JPH0486480A - Hearth electrode in dc electric furnace - Google Patents

Abstract

PURPOSE:To prevent water vapor explosion surely by a method wherein a relation between the diameter of a hearth electrode and the length of the water cooling area in the axial direction of a water-cooled side surface sleeve, surrounding the lower part of the hearth electrode so as to be contacted with the outer side surface of the same, is determined so as to have a predetermined value while the hearth electrode is supported by a non-water-cooled supporting metal contacted with the bottom surface of the electrode. CONSTITUTION:A relation between the diameter D of a hearth electrode 1 and the axial length L of a water-cooled side surface sleeve 4 is determined so as to be L>=1.8D so that the length L of the water-cooled area of the water cooled side surface sleeve 4 is long enough. The hearth electrode 1 is supported by a plate type non-water-cooled supporting metal 15 contacted with the bottom surface of the hearth electrode 1. In order to maintain the boundary surface 1c of the hearth electrode 1 in a hearth refractory 2, the length of the water-cooled area L of the water-cooled side surface sleeve 4 is determined so as to be L>=1.8D. Even when the boundary surface 1c between the melting section 1a of the hearth electrode 1 and a not yet molten part 1b has arrived at the lowest bottom and the non-water-cooled supporting metal 15 is molten, cooling water will never be leaked from the non-water-cooled metal since the supporting metal 15 is not water-cooled type.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a bottom electrode of a DC electric furnace for melting and refining steel using a DC arc.

<Prior art> There are two types of electric furnaces: AC electric furnaces and DC electric furnaces. AC electric furnaces have three graphite electrodes inserted from above the furnace to generate an arc with the molten steel as the center point. In a DC electric furnace, a graphite electrode is inserted from above the furnace, and a DC arc is generated using the bottom of the furnace as the other electrode.

Since AC electrodes have three electrodes, the upper structure of the furnace is complicated, and the three-phase arc is bent outward by mutual 1M1 force, which causes a lot of heat to be dissipated, resulting in poor thermal efficiency.Also, the bending of the arc causes local damage to the furnace wall. . Furthermore, there are problems such as not only a large amount of electrode consumption but also large noise and severe flicker. On the other hand, DC electric furnaces have fewer electrodes, so the area around the electrodes above the furnace is simple, and compared to AC electric furnaces, it has the advantage of reducing graphite electrode consumption and power consumption, as well as reducing flicker. Because of this, it is in the spotlight.

Conventionally, as shown in FIG. 2, the hearth bottom electrode 1 has a diameter of 2
A method is known in which one or several large-diameter steel round bars with a diameter of about 50 mφ or less are buried in the bottom refractory 2. The hearth electrode 1 is exposed on the upper surface of the hearth refractory 2 and protrudes from the hearth shell 3 to the outside of the furnace, and a water-cooled side sleeve (copper) 4 is in contact with the lower part of the hearth electrode 1. Surrounding.

The water-cooled side sleeve 4 is provided with a water-cooling groove 7, and the cooling water supplied from the water supply pipe 5 cools the side surface of the bottom electrode 1 while passing through the water-cooling groove 7 of the water-cooled side sleeve 4, and then passes through a drain pipe. It is discharged from 6.

A water-cooled cap 8 (made of copper) is in contact with the bottom surface of the hearth electrode 1, and the water-cooled cap 8 is fitted with a large number of spring washers 10 and nuts 11 on bolts 9 fixed to the hearth bottom shell 1.
Supported through. The water-cooled cap 8 is provided with a water-cooled groove 13, and the cooling water supplied from the water supply pipe 12 passes through the water-cooled groove 13 of the water-cooled cap 8 and reaches the bottom electrode 1.
After cooling the lower surface of the water, it is discharged from the drain pipe 13. Further, a water-cooled cable 14 is connected to the water-cooled camp 8 to apply electric power to the hearth bottom electrode 1.

When operating a DC electric furnace using the bottom electrode 1 made of steel with the above-described structure, when a current of several tens of kA is passed through the bottom electrode 1, Joule heat is generated within the bottom electrode 1. The electrode temperature rises, but on the other hand, molten steel is present in the DC electric furnace when in this energized state. Especially from the final stage of melting to the refining stage, the temperature of molten steel in the furnace is 1550 to 17
Since the temperature reaches about 00'C, the temperature of the furnace bottom electrode 1 increases due to this heat.

If the DC electric furnace continues to operate in this state, the steel hearth electrode 1 will be melted from the inside of the furnace, but when the melting progresses to the entire length of the hearth electrode 1, the hearth bottom of the DC electric furnace will open. The situation is as if a hole had been opened, and molten steel leaks violently, making it impossible to maintain the DC electric furnace in a normal state.

