Characterization of the thermal flux transferred by the plasma arc to the surface of the liquid bath in the Plasma Arc Melting Cold Hearth Refining process (PAMCHR)

Léa Décultot,Jérôme Delfosse,Fabienne Ruby-Meyer,Stéphane Hans,Emiliane Doridot,Alain Jardy,Jean‐Pierre Bellot

doi:10.1051/matecconf/202032110003

Abstract

Europe is a major provider of titanium scrap but until now there has been no european facility dedicated to the production of aeronautical quality titanium alloys by recycling. UKAD, a joint-venture between Aubert & Duval and UKTMP, ADEME and Crédit Agricole Center France, created the company EcoTitanium, where the recycling of machining scraps is achieved using the Plasma Arc Melting Cold Hearth Refining (PAMCHR) process with the aim of producing such alloy ingots. The determination of the heat flux transferred from the plasma column to the surface of the liquid bath is an important issue needed for the development of a future 3D process modeling based on Ansys-Fluent CFD software. With this preliminary aim of predicting the heat flux, a study coupling pilot furnace testing and numerical modeling has been performed. Melting tests were carried out in a pilot PAMCHR furnace in MetaFensch, with a stationary torch. In parallel, the different contributions of the heat flux transferred to the surface of the liquid bath were identified and implemented in a simple 2D axisymmetric heat transfer model. Numerical results are compared to the experimental measurements, in order to define the heat flux transferred from the plasma torch.

Highlights

Hearth Refining (HR) followed by single VAR (Vacuum Arc Remelting) has been set-up as an alternative route to produced certified premium grade titanium alloys, as compared to the conventional route involving three successive VAR melts
HR basically stands for two different processes: Electron Beam Cold Hearth Refining (EBCHR) and Plasma Arc Melting Cold Hearth Refining (PAMCHR)
Minimizing the volatilization is the main advantage of the PAMCHR process, which uses plasma torches as the heat source: the process is conducted under an atmosphere of inert gas, with an operating pressure lying between 0.4 bar and 1 bar

Summary

Introduction

Hearth Refining (HR) followed by single VAR (Vacuum Arc Remelting) has been set-up as an alternative route to produced certified premium grade titanium alloys, as compared to the conventional route involving three successive VAR melts. The power used in the EBCHR process is generated by electron guns, which sweep rapidly the liquid surface to provide a quasi-stationary heat supply. These electron guns require a high vacuum, which favors the volatilization losses of alloy constituents with a high vapor pressure such as Al and Cr. Minimizing the volatilization is the main advantage of the PAMCHR process, which uses plasma torches as the heat source: the process is conducted under an atmosphere of inert gas, with an operating pressure lying between 0.4 bar and 1 bar. In 1997, Huang et al [1] developed a model of the PAMCHR refining stage, assuming a Gaussian distribution of the heat transfer from the plasma arc applied to the bath surface. These trials and numerical model have been used to analyze the impact of Lorentz forces on the liquid flow

Material and experiments

Experimental results

Model description

Results and discussion

Conclusion and perspectives

Nomenclature