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1902 |
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Wednesday, May 05, 2010, Sophia Room 8:40 AM Process Diagnostics 2 |
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Correlations between the oscillation modes of arc voltage and pressure in cathode cavity of dc plasma torches |
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Vincent Rat* / SPTCS-CNRS-University of Limoges, France Jean-François Coudert/ SPCTS - CNRS - University of Limoges, France |
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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 [1,2]. 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. At last, a new method will be presented to reduce the amplitudes of arc voltage instabilities. [1] J.F. Coudert, V. Rat, D. Rigot, Influence of Helmholtz oscillations on arc voltage fluctuations in a dc plasma spraying torch, J. Phys. D : Appl. Phys. 40, 7357-7366 (2007) [2] J.F. Coudert and V. Rat, Influence of configuration and operating conditions on the electric arc instabilities of a plasma spray torch : role of acoustic resonance, J. Phys. D: Applied Physics 41, 205208 (2008) |