| 摘要 |
<p>A surface discontinuity is formed along an anode nozzle bore sufficiently upstream of a nozzle exit orifice (34a) and of a sufficient size to cause an arc between an electrically conductive end wall of a plasma-arc torch anode nozzle passage (34) and a coaxial cathode (32) coaxially mounted by an opposite end wall of the torch cylindrical casing having a gas under pressure and at an established vortex flow to pass through the nozzle passage (34). A boundary layer of the vortex flow of gas along the anode bore wall provides a path for the arc to pass directly to the anode nozzle passage (34) at or just downstream of the disturbance zone provided by the nozzle passage (34) wall surface discontinuity. A counterbore (57) may extend along a portion of the nozzle axis from the nozzle exit (34a) axially inwardly to form a radial shoulder (58) with the main bore of the anode nozzle (31) and define the discontinuity. Alternatively, a shallow annular groove (60) may be machined into the anode nozzle bore, or an annular ring (76) may project radially inwardly of the nozzle passage bore to constitute such alternative surface discontinuity. Material may be sprayed into a high velocity hot gas stream downstream of the arc column and its downstream ionized region to eliminate excessive heating of the particles sprayed by the torch. A reduced diameter nozzle bore section may be provided between the terminus of the arc column and/or its associated downstream ionized region and the point of the introduction of the material to be sprayed, with the reduced diameter nozzle bore forming a nozzle throat of an expansion nozzle producing a supersonic jet stream at the nozzle exit.</p> |
