GB1209672A - Plasma-jet generation - Google Patents

Abstract

1,209,672. Cutting by fusion. MONTECATINI EDISON S.p.A. 8 Feb., 1968, No. 6220/68. Heading B3V. [Also in Divisions B2, C7, H2 and H3-H5] A plasma-jet generator, e.g. for spraying powder or cutting metal having a nozzle anode 13 spaced by insulator 4 from a tapered cathode 5 is so constructed that the nozzle anode 13 and cathode 5 may be removed in one direction and the cathode alone can be removed in the opposite direction. In the spray-gun shown the anode 13 and cathode 5 may be removed in one direction by removing a front casing part 22 from a central casing 9, removing an anode tightener ring 14 to allow withdrawal of the anode 13 and unscrewing the cathode 5 from member 2. If desired, the cathode 5 may be removed with member 2 in the opposite direction by removing a rear casing part 23 from the central easing 9. The generator has a hollow supply lead 1 through which cooling water flows to cathode 5, passages 60 in the insulator 4, passages 32, 33 in anode 13, passates 12 in an anode support and hollow anode supply lead 17. The insulator 4 is additionally cooled by an air jet from pipe 21 which flows around the insulator 4 and passes out through a slot between the central casing 9 and the anode support 10. A shielding gas is supplied from a tube 24 to an annular aperture 25 between anode 13 and tightening ring 14. A powder injection tube 16 communicates with the anode nozzle. The arc gas is supplied from a pipe 18 which injects gas tangentially into vortex arc chamber 19 whose walls are provided with a ceramic radiation shield 8. An auxiliary electrode is provided for initiating arc discharge. Wear of the tungsten tip of cathode 5 may be compensated by inserting washers into an interfacial zone 6 of the cathode 5 and member 2. Instead of the nozzle exit being perpendicular to the length of casing 9, 22, 23, it may be at 45 degrees thereto or parallel therewith (Figs. 6 and 7 or 8 and 9 respectively). Interchangeable anode and cathode arrangements may be provided for various applications. The tip of cathode may be cropped flat or arcuately as shown (various radii are specified). The tapers of anode and cathode are specified for various applications. The plasma generator may be operated in any of the following modes: totally transferred arc plasma; totally non-transferred; predominantly transferred; or predominantly non-transferred. The supply circuit may include a fuse in the anode nozzle supply. Fluid to cause the generator to change from the non-transferred mode to the totally transferred mode after initiation of the plasma (Fig. 14, not shown). Two rectified power supplies may be used (Figs. 17-19, not shown) to provide predominantly non-transferred, predominantly transferred, or totally transferred operation. The torch, adapted as in Figs. 12A-12C (not shown), and operating in the totally or predominantly transferred mode is used for rapid cutting of metals or alloys. Argon, or a mixture of argon and hydrogen or argon and nitrogen are used as the plasma forming gas. Aluminium, copper and stainless steel may be rapidly cut, using a 50-50 argon-nitrogen gas mixture, a 66<SP>2</SP>/ 3 -33<SP>1</SP>/ 3 argon-nitrogen mixture, and a 66<SP>2</SP>/ 3 -33<SP>1</SP>/ 3 argon-nitrogen mixture respectively. The torch may be operated in the non- transferred mode for slower cutting.