Characteristics of a transferred-arc plasma

by Mustafa Tanju. Mehmetoḡlu

Institution: McGill University
Department: Department of Chemical Engineering
Degree: PhD
Year: 1980
Keywords: Plasma arc melting.
Record ID: 1511021
Full text PDF: http://digitool.library.mcgill.ca/thesisfile68505.pdf


The basic characteristics of a transferred arc argon plasma were determined. A cathode assembly suitable for transferring the electric arc to a molten metal bath or to a cooled anode was designed and constructed to produce the plasma in open air. It included provision for the injection of secondary gas into the arc column. The measured electrical characteristics indicated that the sustained voltage depended strongly on the arc length and much less on current. The inlet gas velocity past the cathode tip was determined to be an important operating parameter, rather than the volumetric gas flowrate. The measurement of the axial and radial profiles of temperature was effected with (+OR-) 8% accuracy by a novel diagnostic technique based on the determination of the variations in the outputs of a two-wavelength pyrometer that views a small section of the plasma, as the latter is swept rapidly by a blocking element. Temperatures up to 18,500 K were observed on the axis of the plasma column. A sweeping microprobe was used to measure the axial and radial profiles of velocity. Velocities up to 190 m/s were recorded. The presence of a relatively colder flow surrounding the plasma column was detected. Mass and energy balances performed by taking this flow into account agreed with the measured input rates.