Investigation of the Plasma Jet and the Powder Injection at a Cascaded, Single-Cathode, Atmospheric Plasma Spray Torch

Abstract

Abstract In atmospheric plasma spraying, the fluctuation of the plasma jet and the velocity of powder injection are important parameters that affect particle acceleration and heating. Additionally, the plasma gas flow often exhibits a swirl, complicating the conditions. Diagnostic methods are necessary to study the behavior of the plasma jet and particles. In this study, a CCD camera in an Accuraspray 4.0 system captured images of the particle jet from two injectors of a cascaded single-cathode plasma torch. Brightness profiles at the spray distance were determined using digital image analysis. For double injection, a single feeder with a Y -branch in the powder line was used. Alternatively operating two separate powder feeders was found to not significantly change the outcome. The bimodal particle density distributions shifted as the carrier gas flow rates varied. Experimentally obtained spray spots confirmed this. The carrier gas flow rates that minimize the distance between spray spots originating from the two injectors and optimize deposition efficiency were identified. Using an 11-mm nozzle instead of the standard 9-mm nozzle did not significantly reduce the distance between the spray spots.