Abstract: The invention is a method and apparatus that comprises supplying a mixture of gases to a constricted plasma arc. The mixture comprises a gas that will sustain the plasma arc at the lower voltages typical of electric-arc welding and in the absence of a plasma and a gas which provides good heat transfer characteristics. The relative proportion of the gas that will sustain the plasma arc at the lower voltages present in the mixture is large enough to support the plasma arc, and the relative proportion of gas having good heat transfer charactristics present in the mixture is small enough to prevent failure of the arc at the lower voltage. A voltage drop is maintained which is high enough to maintaing the plasma arc using the gas mixture while low enough to operate at a substantially constant current using a low voltage constant current power supply.

Abstract: A tuyere is disclosed which is adapted for the injection of gases into a metallurgical vessel. The tuyere includes inner and outer concentric tubes having a radial separation therebetween which defines an annular gap. In use, one gas such as an oxygen mixture flows through the center of the inner tube, and a second normally inert gas flows through the annular gap between the two tubes. In order to provide a closely predetermined and predictable gas flow rate through the annular gap, annular groove is formed in the wall of the outer tube which forms an annular restriction in the gap, and the extent of the restriction may be calibrated so as to provide a closely predetermined gas flow rate therethrough when in use. An annular groove may also be formed in the wall of the inner tube to provide a predetermined restriction in the gas flowing through the inner tube.

Abstract: Apparatus for scarfing defects in a metal workpiece having an oxygen discharge nozzle terminating in a nozzle discharge orifice adapted to discharge a sheet-like stream of cutting oxygen of uniform intensity across the surface of a metal workpiece and means for admixing a gas with the oxygen to be discharged through the discharge orifice wherein at least one edge of the sheet-like stream of oxygen is of reduced privity insufficient to scarf a workpiece, while the remainder of the sheet-like stream is sufficient to scarf defects from a workpiece surface.

Abstract: Supplemental electrode cooling mechanisms are provided for a plasma arc torch, which mechanisms form a part of the gas flow mechanisms through the torch head for circulating the flowing gas through the current transfer assembly of the torch in direct contact with a maximum portion of the entire longitudinal extent of the surface of the upper portion of an electrode received within the current transfer assembly for additional cooling of the electrode to increase the life thereof, while maintaining desired seating of the electrode in the current transfer assembly and transfer of current to the electrode from the current transfer assembly.

Abstract: An instantaneous scarfing cut on the surface of a metal workpiece can be made by:(a) causing relative motion between the workpiece and a stream of scarfing oxygen gas, and simultaneously therewith(1) impinging at least one laser beam on the work surface so as to produce a heated path of desired length across said surface relative to its direction of motion, said heated path being produced by the laser beam heating a series of points on said surface to their oxygen ignition temperature, and(2) impinging a stream of scarfing oxygen onto said heated path, thereby causing an instantaneous scarfing cut to begin along said path, and(b) continuing the flow of scarfing oxygen until the desired length of cut has been produced.