JPH0228550B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a porous refractory for gas injection that has excellent hot strength. In a molten metal container such as a ladle, inert gas is generally blown into the container through a plug attached to the bottom of the container to equalize the temperature and composition of the molten steel, float any intervening materials, and degas the molten steel. ing. In recent years, the trend toward higher-grade steel products has led to increased gas injection volume, longer residence time of molten steel in the pot, oxygen cleaning to prevent deterioration of gas injection function, and improvements in the porous refractories that make up the plug. The conditions of use are becoming increasingly harsh. In order to maintain gas permeability, this porous refractory has a permeability of 0.5 to 3.0cm ³ cm/cm ² sec cmH ₂ O, a porosity of 25 to 30%, and a pore diameter of approximately 50 to 100 μm. Therefore, it has inferior corrosion resistance and strength compared to ordinary refractories. Therefore, with conventional materials made of alumina as aggregate and clay added to it, fire resistance is improved by minimizing the proportion of clay, but on the other hand, there is a decrease in hot strength and deterioration due to penetration of molten steel Structural spalls are likely to occur. As a result, with repeated use,
Cracks occur at right angles to the gas permeation direction and peel off due to back pressure, which is a secondary effect of gas injection, making the porous refractory short-lived. It is also known to further add chromium oxide to the material made of the above-mentioned alumina viscosity. However, in terms of spall resistance, no significant effect can be obtained, and the reactivity with FeO blocks the ventilation holes, reducing the gas blowing function. The present inventors have found that when zircon is added in a specific proportion in place of conventional clay, chromium oxide, etc. in porous refractories using alumina as aggregate, hot strength is improved.
Knowing that the material has excellent spall resistance,
This completes the present invention. In the present invention, 1 to 10 wt% of zircon is 95 wt% or more with a particle size of 1 mm or less, and the balance is 70 wt% with a particle size of 0.15 to 2 mm.
% or more of alumina is kneaded, molded, and then fired. The invention will now be described in further detail. First, some of the experiments that led to the completion of the present invention will be shown. Figures 1 to 3 show porous pores obtained by keeping alumina as the aggregate and various conditions such as kneading, molding, and firing in the refractory manufacturing process constant as shown below, and only changing the type and amount of additives. 2 is a graph showing the results of measuring the strength of quality refractories. (1) Aggregate: Electrocatalyzed alumina (purity 99wt% or more) 1~0.297mm (2) Additive: Clay 0.074mm or less Chromium oxide 0.074mm or less Zircon 0.297~0.149mm Zircon 0.074mm or less (3) Kneading: Dextrin 1wt % and knead with a mixer. (4) Molding: Molded into a regular size (230 x 114 x 65 mm) using a friction press. (5) Firing: After 24 hours of natural drying, it was fired in a tunnel kiln at 1650℃ for 8 hours. In addition, the measurement method of each physical property was the same as the Example mentioned later. Figure 1 shows the change in hot bending strength of porous refractories when clay is added and when clay and chromium oxide are added together. No significant improvement in hot bending strength was observed with any of the additives. At the same time, the presence or absence of peeling is indicated by a border line. Peeling is suppressed above this line, and complete peeling occurs below this line. Figure 2 shows the relationship between zircon addition and hot strength. Those with zircon added have significantly better hot bending strength as the amount of zircon added increases. On the other hand, although the one to which fine zircon powder was added is somewhat inferior to the above-mentioned case, it is clear that the hot bending strength is improved compared to the conventional one. As the amount added increases, peeling is also completely suppressed. FIG. 3 shows the amount of zircon added, the bending strength at room temperature, the elastic modulus that correlates with spalling resistance, and the thermal shock damage resistance coefficient calculated from the formula below. T (bending strength)/E (modulus of elasticity)∝R (thermal shock damage resistance coefficient) It is clear from the same figure that the addition of zircon significantly improves the spalling resistance. The reason why the addition of zircon has such an effect is thought to be due to the following reasons. In other words, as is well known, when zircon is heated to 1530℃, it forms ZrO ₂ and SiO ₂
However, in the present invention, the dissociated SiO ₂
In the molten state, due to its surface tension, it accumulates in the area of minimum surface energy, that is, near the point of contact with the aggregate, and reacts with the alumina aggregate to produce mullite.
Furthermore, this mullite forms a strong composite connective tissue by combining with the direct bonds between the alumina aggregates, resulting in excellent tissue strength despite being porous. On the other hand, with conventional materials that use clay or a combination of clay and chromium oxide, the _SiO2 component in the clay is removed from the aggregate.
