JPH0541280A - Dc arc generating method - Google Patents

Abstract

PURPOSE:To restrain an arc from being unstable when voltage is raised with the arc increased in length by means of heating by a DC arc so that input electric power is increased. CONSTITUTION:Each DC arc 2 is generated between a plural number of electrodes 1 and an opposite electrode 3 which is an object to be heated. The electrodes 1 ere identical in shape with one another, are symmetrically disposed around a reference line, and are connected to each power supply 4. In this case, each arc shall be constant in current I and length D. Equal electromagnetic attraction is developed among the arcs, so that the arcs are thereby restrained mutually so as to be stable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for generating a direct current arc used for various kinds of heating such as heating and melting metals.

[0002]

2. Description of the Related Art Heating by an arc has attracted attention as a metal melting method and a temperature maintaining method for molten metal. When heating is performed using an arc, the input power is represented by the product of current and voltage. Therefore, in order to increase the input power, it is necessary to increase the current and the voltage.

In the method of increasing the current, it is necessary to increase the diameter of the wiring inside and outside the power supply. Further, since the current density is increased, there is a problem in that the electrodes are heavily consumed. Therefore, the method of increasing the voltage is generally advantageous.

In the method of increasing the voltage, the arc voltage is increased by increasing the arc length. But,
When the arc becomes long, the arc becomes unstable, and there is a great risk of damaging surrounding equipment. In addition, the rated voltage of the power supply must be set higher in consideration of the fluctuation of the arc voltage due to the instability of the arc, which requires a high-voltage power supply. This is because when the arc voltage reaches the rated voltage of the power supply, arc breakage occurs.

The arc stabilization technique for suppressing the instability of the arc when the arc length is increased to increase the voltage in order to increase the applied power is the model develo
pment for free burning ACplasma jets (Sonderdru
ck ans ”ele ktrowarme international", 47.Jahrgang,
Heft B 3/1989, S.B124-B130) in more detail. However, when the arc is a direct current, a fluid method in which a gas is flowed around the arc to extend the arc is known (Japanese Patent Laid-Open No. 51-121409).

[0006]

In the fluid method for stabilizing the arc by flowing a gas around the arc, a large amount of gas is required, and moreover, in order to prevent the reaction with an object to be heated such as molten metal, The gas must be an inert gas, which inevitably leads to high operating costs. In addition, plasma airflows are generated from both poles around the arc,
They collide and form a complicated flow field. Therefore, it is difficult to correct these by a fluid method to stabilize the arc, and inevitably the structure around the electrode is complicated.

An object of the present invention is to provide a direct current arc generating method which uses a simple structure and which is economical and stable for generating a stable direct current arc.

[0008]

According to the DC arc generating method of the present invention, a plurality of electrodes each having the same shape and having a power source connected thereto are symmetrically arranged around a reference line which is set between the electrodes and is perpendicular to a counter electrode. The arrangement is characterized in that a direct current arc is generated from each electrode to the counter electrode under the conditions of constant arc current and arc length.

[0009]

In the DC arc generating method of the present invention, a uniform arc is generated from a plurality of electrodes to the counter electrode. A magnetic field is generated around the arc column in a clockwise direction with respect to the direction of the current. If another arc column with the same current direction exists in the magnetic field, each arc column will be attracted to each other and restrained according to Fleming's left-hand rule. as a result,
The fluctuation of each arc is reduced and stabilization is achieved.

When a plurality of electrodes are not of the same shape, share a power source, are asymmetrically arranged with respect to a reference line, and have different arc currents and arc lengths, the electrodes generate from a plurality of electrodes. Equal restraint force does not act on each arc, and each arc is not stabilized.

FIG. 1 is a schematic elevation view showing an embodiment of the present invention. Three electrodes 1 having the same shape are opposed to the counter electrode 3 from above. The counter electrode 3 is an object to be heated, such as molten steel, and is housed in a container 5 such as a tundish. Container 5
The opening is covered with a cover 6, and the inside thereof is filled with a predetermined atmospheric gas. 6a is an atmospheric gas inlet, and 6b is an atmospheric gas outlet.

As shown in FIG. 2, the three electrodes 1 are vertically arranged at the respective vertices of an equilateral triangle and are connected to three independent power sources 4, respectively. A reference line 8 is located at the center of gravity of the equilateral triangle. The arc current I, the arc length D, and the inter-electrode distance L are the same for the three electrodes 1, and the inter-electrode distance L is reduced until a sufficient attractive force is generated between the arcs.

