JP2006111501A - Method for producing unfired carbon-containing brick - Google Patents

Abstract

An object of the present invention is to obtain a non-fired carbon-containing brick having improved oxidation wear resistance while suppressing a decrease in hot strength and corrosion resistance.
A method for producing unfired carbon-containing brick is, by weight, 3 to 40% carbon, 1 to 30% alumina having a purity of 95% or more, 0.5 to 10% aluminum or / and an aluminum alloy, the balance being It is characterized by comprising a molding step of kneading a mixture substantially consisting of magnesia and inevitable impurities to form a molded product, and a heat treatment step for heating the molded product.
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Description

  The present invention relates to a method for producing a non-fired carbon-containing brick used for a lining of a steelmaking furnace.

  Non-fired carbon-containing bricks such as magnesia-carbon bricks, magnesia-silicon carbide-carbon bricks have excellent slag resistance and thermal shock resistance and have been widely used as lining materials for various steelmaking furnaces. .

  However, there is a problem that the unfired carbon-containing brick is easily oxidized. When a decarburized layer is formed in the structure of the brick subjected to this oxidizing action, there is a possibility that the slag infiltrates the brick due to slag. Further, since the decarburized layer formed in the above-mentioned brick has low strength, it is likely to be worn and peeled due to the rocking of the molten metal, causing a serious damage as a lining material. As means for preventing the oxidation of this unfired carbon-containing brick, methods such as addition of aluminum or aluminum alloy, addition of boron oxide, addition of glass powder, etc. are known, but sufficient effects are still obtained. Not.

  Moreover, said additive accelerates | stimulates sintering of a brick, invites oversintering and reduces the thermal shock resistance of a brick. Further, when boron oxide or glass powder is added in a large amount, it is effective in preventing the oxidation of the brick, but since it is a low melting point substance, there is a problem that the corrosion resistance of the brick is lowered.

As means for improving these problems, Patent Document 1 (Japanese Patent Publication No. 8-25788) describes carbon, spinel, aluminum, silicon carbide and magnesia as non-fired carbon-containing bricks having slag resistance and thermal shock resistance. There is a disclosure of a brick of composition consisting of: However, the above composition is not preferable because the same problem as the magnesia-carbon described above remains.
Japanese Patent Publication No. 8-25788

  The present invention has been made in view of the circumstances described above, and provides a method for producing an unfired carbon-containing brick that solves the above-described problems and suppresses a decrease in corrosion resistance and hot strength while improving oxidation wear resistance. The purpose is to establish.

  The present inventor has been diligently developing magnesia-carbon bricks. The magnesia-carbon brick containing aluminum can prevent oxidation of the carbon component by preferentially oxidizing the aluminum component in the structure of the aluminum component. However, this antioxidant effect is not always sufficient, and a decarburized layer is generated in the brick structure. In addition, the thermal shock resistance of the brick may be insufficient due to oversintering. Therefore, the present inventor solved the above problem by blending a specific amount of high-purity alumina together with aluminum or an aluminum alloy.

  The production method of the unfired carbon-containing brick of the present invention is 3 to 40% carbon, 1 to 30% alumina having a purity of 95% or more, 0.5 to 10% aluminum or / and an aluminum alloy, and the balance is substantially It is characterized by comprising a molding step of kneading a mixture of magnesia and unavoidable impurities into a molded product, and a heat treatment step of heating the molded product.

  The particle size of alumina having a purity of 95% or more is preferably 0.3 mm or more, particularly 0.5 mm or more.

  The non-fired carbon-containing brick obtained by the production method of the present invention can improve the oxidation wear resistance while suppressing a decrease in corrosion resistance and hot strength as compared with conventional magnesia-carbon. As a result, as shown in Table 1 to be described later, durability much better than the conventional one can be obtained.

  The non-fired carbon-containing brick according to the present invention can be used as a lining for converters, ladles, vacuum degassing furnaces, kneading furnaces, electric furnaces, and the like. In particular, since the oxidation wear resistance is high, it is possible to exert an excellent effect in durability at a part that is easily subjected to a rocking shock of molten metal by outside refining or the like.

  The magnesia-carbon brick containing aluminum can prevent oxidation of the carbon component by preferentially oxidizing the aluminum component in the structure of the aluminum component. However, this antioxidant effect is not always sufficient, and a decarburized layer is generated in the brick structure. In addition, the thermal shock resistance of the brick may be insufficient due to oversintering. Therefore, the present invention solves the above problem by blending a specific amount of high-purity alumina together with aluminum or an aluminum alloy.

  That is, in the present invention, the added high-purity alumina forms a bond with the base material magnesia, thereby improving the hot strength of the brick structure. As a result, improvement in the hot strength of the brick structure reduces the deterioration in durability even if some decarburized layers are formed. In addition, when aluminum or an aluminum alloy is added to magnesia-carbon brick, aluminum carbide is produced by the reaction of aluminum and the carbon component, the elasticity of the brick structure is increased, and the thermal shock resistance is reduced. Reduction of thermal shock resistance can be overcome by improving the hot strength of the spinel produced by reacting with alumina and magnesia.

