JPH10318684A - Dc arc furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the deflecting direction of an arc, reduce original electrode unit cost, prevent the damage of an equipment and improve a melting efficiency in a dc arc furnace having two upper electrodes. SOLUTION: A dc arc furnace comprises a furnace main body 1 having a furnace bottom electrode 3 on a bottom part, two upper electrodes 4 and 5 elevated and lowered in the furnace main body, upper feed conductors 10 and 11 connected to the upper electrodes 4 and 5, a lower feed conductor 9 connected to the furnace bottom electrode and dc power sources 6 and 7 provided between the ends of the upper feed conductors 10, 11 and the lower feed conductor 9. A magnetic field generator 8 for forming vertical magnetic fields 22 in arc generating positions is provided below the furnace main body. At this time, the horizontally circulating coil shaped lower feed conductor can be also used as the magnetic field generator 8. The intensity of the vertical magnetic field 22 is made larger than that of a horizontal magnetic field 21 or two systems of dc power sources are provided to control individually currents supplied to the two upper electrodes 4 and 5 with larger effect.

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 having two upper electrodes for melting an iron source such as iron scrap and direct reduced iron.

[0002]

2. Description of the Related Art In a steelmaking arc furnace for melting iron scrap, direct reduced iron, and the like, a DC arc furnace with less flicker disturbance of a power source and a smaller electrode unit has been increasingly installed. In order to improve productivity, the size and power consumption have been increased, and DC arc furnaces having a production capacity of 200 tons / hour or more have been operated. DC arc furnaces are mainly furnaces that perform concentric melting by providing one graphite upper electrode at the center of the furnace. In this case, the load current increases with the increase in the size and power of the furnace. Although it is necessary, the upper limit of the size increase is determined by the allowable current limit of the upper electrode. Also, when an excessive current is applied to the graphite upper electrode, abnormal wear such as cracking or breakage of the upper electrode increases, and the effect of reducing the basic unit of electrode which is an advantage of the DC arc furnace cannot be obtained. Also occurred.

[0003] In view of this, a large DC arc furnace having a plurality of upper electrodes has been proposed. For example, Japanese Patent Application Laid-Open No. 6-300467 discloses a furnace as shown in the plan view of FIG. Two upper electrodes 4 made of graphite,
A DC arc furnace having 5 is disclosed. by the way,
In the case of a DC arc furnace, the bottom electrode 3 provided on the bottom of the furnace body 1 is generally used as an anode, and the upper electrodes 4 and 5 are generally used as cathodes.
The current flowing through the upper electrodes 4 and 5 flows upward from the furnace bottom side, and this current causes a horizontal magnetic field 21 (clockwise with respect to the current direction) around the upper electrodes 4 and 5 with respect to the current direction. ) Is formed. Therefore, the upper electrodes 4, 5
An arc 19 generated between the furnace electrode 3 and the bottom electrode 3 causes an electromagnetic force (attraction force) according to Fleming's left-hand rule by a horizontal magnetic field 21 formed around the other upper electrodes 4 and 5.
Works. As a result, the arcs 19 are deflected toward the other upper electrodes 4 and 5.

[0004] For this reason, a large heat load due to the arc 19 is applied to the other upper electrodes 4, 5, and the upper electrodes 4, 5.
5 is excessively consumed. In addition, the arc heat as a heating source is 2
Since it concentrates between the two upper electrodes 4 and 5, only the space between the two upper electrodes becomes the melting zone 20, so that a wide range of melting cannot be performed. In many cases, an increase in heat load causes equipment trouble.

Further, when the current flowing through the power supply conductor for supplying power to the electrodes forms a horizontal magnetic field, and this magnetic field also acts on the arc, the two arcs are deflected in the same direction by the electromagnetic force due to the horizontal magnetic field. Therefore, not only non-uniform melting, but also problems such as damage to the furnace wall in the arc deflection direction occur.

[0006] Japanese Patent Application Laid-Open No. 1-167571 discloses that
A DC arc furnace having three upper electrodes, as well as a three-phase AC arc furnace, is disclosed. However, when the number of the upper electrodes is three, the surface area of the graphite upper electrode becomes large, so that not only the oxidation consumption is increased and the effect of reducing the electrode unit consumption is not obtained, but also the arc is formed by the upper electrode. Because the electromagnetic force of the furnace heads toward the center of the furnace, a strong thermal load is applied to the furnace lid, which further damages and troubles the equipment compared to the case of two upper electrodes.

