JP2000012284A - Plasma arc generating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shield a negative electrode from an oxygen component by a shield gas with sufficient reliability. SOLUTION: Argon gas and an air containing oxygen component are supplied from one negative electrode 3 side situated in the upstream of these gases toward the other positive electrode situated in the downstream thereof in this order, heated by the arc generated between both the electrodes with flowing in a state of rotating an arc heating chamber 5 provided between both the electrodes, and taken out from the other electrode side. The feeding speed Ua of the argon gas is set higher than the feeding speed Ub of the air, and the feeding area length Lb of the argon gas is set 3 times or more the protruding length La to the arc-heating chamber 5 of the negative electrode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc generator for generating an ultra-high temperature gas by heating a gas with an electric arc.

[0002]

2. Description of the Related Art Conventionally, a plasma arc generator is shown in FIG.
As shown in FIG. 3, plasma arc electrodes of a positive electrode 50 and a negative electrode 54 are arranged at both ends of an arc holding portion 53 provided with an arc heating chamber 52 through which a gas and an arc 56 flow. And gas such as nitrogen are sent in a swirling shape. By turning the inner circumference of the arc heating chamber 52 to a lower pressure than the outer circumference by turning the gas, an arc 56 is stably generated between the electrodes 50 and 54, and the gas flowing through the arc heating chamber 52 is discharged by the arc. A configuration is adopted in which the material is heated to an extremely high temperature by 56 and discharged from the positive electrode 50 side.

[0003] The plasma arc generator includes an electrode 5
The cathode 54 is formed of tungsten having excellent corrosion resistance at high temperatures in order to prolong the life of the device 4 and increase the operation rate. Furthermore, since the plasma arc generator reduces the corrosion resistance when tungsten is oxidized, an inert gas such as a nitrogen gas or an argon gas is used to prevent the cathode 54 from being oxidized by an oxygen component when the gas is introduced. A shield gas) and an oxidizing gas containing an oxygen component are caused to flow in this order from the negative electrode 54 side, and the negative electrode 54 is covered with an inert gas (shield gas) to shield from the oxygen component.

[0004]

However, in the above-described conventional configuration, when the pressure on the inner peripheral side is reduced by the inert gas (shielding gas) flowing in a swirl shape, the oxygen may be reduced depending on the degree of the pressure reduction. Since the component gas may flow backward and reach the negative electrode 54, there is a problem that the reliability of shielding is low.

[0005] In particular, when it is necessary to adjust a heated gas component to a predetermined component, such as when using ultra-high temperature air in a re-entry test in the aerospace field, an inert gas (shielding) is used. The smaller the inflow of gas (gas), the more accurate the adjustment can be made. However, if the amount of inflow of the inert gas (shield gas) is small, the above-mentioned decrease in the pressure on the inner peripheral side becomes remarkable, and the reliability of shielding is reduced. It will be extremely low. When the object to be heated is air, the nitrogen gas contained in the air in a large amount is used as the shielding gas, so that a large amount of the shielding gas can reduce the pressure drop on the inner peripheral side. However, in this case, there is a problem that nitrogen and oxygen may not be obtained in a properly mixed state. Therefore, even in this case, it is desirable that the shielding gas has an inflow amount as small as possible.

Accordingly, the present invention aims to provide a plasma arc generator capable of shielding the negative electrode 54 from the oxygen component with sufficient reliability by using a shielding gas.

[0007]

In order to solve the above-mentioned problems, the invention of claim 1 is directed to a method in which a shielding gas comprising an inert gas and an oxidizing gas containing an oxygen component are supplied from one electrode side to the other electrode side. A plasma arc generator that is heated by an arc generated between the two electrodes and taken out from the other electrode side while flowing the arc heating chamber provided between the electrodes in a swirling state, The supply speed of the shield gas is set to be equal to or higher than the supply speed of the oxidizing gas, and the length of the supply region of the shield gas is 3 of the length of the one electrode protruding into the arc heating chamber.
It is characterized by being set to more than twice.

