JPS6127350B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a zircon refractory having low porosity and high strength. [Prior Art] Zircon is attracting attention as a material that has excellent fire resistance and can withstand use at high temperatures up to about 2000°C. In addition, because of its low coefficient of thermal expansion and high thermal shock resistance, it is used as a raw material for refractories such as precision casting, sprue bricks for ladle, metal crucibles, refractory bricks, stamping materials, and high-frequency insulators. For example, in the steel industry, they are used as refractories for lining molten steel ladles, continuous casting nozzles, etc., and as bricks for upper structures in glass melting furnaces. It is also in high demand as foundry sand. In the case of continuous casting nozzles, which is one of these applications, corrosion due to erosion by molten steel components and enlargement of the nozzle hole diameter due to the abrasion effect of the molten steel flow, etc.
The service life of the nozzle is determined. The erosion caused by the molten steel components is caused by the melting away of low melting point compounds generated at the interface as a result of a reaction on the surface of the inner periphery of the nozzle hole that comes into contact with the molten steel. The dissolution rate in this case is influenced by the chemical composition of the nozzle. Furthermore, the abrasion effect of the molten steel flow is greatly influenced by the structure and hot strength of the nozzle. That is, in order to improve wear resistance, it is necessary to densify the structure and improve hot strength. Furthermore, in the case of zircon bricks for glass melting furnaces, the zircon bricks do not come into direct contact with the glass bath of the melting furnace, but are used in the upper part of the side wall. However, since a large load from the ceiling is applied to the upper part of the side wall, it is necessary to have excellent volumetric stability under high temperatures. Furthermore, since the upper part of the side wall is attacked by the glass carrier, it is also required to have excellent corrosion resistance. In order to use zircon bricks with good durability under such high-temperature atmospheres, it is necessary to improve properties such as erosion resistance, abrasion resistance, corrosion resistance, and high-temperature strength. [Problems to be solved by the invention] Until now, in order to obtain zircon bricks that satisfy these various properties, studies have been conducted from various aspects such as particle size composition, additives, molding pressure, and firing temperature. There is. For example, looking at the particle size structure, zircon is only produced in the form of sand grains of 1.0 mm or less, so in order to obtain a particle size structure similar to that of ordinary bricks with zircon, it is necessary to first make rough corners.
It needs to be crushed and blended. However, when using this method, it is difficult to make dense rough corners, and the manufacturing cost is also high. As an alternative method, a method has been proposed in which a large amount of fine zircon powder is blended and the structure is densified by contraction during firing. However, in this case, molding was difficult and the molding yield was low. In order to overcome these drawbacks, it has been proposed to use additives. The additives are mainly oxide-based, and many of them are of the type that promote the dissociation of zircon, form a low melting point compound, and promote sintering through the presence of a liquid phase. Although this improves room temperature strength, hot strength tends to decrease. Even if an attempt is made to make the Zirco sintered body dense by adjusting the firing conditions, there is a limit. That is, as the temperature rises, zircon decomposes more actively, making it difficult to perform high-temperature firing at 1600°C or higher. From this point of view, there is a limit to the strength improvement that can be achieved by increasing the firing temperature. In view of the properties of zircon, the present invention
The purpose is to improve the porosity and high-temperature strength of zircon sintered bodies by improving the composition of firing raw materials and firing conditions. [Means for Solving the Problems] In order to achieve the object, the present invention adds 0.1 to 4% of finely powdered metallic silicon to a refractory raw material whose main component is zircon (ZrO ₂ .SiO ₂ ). A formulation free of carbon and carbon-forming substances is prepared by adding % by weight, and after molding, the formulation is heated to
The method is characterized in that the entire amount of the metal silicon is oxidized to SiO ₂ during firing by heating to a temperature of 1600°C. [Function] As a result of various studies aimed at improving the hot properties of zircon bricks, the present inventors have found that by blending a small amount of finely powdered metallic silicon with zircon and firing it in an oxidizing atmosphere, a low It was discovered that high-strength bricks can be produced with pores. The present invention was completed based on this discovery. The mechanism of this strength development is that metallic silicon dispersed between zircon particles is melted by heating, promoting liquid phase sintering, and the added metallic silicon is oxidized from Si to SiO ₂ without remaining as it is. It is presumed that this is due to the formation of strong bonds. Further, in this case, even if a small amount of components such as zirconia and chromium oxide, which are added to ordinary zircon bricks, are present, the effect of the added metal silicon will not be impaired. However, if carbon or substances that modify carbon are included, the action of metallic silicon will be inhibited and the remaining of metallic silicon will be promoted.
It is necessary to adjust the ingredients so that they do not contain such substances. It is preferable that the metal silicon used here has as high a purity as possible. However, if it is 70% by weight or more, it can be used in the method for producing a refractory of the present invention. Furthermore, although the particle size of metallic silicon is not particularly limited, it is preferable to have a smaller particle size in view of its intended use. In particular, as shown in Example 1 below, when the 44 μm pass is 80% by weight or more, the dispersibility in zircon substances is excellent and good results can be obtained. It is said that the zircon used has a dense structure and high erosion resistance when the ratio of zircon sand to fine powder is approximately 2:1. Therefore, before and after the mixing ratio, that is, 3:1 ~
A range of 3:2 is good. It is preferable that this zircon material be used as a main component, that is, approximately 70% by weight or more, preferably 80% by weight or more. Also,
The amount of other components such as zirconia and chromium oxide added is limited to about 20% by weight at most. In addition,
The amount of metal silicon added and the binder will be explained in the following examples. [Example] Next, the features of the present invention will be specifically explained with reference to Examples. Example 1 As zircon raw materials, both sand and flour were produced in Australia. The silicon metal has a composition of 95% Si and 2.5% SiC, and has a diameter of 44μm.
Particles with a particle size of 90% by weight or more were used. As the binder, a commonly used pulp waste liquid diluted with water was used. These ingredients are kneaded using a regular mixer with tires, and then mixed using an oil press.
It was molded at a pressure of 1300 kg/cm ² and fired by holding it at 1550° C. for 6 hours in a separate kiln. The results are shown in the table. In the table, Example A shows a comparative formulation in which no silicon metal is added. In the case of Example B where the amount of metal silicon added was 0.3% by weight and Experimental Example C where the amount was 0.9% by weight, the strength was improved and the effect of metal silicon was recognized. This increase in strength is due to
It increases as the amount of metal silicon added increases. On the other hand,
As the metal silicon content increases, the influence of residual Si becomes more pronounced, resulting in partial strength deterioration. In particular, in Experimental Example H in which the amount of metal silicon added exceeds 4% by weight, the effect of reducing porosity and improving strength is almost lost, and on the contrary, the quality deteriorates. Therefore, it can be said that the effective range for the amount of metal silicon added is 0.3 to 4% by weight.

