Alumina-magnesia refractory brick

Abstract

To provide an alumina-magnesia refractory brick capable of reducing crack propagation.SOLUTION: A refractory brick includes an alumina raw material, a magnesia raw material, and a used alumina-magnesia-based casting material. A content amount of the used alumina-magnesia-based casting material is 10 mass% or over and 80 mass% or under, and more preferably, 20 mass% or over and 60 mass% or under. The used alumina-magnesia-based casting material may be replaced by a hydrated then fired alumina cement.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a refractory material used in a furnace, and more particularly to a refractory brick that can be applied to a steelmaking ladle. [Background technology]

[0002] Alumina-magnesia refractory bricks or castable materials are used to line steelmaking ladles. Alumina-magnesia refractory bricks can be damaged by crumbling during use, but alumina-magnesia castable materials are less susceptible to crumbling damage.

[0003] The reason for this is thought to be that the CaO contained in the alumina cement added to the alumina-magnesia pourable material gives it hot deformability.

[0004] Paragraph 0031 of Patent Document 1 discloses an alumina-magnesia pourable material containing the above-mentioned alumina cement as a prior art.

[0005] Furthermore, Patent Document 2 discloses a castable refractory in which a calcium aluminosilicate compound is added in addition to an alumina-based raw material, a magnesia-based raw material, and alumina cement, as alumina-magnesia castable refractory is prone to spalling and wear due to volume expansion during use. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-145684 [Patent Document 2] Japanese Patent Application Publication No. 2019-006630 Summary of the Invention [Problem to be solved by the invention]

[0007] The cited document 1 points out the following problem: if alumina cement used in pouring materials is applied to firebricks, the CaO contained in the alumina cement reacts with water, causing the molding mixture to become dry and brittle, making press molding difficult and preventing sufficient packing density from being obtained even after molding (paragraph 0033).

[0008] Furthermore, when attempting to install castable refractories in general, not just the castable refractory disclosed in Cited Document 2, a large amount of equipment and machinery is required for on-site construction of the pouring and drying processes, as explained in the background art section of Patent Document 1. In blast furnace steelworks, gases generated during the ironmaking process can be used in the drying process, but in electric furnace steelworks, no gases are generated, so refractory bricks are required for lining the ladles.

[0009] SUMMARY OF THE INVENTION In view of the above-mentioned conventional circumstances, an object of the present invention is to provide an alumina-magnesia refractory brick that is moldable and reduces the risk of crumbling. [Means for solving the problem]

[0010] According to the present invention, there is provided the following alumina-magnesia refractory brick. (1) Alumina-magnesia refractory bricks containing alumina raw materials, magnesia raw materials, and used alumina-magnesia casting materials. (2) An alumina-magnesia refractory brick having a content of the alumina-magnesia castable material after use of 20% by mass or more and 60% by mass or less. (3) Alumina-magnesia refractory bricks containing alumina raw materials, magnesia raw materials, and alumina cement hydrated and then fired. [Effects of the Invention]

[0011] The used alumina-magnesia casting material contains CaO components that have been subjected to thermal history, so it can be molded during manufacturing and cracks during use can be reduced. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Basic matters> The alumina-magnesia refractory brick of the present invention uses a used alumina-magnesia castable material in addition to an alumina raw material and a magnesia raw material. The used alumina-magnesia castable material contains CaO that has been subjected to a thermal history.

[0013] CaO that has undergone the above thermal history has no reaction activity with water, and the raw material does not become dry during production, making it possible to mold it, and furthermore, expansion during operation can be suppressed.

[0014] <Used alumina-magnesia pourable material> The used alumina-magnesia castable material usually contains about 1 to 5 mass % of CaO. The contained CaO has been subjected to thermal history and has lost its reactivity with moisture. Therefore, even if used alumina-magnesia castable material is added as a raw material for alumina-magnesia refractory bricks, the molding mixture will not become dry and can be molded.

[0015] After use, the alumina-magnesia castable material may have slag or base metal adhering to it, so it is preferable to remove this in the usual way and crush and size the sound portion before use.

[0016] The composition range of the used alumina-magnesia castable material is preferably 90% by mass or more of Al2O3, 10% by mass or less of MgO, and 5% by mass or less of CaO. The content of the used alumina-magnesia castable material in the entire raw material of the alumina-magnesia refractory brick is 10% by mass or more and 80% by mass or less, and if it is 20% by mass or more and 60% by mass or less, the effect of reducing crumbling and spalling resistance will be significant.

[0017] In addition to the above, the CaO source may be a CaO-containing material such as alumina cement that has been hydrated and then fired. The content of the hydrated and fired CaO in the alumina-magnesia refractory brick is preferably 0.1% by mass or more and 1% by mass or less, since this improves spalling resistance.

[0018] <Alumina raw material> Commercially available alumina raw materials can be used as the alumina raw material. Examples include fused alumina, sintered alumina, calcined alumina, brown fused alumina, and alumina shale. The purity of the alumina raw material is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0019] The proportion of the alumina raw material in the total refractory raw material is 15% by mass or more and 92% by mass or less, and more preferably 35% by mass or more and 75% by mass or less.

[0020] <Magnesia raw material> Commercially available magnesia raw materials can be used as the magnesia raw material. Examples include electrofused magnesia, seawater magnesia, and natural magnesia. The purity of the magnesia raw material is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0021] The proportion of the magnesia raw material in the total refractory raw material is 3% by mass or more and 7% by mass or less, and more preferably 4% by mass or more and 6% by mass or less.

