JPH04139384A - Moving type plasma torch - Google Patents

Abstract

PURPOSE:To enable a plasma voltage to be increased without increasing a torch diameter by a method wherein a solenoid is disposed at an end part within a nozzle and a magnetic member is disposed on a concentric circle of at least one of an inside part or an outside part of the solenoid. CONSTITUTION:A solenoid 10 is fixed to an extremity end of a nozzle 6, and a magnetic member 11 is disposed between the nozzle 6 and the coil 10. An electrical current is flowed from a heated item 20 toward an electrical discharging part 4 within a plasma arc 21. When a DC current flows to the coil 10, a magnetic flux of a DC magnetic field B is crossed with an electrical current J within the plasma arc 21, an electro-magnetic force F is generated within the plasma arc 21 in such a direction as it may rotate around an axis and then the plasma arc 21 starts to rotate. As an electrical current path is slightly displaced from its axis symmetrical state, a kink instability and the electromagnetic force F are overlapped to each other to form a circulating plasma. When such a plasma torch is used, a plasma arc having a long arc length is generated and an arc column is cooled and an electrical current path is made narrow, so that a plasma voltage can be substantially increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transition type plasma torch that generates a plasma arc between a cathode and an object to be heated, and is particularly suitable for use in heating molten steel. Regarding transfer type plasma torch.

[Conventional technology] In recent years, in the steelmaking process of steelworks, the development of technology has been progressing to heat molten steel in ladle or tundish with plasma arc, control the molten steel temperature, and perform a scouring reaction. .

For such applications, transfer type plasma torches are used in which the object to be heated is used as a counter electrode.

An example of a conventional transfer type plasma torch is shown in FIG. 3. Reference numeral 1 denotes a cathode, which is composed of a cathode outer cylinder 2 and a cathode inner cylinder 3, and is provided at its tip with a discharge section 4 made of tungsten or the like and shaped like a front. 5
is an electrical terminal. A nozzle 6 is arranged on a concentric circle surrounding the cathode 1. Cathode 1 and nozzle 6
A gap is provided between them, and this gap serves as a flow path for the plasma working gas 7. This flow path is constricted at the tip of the torch, so that the plasma working gas 7 is ejected at a high velocity in the axial direction of the torch. Note that the cathode 1 and the nozzle 6 have a water-cooled structure. 9 represents cooling water, and 8 represents an insulating spacer that separates the cathode 1 and the nozzle 6.

In the above plasma torch, the plasma working gas 7
While spouting, electricity is applied to connect the discharge part 4 and the heated object 20.
A plasma arc 21 is generated between the
Since the plasma working gas 7 is ejected at a high flow velocity,
A stable linear plasma arc is formed.

[Problems to be Solved by the Invention] In the conventional plasma torch described above, the arc voltage varies greatly depending on the atmospheric gas components around the plasma arc, and is extremely reduced in an inert gas atmosphere such as argon. The amount of power input will drop significantly. Increasing the arc current may be considered as a means to avoid a decrease in the amount of input power, but increasing the current causes a rise in the temperature of the discharge section and significantly shortens the life of the discharge section.

Furthermore, since the structure is such that plasma working gas is ejected in a straight line to narrow the current path and generate a stable plasma arc, it is not suitable as an apparatus for heating a large area.

In order to solve these problems, the applicant has filed several patent applications relating to improved transitional plasma torches. Among them, Japanese Patent Application No. 2-125355 (hereinafter referred to as
In the plasma torch of the prior application, an electromagnetic coil is attached to the nozzle to generate a DC magnetic field in the axial direction of the nozzle, suppressing disturbances in the plasma arc, and generating rotational force in the plasma arc, causing it to rotate. This generates a plasma arc that spreads toward the object to be heated. This plasma torch will be explained in more detail.

FIG. 2 is an explanatory diagram of the configuration of an embodiment according to the earlier application of the present invention. Reference numeral 1 denotes a cathode, which is composed of a cathode outer cylinder 2 and a cathode inner cylinder 3, and has a hemispherical discharge section 4 made of tungsten or the like at its tip. 5 is an electrical terminal. A straight nozzle 6 is arranged concentrically on the outside of the cathode 1. For this reason, the plasma torch has a multi-tubular structure. The gap between the cathode 1 and the nozzle 6, which serves as a flow path for the plasma working gas 7, is formed in the shape of a straight tube without narrowing. Cooling water 9 is made to flow through the cathode 1 to cool the discharge section 4 from behind, and also to flow through the nozzle 6 to cool the nozzle 6.