In order to prevent such l/rubs due to melting of the steel bottom electrode 1, the water-cooled side sleeve 4 is provided so as to contact and surround the lower outer surface of the bottom electrode 1 outside the furnace, as described above. In addition, a water-cooled cap 8 that is in contact with the bottom surface and has a size that fits into the lower part of the water-cooled side sleeve 4 is provided to support the water-cooled side sleeve 4 and the water-cooled groove 7, L provided in each of the water-cooled side sleeve 4 and the water-cooled cap 8. The furnace bottom electrode 1 is indirectly cooled by passing cooling water through the furnace and 13. Since the hearth electrode 1 is cooled in this way, as shown in FIG.
will be maintained within the area of the in-furnace refractory 2. The relationship between the diameter (D) of the conventionally used bottom electrode 1 and the axial water cooling area length (L) of the water-cooled side sleeve 4 is empirically determined as D/L#1/1.5. In combination with the cooling of the water-cooled cap 8, cooling of the hearth bottom electrode 1 was ensured.

By the way, when the operation of a DC electric furnace is repeated, the furnace bottom refractory 2
will gradually wear out and its thickness will decrease, but as the thickness of the hearth bottom refractory 2 decreases, the interface 1c of the hearth bottom electrode 1 will also gradually move downward. Thus, if the interface 1c advances significantly downward, or if for some reason the heat generated by the bottom electrode 1 exceeds the heat removed by cooling from the outside of the furnace, the interface 1c will move beyond the bottom of the bottom electrode 1. There is a risk that the copper water-cooled cap 8 will dissolve in the air and lead to steel leakage.

In the unlikely event that the water-cooled cap 8 melts, the cooling water flowing through the water-cooling groove 13 will leak onto the floor above the furnace.
At the same time, the 78 steel in the DC electric furnace will leak. If molten steel leaks so that it covers the cooling water leaking onto the floor, there is a risk of a so-called steam explosion.

<Problems to be Solved by the Invention> As mentioned above, creating a structure in which the outside of the furnace at the bottom t1M, especially the bottom surface, is cooled with a water-cooled cap is effective in terms of cooling the bottom electrode. There is a problem in that when the interface between the melted and unmelted parts of the furnace bottom electrode reaches the lower end, the water-cooled camp melts and cooling water leaks, which is one of the major causes of steam explosions due to steel leakage.

In addition, in order to water-cool the bottom surface of the hearth electrode with a water-cooled cap, it is unavoidable to install cooling water supply and drainage pipes in the lower part of the furnace. The structure is extremely complex due to the connections between the conductive water-cooled cable and the connection bolt, the electrode support bolt and the spring washer, etc., and the cost of designing, manufacturing, assembling the parts, and installing them to the bottom of the furnace is high. There was a problem that it required a lot of effort.

The present invention solves the above-mentioned problems of the prior art.During the operation of a DC electric furnace, if the interface between the melted part and the unmelted part of the furnace bottom electrode reaches the bottom, the molten steel in the furnace The purpose of the present invention is to provide a bottom electrode for a DC electric furnace that can prevent steam explosions even if steel leaks onto the floor below, and that has a simple structure and low cost. It is.

<Means for Solving the Problems> To achieve the above object, the present invention provides a furnace bottom electrode that is embedded in the bottom refractory of a DC electric furnace and whose lower part is indirectly water-cooled outside the furnace bottom shell. The relationship between the diameter (D) of the bottom electrode and the axial water cooling area length (L) of the water-cooled side sleeve that contacts and surrounds the lower outer surface of the cough hearth bottom electrode is set to L≧1.8D, and This is a furnace bottom electrode for a DC electric furnace, characterized in that it is supported by a non-water-cooled support fitting that is in contact with the bottom surface of the furnace bottom electrode.

<Function> Conventionally, the relationship between the diameter of the bottom electrode and the vertical water cooling area length (L) of the water-cooled side sleeve was Lζ1.5D, but in the present invention, the relationship between the diameter of the bottom electrode and the vertical water-cooling area length (L) of the water-cooled side sleeve By setting the water-cooling region length (L) to L≧1.8D, cooling of the bottom electrode by the water-cooled side sleeve is strengthened. This enhanced cooling makes it possible to support the bottom surface of the hearth electrode with a non-water-cooled support metal fitting. Note that it would be wasteful to make the water cooling region length (L) too large, so L=2.5D should be the maximum.

Therefore, even if the interface between the melted and unmelted parts of the furnace bottom electrode reaches the bottom and the non-water-cooled support fittings melt, the cooling water will not leak, and the molten steel in the furnace will not flow under the furnace. Steam explosions can be prevented even if steel leaks onto the floor.

