JPS604781A - DC arc furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] Regarding direct electric arc furnaces for melting electric current, there are two types of arc furnaces: AC three-phase arc furnaces and DC arc furnaces. In a DC arc furnace, one electrode is inserted and the bottom of the furnace is used as the other electrode to generate a DC arc.

When comparing the two, the AC 3-phase arc furnace has three electrodes, so the upper structure of the furnace is rough, the three-phase arc is bent outward due to mutual electromagnetic force, and the amount of heat dissipated is large, resulting in poor thermal efficiency. There are problems such as local damage to the furnace wall due to bending of the arc, large amount of electrode wear, large noise, and severe flicker. On the other hand, DC arc furnaces have problems with the lifespan and safety of the bottom electrode, and as mentioned above, DC arc furnaces are
Despite being superior in various respects to phase arc furnaces, the current situation is that very few have been put into practical use.

Here, the bottom electrode of a DC arc furnace, which has been conventionally considered, will be explained with reference to FIG.

1 in the figure is the furnace bottom plate.
A furnace bottom part 4 is formed by lining the furnace with a stamp 3 and tamping the inner part of the furnace with a stamp 3.

A conventional furnace bottom electrode is constructed by implanting or embedding a large number of spike materials 5 into the stamp 3.

This bike material 5 is usually one type of metal conductor, and one end is in direct contact with the molten steel. Therefore, in order to prevent melting damage, a cooling medium 18 is flowed between the outer plate 6 and the furnace bottom plate 1 to cool the furnace through the bricks 2, but this is not sufficient. Spike material 5
If all of the electrodes are melted away, it will cause a leakage, so when considering the risk of this leakage, the lifespan of this hearth bottom electrode is extremely short.

When comparing the lifespan of the furnace bottom with this furnace bottom electrode to that of an AC 3-phase arc furnace, the lifespan of the DC arc furnace is 100 to 200 heats, whereas the AC 3-phase arc furnace has a lifespan of 100 to 200 heats. There is an overwhelming difference between 20,000 and 30,000 heats. This is largely the reason why, even though they have various advantages over DC arc furnaces and AC arc furnaces, they are still not as good as both AC and DC arc furnaces.

The purpose of the present invention is to significantly extend the life of the furnace bottom electrode and to put a direct current arc furnace into practical use.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view of a direct current arc furnace in which the present invention is implemented. , the furnace bottom part 4, and the furnace lid part 19 has a waste gas outlet 11,
A tapping port 12 and a slag tap port 13 are formed in the furnace bottom portion 4 .

1111 The inner surface of the furnace lid part 19 and the furnace I'11 part 9 are lined with a generally used material (large material 14.15.1ij
J Iie hearth vessel bottom 4 plate 10, Chamotren force etc. 16 lined on the inner surface of the bottom plate 1o, formed by compacting a stamp material that has good conductivity at high temperatures, such as Macnesia (MgO) or zirconium oxide (ZrO,). It consists of a conductive ff1i pyrotechnic layer 17.

Then, an electrode (usually a negative electrode) 20 is inserted through the furnace cover 19, and a group of metal electrode rods 21 is buried in the furnace bottom 4. In the figure, 22 indicates molten steel, and 23 indicates slag.

The hearth bottom electrode 24 facing the electrode 20 is connected to this electrode rod group 2.
1 and a conductive refractory layer 17.

In addition to the above-mentioned materials, the four-conductor layer 17 uses a material having conductive properties such as magnesium carbide (MgC, Mg, C,) whose conductivity improves as humidity increases.

For example, if a regular product with a specific resistance of 10'Ω・σ or more is heated to 1400°C, Macnesia has a resistivity of 560Ω・■
, Macnesia Chrome is 400Ω・C and 1700'
When it comes to C, zirconium oxide has a resistance of only 6 to 7 Ω.

Therefore, the temperature range of the high-grade crystal molten m (1600"C) generated is the temperature range from the surface of the conductive steel refractory layer 17 in contact with the molten steel 22 to 1400"O. is a sufficiently good electrical conductor. The electrode rod Jir21 mentioned above
The tips of each type are designed to reach this electrically conductive part. A cable 25 is connected to the nl1 portion of the electrode group 21 exposed outside the furnace, and the cable 25 connects the electrode group 21 to a power source (not shown).

Next, the operation of the above DC arc furnace will be explained.

First, when starting the arc furnace, scrap etc. are charged and a DC arc is generated, but since the bottom of the furnace is cold, there is no
11. Conductivity ll1 (The specific resistance of the large material layer 17 is very large, and it is impossible to conduct electricity. Therefore, a positive electrode rod (not shown) is inserted into the furnace only at the time of starting, and the electrode rod and the electrode A direct current arc is generated between the rods 20 to produce a small amount of molten steel,
High quality! Create a concentration, then electrode rod 2o and furnace bottom electrode 2
4, a DC arc is generated, and the state shifts to actual operation.

Once molten steel is produced, a small amount of hot water is left behind during tapping, and the high temperature can be maintained by the remaining hot metal, so there is no need to insert a positive electrode rod at the start of the next process.

In the furnace bottom electrode 24, the electrode rod group 21 is directly connected to the molten steel 2.
Since there is no contact with 2, corrosion damage is significantly reduced.

In addition, when using steel, aluminum, etc. as the material for the electrode group 21, which has a melting point lower than the temperature after 1400°C11iT, cool it appropriately and use high-purity tungsten, aluminum, etc.
If a material with a high melting point, such as iron, is used, there is no need for cooling.

Furthermore, since the conductive refractory layer 17 is remolded when the furnace is repaired, there is almost no need to consider wear and tear on the electrode group 21 itself.

In the above embodiment, the material of the electrode rod group was made of gold, but it may of course be made of carbon.

As described above, according to the present invention, (i) the electrode group does not come into direct contact with hot water (1), so the amount of melting can be significantly reduced; (ii)? ; As with conventional DC arc furnaces, many thermocouples are embedded in the bottom of the furnace, and the quality is strictly checked.
First, furnace IE (no need to replace refractories, 611) uses the same refractories as conventional ones, significantly extending the lifespan without increasing equipment costs, (iψ reducing the risk of hot water leakage) (v) It is easy to install horizontally, and it exhibits the excellent effects of '3'.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional furnace bottom electrode, and FIG. 2 is a schematic cross-sectional diagram of a DC arc furnace according to the present invention. 4 is the furnace bottom, 7 is the melting furnace main body, 17 is the 4-electric performance large layer,
21 indicates a group of electrode rods.

Claims (1)

[Claims] 1) Form a conductive refractory layer that has high conductivity at high temperatures on the inner surface of the furnace bottom, and insert a group of electrode rods into the conductive refractory layer from outside the furnace so that their tips reach the surface or l-) to a required depth. A DC arc furnace characterized by a built-in housing.