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

L Prevosto,H Kelly,G Artana,B Mancinelli

doi:10.1063/1.3291099

Abstract

Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes.

Highlights

Plasma cutting is a process of metal cutting at atmospheric pressure by an arc plasma jet, where a transferred arc is generated between a cathode and a work piecethe metal to be cutacting as the anode
These refractive techniques can be divided into two groups: the interference methods, which are based on the difference in length of the light ray paths, and the methods based on the angular deflections of the light rays, such as shadowgraph and schlieren
Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique

Summary

INTRODUCTION

Plasma cutting is a process of metal cutting at atmospheric pressure by an arc plasma jet, where a transferred arc is generated between a cathode and a work piecethe metal to be cutacting as the anode. A high-quality cut requires a narrow, hot, and high-velocity plasma jet, i.e., a high energy density arc jet. To this end, a new generation of cutting torches, the so-called “high energy density torch” has been developed. A quantitative interpretation of the schlieren technique applied to a high energy density cutting arc is for the first time reported. The technique allows measuring plasma composition and temperature by processing the graylevel contrast values of a digital schlieren image recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the optical system.

EXPERIMENTAL ARRANGEMENT

EXPERIMENTAL RESULTS AND DISCUSSION

CONCLUSIONS