JPH0827141B2 - Wall electrode of DC arc furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wall electrode of a DC arc furnace used for melting metal materials, refining molten metal, and the like.

[0002]

2. Description of the Related Art As an arc furnace for melting and refining, an electric current is passed between an electrode arranged above a molten metal charged in the furnace and an electrode attached to a furnace wall such as a furnace bottom or a side wall, A DC arc furnace for melting a metal material and refining a molten metal is known. The furnace wall electrode in this type of DC arc furnace is exposed to extremely harsh working atmosphere due to melting loss due to high temperature molten metal in the furnace, heat reception, Joule heat generated when a supply current passes through, etc. . Therefore, various proposals have been made to withstand this atmosphere and improve the durability of the furnace wall electrode.

For example, in Japanese Unexamined Patent Publication No. 61-24984, there is a metal rod penetrating the bottom of a furnace, MgO bricks are arranged around it, and the rear end of the electrode protruding from the furnace shell is cooled. It is cooled with a coolant such as water.

[0004]

However, even if the rear end portion of the electrode protruding from the furnace shell is cooled and heat is transferred from the front end side to the rear end side by heat conduction, it is caused by the resistance of the electrode itself. It is difficult to maintain the tip of the electrode at a low temperature, and the electrode itself melts by Joule heat generation. At this time, if the sleeve brick around the electrode is healthy, the iron electrode can be melted and solidified repeatedly to maintain its function and continue to operate, but if the sleeve brick is damaged and the extent becomes severe, it will be difficult to continue operation. Become. In other words, the life of the bottom electrode is considered to be one of the main controlling factors of sleeve bricks.

Under these circumstances, the main cause of damage to the sleeve bricks is wear due to the molten iron electrode and slag in the upper portion, and the lower portion in addition to this is cooled by the refrigerant at the rear end portion of the sleeve brick. This is due to the thermal stress due to the large temperature gradient of. In particular, since the furnace shell, refractory, etc. are cold when the furnace is started up, the temperature gradient of the upper and lower sleeve bricks is further increased, and extremely severe thermal stress is generated in the integrated sleeve brick. Therefore, an object of the present invention is to provide a furnace bottom electrode that relieves thermal stress of a sleeve brick, prevents cracking and wear, extends its life, and thus has a long life.

[0006]

[Means for Solving the Problems] A furnace wall of a DC arc furnace having a rod-shaped electrode made of iron or the like in the center, a sleeve brick formed in a tubular shape on the outer side of the electrode, and an area around the brick made of amorphous refractory In the electrode, the furnace wall electrode of the present invention is a double ring sleeve sleeve brick having excellent slag resistance, molten steel resistance, and spall resistance usually around 3 to 5 steps around the electrode in order to achieve the object. It is characterized by having a structure.

The inner ring is made thin so as to bear the thermal shock at the time of start-up, and the outer ring is made thicker than the inner ring so as to bear the molten steel resistance and the slag resistance in a steady state.

[0008] In order to achieve the object, the (height) of the lowermost brick of the sleeve bricks which is usually excellent in slag resistance, molten steel resistance, and spall resistance of 3 to 5 steps around the electrode.
The structure is such that the ratio of (outer diameter-inner diameter) is 0.5 or less.

[0009]

[Function] By adopting a double ring structure as a sleeve brick around the rod-shaped electrode, the inner ring receives the thermal shock at the time of startup, and even if the inner ring is damaged by the thermal shock at the time of startup, a steady state is achieved. Since the outer ring functions as a sleeve brick, it is possible to mitigate the thermal shock in the initial stage of startup, and the sleeve brick can be formed with the outer ring in a stable steady state. A furnace wall electrode with excellent durability can be obtained.

Further, the bottom sleeve brick is extremely important for ensuring the life of the electrode, and a material having a high thermal conductivity is selected in order to improve the cooling effect of the electrode. For this reason, the temperature gradient in the sleeve brick becomes large and the possibility of cracking due to thermal stress increases.
However, according to the results of experiments conducted by the present inventors, by setting the ratio of (height) and (outer diameter-inner diameter) of the lowermost sleeve brick to 0.5 or less, thermal stress generated in the brick is reduced and It is possible to prevent the occurrence of cracks, and it is possible to obtain a furnace wall electrode that is more durable than conventional ones.

