No abstract

The plasma‐forming gas composition is one of the parameters of a plasma spray process which can be adjusted by the operator to obtain deposits with the required properties. The gas composition affects the heat and momentum transfer to the particles injected in the flow, but also the working and stability of the plasma gun. This paper presents an investigation of the effect of gas composition and flow rate, and arc current on arc instabilities. The study was carried out for various ternary gas mixtures of argon, helium and hydrogen. The movement of the arc root attachment spot on the anode wall was characterized from the time‐evolution of arc voltage and the fluctuations of the plasma jet from the velocity fluctuations. The experiments were carried out with a new and a worn anode. The characteristic frequency of arc fluctuations was correlated in terms of the primary parameters of the spray process and gas mixture properties.

This paper is devoted to the investigation of the dynamics of the plasma jet, which is produced by a subsonic DC spray torch operated with an argon-helium mixture as the plasma gas. It focuses on studying the effect of some parameters which influence the arc attachment inside the anode nozzle. For this purpose, the paper uses different means of gas injection, that is straight flow injection and vortex flow injection, and anodes which have experienced different degree of wear. A heavily eroded anode is characterized by large voltage fluctuations at relatively low frequencies, while straight gas injection at high current levels led to a low average voltage with small fluctuations and to low burner performance. The results are interpreted by assuming changes in the thickness of the cold interface between the arc and the anode, and conclusions are drawn as to the voltage characteristics indicative of good torch operation. Paper includes a German-language abstract.