JP7563370B2 - Graphite-containing refractory material and method for producing the same - Google Patents

Description

The present invention relates to a graphite-containing refractory material in which carbon fiber bundles are arranged inside the refractory body.

In steelworks, equipment used in the iron-making and steel-making processes (refining vessels, transport vessels, etc.) are lined with refractories to withstand long-term use at high temperatures. In general, magnesia-carbonaceous refractories are used for the lining of converters used in the refining process, while alumina-silicon carbide-carbonaceous refractories are used for the lining of torpedoes and blast furnace ladles used in the molten iron pretreatment process.
The refractories used for lining these refining vessels and transport vessels are used under extremely harsh conditions, including mechanical shock from the charges, abrasion from stirring of molten steel and molten slag, slag erosion from molten slag, and sudden temperature changes during operation. For this reason, in order to ensure stable operation, it is necessary to use refractories with high durability that can withstand such harsh conditions.

In particular, the tuyere bricks that make up the tuyere of the converter have room temperature gas (oxygen, cooling hydrocarbon gas, etc.) flowing inside, and the inner surface near the inside of the furnace is cooled by the room temperature gas, while the outer surface is exposed to high temperatures due to heat transfer from the molten steel in the furnace, so the thermal gradient inside the tuyere bricks is extremely large, and each time one charge of blowing is completed, the temperature drops due to the discharge of the molten steel, and large thermal fluctuations are repeated. The tuyere bricks installed in converters are used as frequently as 2,500 to 4,000 charges, and are used under extremely harsh conditions where the above-mentioned large thermal gradients and large thermal fluctuations are repeated for each charge, so they need to be highly durable to withstand such conditions. In addition, converter refractory linings other than tuyere bricks (bricks that make up the inner wall of the converter) are also used under harsh conditions where the above-mentioned large thermal fluctuations are repeated, so they need to be highly durable, although not as durable as tuyere bricks.

As a technology for improving the durability of refractories, Patent Document 1 describes how carbon fibers longer than 100 mm are bundled with adhesive and placed inside the refractory in a sticky bundle state, significantly increasing the fracture energy.

Republished Publication No. 2018-155118

However, as a result of the inventors' investigations, it was found that in the technology of inserting carbon fiber bundles inside a refractory material as in Patent Document 1, if commercially available carbon fiber bundles are used as is, defects such as cracks are likely to occur during production, and a high production yield cannot be obtained. Patent Document 1 does not disclose any means of solving such problems.

The object of the present invention is therefore to provide a graphite-containing refractory that solves the problems of the prior art, suppresses the growth of cracks caused by thermal stress, and provides high durability even when used under conditions where temperature increases and decreases are repeated over long periods of time, such as in the lining refractory material of a converter, and that provides high durability even when used under conditions where the internal temperature gradient is particularly large, such as in the tuyere bricks of a converter, and that can be manufactured with a high manufacturing yield without generating defects such as cracks during manufacturing, and a method for manufacturing the same.

The inventors of the present invention have conducted extensive research to solve the above problems, and as a result have found that, although commercially available carbon fiber bundles have a sizing agent attached to the inside and outside of the bundle to hold the carbon fibers together in the bundle, placing the carbon fiber bundle with the sizing agent attached as is inside a refractory material causes defects such as cracks during manufacturing, and therefore, by using a carbon fiber bundle from which at least a portion of the sizing agent attached to the outer surface and inside the bundle has been removed in advance, it is possible to suppress the occurrence of defects during manufacturing. Furthermore, the inventors have found that, preferably, by optimizing the fiber diameter and number of carbon fibers constituting the carbon fiber bundle, high durability can be obtained even in the extremely severe usage environment described above.

The present invention has been made based on these findings, and has the following gist.
[1] A graphite-containing refractory having a carbon fiber bundle (B) disposed inside a refractory body (A),
A graphite-containing refractory material, characterized in that the carbon fiber bundles (B) are carbon fiber bundles having no sizing agent attached to at least a part or all of the outer surface thereof.
[2] The graphite-containing refractory according to the above [1], wherein the carbon fiber bundles (B) are carbon fiber bundles having no sizing agent attached to a part or all of the outer surface and a part or all of the interior of the bundles.

[3] The graphite-containing refractory according to the above [1] or [2], characterized in that the carbon fiber bundles (B) are bonded to the refractory body (A) via an adhesive component (c).
[4] The graphite-containing refractory according to the above [3], wherein the carbon fiber bundles (B) contain an adhesive component (c) in the bundles to which no sizing agent is attached.
[5] The graphite-containing refractory according to the above [3] or [4], wherein the adhesive component (c) is one or more selected from the group consisting of organic resins, inorganic fine particles derived from inorganic sols, organic substances derived from tar and/or pitch, and organic substances derived from organic glues.

[6] The graphite-containing refractory according to any one of the above [1] to [5], wherein the carbon fiber bundle (B) is a bundle of carbon fibers having a length of 100 mm or more and a fiber diameter of 1 to 45 μm, and the number of carbon fibers per bundle is 1,000 to 300,000.
[7] The graphite-containing refractory according to any one of the above [1] to [6], characterized in that a plurality of carbon fiber bundles (B) are arranged in parallel at intervals inside the refractory body (A).
[8] The graphite-containing refractory according to any one of the above [1] to [7], wherein the refractory body (A) contains 1 to 80 mass% of a graphite raw material.

[9] A converter comprising any one of the graphite-containing refractories according to [1] to [8] above.
[10] A molten iron pretreatment vessel comprising the graphite-containing refractory according to any one of [1] to [8] above.
[11] A ladle vessel comprising any one of the graphite-containing refractories described above in [1] to [8].

[12] A method for producing a graphite-containing refractory in which a carbon fiber bundle (B) is disposed inside a refractory body (A), comprising the steps of:
A pre-treatment step (i) of subjecting a commercially available carbon fiber bundle (b) to a sizing agent attached thereto to a treatment for removing a part or all of the sizing agent attached to at least the outer surface of the carbon fiber bundle, among the sizing agents attached thereto;
a preparation step (ii) of applying an adhesive to the carbon fiber bundle (b) that has been subjected to the pretreatment step (i);
a molding step (iii) of embedding the carbon fiber bundles (b) to which the adhesive has been applied in the preparation step (ii) inside a refractory raw material (a) and molding the refractory raw material (a) in which the carbon fiber bundles (b) are embedded to obtain a refractory molded body;
The method for producing a graphite-containing refractory material comprises a drying step (iv) of drying the refractory molded body obtained in the molding step (iii).