[0022] <Binder> Known organic or inorganic binders can be blended. Organic binders include molasses, pulp waste liquor, dextrin, methylcelluloses, polyvinyl alcohol, and phenolic resin. Inorganic binders include bittern (MgCl2), alkali silicates such as sodium silicate and potassium silicate, and sodium aluminate. Known fireclay and silica fume can also be added to improve plasticity.

[0023] <Mixing and molding> A binder or water is added as needed to a raw material mixture prepared according to a conventional method and then kneaded. A known kneading machine can be used for kneading, and a known molding machine can be used for molding.

[0024] <Heat treatment temperature> The heat treatment temperature should preferably be between 110°C and 1200°C. This product utilizes the spinel generated by the reaction between alumina and magnesia during use, so heat treatment above 1200°C is not necessary. The heat treatment time varies depending on the size and shape of the brick, but can be adjusted as appropriate using standard methods. For example, it is preferable to perform the heat treatment at the highest temperature for around 6 to 18 hours. [Example]

[0025] The present invention will be described in detail below with reference to examples.

[0026] [Sample preparation] Table 1 shows the composition of the alumina-magnesia castable material after use. An alumina-magnesia refractory raw material mixture was prepared according to the blending ratios in Table 2. The fused alumina used had a purity of 95% by mass. The sintered magnesia used had a purity of 95% by mass.

[0027] The binder used was liquid sodium silicate containing 56% by mass of SiO2 and 28% by mass of Na2O. The liquid sodium silicate was added in an amount of 2.5% by mass based on the total refractory raw materials (100% by mass).

[0028] The alumina cement used in Comparative Example 2 was 70% by mass of Al2O3 and 25% by mass of CaO. The hydrated and fired alumina cement used in Example 7 was prepared by adding water to alumina cement to hydrate it, and then firing it.

[0029] The mixture of the refractory raw materials and binder was kneaded in a mixer, and the kneaded product was evaluated as "unacceptable" if it was dry and unsuitable for molding, and as "acceptable" if it was moist and suitable for molding. The kneaded product was molded using a friction press.

[0030] [Table 1]

[0031] [Table 2] [Expansion test under load] The expansion under load test was performed in accordance with JIS R2207-2.

[0032] That is, a cylindrical test piece was placed in a heating furnace, and the amount of dimensional change was continuously measured using a contact measuring instrument. A load of 0.2 MPa was applied to the test piece in the vertical direction. The temperature was heated to 1500°C at a rate of 6°C / min, and after reaching 1500°C, it was held for 3 hours. The atmosphere in the furnace was nitrogen, and the flow rate was 0.6 m 3 / h (standard conditions).

[0033] Under the above conditions, the difference between the dimensional change rate after 3 hours of holding at 1500°C and the dimensional change rate immediately after reaching 1500°C (hereinafter referred to as D) was determined. The value of D is preferably in the range of -1.3% to -0.4%, and more preferably in the range of -1.1% to -0.5%. If the value of D is -1.1% or more, joint opening is reduced. Furthermore, if the value is -0.5% or less, spalling resistance is improved. An even more preferable range for the value of D is -0.9% to -0.7%.

[0034] [Spalling resistance] Spalling resistance was evaluated in accordance with JIS R2657. The test specimens were cubic, measuring 50 x 50 x 50 mm. The entire test specimen was inserted into an electric furnace maintained at 1300°C, heated for 15 minutes, then removed and allowed to cool naturally at room temperature for 15 minutes. This cycle was repeated up to 20 times. Under the above conditions, the occurrence of cracks after the test was observed, and specimens that did not crack even after 20 times were rated as A, specimens that cracked after more than 15 but less than 20 times were rated as B, specimens that cracked after more than 10 but less than 15 times were rated as C, and specimens that cracked after 10 or fewer times were rated as D.

[0035] <Test Results> Examples 1 to 6 are alumina-magnesia bricks of the present invention to which recycled alumina-magnesia raw materials have been added. All of them can be press-formed, and all of them have improved spalling resistance compared to Comparative Example 1.

[0036] Of the above Examples 1 to 6, Examples 2 to 5 have D values in the range of -1.1% to -0.5%, which allows for reduction in creasing and provides greater spalling resistance than Comparative Example 1. In particular, Examples 3 and 4 have D values in the range of -0.9% to -0.7%, which provides effects more in line with the object of the present invention.

[0037] It is recognized that Example 1 is superior in both the value of D and spalling resistance to Comparative Example 1. Although the value of D in Example 6 is slightly low, it is within the allowable range, resulting in excellent spalling resistance.

[0038] In Example 7, alumina cement was hydrated, fired, and crushed, and the resulting raw material was added as a CaO source. Press molding was possible, and spalling resistance was improved compared to Comparative Example 1.

[0039] On the other hand, Comparative Example 1 is a conventional alumina-magnesia brick, which is inferior in both the value of D and spalling resistance.

[0040] In Comparative Example 2, alumina cement was added as a CaO source, but press molding was difficult.

Claims

1. An alumina-magnesia refractory brick containing an alumina raw material, a magnesia raw material, and a used alumina-magnesia castable material.

2. An alumina-magnesia refractory brick as described in claim 1, wherein the content of the alumina-magnesia pourable material after use is 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 60% by mass or less.

3. An alumina-magnesia refractory brick containing an alumina raw material, a magnesia raw material, and a raw material obtained by hydrating and then firing alumina cement.

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