JPS6243948B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing carbon-containing magnesia-alumina bricks, which are particularly suitable as linings for steelmaking furnaces. BACKGROUND OF THE INVENTION Carbon-containing bricks have been widely used as linings for pig iron mixers, pig iron mixers, steel pots, vacuum degassing equipment, and the like. The main types of bricks of this type are magnesia-carbon, alumina-carbon, and spinel-carbon. Because it is combined with carbon, which has a high carbon content, it has excellent corrosion resistance and spalling resistance. However, although conventional carbon-containing bricks have excellent corrosion and spalling resistance, they have a residual expansion coefficient due to sintering of oxides or the difference in thermal expansion and contraction between carbon and oxides. Because of their small size, they had the disadvantage that the joints in the brickwork would open during use, causing the bricks to fall off, or that slag and molten steel would enter the joints, leading to further melting and damage. The purpose of the present invention is to obtain a carbon-containing brick that does not have the above-mentioned conventional drawbacks, and is characterized by weight: 3-94% magnesia, 3-94% alumina.
This is a method for producing a carbon-containing magnesia-alumina brick, in which a compound consisting of 94% carbon, 3 to 50% carbon, and a binder is kneaded and molded, and then heat-treated at 1200°C or less. In other words, the refractory obtained by the present invention has magnesia in its composition and alumina that absorb heat during use.
When the temperature exceeds 1200℃, the following reaction occurs. MgO＋Al ₂ O ₃ →MgO・Al ₂ O ₃ (spinel) The specific gravity of magnesia and Al ₂ O ₃ is 3.6 and 3.8, respectively.
However, since the spinel produced in this reaction is 3.5, the brick obtained by the present invention causes residual expansion due to the formation of spinel. The graph in Figure 1 shows the conventional magnesia-carbon system.
spinel-carbon-based, alumina-carbon-based bricks,
It is a linear expansion/contraction curve of a magnesia-alumina-carbon based brick obtained by the present invention. Note that the ratio of oxide to carbon was 8:2. As is clear from this graph, all of the conventional products show linear expansion and contraction, so there is almost no residual expansion, and some even show residual contraction. On the other hand, in the magnesia-alumina-carbon brick obtained by the present invention, expansion due to spinel formation is added at temperatures above 1200°C to the expansion of magnesia and alumina. It is possible to prevent bricks from falling off due to openings in the joints, and slag and molten steel from entering the joints. Carbon contributes to improving the corrosion resistance and spalling resistance of bricks due to its high refractoriness and poor wettability. and play a role in moderating the speed. In other words, when magnesia and alumina come into direct contact over the entire surface,
When the temperature exceeds 1200℃, spinel is rapidly formed and the brick collapses due to the accompanying rapid volumetric expansion, but carbon creates a partial barrier between magnesia and alumina. to solve this problem by suppressing the formation of spinel. Next, the raw materials used in the present invention and their blending ratios will be explained in detail. Examples of magnesia that can be used include seawater magnesia, fused magnesia, and natural magnesia, and examples of alumina that can be used include fused alumina, sintered alumina, bauxite, and aluminum shale. The blending ratio of both of these is 3 to 94%, preferably 5 to 90%. If it is less than 3% or more than 94%, the amount of spinel produced is small and residual expansion is insufficient, so that the effects of the present invention cannot be obtained.
The graph in Figure 2 shows the experimental results that led to this blending ratio.It shows the residual expansion coefficient when heated at 1500℃ while keeping carbon at 10% and varying the ratio of alumina and magnesia. The measurement method is the same as that for the residual expansion coefficient shown in Table 1, which will be described later. The particle size of magnesia and alumina is similar to that of conventional oxides.
It may be used in the same manner as carbon-based refractories, and is not limited in any way. However, as the particle size becomes smaller, the amount of spinel produced and its reaction rate increase, the residual expansion coefficient also increases, and the spalling resistance decreases accordingly, so the particle size must be determined appropriately. As the carbon, for example, natural graphite, artificial graphite, petroleum coke, coal coke can be used, and the blending ratio is 3 to 50%, preferably 5 to 50%.
It is 40%. If it is less than 3%, the effect of preventing penetration of slag and molten steel cannot be expected due to the high corrosion resistance and poor wettability of carbon itself, and the barrier between magnesia and alumina is insufficient, so it is difficult to prevent spinel formation as described above. No effect is obtained. Moreover, if it is more than 50%, the contact between magnesia and alumina is almost prevented, and the formation of spinel becomes extremely small, so that the object of the present invention cannot be achieved. Third
The figure shows the residual expansion when the ratio of magnesia and alumina is set to 1:1, only the carbon content is changed, and heating is performed at 1500℃. This is a graph of the residual expansion coefficient of ~1-10. As the binder, commonly used binders such as phosphates, silicates, borates, petroleum pitch, coal pitch, coal tar, phenolic resins, furan resins, etc. can be used. The present invention limits the heat treatment temperature of bricks to 1200°C or less. If the temperature is 1200° C. or higher, spinel will be generated during the manufacturing stage, and the effects of the present invention, which are produced by spinel generated during use, cannot be obtained. In addition, since the brick obtained by the present invention contains carbon, an antioxidant selected from various metals, carbides, nitrides, phosphorus compounds, and chlorides is required to prevent the oxidation of carbon during use. It may be added depending on the situation. Tables 1 to 3 show examples of the present invention, comparative examples, and physical property values of bricks obtained from them.