[0011]

EXAMPLE FIG. 1 is a longitudinal sectional view showing the vicinity of an example furnace wall electrode buried in the furnace bottom of a DC arc furnace according to the present invention.
The bottom of a DC arc furnace has a furnace shell in which an irregular refractory material 2 is lined inside a perm brick 1 and the outside is supported by a steel shell 3. Then, a perforated bottom electrode mounting hole 4 is formed through the perma brick 1, the amorphous refractory 2 and the iron shell 3.

In FIG. 1, a rod-shaped electrode 5 made of iron, a conductive refractory or the like is arranged inside the hole 4 for mounting the bottom electrode. The tip end of the rod-shaped electrode 5 is formed in the same plane as the inner side surface of the irregular refractory 2 or slightly protrudes into the furnace, and the rear end is protruded from the support plate 3 a which is a part of the iron shell 3. An insulator 6 is attached to a hole formed in the support plate 3a at a position where the rod-shaped electrode 5 exits the furnace from the support plate 3a, and insulates the support plate 3a from the rod-shaped electrode 5. The rear end of the rod-shaped electrode 5 is fixed to a conductive plate 7 made of copper or the like, and is connected to the power supply cable 8 via the conductive plate 7.

The support plate 3a on which the rod-shaped electrode 5 is erected in this way is inserted into the furnace bottom electrode mounting hole 4 and fixed to the iron shell 3 by the fixture 9. Then, with the sleeve brick 11 installed outside the rod-shaped electrode 5, the amorphous refractory material 10 is installed between the perm brick 1 and the sleeve brick 11 and tamped. As a result, the rod-shaped electrode 5 is arranged in the furnace bottom electrode mounting hole 4 so as to penetrate the furnace wall. The sleeve brick 11 is composed of an inner sleeve brick 11-a and an outer sleeve brick 11-b.
The rod-shaped electrode 5 considers the electric power supplied to the arc furnace,
It is preferable to use one having a diameter of 200 to 500 mm. When the diameter of the rod-shaped electrode 5 is within this range, power can be supplied without increasing the electric resistance, and the strength of the rod-shaped electrode 5 itself can be secured. As the material of the sleeve brick 11, MgO brick, 10% to 25% C of MgO-C brick is superior to other bricks in slag resistance and molten steel resistance.
C brick also has excellent thermal shock resistance. Further, when the inner sleeve brick 11-a is vertically divided and the outer sleeve brick 11-b is integrally formed on the outer side of the inner sleeve brick 11-a, the thermal shock resistance is further improved. We have MgO bricks, and 10% to 25% C
A test for confirming the thermal shock resistance of the MgO-C brick of No. 3 and the brick previously divided vertically was carried out. 15% to 20% C M
The gO-C brick showed higher thermal shock resistance than the MgO brick, but the pre-divided MgO brick and the MgO-C brick showed much higher shock resistance than the integral brick. According to the results of the analysis separately conducted by the present inventors, in the case of a sleeve brick divided into four vertically in advance, the generated thermal stress in the circumferential direction is about ⅕ and the generated thermal stress in the height direction is about 1/5 as compared with the integrated type. It becomes 1/7 and the thermal shock resistance is greatly improved. From this result, it is clear that the vertical division of the inner sleeve brick has a great effect on reducing the thermal stress in the sleeve brick. The number of divisions at this time is not limited to four, but 2 to 8
Of course, division etc. are also possible. In the present invention, the inner ring receives the thermal shock at the time of start-up, and even if the inner ring is damaged by the thermal shock at the time of start-up, the outer ring functions as a sleeve brick in a steady state. Although it has a structure, the inner ring may be vertically divided in order to alleviate the thermal stress generated by the thermal shock at the time of startup. Further, the inner ring may be made of a heat insulating brick in order to reduce the thermal stress generated in the outer sleeve brick at the time of starting up.

FIG. 2 is a vertical sectional view showing the vicinity of a furnace wall electrode buried in the furnace bottom of a DC arc furnace according to the second embodiment of the present invention. In the second embodiment, the inner sleeve brick 11a bears the excessive thermal shock at the time of start-up, and then the molten steel resistance, slag resistance and thermal shock resistance in a steady state are taken into consideration by the outer sleeve brick 11b.
Therefore, the rod-shaped electrode in contact with the inner sleeve brick is thinned in advance so that it has a predetermined outer diameter after the inner sleeve brick disappears.

