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 material used in a member for supplying an inert gas to an electric furnace for producing rock wool. [Background technology]

[0002] Rock wool is produced by supplying molten slag, a by-product of blast furnaces, into an electric furnace as the main raw material, heating the molten slag with electricity from electrodes, and then supplying specified auxiliary raw materials to the electric furnace.The slag components and temperature are adjusted to produce molten slag for rock wool.

[0003] The gas bubbling method is a well-known method for shortening the time required to dissolve auxiliary materials in molten slag stored in an electric furnace. In this method, the molten slag is stirred by blowing an inert gas such as nitrogen into it using a refractory lance pipe.

[0004] The lance pipes have traditionally been made of a material containing 90% or more natural graphite, which is similar in composition to the graphite electrodes used in electric furnaces. Graphite is known to provide corrosion resistance to molten slag, and is used as a material for the lance pipes and electrodes in electric furnaces. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 58-167415 Summary of the Invention [Problem to be solved by the invention]

[0006] With conventional lance pipes, the part of the lance pipe located in the gas phase inside the electric furnace is prone to thinning and structural embrittlement due to the oxidation reaction of graphite, and the part of the lance pipe located near the molten metal-gas phase interface is prone to even more severe thinning due to wear caused by the flow of molten metal.

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

[0008] The refractory according to the present invention is characterized in that it is used as a member for supplying an inert gas in an electric furnace for producing rock wool, The composition contains 65% by weight or more and 80% by weight or less of graphite raw material, 10% by weight or more and 25% by weight or less of silicon carbide raw material, and 10% by weight or less of clay raw material.

[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 according to the present invention is characterized in that it is used as a member for supplying an inert gas in an electric furnace for producing rock wool, The composition contains 65% by weight or more and 80% by weight or less of a graphite raw material, a silicon carbide raw material, an alumina raw material, and 10% by weight or less of a clay raw material, and the total of the silicon carbide raw material and the alumina raw material is 10% by weight or more and 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] The refractory material according to the present invention preferably further contains 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 half or more of the silicon carbide raw material has a particle size of 1.0 mm or more. [Effects of the Invention]

[0014] The refractory material according to the present invention contains graphite raw material, which provides corrosion resistance against molten slag. By setting the graphite content to 65% by weight or more and 80% by weight or less, the corrosion resistance effect can be maintained within an acceptable range. Furthermore, by including 10% by weight or more and 25% by weight or less of silicon carbide raw material, a silicon dioxide (SiO2) coating is formed on the surface due to the oxidation reaction of the silicon carbide raw material, thereby suppressing the oxidation reaction of the graphite raw material. Therefore, the refractory material has both oxidation resistance and corrosion resistance. For example, even when the present invention is applied to a lance pipe and used in an electric furnace for producing rock wool, it is less likely to suffer from thinning or structural embrittlement, and can be used for a longer period of time than conventional lance pipes.

[0015] Furthermore, in the refractory according to the present invention, when corrosion resistance is more important than oxidation resistance, the inclusion of an alumina raw material in addition to the silicon carbide raw material can improve corrosion resistance compared to when only the graphite raw material and the silicon carbide raw material are used. Although the alumina raw material has a lower oxidation prevention effect than the silicon carbide raw material, the presence of alumina reduces the contact area between the carbon, which is the main component of the lance pipe, and the outside air, and therefore the oxidation resistance is improved compared to when only the graphite raw material is used. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram of a vertical cross section of a lance pipe. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the refractory material according to the present invention, which is used as a member for supplying an inert gas in an electric furnace for producing rock wool, will be described below.

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

[0019] (inert gas) Examples of inert gases that can be used in the refractory material according to the present invention include, but are not limited to, nitrogen, and any gas that can be blown into the molten slag in an electric furnace to perform stirring by gas bubbling can be used.

[0020] (Inert gas supply component) Examples of components for supplying inert gas to which the refractory material according to the present invention can be applied include lance pipes used in electric furnaces for producing rock wool, nipples for connecting the lance pipes together, etc. The components include not only those consisting of a single lance pipe, but also those consisting of a plurality of lance pipes and nipples for connecting the lance pipes together.

