US3375392A - Plasma generator utilizing a ribbonshaped stream of gas - Google Patents

Description

March 26, 1968 w. BRzozows g ET AL PLASMA GENERATOR UTILIZING A RIBBON-SHAPED STREAM OF GAS 2 Sheets-Sheet 2 Original Filed March 8, 1965 Attorney United States Patent 3,375,392 PLASMA GENERATOR UTILIZING A RIBBON- SHAPED STREAM 0F GAS Wojciech Brzozowski, ul. Kniers 23/31 m. 72, and Janusz Reda, pl. Henkla 6 m. 19, both of Warsaw, Poland Continuation of application Ser. No. 437,745, Mar. 8, 1965. This application Apr. 26, 1967, Ser. No. 634,005 Claims priority, application Poland, Mar. 7, 1964, P 103,947 4 Claims. (Cl. 313-231) ABSTRACT OF THE DISCLOSURE A plasma torch having a central electrode surrounded by an annular gas chamber with an axial outlet in line with the central electrode and a nozzle tangentially entering the chamber for admitting a gas tangentially into the latter. The nozzle has a narrow slot in a radial plane of the annular electrode so that the gas is discharged in a flat ribbon into the chamber This application is a continuation of our application Ser. No. 437,745 filed Mar. 8, 1965 (now abandoned).

Owing to the considerable thermal capacity of nitrogen, nitrogen-operated devices of the type known by the trademark Plasmatron constitute high-power plasma generators. Depending on the manner of operation, i.e. with non-transferred or transferred arc, such Plasmatrons may produce temperatures of the order of 10,000 or 20,000 C., respectively. They serve mainly for metallurgical purposes, cutting metals, and spraying with particularly hard-to-melt powders as well as for chemical analysis and synthesis. Modern Plasmatrons operate on the principle of vortex gas flow, a fact which affords a higher flow stability than that obtainable in the previously used axial-flow Plasmatrons. The Plasmatrons known at present are characterized by a complicated design, and they usually incorporate a ceramic piece located between the anode and the cathode, this piece being provided with small vortex grooves which serve to impart a whirling motion to the gas. Fitting such ceramic pieces tightly in position is difficult; moreover, they are subject to frequent fractures as a result of rapid changes in temperature. The cathode of known Plasmatrons represents a body, generally made of copper, which terminates in a holder for a tungsten point. This cathode is internally cooled with water, the mounting of its end on the ceramic piece preventing the holder for the tungsten point from being cooled additionally by a gas flow. This is determined for the service life of the cathode. The vortex grooves of the ceramic piece have a considerable cross-section, thus causing an increase in the gas mass rate of flow, as well as difiiculties in obtaining high-temperature plasma, coupled with the necessity of substituting a short Plasmatron nozzle for a long one when changing the operation from the transferred-arc to the non-t-ransferred-arc mode Moreover, the vortex grooves of oval or circular crosssection make it impossible to obtain a uniform flow of whirling gas and a uniform distribution of pressure, thus causing the arc to strike at locations of reduced pressure, offset from the cathode axis, which tends to damage the cathode.

The Plasmatron according to our invention is free from any of the disadvantages referred to above; furthermore, it is simple and durable in design. Whirling motion of the supplied nitrogen is achieved by the provision of a metallic slotted gas nozzle positioned tangentially to the Plasmatron gas chamber. A rectangular slot at the nozzle outlet ejects a flat ribbon of nitrogen situated in a plane perpendicular to the gas-flow axis, thus creating optimum aerodynamic conditions of flow, with minimum pressure along the axis of the tungsten piece. This ensures proper ignition of the Plasmatron from the center of the tungsten piece. The metallic nozzle and the slot are of reduced size compared with those of an equivalent nozzle of ceramic material, a fact which affords a decreased rate of mass flow and, in consequence, a higher temperature of the plasma with given electric parameters. The decrease obtained in the rate of mass flow enables also the same Plasmatron nozzle to be used for operation with both non-transferred and transferred arc as more fully described hereinafter.

The construction and the principle of operation of the Plasmatron according to our invention will now be explained with reference to the accompanying drawing wherein:

FIG. 1 represents the Plasmatron in longitudinal section;

FIG. 2 is a transverse section along line II-II of FIG. 1;

FIG. 3 represents the gas nozzle as viewed on the line III+III of FIG. 2; and

FIG. 4 shows water circuits in the nozzle body seen in section along line IVIV of FIG. 2.

