M Razafinimanana

Experimental study of an oxygen plasma cutting torch: II. Arc–material interaction, energy transfer and anode attachment

A study of arc–material interaction and energy transfer in the case of plasma cutting is presented. A fast CCD camera moving with the torch is used to estimate the anodic arc root location inside the kerf. Temperature measurements on the cut-front surface and on the kerf edges are performed by infrared pyrometry. Temperature fields inside the workpiece obtained with inserted thermocouples are compared with the theoretical results of an analytical model to estimate heat conduction losses QHCL (W) dissipated in the plate. For various sets of operating parameters (voltage, inlet oxygen pressure and cutting speed), a complete energy balance of the process is performed with the calculation of the device efficiency on the basis of the various power terms implicated in the cutting tool: the power lost above the workpiece, heat conduction losses, the power involved in melting steel, the energy released by chemical oxidation reactions, the power available for cutting and losses under the plate in the extinguishing plasma.

Temperatures and C2 column densities in a carbon arc plasma

Diagnostic analyses were performed on a d.c. carbon arc discharge using optical emission spectroscopy. The influence of the self-absorption on intensity distribution in the rotational structure of the C2 (d g,v? = 0 a u,v?? = 0) emission band is discussed. The effect of the self-absorption was used in order to determine temperatures and column densities of C2 radicals in the a u,v?? = 0 state in the arc zone. Temperatures within 3500-6500 K and column densities within (0.5-6) ? 1015 cm-2 were found depending upon the arc current and plasma coordinates.

Characterization of a dc plasma torch through its light and voltage fluctuations

The Fast Fourier Transform method has been applied to light and voltage fluctuations in a low power (<5 kW) dc plasma torch burning in argon. The influence of the gas flow on the development of turbulence in the plasma jet has been studied. The temporal and spatial non-homogeneities observed in the plasma flow have been linked to the dynamic processes in a dc plasma torch.

The effect of pressure on a plasma plume: temperature and electron density measurements

Measurements of temperature and electron number density measurements have been carried out on a plasma plume under various pressure conditions (p = 1-0.3 bar) using emission spectroscopy. The anode nozzle used does not generate a shock wave or an expansion-compression zone. Ar- (1%) is used as the plasma gas. Temperature values are obtained from various lines of neutral argon. Electron number densities are obtained from the Stark-effect broadening of the 486.1 nm H line and the continuum measurements. Measurements of temperature and density profiles reveal the general features of a low-pressure plasma jet, namely relatively low temperature and long heating zone of the expanded jet. The LTE criterion is satisfied at higher pressures ( bar). Deviations from ionization equilibrium occur at lower pressure. The variation of excited neutral argon and states has been studied for lower pressures. tends to be overpopulated compared with .

The influence of iron vapour on an argon transferred arc

Spectroscopic measurements have been made on a transferred arc burning in pure argon at atmospheric pressure seeded with iron vapours arising from the anode erosion. The transferred arc was operated with a current intensity of 90 A, an arc length of 18 mm, and a gas flow rate of . Temperature and relative iron concentration profiles determined experimentally were compared to theoretical values obtained from a two-dimensional model based on mass, momentum, and energy conservation equations and taking into account anode erosion. This comparison partially validated the model and showed that the presence of iron vapours, with a relative concentration of about 0.1%, led to a temperature decrease of about 1000 K. Differences between experimental and calculated temperature fields may be due to departures from equilibrium and to uncertainties about the iron vapour concentration and the radiative losses.

Determination of plasma velocity from light fluctuations in a dc plasma torch

The fluctuations generated by arc root motion have been used to determine the velocity in a plasma jet. The phase angle relations resulting from time variations of light intensity profiles taken simultaneously across different sections of the plasma have been used to determine the velocity for different operating conditions of the dc torch. The experimental results have been compared with the theoretical predictions of a 2D MHD model of the dc plasma torch. The experimental and theoretical values appear to agree with a maximum deviation in the 5-10% range.

Departures from equilibrium near the copper anode of an argon transferred arc

Spectroscopic measurements on an argon transferred arc have been performed in the plasma region just above the copper anode, by means of the arc interruption technique. This technique, based on the recording of the transient evolution of total spectral line intensities, allows one to determine the difference Te−Th between the electron temperature and the heavy particle temperature, existing in steady state. During the extinction of the low arc current, the evolution of some argon lines presents first a sudden increase before a slow general decrease, whereas the evolution of copper lines shows first a very fast decrease followed by a slow extinction. These phenomena have been interpreted considering that argon excited-state populations are strongly correlated with ions and electrons (Saha equilibrium) whereas the copper excited-state populations are correlated with the ground-state density (Boltzmann equilibrium). The difference Te−Th deduced from both kinds of measurements varies between 500 and 800 K.

Influence of radiation on temperature field calculation in SF6 arcs

Comparison between measured and calculated temperatures in SF6 arcs shows that the values of the net emission coefficients calculated by various authors are, in all cases, too low. This underestimation of the emission coefficient is of the order of two to three.

An experimental and theoretical study of the influence of copper vapour on a arc plasma at atmospheric pressure

This paper deals with an experimental and theoretical study of the influence of copper vapours on the properties of a arc plasma. Spectroscopic measurements in pure plasma and in a -copper mixture in which copper was provided from the erosion of the anode have been realized. Temperature and relative copper concentration profiles determined experimentally were compared with theoretical values obtained from a two-dimensional physical model. This comparison validated partially the model and the transport coefficients calculated by our team and used in the model. The results showed that the effect of the presence of metallic vapours with a relative concentration of about 1% is too weak to induce noticeable modifications of the properties of plasma. However, a significant cooling of the plasma is calculated for a copper concentration of about 10%.

An experimental and theoretical study of the absorption of arc plasma radiation by cold gas

This study into radiative transfer in a arc plasma is devoted first to measure the relative absorption of the arc radiation by cold gas; second, to calculate this absorption; and third, to obtain a simplified expression for this absorption useful in arc modelling. In general, more than 50% of the radiation emitted by a arc is absorbed in the surrounding gas.