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High Temperature Material Processes: An International Quarterly of High-Technology Plasma Processes

Impact factor: 0.058

ISSN Print: 1093-3611
ISSN Online: 1940-4360

High Temperature Material Processes: An International Quarterly of High-Technology Plasma Processes

DOI: 10.1615/HighTempMatProc.v7.i2.70
11 pages

TRANSIENT EVOLUTION AND SHIFTS OF SIGNALS EMITTED BY A D.C. PLASMA GUN (TYPE PTF4)

D. Rigot
Laboratoire Sciences des Precedes Ceramiques et Traitements de Surfaces IJMR 6638, Universite de limoges, 123 avenue Albert Thomas - 87060 Limoges, France
Guy Delluc
Laboratoire Sciences des Precedes Ceramiques et Traitements de Surfaces UMR CNRS 6638, 123 avenue Albert Thomas 87060 Limoges Cedex
Bernard Pateyron
Laboratoire SPCTS UMR CNRS 7315, ENSCI, Centre Europeen de la Ceramique, Limoges, France
J. F. Coudert
Laboratoire Sciences des Procédés Céramiques et Traitements de Surface, UMR-CNRS 6638, Université de Limoges, 87060 Limoges Cedex, France
Pierre Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France
Jan Wigren
Volvo Aero Corporation, S-461 81 Trollhattan, Sweden

ABSTRACT

The on line monitoring of a plasma gun spray parameters is in full development in industrial plasma spray processes in order to achieve a better reproducibility and reliability of the coatings. This on line monitoring in particular allows to compensate for the torch voltage drop with the electrode erosion but there is a need to determine when this erosion becomes disastrous. To achieve such a goal, the measurement of the signals emitted by a plasma torch (sound and voltage) must be performed very precisely at the frequency of the fluctuation of the arc, but the drift due to the erosion of the electrodes must also be taken into account. The key issue is to know which time scale would be the most relevant to indicate how far can the electrodes could be used before they have to be changed. This paper presents in a first section, the different time scales with their physical phenomena related to: from a short time range of a few microsecond related to the fluctuations of the arc root to the electrode lifetime in the range of tens of hours), and explain how they are linked. The second part is dedicated to the influence of the way to ignite the torch, by studying the transient arc current evolution during the first instant of the restart sequence and its consequence on the electrode erosion. It is shown hereunder, that if there is no burst of arc current intensity, the anode electrode is prevented from premature erosion.