Mullite is produced in the same way by reacting with the Al ₂ O ₃ component, but since this reaction occurs in a low temperature range, mullite is produced without SiO ₂ being sufficiently dispersed, and it is stable and can be used as aggregate as in the present invention. Mullite does not concentrate at the contact area. FIG. 4 schematically shows the bonding form of the aggregate of the porous refractory according to the present invention. 1 is the alumina aggregate, 2 is the sintered part of the alumina aggregate, 3
is mullite produced by the reaction between SiO ₂ due to the dissociation of zircon and the Al ₂ O ₃ component of the aggregate. Mullite 3 covers the direct bonds between alumina aggregates 1, forming a composite connective tissue. Although the bonding structure of the refractory in the present invention is strong, _it exhibits excellent spalling resistance. This is because microcracks are formed in the connective tissue due to the tissue change due to the oblique transition, which absorbs thermal shock and prevents crack propagation. The zircon used in the present invention has a
From the viewpoint of melting and dispersing _SiO2 , it is preferable that the purity is
The content should be 95wt% or more, ideally 99wt% or more. Use particles with a particle size of 1 mm or less that accounts for 95 wt% or more.
If it is more than 1 mm, the strength of the refractory will deteriorate due to the non-uniformity of the zircon, and it will be difficult to form pores to maintain stable air permeability, and the function as a refractory for gas injection will be lost. If the amount of zircon added is less than 1wt%, the hot strength will be low, as is clear from the above experiment.
Poor effectiveness in suppressing structural spalls. 10wt%
Due to excess _SiO2 after zircon dissociation,
The distribution of SiO ₂ to areas other than the aggregate contact points increases, and unreacted SiO ₂ remains in the structure as cristobalite, resulting in a decrease in corrosion resistance. The alumina used as the aggregate may be a sintered product, a fused product, or a combination of both. Purity is not particularly limited, but in terms of hot strength and spall resistance
97wt% or more is preferable. If the purity is low, the SiO ₂ melt generated from the dissociation of zircon has high wettability with the aggregate during firing of the refractory, so it does not flow smoothly on the aggregate surface, and the contact area between the aggregates This is because mullite formation is reduced. In addition, alumina with large crystal grains has a smooth surface, absorbs less SiO ₂ , and allows smooth flow of SiO ₂ . Therefore, among alumina raw materials, electrolytic products with large crystal grains are particularly preferred. The particle size of the aggregate should be 0.15 to 2 mm at 70 wt% or more.
This is to make the refractory porous and have a gas permeation function.If it is less than 70wt%, the air permeability required for gas injection will be 0.5 to 3.0 (C) even if the molding pressure is adjusted.
GS) cannot be obtained. In addition, auxiliary raw materials such as alumina sol, aluminum hydroxide, and conventionally known chromium oxide may be added as necessary, as long as they do not impede the effects of the present invention. Approximately 0.05 to 5 wt% of a binder is added to the above-mentioned mixture, and after kneading, it is molded using an oil press, friction press, or the like. The binder is preferably, for example, isobutyl maleic acid, dextrin, sodium lignin sulfonate, polyvinyl alcohol, phenolic resin, etc., but is not limited to these, and any known organic/inorganic binder can be used. . Depending on the type of binder, water may also be used. The firing temperature is preferably 1600°C. At temperatures below 1600℃, SiO ₂ dissociated from zircon may not melt or
Or, due to insufficient melting, contact with aggregate may occur.
Concentration of SiO ₂ cannot be expected, and hot strength and spalling resistance are not sufficiently improved. The upper limit temperature is not particularly limited, but from the viewpoint of firing effect, it is set at 1800℃.
Temperatures above ℃ are not required. If the temperature is too high, the SiO ₂ produced by the dissociation of zircon will lack viscosity.
Due to the action of gravity, the aggregates do not remain in contact with each other and flow down, resulting in cracks during firing and sagging due to softening due to insufficient bonding strength between the aggregates. Next, examples of the present invention and comparative examples thereof will be shown. For each example, raw materials having the chemical composition shown in Table 1 are blended in the proportions shown in Fig. 2, mixed in 400 kg batches with a mixer, and then mixed with a friction press.
It was molded into a truncated conical shape of 200 mm x bottom surface 150 mmφ x top surface 100 mmφ. Firing was performed in a tunnel kiln.

【table】

【table】

【table】

【table】 [Brief explanation of drawings]

Figures 1, 2, and 3 show some of the experiments that led to the completion of the present invention. Figure 1 shows the relationship between hot bending and the amount of clay added, and Figure 2 shows the relationship between hot bending and the amount of clay added. Figure 3 shows the relationship between bending strength and the amount of zircon added, Figure 4 shows the relationship between the bending strength and modulus of elasticity and the amount of zircon added, and Figure 4 shows the bonding form of the aggregate of the porous refractory in the present invention. FIG. 1...Alumina aggregate, 2...Sintered part of alumina aggregate, 3...Mullite.

Claims (1)

[Claims] 1 Zircon with a particle size of 1 mm or less at 95 wt% or more
1. A method for producing a porous refractory for gas injection, which comprises kneading and molding a compound consisting of alumina of 10 wt% and the remainder having a particle size of 0.15 to 2 mm at 70 wt% or more, followed by firing.