JPS6219392B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a blast furnace lining refractory suitable for blast furnace walls or hearths, which has excellent strength, thermal conductivity,
The purpose of the present invention is to provide a refractory for blast furnace lining that has excellent thermal shock resistance and alkali resistance. Causes of damage to blast furnace lining refractories include abrasion due to contact with charged raw materials, physical and chemical erosion caused by hot metal, slag, etc. in the furnace, and low-boiling metal vapors generated from raw materials, especially alkali metals. steam intrusion,
Collapse due to reactions, oxidation due to oxygen locally present in the furnace, cracks caused by thermal shock, etc.In particular, refractory bricks for lining in high temperature areas such as the lower chest, abdomen, and morning glory areas are exposed to heat. Cracks occur due to impact and alkali infiltration is strong, resulting in large damage. The degree of damage to these refractories varies significantly depending on the environment in which the refractory is placed, for example, the temperature to which the refractory is exposed during use, and the characteristics of the refractory itself. In other words, the resistance of ordinary refractories decreases as the temperature rises, and in order to compensate for this deterioration, conventional refractories have been installed from the lower chest of the reactor to the morning glory using a cooling plate method, a stave method, or a water sprinkling method. Efforts are made to cool the refractories from the inside and outside of the furnace shell to keep the furnace body at a low temperature. As for refractories themselves, graphite/silicon carbide bricks containing graphite and silicon carbide as main components have been used from the standpoint of thermal shock resistance and alkali infiltration resistance. The present applicant also has a patent application filed in 1983-
No. 73972 (Japanese Unexamined Patent Publication No. 57-3768), by weight,
20 to 30 parts of naturally produced phosphorous graphite, 20 to 30 parts of one or more carbon substances such as artificial graphite, anthracite, or earthy graphite, 5 to 30 parts of silicon carbide, metallic silicon, ferrosilicon, etc. Production of a refractory brick for a metal melting furnace, characterized in that 3 to 15 parts of one or a combination of two or more silicon alloys, and 7 to 15 parts of a phenolic resin are mixed, kneaded, pressure-molded, and fired. An invention relating to a method has been disclosed. The refractory brick manufactured according to this earlier invention is made of naturally produced phosphorous graphite 20
~80 mesh, earthy graphite 80 mesh or less, silicon carbide, ferrosilicon, calcined anthracite, and/or artificial graphite mixed with resol type and novolac type phenol resin, kneaded, pressure molded, and fired. Things are the subject. The refractory brick according to the prior invention is less prone to melting than conventional carbonaceous brick graphite and graphite/silicon carbide bricks whose main component is silicon carbide, etc., and has high thermal conductivity, making it suitable for bricks that are used while being cooled. Ori,
Although improvements have been made, in the course of subsequent studies, it was discovered that there were wide differences in quality depending on manufacturing conditions such as the type of natural graphite and the blending ratio. As a result of continued research,
The following knowledge was obtained, and the present invention was constructed based on this knowledge. That is, (1) It is advantageous to use only naturally produced flaky phosphorous graphite and earthy graphite as carbonaceous materials, and avoid using anthracite and artificial graphite. Anthracite and artificial graphite are materials that are stable at high temperatures, have high thermal conductivity, and contribute to improving thermal shock resistance, but their particles contain many pores, and when the pressure is released after forming and pressurizing , the molded body exhibits elastic behavior due to its inherent pores. Therefore, the particle surface of the aggregate is slightly separated from the matrix and gaps are created at the grain boundaries, so when used as firebricks after firing, alkali can easily penetrate into the brick structure through the gaps. Become. It is also clear from the analytical results that alkali infiltration increases at the grain boundaries of used bricks that the intrusion of alkali accelerates the disintegration of the brick structure. It also has an adverse effect on the strength after firing. Therefore, anthracite and artificial graphite cannot be said to be highly suitable materials for refractory bricks used in areas that come into contact with alkali. (2) When earthen graphite is used at 80 mesh or less,
Close packing can be achieved and a dense molded body can be obtained. In addition to being a fine powder, it has a high ash content, so it is resistant to metal vapor entering from the outside. The reason for this is that (a) the molded product made by densely filling fine powder raw materials has small pore diameters;
Due to the low air permeability, it is difficult for alkali to penetrate. (b) It is thought that the ash contained in the earthy graphite reacts with the alkali to produce a low-melting substance, which acts as a barrier and prevents subsequent infiltration of the alkali. (3) Earthy graphite contains a large amount of ash, so
The ash content increases the self-sintering properties of the earthy graphite itself during the firing process, resulting in an improvement in the strength characteristics of the brick structure. In particular, when 32 parts by weight or less of earthy graphite is blended, it greatly contributes to an improvement in hot strength that has not been seen in conventional bricks, and the hot wear resistance is greatly improved. (4) Due to the self-sintering property of earthy graphite as described above, high hot strength can be maintained even if the silicon carbide content is reduced. Therefore, by increasing the content of earthy graphite, silicon carbide By reducing the content of , it is possible to obtain high thermal conductivity and thermal shock resistance while maintaining the above-mentioned high hot strength. (See Tables 1 and 2 in Examples). Next, manufacturing of the refractory according to the present invention will be explained. By weight, 10% natural flake phosphorous graphite
~30 copies used. Flake-like phosphorous graphite is typically produced in China or the island of Madagascar, and is literally shaped like flakes and scales, and is distinguished from vein-like graphite from Ceylon and plumbago, which is produced in the form of lumps. It is something that Flake phosphorous graphite is 50 to 2000μ
The amount used is 10 to 30 parts by weight. If it is less than 10 parts, the thermal shock resistance will not be sufficient and the thermal conductivity will be low. If it exceeds 30 parts, the strength of the molded product will decrease. Earthy graphite with a density of 80 mesh or less is used. A particle size of about 45-65% less than 44μ is suitable. Suitable purity is 75 to 85% carbon content, 10 to 20% ash content, and 0 to 5% volatile content. The amount used is 32 to 60 parts by weight. If the amount is less than 32 parts, the effect of inhibiting alkali attack will be small and the strength will not be sufficiently developed. If it exceeds 60 parts, the thermal conductivity decreases and the thermal shock resistance decreases. Silicon carbide is used to give bricks strength, oxidation resistance, and corrosion resistance against hot metal and slag, but as mentioned above, the strength is increased due to the self-sintering property of earthy graphite, so the amount of earthy graphite is increased. Therefore, the content of silicon carbide can be reduced accordingly, and thermal conductivity and thermal shock resistance can be improved. 10 to 25 parts of silicon carbide are used. If the amount of silicon carbide is less than 10 parts, no effect will be observed, and if it is less than 25 parts, thermal shock resistance and workability during brick production will deteriorate, which is not preferable. Metallic silicon is used in fine powder form to provide strength to bricks. Metallic silicon is used in an amount of 5 to 15 parts. If it is less than 5 parts, it will not be effective.
