GB1160882A - Improvements relating to Plasma Torches - Google Patents

Abstract

1,160,882. Arc blow-torches. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 24 Oct., 1966 [25 Oct., 1965], No. 45096/65. Heading H5H. The unsymmetrical working of a plasma torch on A.C., normally resulting in increased electrode wear, is deliberately exaggerated by suitable selection of electrode materials and spacing in relation to the composition and rate of flow of plasma-forming gas so that electric arcs are struck only during similar half-cycles and the electrodes have the low-wear characteristics usually associated with plasma torches operated on D.C. For example, a pilot plasma is formed by injecting argon at 50 p.s.i. through inlet 14 and applying a rectified voltage between electrodes 10 and 2; nitrogen at 45 p.s.i. is fed through inlet 9 and forms the main plasma with unidirectional current flow from A.C. source 17 to electrodes 2 and 3. The electrodes 2 and 3 are of copper and the extensions 13 and 8, as shown, of thoriated tungsten, spaced respectively 9/ 32 inch and 5/ 32 inch from electrodes 2 and 3, and inlets 9 and 14 are of the order of 0À05 inch. The plasma may be used as a conductive column for transferred working on an electrically conductive workpiece or charge by making connections as in Figs. 2 or 3 (not shown). Two torches may be used to take full-wave current from the supply by cross-connection (as in Fig. 4, not shown) or by using a tapped transformer (as in Fig. 5, not shown), and the corresponding connections for transferred working are as in Figs. 6 and 7 (not shown). Transferred working without a fixed connection to the workpiece may be obtained by using four torches co-operating in pairs as indicated in Fig. 8 (not shown), or, for three-phase working, six torches as in Fig. 9 (not shown).