[0007]

As described above, the conventional DC arc furnace having a plurality of upper electrodes, which has been proposed with the increase in the size and the power of the furnace, has a problem in that the DC is deflected by a horizontal magnetic field. In addition to not being able to reduce the electrode unit consumption, which is a feature of the furnace, it is not possible to say that the effects of the DC arc furnace are fully exerted, causing damage to the equipment and lowering the melting efficiency, and there is much room for improvement. is the current situation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to control the deflection direction of an arc in a large DC arc furnace having two upper electrodes to prevent local melting. An object of the present invention is to provide a DC arc furnace which has a reduced electrode unit consumption, has no damage to equipment, and has a high melting efficiency.

[0009]

A DC arc furnace according to a first aspect of the present invention comprises a furnace main body, a furnace bottom electrode provided at the bottom of the furnace main body, two upper electrodes moving up and down in the furnace main body, and an upper electrode. An upper power supply conductor connected to the furnace bottom electrode, a lower power supply conductor connected to the bottom electrode, and a DC power supply connected between the ends of the upper power supply conductor and the lower power supply conductor. In a DC arc furnace to be generated, a magnetic field generator for forming a vertical magnetic field at an arc generating position is provided below a furnace main body.

FIG. 1A shows a DC arc furnace having a furnace bottom electrode as an anode and two cathodes as cathodes.
It is the front view which showed roughly the deflection direction of the arc which generate | occur | produced in an upper electrode, In the figure, 4 and 5 are upper electrodes, 18 is molten metal,
19 is an arc, 21 is a horizontal magnetic field, I is a current flowing through the upper electrodes 4 and 5, and Fh is an electromagnetic force acting on the arc 19 by the horizontal magnetic field 21. As shown in FIG. 1A, an arc 19 generated between the upper electrode 4 and the molten metal 18 is subjected to framing by a horizontal magnetic field 21 formed by a current I flowing upward from the furnace bottom side through the other upper electrode 5. According to the left-hand rule, an electromagnetic force Fh that directs the arc 19 toward the other upper electrode 5 acts. Similarly, an electromagnetic force Fh directed toward the other upper electrode 4 also acts on an arc 19 generated between the upper electrode 5 and the molten metal 18, so that the arcs 19 are deflected toward the other upper electrode 4, 5. I do. That is, the attraction force acts on the two arcs 19 and 19 mutually, and the arc 1
9 and 19 deflect in directions approaching each other.

In the present invention, a magnetic field generator for generating a vertical magnetic field (the direction of the lines of magnetic force is a vertical magnetic field) is provided below the furnace main body, and this vertical magnetic field is applied to both arcs together with the horizontal magnetic field. FIG. 1B schematically shows the deflection direction of the arc when a horizontal magnetic field and a vertical magnetic field that is directed upward from the bottom of the furnace are applied to the magnetic field generator in the form of a coil that circulates in the horizontal direction. 8 is a plan view, in which 8 is a coil-shaped magnetic field generator, 19a is the deflection direction of the arc when only a horizontal magnetic field is applied, i is the current and its direction flowing through the coil of the magnetic field generator 8, and Fv is the vertical magnetic field. By arc 1
9 is a deflection angle, and the electromagnetic force acting on 9 is shown in FIG.
The description of the same components as described above is omitted. As shown in FIG. 1B, when a vertical magnetic field that is directed upward from the furnace bottom is applied to the arc 19, an electromagnetic force Fv that turns the arc 19 acts on the arc 19. This turning direction is shown in FIG.
In this case, the direction is the same as the current i flowing through the coil of the magnetic field generator 8. In FIG. 1 (b), the current i flowing through the coil of the magnetic field generator 8 is counterclockwise when viewed from above the furnace, so that the electromagnetic force Fv for turning the arc 19 counterclockwise acts, 19 is the other upper electrode 4, 5
Respectively, and is deflected to the left by a deflection angle θ, and finally is deflected in a direction in which the electromagnetic force Fh by the horizontal magnetic field 21 and the electromagnetic force Fv by the vertical magnetic field are balanced.