Uniform arc 2 from three electrodes 1 to counter electrode 3
Is generated, and the arcs 2 are attracted to each other with an equal force to stabilize.

As shown in FIG. 3, when the three electrodes 1 are arranged in a straight line, the electromagnetic attraction force acts on the arc generated from the central electrode 1 from directions different by 180 degrees, and the restraining force does not act. Therefore, the arc does not stabilize. As shown in FIG. 4, in the case of the asymmetrical arrangement in which the distance between the electrodes is not the same, the attracting force of the arc is biased, and the arc is difficult to stabilize. Even when the electrode shape, the arc current I, and the arc length D are not the same, or when the power source 4 is shared, the attracting force of the arc is similarly biased.

FIG. 5 and FIG. 6 show the electrode arrangement positions when the number of electrodes 1 is two and when the number of electrodes 1 is four. When there are three or more electrodes 1, the electrodes 1 are arranged at the vertices of a regular polygon having the reference line 8 as the center of gravity.

The electrode 1 can be tilted with respect to the reference line 8. In that case, as shown in FIG.
The tilt direction and tilt angle θ with respect to are equal so that symmetry is not lost.

Now, the preferable number of the electrodes 1 will be described. There are multiple electrodes 1 to stabilize the arc,
In the case of two lines, the suction force is generated linearly, and some fluctuation remains in the direction perpendicular to the line. Therefore, it is preferable that three or more arcs are applied to each arc from the arcs on both sides. However, the attractive force in this case is a combination of the attractive forces received from the arcs on both sides, and this combined force is
It becomes smaller as the number of electrodes increases, weakening the constraint. Therefore, usually 2 to 4, especially 3 are preferable.

The inclination angle θ of the electrode 1 should not be larger than 45 degrees because an arc may be generated from other than the tip of the electrode 1 when the inclination is tight.

The arc current I, the arc length D and the interelectrode distance L are appropriately determined according to the amount of heat required for the object to be heated. However, if the inter-electrode distance L is too small, a plurality of arcs coalesce and become one arc, so the binding force does not work,
If it is too large, the suction force will not be generated. for that reason,
Normally, L = D × 0.3 to 0.8 is selected.

[0020]

EXAMPLES The effectiveness of the present invention was investigated by the following experiments. Table 1 shows the outline of the experimental apparatus.

[0021]

[Table 1]

The experiment was carried out by starting the arc with a short arc length, gradually extending the arc length, and measuring the arc voltage. FIG. 8 shows how the arc voltage fluctuates at a specific arc length. If the arc becomes unstable, the arc voltage will fluctuate. The degree of arc instability is expressed as a fluctuation range of arc voltage. When the arc voltage reaches the power supply voltage, arc breakage occurs, and the arc voltage fluctuates with the power supply voltage as the upper limit, so if you measure the minimum value of the arc voltage,
The fluctuation range of the arc voltage can be known, and thus the stability of the arc can be known.

Therefore, in the experiment, the stability of the arc was evaluated from the arc length causing the arc break and the minimum value of the arc voltage at the arc length. The longer the arc length causing the arc break and the higher the arc voltage at the arc length, the better the stability of the arc.

In addition, the effect of the electrode distance on the arc length and arc voltage at which arc breakage occurred was investigated by preliminary experiments. FIG. 9 shows the result of the investigation in the case of two electrodes. As can be seen from FIG. 9, the distance between the electrodes is appropriate to be 60 mm under the present experimental conditions. Therefore, in the experiment, the distance between the electrodes was set to 60 mm.

As a first experiment, the relationship between the number of electrodes and arc stability was investigated. Experimental results are shown in FIGS. 10 and 11.
Shown in.

FIG. 10 shows that the arc current per electrode is 1
The relation between the number of electrodes and the arc stability is shown at 20A. When the number of electrodes is one, the arc length at which arc breakage occurs is 151 mm, and the minimum arc voltage at this arc length is 45 mm.
V, but when there are two electrodes, each is 227 mm,
When the voltage was increased to 60 V and the number of electrodes was 3, the arc was further restricted and stabilized, resulting in 242 mm and 63 V. However, in the case of 4 electrodes, the stability is better than in the case of 1 electrode, but it is 218 m rather than in the case of 3 electrodes.
It became m, 58V. Even if the number of electrodes is further increased, there is no effect on stabilization, and in this experiment, three electrodes were optimal.

