Effects of Anode Arc Root Fluctuation on Coating Quality During Plasma Spraying

Abstract

To obtain a coating of high quality, a new type of plasma torch was designed and constructed to increase the stability of the plasma arc and reduce the air entrainment into the plasma jet. The torch, called bi-anode torch, generates an elongated arc with comparatively high arc voltage and low arc fluctuation. Spraying experiments were carried out to compare the quality of coatings deposited by a conventional torch and a bi-anode torch. Alumina coatings and tungsten carbide coatings were prepared to appraise the heating of the sprayed particles in the plasma jets and the entrainment of the surrounding air into the plasma jets, respectively. The results show that anode arc root fluctuation has only a small effect on the melting rate of alumina particles. On the other hand, reduced air entrainment into the plasma jet of the bi-anode torch will drastically reduce the decarbonization of tungsten carbide coatings.

Numerical modelling of a direct current non‐transferred thermal plasma torch for optimal performance

“…[ 9 ] Also, the resulting fluctuations in the jet affect the torch performance. [ 10 ] This entrainment can significantly reduce the plasma jet temperature, which is not suitable for waste treatment applications. On the other hand, laminar plasma jets have lower ambient gas entrainment, higher temperature, and higher velocities for a longer axial length.…”