The horizontal magnetic field strength at the arc generating position is Bh,
Also, assuming that the vertical magnetic field strength at the arc generating position is Bv, the electromagnetic force (Fh) for deflecting the arc by the horizontal magnetic field is obtained from the horizontal magnetic field strength (Bh), the vertical magnetic field strength (Bv), and the current (I) flowing through the upper electrode. ) And the electromagnetic force (Fv) for rotating the arc by the vertical magnetic field is determined. Judgment of the occurrence of the arc based on the investigation of the angle of decrease of the tip of the upper electrode indicates that the arc is generated at an angle of about 20 to 30 degrees with respect to the axis of the upper electrode. The electromagnetic force is represented by the following equations (1) and (2). Fh = (I × cos20 °) × Bh (1) Fv = (I × sin20 °) × Bv (2)

Further, the deflection angle (θ) of the arc from the direction of the other upper electrode is expressed by the following equation (3). sinθ = Fv / Fh ≒ 0.36 × (Bv / Bh) …… (3)

That is, the larger the vertical magnetic field strength (Bv) at the arc generating position, the larger the deflection angle (θ) of the arc becomes. For example, the vertical magnetic field strength (Bv) at the arc generating position is changed to the horizontal magnetic field strength (B). If it is the same as Bh), the deflection angle (θ) is about 20 degrees. Furthermore, if the vertical magnetic field strength (Bv) is equal to or greater than the horizontal magnetic field strength (Bh), the deflection angle (θ) is correspondingly equal to or greater than 20 degrees.

As described above, in the present invention, since the arc can be deflected from the direction of the other upper electrode, a direct thermal effect on the upper electrode is prevented, and the basic unit of the electrode is reduced. Since the arc is deflected away,
The dissolution area is widened, local dissolution is prevented, and dissolution efficiency is improved.

A DC arc furnace according to a second aspect of the present invention is the DC arc furnace according to the first aspect, wherein the magnetic field generator is a lower power supply conductor having a coil shape orbiting in a horizontal direction. .

A part of the lower power supply conductor to the furnace bottom electrode is disposed below the furnace main body in a coil shape that circulates the furnace bottom in the horizontal direction, and is then connected to the furnace bottom electrode. When a DC current for heating and melting is passed between the upper electrode and the furnace bottom electrode, a strong vertical magnetic field is formed in the coil-shaped portion of the lower power supply conductor. The device can also be used. In this case, there is no need to arrange a dedicated magnetic field generator, and the power source of the magnetic field generator can be used together, so that the equipment cost can be reduced.

In a DC arc furnace according to a third aspect of the present invention, in the DC arc furnace according to the first or second aspect, the magnetic field generator forms a vertical magnetic field having a magnetic field strength greater than the horizontal magnetic field strength at the arc generating position. It is characterized by the following.

If the vertical magnetic field strength at the arc generating position is larger than the horizontal magnetic field strength, the deflection angle (θ) of the arc will always be 20 degrees or more, and the direct thermal influence on the upper electrode will be prevented, and the basic unit of the electrode will be reduced. Is reduced. In addition, since the two arcs are deflected in a direction away from each other, a melting region is widened, local melting is prevented, and melting efficiency is improved.

A DC arc furnace according to a fourth aspect of the present invention is the DC arc furnace according to any one of the first to third aspects of the invention, wherein the furnace main body has a tapping port on a straight line passing through the center of the furnace main body. And a working port, the interval between the two upper electrodes is １ ／ to １ ／ of the inner diameter of the furnace main body, and a straight line connecting the centers of the two upper electrodes defines the tapping port and the working port. The arc of the upper electrode near the tap hole is deflected toward the working port while the arc of the upper electrode near the tap port is inclined at 45 degrees or more and less than 90 degrees with respect to the center line of the furnace. The magnetic field generator is arranged so as to be deflected to the right.

The distance between the two upper electrodes is 1/1 / the inner diameter of the furnace body.
If the distance is less than 4, the interval is too narrow to perform melting in a wide area, and at the same time, even if the arc is deflected, a thermal effect occurs on the other upper electrode, so that the effect of improving the basic unit of the electrode is small.
Also, if the distance between the two upper electrodes exceeds half the inner diameter of the furnace body, the electrodes will be closer to the furnace wall, and if only one upper electrode is energized, the heat load on the furnace wall will be excessive. As a result, damage to the furnace wall occurs.

