US 3139509 A
Description (OCR text may contain errors)
June 30, 1964 J. A. BRowNlNG 3,139,509
ELECTRIC ARC TORCH Filed May 7, 1962 2 Sheets-Sheet l EH A22 lll 23 im *ff @y2 W w iii @3,6
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ELECTRIC ARC TORCH Filed May 7, 1962 2 Sheets-Sheet 2 BY www) MQW 3,139,509 ELECTRIC ARC TORCH J ames A. Browning, Hanover, NH., assigner to Thermal Dynamics Corporation Filed May 7, 1962, Ser. No. 192,746 4 Claims. (Cl. 219-75) My invention relates to electric arc torches and relates more particularly to such torches in which plasma forming gases are used in conjunction with an electric arc to provide a source of extremely high temperatures.
Plasma torches conventionally consist, basically, of two electrodes between which an arc column is established. Gas is made to iiow along the arc column, and is thereby heated, often to the plasma state. Such devices may be used kfor cutting, plating of fused materials, chemical synthesis, wind tunnel re-entry simulation, and variety of other commercial and experimental applications.
Prior arc torches of the type under discussion have utilized a ow geometry in which all the gas flows uni-directionally through the nozzle passage from the cathode, or electron emitting electrode. A device of this general type is exemplified by U.S. Patent No. 3,027,446, issued March 27, 1962, to lames A. Browning et al.
Such a uni-directional ilow pattern presents some in-y herent problems. In particular, any electrode erosion (and erosion is almost always present) serves to contaminate the effluent plasma. Secondly, gas owing in a single axial direction often cannot be made as effective use of as two directional gas streams.
My invention, therefore, is directed to providing an improved electric yarc torch in which the gas stream is divided to flow in opposite directions. For the particular advantages accruing from such a novel arrangement, and for a better understanding of the invention, reference to the following detailed description and accompanying figures should be made. In the figures:
FIGURE 1 is a schematic view, partly in section, kof a torch embodying the principle of the invention;
FIGURE 2 is a torch, in section, in which the invention is applied to the transferred mode of operation;
FIGURES 3a and 3b are simplified schematic views of electric arc torch elements to explain the mechanism of gas stabilization;
FIGURE 4 illustrates still another embodiment of the invention using two hollow electrodes;
FIGURE 5 is a view, in section, of a torch employing the invention to provide a supersonic jet stream; and
FIGURE 6 is a graph plotting current in amperes against pressure in a device of the type shown in FIG- URE 5. f
Referring now more particularly to the drawings, the torch of FIGURE l employs two nozzle sections 10 and 11. They may be separated by a ceramic swirl ring 12. The ring 12 is employed to impart a vortex flow of gas introduced to the torch through aperture 13 as shown. The action of ring 12 is fully explained in U.S. Patent No. 3,027,446, issued March 27, 1962, to the present inventor. In this case, however, the swirling gases divide at the ring 12, a portion entering the nozzle 10 and a portion entering the nozzle 11.
An arc is established between the nozzle 10 and a cathode 14 by means of a suitable power supply 15. The arc is stabilized and contained by the gases flowing as described above. The arc electrons are emitted at the arc spot 16 on the cathode 14, which is preferably made of a refractory material. The gas is heated by the arc and issues from the nozzle 10 in the form of a plasma flame 17. However, it is clearly evident that the gas flowing toward the cathode 14 (through nozzle 11) is also heated. The heat in this counter-flowing stream must be considered lost, and it is therefore advisable to UnitedStates Patent() 3,139,509 Patented June 30, 1964 ICC minimize the percentage of total available heat entering suchstream. Accordingly, I keep the length of nozzle L11 to a minimum. The major voltage drop thus occurs along the arc in the direction of ow in the nozzle 10.
In any torch, erosion of the cathode occurs at a rate depending on torch design, power levels operated, and other factors. The eroded cathodekmaterial invariably forms a part of the efuent in prior arc torches. In many applications a pure, electrically neutral plasma llame is desired. In the torch of FIGURE l the divided portion of the gas stream which travels toward the cathode 14 k carries contaminants out and away from the working end of the device represented by nozzle 1l). Furthermore, the cathode spot 16 operates in a region of relatively low pressure with attendant advantages discussed below in connection with FIGURE 6.
In FIGURE 2, a torch is shown having two nozzles 20 and 22. In this case, the swirl ring 12 again divides the gas stream, with the working portion flowing through nozzle 22 toward a workpiece 23 to which heat is being applied. The workpiece 23 acts as the cathode. It should be pointed out here that the torch of FIGURE 2 is operating in what is called the transferred mode, in which the arc is not wholly contained within the torch as in yFIG- URE l.
The necessity of providing this double iiow of gas is better understood by an appreciation of the mechanism of gas-stabilization of an arc within a passage. The FIGURES 3a and 3b are identical except for the direction of gas flow. Let it be assumed that an arc length as shown strikes from cathode 25 to point A, and that this arc length is desired. In FIGURE 3a, the gas flow (shown by the arrows) tends to sweep the arc further down in the nozzle passageway toward point C. This tends to lengthen the arc, thus tending to increase the arc voltage. An essentially stable condition is thus created and a balance between gas action and arc voltage is maintained.