[0021] 1, in this embodiment, an example of a member is shown that includes two lance pipes 1 and 2 and a nipple 3 for connecting the two lance pipes 1 and 2. The size of the lance pipe may be, for example, 1200 mm in length, 100 mm in diameter, and 13 mm in hole diameter.

[0022] The lance pipe 1 disposed on the upper side has a through-hole 10 formed in its axial center along the entire length, through which an inert gas can flow, and further has a fitting portion 12 having a male thread portion and a socket portion 11 having a female thread portion formed at each of its longitudinal ends. The socket portion 11 is configured so that a nipple 3 can be screwed into it. Although not shown, the fitting portion 12 is configured so that it can be connected to an inert gas supply device (not shown).

[0023] The lance pipe 2, which is located on the lower side, has a through hole 20 formed in the axial center portion that runs along the entire length, allowing inert gas to flow through, and further has socket portions 21 with female thread portions formed at both ends in the longitudinal direction.

[0024] The nipple 3 has a through hole 30 formed in its axial center over the entire length direction, through which an inert gas can flow, and has a male thread formed on its outer circumferential surface.

[0025] The two lance pipes 1 and 2 are connected by threading a nipple 3 into the socket portion 11 of the upper lance pipe 1 and the socket portion 21 of either the lower lance pipe 2. Of course, the length of the component can be extended by preparing an additional lower lance pipe 2 and nipple 3 and connecting them. For example, one upper lance pipe 1, two lower lance pipes 2, and two nipples 3 may be prepared and connected to form an inert gas supply component having three lance pipes. In this embodiment, after use in an electric furnace for a predetermined period of time, the lance pipe located in the second tier may be replaced with a new lance pipe, the lance pipe located in the second tier may be moved to the third tier, and the lance pipe located in the third tier (the lance pipe with the most recent wall thinning and structural embrittlement) may be discarded. Furthermore, the nipple does not necessarily have to have the refractory structure of the present invention; conventional nipples may also be used.

[0026] (Refractories) The refractory material according to the present invention contains a graphite raw material, a silicon carbide raw material, and a clay raw material. It is preferable that at least half of the silicon carbide raw material has a particle size of 1.0 mm or more. If necessary, the refractory material may further contain an alumina raw material and a metal silicon raw material, and may also contain optional components described below.

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

[0028] Examples of silicon carbide raw materials applicable to the present invention include silicon carbide raw materials commercially available for industrial use, and these may be used alone or in combination of two or more. The content of the silicon carbide raw material in the refractory 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. It is also preferable that more than half of the silicon carbide raw material has a particle size of 1.0 mm or more. The inclusion of a silicon carbide raw material improves the oxidation resistance of the refractory. Silicon carbide reacts with oxygen in the atmosphere to form silicon dioxide (SiO2), forming a coating, which improves the oxidation resistance of the refractory. Furthermore, if the particle size is 1.0 mm or more, the antioxidant coating is more likely to be maintained. The particle size and particle size distribution of the silicon carbide raw material are determined in accordance with the "dry sieving test" in JIS Z 8815:2019. The definition of the sieve follows the "plain weave sieve" in JIS Z 8801-1:2019.

[0029] When the raw materials contain an alumina raw material, the silicon carbide raw material and the alumina raw material are blended so that the total amount of the silicon carbide raw material and the alumina raw material is 10% by weight or more and 25% by weight or less, and the weight ratio of the silicon carbide raw material to the 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 alumina raw materials for industrial use 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 likely to be improved. Furthermore, it is desirable that the amount of alumina raw material substituted for the silicon carbide raw material in the refractory is 85% by weight or less. If the amount of substitution is 85% by weight or less, the antioxidant effect is likely to be exhibited.

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

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

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

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

[0035] In the kneading step, other additives (for example, a binder) may be further added and kneaded as necessary.