If the straight line connecting the centers of the two upper electrodes is less than 45 degrees with respect to the center line of the furnace connecting the tapping port and the working port,
Since the distance between the working port and the upper electrode near the working port is shortened, the upper electrode near the working port is easily oxidized by oxygen for heating or decarburization blown into the furnace body from the working port during operation, This results in an increase in electrode unit consumption, which is not preferable. In the present invention, the angle formed by the straight line connecting the centers of the two upper electrodes with the center line of the furnace is represented by a smaller angle, that is, an acute angle. On the other hand, an angle of 90 degrees is not preferable because the arrangement of the power supply and the upper power supply conductor is complicated.

Since the arc of the upper electrode near the tapping port is deflected toward the working port and the arc of the upper electrode near the working port is deflected toward the tapping port, the melting area is widened and the melting efficiency is increased. Is improved.

A DC arc furnace according to a fifth aspect of the present invention is the DC arc furnace according to any one of the first to fourth aspects of the invention, wherein two series of DC power supplies are arranged, and a current flowing through two upper electrodes is provided. Are individually controllable.

Since two DC power supplies are arranged and the current flowing through the two upper electrodes can be individually controlled, the current flowing through only one of the upper electrodes is changed to reduce the current flowing through the two upper electrodes. You can make a difference. Then, for example, if the current of one upper electrode is reduced, the horizontal magnetic field formed by the upper electrode is weakened, so that the ratio of the electromagnetic force due to the vertical magnetic field increases, and the deflection angle (θ) increases. Thereby, the deflection angle of the arc can be arbitrarily controlled, and a wider melting zone can be formed.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
FIG. 2 is a schematic cross-sectional front view of a DC arc furnace according to one embodiment of the present invention, and FIG. 3 is a schematic cross-sectional plan view of a furnace body.

In the drawing, a furnace main body 1 having an oblong planar shape is shown.
Is a work bottom 16 on the center line p passing through the tapping hole 15 and the center of the furnace main body 1 and on the opposite side of the tapping hole 15. It has. Furnace body 1
A furnace lid 2 is disposed in the upper opening of the furnace, and upper electrodes 4 and 5 are provided through the furnace lid 2. Upper electrodes 4, 5
The horizontal positional relationship is such that, with respect to the center of the furnace main body 1, the upper electrode 4 is shifted toward the working port 16 and the upper electrode 5 is shifted toward the tapping outlet 15. At that time, the tap hole 15
The angle ψ formed by a straight line connecting the center of the upper electrode 4 and the center of the upper electrode 5 with respect to the center line p of the furnace main body 1 connecting the 4
And the distance between the upper electrode 5 and the inner diameter of the furnace body 1 are 1/4 to 1 /
It is preferably 2. And the upper electrodes 4 and 5
Electrode clamp 1 provided at tip of electrode support arm 13, 13a
Supported by the electrode support arms 13 and 13a via 4, 14a,
The other ends of the electrode support arms 13 and 13a are connected to the lifting devices 12 and 12a, and thus the upper electrodes 4 and 5 are independently raised and lowered into the furnace main body 1 by the lifting devices 12 and 12a. The upper power supply conductors 10 and 11 whose other ends are connected to the cathodes of the DC power supplies 6 and 7 are connected to the electrode clamps 14 and 14a,
Further, a lower power supply conductor 9 having the other end connected to the anodes of the DC power supplies 6 and 7 is connected to the furnace bottom electrode 3 to form a power supply circuit. The lower power supply conductor 9 was arranged on the bottom of the furnace main body 1 in a coil shape orbiting around the bottom electrode 3 in the horizontal direction, and then connected to the bottom electrode 3. Thus,
The coil-shaped lower power supply conductor 9 functioned as a magnetic field generator 8 for generating a vertical magnetic field. The current i flowing through the coil of the magnetic field generator 8 is counterclockwise when viewed from above the furnace.

The melting and refining of the DC arc furnace is performed by removing the furnace lid 2 and loading the iron scrap 17 into the furnace main body 1 and raising and lowering the upper electrodes 4 and 5 while supplying power from the DC power supplies 6 and 7. An arc 19 is generated between the upper electrodes 4 and 5, the furnace bottom electrode 3 and the iron scrap 17. The arc heat dissolves the iron scrap 17 to generate the molten metal 18. Molten 18
Is generated between the upper electrodes 4 and 5 and the molten metal 18 to continue the melting.