  Alumina has a small coefficient of thermal expansion, makes it difficult to form gaps between particles due to heat, can suppress the permeation of oxygen and the like, and as a result, can suppress the progress of oxidation of brick.

  Furthermore, although the presence of alumina generally causes a melting loss of brick, the use of a material having a purity of 95% or more can remarkably improve the corrosion resistance against slag, which has been regarded as a problem in the past. Therefore, as alumina, an electrofused or fired product having a purity of 95% or more can be used. If the purity is less than 95%, the above point is not improved, which is not preferable.

  The method for producing the unfired carbon-containing brick of the present invention is to knead a mixture of 3 to 40% carbon, 1 to 30% alumina with a purity of 95 or more, 0.5 to 10% aluminum or / and an aluminum alloy, and the balance being magnesia. Then, it consists of a molding step for molding into a predetermined shape and a treatment step for heating the molded product. Here, the purity of 95% or more is based on the weight ratio.

  The molding step and the heat treatment step can be performed in the same manner as normal conditions for non-fired bricks. That is, for example, at least one of a phenol resin, a furan resin, an epoxy resin, and the like is used as a binder, and 1 to 15 parts by weight of pitch or the like is added to 100 parts by weight of the brick composition and kneaded. Then, in accordance with the use / manufacturing equipment of the brick, the brick is formed by using a pressurizing means such as a reflection press, an oil press, or a rubber press. Next, a predetermined heat treatment is performed. As the heat treatment, it has an effect of preventing smoke generation from the binder in the initial use of the brick and a decrease in strength of the tissue, and it varies depending on the binder, but is, for example, 1000 ° C. or less, preferably 110 to 500 ° C. 130-400 ° C, 140-350 ° C, and 180-280 ° C. The heating time may be appropriately set such as 10 minutes to 40 hours, 20 minutes to 20 hours, 10 minutes to 10 hours, etc., although it depends on the material of the resin.

  The composition content of the mixture will be described below.

  Carbon: Effective for slag resistance and thermal shock resistance. Specific examples include natural graphite, artificial graphite, pitch coke, anthracite, and carbon black. Of these, highly scaly graphite is preferred. If the proportion of carbon is less than 3% by weight, the effect of adding carbon is not sufficiently exhibited, and if it exceeds 40% by weight, the strength and wear resistance of the brick are lowered, which is not preferable. As carbon, 5-35%, 5-30%, and 10-20% can be adopted. The lower limit of carbon can be 4% by weight or more, 5% by weight or more, 7% by weight or more, and 10% by weight or more. The upper limit value of carbon that can be combined with the lower limit value of carbon described above can be 35% by weight or less, 30% by weight or less, 20% by weight or less, or 17% by weight or less. The particle size of carbon is not particularly limited, but is preferably 0.3 mm or less or 0.5 mm or less, for example.

  Alumina: It is preferably added in the range of 1 to 30% by weight. If the addition amount is less than 1% by weight, the effect of addition cannot be obtained sufficiently, which is not preferable. Addition of more than 30% by weight is not preferable because the hot strength decreases. Therefore, as alumina, the range of 5 to 25% by weight and 10 to 20% by weight can be adopted. The lower limit of alumina can be 2% by weight or more, 4% by weight or more, or 6% by weight or more. The upper limit value of alumina that can be combined with the lower limit value of alumina described above can be 25 wt% or less, 20 wt% or less, or 15 wt% or less. As described above, alumina has a purity of 95% or more, and its particle size is preferably 0.3 mm or more or 0.5 mm or more. The upper limit of the particle size is preferably 10 mm, 5 mm, 2 mm, or 1 mm. If the particle size is less than 0.3 mm, the slag resistance is lowered, and the effect of the present invention cannot be obtained, which is not preferable.

  Aluminum: Not only aluminum but also aluminum alloys can be used. Examples of the aluminum alloy include an Al—Mg alloy, an Al—Si alloy, an Al—Mg—Si alloy, an Al—Mg—Cr alloy, and an Al—Ca alloy. These can be in the form of particles or powder. If the blending ratio is less than 0.5% by weight, the effect of preventing oxidation is small, and the corrosion resistance of the brick is lowered. On the other hand, if it exceeds 10% by weight, the corrosion resistance and thermal shock resistance are inferior. The compounding composition of aluminum or aluminum alloy is selected in consideration of the required oxidation wear resistance, corrosion resistance, thermal shock resistance, cost, etc., but by weight, 0.5 to 10%, 0.5 to 5 %, 0.5 to 4%. The upper limit of the compounding blend of aluminum or aluminum alloy includes 8%, 7%, 6%, and 5% by weight, and the lower limit that can be combined with the upper limit is 0.6% by weight. Although 0.7% and 1% are mentioned, it is not limited to these. The size of the aluminum or aluminum alloy to be blended can be selected as appropriate, and examples thereof include 3 mm or less, 2 mm or less, 1 mm or less, 0.5 mm or less, 0.15 mm or less, but are not limited thereto.

