JPH11351762A - Bottom electrode of dc electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong lifetime of an electrode by dispersing a part of current flowing through the pin of a furnace bottom electrode to an electrode block thereby reducing heat generation rate of the electrode pin. SOLUTION: The furnace bottom electrode comprising a supporting base 6, a stamp material 17 arranged thereon, and an electrode block 8 of conductive refractories 16 mounted on the stamp material 17 is provided with a plurality of conductive contact pins 7 penetrating the supporting base 6, the stamp material 17, and the electrode block 8 and the gap between the contact pin 7 and the electrode block 8 of conductive refractories 16 is filled with irregular conductive refractories 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bottom electrode for a DC electric furnace for melting metal scrap such as steel.

[0002]

2. Description of the Related Art A DC electric furnace differs from an AC electric furnace in that it has a single electrode, so that the basic unit of the electrode is small, the noise during the melting period is small, and an arc is generated from one cathode toward the bottom electrode. Flies vertically downward, resulting in a uniform temperature distribution.
There are various advantages such as no hot spots, no induction loss and good energy efficiency. For this reason, a DC electric furnace has recently become the mainstream as a melting furnace in place of the AC electric furnace.

As shown in FIG. 2, a conventional DC arc furnace 1
Has a furnace bottom electrode 10 as an anode at the furnace bottom and a graphite electrode 9 as a cathode disposed at the furnace upper part. During operation, scrap and auxiliary materials are charged into the furnace, direct current is conducted between the contact pin 7 at the bottom of the furnace and the upper electrode 9, and the scrap is melted by this electric heat energy. . In a 60-ton electric furnace, for example, the voltage is 500 to 600 volts, and the current is about 100 kA.

An electrode block 8 made of a magnesia-carbon refractory is housed in a steel case enclosing the whole, and a large number of contact pins 7 penetrate the electrode block 8 and only the upper end thereof is exposed in the furnace. doing. The electrode block 8 is supported by a support substrate 6 via a stamp material, and the support substrate 6 is supported on an iron shell 1b of the furnace body via an insulating material.

[0005] The contact pins 7 are connected to the current board 5, and the connection portions 4 and the terminals 3 are attached to the lower surface side of the current board 5. The conductor 2 is connected to the terminal 3 and the conductor 2
Is supplied from the power supply to the current board 5 via the power supply, and the current is distributed to each of the contact pins 7. The gap between the contact pin 7 and the electrode block 8 is filled with a non-conductive magnetic filler, for example, a magnetic stamp material (MgO: 96 wt%, SiO ₂ : 2 wt%, other: 2 wt%). Pin 7
Does not flow in the electrode block.

The connecting portion 4 is a hollow body, and the upper end of the internal passage 4a is open. This internal passage 4a is connected to an air supply source (not shown) for air cooling. The upper opening of the passage 4a faces the lower surface of the upper support substrate 6, and
The current substrate 5 and the support substrate 6 are forcibly air-cooled by blowing air.

[0007]

As shown in FIG. 2, since the upper surface of the electrode block 8 is continuous with the hearth surface of the hearth refractory, the electrode block 8 comes into contact with a molten metal, for example, molten steel, and is partially melted. I do. Further, the upper surface of the electrode block 8 is formed by flowing molten steel,
Since it is exposed to slag during tapping, the electrode block made of a refractory is eroded. If the amount of erosion or the depth exceeds a predetermined value, the electrode block must be replaced.

The conventional furnace bottom electrode has the following problems. (1) Carbon brick is mainly used as a refractory used for the electrode block of the hearth electrode. However, since the upper surface of the electrode block is a part of the upper surface of the hearth refractory, the atmosphere during tapping is required. In an oxidizing atmosphere such as contact, the refractory on the surface of the electrode block is oxidized, leading to accelerated wear.

(2) Further, the upper surface of the electrode block was affected by the flow of the molten steel, and was greatly damaged by erosion. (3) The pin at the top of the furnace bottom electrode block that contacts the molten steel
Insufficient heat removal capability and Joule heat generated in the pin itself caused a portion of the upper end to melt, causing the block refractory to crack. (4) When a part of the furnace bottom operating surface is covered with an electrically insulating slag or the like, current drift may occur. In this case, current concentrates on electrode pins existing in the drift range. The Joule heat accelerated the wear of the pins and the electrode block, and sometimes caused melting of the support base, which shortened the electrode life.

[0010] As described above, there has been a demand for an electrode structure in which the heat removal capability of the furnace bottom electrode is increased to reduce the erosion of the pin, and furthermore, the current concentration does not occur.