[0036] The molding process is not particularly limited, but is preferably performed by, for example, the CIP (Cold Isostatic Press) molding method. CIP molding is performed using a molding device that applies uniform pressure to the entire molding frame (or molded object) using hydrostatic pressure. Because hydrostatic pressure is used and a rubber mold is used as the medium for transmitting it, it is sometimes called an isostatic press or rubber press. Specifically, powder is filled into a rubber mold, which is then placed in a container filled with liquid. The hydrostatic pressure of the liquid is used to apply high pressure to the powder inside the rubber mold, molding the material. Compared to uniaxial molding using a mold press, infinite multiaxial pressure is used, making it easier to obtain uniform molded objects even with large length-to-diameter ratios, such as spheres. In addition, when molding a lance pipe, for example, a cylindrical frame containing the kneaded material can be placed in a mold with upper and lower bases fixed by four supports and molded. Furthermore, the upper and lower molds may be formed with threads to create the shape of the socket. CIP molding applies pressure to the mixture from all directions, but the support prevents pressure from being applied in the vertical direction. This prevents dimensional changes in the vertical direction of the lance pipe, maintaining uniformity in length.

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

[0038] In the firing step, reduction firing is carried out under a predetermined temperature condition (for example, 1330°C).

[0039] In the machining step, for example, lathe machining is performed using a known lathe device. [Example]

[0040] Two types of block specimens with different sizes (Sample I: 30 mm × 30 mm × 30 mm, Sample II: 180 mm × 25 mm × 25 mm) were prepared for each of Examples 1 to 9 and Comparative Examples 1 to 4 according to the above-mentioned manufacturing method using the weight ratios of the raw materials shown in Tables 1 and 2. Sample I of each Example and Comparative Example was subjected to an oxidation resistance evaluation test, and Sample II was also subjected to a corrosion resistance evaluation test. [Table 1] [Table 2]

[0041] (Oxidation resistance evaluation test) In an electric furnace, samples I from each example and comparative example were tested at two test temperatures: 1400°C for 3 hours and 1600°C for 3 hours. The appearance, cut surface, and weight change rate of samples I before and after the test were evaluated on a six-point scale (AAA (excellent) > AA (excellent) > A (second-rate) > B (good) > C (fair) > D (unacceptable)). Sample I from Comparative Example 3 disappeared due to an oxidation reaction at both 1400°C and 1600°C, whereas sample I from the examples showed weight loss but did not disappear. The appearance and cut surface were qualitatively evaluated based on whether the sample had become brittle before and after the test and whether the sample crumbled due to the resistance of the cutting blade. Regarding the weight change rate, samples closer to AAA (excellent) were judged to have better oxidation resistance because the weight loss before and after the test was small. Samples closer to D (unacceptable) were quantitatively judged to have poorer oxidation resistance because the weight loss was large.

[0042] (Corrosion resistance evaluation test) Tests were conducted in a high-frequency induction furnace at a test temperature of 1550°C using 20 kg of pig iron and 1.5 kg of blast furnace slag for Sample II in each example and comparative example, and the dimensional change of Sample II before and after the test was evaluated on a six-point scale (AAA (excellent) > AA (excellent) > A (second-excellent) > B (good) > C (fair) > D (unsuitable)). Regarding the evaluation of corrosion resistance, the change rate between the dimensions before the test (Sample II: 180 mm × 25 mm × 25 mm, two 25 mm sides) and after the test (the 25 mm was reduced due to immersion in molten metal) was calculated, and the smaller the reduction, the better the grade of AAA (excellent), and the larger the reduction, the better the grade of D (unsuitable). [Industrial Applicability]

[0043] The refractory material according to the present invention can be suitably used, for example, as a lance pipe in an electric furnace for producing rock wool. [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 as a member for supplying inert gas in an electric furnace for producing rock wool, A refractory material comprising 65% by weight or more and 80% by weight or less of a graphite raw material, 10% by weight or more and 25% by weight or less of a silicon carbide raw material, and 10% by weight or less of a clay raw material.

2. 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 as a member for supplying inert gas in an electric furnace for producing rock wool, A refractory comprising 65% by weight or more and 80% by weight or less of a graphite raw material, a silicon carbide raw material, an alumina raw material, and 10% by weight or less of a clay raw material, wherein the total amount of the silicon carbide raw material and the alumina raw material is 10% by weight or more and 25% by weight or less.

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

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

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