According to the above configuration, the pressure on the inner peripheral side decreases due to the swirling of the shield gas, so that the oxygen component of the oxidizing gas supplied to the downstream side of the shield gas is reduced toward the one electrode on the upstream side. Even if the gas flows backward, the oxygen component does not reach the electrode on the upstream side, so that the oxygen component can be reliably shielded from the electrode.

According to a second aspect of the present invention, there is provided the plasma arc generating apparatus according to the first aspect, wherein the arc heating chamber has a cross-sectional area of a part of a supply region of the shield gas which is larger than a cross-sectional area of another part. Is also formed to be small.

According to the above arrangement, when the shield gas flows while swirling, it gathers on the inner peripheral side in a portion having a small cross-sectional area in the supply area, so that in this portion, the shield gas on the inner peripheral side of the shield gas flows. Pressure rises. Therefore, even when the oxygen component of the oxidizing gas flows backward in the direction of one electrode on the upstream side due to the decrease in the pressure on the inner peripheral side due to the turning of the shield gas, the portion where the pressure increases and the cross sectional area is small Thus, the oxygen component can be reliably shielded.

According to a third aspect of the present invention, there is provided the plasma arc generator according to the first or second aspect, wherein the electrode surface flow means for ejecting the shield gas to the arc heating chamber along the surface of the one electrode. It is characterized by having. According to the above configuration, by flowing the shield gas along the surface of the electrode, the oxygen component can be more reliably shielded from the electrode by the Coanda effect.

According to a fourth aspect of the present invention, there is provided the plasma arc generator according to any one of the first to third aspects,
The one electrode is formed so as to eject the shield gas from the inside to the surface. According to the above configuration, the oxygen component traveling toward the electrode can be pushed back by the shield gas ejected from the inside of the electrode to the surface, so that the oxygen component can be more reliably shielded from the electrode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The plasma arc generator according to the present embodiment has a negative electrode portion having a negative electrode made of tungsten, an arc holding portion provided with an arc heating chamber for flowing gas and an arc, and a positive electrode made of tungsten. The positive electrode unit is connected in series. Each electrode may be formed of a material other than tungsten as long as it has excellent corrosion resistance at high temperatures. The arc holding portion is set to the smallest possible inner diameter in consideration of heat loss, arc stabilization, and the like. In addition, the positive electrode part is formed by forming the above-mentioned positive electrode in a ring shape,
The magnetic field generating member is arranged around the positive electrode, and the arc is moved around the positive electrode by Lorentz force (see FIG. 9).

On the other hand, as shown in FIG.
It has an electrode block 2 formed in a disk shape. A cooling water passage 2a is formed inside the electrode block 2, and cooling water is supplied to the cooling water passage 2a from a cooling water supply system (not shown). At the center of the electrode block 2, the above-described negative electrode 3 made of tungsten is provided. The negative electrode 3 has a cylindrical columnar portion 3a penetrating through the center of the electrode block 2, an outer peripheral support portion 3b formed in an outer peripheral direction from one end of the columnar portion 3a on the side of the arc heating chamber 5, and a columnar portion. Arc heating chamber 5 from one end face of section 3a
And an arc generating unit 3c protruding from the inside.

A cylindrical arc holding portion 4 is joined to the side surface of the electrode block 2 in a state of being electrically insulated. The arc holding part 4 is composed of an aggregate of a number of constrictors 6 formed in an annular shape. An O-ring 7 is interposed between the adjacent restrictors 6. The O-ring 7 is connected to the arc heating chamber 5 in the arc holding unit 4.
And the outside of the device are sealed in an airtight state. In addition, a gas injection ring 8 is provided between the restrictors 6.
Are provided on the inner peripheral side of the O-ring 7 (on the side of the arc heating chamber 5). As shown in FIG.
As shown in (a), a plurality of communication holes 8a communicating from the outer peripheral surface to the inner peripheral surface are formed, and these communication holes 8a are inclined in the same direction with respect to the radial direction so that the gas flows. Is ejected along the inner wall surface of the constrictor 6.

