JPH04355100A - High enthalpy plasma torch - Google Patents

Abstract

PURPOSE: To heighten enthalpy by fitting torch housings at spaces on the same axis, and providing a vortex generator for introducing a tangent flow of gas through a gap between a rear tubular electrode and a front tubular electrode, and a cooling system for cooling the electrodes. CONSTITUTION: A rear electrode 10 and a front electrode 12 are coaxially installed in the stainless housing. The electrode 10 is screwed in one end of a metal holder 22, the holder 22 also serves as a flid conduit for a torch cooling system and is provided with a hole 24 communicated with the radial opening 26 for passing a cooling fluid, and a water guide device 28 forms an annular passage 30 for cooling the electrode 10. The electrode 12 is fitted to a tubular electrode holder 34 between the rear part 14 of the housing and the front part 16 thereof. A vortex generating ring 62 is provided with a hole 64 in the tangential direction for creating two gas vortexes in the opposite directions to separate the arc adhering point from the ring 62. Thus, the electrode eroding rate is low, and the voltage is high to enable stable operation.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD This invention relates to high enthalpy plasma torches.

0002

BACKGROUND OF THE INVENTION Plasma can be generated using three basic plasma generation devices: high frequency or induction torches, transfer arcs,
and various modifications of DC torches. This high-frequency torch uses no electrodes, and energy is transferred to the plasma by induction from a high-frequency electromagnetic source. but,
Transfer arcs and DC torches both use electrodes to pass current through a gas, thereby creating a plasma. The shape, size, and composition of these electrodes are important in determining the operation and application of the torch. Since this innovation primarily concerns new electrode structures for DC torches, a more elaborate discussion of conventional electrode technology is warranted.

Two types of DC torches are commonly used. The first type uses a conical thorium tungsten rod as the cathode and a copper tube as the anode. Gas is introduced tangentially after the cathode, creating a vortex past the cathode and through the anode located at the front of the torch. The arc attaches to one end of the cathode tip and rotates along the inner surface of the anode at the other end. The length of the arc can be controlled using the momentum of the plasma gas vortex, the composition of the plasma gas, the diameter of the anode, and the arc current. Since the cathode attachment point is fixed, the anode attachment point determines the length of this arc. These torches, also known as FCC or fluid convection cathode torches, are most commonly used for low power applications such as plasma injection, cutting, and laboratory research. Typical operating characteristics at atmospheric pressure and with nitrogen plasma gas are as follows. That is, plasma gas flow rate = 50-
100 liters/min, arc current = 200-600 amperes, arc voltage = 70-110 volts, and plasma gas enthalpy = 1-3 kJ/kg. The fixed point of attachment of the cathode prevents this torch from operating at very high currents, and the use of thoriated tungsten reduces the composition of the available plasma gas to some inert, reducing gas (e.g. Ar, Ar/H2 mixture, N2, He
). Neither oxygen nor halides can be used as plasma gases. FCC torches are currently commercially available from a wide variety of companies.

A second type of DC torch uses two coaxial tubes as electrodes. Plasma gas is introduced tangentially between these two electrodes by a vortex generating ring, generating two vortices in opposite directions. Each vortex pushes the arc attachment point away from this vortex generating ring. This arc then extends and the tubular torch provides a significantly higher voltage than the FCC torch. Tubular torches can use electrodes of many different compositions, but copper is the most common. Thorium tungsten is not used because it cannot be made into the large tube sizes needed. One exception is the small (6 mm inner diameter, 16 mm outer diameter) tubular thorium tungsten cathode used by Nippon Steel Corporation. However, the electrode was used in a transfer arc system where the plasma was generated between the lip of the tube and the anode located outside the torch.

Tubular torches are mostly used for melting and as heaters for high temperature reactors. Unfortunately, they require extremely high gas flow rates to stabilize the arc and prevent electrode destruction. Typical operating characteristics for a 1 megawatt tubular torch at atmospheric pressure and using nitrogen plasma gas are as follows. That is, plasma gas flow rate = 3000-
10000 liters/min, arc current = 500-800
Amps, arc voltage = 700-2000 volts, and plasma gas enthalpy = 0.5-1.5 kJ/kg
. Companies such as Plasma Energy and Aerospeciale sell tubular torches. Their most effective role is as an air heater. However, they run into serious electrode erosion problems when arc currents exceed 800 amps. Conventional tubular torches cannot be used when low plasma gas flow rates are required, such as in plasma spraying and reactors using inert plasma gases. Furthermore, the enormous gas flow rates required make them uneconomical in many applications. Finally, they cannot use halide plasma gases because the halide would destroy conventional electrodes and condense in the gas supply tubes.

