JPH0666483A - Dc arc furnace - Google Patents

Abstract

PURPOSE:To prevent an accident of leakage of molten steel by a method wherein a plate electrode assembled in a grid shape is arranged at an upper part of a contact pin of a furnace bottom electrode. CONSTITUTION:A furnace bottom electrode 10 is provided with a plurality of contact pins 25 for continuity of an arc forming current to molten items within a furnace and a grid-like plate electrode 26 arranged between these contact pins 25 and the molten items for dispersing and unifying an arc forming current. Due to this fact, an electrical current concentrated at one upper point flows in such a manner that it is expanded within a horizontal plane along the grid-like plate electrode 26 and further uniformly dispersed to each of the contact pins 25 without generating local continuity. With such an arrangement as above, since there occurs no concentration of local current in the contact pins 25, it is possible to prevent an accident of leakage of molten steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC arc furnace for arc melting a material such as scrap.

[0002]

2. Description of the Related Art Compared to a three-phase (alternating current) arc furnace, a DC arc furnace has a single cathode, which reduces the electrode unit consumption and noise during the melting period. Since the arc flies vertically downward toward the electrode, a uniform temperature distribution can be obtained and hot spots do not occur, and there are various advantages such as no induction loss and good energy efficiency. Therefore, recently, a DC arc furnace has been attracting attention as a melting furnace that replaces the three-phase arc furnace.

A DC arc furnace has a furnace bottom electrode as an anode at the furnace bottom and a graphite electrode as a cathode at the furnace top. During operation, scrap and auxiliary materials are charged into the furnace, a DC arc is generated between the furnace bottom electrode and the upper electrode, and this arc heat energy is applied to the scrap to melt it.

The furnace bottom electrode has a large number of contact pins made of a conductive material such as a metal rod. These contact pins are housed in a steel case filled with a stamp material, and only the upper ends of the contact pins are exposed in the furnace. Arcs are generated between the exposed ends of these pins and the upper electrode. The stamp material is, for example, a magnesia-shaped amorphous refractory material that is compacted, and has a role of preventing the contact pins from melting. Recently, there is a tendency to increase the number of contact pins of the bottom electrode in order to increase the capacity of the furnace and improve the conductivity.

[0005]

However, in the conventional DC arc furnace, there may be a case where conduction failure occurs between the contact pin and the molten steel, and the arc current concentrates on only one contact pin, and the contact pin is May be melted by Joule heat. If the contact pin melts, the molten steel in the furnace will leak out from the bottom of the furnace to a major accident.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a DC arc furnace capable of preventing damage to the furnace bottom electrode due to concentration of arc current.

[0007]

A DC arc furnace according to the present invention is a DC arc furnace for melting a material to be melted by arc heat generated between a furnace bottom electrode and an upper electrode,
The furnace bottom electrode is provided with a large number of contact pins that conduct an arc forming current to the material to be melted in the furnace, and a grid plate plate that is provided between these contact pins and the material to be melted to disperse and average the arc forming current. And an electrode.

[0008]

In the DC arc furnace according to the present invention, since the plate-shaped electrodes assembled in a lattice type are provided above the contact pins of the bottom electrode of the furnace, the current concentrated at one point on the upper portion is the grid-type plate electrode. Along a horizontal plane, and is evenly distributed to each contact pin without causing local conduction.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 2, a bottom electrode 10 is fitted in the center of the bottom of a DC arc furnace. Furnace bottom electrode 10
Is unitized and surrounded by block bricks 31 provided at appropriate places on the refractory lining 30 of the furnace. A joint material made of magnesia castable is filled between the case 32 of the furnace bottom electrode 10 and the block brick 31.

The water-cooled copper tube 12 of the furnace bottom electrode 10 is connected to the anode side of a DC power source (not shown). The cathode side of this DC power supply is connected to a graphite electrode (not shown). The graphite electrode penetrates a lid (not shown) at the top of the furnace, and the lower end of the graphite electrode faces the material to be melted (scrap and auxiliary materials) in the furnace. The end of the copper tube 12 is connected to the terminal 11 via the bracket 13. Further, the terminal 11 is connected to the current collector plate 16 via the cooling air introduction pipe 14.

A lower substrate 17 is provided directly above the current collector plate 16. The current collector plate 16 and the lower substrate 17 are attached to the furnace bottom electrode unit substantially horizontally and in parallel.
The lower substrate 17 is supported by the iron shell of the furnace body via a bracket 18. In addition, the lower base 17 and the bracket 1
8 is insulated from each other by an insulating member.

