Anode attachment stability for high intensity arcs with helium, nitrogen and argon gas flow parallel to the anode

Summary form only given, as follows. The arc-anode attachment plays an important role for the anode erosion characteristics and the anode lifetime. A better knowledge of these phenomena is required to optimize the anode performance In this study we have addressed the question of the interaction of the arc with an anode when there is a cold gas flow parallel to the anode surface forming a cold boundary layer leading to a constant motion of the anode attachment with a corresponding fluctuation in plasma power. This situation is encountered in many applications of non-transferred plasma torches such as plasma spraying where the fluctuation in plasma jet power can have a detrimental influence on the quality of the produced coating In this paper, the motion of the anode attachment to the anode have been determined for a configuration where the arc axis is perpendicular to the anode surface with the plasma, gas flowing along the arc axis, and with lateral injection of different gases parallel to the anode surface. The arc is stabilized by a constrictor except for a gap of 10 mm between the constrictor and the anode. The constrictor channel diameter is 10 mm, arc currents ranged from 50 to 150 A, the plasma gas flow rate was 3.5 to 20 slpm of argon, and the lateral gas flow rate was 0 to 60 slpm, with argon, helium or nitrogen the gases injected laterally. High speed videography have been used to characterize the anode attachment. The results show that different modes of anode attachment exist, including a steady deflected anode root, and a randomly fluctuating attachment, and a periodically fluctuating attachment.