Abstract: There are provided a plasma arc torch and associated methods for selectively switching between a working mode and a standby mode. An electric arc is established between an electrode and a workpiece, and the torch is operated selectively in the working and standby modes. In the working mode, the arc extends between the electrode and the workpiece, the arc has a working arc current, and a plasma gas flows through a nozzle at a working flow rate. In the subsequent standby mode, the arc extends between the electrode and the nozzle and has a current less than the working arc current. The gas flow rate in the standby mode can be reduced to less than the working flow rate, and the plasma gas can be switched from an oxidizing gas to a non-oxidizing gas.

Abstract: There are provided a plasma arc torch and associated methods for selectively switching between a working mode and a standby mode. An electric arc is established between an electrode and a workpiece, and the torch is operated selectively in the working and standby modes. In the working mode, the arc extends between the electrode and the workpiece, the arc has a working arc current, and a plasma gas flows through a nozzle at a working flow rate. In the subsequent standby mode, the arc extends between the electrode and the nozzle and has a current less than the working arc current. The gas flow rate in the standby mode can be reduced to less than the working flow rate, and the plasma gas can be switched from an oxidizing gas to a non-oxidizing gas.

Abstract: A method of fabricating an electrode is disclosed, wherein the electrode comprises a copper holder defining a cavity in a forward end. An emissive element and separator assembly is positioned in the cavity. An intermetallic compound is formed between the emissive element and the separator by heating a relatively non-emissive material until it melts and dipping the emissive element therein before cooling the assembly. As a result, the intermetallic compound is formed significantly faster than by conventional methods.

Abstract: A method of forming an electrode for a plasma arc torch is disclosed, and wherein the electrode comprises a copper holder defining an opening therein. An emissive element is secured to a cavity formed in a relatively non-emissive separator having a solid rear wall at one end thereof. The emissive element and separator are positioned within the opening defined by the copper holder such that the emissive element is surrounded by the separator and the copper holder. In this regard, the emissive element is prevented from movement along the longitudinal axis of the torch relative to the separator during a post-assembly heating step. In addition, the emissive element is not exposed to the atmosphere during the heating step, which allows a greater bond between the emissive element and the separator.

Abstract: An electrode for a plasma arc torch and method of fabricating the same are disclosed, and wherein the electrode comprises a copper holder defining a cavity in a forward end. An emissive element and separator assembly is positioned in the cavity. The emissive element is formed from the powders of at least two materials, and the separator includes a material that is substantially similar to one of the materials forming the emissive element. The emissive element is heated and a plurality of thermal conductive paths are formed that extend from within the emissive element to the separator that improve the thermal conductivity of the electrode.

Abstract: An electrode for a plasma arc torch comprises a copper holder having a lower end which mounts an emissive element serving as the cathode terminal for the arc during operation. A relatively non-emissive separator formed of silver alloyed with 0.5 to 4 percent of copper or other metals surrounds the emissive element and separates the emissive element from the copper holder at the exposed end face of the electrode. The separator serves to prevent the arc from detaching from the emissive element and attaching to the copper holder.

Abstract: The invention relates to an emissive element for supporting an electric arc in a plasma arc torch using an oxygen gas to create the plasma. The element includes a body having a front face for supporting the electric arc which is defined by at least two distinct components formed from different materials. The first component is an emissive material having a low work function for readily emitting electrons in support of the arc and being reactive with the oxygen plasma gas to form an oxide during an operation of the torch. The oxide forms an electrically resistive layer on the front face of the body upon cooling subsequent to the operation of the torch. Hafnium is a preferred material for the first component. The second component comprises a conductive material having an electrical conductivity greater than the oxide layer for supporting the arc during the initiation of a subsequent torch operation at least until the oxide reaches an operating temperature.

Abstract: An electrode for a plasma arc torch comprises a copper holder having a lower end which mounts an emissive element serving as the cathode terminal for the arc during operation. A relatively non-emissive separator formed of silver alloyed with 0.5 to 4 percent of copper or other metals surrounds the emissive element and separates the emissive element from the copper holder at the exposed end face of the electrode. The separator serves to prevent the arc from detaching from the emissive element and attaching to the copper holder.

Abstract: A plasma arc torch having a nozzle assembly positioned adjacent the discharge end of the electrode of the torch, and wherein the nozzle assembly comprises a nozzle base defining an annular outer surface and a lower nozzle member defining an annular inner surface which is spaced from the outer surface so as to define an annular water passageway therebetween. The annular water passageway defines an angle with the longitudinal axis of the torch which is less than about 30.degree. which provides both an efficient cooling of the nozzle assembly and constriction of the plasma arc, and without unduly cooling the plasma arc.

Abstract: An electrode and method of operating a plasma arc torch is provided which extends the useful service life of the torch. The electrode includes an elongate tubular holder defining a longitudinal axis and having a discharge end. An endwall closes the discharge end and includes an emissive insert. In one embodiment, the endwall also includes an annular sleeve which separates the insert from physical contact with the holder. Channels formed in the discharge end of the electrode direct a portion of a swirling vortex of gas across the surface of the endwall. The swirling vortex of gas removes products of erosion of the insert and adjacent portion of the sleeve such that the likelihood that arcing will transfer from the insert to the sleeve and/or holder is reduced, and the useful service life of the nozzle-electrode pair is thereby extended.