[13] The method for producing a graphite-containing refractory according to the above [12], wherein in the molding step (iii), the carbon fiber bundles (b) are bonded to the refractory raw material (a) via an adhesive.
[14] The method for producing a graphite-containing refractory material according to the above [12] or [13], characterized in that in the pre-treatment step (i), a treatment is carried out to remove a part or all of a sizing agent adhering to an outer surface of the carbon fiber bundle and a part or all of a sizing agent adhering to an inside of the carbon fiber bundle.
[15] A graphite-containing refractory material, characterized in that in the production method according to the above [14], in the preparation step (ii), an adhesive is contained in the carbon fiber bundles (b) to which no sizing agent is attached.

[16] The method for producing a graphite-containing refractory material according to any one of the above [12] to [15], wherein the adhesive is one or more selected from the group consisting of organic resins, inorganic sols, tar, pitch, and organic glues.
[17] In any one of the manufacturing methods [12] to [16] above, the carbon fiber bundle (b) is a bundle of carbon fibers having a length of 100 mm or more and a fiber diameter of 1 to 45 μm, and the number of carbon fibers per bundle is 1,000 to 300,000.
[18] The method for producing a graphite-containing refractory according to any one of the above-mentioned [12] to [17], wherein in the molding step (iii), a plurality of carbon fiber bundles (b) are arranged in parallel at intervals inside the refractory raw material (a).

The graphite-containing refractory of the present invention has high fracture energy, and therefore even when used under conditions where temperature rise and fall are repeated over a long period of time, such as the lining refractory of a converter, the growth of cracks caused by thermal stress is suppressed, and high durability is obtained, particularly when used under conditions where the internal temperature gradient is very large, such as the tuyere bricks of a converter. Moreover, since it can be produced with a high production yield without generating defects such as cracks during production, production costs can be kept low.
Moreover, according to the production method of the present invention, such a graphite-containing refractory can be stably produced.

FIG. 1 is a schematic diagram showing one of the brick components constituting the tuyere brick in one embodiment in which the graphite-containing refractory of the present invention is applied to a tuyere brick, in which FIG. 1(A) is a perspective view, and FIG. 1(B) is a cross-sectional view taken along the dashed line in FIG. 1(A) (a cross-sectional view parallel to the refractory operating surface). FIG. 1 is a flow chart showing an example of a process for producing the graphite-containing refractory material of the present invention. FIG. 3 shows a test method for evaluating the corrosion resistance of a graphite-containing refractory in an embodiment. FIG. 3(A) is an explanatory diagram showing a test furnace and a cylindrical sample in vertical section as the test is carried out. FIG. 3(B) is a plan view of the cylindrical sample shown in FIG. 3(A). FIG. 3(C) is a perspective view showing one of the test pieces constituting the cylindrical sample shown in FIGS. 3(A) and (B). FIG. 4 shows a method for measuring the bending strength of a graphite-containing refractory in an embodiment. FIG. 4(A) is an explanatory diagram showing a typical implementation state of a three-point bending strength test, and FIG. 4(B) is an explanatory diagram showing a typical end face of the test piece in FIG. 4(A). FIG. 1 is a diagram showing an example of fracture energy calculated from a load-displacement curve obtained in a three-point bending strength test in an embodiment.

The graphite-containing refractory of the present invention is a graphite-containing refractory having a carbon fiber bundle B disposed inside a refractory body A, and is characterized in that the carbon fiber bundle B is made of a carbon fiber bundle having no sizing agent attached to at least a part or all of its outer surface, and preferably is made of a carbon fiber bundle having no sizing agent attached to a part or all of its outer surface and a part or all of the interior of the bundle.
In general, the fiber diameter of carbon fiber strands is on the order of μm. Usually, carbon fibers are sold in a state where a resin called a sizing agent is applied to the fiber strands, bundled, and solidified (i.e., the bundle of fiber strands is solidified with the sizing agent) in order to prevent damage to the fiber strands and to facilitate handling. However, since the sizing agent is solidified at the stage when the carbon fiber bundles are sold commercially, the elastic modulus (bending resistance) in the bending direction of the carbon fiber bundles is large.

In manufacturing a graphite-containing refractory in which carbon fiber bundles are disposed (embedded) inside the refractory body (refractory raw material), for example, the refractory raw material and the carbon fiber bundles are filled into a mold and press-molded. The grain size composition of the refractory raw material varies, but in refractories used in steelmaking, coarse grains of 3 to 30 mm, called aggregates, are generally blended in order to improve corrosion resistance. The inventors of the present invention have focused on the fact that when the refractory raw material and the carbon fiber bundles are filled into a mold and press-molded, the carbon fiber bundles are bent due to the difference in the degree of contraction between the coarse grains and the other fine grains in the part where the carbon fiber bundles are adjacent to the coarse grains, and have investigated the relationship with the occurrence of defects during manufacturing. As a result, it has been found that, as described above, the large elastic modulus in the bending direction of the carbon fiber bundles generates internal stress when the refractory raw material and the carbon fiber bundles are filled into a mold and press-molded, which causes defects such as cracks. It was also found that when the carbon fiber bundle is bent during molding, the adhesion between the solidified sizing agent and the surface of the carbon fiber bundle wires peels off, resulting in a decrease in the effect of improving the fracture energy due to the adhesion between the carbon fiber and the refractory raw material. Even when the refractory raw material is cast in place of press molding, the carbon fiber bundle, which does not flow and has a high bending resistance, is thought to cause voids and unevenness.

From the above, it was found that defects during manufacturing can be reduced by removing at least a portion of the sizing agent attached to the carbon fiber bundles beforehand, and then placing the carbon fiber bundles inside the refractory raw material and molding them. This is because the elastic modulus (bending resistance) in the bending direction of the carbon fiber bundles is reduced, which reduces the phenomenon known as springback, in which cracks occur in the product due to internal stresses generated during press molding. It was also found that removing the sizing agent increases the adhesion (adhesion) between the carbon fiber and the refractory, and prevents the sizing agent from hindering the effect of improving the fracture energy.

As described later, in order to remove the sizing agent from the carbon fiber bundles, a method is adopted in which the carbon fiber bundles are immersed in a dissolving solution for the sizing agent (such as an organic solvent). If the sizing agent on the outer surface (at least a part of the outer surface) of the carbon fiber bundle is dissolved and disappeared, and the carbon fiber strands are partially exposed, the effect of removing the sizing agent can be obtained. However, if the sizing agent is dissolved and disappeared even within the carbon fiber bundles (at least a part of the bundles) and the carbon fiber strands are disintegrated into small pieces, the elastic modulus in the bending direction of the carbon fiber bundle becomes extremely small, and the adhesion (adhesion) between the carbon fibers and the refractory raw material becomes stronger, which is desirable.
For this reason, the graphite-containing refractory of the present invention is configured such that the carbon fiber bundle B is composed of a carbon fiber bundle having no sizing agent attached to at least a portion or all of its outer surface, and is preferably composed of a carbon fiber bundle having no sizing agent attached to a portion or all of its outer surface and to a portion or all of the interior of the bundle.

