Plasma properties in a highly constricted arc were measured using spectroscopic techniques. The arc configuration studied is typical of those produced by plasma cutting equipment. Temperatures and electron densities in the arc were measured using several different emission lines and several different methods for property calculation. Factors such as fluctuations in the arc intensity, arc asymmetry and the validity of the assumptions used for property calculation were shown to affect the accuracy of the measurements. Selection of the temperature measurement method can influence the measurement results. For this arc configuration, methods which use oxygen ion emission lines provide the most accurate results. The measurement methods developed in this study were used to investigate differences in arc properties related to arc current and nozzle diameter. Large changes in the temperature and electron density due to shocks were measured in the under-expanded region near the nozzle exit.
The relationship between plasma properties and cutting performance for a plasma arc cutting system was investigated. Plasma properties such as temperature and composition were measured using spectroscopic techniques in a 200 amp oxygen plasma cutting system. In addition to the plasma properties, the symmetry of the cylindrical cutting arc was also quantified. Cutting performance was measured by analyzing the edge quality of sample cuts. The most important measure of edge quality for this study was the angle of the cut edge. Operating parameters investigated included the effect of shield gas flow and geometry changes caused by cathode erosion. The measured plasma properties are used to account for the observed increase in recommended cutting speed for different consumable designs which operated at the same current level. A strong correlation was also shown between the measured arc symmetry and the cutting performance.
Plasma cutting is commonly used to cut metals in a variety of applications. This research is motivated by the lack of fundamental understanding of the dynamics of the plasma flow interacting with cold gas environment. It is focused on the characterization of the arc instabilities that affect the quality and consistency of a cut. The characterization of instabilities has been performed with high-speed Schlieren imaging technology to visualize the arc width and the light intensity fluctuations in the arc boundary layer. Measurements of arc symmetry using Fourier and wavelet transforms of the light intensity fluctuations in individual pixels in the Schlieren images are able to provide a quantitative measure for the degree of instability. Ambient gas entrainment into the plasma jet is measured using a CCD camera with a narrow bandpass filter centred on the nitrogen atomic line to detect nitrogen concentrations throughout the arc, thus showing the penetration of shield and ambient gas into the pure oxygen plasma. The effects of torch design features on these characteristics are investigated by comparing two different torch designs. The results show that the developed diagnostics are useful for evaluating new torch designs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.