JPH0411510B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to a dry spraying material for hot repairs that has excellent corrosion resistance. Conventionally, various wet or dry spraying materials have been used for hot spraying repairs of metal smelting furnaces such as converters and electric furnaces, but conventional spraying materials have various drawbacks, including poor corrosion resistance. There is a drawback. In other words, wet spraying materials are used by adding anhydrous inorganic salts such as phosphates and silicates as binders to refractory aggregate whose particle size has been adjusted, and mixing it with water in a spray nozzle to develop stickiness and make it adhere. However, because it contains a large amount of water, the refractory structure of the sprayed material becomes porous, deteriorating its corrosion resistance, and it also has the disadvantage of causing thermal spalling on the lining of converters, etc. There is. In addition, dry spraying materials include those using thermosetting resin powder such as phenolic resin or urethane resin as a binder, those using a combination of the above resin powder and pitch powder such as coal pitch or petroleum pitch, magnesium sulfate, or borosilicate powder. There are known methods that use powdered water-containing inorganic substances such as sand that melt at relatively low temperatures. However, among the above, those using thermosetting resin powder have a large volatile content, low volatilization temperature, and low ignition temperature, so foaming and combustion occur during spraying, making the sprayed material fireproof. The disadvantage is that the material structure becomes extremely porous and corrosion resistance deteriorates. In addition, although Pituchi has lower volatile content, higher volatilization temperature, and higher ignition temperature than thermosetting resins, it has properties similar to those of thermosetting resins, so it is still necessary to use Pituchi powder. Similarly, it has the disadvantage that it becomes porous and its corrosion resistance deteriorates. In order to improve the drawbacks of using thermosetting resin and pitch, as mentioned above,
Attempts have been made to suppress combustion by using _N2 gas instead of air as the blown carrier gas.
Not enough effect has been obtained. In addition, for products using powdered hydrated inorganic substances, since hydrated inorganic substances generally have a significantly higher melting temperature than thermosetting resins, it is necessary to It is necessary to use a large amount of the substance, and in that case, the substance has a very high water content, which has the disadvantage that the water content in the structure increases during spraying, making it porous and reducing corrosion resistance. In order to eliminate the above-mentioned drawbacks of conventional spray materials, the present inventor has conducted intensive research on binders for dry spray materials, and has developed a method to use pitch powder, which has less foaming and combustion than thermosetting resins.
Since the foaming phenomenon and the formation of porous structure due to combustion cannot be avoided with only pitch powder, we considered using inorganic salts that do not cause foaming and produce a highly viscous melt. That is, we considered preventing foaming of the pitch by using the high adhesive strength of the inorganic salt melt, and preventing combustion by coating the pitch with the melt. In this case, since the melting temperature of the inorganic salts is very high, a sufficient melt cannot be generated even in hot conditions, and certain measures are required to melt the inorganic salts. The present inventor further continued his research and discovered that the inorganic salts can be easily melted by compounding the inorganic salts and graphite. In other words, when considering the supply of heat to sprayed materials, radiation is considered to be the main source of heat transfer, so fire-resistant materials have a much higher ability to absorb radiant heat than the fire-resistant materials used for sprayed materials, and have a lower specific gravity. By combining inorganic salts with graphite, which has a large specific surface area and absorbs a large amount of heat during spraying, the heat of fusion of the inorganic salts is sufficiently supplied, and as a result, it has the effect of preventing foaming and combustion phenomena in pitch. was obtained, and the structure was found to become denser. In addition, in order to compound inorganic salts and graphite, which are inherently less reactive, it is necessary to simultaneously grind and mix the two. The mechanical energy generated is partially converted into thermal energy and chemical energy, but it was discovered that in this case, it was converted into adhesion energy, which caused the inorganic salts and graphite to adhere. In fact, observation of the fine structure of the pulverized mixture of graphite and inorganic salts revealed strong adhesion between the two, and it was found that adhesion and pulverization of graphite could be achieved simultaneously by the above treatment. As a result of further research based on the above-mentioned various findings, the present inventor found that when specific amounts of pitch powder and the above-mentioned mixed pulverized product are used as binders, it is possible to prevent the structure from becoming porous (the structure becomes denser). The inventors have discovered that a dry spray material with particularly excellent corrosion resistance can be obtained by doing this, and have completed the present invention. That is, in the present invention, for 100 parts by weight of the refractory aggregate,
The present invention relates to a dry spraying material for hot repair characterized in that 8 to 30 parts by weight of pitch powder and 2 to 14 parts by weight of a mixed pulverized mixture of inorganic salts and graphite are blended as a binder. The fire-resistant aggregate in the present invention is not particularly limited, and any materials commonly used for this type of spray material can be used, such as magnesia,
Examples include dolomite, lime, chromium, alumina, spinel, silicon carbide, silica, silica, zircon, metallic aluminum, metallic silicon, etc., and one or more of these are used after adjusting the particle size. The particle size adjustment may be the same as the adjustment normally performed for this type of spray material, but just to be sure, to give an example, for particles with a particle size of about 5 to 1 mm, it is about 0 to 60% by weight, and about 1 to 0.074 mm. It is common to use particles with a particle size of about 0 to 80% by weight, and about 10 to 50% by weight of particles with a particle size of about 0.074 mm or less. The pitch powder used in the present invention preferably has a fixed carbon content of 55% by weight or more from the viewpoint of carbon bond formation, and may be either coal-based or petroleum-based. The particle size is preferably about 3 mm or less. The amount used is 8 to 30 parts by weight per 100 parts by weight of the refractory aggregate. If it is less than 8 parts by weight, the adhesion will be reduced due to insufficient liquid phase, and if it is more than 30 parts by weight, the adhesion will be reduced due to the flow-down phenomenon due to excess liquid phase. Examples of the graphite in the present invention include scale graphite, earthy graphite, and artificial graphite for electrodes, and at least one of these is used. Moreover, the inorganic salts in the present invention include not only various salts conventionally used as binders but also inorganic acids such as boric acid. In addition, anhydrous materials are preferable, but even water-containing materials can be used because the amount used is small and the structure does not become porous.
Examples include phosphates such as sodium hexametaphosphate, sodium acid pyrophosphate, sodium tetrapolyphosphate, and monobasic sodium phosphate; borates such as boric acid, borax, sodium borate, potassium borate, and lithium borate; Examples include silicates such as acid soda, orthosilicate sodium, and amorphous sodium silicate, and at least one of these is used. In the present invention, it is necessary to use the above-mentioned graphite and inorganic salts in a composite form, which can be achieved by mixing and pulverizing the two. The mixing ratio of both is 2:1 by weight of inorganic salts: graphite.
A ratio of about 1:10 to about 1:10 is preferable from the viewpoints of adhesiveness between the two and formation of a melt of inorganic salts. The method of pulverizing the mixture is not particularly limited and can be carried out by any known means, but it is preferable to use a vibrating mill, a ball mill, etc., which have a large pulverizing effect. Although the grinding conditions such as the grinding time vary depending on the equipment used and are not constant, it is preferable from the viewpoint of adhesion to grind the mixed pulverized product until it becomes a fine powder with a specific surface area of about 10 m ² /g or more. In this way, a pulverized mixture of inorganic salts and graphite firmly adhered to each other is obtained. The amount of the mixed pulverized product used is 2 to 14 parts by weight per 100 parts by weight of the refractory aggregate.
If the amount is less than 2 parts by weight, the adhesion will decrease, and if it is more than 14 parts by weight, the structure will tend to become porous, which is not preferable. According to the dry spraying material of the present invention, by blending the mixed pulverized product of inorganic salts and graphite, the inorganic salts can be easily melted, thereby preventing the foaming phenomenon and combustion of the pitch as described above. It is possible to prevent the refractory structure of the material from becoming porous (that is, the structure becomes dense), resulting in the remarkable effect of significantly improving corrosion resistance. Further, the dry spray material of the present invention is extremely good in terms of adhesion, strength, etc. Therefore, the dry spraying material of the present invention is extremely suitable for hot repair of metal refining furnaces such as converters, electric furnaces, AOD furnaces, and VOD furnaces, RH degassing vessels, DH degassing vessels, and the like. Hereinafter, the present invention will be explained in more detail with reference to Production Examples, Examples, and Comparative Examples. Production example 1 Sodium hexametaphosphate and scaly graphite were mixed in 1 part
1.5 kg of the mixture at a weight ratio of 1, 1:2, 1:4, or 1:8 was placed in a vibration mill (manufactured by Chuo Kakoki Co., Ltd.,
The mixture was mixed and pulverized for about 2 hours under the conditions of a vibration motor with an amplitude of 6 mm and a rotation speed of 1700 rpm (capacity 2.2 kW). The specific surface area of the obtained mixed pulverized product is shown in Table 1 below.