The graphite-containing refractory of the present invention is produced, for example, by adding an appropriate amount of binder to the refractory raw material, kneading the mixture, filling a mold and press molding it. Although the binder is originally added to bond the refractory raw material together, when the kneaded mixture of the refractory raw material is filled into a mold together with carbon fiber bundles and press molding is performed, the binder also acts to bond the refractory raw material and the carbon fiber bundles.
In contrast, when producing the graphite-containing refractory of the present invention, the adhesive component is applied to the carbon fiber bundles, and then the adhesive component is filled into a mold together with a kneaded product of the refractory raw materials while the adhesive component is in a sticky state, thereby further strengthening the adhesion between the carbon fiber bundles and the refractory raw materials and further increasing the fracture energy of the refractory. In this case, the graphite-containing refractory of the present invention is composed of carbon fiber bundles having no sizing agent attached to at least a part or all of their outer surfaces, and preferably carbon fiber bundles having no sizing agent attached to a part or all of their outer surfaces and a part or all of their interiors, so that the adhesive component can directly adhere to the outer surface or interior of the carbon fiber bundles, further strengthening the adhesion between the carbon fiber bundles and the refractory raw materials, and further increasing the fracture energy of the refractory.
Therefore, in the graphite-containing refractory of the present invention, it is preferable that the carbon fiber bundles B are adhered to the refractory body A via an adhesive component c, and further it is preferable that the adhesive component c is contained in the bundles to which no sizing agent is attached.

In the graphite-containing refractory of the present invention, when the carbon fiber bundle B is composed of a carbon fiber bundle with no sizing agent attached to part or all of the outer surface and part or all of the inside of the bundle (particularly preferably, the carbon fiber bundle with no sizing agent attached to substantially the outer surface and the entire inside of the bundle), the carbon fiber bundle B arranged inside the refractory body A is integrated as a bundle by containing the adhesive component c in the bundle, and is bonded to the refractory body A via the adhesive component c, so that the carbon fiber bundle B is integrated with the refractory. That is, the adhesive component c exists (permeates) in the carbon fiber bundle (gaps between the carbon fibers) to integrate the carbon fiber bundle B as a bundle, and covers the outer surface of the carbon fiber bundle B to bond the carbon fiber bundle B to the refractory body A, so that the carbon fiber bundle B is integrated with the refractory. This results in a particularly high fracture energy that can suppress the occurrence of cracks.

The adhesive component c adheres the carbon fiber bundles B to the refractory body A, and further exists (permeates) in the carbon fiber bundles (gaps between the carbon fibers) to integrate the carbon fiber bundles B into a bundle. Therefore, it is desirable that the adhesive used is a liquid or fine solid particles. In addition, the adhesive component c must remain without decomposition or evaporation even at high temperatures, but since oxygen combustion hardly occurs when used with graphite-containing refractories, it is possible to use a resin that is highly combustible in the presence of oxygen. In view of these conditions, the adhesive component c is suitable to be one or more selected from organic resins, inorganic fine particles derived from inorganic sols, organic matter derived from tar and/or pitch, and organic matter derived from organic glue (i.e., any one of these or a mixture of these).

Therefore, examples of adhesives (tackifiers) that are applied to the carbon fiber bundles during production include organic resins (solutions), inorganic sols, pitch, tar, and organic glues. Specific examples include phenolic resins, epoxy resins, melamine resins, urea resins, alkyd resins, unsaturated polyester resins, polyurethane resins, thermosetting polyimide resins, alumina sols, silica sols, zirconia sols, chromia sols, titania sols, magnesia sols, calcia sols, yttria sols, pitch, tar, and starch glues, and one or more selected from these can be used.

The configuration and embedding conditions of the carbon fiber fabric B will be described below.
Fig. 1 is a schematic diagram showing one embodiment of the graphite-containing refractory of the present invention (a brick component constituting a tuyere brick), in which Fig. 1(a) is a perspective view and Fig. 1(b) is a cross-sectional view (a cross-sectional view parallel to the refractory working surface) taken along the dashed line in Fig. 1(a), where x is the working surface of the refractory (y is the counter-working surface). In the graphite-containing refractory of this embodiment, a plurality of carbon fiber bundles B are arranged (embedded) in parallel at predetermined intervals inside a refractory body A.

The arrangement of the carbon fiber bundles B inside the refractory body A is arbitrary and is not particularly limited, but since the tensile stress that causes cracks occurs in the longitudinal direction of the refractory during operation, it is preferable to arrange (embed) the carbon fiber bundles B linearly along one direction, and particularly preferable to arrange (embed) the carbon fiber bundles B along a direction perpendicular to the operating surface x of the refractory. In addition, when a plurality of carbon fiber bundles B are arranged, it is preferable to arrange (embed) them in parallel at a predetermined interval.
The carbon fiber bundles B embedded inside the refractory body A may or may not have their ends exposed on the surface of the refractory body A. In the latter case, on the working surface x side of the refractory, it is preferable that the distance between the end of the carbon fiber fabric B and the working surface x is as small as possible, but on the counter working surface y side, the distance between the end of the carbon fiber bundles B and the counter working surface y may be relatively large. This is because the carbon fiber bundles B do not need to be embedded in the part on the counter working surface y side of the refractory that is expected to remain even after use is finished.

The carbon fiber bundle B is a bundle of carbon fibers having a length L of 100 mm or more and a fiber diameter of 1 to 45 μm, and preferably contains 1,000 to 300,000 carbon fibers per bundle.
When the length L of the carbon fiber (the length of the carbon fiber bundle B) is less than 100 mm, the binding force between the refractory body A is small, so that the effect of the carbon fiber bundle B in suppressing the crack growth is small. When the fiber diameter of the carbon fiber is less than 1 μm or the number of carbon fibers per bundle is less than 1000, the carbon fiber bundle B is too thin, so that the effect of suppressing the local crack growth is reduced, and the increase in fracture energy is small. On the other hand, when the fiber diameter of the carbon fiber is more than 45 μm or the number of carbon fibers per bundle is more than 300,000, the carbon fiber bundle B is too thick, so that the compatibility between the refractory raw material (refractory body A) and the carbon fiber bundle B is poor, and defects due to the elasticity of the carbon fiber bundle, called springback, are likely to occur during molding.

Next, the composition of the refractory body A (the refractory raw material) will be described.
The refractory body A preferably contains 1 to 80 mass % of graphite raw material. By making the content of the graphite raw material 1 mass % or more, it is possible to suppress the oxidation loss of the carbon fibers inside the refractory. On the other hand, by making the content of the graphite raw material 80 mass % or less, it is possible to suppress the oxidation loss of the graphite raw material on the surface of the refractory. As the graphite (carbon raw material), scaly graphite or the like is generally used.
In general, the lining (including the tuyere) of the converter used in the refining process is made of a magnesia-carbonaceous refractory (a graphite-containing refractory with magnesia raw material as aggregate), which is a refractory mainly composed of magnesia and carbon. When the refractory body A is a magnesia-carbonaceous refractory, the refractory body A preferably contains 20 to 99 mass% of magnesia raw material, which suppresses cracking due to thermal spalling and provides a refractory with corrosion resistance that can withstand the erosion of converter slag containing a large amount of FeO. It is preferable to use a high-purity magnesia raw material with a magnesia concentration of 90 mass% or more as the magnesia raw material.