In Japanese Patent Application Laid-Open No. 4-295592, the life of the electrode block is extended by press-molding the electrode block in order to extend the life of the electrode. However, this method cannot suppress the wear of the pin itself, which wears faster than the electrode block, and is therefore insufficient for extending the life of the furnace bottom electrode. The present invention has been made to solve these problems, and an object of the present invention is to provide a multi-pin type bottom electrode having an electrode structure that can withstand continuous use for a longer period of time.

[0012]

Means for Solving the Problems In order to solve the above problems, the following invention has been made. A first aspect of the invention is
A bottom electrode of a DC electric furnace having the following structure. (A) a furnace bottom electrode including a support base, a stamp material disposed on the support base, and an electrode block made of a conductive refractory placed on the stamp material; A conductive base having a plurality of conductive contact pins penetrating the support base, the stamp material and the electrode block; and (b) an electrically conductive irregular shape for conducting a current through a gap between the contact pin and the electrode block made of the conductive refractory. Refractory is filled.

Since the furnace bottom electrode is filled with a conductive refractory between a contact pin and an electrode block made of a conductive refractory, a part of the current flowing through the contact pin reduces the conductive refractory. Joule heat generated in the contact pin is reduced because the current also flows through the electrode block through the electrode block, and this has the effect of extending the life of the pin.

According to a second aspect of the present invention, the electrode block is constructed of any one of a magnesia-carbon refractory brick, an alumina-carbon refractory brick, and a magnesia-alumina spinel-carbon refractory brick. It is a bottom electrode for a DC electric furnace. Magnesia-carbon-based refractory brick, alumina-carbon-based refractory brick, magnesia-alumina spinel-
Since all carbon-based refractories have high electrical conductivity, they have the effect of reducing the current flowing through the contact pins and extending the life of the furnace bottom electrode.

According to a third aspect of the present invention, there is provided a method for a DC electric furnace, wherein the conductive amorphous refractory is an amorphous refractory containing at least one of graphite powder, metal powder and cermet powder. Of the furnace bottom electrode. When the conductive irregular-shaped refractory contains graphite powder, metal powder, and cermet powder, the electrical conductivity increases, and a part of the current flowing through the contact pin flows into the surrounding electrode block to reduce the current flowing through the contact pin. It has the effect of extending the life.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
Has a furnace bottom electrode 10 as an anode on the furnace bottom and a graphite electrode 9 as a cathode disposed on the furnace upper part. In operation, scrap and auxiliary materials are charged into the furnace, DC electricity is generated between the steel contact pins 7 at the bottom of the furnace and the upper electrode 9, and the scrap is melted by this electric heat energy.

FIG. 1 shows a part of a bottom electrode for a DC electric furnace according to the present invention. The structure is as follows. (A) a furnace bottom electrode including a support base, a stamp material disposed on the support base, and an electrode block made of a conductive refractory placed on the stamp material; A conductive base having a plurality of conductive contact pins penetrating the support base, the stamp material and the electrode block; and (b) an electrically conductive irregular shape for conducting a current through a gap between the contact pin and the electrode block made of the conductive refractory. The structure is filled with refractories.

Normally, the electrode block 8 is made of a magnesia-carbon brick or a stamp material containing about 78% by weight of a highly fire-resistant magnesia and about 17% by weight of carbon, so that it has electric conductivity. The electrode block 8 is provided on a metal support substrate via the stamp material 17. The stamp material 17 prevents the heat of the electrode block 8 from being directly transmitted to the supporting substrate 6 and preventing the deformation. The metal supporting substrate supplies electricity to the contact pins 7.

The length of the contact pins from the conventional support substrate to the upper surface of the electrode is, for example, about 1 in the case of a 60-ton electric furnace.
000 mm. Heat from the molten steel at the top is transmitted to the pin, and Joule heat is generated by the current flowing through the pin, so that the pin is easily melted.

Therefore, in the present invention, an electrically conductive filler is filled between the electrode block and the pin. In this way, a part of the current flowing through the pin flows to the conductive electrode block via the filler, and the Joule heat generated in the pin can be reduced.

The electrically conductive refractory is preferably an amorphous refractory containing, for example, 7 wt% or more of at least one of graphite powder, metal powder and cermet powder. If the amorphous refractory contains graphite powder, metal powder, cermet powder, etc., the electrical conductivity will increase, the current flowing to the pins will flow to the electrode block, the current will also be distributed to adjacent pins, and the current will flow to specific pins. It has the effect of suppressing dissolution of the pins without concentrating and extending the life of the electrodes. As the electrically conductive amorphous refractory, for example, powder of magnesium graphite is desirable.

