Multi-Electrode Plasma Torches: Motivation for Development and Current State-of-the-Art

Abstract

Multi-electrode plasma torches are becoming increasingly popular in the thermal spray community due to their good stability and high power plasma jet even when operated with inert gases. Currently the models in use feature either three cathodes and a single anode or three individual anodes connecting to a single cathode. The motivation for development of these plasma torches is based on the inherent instability of single anode/single cathode systems which leads to fluctuating plasma jets resulting in inhomogeneous particle heating. The use of multi-electrode systems has expanded into the realm of low pressure plasma spraying and vacuum plasma spraying with promising results, while atmospheric plasma spraying results show improved coating quality compared to conventional systems. Current research focuses on the development of numerical process modeling as well as the application of advanced diagnostics for process analysis, opening up opportunities for improvement and process control.

Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma

“…The feeding rate of the suspension was 45 standard cubic centimeters per minute (sccm), and the flow rate of nitrogen atomizing gas was 30 sccm. The atomizing gas, which is injected to the feeding flow and splits the suspension droplets into small ones, turned out to affect the quality of the YOF coating because it made the droplet size of the suspension smaller and thus, the particles in the droplet melted more easily [14,15]. The transverse speed of the plasma gun was 1000 mm/s, and coating cycles were repeated 20 times during the entire spraying process.…”

Numerical and experimental determination of plasma temperature during air plasma spraying with a multiple cathodes torch

“…The tomography reconstruction requires the plasma to be optically thin. If LTE of plasma is assumed, then the emissivity of the plasma gas is a known function of the gas temperature according to a standard calculation based on the Saha equation (Marqués et al, 2009).…”

Modelling and diagnostics of multiple cathodes plasma torch system for plasma spraying

“…The tomography reconstruction nevertheless required the plasma jet to be optically thin. If local thermodynamic equilibrium is assumed, then the emissivity of the plasma gas is a known function of the gas temperature according to a standard calculation based on the Saha equation, whose details are discussed elsewhere [15].…”