In addition, generally, alumina-silicon carbide-carbonaceous refractories (graphite-containing refractories with aggregates of alumina raw materials and silicon carbide raw materials) which are refractories mainly composed of alumina, silicon carbide, and carbon, and alumina-silicon carbide-silica-carbonaceous refractories (graphite-containing refractories with aggregates of alumina raw materials, silicon carbide raw materials, and silica raw materials) which are refractories mainly composed of alumina, silicon carbide, silica, and carbon are used for the lining of torpedoes and blast furnace ladles used in the hot metal pretreatment process. When the refractory body A is an alumina-silicon carbide-carbonaceous refractory or an alumina-silicon carbide-silica-carbonaceous refractory, it is preferable that the alumina raw material is contained at 10 to 95 mass%, which provides high corrosion resistance against hot metal pretreatment slag and further suppresses the occurrence of cracks due to thermal spalling. It is preferable to use a high-purity alumina raw material with an alumina concentration of 70% by mass or more.

Furthermore, when the refractory body A is an alumina-silicon carbide-carbonaceous refractory or an alumina-silicon carbide-silica-carbonaceous refractory, it is preferable that the refractory body A contains 1 mass% or more of silicon carbide raw material. By containing 1 mass% or more of silicon carbide raw material, oxidation of graphite in the air atmosphere can be suppressed, so that high crack resistance can be maintained. In addition, it is preferable to use a high-purity silicon carbide raw material with a silicon carbide concentration of 80 mass% or more as the silicon carbide raw material.
When the refractory body A is an alumina, silicon carbide, silica or carbonaceous refractory, it preferably contains 1 to 50 mass % of silica raw material, which allows both high cracking resistance and high resistance to melting damage to be achieved.

The magnesia-carbon refractories used for lining the converter are used under very severe conditions, such as mechanical impacts from the charge, abrasion from stirring of molten steel and molten slag, slag erosion from molten slag, and sudden temperature changes during converter operation. For this reason, it is preferable to use magnesia-carbon refractories that are highly durable and can withstand the severe conditions in order to ensure stable operation. Similarly, alumina-silicon carbide-carbon refractories and alumina-silicon carbide-silica-carbon refractories used for lining the molten pig iron pretreatment vessels such as torpedoes and blast furnace ladles are also used under very severe conditions, so it is preferable to use refractories that can withstand these conditions. According to the present invention, the fracture energy of the graphite-containing refractories used under these very severe conditions is significantly improved compared to conventional graphite-containing refractories, and high durability is obtained.

In addition, when the refractory body A is a silica-silicon carbide-carbonaceous refractory, which is a refractory whose main components are silica, silicon carbide, and carbon, it is preferable that the refractory contains 1% by mass or more of silicon carbide raw material and 1 to 50% by mass of silica raw material, thereby achieving both high crack resistance and high resistance to melting damage. By containing 1% by mass or more of silicon carbide raw material, oxidation of graphite in the air atmosphere can be suppressed, so high crack resistance can be maintained. Note that it is preferable to use a high-purity silicon carbide raw material with a silicon carbide concentration of 80% by mass or more as the silicon carbide raw material.

Here, as the alumina raw material, for example, one or more of alumina shale, white alumina, brown alumina, etc. are used. As the silicon carbide raw material, for example, one or more of green silicon carbide, black silicon carbide, etc. are used. As the silica raw material, for example, one or more of azalea, mullite, etc. are used.
The graphite-containing refractory may further contain (mix) a metal powder raw material for the purpose of suppressing the amount of heat radiation from the steelmaking vessel while increasing durability. Examples of the metal powder raw material include metal Si, metal Al, metal Al-Si, Al ₄ SiC ₄ , and B ₄ C, and one or more of these may be contained. The content of the metal powder raw material is not particularly specified, but is usually preferably about 1 to 5 mass %. If the content (mixture amount) of the metal powder raw material is less than 1 mass %, the effect of improving durability by mixing the metal powder raw material is not sufficiently obtained, while if it exceeds 5 mass %, the strength becomes too high, so that cracks are likely to occur when used in an actual machine, making the bricks more likely to break, and the number of times of use in the actual machine may be reduced.

The refractory body A can contain about 10 to 90 mass % of refractory chips obtained by crushing used refractories as an aggregate raw material. In particular, when the refractory body A is an alumina/silicon carbide/carbonaceous refractory (including alumina/silicon carbide/silica/carbonaceous refractories further containing a silica raw material; the same applies below), the refractory chips obtained by crushing used alumina/silicon carbide/carbonaceous refractories (including alumina/silicon carbide/silica/carbonaceous refractories further containing a silica raw material; the same applies below) can be suitably used as the aggregate raw material.
When the refractory waste is contained in this manner, the remainder of the refractory raw material is unused raw material (virgin raw material).

In the refractory body A made of alumina, silicon carbide, and carbonaceous refractories, when the content of refractory scrap obtained by crushing used alumina, silicon carbide, and carbonaceous refractories is 10 to 90 mass %, the cracking resistance and corrosion resistance are the same as those of a graphite-containing refractory using only virgin raw materials. The reason for this is that although the purity of the refractory scrap raw material is lower than that of the virgin raw material, by using the refractory scrap raw material and the virgin raw material in combination, a significant decrease in corrosion resistance of the Al ₂ O ₃ component in the refractory scrap raw material can be suppressed. However, when the content of the refractory scrap is more than 90 mass %, the content of the virgin raw material is too small, so that a significant decrease in corrosion resistance of the Al ₂ O ₃ component in the refractory scrap raw material cannot be suppressed. In addition, when the content of the refractory scrap is less than 10 mass %, the reuse rate of the refractory scrap is too low, so the cost of processing the refractory scrap as industrial waste increases significantly.

The graphite-containing refractory of the present invention can be applied to various steelmaking vessels such as converters, molten iron pretreatment vessels, and ladle vessels.
As described above, converters are used under harsh conditions with repeated thermal fluctuations, and therefore the effects of the present invention are significant, and the graphite-containing refractory of the present invention is therefore suitable for use in converters. Among these, converter tuyere bricks are particularly susceptible to large thermal fluctuations and cracking due to thermal expansion, and therefore the effects of the present invention are particularly significant and the refractory is particularly suitable.
In addition, the molten iron contained in the molten iron pretreatment vessel contains 2 mass % or more of carbon. When the graphite-containing refractory of the present invention is applied to a molten iron pretreatment vessel, the graphite and carbon fibers constituting the refractory are little dissolved and lost, making the refractory suitable for use in a molten iron pretreatment vessel.
Furthermore, since ladle vessels are used under harsh conditions where thermal fluctuations are repeated due to the repeated receipt and discharge of molten iron in a relatively short period of time, the effects of the present invention are significant, and therefore the graphite-containing refractory material of the present invention is also suitable for use in ladle vessels.