[0006]

OBJECTS OF THE INVENTION The object of the present invention is to provide a torch with higher enthalpy, very low electrode erosion rate, extremely stable operation, high voltage, low plasma gas flow rate, and metal halide plasma. An object of the present invention is to provide a direct current plasma torch that can be operated with gas.

[0007]

A plasma torch according to the invention comprises a torch housing, a rear tubular electrode and a front tubular electrode, both made of copper and having a tubular insert of refractory material, coaxially mounted spaced apart from each other within this housing. , a vortex generator for introducing gas tangential flows in opposite directions into these tubular electrodes through the gap between the two electrodes, and a cooling system for cooling these tubular electrodes.

A plasma gas supply system is mounted within the housing and includes an insulated tube to prevent plasma gas from condensing on the cooled electrodes.

The pre-electrode includes a cup-shaped outlet section including an expanding section followed by a contracting section, both of which provide a back pressure of the plasma gas to improve the rotation of the arc inside the electrode of the torch. This minimizes erosion of the electrode and prevents material from the surrounding atmosphere from entering the electrode area.

[0010] The refractory electrode material may be a tantalum carbide composite material comprising tantalum carbide infiltrated with thorium tungsten or aluminum or copper. Other refractory electrode materials can be used.

The cooling system includes a water guide surrounding the rear electrode, a brass cooling jacket surrounding the front electrode, and a cooling fluid circulating in continuous relationship around the rear electrode and then around the front electrode. an annular passageway between the water guiding device and the rear electrode and between the cooling jacket and the front electrode for the purpose of cooling.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG. Referring to the drawings, the rear section 14 and the front section 16
A plasma torch is shown that generally includes a rear electrode (anode) 10 and a front electrode (cathode) 12 coaxially mounted within a stainless steel housing made by assembling the two by bolts 18.

The rear electrode includes a copper tubular metal member 20 screwed into one end of a metal electrode holder 22 . The metal electrode holder 22 also provides a fluid conduit for the torch cooling system, and for this purpose the rear end of the holder includes:
Radial opening 2 for passing cooling fluid, e.g. water
6. A water guiding device 28 in the form of a thin-walled metal tube is screwed into this electrode holder and forms an annular water passage 30 that surrounds and is part of a fluid cooling system for cooling the rear electrode. .

The front electrode 12 is mounted within a brass annular member 32 which is itself screwed into a stainless steel tubular electrode holder 34 with a flange 36 clamped between the rear 14 and front 16 of the housing. ing. The pre-electrode holder is electrically isolated from the housing by an insulating annular member 38 made of high temperature chemical resistant plastic material.

The front and rear electrodes are connected by an annular insulating member 40 made of high temperature chemical resistant plastic material and extending rearwardly between the housing portion 14 and the water guide device 28.
isolated from each other. The upper part of this insulating member 40 is
It has an extension 41 made of electrically insulating plastic material, which is fixed to this housing part 14 by a threaded insulating member 42 also made of electrically insulating plastic material. A narrow annular water passage 43 is provided in this annular insulating member 40 after this guide device for purposes to be explained later. A plurality of holes 44 leading to channels 46
opens into an annular water passage 43 spaced around the annular member 40 and forming part of the fluid cooling system. This brass annular member 32 also includes a narrow annular water passage 48, which is part of the cathode cooling system. A plurality of radial holes 50 connect the channel 46 to this annular water passageway 4.
8 is provided at the rear end of the brass member 32. A plurality of radial holes 52 also extend through this water passageway 4.
8 is provided to communicate the front end of the anode holder 34 to an annular passage 54 created between the anode holder 34 and the housing 16 to direct cooling water to an outlet 56.

According to the main feature of the invention, these copper electrodes 10 and 12 are provided with inserts 58 and 59, respectively, attached by high temperature soldering. This allows a wider range of electrode materials to be used. In fact, this torch is made of thorium tungsten or 19909
Canadian Patent Application No. 2,025,619 filed on May 18th
operating with all suitable refractory electrode materials, including both tantalum carbide infiltrated with aluminum or copper as described in No. 1, and composite materials suitable for use with metal halide plasma gases. be able to. The rear end of the refractory insert 58 is insulated from the electrode holder 22 by a ceramic electrical insulator 60. Similarly, the rear end of the refractory insert 59 is separated from this plastic insulation material by a ceramic electrical insulation ring 61.