As shown in FIG. 1, a gas supply passage 6a and a cooling water passage 6b are formed in each of the constrictors 6 on the outer peripheral side and the inner peripheral side, respectively. Cooling channel 6b
Are connected to a cooling water supply system (not shown), and the cooling water from the cooling water supply system flows to prevent overheating of the constrictor 6 during arc heating. On the other hand, the gas supply path 6a is connected to the gas injection ring 8 and the O.O.
It is communicated to the wall between the rings 7. Each gas supply path 6a is connected to one of a shield gas supply system for supplying an argon gas (shield gas) and an air supply system for supplying air. still,
The shield gas supply system may supply another inert gas such as nitrogen gas as a shield gas.
The air supply system supplies air as a representative example of an oxidizing gas containing an oxygen component, but is replaced with a gas supply system that supplies an oxidizing gas containing an oxygen component at a content other than air. be able to.

In the above shield gas supply system, when the distance from one end surface of the cathode 3 is defined as the supply region length Lb of the shield gas, the projection length L of the arc generating portion 3c in the cathode 3 is set.
The shield gas is connected to the gas supply path 6a of the restrictor 6 which is at least three times as long as the shield gas supply area Lb. On the other hand, the air supply system is connected to a gas supply path 6a of the restrictor 6 existing in a downstream area excluding the shield gas supply area. Thereby, the shield gas supply region of the arc heating chamber 5 is supplied with the argon gas from the shield gas supply system in a swirling state via the gas supply path 6a and the gas injection ring 8, while
The downstream area is supplied with air from the air supply system in a swirling state.

The shield gas supply system and the air supply system are arranged such that the argon gas shield gas supply speed Ua (m / s) when flowing into the arc heating chamber 5 is equal to or higher than the air supply speed Ub (m / s). Thus, the supply pressure and supply amount of the argon gas and the air are controlled.

The operation of the plasma arc generator in the above configuration will be described. First, the cooling water passage 2a of the electrode block 2 and the gas supply passage 6a of the restrictor 6
Is supplied with cooling water, thereby cooling the electrode block 2 and the constrictor 6. Thereafter, the pressure in the arc heating chamber 5 of the plasma arc generator is reduced to a vacuum state, and then argon gas and air are supplied from the argon gas supply system and the air supply system to the gas inlet 4 of each of the constrictors 6.
a.

The argon gas and air supplied to each gas supply path 6a are supplied from the gas supply path 6a to the restrictor 6a.
Flows into a space surrounded by 6, the O-ring 7, and the gas injection ring 8, and flows into the arc heating chamber 5 through the communication hole 8a of the gas injection ring 8 in FIG. At this time, each communication hole 8a is formed to be inclined in the same direction with respect to the radial direction. Therefore, the argon gas and the air flow along the inner wall surface of the arc heating chamber 5 (the constrictor 6) by jetting in the direction in which the inclined communication hole 8a is formed. Then, by proceeding to the downstream side while flowing in a swirling state in the arc heating chamber 5, the pressure on the inner peripheral side of the arc heating chamber 5 becomes lower than that on the outer peripheral side.

Next, an arc power supply device (not shown) is operated, and a predetermined voltage is applied between the negative electrode 3 and the positive electrode to generate an arc. The arc proceeds stably on the low-pressure inner peripheral side of the arc heating chamber 5 and heats the flowing argon gas and air while rotating in the arc heating chamber 5. Then, these argon gas and air are discharged as an ultra-high temperature gas and used for various tests and experiments.

When the pressure of the shield gas supply region by the argon gas is lower than the pressure of the downstream region by the air, the air in the downstream region flows back to the shield gas supply region and moves in the negative electrode 3 direction. I do. When the movement amount is large, as shown in FIG. 3, the air reaches the cathode 3, and the cathode 3 is oxidized by the oxygen component in the air. As a result, the negative electrode 3 has a reduced corrosion resistance at a high temperature, so that it is difficult to use the negative electrode 3 suitable for arc discharge in a short time.

