JPH0742173B2 - Dry ramming material for induction furnace - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dry ramming material for lining low-frequency and high-frequency induction furnaces.

2. Description of the Related Art Conventional techniques and their problems In general, as a lining material for low-frequency and high-frequency induction furnaces, a dry ramming material made of a dry material having a controlled grain size is widely used. Conventionally, in order to form a refractory lining layer on the inner wall of an induction furnace, a dry ramming material and a binder are mixed, and this mixture is dry-filled by a vibrator etc. to the lining corresponding to the steel core of the induction furnace. Then, the applied mixture is induction heated together with a steel core to form an integrated refractory lining layer.

As a conventional ramming material, a material made of silica stone and boric acid whose particle size is adjusted can be mentioned. The refractory lining layer that uses this ramming material is sintered only on the operating surface that contacts molten steel during furnace operation, and the back side that is in contact with the inner wall of the furnace is a powdery unsintered layer. There is. Therefore, even if a crack occurs, it does not reach the back surface and damages the furnace, and even if a crack occurs, the operation of the furnace is continued. However, in recent years, when high-temperature operation, melting of special cast steel and the like have been performed in induction furnaces, the durability of conventional ramming materials such as those described above becomes insufficient, and instead alumina, magnesia, alumina-magnesia, etc. Materials are being used. Since these materials have high corrosion resistance and high fire resistance, they have the advantages of less melting loss in actual use and higher strength than the above ramming material. However, since the above materials have low thermal shock resistance and the furnace is operated intermittently, cracks occur during use due to the heat cycle of heating and cooling and they expand, and their durability is still sufficient. No, you must stop using it. Therefore, the life of the furnace is not sufficiently improved. In particular, since the alumina-based material has high thermal conductivity, in the refractory lining layer using the alumina-based material, the working surface becomes dense and the sintering progresses to the back side (oversintering), and once cracks occur, There is a serious flaw in that the molten metal penetrates deep into the crack, damaging the backside induction coil. Further, the high thermal conductivity of the alumina-based material causes a problem that the heat loss during the operation becomes large and the unit price of electric power becomes high.

In order to solve the above problems, 1) a method of suppressing sintering by using a high-purity raw material, 2) a method of suppressing sintering by using a mixed material of alumina and magnesia, that is, alumina Utilizing the fact that the material expands due to the spinel reaction with magnesia, a method of suppressing the sintering by adjusting the expansion amount by appropriately changing the use ratio of alumina and magnesia has been tried, but it is sufficient. Ineffective,
The durability has not been significantly improved.

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in view of the above-mentioned problems of the prior art, and as a result, a conventional magnesia-alumina raw material, fused alumina which is granulated with a fine powder of a refractory material. It was found that a dry ramming material having a low thermal conductivity and not causing oversintering can be obtained by adding the hollow particles of
The present invention has been completed.

That is, the present invention is an induction furnace containing 100 parts by weight of a refractory raw material composed of 10 to 90% by weight of an alumina material and 90 to 10% by weight of a magnesia material, and 3 to 15 parts by weight of granulated fused alumina hollow particles. For dry lamming materials

In the present invention, an alumina material and a magnesia material are used as the refractory raw material. As the aluminous material, any ordinary material can be used, and examples thereof include those having an Al ₂ O ₃ content of 99.6% or more. Among them, electrofused products are particularly preferably used. As the magnesia material, any ordinary material can be used, and it is particularly preferable to use a high-purity material having an MgO content of 99.6% or more.

The use ratios of the alumina-based material and the magnesia-based material may be about 10 to 90% by weight and about 90 to 10% by weight, respectively. If the proportion of either material used is less than 10% by weight, the expansion property due to spinel formation and the corrosion resistance are insufficient, which is not preferable. The grain size composition may be similar to that of a normal ramming material. For example, in the grain size composition of the entire refractory raw material including both raw materials, one having a diameter of about 5 to 1 mm is 30 to 50 mm.
%, Those having a diameter of about 1 to 0.074 mm may be about 20 to 40% by weight, and those having a diameter of 0.074 mm or less may be about 20 to 40% by weight. However, it is necessary to change the grain size composition of each material depending on the usage ratio of the alumina-based material and the magnesia-based material. For example, it is necessary to increase the amount of magnesia fine powder (having a diameter of 0.074 mm or less) used in an alumina-rich structure, and to increase the amount of alumina fine powder used in a magnesia-rich structure.

In the present invention, hollow particles of fused alumina which are granulated with a fine powder of a refractory material and a binder are used. As the hollow particles of the fused alumina, any of ordinary ones can be used, and in particular, fused alumina having an Al ₂ O ₃ content of 99.6% or more and a bulk specific gravity of 0.8 or less can be preferably used. The particle size may be about 3 to 0.5 mm. Even if the fused alumina is used as it is, the effect of lowering the thermal conductivity and suppressing oversintering is exhibited. However, hollow particles of fused alumina have a lower bulk specific gravity than ordinary alumina-based materials, and since the particles are spherical,
Segregation of materials is likely to occur during construction. Further, since the particles themselves are hollow, there is a problem in that they have poor corrosion resistance. Therefore, the present invention succeeds in eliminating the defects of hollow particles by granulating the hollow particles of fused alumina. As the fine powder of the refractory material used in the granulation treatment, the same fused alumina or magnesia material as described above can be used, and if necessary, a small amount of silicon carbide or the like may be added. The fine powder may be used in an amount of about 7.5 to 40 parts by weight with respect to 100 parts by weight of hollow particles of fused alumina. If it is less than 7.5 parts by weight, the prevention of the segregation of hollow particles and the corrosion resistance of the refractory obtained will be insufficient, while if it exceeds 40 parts by weight, the granulation process will be difficult. As the binder used in the granulation treatment, a binder having a small amount of impurities and exhibiting a high strength in a low temperature region and a medium temperature region can be used, and examples thereof include alumina sol. As the alumina sol, any ordinary one can be used. The amount of alumina sol used is preferably about 0.1 to 5 parts by weight in terms of solid content with respect to 100 parts by weight of hollow particles of fused alumina. If the amount is less than 0.1 part by weight, the above effect is not sufficiently exhibited, while if the amount exceeds 5 parts by weight, the coating layer tends to be easily sintered and hollow particles are cracked during use.