Next, a method for producing the graphite-containing refractory material of the present invention will be described.
2 shows an example of a manufacturing process for the graphite-containing refractory of the present invention. This manufacturing process includes a pretreatment step (i) of removing a sizing agent from a commercially available carbon fiber bundle b to which the sizing agent is attached, a preparation step (ii) of attaching an adhesive to the carbon fiber bundle b that has been subjected to the pretreatment step (i), a molding step (iii) of embedding the carbon fiber bundle b to which the adhesive is attached in the preparation step (ii) inside a refractory raw material a, molding the refractory raw material a in which the carbon fiber bundle b is embedded to obtain a refractory molded body, and a drying step (iv) of drying the refractory molded body obtained in the molding step (iii).

Resins such as epoxy resins are often used as sizing agents, and the sizing agent can be removed from the carbon fiber bundles b in the pretreatment step (i) by baking in a non-oxidizing atmosphere, or by dissolving by immersing in a dissolving solution or washing with a dissolving solution. In the latter case, acids, alkalis, organic solvents, etc. can be used as dissolving solutions, but dissolving with an organic solvent is preferable because it does not require large-scale equipment and has excellent removal rate and removal speed. As an organic solvent, acetone is preferable in terms of cost, removal rate, and removal speed.

When the sizing agent of the carbon fiber bundle b is removed by immersion in a dissolving liquid such as an organic solvent, if the sizing agent on the outer surface of the carbon fiber bundle b is dissolved and disappears, leaving the carbon fiber strands partially exposed, the carbon fiber bundle B having no sizing agent attached to at least part or all of its outer surface will be disposed inside the refractory body A, and the effect of the present invention will be obtained. However, if the sizing agent is dissolved and disappears even inside the carbon fiber bundle b, leaving the carbon fiber strands in a state of being broken into pieces, the carbon fiber bundle B having no sizing agent attached to part or all of its outer surface and part or all of its interior will be disposed inside the refractory body A, which is desirable as it makes the adhesion between the carbon fiber B and the refractory body A stronger. Therefore, in the pre-treatment step (i), a treatment is performed on the commercially available carbon fiber bundles b to which a sizing agent is attached, to remove at least some or all of the sizing agent that is attached to the outer surface of the carbon fiber bundle, and preferably, a treatment is performed to remove some or all of the sizing agent that is attached to the outer surface of the carbon fiber bundle and some or all of the sizing agent that is attached to the inside of the carbon fiber bundle.

In the preparation step (ii), an adhesive is applied to the carbon fiber bundles. At this time, the adhesive is applied so as to cover the outer surface of the carbon fiber bundles in order to bond and integrate the carbon fiber bundles b and the refractory raw material a, and more preferably, the adhesive is permeated (impregnated) into the carbon fiber bundles (gaps between the carbon fibers) in order to integrate the carbon fiber bundles b as a bundle.
In the preparation step (ii), when the adhesive is applied so as to cover the outer surface of the carbon fiber bundle and is made to penetrate (impregnate) the inside of the carbon fiber bundle (the gaps between the carbon fibers), for example, the carbon fiber bundle b is immersed in a resin (resin solution) or sol serving as an adhesive, or the resin (resin solution) or sol serving as an adhesive is sprayed onto the carbon fiber bundle b.

As the solvent for the adhesive (solution), any of water solvent, organic solvent (organic solvent), and organic-water mixed solvent may be used, but from the viewpoint of improving the bending strength and fracture energy and increasing the production yield, organic-water mixed solvent is particularly preferred. When a water solvent is used as the solvent, a large amount of volatilization escapes from the inside of the refractory molded body when drying the refractory molded body, and many defects such as pores are formed, so that cracks are likely to occur, compared to when an organic solvent-water mixed solvent is used. In addition, when an organic solvent is used as the solvent for the adhesive solution, the entanglement of the carbon fiber bundle and the adhesive is poor, and there is a risk that the adhesiveness is not uniformly imparted to the carbon fiber bundle, compared to when an organic solvent-water mixed solvent is used. As a result, when a water solvent or an organic solvent is used, the effect of improving the bending strength and fracture energy and the production yield are slightly lower than when an organic solvent-water mixed solvent is used.
Examples of organic substances used in the organic solvent or organic-water mixed solvent include ethylene glycol, and these can be used alone or in combination of two or more.

In the molding step (iii), the carbon fiber bundles b to which the adhesive has been applied in the preparation step (ii) (preferably the carbon fiber bundles b to which the adhesive has been permeated (impregnated) into the inside of the bundle and also applied to the outer surface) are embedded inside the refractory raw material a while the adhesive is still viscous, and the refractory raw material a with the embedded carbon fiber bundles b is molded to obtain a refractory molded body (molded product of the refractory raw material). When molding is performed by press molding as shown in FIG. 2, an appropriate amount of binder is usually added to the refractory raw material and kneaded, the carbon fiber bundles b are embedded in the kneaded product, and then press molding is performed. Examples of binders that can be used include phenol resin (base agent) + hexamine (hardener), carbon bond, and ceramic bond.

Here, the adhesive attached to the carbon fiber bundles b may be in a state in which it has a certain degree of hardening when the carbon fiber bundles b are embedded in the kneaded material, as long as it has enough adhesiveness to bond the carbon fiber bundles b and the refractory raw material a (kneaded material) as described above (a so-called semi-dried state).
As a method for filling the kneaded material of the refractory raw material a together with the carbon fiber bundles b into a mold, for example, there is a method in which a certain amount of the kneaded material is charged into the mold, and then a plurality of carbon fiber bundles b are arranged (charged) in parallel, and a certain amount of the kneaded material is further charged into the mold. Therefore, in order to produce a graphite-containing refractory in which a plurality of carbon fiber bundles B are embedded inside the refractory body A as shown in Fig. 1 by this method, a step of charging a certain amount of the kneaded material into the mold, and then arranging a plurality of carbon fiber bundles arranged in parallel on the kneaded material, and a step of charging a certain amount of the kneaded material on the kneaded material are repeatedly performed.

