KR940006428B1 - Process for the preparation of firebrick - Google Patents

Abstract

The silicon carbide based refractory brick is manufactured by (a) mixing 65-80 wt.% silicon carbide and 20-30 wt.% the mixture of which SiC and metallic silicon powder and residual carbon are contained in the ratio of 2.5:1.0-3.7:1.0, (b) carbonizing this mixture at 800-1,100 deg.C, (c) adding 4.0-7.0 wt.% phenolic resin to the carbonized mixture, (d) molding the secondary added mixture with uniaxial or isotropic pressing and drying, (e) firing the molded brick at 1,500-1,600 deg.C for 30-40 hrs. in atmosphere of argon.

Description

Manufacturing Method of Silicon Carbide Refractory Brick

1 is a process for manufacturing a firebrick, showing a process for producing a silicon carbide firebrick according to the present invention method and a conventional method.

FIG. 2 is a cross-sectional schematic diagram showing the surface state of silicon carbide aggregate in a molded article produced according to the present invention method and the conventional method. FIG.

The present invention relates to a method for producing silicon carbide refractory bricks used in blast furnace-embedded refractories for steel smelting, and more particularly, to silicon carbide refractory bricks having excellent corrosion resistance, oxidation resistance and spalling resistance. It relates to a manufacturing method.

Conventional silicon carbide refractory bricks are manufactured by inserting metal silicon and organic binder into silicon carbide aggregate, kneading and molding and firing at 1550 ° C. in coke, β-SiC, Si ₂ ON ₂ , Si ₃ Since it mainly produces N ₄ and SiO ₂ , the glass material, which is a defect of the bonding layer of the silicate-bonded silicon carbide refractory brick, was excluded to compensate for the high temperature property and the corrosion resistance to slag, but there are still many manufacturing problems. , Densification is a problem.

That is, in the related art, as shown in FIG. 1 (a), an organic binder (carbon source) and silicon powder are simultaneously kneaded with silicon carbide aggregate, and then molded, dried and calcined to produce a silicon carbide firebrick.

As shown in FIG. 2 showing the surface state of the silicon carbide aggregate in the molded body, the silicon carbide refractory brick can be seen that the silicon carbide and metal silicon surfaces in the molded body are covered with phenol resin, which is an organic binder. As the volatilization of the phenol resin in the molded body is volatilized, many pores remain and it is difficult to produce a refractory brick of dense structure. In addition, since the coking is filled and calcined during firing, all the bonding layers of the brick cannot be β-SiC, and after firing, Si ₃ N ₄ , Si ₂ ON _2, etc. are generated in addition to β-SiC. Since the amount of carbon added in the binder is excessively large, unreacted metal silicon remains in the interior of the fired product, and this residual metal silicon inhibits physical properties at high temperatures when the silicon carbide refractory brick is used at high temperatures. Done.

Accordingly, the present inventors have conducted studies to solve the drawbacks of the conventional silicon carbide firebrick, and the present invention has been proposed by the results of the research, and the present invention improves the density and thermal conductivity, thereby improving corrosion resistance, oxidation resistance and An object of the present invention is to provide a method for producing a silicon carbide firebrick having excellent spalling resistance.

Hereinafter, the present invention will be described.

In the present invention, 20-35 weight of the metal silicon powder and phenol resin are combined so that the weight ratio of 65-80% by weight of silicon carbide, metal silicon powder and residual carbon of phenol resin is 2.5: 1.0-3.7: 1.0 as an aggregate part. Mixing the first mixture by mixing%; Degreasing (carbonization of phenol resin) the first kneaded mixture as described above; Adding a 4.0 to 7.0% by weight of a molding phenol resin to the mixture which has been subjected to the degreasing step as described above, and secondly kneading; And it relates to a method for producing a silicon carbide refractory brick comprising the step of molding, drying and calcining the secondary kneaded mixture in a conventional manner.

Hereinafter, the present invention will be described in more detail.

As the silicon carbide aggregate used in the present invention, it is preferable to use commercially available silicon carbide having a purity of 95% or more, and the particle size is preferably adjusted according to the size of the molded body, and the particle size distribution is adjusted to achieve the closest filling.

As the metal silicon powder, an average particle size of 0.044 mm or less is preferably used with a purity of 95% or more.

As said phenol resin, it is preferable to use the resol type industrial grade which can be knead | mixed and shape | molded at normal temperature and expresses sufficient strength to handle when drying a molded object at 50-110 degreeC.

In the present invention, the aggregate portion of the refractory brick is preferably 65-80% by weight, and the bonding portion is limited to 20-35% by weight, because the corrosion resistance is poor when the aggregate portion is 65% by weight or less in the refractory brick. This is because it is not good, and if it is 80% by weight or more, it is difficult to obtain sufficient strength due to the small amount of the bonding portion.