The granulation treatment method may be according to a conventional method, for example, the hollow particles of the fused alumina, fine powder of the refractory material and a predetermined amount of alumina sol are mixed by using a low-speed rotating blade-type mixer or the like, and then granulated. Drying may be performed using a fluidized dryer or the like. In the granulation process, it is preferable to first coat hollow particles of fused alumina with alumina sol and then add fine powder.

The granulated electrofused alumina thus obtained has a particle size of about 5 to 1 mm, and the amount used is preferably about 3 to 15 parts by weight per 100 parts by weight of the refractory raw material. If it is less than 3 parts by weight, the effect of lowering the thermal conductivity and suppressing oversintering is poor, while if it exceeds 15 parts by weight, the filling property deteriorates.
Corrosion resistance is significantly reduced.

The dry ramming material of the present invention is produced by mixing a predetermined amount of the refractory raw material and the granulated hollow particles of fused alumina with a conventional method such as an Erich mixer.

When lining the dry ramming material of the present invention in an induction furnace, any ordinary method can be adopted. For example, the ramming material of the present invention is filled in a portion corresponding to the lining of the induction furnace by a vibrator or the like, and then induction heating is performed. Good.

EFFECTS OF THE INVENTION The dry ramming material of the present invention has a low thermal conductivity and does not cause oversintering, so that cracks do not occur even when the furnace is used intermittently, and it has excellent spalling resistance.

EXAMPLES The present invention will be further clarified by giving Examples and Comparative Examples below.

Examples 1 to 3 Using blade-type mixer, usage ratio shown in Table 1 (parts by weight)
The hollow particles of fused alumina, the fused alumina fine powder and alumina sol were mixed and granulated, and then dried using a fluid dryer to obtain hollow particles of fused alumina.
The particle size of the obtained hollow particles was 5 to 1 mm.

Refractory raw material (electrofused alumina / Al ₂ O ₃ content 99.9% and seawater magnesia / MgO content 99.8%) and granulated electrofused alumina in an Erich mixer at the use ratio (parts by weight) shown in Table 2. The hollow particles were mixed to obtain the dry ramming material of the present invention.

Using the obtained dry ramming material of the present invention (Examples 1 to 3), measurement of thermal conductivity, corrosion resistance test and spalling test were performed.

1) Measurement of thermal conductivity The thermal conductivity was measured according to JIS R-2618 by the unsteady heat wire method at room temperature and 1000 ° C. The sample was prepared by referring to DIN-51046, filling a castable frame with a ramming material, and stretching a heating wire and a thermocouple.

2) Corrosion resistance test As the corrosion resistance test, the rotary erosion method commonly used for testing refractories was adopted. Samples are two large and small pipes (diameter 200mm and diameter 100mm, both length 100m in the rotary drum.
m) was installed, and the ramming material was vertically filled between the two pipes. The inner pipe was melted by heating and removed during the test. The test was performed using C / S = 1 as an erosion agent and Fe ₂ O ₃ 20
% Slag was used and it was carried out at 1600 ° C. for 3 hours. After the test was completed, the sample was cut in the lateral direction together with the outer pipe, and the melt loss thickness and the thickness of the sintered layer were measured. As for the thickness of the sintered layer, the solidified portion on the working surface side which is not in the powder state was measured.

3) Spalling test The spalling test was carried out according to the corrosion resistance test. However, as the lining method of the ramming material, a method of filling the ramming material laterally (layered) was adopted. The test was carried out by repeating 20 cycles of heating at 1650 ° C. for 1 hour and air cooling for 30 minutes (the temperature dropped to 500 ° C.). After the test was completed, the sample was laterally divided to determine the occurrence of cracks. The results are shown in Table 2.

Comparative Examples 1 and 2 Conventional ramming materials were obtained in the same manner as in Examples 1 to 3 except that the hollow particles of the fused and fused alumina were not used. The obtained conventional ramming material was subjected to the same performance test as in the example. The results are shown in Table 2.

Table 1 Fused alumina hollow particles (3 to 0.5 mm) 100 Fused alumina fine powder (0.074 mm or less) 10 Alumina sol (5% aqueous solution) 3.5 From Table 2, the ramming material of the present invention has (1) lower thermal conductivity and less oversintering than the conventional ramming material, and (2) no cracks are generated, and the ramming material is resistant to use. It can be seen that the spalling property is excellent.

Claims (1)

[Claims] 1. An induction furnace containing 100 parts by weight of a refractory raw material composed of 10 to 90% by weight of an alumina-based material and 90 to 10% by weight of a magnesia-based material and 3 to 15 parts by weight of granulated fused alumina hollow particles. Dry lamming material for