graphite raw material is used. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of the longitudinal cross-section of the lance pipe. [Modes for carrying out the invention]

[0017] The following describes an embodiment of the refractory material used in a component for supplying inert gas in an electric furnace for rock wool production, according to the present invention.

[0018] (Electric furnace for manufacturing rock wool) As an electric furnace for manufacturing rock wool to which the refractory according to the present invention can be applied, it includes electrodes for heating molten slag, lance pipes for supplying inert gas, etc., and a known electric furnace capable of manufacturing molten slag for rock wool can be used.

[0019] (Inert gas) Examples of the inert gas applicable to the refractory according to the present invention include nitrogen, etc., but it is not limited thereto, and any gas that can be blown into the molten slag of the electric furnace to perform stirring by gas bubbling may be used.

[0020] (Member for supplying inert gas) Examples of the member for supplying inert gas applicable to the refractory according to the present invention include lance pipes used in an electric furnace for manufacturing rock wool, nipples for connecting the lance pipes to each other, etc. The member includes not only those composed of a single lance pipe, but also those composed of a plurality of lance pipes and nipples for connecting the lance pipes to each other.

[0021] As shown in FIG. 1, in the present embodiment, a member including two lance pipes 1 and 2 and a nipple 3 for connecting the two lance pipes 1 and 2 is illustrated. Examples of the size of the lance pipe include those with a length of 1200 mm, a diameter of 100 mm, and a hole diameter of 13 mm.

[0022] In the lance pipe 1 arranged on the upper side, a through hole 10 extending in the longitudinal direction through which inert gas can flow is formed in the axial center portion, and further, at each of both ends in the longitudinal direction, a fitting portion 12 having a male screw portion and a socket portion 11 having a female screw portion are formed. Note that the socket portion 11 is configured such that the nipple 3 can be screwed. Although not shown, the fitting portion 12 is configured to be able to be connected to an inert gas supply device (not shown).

[0023] The lance pipe 2, positioned on the lower side, has a through hole 20 extending along its entire longitudinal direction, through which an inert gas can flow, formed in its axial center, and socket portions 21 with female threads are formed at both ends in the longitudinal direction.

[0024] The nipple 3 has a through hole 30 that extends along its entire longitudinal direction, allowing an inert gas to flow through, formed in its axial center, and a male threaded portion formed on its outer circumferential surface.

[0025] The two lance pipes 1 and 2 are connected by screwing a nipple 3 into either the socket portion 11 of the upper lance pipe 1 or the socket portion 21 of the lower lance pipe 2. Of course, the length of the member can be extended by further preparing a lower lance pipe 2 and a nipple 3 and connecting them. For example, one upper lance pipe 1, two lower lance pipes 2, and two nipples 3 can be prepared and connected to form an inert gas supply member with three lance pipes. In this embodiment, after use in an electric furnace for a predetermined period, the lance pipes placed in the second stage can be replaced with new lance pipes, the lance pipes that were in the second stage can be moved to the third stage, and the lance pipes that were in the third stage (the lance pipes that have relatively undergone the most thinning and structural embrittlement) can be discarded. Furthermore, the nipples do not necessarily have to have the refractory structure according to the present invention; conventionally used nipples can be used.

[0026] (Refractories) The refractory material according to the present invention comprises a graphite raw material, a silicon carbide raw material, and a clay raw material. Preferably, the particle size of more than half of the silicon carbide raw material is 1.0 mm or larger. In addition, alumina raw material and metallic silicon raw material may be further included as needed, and optional components described later may also be included.

[0027] Examples of graphite raw materials applicable to the present invention include known graphite raw materials such as various types of graphite, carbon black, pitch, and resin charcoal, and one of these may be used alone or two or more may be used in combination. The graphite raw material content in the refractory material is 65% by weight or more and 80% by weight or less, more preferably 67% by weight or more and 72% by weight or less. The inclusion of graphite raw materials improves corrosion resistance to molten slag.