S represents a DC supply unit, R is an electric resistance, M is an external anode, Z and Z; ;are switch contacts. When operating the Plasmatron with the nontransferred-arc mode (dot-dash lines), switch Z is in horizontal position to disconnect the auxiliary anode M, switch Z being opened. When operating the device with the transferredarc mode (full lines) switch Z is situated in vertical position, switch Z being closed to provide a resistive path for the energization of a main anode 14, 15 to which an arc lit between anode M and a cathode (described below) is subsequently transferred. Nitrogen is fed to the Plasmatron through a flexible hose 1 leading to a gas nozzle 2 terminating in a slot 2 (see FIG. 3) positioned tangentially to a gas chamber 3. The chamber contains a tungsten piece 4 soldered into a copper holder 5. Tangential feeding of nitrogen at a pressure of 6 to 7 atmospheres creates a vortical flow in the space between the conical end of the chamber 3 and the conical holder 5 situated in that chamber. Cooling water is introduced by a flexible hose 6 through the length of which runs a power cable 7. Flexible hose 6 terminates in a threaded nipple 8 which receives, by a soldered joint, the cable 7. Nipple 8 of flexible hose 6 is screwed into a cathode body 9 which terminates in a pipe 10 feeding water to the interior of holder 5. The cathode body 9 and flexible hose 6 are secured to a cathode sleeve 11- by means of a nut 12. The water, after leaving holder 5, flows through an insulating spacer 13 into a support 14 for an ejection nozzlelS forming part of the anode. Water flowing through the body 14 sweeps past the Plasmatron ejection nozzle 15, next enters a pipe 16, and finally, via a threaded nipple 17, flows into a flexible hose 18 discharging the water to a drain (not shown). The flexible hose 18 surrounds a power cable 19 which is soldered into nipple 17. The Plasmatron ejection nozzle 15 is secured to the support 14 by means of a nut 20 and is sealed by two rubber gaskets 21. The cathode assembly 4, 5, 9-12 is sealed by two gaskets 22. The ejection-nozzle support 14 is separated from the cathode sleeve 11 by spacer 13. Flexible hose 1, supplying nitrogen, and water pipe 16 pass through a plate 23 which is traversed by three tubes 24, 25 and 26. Insulating spacer 13 is screened by a nickel-brassplate coating 27 protecting it against the radiation of the electric arc. The Plasmatron is provided with a housing, which consists of a casing 28 for the ejection-nozzle support 14, a conical ring 29, a casing 30 protecting the flexible hoses, and an insulating shield 31 lining the inner surface of the latter.

elect-rode transverse to its axis and communicates with an axially extending bore 33 receiving the conduit 1 through which the nitrogen gas is admitted into the annular interelectrode space defining the gas chamber 3. Inlet nozzle 2, which has a closed outer end, is received in channel 32 and has a lateral aperture 2a (FIG. 1) through which the conduit 1 enters the nozzle to communicate with its slot 2'. This narrow slot 2 (FIG. 3) has its dirnension of width extending, together with its dimension of length, within the aforementioned radial plane, i.e. the plane defined -by the section line 11-11 of FIG. 1, and has a height perpendicular thereto which is substantially less than its width, as best seen in FIG. 3. Moreover, as shown in FIG. 2, slot 2' is bounded by an outer edge 2b, which is substantially tangent to the outer periphery of chamber 3, and by an inner edge 20 on a line that is substantially tangent to the inner periphery of that chamber, i.e. to the annular extension 13' of spacer 13 surrounding the central electrode (cathode) 4, the two edges 2b, form a diverging discharge end for the nozzle 2 so that, as will be readily apparent from FIG. 2, the gas issues therefrom within the plane II-II in a fiat, thin ribbon occupying substantially the full width of the annular chamber 3 in which it whirls in a clockwise sense as viewed in that figure, spiraling with progressively decreasing pressure toward the axially extending outlet 34 (FIG. 1).

The cooling water introduced via conduit 6 and removed via conduit 18 flows through a passage 35 (FIG. 4) in spacer 13 before reaching a cavity 36 formed in the two-piece annular anode body 14, 15, this cavity extending around part of the chamber 3 and the outlet 34 for an effective cooling of the anode surfaces heated by the exiting gas.

We claim:

1. In a plasma generator having a central electrode and an annular electrode coaxially surrounding saidoentral electrode and defining therewith an annular' gas chamber, said annular electrode forming an axial outlet communicating with said chamber beyond and in line with said central electrode, the combination therewith of inlet means for admitting a gas with whirling motion to said chamber, said inlet means including a nozzle entering said chamber tangentially from without, said nozzle being provided with a narrow slot having its dimensions of width and length in a radial plane of said annular electrode transverse to the axis thereof and having a height substantially less than its width in a direction perpendicular to said plane whereby a fiat ribbon of gas is discharged in said radial plane from said nozzle into said chamber, said slot having a discharge end dimensioned to make the Width of said ribbon equal to more than half the width of said annular chamber.

2. The combination defined in claim 1 wherein said discharge end diverges outwardly in said plane.

3. The combination defined in claim 1 wherein said annular electrode is provided with a channel in said plane receiving said nozzle and with a larger axially extending bore terminating at said channel, said nozzle having a lateral aperture which opens into said channel, said inlet means including a conduit extending within said bore to said aperture for communication with said slot.

4. The combination defined in claim 1 wherein said annular electrode is hollow and forms a cavity around part of said chamber and said outlet, further comprising conduit means for circulating a cooling fluid through said cavity.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

S. D. SCHLOSSER, Assistant Examiner.

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