US3131288A - Electric arc torch - Google Patents

Description

Q, 1 Z 'StAhCH ROOM April 23, 1964 J. A. BROWNING 3,

\ ELECTRIC ARC TORCH File d Aug. 7. 1961 INVENTOR. I

"WWWW United States Patent 3,131,288 ELECTRIC ARC TORCH James A. Browning, Hanover, N.H., assignor to Thermal Dynamics Corporation, a corporation of New Hampshire Filed Aug. 7, 1961, Ser. No. 129,750 1 Claim. (Cl. 219-121) My invention relates to electric arc torches and relates more particularly to a torch in which a plasma forming gaseous element may be introduced to stabilize and be heated by a high-pressure electric arc. Such torches are well exemplified by the device shown in US. Patent No. 2,960,594, issued to Merle L. Thorpe.

In accordance with my invention, I propose to add to the conventional gaseous elements a liquid such as water. The resulting dual mixture is preferably introduced into a flow passage through which an electric arc is established. If this is done in such a way as to create a strong vortex, the heavier liquid particles will form a film on the inside walls of the arc passageway for purposes hereinafter explained.

It is, therefore, a principal object of my invention to provide improved means for operating arc torches using both liquid and gaseous elements.

It is a further object of my invention to employ the methods thereof with minimum modifications of known devices, thereby realizing the advantages at minimum expense.

For a better understanding of the invention reference is now made to the following detailed description and the accompanying drawing, in which FIGURE 1 is a torch of simplified design, in longitudinal cross section; and

FIGURE 2 is a plan view of a swirl ring element used in the torch of FIGURE 1.

Referring now more particularly to FIGURE 1, a torch body 11 is shown containing an electrode 12, a swirl ring 13 and a nozzle 14. These last three elements are held securely by means of a nut 15 threaded on to the end of the torch body 11. A tube 19 is used to supply a mixture of plasma forming gas and water (both under suitable pressure) through a slot 21 and thence into annular chamber 22 surrounding the electrode 12. The mixture travels through tangential slots in swirl ring 13, best shown in FIGURE 2, and enters the arc passage in the nozzle 14 in the form of a strong vortex.

An electric arc is provided by supplying the torch with a source of current, not shown, through lead 27, to the electrode 12. The electrical circuit is completed by the arc itself, shown at 17, the Work 25, and lead 26 connected to the source. It will be appreciated that the device is shown in the transferred mode of operation; that is, the Work acts as the second electrode. If it is desired that the are be wholly contained in the torch itself, the nozzle 14 may serve as the second electrode in which case the lead 26 would be attached thereto. Both of these modes of operation are well known in the prior art, and this invention is applicable in either case. In FIGURE 1, the device is shown being employed as a cutting torch applied to the work piece 25.

Before reaching the swirl ring 13, the liquid portion of the mixture introduced through tube 19 serves to provide a cooling film over the body of electrode 12. After entering the passageway of the nozzle 14, the centrifugal 3,131,288 Patented Apr. 28, 1964 forces set up by the action of the vortex drive the heavier liquid against the inner walls of the arc passageway. This film effectively cools and insulates the material of the nozzle from the heat of the are 17. The arc creates a plasma stream with the lighter gaseous element which remains nearer the center of the vortex. Since the cooling medium is on the interior surfaces of the nozzle pas sage it is possible to use materials of low thermal conductivity for nozzle pieces, such as ceramics.

The rapidly rotating film of cooling liquid passes downward (as seen on FIGURE 1) and emerges from the torch in a diverging spray cone 18. The shape of this cone may be controlled by vortex intensity, nozzle length, and nozzle exit configuration. I have found that the amount of divergence is important in many practical applications, since water emerging too close to the zone of operation may interfere with the heating (and in the case shown) and cutting action. However, it is sometimes desirable to provide a divergence just wide enough to avoid the desired heated zone, yet close enough to aid in cooling the work piece in the areas not to be heated. For example, in cutting thin metal plates the warpage of the sheet may be greatly reduced by supplying the cooling medium to the area immediately adjacent to the cut.

I have also found it desirable in some instances to suspend small particles of an opaque substance in the liquid supplied to the torch. Fine particles of silicon carbide, for example, further aid cooling action by markedly reducing radiation through the film. In addition, the intense glare of the arc extending from the torch is attenuated by the resulting cone of opaque particles and liquid.

The liquid provides a practical vehicle for opaque particles and I have found that the liquid film has much greater ability to constrict and thereby control the arc column than the use of a compressible gas alone. While this desirable action is not completely understood, I theorize that ionization levels in the annular region around the are are kept low and the arc is kept constricted much more effectively. Thus higher current densities with torches no larger than prior art devices are easily achieved.

While I have described a particular embodiment of my invention for illustrative purposes, modifications within the spirit and scope of the appended claims hereto may occur to persons skilled in this art. For example, instead of solid particles in suspension, a dye may be added to the liquid to increase its opacity. This is most effective in achieving the desired results.

I claim:

The method of operating an electric arc torch of the type described, in which one or more plasma forming gaseous elements are supplied under pressure to said torch, comprising mixing a liquid with said gaseous elements, and introducing the resulting mixture under pressure tangentially into the arc passageway of said torch to form a vortex driving the liquid portion of said mixture against the inner walls of said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 1,935,593 Wist Mar. 14, 1933 1,963,729 Alexay June 19, 1934 2,768,278 Gaines Oct. 23, 1956 2,768,279 Rava Oct. 23, 1956 2,906,858 Morton Sept. 29, 1959

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