FIG. 3 is a vertical cross-sectional view showing the vicinity of the furnace wall electrode buried in the furnace bottom of the DC arc furnace of the third embodiment of the present invention. In the third embodiment, the contact portion between the inner sleeve brick and the outer sleeve brick may be tapered to prevent the inner sleeve brick from floating. FIG. 4 is a vertical cross-sectional view showing the vicinity of a furnace wall electrode buried in the furnace bottom of a DC arc furnace according to the fourth embodiment of the present invention. In the fourth embodiment, the ratio of (height) to (outer diameter-inner diameter) is set to 0 in order to reduce the thermal stress generated in the lowermost sleeve brick and prevent the occurrence of cracks.
It is 5 or less.

The present inventors have found that MgO bricks, and 10% to 2
When the test for confirming the thermal shock resistance of the 5% C MgO-C brick was carried out, the ratio of (height) to (outer diameter-inner diameter) of the brick was 11 ．
Horizontal cracks occurred in the vicinity of No. 5, and as shown in FIG. 5, the frequency of horizontal cracks increased as the ratio of (height) to (outer diameter-inner diameter) increased. In addition, according to the results of tests conducted separately by the present inventors, horizontal cracks did not occur in bricks in which the ratio of (height) to (outer diameter-inner diameter) was 0.5 or less in advance. From this result, by setting the ratio of (height) to (outer diameter-inner diameter) of the ring-shaped sleeve brick to be 0.5 or less, it is possible to alleviate the thermal stress generated in the sleeve brick and prevent horizontal cracking. I understand. Not limited to the bottom sleeve brick, it goes without saying that the sleeve brick having an arbitrary number of stages may be configured such that the ratio of height to (outer diameter-inner diameter) is 0.5 or less.

[0017]

As described above, according to the present invention, the life of the furnace wall electrode can be extended by making the sleeve brick having the rod-shaped electrode in the central portion and the sleeve brick arranged outside thereof have the double ring structure. This greatly contributes to productivity improvement and production cost reduction.

In the fourth embodiment of the present invention shown in FIG. 4, a rod-shaped electrode is provided in the center and a sleeve brick is arranged outside the rod-shaped electrode. The height of the lowermost sleeve brick and the (outer diameter-inner diameter) By setting the ratio of 0.5 to 0.5 or less, it is possible to prevent damage to the bottom sleeve brick, which greatly affects the life of the furnace wall electrode, and thus to extend the life of the furnace wall electrode and improve the productivity of the electric furnace. This greatly contributes to the reduction of production costs.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a furnace wall electrode according to an embodiment of the present invention applied to the bottom of a DC arc furnace.

FIG. 2 is a vertical sectional view of a second embodiment of the present invention.

FIG. 3 is a partially enlarged vertical sectional view of a third embodiment of the present invention.

FIG. 4 is a vertical sectional view of a fourth embodiment of the present invention.

FIG. 5 is a view showing the relationship between the frequency of horizontal cracks and the height of bricks / (outer diameter-inner diameter).

[Explanation of symbols]

1: Permanent brick 2: Irregular refractory 3: Iron crust 3a: Support plate 4: Hole for bottom electrode installation 5: Rod electrode 6: Insulator 7: Conductive plate 8: Power supply cable 9: Fixture 10: Irregular shape Refractory (filler) 11: Sleeve brick 11-a: Inner sleeve brick 11-b: Outer sleeve brick 11-c: Bottom sleeve brick

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-48190 (JP, A) SAIkai HEI 2-28094 (JP, U) JP-B 62-55070 (JP, B2) JP-B 4- 60315 (JP, B2)

Claims (2)

[Claims] 1. A bar-shaped electrode made of iron or the like is provided at the center,
A tubular brick sleeve was placed on the outside of the tubular brick, and the surrounding area was a double-ring structure for the sleeve brick around the rod-shaped electrode in the wall electrode of a DC arc furnace constructed of irregular refractory material. The wall electrode of the DC arc furnace. 2. A bar-shaped electrode made of iron or the like is provided at the center,
At the outer wall of the wall brick of a DC arc furnace, in which a sleeve brick formed in a tubular shape was arranged, and the surrounding area was constructed of irregularly shaped refractory, at least the (height) of the sleeve brick at the bottom
A furnace wall electrode for a DC arc furnace, which is composed of a brick having an (outer diameter-inner diameter) of 0.5 or less.