A large number of contact pins 25 are provided on the collector plate 16.
Are attached to and supported by and are erected parallel to each other through the lower base plate 17. The contact pins 25 are, for example, 24 in 8 rows and a total of 192 are arranged at substantially equal pitch intervals. Each contact pin 25 reaches the upper base 24. A stamp material 37 is compacted by a rammer or the like between the upper and lower bases 17 and 24 and filled without any gap.

Further, a grid type plate electrode 26 is provided on the upper side of the upper substrate 24. This lattice type plate electrode 26
Are connected to a large number of contact pins 25 via the upper substrate 24. The grid-type plate electrode 26 is a plate member made of a good conductor, which is erected upright in a grid shape and integrally assembled. The refractory bricks 38 are also filled between the plate members of the grid-type plate electrode 26. These upper and lower bases 17,2
4, upper half of contact pin 25, grid-type plate electrode 2
6. Each of the stamp materials is housed in a steel case 32.

As shown in FIG. 1, the contact pins 25 are arranged in a spiral shape, and the grid type plate electrodes 26 are arranged in a square grid shape. In this case, contact pin 2
5 has a length of 522 mm and a diameter of 42 mm, and the grid-type plate electrode 26 has a plate thickness of 19 mm, a height of 670 mm, and a grid pitch interval of 329 mm. The material of the contact pin 25 is S
S400, and the material of the grid-type plate electrode 26 is SGD4.
00-D. Next, a case will be described in which scrap is melted by a DC arc furnace having the above-mentioned bottom electrode to melt a predetermined molten steel.

A predetermined amount of scrap and auxiliary raw materials are put into the furnace, and the furnace bottom electrode 10 and the graphite electrode are energized. An arc is generated between the graphite electrode and the scrap, and the scrap is melted by the arc heat. Maximum furnace temperature is 1550-16
Reach 00 ℃.

At this time, the direct current flowing through the electric furnace is
From the copper tube 12 through the terminal 11 to the collector plates 16 to 192
It is divided into contact pins 25 of a book, and further divided into plate-shaped plate electrodes 26, averaged, enters scrap in the furnace, and flows to a graphite electrode through a discharge arc.

Here, it is assumed that there is poor conduction between the molten steel and the lattice type plate electrode 26. In a conventional arc furnace, scrap (partly molten steel) exists as a material to be melted between the contact pin and the graphite electrode, so current concentrates only on a specific contact pin, which causes overcurrent. Overheating and melting of the contact pin sometimes occurred. On the other hand, in the arc furnace of the present embodiment, the current is evenly distributed over the entire bottom of the furnace by the action of the grid-shaped plate electrode 26 even when the conduction is defective, so that only a part of the contact pins is locally affected. No current is concentrated and no melting loss of the contact pin occurs. Therefore, there is no accident that the molten steel in the furnace leaks to the outside, and the melting operation can be performed safely.

[0019]

According to the present invention, since the concentration of local current on the contact pin does not occur, it is possible to prevent molten steel from leaking out, and the melting work becomes safe. Further, since the contact pin is not partially damaged, the life of the furnace bottom electrode can be extended.

[Brief description of drawings]

FIG. 1 is a plan view showing a furnace bottom portion of a DC arc furnace according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing a furnace bottom portion of a DC arc furnace according to an embodiment of the present invention.

[Explanation of symbols]

10; Furnace bottom electrode, 11; Electrode terminal, 12; Copper tube, 13,
18; Bracket, 16; Current collector, 17; Support plate, 2
5: Contact pin, 26: Lattice type plate electrode, 30, 3
1; refractory, 32; case, 37; stamp material, 38;
Fireproof brick

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Noriichi Otani, 1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd. (72) Norio Ao, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Tube Co., Ltd. (72) Inventor Shigeo Ueda 495-56 Nijima, Wakamatsu-ku, Kitakyushu, Fukuoka Prefecture Kyushu Plant, Tokyo Steel Co., Ltd. (72) Toshikazu Nishimoto 495, Nijima, Wakamatsu-ku, Kitakyushu, Fukuoka 56 Tokyo Steel Co., Ltd. Kyushu factory

Claims (1)

[Claims] 1. A direct current arc furnace for melting a material to be melted by arc heat generated between a furnace bottom electrode and an upper electrode, wherein the furnace bottom electrode conducts an arc forming current to the material to be melted in the furnace. A large number of contact pins, provided between these contact pins and the material to be melted,
A DC arc furnace, comprising: a grid-type plate electrode for averaging the arc forming current in a distributed manner.