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[Table] The method for measuring physical property values is as follows. (1) Porosity Based on JIS: R2205. (2) Porosity after reduction heating at 1500°C After heating at 1500°C for 2 hours in an electric furnace in a nitrogen atmosphere,
The rest was JIS: R2205. (3) Residual expansion coefficient after reduction heating at 1500°C Measured according to JIS R2208 after heating under the same conditions as in (2) above. Table 1 shows natural flaky graphite kept constant at 10% and the ratio of fused magnesia and fused alumina varied.
Kg/cm ² and heat treated at 200°C for 16 hours to obtain bricks. As is clear from the same table, the bricks obtained from the examples of the present invention are Comparative Example 1-1 without the combination of fused alumina, Comparative Example 1-3 without the combination of fused magnesia, or the blending ratio of fused magnesia. The residual expansion coefficient is significantly larger than that of Comparative Example 1-2, which is outside the scope of the present invention. Table 2 shows a combination of sintered magnesia, sintered alumina, Kitsuyu graphite, and aluminum.As is clear from the table, Comparative Example 2-1, in which no Kitsuyu graphite is added, has a carbon component. Because it does not contain any In addition, in Comparative Example 2-2, almost no residual expansibility was observed because the content of carbon components was small. On the contrary,
Examples of the present invention exhibited moderate residual expansion. All of Table 3 are examples of the present invention. As described above, the carbon-containing brick obtained by the present invention exhibits significant residual expansion during use due to the formation of spinel, so it has an excellent effect of not having any joints when bricked up. Therefore, since there is no falling of bricks or infiltration of slag, molten steel, etc. into the joints, the high corrosion resistance of carbon-containing bricks can be fully utilized, and various types of kilns lined with these bricks can be used. It has advantageous features that greatly extend the life of the furnace.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing hot linear expansion and contraction curves of various carbon-containing bricks, FIG. 2 is a diagram showing the magnesia-alumina ratio and residual expansion coefficient, and FIG. 3 is a diagram showing carbon content and residual expansion coefficient.

Claims (1)

[Claims] 1. A carbon-containing material characterized by kneading and molding a compound consisting of 3 to 94% magnesia, 3 to 94% alumina, 3 to 50% carbon, and a binder in weight proportions, and then heat-treating the mixture at 1200°C or less. A method for producing magnesia-alumina bricks.