The press molding can be a general die press molding in which compression is performed in one direction in a die, but it can also be CIP molding in which pressure is applied evenly from all directions using a liquid. For shapes where it is difficult to apply even pressure by unidirectional compression, such as shapes with different thicknesses depending on the part, it is preferable to use CIP molding because it reduces bias in the degree of compression depending on the part.
The molding step (iii) may be performed by a molding method other than press molding. Examples of molding methods other than press molding include molding by pouring, one of which is a method of installing an inner frame at a construction site, which is a working surface of a pot or tundish, pouring an amorphous refractory (a refractory raw material) into the inner frame, drying (drying step) and solidifying, and then removing the inner frame. There is also a method of pouring an amorphous refractory (a refractory raw material) into a formwork of a refractory shape, rather than pouring it into the construction site, and transporting the refractory removed from the formwork after drying (drying step) and solidifying to the construction site, and although this method requires a lot of work to install the refractory at the construction site, it is desirable because it is easy to embed the carbon fiber bundle when pouring the amorphous refractory into the formwork and to control the temperature during solidification. In these casting molding methods, carbon fiber bundles are placed in the inner frame or mold described above, and then amorphous refractory (refractory raw material) is poured into the inner frame or mold, and then dried (drying process) and solidified.

The refractory molded body (molded product) obtained as described above is dried in a drying step (iv). This drying is usually carried out at about 200 to 230° C. for the purpose of drying (curing) the refractory molded body. After drying (curing), the refractory molded body may be subjected to reduction firing (caulking treatment) to produce a product brick (fired brick).
In addition, the refractory molded body obtained by the above-mentioned casting molding is dried and solidified by heating the refractory molded body held in an inner frame installed at the construction site or in a form installed in another location with a heating means such as a heating burner, after which the inner frame is removed and the mold is taken out.

As a result of the above, a graphite-containing refractory of the present invention is obtained, in which carbon fiber bundles B are arranged inside a refractory body A, and the carbon fiber bundles B are made of carbon fiber bundles having no sizing agent attached to at least a part or all of their outer surface, preferably carbon fiber bundles having no sizing agent attached to a part or all of their outer surface and a part or all of the interior of the bundle, and are bonded to the refractory body A via adhesive component c. As described above, the graphite-containing refractory of the present invention is less likely to develop defects such as cracks during production, and can be produced with a high production yield.

In order to study the blending of magnesia-carbonaceous refractories (graphite-containing refractories with magnesia raw materials as aggregate) used in converters, refractory molded products were produced using magnesia raw materials as aggregate with the raw material blend shown in Table 1, i.e., graphite-containing refractories without embedded carbon fiber bundles. When kneading and molding the refractory raw materials, 3 mass% of phenolic resin and 0.3 mass% of hexamine were blended as binders on an outer basis relative to the refractory raw materials. The melting resistance and cracking resistance of the graphite-containing refractories produced were evaluated using the following methods. The results are also shown in Table 1.

The corrosion resistance was evaluated based on the amount of corrosion measured by the lining method using a high-frequency induction furnace as shown in Fig. 3 (Test Method). In the test using the lining method, the test temperature was 1650°C, the temperature was held for 4 hours, and synthetic slag having the composition shown in Table 2 was added every hour. After cooling, the amount of corrosion on the working surface was measured. From the amount of corrosion, a corrosion index was calculated with the amount of corrosion of Blend Example 1-4 in Table 1 taken as 100. Fig. 3(A) is an explanatory diagram showing the test implementation state in a vertical cross section of the test furnace and the cylindrical sample, Fig. 3(B) is a plan view of the cylindrical sample shown in Fig. 3(A), and Fig. 3(C) is a perspective view showing one of the test pieces constituting the cylindrical sample shown in Figs. 3(A) and (B).
For crack resistance, the dynamic modulus of elasticity _E0 in the longitudinal direction of a 40 x 40 x 200 mm sample was measured according to the ultrasonic pulse method specified in JIS R1605, and then a cycle of heating at 1500°C for 10 minutes, water cooling for 5 minutes, and air cooling for 10 minutes was repeated three times. After these three cycles were completed, the dynamic modulus of elasticity _E3 was measured again by the above method, and the rate of change in the dynamic modulus of elasticity _E3 / _E0 before and after the test was used as an index for evaluation.

As shown in Example 1-2 to Example 1-8 in Table 1, when the graphite content was 1 to 80 mass% and the magnesia raw material content was 20 to 99 mass%, the corrosion resistance and cracking resistance were almost constant. However, as shown in Example 1-1, when the graphite content was less than 1 mass%, the corrosion resistance was significantly reduced. Also, as shown in Example 1-9, when the magnesia raw material content was less than 20 mass%, the corrosion resistance was significantly reduced. From these results, it can be seen that in order to ensure the cracking resistance of graphite-containing refractories, the graphite content must be 1 mass% or more, and further, in order to achieve both corrosion resistance and cracking resistance in the compounding of magnesia and carbonaceous raw materials, it is preferable to set the graphite content to 1 to 80 mass% and the magnesia raw material content to 20 to 99 mass%.

As shown in Fig. 1, a plurality of carbon fiber bundles B were arranged (embedded) in parallel at equal intervals along the longitudinal direction inside a refractory body A to produce a graphite-containing refractory (brick) having a size of 1000 mm in the longitudinal direction, 300 mm in the lateral direction, and 90 mm in height. The bending strength and fracture energy of this graphite-containing refractory were evaluated by the following methods.
The bending strength was measured using a test piece cut to a size of 40×40×160 mm, with a center distance of 100 mm and a load application speed of 0.5 mm/min, in accordance with the three-point bending test method described in JIS R2213, as shown in Fig. 4 (Test Method). Fig. 4(A) is an explanatory diagram showing a schematic diagram of the implementation of the three-point bending strength test, and Fig. 4(B) is an explanatory diagram showing a schematic diagram of the end face of the test piece in Fig. 4(A).

As shown in FIG. 5, the breaking energy was determined by taking the position at which the first peak value was shown in the load-displacement curve obtained in the three-point bending strength test as the reference position and calculating the area within a range of 1 mm of displacement from the reference position.
Tables 3 to 7 show the configurations and characteristics (flexural strength, fracture energy) of the graphite-containing refractories (graphite-containing refractories in which the carbon fiber woven bundles B are embedded inside the refractory body A) of the invention examples and comparative examples. Tables 6 and 7 also show the production yields of the graphite-containing refractories.

The examples in Table 3 examine the effect of the length L of the carbon fibers constituting the carbon fiber bundle B embedded inside the refractory body A on the bending strength and fracture energy of the graphite-containing refractory.
In this example, a graphite-containing refractory (brick) was produced according to the production flow of Fig. 2. When the refractory raw materials were kneaded and molded, 3 mass % of phenol resin and 0.3 mass % of hexamine were blended as binders based on the refractory raw materials.

