GB943793A - Electric arc apparatus and processes - Google Patents

Abstract

In an arc torch a highly heated arc-and-gas stream flows at high velocity from a constricting passage 8 into an expansion-and-mixing chamber 12 into which additional matter can be introduced through at least one inlet port 13, and the chamber 12 is so designed that the resulting effluent is discharged without any sudden constriction. Erosion or contamination of the main electrode 6 and the passage 8 and erosion of the outlet from the chamber 12 are thus avoided, particularly when the additional matter is powdered refractory material. The torch shown is intended primarily for spraying metals and refractory materials and comprises a rod electrode 6 of tungsten, preferably coated with zirconia, held by a collet 5 in a water-cooled holder 4 mounted in an upper body 1 of insulating material which is clamped by a ring 3 to a lower body 2 in which is mounted a water-cooled annular electrode 7 defining the passage 8. The water-cooled chamber 12 which may be cylindrical, slightly divergent, or preferably <PICT:0943793/C3/1> slightly convergent as shown, is made of copper and may include a refractory lining (not shown). The torch is started by establishing a pilot arc between electrodes 6 and 7 by applying a h.f. potential, and then operates on D.C. Inert gas, preferably argon, is supplied through the collet 5. Powdered metals such as tungsten, zirconium, tantalum and copper, or refractory materials such as alumina, magnesia, zirconia and tungsten carbide or alloys such as nickel-chromium-boron are introduced tangentially through the port 13 and are sprayed in liquid or vapour form on to for example a metal workpiece which may be connected to the positive pole of the arc supply to act as an electrode if additional heating of the workpiece is required. Dimensions of the apparatus are given. The workpieces which may be coated are copper, iron or tungsten.