A conventional vortex generating ring 62 is then mounted between the rear and front electrodes. This vortex generating ring is
A tangential hole 64 is provided in the center of the annular anode and cathode to create two gas vortices (A) and (B) pointing in opposite directions. Each vortex pushes the arc attachment point away from this vortex generating ring 62. This arc then extends and such tubular torches provide significantly higher voltages than FCC torches.

According to another feature of the invention, gas is routed to the vortex ring through an insulated tube 66, such as quartz, which prevents the plasma gas from condensing on the torch body. The plasma gas is fed from the inlet 68 through the opening 70 of the insulating ring 38, through the tube 66, and into the tangential hole of the vortex generating ring 62 through an annular passage 72 around the vortex generating ring.

At the front end of the front electrode (cathode) there is an expansion section 73 followed by a contraction section 74 near the outlet. This design creates a backpressure of the plasma gas, which considerably improves the rotation of the arc inside the electrode of this torch, thereby minimizing electrode erosion. It provides an area for the arc to stably attach, thereby minimizing power fluctuations. It also confines the arc jet within the expansion, thereby providing a long-tailed, symmetrical flame that is ideally suited for cutting, welding, and spray forming operations. lastly,
It prevents material from the surrounding environment from entering the electrode area and destroying the electrode.

[0020] The plasma torch cooling system is such that a cooling liquid, such as water, is then applied to the rear electrode 10 and the front electrode 12.
and allows for continuous heat exchange. The cooling water enters the torch through holes 24 in electrode holder 22. This water then flows through the radial holes 26 into an annular passage 30 between the outer surface of the rear electrode and the water guiding device 28 to cool the latter electrode (anode). This water then flows back behind the water guide, enters the hole 44 in the annular insulating member 40 and flows through the channel 46 . These holes 4
It should be noted that 4 is towards the rear of this annular insulating member 40 to avoid the possibility of these electrodes shorting through the cooling water. The cooling water then passes through the holes 50 in the brass cooling jacket 32 and the annular passage 48 around the front electrode 12 to cool the front electrode (anode). This water then passes through the holes 52 in the front end of the cooling jacket and the annular space 54 after the cooling jacket to the water outlet 56.
Return to

Although the invention has been described by way of example with reference to preferred embodiments, it is understood that the invention is not limited to such embodiments, but that other alternatives are intended to be included within the scope of the appended claims. should be understood.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a plasma torch according to the invention.

FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1.

[Explanation of symbols]

10　Back electrode 12 Front electrode 14 Housing rear 16 Front part of housing 28 Water guide device 30 Circular passage 32 Cooling jacket 48 Annular passage 58 insert 59 insert 62 Vortex generator 66 Insulated pipe 73 Expansion part 74 Shrinkage part

Claims (6)

[Claims] 1. A plasma torch comprising: a) a torch housing (14, 16); b) a tubular insert of refractory material ( 58, 59) with a rear tubular electrode (10) and an anterior tubular electrode (12), c)
a vortex generator (62) for introducing a tangential flow of gas in opposite directions into the tubular electrodes through the gap between these two electrodes; and d) a cooling system for cooling these tubular electrodes. plasma torch. 2. A plasma torch according to claim 1, further comprising: a plasma torch mounted within the housing (14, 16), and wherein the plasma gas is connected to the cooled electrodes (10, 16);
12) A plasma torch including a plasma gas supply system including an insulated tube (66) to prevent condensation on it. 3. Plasma torch according to claim 1, wherein the front electrode (12) comprises a cup-shaped outlet section comprising an expanding section (73) followed by a contracting section (74). 4. A plasma torch according to claim 1, wherein the refractory electrode material is thorium tungsten. 5. The plasma torch according to claim 1, wherein the refractory electrode material is a tantalum carbide composite comprising tantalum carbide impregnated with aluminum or copper. The material is a plasma torch. 6. A plasma torch according to claim 1, 2 or 3, wherein the cooling system comprises a water guiding device (28) surrounding the rear electrode (10).
, a brass cooling jacket (32) surrounding the front electrode (12)
and a cooling jacket between the water guiding device (28) and the rear electrode (10) for circulating a cooling liquid in heat exchange relationship around the rear electrode (10) and then around the front electrode. (32) and the annular passageway (
30, 48).