A carbon fiber bundle consisting of 60,000 carbon fibers with a fiber diameter of 7 μm was cut into seven lengths: 90 mm, 100 mm, 200 mm, 400 mm, 600 mm, 800 mm, and 1000 mm. These carbon fiber bundles were immersed in acetone to remove the sizing agent, and then, in order to improve the adhesion (adhesion) between the carbon fiber bundle and the refractory raw material as well as the adhesion (adhesion) between the carbon fibers that make up the carbon fiber bundle, the carbon fiber bundle was immersed in a phenol resin (adhesive) solution using a mixture of organic matter (ethylene glycol) and water as a solvent to impart adhesion, and the carbon fiber bundle and magnesia-carbonaceous raw material in this adhesive state were filled into a press molding die using the following method.

After 10% by mass of magnesia-carbonaceous raw material (the amount of raw material when the amount of raw material that can fill the mold volume to capacity is 100% by mass; the same applies below) was spread on the bottom of the mold, several carbon fiber bundles to which adhesiveness was imparted were arranged in the longitudinal direction at intervals of 5 mm in the short direction. Next, 15% by mass of magnesia-carbonaceous raw material to the mold volume was charged into the mold, and carbon fiber bundles to which adhesiveness was imparted were arranged again in the same manner, and then 15% by mass of magnesia-carbonaceous raw material to the mold volume was charged. As described above, after charging the magnesia-carbonaceous raw material, the process of arranging the carbon fiber bundles to which adhesiveness was imparted in the long direction at intervals of 5 mm in the short direction was repeated, and the magnesia-carbonaceous raw material and the carbon fiber bundles were filled into the mold. After filling was completed, press molding was performed to obtain a refractory molded body, which was then dried to obtain the product (magnesia-carbonaceous brick containing carbon fiber).

As shown in Examples 1-1 to 1-6, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which carbon fiber bundles with a fiber length of 100 mm or more were embedded were significantly high. On the other hand, as shown in Example 1-0, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which carbon fiber bundles with a fiber length of less than 100 mm were embedded were lower than those of the above examples. One reason for this is that the short fiber length did not provide a high crack growth inhibition effect. From these findings, it was found that in order to provide a high crack growth inhibition effect and to sufficiently increase the bending strength and fracture energy, it is preferable to set the carbon fiber length to 100 mm or more.

The examples in Table 4 examine the effect of the fiber diameter of the carbon fibers constituting the carbon fiber bundle B embedded inside the refractory body A on the bending strength and fracture energy of the graphite-containing refractory.
In this example, the fiber diameter was set to five levels, i.e., 1 μm, 7 μm, 23 μm, 45 μm, and 50 μm, and 60,000 carbon fibers with a fiber length of 600 mm were bundled together to form a carbon fiber bundle. Carbon fiber-containing magnesia-carbonaceous bricks were produced in the same manner as in the examples of Table 3.

As shown in Examples 1-4 and 2-1 to 2-3, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which a carbon fiber bundle consisting of 60,000 carbon fibers with a fiber diameter of 1 to 45 μm was embedded was high. On the other hand, as shown in Example 2-4, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which a carbon fiber bundle consisting of 60,000 carbon fibers with a fiber diameter of 50 μm was embedded was lower than those of the above examples. One of the reasons for this is that the carbon fiber bundles were too thick, which resulted in poor entanglement between the carbon fiber bundles and the magnesia-carbonaceous raw material, making it easy for springback to occur during molding. From these facts, it was found that in order to achieve a high crack growth inhibition effect and to sufficiently increase the bending strength and fracture energy, it is preferable for the carbon fiber diameter to be 1 to 45 μm.

The examples in Table 5 examine the effect of the number of carbon fibers per bundle of carbon fiber bundle B embedded inside the refractory body A on the bending strength and fracture energy of the graphite-containing refractory.
In this example, the number of carbon fibers per bundle of carbon fiber bundle B was set to eight levels of 900, 1000, 30,000, 60,000, 120,000, 240,000, 300,000, and 350,000, and carbon fiber bundles having a fiber length of 600 mm and a fiber diameter of 7 μm were bundled together to form carbon fiber bundles. Carbon fiber-containing magnesia carbonaceous bricks were produced in the same manner as in the examples of Table 3.

As shown in Examples 1-4 and 3-1 to 3-5, the fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which carbon fiber bundles of 1,000 to 300,000 carbon fibers were embedded was high. On the other hand, as shown in Example 3-0, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which carbon fiber bundles of 900 carbon fibers were embedded were lower than those of the above examples. This is because the number of carbon fibers per carbon fiber bundle was small, so a high crack propagation suppression effect could not be achieved. In addition, as shown in Example 3-6, the bending strength and fracture energy of the carbon fiber-containing magnesia-carbonaceous bricks in which carbon fiber bundles of 350,000 carbon fibers were embedded were also lower than those of the above examples. The reason for this is that the carbon fiber bundles were too thick, which resulted in poor entanglement between the carbon fiber bundles and the magnesia-carbonaceous raw materials, making springback likely to occur during molding. Based on these factors, it was found that in order to achieve a high crack growth inhibition effect and to sufficiently increase bending strength and fracture energy, it is preferable to set the number of carbon fibers per bundle of carbon fiber bundle B to 1,000 to 300,000.

The examples in Table 6 examine the effect of removing the sizing agent on the bending strength, fracture energy, and production yield of the graphite-containing refractory material, for carbon fiber bundles B embedded inside the refractory body A.
A magnesia-carbonaceous brick containing carbon fiber of Comparative Example 4-1 was produced under the same production conditions as the magnesia-carbonaceous brick containing carbon fiber of Inventive Example 1-4, except that a carbon fiber bundle from which a sizing agent had not been removed was used, and the fracture energy was measured. Ten magnesia-carbonaceous bricks containing carbon fiber of Inventive Example 1-4 and Comparative Example 4-1 were produced, and the production yield was compared.

The carbon fiber-containing magnesia-carbonaceous brick of Example 1-4 had a high fracture energy and a production yield of 100%. On the other hand, the carbon fiber-containing magnesia-carbonaceous brick of Comparative Example 4-1, which used a carbon fiber bundle from which the sizing agent had not been removed, had a low fracture energy and a significantly reduced production yield of 40%. The reason for the low fracture energy is that the sizing agent of the carbon fiber bundle was not removed, so the adhesive only adhered to the surface of the carbon fiber bundle via the sizing agent, resulting in low adhesion (adhesion) between the carbon fiber bundle and the refractory material and low adhesion (adhesion) between the carbon fibers forming the carbon fiber bundle. In addition, when the carbon fiber bundle is bent during molding, the adhesion between the sizing agent and the surface of the wires of the carbon fiber bundle peels off, reducing the effect of improving fracture energy by properly adhering and integrating the carbon fiber and the refractory raw material. Another factor behind the low manufacturing yield is that carbon fiber bundles from which the sizing agent has not been removed have a high elastic modulus in the bending direction, which creates internal stress when the refractory raw material and carbon fiber bundles are filled into a mold and press-molded, causing defects such as cracks. Based on these findings, it was found that by placing carbon fiber bundles from which the sizing agent has been removed in advance inside the refractory body, it is possible to increase the fracture energy and maintain a high manufacturing yield.

