Improvement of Plasma Gun Performance using Comprehensive Fluid Element Modeling: Part I

Abstract

The use of computational fluid dynamics (CFD) to model the operation of thermal-spray processes has gained interest in the thermal-spray community, able to provide an understanding as to how a process functions, and better how to make a process work better. Advancements to the science of modeling now permits the ability to create a comprehensive model of a plasma gun that not only simulates the dynamics of the gas, but also the mechanics of arcs (plasma), thermodynamics, and entrained particulates to form a nearly complete model of a working thermal-spray process. Work presented includes the methods and procedures used to validate the model to a Sulzer Metco TriplexPro TM -200 plasma gun and exploration of the operating regime to give an in depth and insightful look into the physics behind the operation of a triple-arc cascaded plasma gun.

Modeling of the Plasma Flow and Anode Region Inside a Direct Current Plasma Gun

“…Multiple cathode systems such as the Triplex gun from Sulzer-Metco (Winterthur, Switzerland) ( Ref 1,2) or the Axial III system from Mettech (North Vancouver, Canada) and multiple anode torches such as the Delta gun from GTV (Luckenbach, Germany) have been commercialized. The main benefits of this new generation of torches concern (1) their ability to provide an improved stability of the arc and (2) their elevated power allowing increased deposition rates.…”

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

“…(13) the contour of a constant temperature of 17000 K is displayed, showing the effect of the pronounced swirl imposed on the injected gas flow at the torch inlet. The mentioned simplification regarding the heat sources as an acceptable effective implementation of the interaction between electric arc and gas flow has been observed to reproduce reasonably well the velocity and temperature distribution at least at locations near to the outlet nozzle [47,48] Fig. (14).…”

“…Characteristic for the Triplex torch, the presence of three isolated electric arcs leads to a very slow convergence of the fluid dynamics equations coupled to the electric and magnetic fields generated by these arcs. Therefore, at first, only a steady state model has been attempted [46][47][48], which for a plasma torch operating with fixed anodic root locations has a higher validity as for the single-cathode torch with moving anode root. In all the models for the Triplex torch the same simplifications regarding the sheath and pre-sheath close to the cathode apply as for the single-cathode torch, in particular the indefinition of the cathode spot size, which has to be incorporated by hand.…”

“…In all the models for the Triplex torch the same simplifications regarding the sheath and pre-sheath close to the cathode apply as for the single-cathode torch, in particular the indefinition of the cathode spot size, which has to be incorporated by hand. Of high relevance is the reported modelling result that, for the Triplex torch in its advanced design TriplexPro with a narrower torch outlet and amplified operation power, the three cathodic arcs tend to merge in a single arc inside the torch [47,48]. Neverthelss, such modelling has been carried out for gas flows considerably higher than the usual operating conditions and thus the stated result cannot be probably applied to the typical parameters for spraying with the Triplex torch.…”

D.C. Plasma Spraying

“…However, one has to keep in mind that very strong fluctuations exist of the plasma properties, and averages can reproduce only a part of the process. Nevertheless, such models have been used to evaluate operational characteristics of new torch designs, e.g., for the Sulzer Metco Triplex torch [59,60], and the potential for expanding their range of operating conditions.…”