In FIGURE 3b, on the other hand, gas iiow (again shown by arrows) tends to drive the arc towards point B. The arc column length drops and the condition is unstable. Thus it is seen that gas passing through an arc region must ilow in that direction which tends to increase the arc voltage. Referring again to FIGURES l and 2, the situation is arranged in both cases so that in the nozzle passage where the arc strikes to the passage wall, the gas is flowing in the direction which produces arc stability.
In the case of FIGURE 2 this permits use of the workpiece 23 as the cathode, and substantially no cathode materialy contaminant can enter the torch body due to the direction of gas ow. Also, reactive gases, such as air or other mixtures containing oxygen may be used with torch deterioration being kept at a minimum. Cathode deterioration, where the cathode is a workpiece being cut,
- may actually be desirable, and the dual directional ow of gas provided by my invention makes this advantage also realizable.
In FIGURE 4 I provide a torch with two nozzles 30 and 32 of equal length. An arc is established as shown by a suitable power supply 34 which may be A.C. or D.C. current. A swirl ring 36 shapes the incoming plasma forming gas into two diverging vortices. With the principles discussed in connection with FIGURES 3a and 3b in mind, it will be seen that the ilow in the two opposite directions provides a stable arc running from rpoint X to point Y. The useful eiuent of the torch of FIGURE 4 is divided into two parts, of course, represented by llames 38 and 40. This is of no moment in some applications, such for example as in the use of heat for chemical synthesis. If desired, curved nozzle passages may be employed thus combining the two llames of FIGURE 4 into one.
An additional feature of the multi-flow design is its ability to operate at extremely high gas pressures. The major limitation on prior high pressure arc torch operation has been electrode erosion. Using the principles of my invention, the electrodes may be placed outside the region of high pressure. This can be best appreciated from a study of FIGURE 5.
In FIGURE 5, a torch is used to create a supersonic jet stream for introduction into an evacuated chamber. Hollow electrodes and 51 are electrically and geometrically separated and positioned by a ceramic piece 52. The piece 52 also serves as the gas injector and has a tangentially disposed injector hole 55 asy shown. Gas is introduced through the manifold piece 53 via hole 54. The gas splits into two streams within the torch. One portion flows towards a supersonic nozzle section 58 and is discharged into the vacuum chamber 60 to form a supersonic jet 61.
The remaining gas ows in the opposite direction through hole 57 in piece 50. Assuming piece 50 to be serving as the negative, or cathode, electrode, the arc is seen to issue to form the fountain geometry 63. The cathode spot 64 is contained in an environment of much lower pressure than would be experienced within the torch body, thus allowing for the use of much higher amperages.
In FIGURE 5 the arc column strikes the anode within the high-pressure region. Anode action, however, is less prone to high-pressure diliiculties. In severe cases the geometry of the nozzle at 5S can bevchanged to provide for arc passage through the nozzle to strike and terminate in a fountain configuration in the low-pressure region beyond the nozzle opening. In any case it will be appreciated that my invention provides, in the caseof FIGURE 5, the dual advantage of no cathode contamination of the useful eluent, and the operation of the electrodes in low pressure regions.
The benets of this latter advantage can be seen from the graph of FIGURE 6. Here is shown actual experimental data of the effect pressure (in the cathode region) has on the allowable maximum current ilow. Operation at atmospheres is limited to less than 300 amperes. A device operating at such parameters would require an arc voltage drop of over 3000 volts to produce one megawatt of power. If the electrodes were to be operated at approximately one atmosphere at 3000 volts torch output could be raised to 10 megawatts. Any reduction in electrode-region pressure is desirable and my dual flow invention makes this result a practicality.
While I have illustrated a few applications of the basic principles of my invention, these have been discussed by way of explanation; and within the spirit and scope of the following claims modifications and further applications may occur to those skilled in this art.
I claim: l 1. A transferred arc torch comprising a nozzle shaped electrode having an arc passage, means for establishing an arc between a work piece and said electrode, and gas means for stabilizing said arc in said passage with gas directed from a point along said passage toward said work piece and simultaneously toward the terminal point of said varc on said electrode.
2. A double-ended electric arc torch comprising a pair of nozzle shaped electrodes having arc passages therein, said electrodes being arranged with their nozzles on the same axis; means for establishing an arc within said passages and between said electrodes; and means providing a split gas flow from a point between said electrodes into both said passages to stabilize said arc.
3. A torch according to claim 2 in which said arc passages are curved such that the two effluents (from each end of said torch) are directed less than degrees apart.
4. An electric arc torch comprising a lirst electrode in annular form, a second elongated electrode having a nozzle passage, a gas swirl ring of insulating material separating said electrodes, means for establishing an arc between said electrodes, and means for introducing gas to dow in opposite directions from said swirl ring into said passage and through said rst electrode.
References Cited in the lile of this patent UNITED STATES PATENTS Re. 25,088 Ducati et al Nov. 21, 1957 2,806,124 Gage Sept. l0, 1957 2,922,869 Giannini et al Jan. 26, 1960 2,967,926 Edstrom Ian. 10, 1961