In addition, in the present invention, the addition amount of the metal silicon powder and the phenol resin forming the joining portion of the refractory brick is preferably limited so that the weight ratio of the metal silicon powder and the residual carbon of the phenol resin is 2.5: 1.0 to 3.7: 1.0. The reason is that the theoretical weight ratio of Si and C for the production of β-SiC is 2.3: 1.0, but when the weight ratio of residual silicon of the metal silicon powder and phenol resin is greater than 3.7: 1.0, the metal silicon inside the silicon carbide refractory brick It remains because it lowers the high temperature property of the refractory bricks, and when the weight ratio of the metal silicon powder and the residual carbon of the phenol resin is less than 2.5: 1.0, the unreacted residual carbons weaken the structure of the refractory bricks and lower the oxidation resistance. to be.

When primary kneading of silicon carbide, metal silicon powder and phenol resin at the above weight%, the phenol resin completely covers the surfaces of the silicon carbide aggregate and the metal silicon powder. The coated phenol resin retains carbon when degreased, facilitates the generation of β-SiC from reaction with the metal silicon powder during firing, and evenly coats residual carbon on the fine silicon carbide powder added as aggregate. It is formed on the surface of the SiO ₂ oxide film layer is easily removed, which helps the sintering of α-SiC itself.

As shown in FIG. 1 (b) showing the manufacturing process of the present invention, as described above, the silicon carbide aggregate, the metal silicon powder, and the phenol resin are mixed and kneaded, and then the mixture is degreased. It is preferable to carry out in a gas atmosphere, and in the case of degreasing, residual carbon produced from phenol resin completely covers the surfaces of the silicon carbide aggregate and the metal silicon powder.

In the degreasing step, the degreasing temperature and the degreasing time are limited depending on whether or not enough degreasing depending on the amount of degreasing, the degreasing temperature is preferably limited to a temperature range of 800-1100 ℃, because the degreasing temperature is 800 ℃ In the following, it takes a long time to degrease, and above 1100 ° C is a problem when re-kneading the resulting sintering mixture of β-SiC.

In this degreasing process, the metal silicon powder and the residual carbon start a little reaction to produce a small amount of β-SiC. It is known that the reaction between metal silicon and carbon powder is difficult to proceed due to insufficient contact between them at the melting point of metal silicon below 1410 ℃, but the residual carbon carbonized from phenol resin closely surrounds the surface of metal silicon. Therefore, the reactivity is good, and since the reaction product β-SiC has a smaller grain size than the silicon carbide aggregate, it is effective in enhancing the sinterability of silicon carbide refractory bricks.

As described above, the phenol resin, which is a molding binder, is added to the silicon carbide aggregate coated with residual carbon and the fine powder of metal silicon by adding 4.0 to 7.0% by weight to the first kneaded mixture, followed by second kneading.

If the addition amount of the molding phenol resin is less than 4% by weight, the moldability is poor, and if it exceeds 7% by weight, the volatiles will leave pores, so it is preferable to limit the amount to 7% by weight or less within the moldable range. Do.

After the second kneading as described above, the mixture is uniaxially pressurized and isotropically pressurized to produce a molded body by a conventional method. In this case, the uniaxial pressurized mold is pressurized with 100-1000kg / cm 2 depending on the size of the molded body Press-molding is preferably performed by applying a pressure of about 2 ton / cm 2.

After molding as described above, the molded body is dried and fired in a conventional manner, wherein the drying temperature is preferably about 50-110 ° C. Although the firing temperature at the time of baking is possible at 1400 degreeC or more, considering the physical property and energy aspect which are required for a firebrick, the temperature range of 1500-1600 degreeC is preferable, and the baking time is about 30-40 hours.

The firing is preferably carried out in an argon gas atmosphere, which is an inert gas. The reason for this is that when firing in an argon gas atmosphere, the metal silicon powder reacts with the residual carbon to generate only a silicon carbide single phase, thus the amount of the metal silicon powder This is because it is easy to adjust the temperature, and the sintering property of the silicon carbide refractory brick can be improved.

On the other hand, when the coke is filled and calcined by a known technique, it is difficult to control the small-component crisis, and the metal silicon powder added to generate β-SiC reacts with N ₂ or O ₂ in the atmosphere to form Si ₃ N ₄ ·. Si ₂ ON ₂ · SiO ₂ and the like are produced. Therefore, it is difficult to adjust the amount of the metal silicon powder to react with the residual carbon.