If it exceeds 15 parts, the softening property under load at high temperatures will deteriorate, which is not preferable. 7 to 15 parts of phenolic resin is used. Good results can be obtained by using both novolac type and resol type phenolic resins. For example, a suitable resin amount is 7 to 15 parts by combining 2 to 5 parts of novolak type resin and 5 to 10 parts of resol type resin. If it is less than 7 parts, there is too little of it as a binder, making it difficult to mold, and the strength is not obtained, resulting in unsatisfactory manufacturing or quality issues.If it is more than 15 parts, the amount of liquid is too large and the porosity of the brick increases after firing. This results in unsatisfactory quality. For novolak type resins, those containing 8 to 15% of hexamethylenetetramine as a hardening agent based on the resin increase residual carbon after firing and are effective in reducing the pore size of the brick structure. In the case of the present invention, the average pore diameter is approximately
It becomes 0.05μ. When the pore size is small in this way, the effect of preventing infiltration of metal vapor is large, and good results can be obtained. These raw materials are mixed, kneaded using a kneader, pressure molded, and fired in a reducing atmosphere. Firing is carried out at a maximum temperature of 1100°C or higher by placing the molded product inside a sheath filled with carbon grains and wool. Metallic silicon in the compound sufficiently reacts with carbon to produce β-type silicon carbide within the brick, and sufficient strength is obtained due to the self-sintering action of the earthy graphite. Examples Table 1 Blend examples No. 1 to No. 3 are bricks according to the present invention, and No. 4 is a carbon-silicon carbide brick according to the invention of the prior application. Table 2 shows the formulations at a molding pressure of 250
The results are the results of various measurements performed using test specimens molded at kg/cm ² and reduced and fired at a maximum temperature of 1350°C. The fired body was cut into 40 x 40 x 40 mm specimens for compressive strength, apparent porosity, and bulk specific gravity, and 35 to 53 x 20 x 120 mm as specimens for corrosion resistance.
The specimen was cut out so that its cross section was trapezoidal, 60 x 60 x 170 mm as a thermal shock resistance specimen, and 20 x 20 x 60 mm as an alkali resistance specimen. The thermal shock resistance test was conducted using the AE method. When a brick is heated from one side, significant thermal stress is generated inside the brick, and when this stress becomes greater than the strength of the brick, cracks occur and propagate through the brick. A part of the energy released at this time is observed as an elastic wave by the AE measurement device. The AE value is expressed by the number of AE counts, and a brick with a large number of AE counts indicates that many cracks have generated and propagated, which means that the brick has poor thermal shock resistance. The AE values of the products of the present invention were 150 to 550. The comparison product was 850. Table 3 is a comparison of various refractories. The corrosion resistance test was carried out using a high frequency induction furnace.
Eight specimens were assembled into a ring shape, and the outside was fixed with monolithic refractories. Put 200g of slag and 5kg of FC20 (cast iron) into the space obtained by the specimen, and
It was melted at ℃ and subjected to a 2 hour erosion test. The alkali resistance test was conducted using a multiphase method. The specimen was placed in a filling containing a mixture of coke and potassium carbonate at a ratio of 8:2, held at 1300°C for 3 hours, cooled, and this was repeated 5 times. Dimensional change (Δ%) and The occurrence of cracks was observed. Cracks did not occur in either the product of the present invention or the comparative product. However, the dimensional change was smaller in the product of the present invention, indicating that it remains constant against alkali. As mentioned above, the present invention does not use artificial graphite or anthracite as in the earlier application, and the amount of earthy graphite blended is 32 to 60 parts by weight, which is significantly increased from the 20 to 30 parts by weight of carbon material in the earlier application. So,
As is clear from the test results in Tables 1 and 2 above, the compressive strength, bending strength at room temperature and hot temperature, thermal conductivity, thermal shock resistance, and alkali resistance are significantly superior to the comparative product related to the prior application. A blast furnace lining refractory with excellent properties was obtained, and the results of an insertion test using the test bricks as part of the blast furnace lining refractory were also very good.

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Claims (1)

[Claims] 1 Naturally produced flaky phosphorous graphite 10-30% by weight
32 to 60 parts of earthy graphite of 80 mesh or less, 10 to 25 parts of silicon carbide, 5 to 15 parts of metallic silicon, and 10 to 20 parts of phenolic resin are mixed, kneaded, pressure-molded, and fired. Refractories for blast furnace lining.