MODELLING AND COMPARISON OF DIFFERENT DESIGN SOLUTIONS AND EXPERIMENTAL RESULTS FOR DC TRANSFERRED ARC PLASMA CUTTING TORCHES

The aim of this work is mainly to investigate by means of a 2-D FLUENT© based numerical model the behaviour of different types of transferred arc dual gas plasma torches used for cutting of metallic materials, giving the physical reasons for the industrial success of various design and process solutions appeared over the last years. Flow and heat transfer equations are solved with coupled electromagnetic ones, for an optically thin LTE plasma, while turbulence phenomena are taken into account by means of a k-ε RNG model, including the prediction of thermal behaviour of the solid components of the torch head and the efficiency of nozzle and electrode cooling systems in various operating conditions including gas mixtures (O2/air, H35/N2, N2/N2). Radiation is included in the calculation of heat transfer to the surfaces of the components using a customized Discrete Ordinate (DO) model. Additional experimental results have been obtained using a high speed camera (HSC), during pilot arcing and piercing of mild and stainless steel plates of various thickness and in different operating conditions. The technique has provided new insight of the PAC process and some interesting phenomena have been highlighted: such as, the trajectory and velocity of hafnium particles emitted from the electrode during pilot arcing and the effect of non perfectly aligned consumables (shield-nozzle) on inducing destructive piercing.