FIG. 11 shows the currents per electrode when the number of electrodes is 1, 2, 3, 4 and 120 A and 60, respectively.
A, 40A, and 30A show the results when the current of the entire system was maintained at 120A. Even when the current value of the entire system was kept constant, the electrodes were made plural and the arcs were restrained to stabilize the arcs. In this experiment, the optimum number was three.

As a second experiment, the relationship between the electrode symmetry and the arc stability was investigated. The number of electrodes was 3, the current per electrode was 120 A, and the arc length was the same for all three electrodes. As for the arrangement of electrodes, when L = 60 mm in FIG. 2 and when L = L ′ = 60 mm in FIG.
In the case of L ′ = 60 mm and L ″ = 30 mm, the results are shown in FIG. 12, and the arc is most stable when the three electrodes are symmetrically arranged.

As a third experiment, the influence of the difference in arc length on the arc stability was investigated. There were two electrodes, and the current per electrode was 120A. FIG. 13 shows the results when both arc lengths were the same and when the arc lengths were different by 40 mm. In the latter case, the arc length shows the longer value. It is more stable if the arc lengths are the same.

As a fourth experiment, the effect of the difference in arc current on the arc stability was investigated. There are two electrodes,
FIG. 14 shows the results when a current of 60 A was applied to each, and the results when a current of 60 A was applied to one and 100 A to the other. The arc current needs to be evenly applied to each electrode.

As a fifth experiment, the relationship between the electrode symmetry and the arc stability was investigated in terms of the attitude of the electrode. There were two electrodes, and the current per electrode was 120A. Two electrodes are parallel, one is inclined 30 ° outward, both are outward 3
It was set under three conditions of 0 ° tilt. The results are shown in Fig. 15. It is important to arrange the electrodes symmetrically, because the arc stability deteriorates in the order of the electrodes being parallel, both electrodes being inclined uniformly, and only one electrode being inclined.

In the DC arc generating method of the present invention, it is difficult to realize the symmetry and the identity completely in the actual operation. Therefore, the variation up to ± 10%, which does not significantly affect the arc stability, is in the same category as the symmetry.

[0033]

As is apparent from the above description, since the DC arc generating method of the present invention uses the magnetic field generated by the arc itself to electromagnetically stabilize the arc, the arc method is a fluid method. The operating cost can be reduced and the equipment around the electrode can be simplified as compared with the case where the electrode is stabilized.

By stabilizing the arc, damage to peripheral equipment is reduced, and high voltage is easily obtained. By suppressing fluctuations in the arc voltage, it is possible to reduce the margin of the arc voltage with respect to the rated voltage of the power supply, and use the power supply with high efficiency. Since a plurality of electrodes are used, the current capacity per electrode is reduced and the consumption of the electrodes is suppressed. When heating in steel making equipment, etc., a large amount of electric power is input, so a large-capacity custom power supply is usually required, but since multiple power supplies are combined with each power supply, it is possible to use a ready-made power supply. In many cases, equipment costs are reduced.

[Brief description of drawings]

FIG. 1 is a schematic elevational view showing an embodiment of the present invention.

FIG. 2 is a plan view showing an electrode array when there are three electrodes.

FIG. 3 is a plan view showing an improper electrode arrangement.

FIG. 4 is a plan view showing an improper electrode arrangement.

FIG. 5 is an elevation view showing an electrode array in the case of two electrodes.

FIG. 6 is a plan view showing an electrode array when there are four electrodes.

FIG. 7 is an elevational view showing tilted electrodes.

FIG. 8 is a graph showing changes in arc voltage.

FIG. 9 is a graph showing the influence of the distance between the electrodes on the arc stability.

FIG. 10 is a graph showing the relationship between the number of electrodes and the arc stability when the current per electrode is constant.

FIG. 11 is a graph showing the relationship between the number of electrodes and arc stability when the current of the entire system is constant.

FIG. 12 is a graph showing the relationship between electrode symmetry and arc stability.

FIG. 13 is a graph showing the effect of different arc lengths on arc stability.

FIG. 14 is a graph showing the effect of differences in arc current on arc stability.

FIG. 15 is a graph showing the relationship between electrode symmetry and arc stability in terms of electrode attitude.

[Explanation of symbols]

 1 electrode 2 DC arc 3 counter electrode 4 power supply 8 reference line

Claims (1)

[Claims] 1. A plurality of electrodes having the same shape, each of which is connected to a power source, are arranged symmetrically around a reference line which is set between the electrodes and is perpendicular to a counter electrode, and the arc current and the arc length are constant. Then, a DC arc generating method, characterized in that a DC arc is generated from each electrode to the counter electrode.