When a direct current i for melting the iron scrap 17 flows, a vertical magnetic field 22 is generated in the magnetic field generator 8, and a horizontal magnetic field 21 is formed around the upper electrodes 4 and 5. still,
Arrows of the horizontal magnetic field 21 and the vertical magnetic field 22 indicate the directions of the lines of magnetic force. In the present embodiment, the horizontal magnetic field 21 is counterclockwise when the furnace body 1 is viewed from above, and the vertical magnetic field 22 is the magnetic field generator 8. Is formed so as to pass through the inside of the coil upward from the furnace bottom side. The arc 19 generated in the upper electrode 5 by the electromagnetic force generated by the vertical magnetic field 22 shifts by a deflection angle (θ) counterclockwise when viewed from above the furnace body 1 with respect to a straight line connected to the upper electrode 4. Occur. Similarly, the arc 19 generated on the upper electrode 4 is generated counterclockwise and shifted by the deflection angle (θ). In this way, the deflection direction of the arc 19 of the upper electrode 5 on the tapping port 15 side is in the direction of the working port 16,
Since the deflection direction of the arc 19 of the upper electrode 4 on the side is in the direction of the tapping outlet 15, the arcs 19 are mutually opposite.
5 has no direct thermal effect, and a wide melting zone 20 can be formed.

If the deflection angle (θ) is small, the influence of heat on the other upper electrodes 4 and 5 cannot be prevented, and the melting region 20 becomes narrow. Therefore, the vertical magnetic field intensity at the arc generating position is reduced by the horizontal magnetic field intensity at the arc generating position. Bigger,
It is desirable that the deflection angle (θ) be 20 degrees or more.
On the other hand, if the deflection angle (θ) is too large, the arc 19 is directed to the furnace wall of the furnace body 1 and the furnace wall is melted.
It is desirable that the deflection angle (θ) be 90 degrees or less. Since the deflection angle (θ) is determined by the ratio between the vertical magnetic field strength and the horizontal magnetic field strength at the arc 19 generating position as shown in the above equation (3), in order to obtain the optimum range of the deflection angle (θ), The horizontal magnetic field strength based on the normal melting current value is calculated, the required vertical magnetic field strength is obtained for the horizontal magnetic field strength, and the number of turns of the coil of the magnetic field generator 8, that is, the vertical magnetic field strength can be determined. In addition, since the power supplies 6 and 7 are separately provided, the deflection angle (θ) can be arbitrarily controlled by individually controlling the current value flowing through each of the upper electrodes 4 and 5, and the melting is appropriately performed during operation. The area of the area 20 can be controlled.

Note that the present invention is not limited to the above. For example, even if the winding direction of the coil of the magnetic field generator 8 is reversed, the arc deflection angle (θ) is Only clockwise, the same effect as described above can be obtained, and the positional relationship between the tapping port 15 and the working port 16 is 90 degrees with respect to the center of the furnace body 1. Also,
It does not hinder the present invention at all. Further, a single DC power supply may be used, and if a dedicated magnetic field generator 8 is arranged instead of the coil-shaped lower power supply conductor 9, the vertical magnetic field strength can be arbitrarily changed while maintaining the melting speed. , The deflection control of the arc 19 becomes easier, but in this case the equipment cost increases.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the DC arc shown in FIGS. 2 and 3 will be described below.

The furnace body has an inner diameter of 7.2 m and a capacity of 150 tons. 2.5m graphite top electrode with 24 inch diameter
And one upper electrode was displaced by 0.7 m from the center of the furnace main body to the working port side, and the other upper electrode was displaced by 0.7 m from the center of the furnace main body to the steel outlet side. . In this case, the angle ψ between the straight line connecting the centers of the two upper electrodes and the center line of the furnace main body is about 56 degrees. A current of up to 70 kA is supplied to each of the upper electrodes from an individual DC power supply. On the other hand, a furnace bottom electrode having a diameter of 3 m is provided on the bottom of the furnace body, and the lower power supply conductor is common to the two DC power supplies, and is formed into a coil shape that makes a circumference of the furnace bottom electrode one and a half turns. It is connected to the furnace bottom electrode. Since it is common to the two DC power supplies, the lower feed conductor has a maximum of 140k
A current flows.

As a result, the horizontal magnetic field strength at the arc generating position was about 80 gauss and the vertical magnetic field strength was 150 gauss. From the investigation of the declining direction of the tip of the upper electrode after melting and the observation in the furnace during melting, the arc was It was found that the deflection was performed with the deflection angle (θ) set to about 45 degrees in the counterclockwise direction.
When the current value of the other upper electrode was halved, the arc further turned, the deflection angle became about 60 degrees, and the melting range was widened.