  Magnesia occupying the balance: Magnesia substantially shows the balance. Although natural or synthetic sintered products and electromelted products can be used, it is preferable to use a synthetic product having a constant quality. The particle size is adjusted to coarse, medium and fine so that a densely packed brick structure can be obtained.

  In general, it is preferable to use magnesia as the main material for the aggregate. As long as the characteristics of the carbon-containing refractory of the present invention are not lost, a part of magnesia can be replaced with one or more selected from refractory raw materials such as dolomite, calcia, spinel, zirconia. In addition, metal powders other than aluminum and aluminum alloys, such as silicon, magnesium and iron or alloy powders thereof, carbides such as boron carbide, silicon nitride and boron oxide, nitrides, borides, metal fibers, ceramic fibers, carbon fibers, etc. It is also possible to add an appropriate amount of one or more selected from fibers, glasses and the like. Silicon carbide is not actively contained. Even if silicon carbide is contained, it may be less than 0.4%, less than 0.2%, or less than 0.1% when the mixture is taken as 100%.

  As the binder, a resin system, particularly a thermosetting resin that is cured by heat treatment, can be employed. It depends on the properties required for non-fired bricks, but when the mixture is 100%, the binder may be 0.5-10% by weight, 1-8% by weight, 1-5% by weight. Or 1.5 to 6% by weight, or 2 to 5% by weight. Examples of the upper limit of the blending ratio of the binder include 8%, 7%, 6%, and 5% in terms of weight. The lower limit that can be combined with the upper limit is 0.6% in terms of weight. Examples include 7% and 1%, but are not limited thereto. Examples of the thermosetting resin include phenol resin, epoxy resin, and polyester resin.

Hereinafter, the present invention will be described by way of specific examples. A formulation weighed at a weight ratio as shown in Table 1 was used, and a phenol resin, which is a thermosetting resin, was added to the formulation as a binder and kneaded with a kneader to form a mixture. Alumina has a high purity, and has a weight ratio of 95% or more and a particle size of 0.5 mm or more. The remaining magnesia was used, and a particle size of 3 mm or less was used. Carbon having a particle size of 180 μm or less was used. Silicon carbide is not actively contained. And the above-mentioned mixture was pressurized with a friction press and the molded object was shape | molded. Thereafter, the compact was heat-treated at 230 ° C. for 24 hours to produce an unfired carbon-containing brick. Since this brick has not undergone the firing step, it is a non-fired type. The resulting bricks were evaluated by conducting tests on oxidation wear resistance, corrosion resistance and hot strength.
Evaluation of oxidation wear resistance: 5 kg of zirconia was put as a wear agent in a rotating drum lined with the specimen, and the amount of wear of the specimen after rotating for 5 hours while heating the inside of the drum at 1500 ° C. was measured.

  Evaluation of corrosion resistance: CaO / SiO2 slag collected from a ladle was used as an erodant, and erosion was performed at 1500 ° C. for 4 hours by a rotary erosion method, and the erosion dimension was measured.

  Evaluation of hot strength: The bending strength at 1400 ° C. in an electric furnace was measured by a three-point bending method with a span of 100 mm for a specimen cut into a size of 40 × 40 × 160 mm.

Examples 1 to 6, Comparative Example 1 and Comparative Example 2 contain 3% by weight of aluminum metal. Examples 1 to 6 contain 1 to 30% by weight of alumina. In Comparative Example 1, the amount of alumina is larger than that of the invention. Comparative Example 2 basically does not contain alumina. As shown in Table 1, Examples 1 and 2 are evaluated for oxidation wear resistance, corrosion resistance, and hot strength as ◎. It was good. In Example 3 and Example 4, the evaluation was good with respect to oxidation wear resistance, corrosion resistance, and hot strength, and was good. For Comparative Example 1, the evaluation of oxidation wear resistance, corrosion resistance, and hot strength was x. For Comparative Example 2, the evaluation of oxidation wear resistance and hot strength was x. Although the binder is 3%, basically the same effect can be expected at 2%, 5% and 7%. Aluminum is considered to be 3%, but basically the same effect can be expected even at 1%, 5%, and 7%. Thus, according to this example, it is possible to provide a non-fired carbon-containing brick having improved oxidation wear resistance while suppressing a decrease in hot strength and corrosion resistance.

Claims (2)

A mixture of 3 to 40% carbon, 1 to 30% alumina having a purity of 95% or more, 0.5 to 10% aluminum or / and an aluminum alloy, and the balance substantially consisting of magnesia and inevitable impurities is kneaded. Molding process to make a molded product,
A method for producing unfired carbon-containing bricks, comprising a heat treatment step for heating the molded article.   The method for producing unfired carbon-containing brick according to claim 1, wherein the alumina having a purity of 95% or more has a particle size of 0.5 mm or more.