However, in the present embodiment, the shield gas supply speed Ua (m / s) of the argon gas when flowing into the arc heating chamber 5 is equal to the air supply speed Ub (m / s).
s) As described above, the supply pressure and the supply amount of the argon gas and the air are controlled (first condition). further,
The shield gas supply area is the protrusion length La of the arc generating unit 3c.
Is set to be three times or more (second condition). Therefore, since the first condition and the second condition are satisfied, even if the air flows backward in the direction of the negative electrode 3, the moving amount of the backward flow reaches the negative electrode 3 as shown in FIG. Not much. Thereby, the cathode 3 maintains the state of tungsten without being oxidized by the oxygen component of the air, so that it can be used for a long time.

Next, it was confirmed by experiments that if the first condition and the second condition were satisfied, the air would not reach the negative electrode 3 even if the air flowed backward.

That is, the protrusion length La of the arc generation unit 3c is set to 1
A plasma arc generator was prepared in which the length Lb of the shield gas was set at 5 mm and the supply region length Lb of the shield gas was set at 50 mm. Then, the shield gas supply speed Ua (m / s) and the air supply speed Ub
While changing the speed ratio (Ub / Ua) with respect to (m / s), the erosion rate (corrosion rate) of the negative electrode 3 when performing the arc heating was measured. In addition, the pressure of the arc heating chamber 5 was set to 4 atm.

As a result, as shown in FIG. 4, the shield gas supply speed Ua is set to 10 (m / s), and the air supply speed Ua
The erosion rate when b is 40 (m / s) is 1.2 (μg / c), the shield gas supply speed Ua is 40 (m / s), and the air supply speed Ub is 40 (m / s).
(M / s), the erosion rate is 0.0
3 (μg / c).

The pressure of the arc heating chamber 5 is set at 1.2 at.
m, and the shield gas supply speed Ua is 53.3 (m
/ S), and the erosion rate when the air supply speed Ub was 32.7 (m / s) was measured.
04 (μg / c). Further, the pressure of the arc heating chamber 5 is set to 2.3 atm, the shield gas supply speed Ua is 11.6 (m / s), and the air supply speed U
When the erosion rate when b was set to 17.1 (m / s) was measured, it was found to be 0.007 (μg / c).

Thus, according to the above relationship, the supply region length Lb of the shield gas is equal to the protrusion length L of the arc generating portion 3c.
If the plasma arc generator is configured so as to satisfy the first condition that is three times or more a and the second condition that the shield gas supply speed Ua is equal to or more than the air supply speed Ub, the negative electrode 3 is converted from the oxygen component. It was confirmed that it was possible to reliably shut off and extend the life of the negative electrode 3.

As described above, the plasma arc generator of the present embodiment, as shown in FIG. 1, uses a shield gas made of an inert gas such as an argon gas or a nitrogen gas and an oxidizing gas such as air containing an oxygen component. Are supplied in this order from one electrode (negative electrode 3) located on the upstream side to the other electrode (positive electrode) located on the downstream side, and an arc heating chamber provided between the electrodes. 5 is heated by an arc generated between the two electrodes and taken out from the other electrode side while flowing in a swirling state. The supply speed Ua of the shield gas is set to be equal to or higher than the supply speed Ub of the oxidizing gas. And the length Lb of the supply region of the shielding gas is such that the protruding length La of the one electrode (negative electrode 3) into the arc heating chamber is set.
Is set to be three times or more.

According to the above configuration, the pressure on the inner peripheral side decreases due to the swirling of the shield gas, so that the oxygen component of the oxidizing gas supplied downstream of the shield gas flows backward in the direction of the upstream electrode. Even in this case, since the oxygen component does not reach one electrode (negative electrode 3) on the upstream side, the oxygen component can be reliably shielded from this electrode (negative electrode 3).