A coil 10 is attached to the tip of the nozzle 6, and this coil 10 is connected to a DC power source (not shown). Further, a magnetic material member 11 is interposed between the nozzle 6 and the coil 10.

When the arc is generated by the plasma torch, the sixth
As shown in the figure fat, a current flows in the plasma arc 21 from the object to be heated 20 toward the discharge section 4. When a direct current is passed through the coil 10, a current J in the plasma arc 21 is caused to flow. The magnetic flux of magnetic field B interlinks, and plasma arc 2
An electromagnetic force F is generated within 1.

F=JXB This electromagnetic force F is generated in the direction of rotation of the plasma arc 21 around its axis, and the plasma arc 21 begins to rotate as indicated by the arrow shown in FIG. 6(b).

When the current path slightly deviates from axial symmetry, kink instability and electromagnetic force F are superimposed to form swirling plasma.

When the plasma torch described above, which generates swirling plasma, is used, a plasma arc with a long arc length is generated, and the arc column is cooled and the current path is narrowed.
This makes it possible to significantly increase plasma voltage.

Furthermore, in the plasma torch of the previous application, a magnetic material member 11 is interposed between the nozzle 6 and the coil 10. By arranging this magnetic material member 11, the DC magnetic field can be effectively linked to the arc column. However, the power consumption of the electromagnetic coil 10 can be reduced.

In this way, the problems of the prior art have been solved by the technology of the prior application. However, even in the previous application, there were still problems that needed to be improved. That is, the electromagnetic coil 10 is connected to the nozzle 6
If the plasma torch is arranged outside of the nozzle, the diameter of the lower part of the plasma torch will be larger than the diameter of the nozzle. A plasma torch having such a configuration requires care when inserting and removing the torch into a heating container such as a tundish, or requires a heat-resistant coating to protect the coil 10 from a high-temperature atmosphere.

The present invention was made to solve the problems of the prior art as well as the problems of the plasma torch of the previous application, and it is possible to increase the plasma voltage without increasing the torch diameter. The purpose of the present invention is to provide a transitional plasma torch.

[Means and effects for solving the problem] In order to achieve the above object, in the first invention, an electromagnetic coil is disposed at the end inside the nozzle, and at least one of the inside and outside of the electromagnetic coil is disposed at the end of the nozzle. Magnetic material members are arranged on the concentric circle on the side!
are doing.

Also, like the second invention, the magnetic material member is arranged inside the cathode behind the discharge part! It is better to do so.

The length of this magnetic material member is preferably longer than the length of the electromagnetic coil.

In the present invention, an electromagnetic coil is placed inside the nozzle,
The diameter of the lower part of the plasma torch is not larger than the nozzle diameter. In order to accommodate the magnetic coil in the nozzle, it is necessary to make the electromagnetic coil small, and only when the electromagnetic coil is miniaturized can it be stored.

The electromagnetic coil is miniaturized as follows. When a magnetic material member is placed near the electromagnetic coil, the magnetic field becomes stronger near the end of the magnetic material member, and the number of magnetic fluxes that intersect with the current in the arc column increases compared to the case where no magnetic material member is placed. Therefore, the power consumption of the electromagnetic coil is significantly reduced, and as a result, the number of turns of the electromagnetic coil can be reduced to make it smaller.

In this case, the number of magnetic fluxes that effectively interlink with the current in the arc column varies greatly depending on the length of the magnetic material members and their placement. Of these, the longer the length of the magnetic material member, the greater the magnetic flux density at the end of the magnetic material member. Therefore, the length of the magnetic material member is preferably set to It is better to make it longer than the length of the electromagnetic coil, more preferably 1 to 4 times the length of the electromagnetic coil.
If the length of the magnetic material member is less than one time the length of the electromagnetic coil, the magnetic flux will concentrate on the magnetic material member and the magnetic field will not work effectively. The effect is insufficient and undesirable, and even if the length is made more than four times the length of the electromagnetic coil, the increase in magnetic flux density is saturated.

