Triplex – An Innovative Three-Cathode Plasma Torch

Abstract

Present standard d.c. plasma torches are characterized by the combination of a single rod-shaped cathode and a conical one-piece anode. Mixtures of inert gases and molecular gases are used for plasma spraying of high melting powders. By adding the molecular gases high enthalpy plasma jets are generated, but simultaneously the well-known art root fluctuations cause an inhomogeneous treatment of the injected powder. The innovative plasma torch system TRIPLEX is characterized by a long nozzle and by three parallel cathodes. The nozzle consists of several rings all electrically insulated except for the last one which operates as an anode. By increasing the number of rings the three arts between the cathode tips and the anode ring can be lengthened. This leads to a higher art voltage and therefore to a higher enthalpy in the plasma jet. No molecular gases have to be used and are root fluctuations are prevented. The result is a uniform treatment of the injected powder. Using optical and electrical diagnostics the TRIPLEX torch ist compared to a typical conventional plasma torch. High spray rates and deposition efficiencies show the good performance of TRIPLEX.

Understanding plasma spraying

“…To limit the plasma jet fluctuations, a new torch called TRIPLEX from Sultzer Metco [12], has been recently introduced. It has three counter insulated cathodes supplied by independent sources, distributing the energy to three parallel arcs striking at a unique anode preceded by insulated rings allowing the production of a long arc, thus reducing the percentages of voltage fluctuations drastically.…”

Pending problems in thermal plasmas and actual development

“…This phenomenon produces variations in the enthalpy levels of the jet and, therefore, in the heating rates. This is why studies are in progress to design new torches with longer arc columns reducing correlatively the amplitude of the voltage fluctuation relative to the mean voltage [36].…”