US3472995A - Electric arc torches - Google Patents

Description

Oct. 14, 1969 BRQWNING ET AL 3,472,995

ELECTRIC ARC TORCHES Filed Aug. 8, 1966 2 Sheets-532'? 1 29 I 2 JAMEJA fifiow/m/a (AW *0 WW Oct. 14, 1969 J. A. BROWNING ET AL 3,472,995

ELECTRIC ARC TORCHES Filed Aug. 8, 1966 2 Sheets-Sheet 2 LAM-'5 A. 5/?0 w/w/ve O/A P/A/A. PM 77 @4 I fWO MJIW United States Patent Ofice Patented Oct. 14, 1969 US. Cl. 219-75 1 Claim ABSTRACT OF THE DISCLOSURE Plasma generating arc torches in which an arc is passed between two electrodes. The two terminal portions of the arc length are confined in nozzle passages for a distance from each electrode and they are gas stabilized therein. The central portion of the arc length extends beyond the nozzles into a plenum chamber in one embodiment, Where hot, ionized gases issue through a discharge throat from the chamber. In alternative embodiments, the central portion extends directly from the nozzles such that the ionized gases issue directly into the atmosphere. They may be employed to melt substances for producing spray coatings, to clean wire and other surfaces, or for use in high temperature research.

Our invention relates to electric arc torches of the type capable of utilizing a plasma forming gas as a heat transfer agent and are stabilizing means. Our invention relates more particularly to improvements in such torches wherein the arc column extends out of the torch body proper into the atmosphere.

Electric arc torches which are operated with the arc column partially outside the torch are well known and have found increasing acceptance and utilization in a wide variety of industrial and research applications. There are two general modes of operation in which the arc column itself leaves the torch. In one, the object to be heated or otherwise treated forms a part of the arc circuit and the arc is then termed transferred; that is one terminus of the arc is an electrode in the torch, whilst the other terminus may be the workpiece external to the torch.

. The second mole, and the one with which this invention is primarily concerned is called non-transferred. characteristically, the non-transferred torch has a cathode and an anode in the form of a nozzle. Practical considerations make it desirable to keep the arc within the nozzle, with the arc terminating on the inner nozzle wall. If an extended arc is desired, the arc column must go through the nozzle, into the atmosphere, and then fold back, establishing a terminus on the external face of the torch. This method of operation, though it provides the advantages of an extended (yet non-transferred) arc, results in rapid deterioration of the nozzle face. This is very evident when it is realized that the electrode spot (usually the anode) is thus heated to elevated temperatures in the presence of the oxidizing gas of the atmosphere.

The purpose of our invention is to retain the advantages of an arc extended into the atmosphere, yet operate in the non-transferred mode.

For a more complete understanding of our invention reference is now made to the accompanying drawings in which FIGURE 1 is a representation of a prior arc torch;

FIGURES 2, 2a, and 2b and 2c are representations of torches of the invention as applied to a practical work heating problem;

FIGURE 3 is a view, in section of an improved torch as applied to the spraying of fusible materials; and

FIGURE 4 is a torch similar to that of FIGURE 3 used as a plasma flame generator for wind tunnel and other research applications.

Referring now more particularly to FIGURE 1, and with the foregoing discussion on non-transferred, extended arc torches in mind, it will be seen that an electrode 13 and a nozzle electrode 14 are electrically separated by a ceramic element 15 which defines with the rearward portion of the electrode 14 and plenum chamber into which a plasma forming gas may be tangentially introduced at inlet 16. An arc column is established and supported by a suitable power supply 11 and is stabilized and extended to return, fountain like to the face of the nozzle as shown by the column 18. Rapid erosion, due to exposure to the atmosphere, is depicted at 19. This erosion may be avoided by utilizing a nozzle of greater length, within which the arc may actually terminate. However, the advantages of an are extending free of the torch cannot then be realized. Furthermore, heat losses by radiation to the nozzle wall (and thence to water cooled jackets usually provided for) become prohibitive as this heat energy is not usefully applied outside the torch as in the case of the extended arc.

To overcome these difliculties we provide a torch combination comprising two electrodes (as before) but with each electrode in a protected environment at the arc terminal points. One possible arrangement is shown in FIGURE 2 where an extended arc, free of the torch elements, impinges on a workpiece which is not serving as a current return to the power supply as in known types of transferred arc torches.

In FIGURE 2 is shown a power circuit comprising suitable power supplies 29 and 30. A common lead joins the supplies, and leads 32 and 39 connect to torch electrodes 28 and 13 respectively. The electrode 13 may serve, for example, as a cathode mounted in a shell 14 which defines a plenum chamber and a nozzle-like opening as shown. A suitable gas may be introduced tangentially around the electrode 13, and said gas is then emitted as a stabilizer for the arc column 24a and also to form a plasma stream along the column 24a. Similarly, the electrode 28 is arranged to serve as an anode, and the electrically positive arc terminus is positioned within the electrode 28 and may impinge on the shoulder as at 25. A plasma forming gas is also introduced tangentially to produce a stabilizing vortex, and this gas is also emitted toward the work piece 23 while maintaining the remaining portion of the arc column 24b. The anode spot on the shoulder 25 is well away from exposure to the atmosphere and it may be rotated by the gas or in combination with a magnetic field established by the coil 26, thus further reducing erosive effects at any one point.

