Transient Evolution and Shifts of Signals Emitted by a D.C. Plasma Gun (Type Ptf4)

D.C. Plasma Spraying

“…The erosion patterns can result in preferred arc attachment spots leading to increased erosion and establishment of preferred tracks for the arc attachment movements. A study of the erosion patterns and the associated arc voltage traces [42] has shown that the preferred anode attachment slightly moves upstream and becomes slightly more constricted. The amount of erosion has been found to correlate with the residence time of the arc (time of a constant voltage value) at a specific location.…”

“…While for the new anode the attachment times remain smaller than 150 μs, the worn anode shows an increasing fraction of residence times at a specific attachment location exceeding this value. A thermal analysis indicates that with residence times of 150 μs a strong increase in erosion can be expected, i.e., once a slightly eroded spot has formed, the arc prefers to attach at this spot, rapidly increasing the erosion rate [42]. Clearly, control of the anode heat flux must be achieved to control anode erosion.…”

Direct Current Plasma Spraying: Diagnostics and Process Simulation

“…This is due to: -The development of diagnostic tools both for plasma jet [7] and particles in flight, [8,9] -A better understanding of the effect of arc root fluctuations on plasma jet, anode erosion [10,11] and particle behavior, [12] -The development of robust sensors able to work in the harsh conditions of industrial spray booths and to monitor, and in a next future, control, the plasma spray process, [13,14] -The observation of splat formation thanks to dedicated systems making it possible to measure the parameters of single particles before impact and follow the evolution of the material spreading on the surface and its temperature for substrate with different roughness, cleanness and temperature, [15] -The numerous mathematical models of the atmospheric plasma spray process proposed in the literature, [16][17][18][19][20] -The recent 3-D transient models of splat formation, [21,22] -The first attempts to link coating thermo-mechanical properties to spray parameters through statistical models of splat layering, models that, however, are still in their infancy. [23,24] …”

“…If these fluctuations limit the anode erosion as long as the arc root residence time at the same location is shorter than 150-180 ls, [11,26] they result in time variation of the length, width, momentum and temperature of the plasma jet. [2] Three different arc operation modes have been identified for a d.c. plasma torch: the steady mode, the takeover mode and the restrike mode.…”

A Study of the Influence of the Surrounding Gas on the Plasma Jet and Coating Quality During Plasma Spraying

“…It is generally accepted that the source of such kind of instabilities is numerous: fluctuations of arc voltage, plasma gas composition, variations in powder feeding, entrainment of the surrounding gas, etc. [18][19][20][21][22][23]. Regarding the time scale, the instabilities can be imaginarily classified into two categories: high-frequency fluctuations, denoted as "uncertainty" which mainly results from the unstable discharge of arc [18] (Fig.…”