Since the direction of the arc is deviated from the direction of the other upper electrode, there is no damage or wear to the other upper electrode due to the arc heat, and the unit energy of the electrode is estimated to be a single upper electrode. The increase was only about 10% against exhaustion. If a current of 140 kA was applied to one upper electrode, the electrode unit consumption would be much worse due to abnormal wear such as chipping or cracking at the tip of the upper electrode, but a good electrode unit amount could be maintained.

The arcs are mutually offset from the center of the furnace body and face outward, and the arc of the upper electrode close to the working port melts up to the tapping port, and the arc of the upper electrode near the tapping port is close to the working port side. By dissolving up to, a wide range of dissolution close to concentric circles was realized. And the heat load on the furnace lid did not matter at all. Further, since the distance from the arc was large, the heat load on the furnace wall was light, and the furnace wall was not damaged.

[0037]

According to the present invention, the deflection direction of the arc can be deviated from the direction of the other upper electrode, and it is possible to prevent an excessive heat load of the arc from being directly applied to the other upper electrode. Oxidation wear and abnormal wear of the upper electrode are reduced, and a good electrode unit can be obtained.
Further, since the arc heat can be spread over a wide range, a wide melting range close to concentric circles can be realized, and efficient melting with little heat loss can be achieved. At the same time, by dispersing the arc heat, the heat load on the furnace lid and the furnace wall is reduced, and troubles such as damage to equipment are prevented.

[Brief description of the drawings]

1A and 1B are diagrams schematically showing a deflection direction of an arc by a magnetic field, wherein FIG. 1A is a front view showing a deflection direction by a horizontal magnetic field, and FIG. 1B is a plane showing a deflection direction by a horizontal magnetic field and a vertical magnetic field. FIG.

FIG. 2 is a schematic front sectional view of a DC arc furnace according to one embodiment of the present invention.

FIG. 3 is a schematic plan view of a furnace body of a DC arc furnace according to one embodiment of the present invention.

FIG. 4 is a plan view schematically showing an arc deflection direction and a melting zone in a conventional DC arc furnace having two upper electrodes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace main body 2 Furnace lid 3 Furnace bottom electrode 4 Upper electrode 5 Upper electrode 6 DC power supply 7 DC power supply 8 Magnetic field generator 9 Lower power supply conductor 10 Upper power supply conductor 11 Upper power supply conductor 12 Elevating device 13 Electrode arm 14 Electrode clamp 15 Exit Steel port 16 Working port 17 Iron scrap 18 Molten metal 19 Arc 20 Melting zone 21 Horizontal magnetic field 22 Vertical magnetic field

Claims (5)

[Claims] 1. A furnace body, a furnace bottom electrode provided at the bottom of the furnace body, two upper electrodes which move up and down in the furnace body, an upper power supply conductor connected to the upper electrode, and a connection to the furnace bottom electrode. In a DC arc furnace that includes a lower power supply conductor and a DC power supply connected between ends of the upper power supply conductor and the lower power supply conductor, and generates an arc between the upper electrode and the furnace bottom electrode, a vertical magnetic field is generated at an arc generation position. A DC arc furnace, wherein a magnetic field generator to be formed is provided below a furnace body. 2. The direct current arc furnace according to claim 1, wherein the magnetic field generator is a lower power supply conductor in the form of a coil circling in a horizontal direction. 3. The DC arc furnace according to claim 1, wherein the magnetic field generating device forms a vertical magnetic field having a magnetic field strength greater than a horizontal magnetic field strength at an arc generating position. 4. The furnace body has a tapping port and a working port on a straight line passing through the center of the furnace body, and a distance between two upper electrodes is １ ／ to １ ／ of an inner diameter of the furnace body. And, the straight line connecting the centers of the two upper electrodes is inclined at 45 ° or more and less than 90 ° with respect to the center line of the furnace connecting the tap hole and the working port, and the upper electrode near the tap hole is 4. The magnetic field generating device according to claim 1, wherein the arc is deflected in a direction toward the working port, and the arc of the upper electrode close to the working port is deflected in a direction toward the tapping port. A DC arc furnace according to any one of the above. 5. The DC power supply according to claim 1, wherein the DC power supplies are arranged in two lines, and currents flowing through two upper electrodes can be individually controlled. Arc furnace.