The examples in Table 7 were obtained by investigating the effect of the type of adhesive solvent in which carbon fiber bundles were immersed to impart tackiness on bending strength, fracture energy, and production yield.
In this example, phenol resin, epoxy resin, alumina sol, and silica sol were used as adhesives, and the carbon fiber bundles from which the sizing agent had been removed in advance by immersion in acetone were immersed in solutions of a mixed solvent of organic matter (ethylene glycol) and water, a water solvent, and an organic solvent (methanol) to impart adhesiveness. Carbon fiber bundles were made by bundling 60,000 carbon fibers with a fiber length of 600 mm and a fiber diameter of 7 μm, and a magnesia-carbonaceous brick containing carbon fiber was manufactured in the same manner as in the examples of Table 3.

As shown in Examples 1-4, 5-3, 5-6, and 5-9, when an organic-water mixed solvent was used as the solvent for the adhesive solution, the bending strength and fracture energy were high and the manufacturing yield was 100%. On the other hand, as shown in Examples 5-1, 5-2, 5-4, 5-5, 5-7, 5-8, 5-10, and 5-11, when a water solvent or an organic solvent was used as the solvent for the adhesive solution, the bending strength and fracture energy were slightly lower and the manufacturing yield was also slightly lower. One factor that may be contributing to this is that when a water solvent is used as the solvent for the adhesive solution, a larger amount of vapor escapes from the inside of the brick when drying the bricks compared to when a mixed organic-water solvent is used as the solvent for the adhesive solution, and many defects such as pores are formed, making it easier for cracks to occur. In addition, when an organic solvent is used as the solvent for the adhesive solution, the carbon fiber bundles and the adhesive do not bond well together, and the adhesive is not uniformly imparted to the carbon fiber bundles, compared to when an organic-water mixed solvent is used. From these findings, it was found that when imparting adhesiveness to carbon fiber bundles with an adhesive, the fracture energy is particularly increased and the manufacturing yield can be maintained high when an organic-water mixed solvent is used as the solvent for the adhesive solution.

Next, the wear rate of the refractory bricks was examined by applying them to a steelmaking vessel. The examples in Table 8 show the wear rate of the carbon fiber-containing magnesia-carbonaceous bricks of Examples 1-4, 5-3, 5-6, and 5-9, which were applied to the tuyere of a converter. The wear rate is calculated by dividing the wear amount (mm) by the number of times of use (ch) (mm/ch), where the difference between the initial thickness D ₀ (mm) and the remaining thickness D ₁ (mm) is D ₀ -D ₁ (mm). According to Table 8, the wear rate of the brick of the present invention (graphite-containing refractory) was reduced by 50% or more compared to the conventional brick (graphite-containing refractory without carbon fiber embedded therein).

In the examples shown in Table 9, the carbon fiber-containing magnesia-carbonaceous bricks of Examples 1-4, 5-3, 5-6, and 5-9 were applied to the sidewall of the slag line of a ladle, and the wear rate was evaluated in the same manner. The wear rate was the same as above. According to Table 9, the wear rate of the brick of the present invention (graphite-containing refractory) was reduced by 50% or more compared to the conventional brick (graphite-containing refractory without embedded carbon fiber). From these results, it was found that the wear rate of the actual equipment can be significantly reduced by applying the carbon fiber-containing magnesia-carbonaceous brick of the present invention to the tuyere of a converter or the sidewall of a ladle.

In the examples of Table 10, alumina-silicon carbide-silica-carbonaceous refractories (graphite-containing refractories) using the alumina raw material, silicon carbide raw material, and silica raw material used for lining the molten iron pretreatment vessel as aggregates were applied to the side walls of blast furnace ladles, and the wear rate was evaluated. That is, except that the alumina raw material, silicon carbide raw material, and silica raw material were used as aggregates, alumina-silicon carbide-silica-carbonaceous refractories were manufactured under the same manufacturing conditions as the carbon fiber-containing magnesia-carbonaceous bricks of Invention Examples 1-4, 5-3, 5-6, and 5-9, and these were applied to the side walls of blast furnace ladles to evaluate the wear rate.
According to Table 10, the wear rate of the brick of the present invention (graphite-containing refractory) was reduced by about 20 to 30% compared to the conventional brick (graphite-containing refractory without embedded carbon fibers). From these results, it was found that the wear rate of an actual machine can be significantly reduced by applying the carbon fiber-containing alumina-silicon carbide-silica-carbonaceous brick of the present invention to the lining of a molten iron pretreatment vessel.

A Refractory body B Carbon fiber bundle c Adhesive component x Working surface y Non-working surface

Claims (6)

A method for producing a graphite-containing refractory having a refractory body (A) and a carbon fiber bundle (B) disposed therein, comprising the steps of:
A pre-treatment step (i) of subjecting a commercially available carbon fiber bundle (b) to a sizing agent attached thereto to a treatment for removing a part or all of the sizing agent attached to at least the outer surface of the carbon fiber bundle, among the sizing agents attached thereto;
a preparation step (ii) of applying an adhesive to the carbon fiber bundle (b) that has been subjected to the pretreatment step (i);
a molding step (iii) of embedding the carbon fiber bundles (b) to which the adhesive has been applied in the preparation step (ii) into the refractory raw material (a) while the adhesive is still tacky, and molding the refractory raw material (a) in which the carbon fiber bundles (b) are embedded to obtain a refractory molded body;
A drying step (iv) of drying the refractory molded body obtained in the molding step (iii),
A method for producing a graphite-containing refractory, characterized in that in the molding step (iii), the carbon fiber bundles (b) are bonded to the refractory raw material (a) via an adhesive. 2. The method for producing a graphite-containing refractory material according to claim 1, characterized in that in the pre-treatment step ( i ), a treatment is carried out to remove a part or all of the sizing agent adhering to the outer surfaces of the carbon fiber bundles and a part or all of the sizing agent adhering to the inside of the carbon fiber bundles. 3. The graphite-containing refractory according to claim 2 , characterized in that in the preparation step (ii), an adhesive is contained within the carbon fiber bundles (b) to which no sizing agent is attached. 4. The method for producing a graphite-containing refractory material according to claim 1 , wherein the adhesive is at least one selected from the group consisting of organic resins, inorganic sols, tar, pitch and organic glues. The method for producing a graphite-containing refractory material according to any one of claims 1 to 4, characterized in that the carbon fiber bundle (b) is a bundle of carbon fibers having a length of 100 mm or more and a fiber diameter of 1 to 45 µm, and the number of carbon fibers per bundle is 1,000 to 300,000. The method for producing a graphite-containing refractory according to any one of claims 1 to 5, characterized in that in the molding step (iii), a plurality of carbon fiber bundles (b) are arranged in parallel at intervals inside the refractory raw material (a).

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