Furthermore, the closer the magnetic material member is placed to the axis of the cathode (discharge portion), the stronger the magnetic field acting on the plasma arc becomes. In the second aspect of the invention, the magnetic material member is arranged in the cathode located behind the discharge section. With this arrangement, the electromagnetic coil can be further miniaturized.

[Embodiment] FIG. 1 shows an embodiment of the present invention, and is a sectional view of the lower part thereof. In FIG. 1, the parts other than the lower part have the same structure as in FIG. 2, so their description is omitted. Furthermore, the configuration of the plasma torch shown in FIG. 1 is the same as the plasma torch shown in FIGS. 2 and 3 except for the arrangement of the electromagnetic coil and the magnetic material member, so the description of the plasma torch shown in FIGS. 2 and 3 overlaps. The details will be omitted.

1 is a cathode consisting of a cathode outer cylinder 2 and a cathode inner cylinder 3; 4 is a tungsten discharge part (tungsten electrode); and 6 is a nozzle that surrounds the cathode 1 and is arranged on a concentric circle of the cathode 1.

An electromagnetic coil 10 is provided at the tip of the nozzle 6 (cooling water flow path). Reference numeral 12 denotes a wiring connecting the coil 10 and a coil power source (not shown). Also, a magnetic material member 11 is arranged inside the cathode 1 behind the discharge section 4. 8 is an insulating spacer. The length C of the magnetic material member 11 is equal to or longer than the length of the coil 10.

Next, the results of actually generating plasma using the plasma torch shown in FIG. 1 will be explained.

(Example 1) Configuration of plasma torch Diameter of cathode; 20 - Length of electromagnetic coil; 50 - Number of turns of Otori coil; 350 times Magnetic material member: Length of the magnetic material member in the iron cylindrical cathode; 150 m ■ Length of the magnetic material member outside the electromagnetic coil; 50111 Plasma generation conditions Working gas: Argon working gas flow rate; 30 ρ/min Plasma current: 90 OA Anode: Carbon block Distance between the anode and the discharge section; 200 m ■ Under the above conditions: The relationship between the excitation current of the electromagnetic coil and the state of the generated plasma arc was as follows.

■When the excitation current was DCo and 5A or less, a straight and stable plasma arc was generated.

■When the excitation current is DCo, between 6 and 0.8 A, only the downstream (anode side) spreads, and the plasma with weak swirling
A problem occurred.

(2) When the excitation current was DCo, 8A or higher, the plasma arc spread from near the cathode toward the anode and rotated at high speed.

The plasma voltage and input power at each of the above excitation current values are such that when no excitation current is applied, the plasma voltage is 170
, the input power was 153kW, but the excitation current was DCo
, 8A to generate a rotating plasma arc, the plasma voltage increased to 330V and the input power increased to 297kW.

In this way, by flowing the excitation current, the plasma voltage can be changed significantly (that is, the input power can be changed significantly), and the amount of heating can be easily controlled. In addition, by forming a swirling plasma arc, the heating area is expanded,
Local overheating is avoided.

(Example 2) The same conditions as in Example 1 were used except that the length of the magnetic material member in the cathode was 50 mm, which was the same as the length of the electromagnetic coil.

After generating a stable plasma arc under these conditions, a current was passed through the electromagnetic coil and the current was gradually increased.
When DCl was set to 5A, the plasma arc was observed to spread toward the anode and swirl at high speed. The plasma voltage at this time was 320V, and the input power was 288V.
It was kw.

(Comparative Example) The magnetic material member was removed from the plasma torch having the configuration shown in FIG. 1 used in Example 1, and plasma was generated using this torch.

Then, when a current was passed through the electromagnetic coil in the same manner as in Example 1, when the voltage was set to DC4, OA, a plasma arc spreading toward the anode and rotating at high speed was observed. was 325 cm, and the input power was 293 kW.

Comparing the excitation current of the electromagnetic coil with respect to the results of Example 1.2 and Comparative Example above, the excitation current of Example 1 and Example 2 is Q 2, approximately 0.4, respectively, compared to that of the Comparative Example. The value was extremely small. As a result, it was confirmed that the electromagnetic coil could be significantly downsized by arranging the magnetic material member.