The configuration of FIGURE 2 is useful in the tempering, cleaning, or otherwise treating elongated object like mill stock which may be passed along through the column of arc and hot gases. For small diameters the arc column usually divides and flows around the work piece. For larger diameters, and depending on parameters like surface condition and conductivity of the work piece material, the electrical circuit may be completed through the work piece with the are divided into two distinct sections as in FIGURE 2a. If this action is for any reason desirable, it can be induced in any case by the arrangement of FIGURE 2b where the electrode pair is offset by a distance d to create an electrical condition resulting in electron conduction in the work and a pair of distinct arc segments. It is important to note that under all these conditions, FIGURES 2, 2a, or 2b, the work piece is electrically isolated from the power supply and conventional transferred arc considerations do not apply. For even higher level of heating, and for large rods or tubes, multiple pairs of torches may be arranged as shown schematically in FIGURE 2c. v

Referring again to FIGURE 2, it will be appreciated that each section of the torch has an independent current return through resistors R-1 and R-2 such that pilot arcs can be struck before the main flow of gas is introduced, leading to the establishment of the main external arc column 24a-24b.

In cases where the process must be carried on in inert or otherwise special environments an envelope may be provided as shown by the dashed lines in FIGURE 2b.

The general approach afforded by our invention also finds a useful embodiment in an integral torch of FIG- URE 3, where as before the arc termini are protected and yet a substantial proportion of the arc column is freely extended into the atmosphere. Here the configuration and circuitry permit a common starting resistor R-3 for pilot arcs. The main body element 33 forms two chambers terminating in two passages 34 and 36. The electrodes 32 and 37 are electrically isolated by ceramic spacers, and gas is introduced, preferably tangentially as shown, to stabilize the arc column 35 at its two terminal regions. While both electrodes 32 and 37 are shown with truncated tips and are identical, it is often desirable for one to be as shown (serving as the cathode) and the other as an anode with a structure like that of electrode 28 in FIGURE 2. Thus optimum structures are possible at each arc terminus.

With resistor R-3 of sufficiently high value, the main are column will extend outwardly from the torch along with the flowing gas from each passageway, much of it in the plasma state. I

The torch of FIGURE 3 is useful as a heat source in combination with means for feeding wires or powders into the arc column to be fused and then sprayed as coatings. The particular feeding means must be adapted to the form of the material being sprayed, and we have shown for illustrative purposes a pair of powered rollers 42 which drive a continuous wire 40 into the arc apex at 28. The wife 40 is fused and carried by the plasma stream as at 41 and may be directed against a surface to be coated. Powdered material'may be transported on a carrier gas into the arc column, as is well understood in the art of flame spraying. The arc developed by our torch, with its substantial length outside the torch body makes it particularly suitable for the spraying of materials. This is so because the materials can be introduced into the system without interfering in any way with the nozzle passage themselves. The long external arc provides heat which is not dissipated in the torch body, and the plasma further contributes to the transport of the fused material. At the same time, each arc terminal is in a protected zone within the torch and the long electrode life necessary for a practical spraying operation is assured.

The arrangement of FIGURE 4 is an adaptation of FIGURE 3 suitable for producing high temperature gas streams for re-entry studies and other research applications. Plasma streams issuing from nozzle passageways 50 and 51 easily merge as they are nearly parallel, and are further heated by the long arc column 45 formed in the plenum volume 47. The stream 46 passes through throat 48 and expands at supersonic velocity to form the jet 49. Such a torch may be used in connection with a vacuum chamber, for example, to test materials for space vehicles. It is also an efficient heat source useful in chemical synthesis, metallurgical processes and the like.

As in FIGURE 3, the two electrode-nozzle elements in FIGURE 4 need not be identical, and indeed, in most cases should be shaped to optimize conditions. For example, one electrode may be as shown (a typical cathode configuration) and the other electrode may be in cavity form as shown by electrode 28 in FIGURE 2, to serve most efiiciently as an anode.

While we have described our invention with reference to particular embodiments, the descriptions are merely illustrative, and further variations and adaptations within the spirit and scope of the invention as claimed may occur to persons skilled in this art.

We claim:

1. Electric arc torch apparatus comprising a first electrode-nozzle element; a second electrode-nozzle element spaced from said first element to define an arc path therebetween extending in part into a plenum chamber;

electrical power means for establishing and maintaining an electric are between said elements; gasmeans at each element for stabilizing the arc within the nozzle portion of each electrode-nozzle element before said are extends into said chamber; and a plasma delivery aperture leading from said chamber.

References Cited I UNITED STATES PATENTS 2,903,559 9/1959 Wempe 2l975 2,923,811 2/ 1960 Feldmeyer et a1.

3,324,334 6/1967 Reed 219-121 X 3,147,329 9/1964 Gage.

JOSEPH V. TRUHE. Primary Examiner J. G. SMITH, Assistant Examiner U.S. c1. X.R. 219-76, 121

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