JPH03215315A - 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 oxygen-containing gas from the bottom of the electric furnace during the melting operation, thereby keeping the oxidative atmosphere 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. Air is blasted from the furnace bottom with a blower 6 during the electrification process. 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] The raw material, magnesia clin or natural magnesia, is charged in advance as a bottom layer into an electric furnace, and a graphite current-carrying material is placed on top of it. Next, the electrode is lowered and brought into contact with the current-carrying material. In the open arc melting method, electricity is applied to the electrode to start melting, and as the melting progresses, the electrode is pulled up and raw material suitable for melting is charged. The melting process ends when the amount of raw material charged reaches a predetermined amount. In the electrode buried melting method, after the electrode comes into contact with the current-carrying material, the raw material is further charged, and after the amount equivalent to one charge has been charged, electricity is applied to start melting. As the melting progresses, the electrode is pulled up and the melting process ends when it reaches near the surface of the raw material. After electricity is applied, Joule heat is applied to the raw materials and melting begins. When the raw material is melted, even if there is no current-carrying material, electricity is applied through the melted part and the raw material continues to melt. 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. [Problems to be Solved by the Invention] Electrofused magnesia is usually white in color, but black or gray (hereinafter simply referred to as black) electrofused magnesia may be observed above the above-mentioned fused portion. Apart from its properties as a raw material for refractory materials, black fused magnesia has
Product value decreases. In addition, according to the oven arc melting method, the melted part is exposed to the air and creates an oxidizing atmosphere, so it can be expected to reduce the amount of black products, but the amount of electricity used per unit weight of the product (power consumption) is buried! Increases compared to the extreme method.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for producing fused magnesia in which the generation rate of black fused magnesia and the electric power consumption rate are reduced. [Means and effects for solving the problems] The method for producing electrofused magnesia according to the present invention is a method for producing electrofused magnesia in which raw material magnesia clinker or natural magnesia is melted in an electric furnace. After charging the electric furnace, the raw material is melted by the buried electrode melting method in which electricity is applied while the electrode is buried in the raw material, and while the raw material is melting, oxygen-containing gas is blown from the bottom of the electric furnace to oxidize the inside of the furnace. It is characterized by creating an atmosphere. The reasons why black fused magnesia is generated are thought to be: (1) MgO is reduced and becomes black due to the precipitation of Mg, or (2) carbon from the current-carrying material and electrode remains. In order to prevent the above-mentioned Mg precipitation or carbon residue, and to promote the oxidation of the deposited Mg or carbon, an oxygen-containing gas is blown into the electric furnace to create an oxidizing atmosphere inside the furnace. [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 fused 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 above will be explained. In the preparatory process before energizing the electrode 4, magnesia chlorine or natural magnesia, which is a raw material, is crushed and charged into a size of about 5 to 20 mm as a bottom layer in an electric furnace, and graphite is placed on top of it. Install electrically conductive materials. Next, after lowering the electrode 4 and bringing it into contact with the current-carrying material, one charge of the raw material 3 is charged. When power is applied to the electrode 4 after the raw material 3 is filled, the electrode 4 is initially energized through the current-carrying material and Joule heat is applied to the raw material 3. When the raw material is melted, even if there is no current-carrying material, electricity is applied through the melted part and the raw material 3
The dissolution progresses. During the energization, the blower 6 blows air from the bottom of the furnace. The gas to be blown is not limited to air, but any gas that creates an oxidizing atmosphere in the furnace and is inexpensive and easy to handle may be used. Additionally, if necessary, oxygen gas may be mixed into the air to increase the oxygen concentration of the blown gas. As the raw material melts, 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. Because the inside of the furnace is considered to be an oxidizing atmosphere! Precipitation of Mg, which is the cause of blackening of molten magnesia, is reduced, and the precipitated Mg is easily oxidized to become M[0. Furthermore, the carbon in the electrodes is oxidized and discharged as CO or CO2 gas. In the above manner, blackening of the fused magnesia is reduced. 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. Table 1 compares this example and the conventional example. Conventional example (1). (2> are the buried electrode melting method and the open arc melting method, respectively. As is clear from the table, this example reduces both the incidence of black products and the electric power consumption rate compared to the conventional example. Note that the unit of air blowing amount in Table 1 is the cross-sectional area m2 of the electric furnace, Hr
The body of air in the standard state is Nl3.

Table 1 [Effects of the Invention] According to the method of the present invention, raw materials are melted by the buried electrode melting method, and oxygen-containing gas is blown from the bottom of the electric furnace during melting of the raw materials to create an oxidizing atmosphere inside the furnace. Therefore, the incidence of black products and the electric power consumption of the fused magnesia product are reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an electric furnace for carrying out the method of the present invention.

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,
After charging one charge of raw material, the raw material is melted by a buried electrode melting method in which electricity is applied while the electrode is buried in the raw material, and while the raw material is melting, oxygen-containing gas is blown from the bottom of the electric furnace. A method for producing electrofused magnesia characterized by creating an oxidizing atmosphere in a furnace.