JPH03215316A - Production of electrofused magnesia - Google Patents

Abstract

PURPOSE:To decrease the black generation ratio of electrofused magnesia and electric power consumption rate by melting a raw material by an electrode- embedding melting process while blasting a gas containing non-oxidizing gas from the bottom of the electric furnace during the melting operation, thereby cooling the circumference of the melting zone in the furnace. CONSTITUTION:Magnesia clinker or natural magnesia used as a raw material 3 is charged to an electric furnace as a bottom-laying material and a conductive material made of graphite is placed on the laying material. An electrode 4 is lowered and contacted with the conductive material, a raw material 3 of an amount corresponding to one charge is charged to the furnace, the electrode 4 is connected to a power source and the raw material is melted. During the electrification process, non-oxidizing gas or a gas containing a non-oxidizing gas is blasted as a cooling gas from the furnace bottom with a blower 6 to cool the circumference of the melting zone 2. The electrode is pulled up according to the progress of the melting of the raw material to solidify the molten part and successively form fresh molten part at the upper part. The melting operation is finished when the electrode reaches a prescribed height.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing fused magnesia, which is a raw material for refractory materials. [Prior art] Magnesia tarinka or natural magnesia, which is a raw material, is charged in advance as a bottom layer into an electric furnace, and a graphite conductive material is placed on top of it. Next, after the electrode is lowered and brought into contact with the current-carrying material, raw materials are further charged in an amount equivalent to one charge. After a predetermined amount of raw material has been charged, power is applied to the electrodes, initially through the current-carrying material, and heat is applied to the raw material. Once the raw materials are melted, even if there is no current-carrying material,
Electricity is passed through the melting part and the raw material melts. As the melting of the raw material progresses, the electrode is pulled up, and as the melted portion solidifies, new melted portions are sequentially formed upward, and the melting process ends when the electrode reaches a predetermined height. After the melting process is completed, the melted and solidified electrofused portion is taken out, crushed and purified, and shipped as an electrofused magnesia product. [Problem to be solved by the invention] The columnar crystals of electrofused magnesia have few grain boundaries. Therefore, since it contains few impurities, it is highly valued as a raw material for refractory materials and is traded at a high price. However, since electrofused magnesia produced by conventional methods has many equiaxed crystals and a low production rate of columnar crystals, it is usually mixed together with the equiaxed portion and shipped as a product. The present invention has been made in view of the above circumstances, and aims to provide a method for producing fused magnesia with a high production rate of columnar crystals. [Means and effects for solving the problems] The method for producing electro-fused magnesia according to the present invention is a method for producing electro-fused magnesia in which magnesia curing power or natural magnesia as a raw material is melted in an electric furnace. It is characterized by blowing a non-oxidizing gas or a gas containing a non-oxidizing gas into the bottom of the furnace as a cooling gas to cool the area around the melting zone in the furnace and increase the rate of columnar crystal formation of fused magnesia. .

In addition to the purity of the raw materials, the temperature gradient at the solid-liquid interface and its stability are important factors for the development of columnar crystals.

In the conventional example, since the temperature gradient is small and unstable, the development of columnar crystals is inhibited and the production rate is low. Therefore, in the present invention, in order to make the temperature gradient larger and more stable than before, cooling gas is supplied from the bottom of the electric furnace to cool the solid-liquid interface on the surface of the melting zone, thereby increasing the temperature gradient. and adjust the supply amount of cooling gas to stabilize the temperature gradient.
This is intended to promote the development of columnar crystals. Although air is usually the most convenient cooling gas to use,
When reacting with, for example, carbon in the furnace and generating heat, making the cooling effect insufficient, it is necessary to mix in an inert gas to suppress the heat generation effect. If it is necessary to further enhance the cooling effect, it may be possible to use a gas that does not contain oxygen. [Embodiments] Examples of the present invention will be described in detail with reference to the attached drawings. Figure 1 is a longitudinal sectional view of an electric furnace in which the method of the present invention is carried out. In the figure, 1 is electromagnetic magnesia obtained by melting and solidifying the raw material 3, 2 is a molten zone, 4 is an electrode, 5 is a furnace wall,
6 is a blower that blows air into the furnace. The operation of the electric furnace configured as described above will be explained.

In the preparation process before energizing ti4, the raw material magnesia clin or natural magnesia is crushed and charged to about 5 to 2 (lawφ) as a bottom layer in the electric furnace, and a graphite current-carrying material is placed on top of it. Next, after the electrode 4 is lowered and brought into contact with the current-carrying material, the raw material 3 is further charged, and after the amount equivalent to one charge has been charged, energization is started.
When power is applied to the electrode 4, electricity is first applied to the electrode 4 through the current-carrying material, and Joule heat is applied to the raw material 3. When the raw material 3 is melted, even if there is no current-carrying material, electricity is applied through the melted part and the melting of the raw material 3 progresses. During the energization, the blower 6 blows cooling gas from the bottom of the furnace. As the melting of the raw material 3 progresses, the electrode 4 is pulled up, the melted portion solidifies, and new melted portions are sequentially formed upward, and the melting process ends when the electrode reaches a predetermined height. After that, it is left to cool in the furnace and then taken out as a solidified block.

Figure 2 shows the coagulation block 1 taken out as described above.
It is 0. In the figure, 14 is a sintered layer that is heated and sintered around the solidified electrofused magnesia 1 during melting, 11 is a columnar crystal portion whose production rate is aimed at by the present invention, and 12
13 is an equiaxed crystal portion, and 13 is a shrinkage cavity generated during solidification.

After the sintered layer 14 is removed from the solidified block 10, the columnar crystal portions 11 are separated in a crushing and refining process, and are shipped together with the equiaxed crystal portions 12 as fused magnesia products. Table 1 compares the incidence of columnar crystals between this example and the conventional example. The unit of air blowing amount in Table 1 is the volume of air in the standard state x3 per hour of the cross-sectional area of the electric furnace *2. As seen in the table, the effect of increasing the columnar crystal formation rate in this example is clear compared to the conventional example. Table 1 [Effect of the invention] According to the method of the present invention, Cooling gas is blown into the furnace from the bottom of the electric furnace to cool the area around the melting zone, increasing the rate of columnar crystal formation in the product, electrofused magnesia.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of an electric furnace for carrying out the method of the present invention, and Fig. 2 is a longitudinal sectional view of a solidification block. 1... Electrofused magnesia, 2... Melting zone, 3... Raw material, 4...
- Electrode, 5... Furnace wall, 6... Prower 10... Solidification block, 11... Columnar crystal portion, 12... Equiaxed crystal portion, 13... Shrinkage cavity, 1 4... Sintered layer.

Claims (1)

[Claims] In the method for producing fused magnesia, which involves melting the raw material magnesia clinker or natural magnesia in an electric furnace,
A non-oxidizing gas or a non-oxidizing gas-containing gas is blown from the bottom of the electric furnace during melting of the raw materials to cool the area around the melting zone in the furnace, thereby increasing columnar crystals of fused magnesia. A method for producing electrofused magnesia.