In this embodiment, the arc holding portion 4 is formed by assembling the constrictors 6 having the same shape, so that the arc heating chambers 5 having the same diameter (the same cross-sectional area) from the upstream side to the downstream side. However, the present invention is not limited to this, and as shown in FIG. 5, the inner diameter (cross-sectional area) of a part of the shield gas supply region is made smaller than the inner diameter (cross-sectional area) of the other part. Arc heating room 5
It may be.

That is, the negative electrode 3 is provided in the shield gas supply area.
The small-diameter restrictor 20 is disposed at a position downstream from the tip of the arc generator 3c. The small-diameter constrictor 20 is set to have an inner diameter smaller than the inner diameter of a normal constrictor 6 arranged in a downstream region or the like. Also,
The inner peripheral surface of the constrictor 6 disposed on both sides of the small-diameter constrictor 20 is inclined so as to increase the diameter from one end to the other end on the small-diameter constrictor 20 side. Thus, when the argon gas is supplied to the arc heating chamber 5, when the argon gas flows downstream, it is gathered in the inner circumferential direction at the small diameter constrictor 20 having a small cross-sectional area, and the pressure is increased. Since the backflow of air can be prevented by the increase in the pressure, the oxidation of the negative electrode 3 can be more reliably prevented.

Further, in this embodiment, as shown in FIG. 6, the argon gas is ejected from between the constrainers 6, 6, and further, the argon gas is ejected from the cathode 3 side. May be configured to be performed.

That is, the plasma arc generator supports the columnar negative electrode 21, the negative electrode 21, and the negative electrode 2.
1 and an electrode support 23 that forms a gas flow path 22 between the electrode block 2 and the electrode surface flow mechanism, so that argon gas is supplied to the negative electrode 21 through the gas flow path 22. You may make it flow along a surface. With this configuration, the argon gas flows into the arc heating chamber 5 without being separated from the surface of the negative electrode 21 by the Coanda effect, so that the negative electrode 3 and the oxygen component are sufficiently shielded, and Oxidation can be more sufficiently prevented.

In the plasma arc generator, the cathode 3 may be formed so that argon gas is ejected from the inside to the surface. That is, as shown in FIG. 7, the cathode 3 has a through hole 3d formed in the axial direction of the cathode 3, and an argon gas is ejected from the tip of the cathode 3 through the through hole 3d. It may be configured. With this configuration, the through hole 3 d is formed in the inner peripheral side of the arc heating chamber 5.
Since the argon gas can be supplied through the anode, the oxygen component traveling in the direction of the negative electrode 3 can be pushed back by the argon gas, and the back pressure of the oxygen component can be surely prevented by preventing the pressure on the inner peripheral side from lowering. Can be prevented.

As shown in FIG. 8, the negative electrode 3 may be formed by forming the negative electrode 3 by a porous body having continuous pores and ejecting an argon gas from the surface of the negative electrode 3. . With this configuration, the oxygen component traveling in the negative electrode 3 direction can be pushed back by the argon gas, so that the oxidation of the negative electrode 3 can be reliably prevented.

[0037]

According to the first aspect of the present invention, a shield gas composed of an inert gas and an oxidizing gas containing an oxygen component are supplied in this order from one electrode side to the other electrode side, and are provided between these electrodes. A plasma arc generator that is heated by an arc generated between the two electrodes and taken out from the other electrode side while flowing the arc heating chamber in a swirling state, wherein the supply rate of the shielding gas is The supply speed is set to be higher than or equal to the supply speed, and the length of the supply region of the shield gas is set to be at least three times the length of the one electrode protruding into the arc heating chamber.

According to the above configuration, the pressure on the inner peripheral side is reduced by the swirling of the shield gas, so that the oxygen component of the oxidizing gas supplied to the downstream side of the shield gas is reduced toward the one electrode on the upstream side. Even if the gas flows backward, the oxygen component does not reach the electrode on the upstream side, so that the oxygen component can be reliably shielded from the electrode.