[Table] Examples 1 to 14 and Comparative Examples 1 to 6 The present invention or comparative dry spray materials having the formulations shown in Tables 2, 3, and 4 (numbers in the tables indicate parts by weight) were sprayed. A spray gun was used to spray the magnesia panel bricks of an experimental furnace maintained at an internal temperature of 1200°C. In order to examine the adhesion of each sprayed material, the adhesion rate to the panel bricks during spraying was measured, and the adhesive strength with the panel bricks after spraying was determined. Furthermore, samples were taken after spraying to determine the density of the structure.
Compressive strength and corrosion resistance were investigated. The test method is shown below. Γ Adhesion rate: Rebound loss was collected and weighed, and calculated according to the following formula. Adhesion rate (%) = Spray amount - Rebound loss amount / Spray amount x 10
0 Γ Adhesive strength...Based on the following criteria. ○: Very strong (does not peel off even when hit with a small hammer). △: Intermediate (peel off when hit with a small hammer). ×: Weak (peels off when touched). Γ Porosity: Measured according to JIS R2205. Γ Water absorption rate: Measured according to JIS R2205. Γ Apparent specific gravity...Measured in accordance with JIS R2205. Γ Bulk specific gravity: Measured according to JIS R2205. Γ Compressive strength...Measured according to JIS R2206. Γ Corrosion resistance test...A sample with a shape of 40 x 40 x 115 mm was used as the lining of a high frequency induction heating furnace, and heated to 1750℃.
It is expressed as the maximum melting thickness (mm) in the 40mm direction when held for 3 hours. As the slag, 2 kg of converter slag was used. The results of each test are shown in Tables 5, 6 and 7.

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[Table] As is clear from Tables 5, 6, and 7, the dry sprayed materials of the present invention have better adhesion and densification than the comparative materials, and are particularly corrosion resistant and It can be seen that the strength is excellent. Furthermore, with the dry spraying material of the present invention, neither pitch foaming nor combustion was observed during spraying. Next, Table 8 shows the results of actually using the dry spray materials of Example 6 and Comparative Example 2 in a top-blowing converter.

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[Table] As shown above, the dry spraying material of the present invention has particularly excellent corrosion resistance, adhesion, and
It is clear that the durability is significantly improved since the strength etc. are also excellent.

Claims (1)

[Claims] 1. 8 to 30 parts by weight of pitch powder and 2 to 14 parts by weight of a pulverized mixture of inorganic salts and graphite are blended as a binder to 100 parts by weight of the refractory aggregate. Dry spray material for hot repairs. 2. The dry spray material for hot repair according to claim 1, wherein the inorganic salt is at least one of phosphate, boric acid, borate, and silicate.