As shown in FIG. 2 showing the surface state of the silicon carbide aggregate in the molded article molded according to the present invention, it can be seen that the surfaces of the silicon carbide aggregate and the metal silicon powder in the molded article are covered with residual carbon. When the molded body is calcined as described above, both the metal silicon and the residual carbon are β-SiC, which serves to bond the silicon carbide aggregate, thereby producing a high-strength, high-density silicon carbide refractory brick.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Silicon carbide aggregates, metal silicon powder and phenol resin (49% fixed carbon) for the refractory material were kneaded first at room temperature (inventive material and comparative material) in the mixing ratio as shown in Table 1 below. In the invention and the comparative material, the first kneaded mixture was heated to 1100 ° C. under an argon gas atmosphere at a temperature increase rate of 5 ° C./min, and then degreased to sufficiently carbonize the phenol resin for 6 hours at this temperature.

4 wt% of the phenol resin for molding was added to the degreasing mixture as described above, followed by secondary kneading and uniaxial pressure at 400 kg / cm 2 to produce a 120 × 120 × 400 mm molded body, followed by a pressure of 2 ton / cm 2. Isotropic pressing was performed.

The molded article molded as described above was dried, and then heated to 1550 ° C. at a rate of 5 ° C./min in an argon gas atmosphere, and maintained at this temperature (baking) for 30 hours to prepare a firebrick.

On the other hand, conventional materials are mixed with silicon carbide aggregate and silicon silicon phenol resin at the same time as shown in Table 1, kneaded at 120-140 ℃ and then aged to uniaxially pressurized at a pressure of 400kg / ㎠ to produce a molded body of 120 × 120 × 400mm Then, isostatic pressing was performed at a pressure of 2 ton / cm 2.

Cooling or drying to have the strength necessary to handle the molded article as described above, buried in the coke and baked for 30 hours at 1400 ℃ to produce a refractory brick.

For each refractory brick specimen prepared as described above, the specific gravity, porosity, compressive strength, and hot bending strength (1400 ° C.) were measured, and the measurement results are shown in Table 1 below.

TABLE 1

As shown in Table 1, the present invention material (1-3) is a comparative material (4) and (5) in which the weight ratio of metal silicon and residual carbon is outside the range of 2.5: 1.0 ~ 3.7: 1 of the present invention Compared to), it is excellent in volume specific gravity, porosity, compressive strength and hot bending strength.

That is, the comparative material 4 has a higher amount of carbon remaining than the metal silicon powder, so that the amount of β-SiC produced in the bonding portion is small, and the porosity is high due to the unreacted carbon, thereby decreasing the room temperature strength and the high temperature strength. 5) is an excessive addition of metal silicon powder, and there is no significant difference in room temperature strength or porosity, but physical properties at high temperature are deteriorated because unreacted metal silicon is present inside the refractory brick.

On the other hand, the prior art material was formed without undergoing a degreasing process, unlike the one manufactured by the present invention, and volatilized volatilized when the phenol resin coated on the silicon carbide aggregate and the metal silicon powder was fired during firing. Pore remains in the interior of the brick and cannot be obtained. Also, because it is buried in the coke during firing, it has a temperature raising effect, but it is difficult to control the amount of metal silicon necessary for the formation of the bonding part β-SiC due to the difficulty of controlling the minor component crisis .

As described above, the present invention has the effect of providing a dense silicon carbide brick having excellent corrosion resistance and strong thermal spalling as well as excellent at room temperature and hot strength.

Claims (5)

20-35% by weight of the metal silicon powder and the phenol resin are combined so that the weight ratio of the silicon carbide 68-80% by weight as the aggregate portion and the residual carbon of the metal silicon powder and the phenol resin is 2.5: 1.0 to 3.7: 1.0. Mixing and kneading firstly; Degreasing the first kneaded mixture as described above; Adding a 4.0 to 7.0% by weight of a molding phenol resin to the mixture which has been subjected to the degreasing step as described above, and secondly kneading; And forming, drying and firing the secondary kneaded mixture as described above. The method for producing silicon carbide-based refractory brick according to claim 1, wherein the degreasing step is performed in an argon gas atmosphere in a temperature range of 800-1100 ° C. The method for producing silicon carbide-based refractory brick according to claim 1, wherein the forming step is performed by uniaxial press molding of 100-1000 kg / cm < 2 > and isotropic pressing molding of about 2ton / cm < 2 >. The method for producing silicon carbide-based refractory brick according to claim 1, wherein the drying temperature is in the range of 50-110 ° C. The method for producing silicon carbide refractory brick according to any one of claims 1 to 4, wherein the firing step is performed for 30-40 hours in a temperature range of 1500 to 1600 ° C.