According to a second aspect of the present invention, in the plasma arc generator according to the first aspect, the arc heating chamber has a cross-sectional area of a portion of the shield gas supply region that is larger than a cross-sectional area of another portion. Is also configured to be small.

According to the above configuration, when the shield gas flows while swirling, it gathers on the inner peripheral side in a portion having a small cross-sectional area in the supply area, and in this portion, the inner portion of the shield gas on the inner peripheral side of the shield gas flows. Pressure rises. Therefore, even when the oxygen component of the oxidizing gas flows backward in the direction of one electrode on the upstream side due to the decrease in the pressure on the inner peripheral side due to the turning of the shield gas, the portion where the pressure increases and the cross sectional area is small Thus, there is an effect that the oxygen component can be surely shielded.

According to a third aspect of the present invention, there is provided the plasma arc generator according to the first or second aspect, wherein the electrode surface flow means for jetting the shield gas into the arc heating chamber while following the surface of the one electrode. It is a configuration having
According to the above configuration, by flowing the shield gas along the surface of the electrode, there is an effect that the oxygen component can be more reliably shielded from the electrode by the Coanda effect.

According to a fourth aspect of the present invention, there is provided the plasma arc generator according to any one of the first to third aspects,
The one electrode is formed so as to eject the shield gas from the inside to the surface. According to the above configuration, since the oxygen component traveling in the direction of the electrode can be pushed back by the shield gas ejected to the surface from the inside of the electrode, the effect that the oxygen component can be more reliably shielded from the electrode can be obtained. Play.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a main part of a plasma arc generator.

FIGS. 2A and 2B are explanatory diagrams showing a gas flowing state in an arc heating chamber, wherein FIG. 2A is an explanatory diagram viewed from a side, and FIG.

FIG. 3 is an explanatory diagram showing a flow state of gas in an arc heating chamber.

Fig. 4 Erosion rate and speed ratio (Ub / Ua)
6 is a graph showing a relationship with the graph.

FIG. 5 is an enlarged sectional view of a main part of the plasma arc generator.

FIG. 6 is an enlarged sectional view of a main part of the plasma arc generator.

FIG. 7 is an explanatory diagram showing a flow state of gas.

FIG. 8 is an explanatory diagram showing a flow state of gas.

FIG. 9 is a schematic configuration diagram showing a part of a conventional plasma arc generating apparatus with a part omitted.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Negative electrode part 2 Electrode block 3 Negative electrode 3a Column part 3b Peripheral support part 3c Arc generation part 3d Through hole 4 Arc holding part 5 Arc heating chamber 6 Contractor 7 O-ring 8 Gas injection ring 20 Small diameter restrictor 21 Negative electrode 22 Gas flow path 23 Electrode support

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Oda 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Inside Kobe Research Institute, Kobe Steel Co., Ltd. 2-3-1 in Kobe Steel, Ltd. Takasago Works

Claims (4)

[Claims] 1. A shield gas comprising an inert gas and an oxidizing gas containing an oxygen component are supplied in this order from one electrode side to the other electrode side, and an arc heating chamber provided between these electrodes is swirled. A plasma arc generator heated by an arc generated between the two electrodes and taken out from the other electrode side while flowing at a rate of supply of the shield gas equal to or higher than the supply rate of the oxidizing gas. And a length of the shield gas supply region is set to be three times or more a length of the one electrode protruding into the arc heating chamber. 2. The arc heating chamber according to claim 1, wherein a sectional area of a part of the supply region of the shield gas is smaller than a sectional area of another part. Plasma arc generator. 3. An electrode surface flowing means for injecting the shielding gas into an arc heating chamber along the surface of the one electrode.
The plasma arc generator according to any one of the preceding claims. 4. The plasma arc generator according to claim 1, wherein said one electrode is formed so as to jet the shielding gas from the inside to the surface.