JP7801614B2 - Manufacturing method of alumina-magnesia refractory bricks - Google Patents

Description

The present invention relates to a refractory material used in a furnace, and more particularly to a method for producing a refractory brick applicable to a steelmaking ladle.

Alumina-magnesia refractory bricks or castable material are used to line the interior of steelmaking ladles. Alumina-magnesia refractory bricks can be damaged by crumbling during use, but alumina-magnesia castable material is less susceptible to crumbling damage.

The reason for this is thought to be that the CaO contained in the alumina cement added to alumina-magnesia pourable materials gives them hot deformability.

Patent Document 1, paragraph 0031, discloses an alumina-magnesia pourable material containing the above-mentioned alumina cement as prior art.

Patent Document 2 also states that alumina-magnesia castable refractories are prone to spalling and wear due to volume expansion during use, and discloses a castable refractory that contains an alumina raw material, magnesia raw material, alumina cement, and a calcium aluminosilicate compound.

Japanese Patent Application Laid-Open No. 2007-145684 JP 2019-006630 A

The above-mentioned cited document 1 points out the following problem: if the alumina cement used in pouring materials is applied to firebricks, the CaO contained in the alumina cement will react with water, causing the molding mix to become dry and crumbly, making press molding difficult and preventing sufficient packing density from being achieved even after molding (paragraph 0033).

Furthermore, when attempting to install castable refractories in general, not just the castable refractory disclosed in Cited Document 2, as explained in the background art section of Patent Document 1, a large amount of equipment and machinery is required for on-site construction of the pouring and drying processes. In blast furnace steelworks, gases generated during the steelmaking process can be used in the drying process, but in electric furnace steelworks, gases are not generated, so refractory bricks are required to line the ladles.

Based on the above-mentioned conventional circumstances, the present invention aims to provide an alumina-magnesia refractory brick that is moldable and reduces crumbling.

According to the present invention, there is provided the following method for producing an alumina-magnesia refractory brick.
(1) A raw material blend containing 15% by mass or more and 92% by mass or less of alumina raw material , 3% by mass or more and 7% by mass or less of magnesia raw material , and 10% by mass or more and 80% by mass or less of used alumina-magnesia castable material is kneaded, molded, and heat-treated.
(2) A raw material mixture containing 15% by mass or more and 92% by mass or less of an alumina raw material, 3% by mass or more and 7% by mass or less of a magnesia raw material, and a raw material obtained by hydrating and then firing alumina cement is kneaded, molded, and heat-treated.

Since a used alumina-magnesia castable material containing a CaO component that has been subjected to thermal history is used, it is possible to form the material during production, and an alumina - magnesia refractory brick that can reduce crumbling during use can be obtained.

<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.

CaO that has undergone the above thermal history is inactive in reaction with water, and the raw material does not become dry during production, making it moldable, and it also helps prevent expansion during operation.

<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 the used alumina-magnesia castable material is added as a raw material for alumina-magnesia refractory bricks, the kneaded clay for molding will not become dry and can be molded.

After use, alumina-magnesia castable material may have slag or metal adhering to it, so it is recommended that you remove this using standard methods and crush and size the sound portion before using it again.

The composition range of the used alumina-magnesia castable material is preferably 90 mass % or more of Al ₂ O ₃ , 10 mass % or less of MgO, and 5 mass % or less of CaO. The content of the used alumina-magnesia castable material in the entire raw material for the alumina-magnesia refractory brick is 10 mass % or more and 80 mass % or less, and if it is 20 mass % or more and 60 mass % or less, the effect of reducing crumbling and spalling resistance will be significant.

In addition to the above, the CaO source may also be a CaO-containing substance such as alumina cement that has been hydrated and then fired. It is preferable to set the content of the hydrated and fired CaO in the alumina-magnesia refractory brick to between 0.1% and 1% by mass, as this improves spalling resistance.

<Alumina raw material>
As the alumina raw material, commercially available alumina raw materials can be used. 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.

The proportion of alumina raw material in the total refractory raw materials 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.

<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.

The proportion of magnesia raw materials in the total refractory raw materials 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.

<Binder>
The binder may be a known organic or inorganic binder. Examples of organic binders that can be used include molasses, pulp waste liquor, dextrin, methylcelluloses, polyvinyl alcohol, and phenolic resin. Examples of inorganic binders that can be used include bittern ( _MgCl2 ), alkali silicates such as sodium silicate and potassium silicate, and sodium aluminate. Furthermore, known fireclays and silica fume can also be added to improve plasticity.

<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.

<Heat treatment temperature>
The heat treatment temperature is preferably between 110°C and 1200°C. This product utilizes 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 about 6 to 18 hours.

The following examples will explain the present invention in more detail.

[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.

The binder used was liquid sodium silicate containing 56 mass % of SiO ₂ and 28 mass % of Na ₂ O. The liquid sodium silicate was added in an amount of 2.5 mass % based on the total mass of the refractory raw materials (100 mass %).

The alumina cement used in Comparative Example 2 contained 70% by mass of Al ₂ O ₃ 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.

The above mixture of refractory raw materials and binder was kneaded in a mixer, and mixtures that were dry and unsuitable for molding were rated as "unacceptable," while mixtures that were moist and suitable for molding were rated as "acceptable." The mixtures were molded using a friction press.

[Expansion under load test]
The expansion under load test was carried out in accordance with JIS R2207-2.

That is, a cylindrical test piece was placed in a heating furnace, and the 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 ^m3 /h (standard conditions).

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%. A D value of -1.1% or more reduces joint opening. Furthermore, a value of -0.5% or less improves spalling resistance. An even more preferable range for the value of D is -0.9% to -0.7%.

[Spalling resistance]
The spalling resistance was evaluated in accordance with JIS R2657. The test specimens were cubic, measuring 50 × 50 × 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 crack occurrence state after the test was observed, and those that did not crack even after 20 times were rated as A, those that cracked after more than 15 times but less than 20 times were rated as B, those that cracked after more than 10 times but less than 15 times were rated as C, and those that cracked after 10 times or less were rated as D.

<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.

Of the above Examples 1 to 6, Examples 2 to 5 have D values in the range of -1.1% to -0.5%, which reduces crumbling 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%, demonstrating effects that are more in line with the objectives of the present invention.

Example 1 is recognized as superior in both D value and spalling resistance compared to Comparative Example 1. Although Example 6 had a slightly lower D value, it was within the acceptable range, resulting in excellent spalling resistance.

In Example 7, alumina cement was hydrated, fired, and crushed, and the resulting raw material was added as a CaO source. It can be press-formed, and has improved spalling resistance compared to Comparative Example 1.

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

In addition, in Comparative Example 2, alumina cement was added directly as a CaO source, but press molding was difficult.

Claims (2)

The method for producing an alumina-magnesia refractory brick is obtained by kneading, molding, and heat treating a raw material blend containing 15% by mass or more and 92% by mass or less of an alumina raw material, 3% by mass or more and 7% by mass or less of a magnesia raw material, and 10% by mass or more and 80% by mass or less of a used alumina-magnesia castable material . The method for producing an alumina-magnesia refractory brick is obtained by kneading, molding, and heat treating a raw material blend containing 15% by mass or more and 92% by mass or less of an alumina raw material, 3% by mass or more and 7% by mass or less of a magnesia raw material, and a raw material obtained by hydrating and then firing alumina cement.