(Example 3) The strength of the magnetic field that effectively acts on the plasma arc was measured for various plasma torches in which the length of the magnetic material member disposed inside the cathode was varied. Arrangement of coil and magnetic material parts! was made as shown in Figure 4. Coil 1 at this time
0 is the number of turns 385 and the length GL is 55 mm, and the length 12 of the magnetic material member 11 is 55 mm to 330 mm.
Various types of (2) were used. Then, the excitation current of the coil 10 was set to DCIA, and the axial magnetic field at a point A on the coil axis 12 corresponding to the position of the tip of the cathode was measured.

This result is shown in Fig. 5. As is clear from this figure, the ratio of the coil length J to the magnetic material member length ρ2 < 612
/41) increases (as the length j2 of the magnetic material member 11 increases), the magnetic field at point A gradually becomes stronger. When the ratio (ff12/f+) of the coil length gl to the magnetic material member length 12 becomes around 4, the strength of the magnetic field becomes approximately constant.

Note that the present invention is not limited to the above embodiments.
For example, in each of the above-mentioned embodiments, only the case where the electromagnetic coil 10 is provided in the nozzle 6 has been described, but it may also be incorporated behind the discharge section 4, and the placement position of the electromagnetic coil 10 may be changed accordingly. A part of the electromagnetic coil 10 may be away from the tip of the discharge part 4 as long as it is within the range where the magnetic field generated by the electromagnetic coil 10 and the plasma arc can be interlinked, and the current flowing through the electromagnetic coil 10 is It may be an exchange.

[Effect of the invention] The present invention includes an electromagnetic coil at the tip of the nozzle,
Since it is possible to generate a magnetic field that interlinks with the current in the plasma arc column, it is possible to form a plasma arc that spreads radially toward the object to be heated and rotates at high speed.

Therefore, the plasma voltage can be increased, and the heating ability of the plasma torch is improved. Since the electromagnetic coil is disposed within the nozzle, there is no need to cover the electromagnetic coil with heat-resistant coating, and the diameter of the torch does not increase due to the provision of the electromagnetic coil.

Since the magnetic material member is disposed on the concentric circle of the electromagnetic coil, the power consumption of the electromagnetic coil is reduced and the electromagnetic coil is made smaller.

Furthermore, by arranging the magnetic material member within the cando, or by making the length of the magnetic material member longer than the length of the electromagnetic coil, the magnetic field acting on the plasma arc becomes even stronger, which causes the electromagnetic The power consumption of the coil is significantly reduced, and the electromagnetic coil can be further miniaturized.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, a sectional view of the lower part thereof,
Fig. 2 is an explanatory diagram of the configuration of a transfer type plasma torch according to the earlier application of the present invention, Fig. 3 is an explanatory diagram of the configuration of a conventional transfer type plasma torch, and Fig. 4 is a positional relationship between the coil and the magnetic material member in the present invention. FIG. 5 is a diagram showing the relationship between the length of the magnetic material member and the strength of the magnetic field at its end in the present invention, and FIG. 6 is an explanatory diagram of the operating principle of the present invention. DESCRIPTION OF SYMBOLS 1... Cathode, 2... Cathode outer cylinder, 3... Quad inner cylinder, 4... Discharge part (tungsten electrode), 6...
- Nozzle, 7... Plasma working gas, 10. Electromagnetic coil, 11... Magnetic material member, 20. Heating object, 21
...Plasma arc.

Claims (3)

[Claims] (1) In a transfer type plasma torch consisting of a cathode with a discharge part at the tip and a nozzle surrounding the cathode and arranged on a concentric circle of the cathode, an electromagnetic coil is arranged at the end inside the nozzle, and the electromagnetic coil is A transfer type plasma torch characterized in that a magnetic material member is arranged concentrically on at least one of the inner and outer sides. (2) The transfer type plasma torch according to claim 1, characterized in that the magnetic material member is disposed within the cathode behind the discharge section. (3) The transfer type plasma torch according to claim 1 or 2, characterized in that the length of the magnetic material member is longer than the length of the electromagnetic coil.