[Table] The refractory obtained with the formulation of Example C was compared with the conventional product obtained with the formulation of Experimental Example A in a 10 ton tundish. As a result, the service life of conventional product A was only three continuous castings, while the former could withstand four continuous castings. Furthermore, even after four continuous castings, the expansion of the pore diameter was small and stable, and it was found that it could withstand at least four continuous castings or more. Example 2 The table shows an example in which zirconia or chromium oxide was partially blended as other components. As the zircon in this example, unlike the case of the example, zircon produced in South Africa was used. As the zirconia, a fine powder with a ZrO ₂ content of 98% by weight and a particle size passing through 200 meshes was used. As the chromium oxide, a fine powder with a Cr ₂ O ₃ content of 98% by weight and a particle size passing through a 325 mesh was used. The manufacturing conditions were the same as in Example 1 for Experimental Examples J and K, and only the firing temperature was 1600°C for Experimental Examples L, M, and N.
That's high. In this case as well, addition of excessive metallic silicon causes partial strength deterioration due to residual silicon.

〔Effect of the invention〕

As explained above, in the present invention, since a specified amount of fine powder metal silicon is added to the refractory material containing zircon as the main component and fired, the total amount of added metal silicon is It is oxidized to SiO ₂ and forms a strong bond within the refractory, greatly reducing the porosity of the sintered body. As a result, compressive strength,
A product with excellent bending strength, high-temperature strength, etc. can be obtained.
In addition, the addition of a specific amount of fine powdered silicon metal
Since no free silicon remains in the sintered body, the strength of the sintered body does not deteriorate partially. The sintered body thus obtained can be used as a product with excellent durability in various industrial fields such as iron manufacturing, ceramics, and glass.

Claims (1)

[Claims] 1. A blend containing no carbon or carbon-forming substances by adding 0.1 to 4% by weight of finely powdered metallic silicon to a refractory raw material whose main component is zircon (ZrO ₂ /SiO ₂ ). After preparing the compound and molding the compound, it is heated to 1200 ~
A method for producing a zircon refractory, characterized in that the entire amount of the metal silicon is oxidized to SiO ₂ during firing by heating to a temperature of 1600°C.