Complementary experimental and theoretical approaches to the determination of the plasma characteristics in a cutting plasma torch

Abstract

In this paper, a cutting plasma torch is studied. We show how experimental and theoretical approaches are complementary for a full characterization of the plasma due to its specific parameters: high temperature, shock wave, pumping of surrounding gas, high velocity. Classical measurement methods cannot be used and two original methods are proposed: the first in the shock wave, where the pressure is unknown, and the second 11.2 mm from the nozzle exit, where the plasma composition depends on the pumping of ambient air.By using a back and forth approach between the theory and experiment, all the plasma characteristics can be estimated. The shock wave location is well predicted and temperatures around 18 kK are obtained in the shock wave and around 14 kK near the anode.

Schlieren technique applied to the arc temperature measurement in a high energy density cutting torch

“…These torches are characterized by an arc current intensity in the range of 30-100 A, flat cathodes, oxygen as the plasma gas, very small nozzle diameters ͑Ϸ1 mm͒, and by the generation of an underexpanded supersonic arc jet with a shock wave close to the nozzle exit. [1][2][3][4] Optical methods represent a versatile tool for performing nonintrusive, quantitative measurements in transparent media. In particular, refractive techniques allow the investigation of the temperature distribution in transparent flows by measuring its index of refraction ͑or its spatial derivatives͒.…”

Anode energy transfer in a transient arc

“…While nitrogen is distributed rather homogeneously in the plasma, a darker zone (indicating a low neutral nitrogen concentration area) can always be observed below the cathode for imaged recorded with the filter centered on nitrogen lines [3]. This can be explained by the prevalence of ionized lines over neutral lines considering the high temperature (> 20 000 K) [5,6] encountered. Its size differs according to the nature of the anode material: it is larger and can be observed for a longer time with pure graphite than with copper containing anode.…”

Developments in Plasma Arc Cutting (PAC) of Steel Alloys: A Review

“…Nevertheless, the anode is assumed as solid state anode and this condition prevents the plasma jet to flow through the metal plate. In other words, this condition is not representing realistic results for cutting process except maybe the initial phase of piercing in Zajac et al (2003).More realistic assumption in the work-piece was made in Freton et al(2001) and Freton et al (2003) and anode was represented by a plate with a hole. Freton et al(2001) and Freton et al (2003) are included turbulence in their model.…”