[0028] Suitable silicon carbide raw materials for this invention include commercially available silicon carbide raw materials for industrial use, and one of these may be used alone or in combination of two or more. The silicon carbide raw material content in the refractory material is 10% by weight or more and 25% by weight or less, more preferably 18% by weight or more and 23% by weight or less. Furthermore, it is preferable that the particle size of more than half of the silicon carbide raw material is 1.0 mm or larger. The inclusion of silicon carbide raw material improves the oxidation resistance of the refractory material. Silicon carbide reacts with oxygen in the atmosphere to form silicon dioxide (SiO2), which forms a film and thereby improves the oxidation resistance of the refractory material. Furthermore, if the particle size is 1.0 mm or larger, the antioxidant coating is more easily maintained. The particle size and particle size distribution of the silicon carbide raw material are determined according to the "dry sieving test" in JIS Z 8815:2019. The definition of sieve follows the "plain weave sieve" in JIS Z 8801-1:2019.

[0029] Furthermore, if alumina is included as a raw material, the total of silicon carbide and alumina must be 10% by weight. more The mixture is formulated to be 25% by weight or less. In this case, the weight ratio of silicon carbide raw material to alumina raw material is preferably in the range of 1:5 to 5:1.

[0030] Examples of alumina raw materials applicable to the present invention include commercially available industrial alumina raw materials with an alumina content of 85% or more. Only one of these may be used, or two or more may be used in combination. When the alumina content is 85% or more, corrosion resistance is easily improved. Furthermore, it is desirable that the substitution amount of alumina raw material for silicon carbide raw materials in refractories be 85% by weight or less. When the substitution amount is 85% by weight or less, the antioxidant effect is easily achieved.

[0031] Examples of clay raw materials applicable to the present invention include commercially available clay raw materials for refractories, and one type may be used alone, or two or more types may be used in combination. The clay raw material content in the refractory material is 10% by weight or less. The inclusion of clay raw materials improves the strength of the refractory material. In particular, the moldability during molding by the CIP molding method in the manufacturing method described later is improved, and the strength after reduction firing is also improved.

[0032] Examples of metallic silicon raw materials applicable to the present invention include commercially available metallic silicon raw materials for industrial use, and only one of these may be used, or two or more may be used in combination. Preferably, the metallic silicon raw material content in the refractory material is 10% by weight or less. During the reduction firing process in the manufacturing method described later, the metallic silicon raw material reacts with the residual char of the binder (such as a phenol binder) to produce silicon carbide (SiC), which then self-bonds to improve strength.

[0033] The refractory material according to this embodiment may contain other components (optional components) other than the graphite raw material, silicon carbide raw material, alumina raw material, clay raw material, and metallic silicon raw material described above. Examples of such optional components include, but are not limited to, silica raw material, magnesia raw material, zirconia raw material, and boride raw material as an antioxidant. It is preferable that the content of optional components is 0% by weight or more and 25% by weight or less.

[0034] (Method of manufacturing refractories) The method for producing a refractory material according to the present invention comprises a blending step of blending the above-mentioned graphite raw material, silicon carbide raw material, clay raw material, and, if necessary, metallic silicon raw material; a kneading step of kneading the blended raw materials using a known mixer or the like; a molding step of shaping the kneaded material; a drying step of drying the molded material; a firing step of firing the dried material; and a processing step of processing the fired material.

[0035] During the mixing process, other additives (e.g., binders) may be added and mixed as needed.

[0036] The molding process is not particularly limited, but it is preferable to carry it out using the CIP (Cold Isostatic Press) molding method. The CIP molding method uses a device that applies uniform pressure to the entire molding frame (or workpiece) using hydrostatic pressure. Because hydrostatic pressure is used and a rubber mold is used as the medium for transmitting it, it is sometimes called a hydrostatic press or rubber press. Specifically, powder is filled into a rubber mold, and the rubber mold is placed in a container filled with liquid, and high pressure is applied to the powder inside the rubber mold by the hydrostatic pressure of the liquid to form the object. Compared to uniaxial molding with a die press, it provides infinite multiaxial pressure, making it easier to obtain uniform molded products even for objects with a large ratio of length to diameter, or spheres. When molding a lance pipe, for example, a cylindrical frame into which the kneaded material has been introduced can be placed in a mold with upper and lower bases fixed by four support columns for molding. In addition, threaded shapes may be formed in the upper and lower molds to create the shape of the socket. While CIP molding applies pressure to the mixture from all directions, the support columns prevent pressure from being applied in the vertical direction. This minimizes vertical dimensional changes in the lance pipe, thus maintaining uniformity of length.

