Abstract: A plasma arc cutting torch and method for obtaining more efficient cuts underwater, and for muffling the noise and radiation of a plasma cutting torch when used above water, surrounds the plasma arc with high-pressure, high-velocity annular flows of air and water. In one embodiment, a radially inward air flow creates a high-pressure, water-free cutting zone around the plasma while a surrounding radially outward water flow cooperates with and stabilizes the air flow. The water-free cutting zone created during underwater cutting, or above-water cutting on a water-table, includes the cut itself and the underside of the workpiece in the vicinity of the plasma. The air flow prevents water from interfering with the progress of the cut and hydrogen gas from accumulating under the workpiece.

Abstract: An arc plasma torch includes a moveable cathode and a fixed anode which are automatically separated by the buildup of gas pressure within the torch after a current flow is established between the cathode and the anode. The gas pressure draws a nontransferred pilot arc to produce a plasma jet. The torch is thus contact started, not through contact with an external workpiece, but through internal contact of the cathode and anode. Once the pilot arc is drawn, the torch may be used in the nontransferred mode, or the arc may be easily transferred to a workpiece. In a preferred embodiment, the cathode has a piston part which slidingly moves within a cylinder when sufficient gas pressure is supplied. In another embodiment, the torch is a hand-held unit and permits control of current and gas flow with a single control.