The filling length of the conductive irregular-shaped refractory is desirably 100 mm or more from the lower part of the electrode block in order to reduce the current flowing through the pin. If the thickness is less than 100 mm, sufficient current flow between the pin and the electrode block cannot be ensured. However, it is desirable that the upper part be filled with a normal amorphous refractory. In general, a refractory having electrical conductivity, for example, a magnesium-carbon material reacts with oxidation or molten metal with a pin material more than a normal magnesium, and the pin is easily melted.

The electrode pins are usually made of steel rods. Its diameter is, for example, 40 mmφ to 60 mmφ. In this case, in order to suppress heat generation during energization, the current per sectional area is desirably, for example, 0.5 A / mm ² or less.

Further, a metal plate having electrical conductivity is used for the support substrate so as not to impair the original function of the electrode. Since the metal plate as the supporting substrate serves as a current header, current concentration is reduced.

[0025]

[Example] Approximately 1000 m from the support substrate to the furnace bottom level
m, 60t with electrode block of about 2000mm diameter
In an electric furnace, the gap between the contact pin and the electrode block between the position of about 200 mm thickness stamp material on the support substrate and the electrode block is filled with an electrically conductive irregular-shaped refractory, Was filled with magnesia having no electrical conductivity.

The distance between the electrode block and the contact pins is about 5 mm, and the filler is a carbon material 5 having a particle size of 1 mm or less.
0 wt%, Magnesia 50 wt% with a particle size of 0.2 mm or less
It is an amorphous refractory consisting of The electrode block is composed of 79 wt% of magnesium, 16 wt% of graphite, and 5 wt% of others.
It is constructed of refractory brick consisting of

The electrode pins had a diameter of 45 mmφ, and 200 electrode pins were arranged on an electrode block having a diameter of about 2000 mm.
As a result, the current density was 0.3 A / mm ² or less. The hearth refractories around the electrodes were repaired several times while monitoring the situation.

The temperature of the pins in melting the steel using this electrode block was measured for 12 pins. The location of the temperature measurement is the position of the support base at the center of the contact pin. For comparison, the temperature was also measured for a case filled with a conventional magnesia amorphous refractory having no electrical conductivity. As a result, in the case of the present invention, the maximum temperature difference between the twelve pins was reduced by 50 ° C. as compared with the conventional case, and the effect that the current was not concentrated on a specific pin and was uniformly dispersed was confirmed. Was.

As a result, although the refractory around the electrode was repaired several times, the furnace bottom electrode itself could be continuously used on average 2000 channels. The conventional electrode life is about 1500 ch
According to the present invention, as described above, the electrode life was extended by 1.3 times. Therefore, the intensity of repair of the furnace bottom electrode is reduced, and
Productivity has also been improved by reducing the number of electrode replacements.

[0030]

As described above, according to the present invention, as a result of dispersing a part of the current flowing through the pins of the furnace bottom electrode to the electrode blocks, the calorific value of the electrode pins can be reduced.
The life of the electrode can be increased. As a result, the following effects can be obtained. Reduction of furnace bottom electrode repair basic unit Realization of stable operation Reduction of maintenance cost A great effect such as improvement of productivity by reducing the number of furnace repairs can be expected.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a pin of a furnace bottom electrode of the present invention.

FIG. 2 is a view showing the entire structure of a conventional furnace bottom electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC electric furnace 1a Hearth refractory 2 Conductor 3 Terminal 4 Connection part 5 Electrode substrate 6 Support substrate 7 Pin 8 Electrode block 9 Cathode 10 Furnace bottom electrode 15 Irregular refractory 16 Conductive irregular refractory 17 Stamp material

Claims (3)

[Claims] 1. A bottom electrode of a DC electric furnace having the following structure. (A) a furnace bottom electrode including a support base, a stamp material disposed on the support base, and an electrode block made of a conductive refractory placed on the stamp material; A conductive base having a plurality of conductive contact pins penetrating the support base, the stamp material and the electrode block; and (b) an electrically conductive irregular shape for conducting a current through a gap between the contact pin and the electrode block made of the conductive refractory. Refractory is filled. 2. An electrode block made of a conductive refractory material, wherein the electrode block is made of any one of a magnesium-carbon refractory brick, an alumina-carbon refractory brick, and a magnesium-alumina spinel-carbon refractory brick. A bottom electrode of the DC electric furnace according to claim 1. 3. The DC electric furnace according to claim 1, wherein the electrically conductive amorphous refractory is an amorphous refractory containing at least one of graphite powder, metal powder, and cermet powder. Furnace bottom electrode.