Tapered electrode for plasma arc cutting torches

A plasma arc cutting torch comprising:

• a nozzle assembly defining a bore therethrough;
• a process gas supply adapted to provide a process gas flow through the bore in the nozzle;
• and
• an electrode disposed adjacent the bore in the nozzle and comprising:
• an elongate emissive element defining a central axis and having an end surface adapted to emit an arc to a workpiece, said emissive element being comprised of an erodible material and defining an erosion rate in the axial direction as the arc is emitted from the end surface and gradually erodes the emissive element;
• and
• a holder having an end for holding the emissive element such that the end surface of the emissive element is exposed to allow emission of the arc through the bore, the holder also comprised of an erodible material and dimensioned so as to define an erosion rate in the axial direction that is substantially the same as the erosion rate of the emissive element such that the emissive element and the holder erode substantially simultaneously as the torch is operated.

A method of operating a plasma arc torch having a nozzle defining a bore and having an electrode with an emissive element and a holder adjacent the bore and defining an axis, said method comprising the steps of:

• flowing a process gas through the nozzle, about the electrode, and through the bore;
• applying an electrical current to the electrode;
• emitting a plasma arc from the emissive element, in cooperation with the process gas, through the bore;
• eroding the emissive element by way of the arc so as to define an erosion rate in the axial direction;
• and
• eroding the holder by way of the arc at an erosion rate in the axial direction substantially equal to the erosion rate of the emissive element.