Correlations Between the Oscillation Modes of Arc Voltage and Pressure in Cathode Cavity of Dc Plasma Torches

Abstract

Abstract The development of coating elaboration processes involving electric arcs depends on process stability and the capacity to ensure a constant reproducibility of coatings properties. This is particularly important when considering the plasma treatment of submicron or nanosized particles in Suspension Plasma Spraying (SPS). Submicron particles closely follow plasma instabilities and have non-homogeneous plasma treatment. Recently, it has been shown that arc voltage fluctuations in dc plasma torches, showing dominant fluctuation frequencies between 4 – 6 kHz, are linked to pressure oscillations in cathode cavity in the rear part of the plasma torch. These resonant oscillations are linked to plasma torch geometry. In this paper, first, we will present a method to isolate the different oscillations modes in measured arc voltage and pressure signals by the use of signal processing methods. Second, correlations between the different modes of oscillations are analyzed following the plasma torch operating parameters.