<Example> An example of the present invention will be described below based on the drawings. As shown in FIG. 1, similar to the conventional example shown in FIG. 2, the present invention uses a large-diameter steel round bar with a diameter of about 250 φ or less as the hearth refractory 2 as the hearth electrode 1. to be buried. The bottom electrode 1 is exposed on the upper surface of the bottom refractory 2, the bottom shell 3 protrudes outside the furnace, and the bottom electrode 1 has a water-cooled side sleeve with a water cooling groove 7 at the bottom. (made of copper) 4 surrounding it is also the same as before.

In the conventional example shown in FIG. 2, the relationship between the diameter of the hearth electrode 1 and the axial water-cooling area length (L) of the water-cooled side sleeve 4 was L'i1.5D. In the present invention, L
As ≧1.8D, the water-cooling area length of the water-cooled side sleeve 4 (
L) is larger than before. In addition, in the conventional example,
@, Whereas the pole 1 was supported by a water-cooled cap 8 in contact with the bottom surface of the electrode, in the present invention, it is supported by a plate-shaped non-water-cooled support fitting 15 in contact with the bottom surface of the bottom electrode 1. It has become.

The non-water-cooled support fitting 15 is supported by a port 9 fixed to the hearth bottom shell 1 via a number of spring washers 10 and nuts 11, and a water-cooled cable 14 is connected to the non-water-cooled support fitting 15. power is applied to the hearth bottom electrode 1.

As mentioned above, the water-cooling area length (L) of the water-cooled side sleeve 4
The reason for setting L≧1.8D is that when the operating conditions of the DC electric furnace are the number of continuous charges, molten steel temperature, current value, current density, etc., are the same as the conventional method, the interface IC of the furnace bottom electrode 1 can be changed from the conventional method. This is to maintain it within the hearth bottom refractory 2 at the same position. At this time, the structure of the water-cooled side sleeve 4 itself does not need to be changed in any way from the conventional example, and it is only necessary to increase the length of the hearth bottom electrode 1 in the axial direction. 15, the bottom electrode 1 and the non-water-cooled support fitting 15 can be connected simply, and the lower structure of the bottom electrode 1 can be extremely simple.

When operating a DC electric furnace using the furnace bottom electrode of the present invention, when melting scrap and refining molten steel by passing a current of several tens of kA through the furnace bottom electrode 1, it is possible to melt the scrap and refine the molten steel. The molten steel temperature inside is 1550-170
The temperature reaches about 0°C, and the furnace bottom electrode 1 is melted from inside the furnace.

At this time, the interface 1c between the melted part 1a and the unmelted part 1b of the furnace bottom electrode 1 is heated only by the water-cooled side sleeve 4 manufactured under the condition that the water-cooled area length is 1.8D. The interface 1c can be maintained within the hearth bottom refractory 2 with a heat removal effect comparable to that of the conventional example shown in the figure.

Even if the interface 1c between the melted part 1a and the unmelted part 1b of the hearth electrode 1 reaches the bottom and the non-water-cooled support fitting 15 melts, the non-water-cooled support fitting 15 will be cooled from the non-water-cooled support fitting. Since water does not leak, a steam explosion can be prevented even if molten steel in the furnace leaks.

<Effects of the Invention> As explained above, the present invention provides the following effects.

(1) Since there is no water cooling part on the bottom of the hearth electrode, even in the unlikely event of steel leakage, there will be no water leakage, and a steam explosion can be reliably prevented.

(2) In addition, since no water cooling piping is required on the bottom of the bottom electrode, the structure near the bottom of the bottom electrode, including the electrode support and power supply cable, is simple and has fewer components, making it easy to manufacture, assemble, and install.
Costs such as maintenance can be reduced to about 40 to 50% of conventional costs.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a bottom electrode of a DC electric furnace according to the present invention, and FIG. 2 is a longitudinal sectional view showing a bottom electrode of a DC electric furnace according to a conventional example. DESCRIPTION OF SYMBOLS 1... Hearth bottom electrode, 3... Hearth bottom shell, 5... Water supply pipe, 7... Water cooling groove, 9... Bolt, 11... Nut, 13... Drain pipe,

Claims (1)

[Claims] In a hearth electrode that is buried in the hearth refractory of a DC electric furnace and whose lower part is indirectly water-cooled outside the hearth bottom shell, the diameter (D) of the hearth electrode and the diameter (D) of the hearth electrode and the The relationship between the enclosing water-cooled side sleeve and the axial water-cooled area length (L) is set to L≧1.8D, and the furnace bottom electrode is supported by a non-water-cooled support fitting that is in contact with the bottom surface of the furnace bottom electrode. Characteristics of the furnace bottom electrode in a DC electric furnace.