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1250 |
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Wednesday, June 04, 2008, Room 08 11:00 AM Diagnostics and Sensors 1 Modern process diagnostics offer a lot of possibilities for gaining data for both quality control and process knowledge. The recorded data is the base for process models and enhances the process knowledge |
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Effect of spray torch nozzle design modifications on arc and plasma jet characteristics and coating properties |
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Joachim Heberlein* / University of Minnesota, USA David Outcalt / University of Minnesota, USA Sho Suzuki/ Tokyo Institute of Technology, Japan Lorenzo Vincenzi/ Università di Bologna, Italy |
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In order to identify means to improve plasma spray consistency, various modifications to the design of a commercial plasma torch nozzle have been investigated. The modifications consist of preparing anode inserts with grooves in the axial direction (spline insert), and introducing a fraction of the plasma gas through a ring of micro-nozzles surrounding the anode nozzle (micro-jet ring). Different designs for each modification have been investigated, and these modifications have also been paired with a modified upstream gas injector. For each of the modified designs, the following characteristics have been measured: the arc voltage traces captured with a high speed digital oscilloscope, the fluctuations of the jet luminosity measured with a photodiode array, the pressure fluctuations in the jet measured with a microphone, the average jet length measured with a high speed video camera, the jet divergence measured with a high framing rate Schlieren imaging system, average plasma velocity, temperature and cold gas entrainment with an enthalpy probe system, the spray particle velocity and temperature distributions determined from DPV 2000 measurements, and the coating characteristics derived from optical and scanning electron microscopy measurements. Two commercial nozzles served as the base line. The results show that most nozzle modifications lead to higher particle velocities and temperatures and more reproducible coating characteristics. The plasma jet is significantly elongated by using the modified nozzles, and the cold gas entrainment somewhat reduced. The arc voltage and the luminosity fluctuations are little affected by the nozzle modifications, however, the modification of the gas injector does change the frequencies of the fluctuations. Each of the nozzle modifications can be easily implemented offering an economical way to enhance process reliability. |