[0037] In the drying process, the drying treatment is carried out under predetermined temperature conditions (for example, 250°C).

[0038] In the firing process, reduction firing is performed under predetermined temperature conditions (for example, 1330°C).

[0039] In the machining process, for example, turning is performed using a known turning machine. [Examples]

[0040] Based on the weight ratios of the raw materials shown in Tables 1 and 2 below, two types of block samples of different sizes (Sample I: 30mm × 30mm × 30mm, Sample II: 180mm × 25mm × 25mm) were prepared for each of Examples 1 to 9 and Comparative Examples 1 to 4 according to the manufacturing method described above. Oxidation resistance evaluation tests were performed on Sample I of each Example and Comparative Example, and corrosion resistance evaluation tests were performed on Sample II. [Table 1] [Table 2]

[0041] (Oxidation resistance evaluation test) In an electric furnace, sample I of each example and comparative example was tested at two test temperatures: 1400°C for 3 hours and 1600°C for 3 hours. The appearance, cross-section, and weight change rate of sample I before and after the test were evaluated on a 6-point scale (AAA (Excellent) > AA (Good) > A (Good) > B (Good) > C (Acceptable) > D (Unacceptable)). Sample I of Comparative Example 3 disappeared due to oxidation at both test temperatures of 1400°C and 1600°C, but sample I of the example did not disappear, although a weight decrease was observed. Regarding the appearance and cross-section, a qualitative judgment was made based on whether the sample was embrittlemented before and after the test, and whether the sample disintegrated due to resistance with the blade during cutting. Regarding the weight change rate, a score closer to AAA (Excellent) indicated a smaller weight decrease before and after the test, indicating superior oxidation resistance, while a score closer to D (Unacceptable) indicated a larger weight decrease, indicating inferior oxidation resistance.

[0042] (Corrosion resistance evaluation test) In a high-frequency induction furnace, each example and comparative example sample II was tested at a test temperature of 1550°C using 20 kg of pig iron and 1.5 kg of blast furnace slag. The dimensional change of sample II before and after the test was evaluated on a 6-point scale (AAA (Excellent) > AA (Very Good) > A (Good) > B (Good) > C (Acceptable) > D (Unacceptable)). For corrosion resistance evaluation, the rate of change between the dimensions before the test (sample II: 180 mm × 25 mm × 25 mm, with two 25 mm sides) and the dimensions after the test (a reduction of 25 mm due to immersion in molten metal) was calculated. A smaller reduction in dimension was rated as AAA (Excellent), and a larger reduction in dimension was rated as D (Unacceptable), and the evaluation was made quantitatively. [Industrial applicability]

[0043] The refractory material according to the present invention can be suitably used, for example, as a lance pipe in electric furnaces for rock wool production. [Explanation of symbols]

[0044] 1: Upper lance pipe 10: Through hole 11: Socket part 12: Fitting part 2: Lower lance pipe 20: Through hole 21: Socket part 3: Nipple 30: Through hole

Claims

1. A refractory material used in components for supplying inert gas in an electric furnace for rock wool manufacturing, A refractory material comprising 65% to 80% by weight of graphite raw material, 10% to 25% by weight of silicon carbide raw material, and 10% or less by weight of clay raw material (excluding 0% by weight).

2. The refractory material according to claim 1, wherein the graphite raw material is 67% by weight or more and 72% by weight or less, and the silicon carbide raw material is 18% by weight or more and 23% by weight or less.

3. A refractory material used in components for supplying inert gas in an electric furnace for rock wool manufacturing, A refractory material comprising 65% by weight or more and 80% by weight or less of graphite raw material, 10% by weight or more of silicon carbide raw material, alumina raw material, and 10% by weight or less (excluding 0% by weight) of clay raw material, wherein the sum of the silicon carbide raw material and the alumina raw material is more than 10% by weight and 25% by weight or less.

4. The refractory material according to claim 3, wherein the weight ratio of the silicon carbide raw material to the alumina raw material is in the range of 1:5 to 5:

1.

5. A refractory material according to any one of claims 1 to 4, further comprising 10% by weight or less of a metallic silicon raw material.

6. The refractory material according to any one of claims 1 to 4, wherein more than half of the silicon carbide raw material has a particle size of 1.0 mm or larger.

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