Abstract: An arc plasma torch having a tapered-bore electrode provides a long, columnar plasma arc. The torch includes a torch housing, a tapered-bore electrode, a gas-constricting nozzle, and a swirling gas flow generator.The electrode is mounted within the housing and has a closed inner end and an open outer mouth. The electrode has a longitudinally extending, tapered bore. The bore has its largest dimension at the mouth. The nozzle has a bore and is also mounted within the housing. The nozzle is in axial alignment with, forwardly spaced with respect to and insulated from, the tapered-bore electrode. The torch introduces a swirling flow of gas at a location intermediate the electrode and the gas-constricting nozzle, resulting in gas flowing past the electrode during use of the torch. In operation, an electric arc emanating from the electrode ionizes the gas flow.

Abstract: The disclosure is made for the use of a hearth for receiving metals to be melted and exposing the molten metals to the furnace atmosphere with the upper surface of the molten metal free to float impurities such as oxides, carbides, or other undesirable materials on the upper surface of the molten metal or alloy. Gas jets blow an inert gas in one direction over the upper surface of the molten metal, generally parallel to the upper surface of the molten alloy. Thus, the gas jets remove impurities from the upper surface of the molten alloy by blowing or skimming the impurities off the top of the pool toward the walls of the hearth. The preferred position of the gas jets is in the notch of the hearth over which the molten alloy flows from the main body of the hearth into a withdrawal crucible.