A theoretical and experimental investigation of copper electrode erosion in electric arc heaters: I. The thermophysical model

Esipchuk

et al. 2005

J Eng Phys Thermophys

Indirect data on the features of the dynamics of a cathode spot in different erosion regimes have been obtained by investigation of the fluctuations of the intensity of radiation from the arc of the 5218 A° CuI copper spectral line modulated by the rotational frequency in a magnetic field. It has been revealed that the velocity of the cathode spot in the regime of intense radiation of this line in macroerosion is always lower than that in the regime of weak radiation in microerosion, whereas the variance of its distribution is, conversely, higher. A hypothesis for the relationship between the line-radiation intensity and the occurrence of a cathode copper-vapor jet affecting the mobility and dynamics of the spot and, in terms of them, the erosion has been proposed.Introduction. As has been reported in [1], to determine the density of the current in a cathode arc spot by the thermospectroscopic method we measured the intensity of the radiation of the 5218 A° CuI spectral line of copper from the arc rotating in a coaxial gap in a magnetic field. The beginning of an intense radiation of this line was taken as the beginning of macrofusion in the spot and the beginning of macroerosion, i.e., an intense form of erosion, instead of the low-intensity one called "microerosion." In [2,3], in experiments on a vortex electric-arc heater (EAH), An'shakov et al. observed the outflow of high-power cathode jets from the spot in passage of erosion from the lowintensity form to an intense one; these jets destroyed the structure of the vortex flow and disturbed regular rotation of the arc. This disturbance of the vortex stabilization of discharge was considered by An'shakov et al. to be predominantly responsible for the erosion becoming intense. Since we recorded the rotational velocity of the arc in both regimes -before the increase in the intensity of the copper spectral line and after it, which, presumably, corresponded to the regimes of micro-and macroerosion, the results of such recording also had to contain information on the features of the arc motion in them in the total absence of vortex stabilization of the discharge. To obtain this information we carried out special processing of the experimental results.Experimental Procedure. The experiments were carried out on a coaxial electric-arc unit with magnetic movement of the arc and axial feeding of a gas to the discharge zone. The unit had been described earlier (see [4,5]) in detail; therefore, we do not give its description here. In these experiments, the image of the entire coaxial interelectrode gap with an electric arc moving in its circle was projected onto the section of a light guide, after which the light signal was fed to the entrance slit of a spectrometer. A small segment of the aperture of the interelectrode gap was covered by an opaque screen. Owing to this, the light signal was modulated by the rotational frequency of the arc in the gap.Applying the fast Fourier transformation in the Origin program to processing of the signal of the line intensity recorded wit...

mentioning

confidence: 79%

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. II. Dynamics of movement of the spot

Bublievskii

Esipchuk

et al. 2005

J Eng Phys Thermophys

“…Therefore, in practical calculations of the thermal load of the electrode (for example, cold electrode erosion estimation [11]), the arc spot volt-equivalent of thermal flux U is normally used, defined by the equation (see [12]):…”

Section: Introductionmentioning

confidence: 99%

Magnetic Field Effect on the Volt‐Equivalent of Arc Spot Heat Flux

Essiptchouk¹,

Sharakhovsky

2005

Contrib. Plasma Phys.

The results of an experimental study of the arc spot heat flux on the copper cathode of a coaxial Electric Arc Heaters (EAH), with magnetically driven arc, in air are presented. The three rings method was used for indirect separation of arc spot heat flux from total heat entering the electrode. As a result of joint generalizing new and previously published data, the linear dependence of the volt equivalent of arc spot heat flux on magnetic field was obtained for the range B = 0.01 − 1 Tesla and atmospheric pressure. A method, which allows to improve the measurement of the volt equivalent in highly unsteady arc spots, is proposed.

“…It has also been shown 3 that the dynamics of the motion of the arc spot over the electrode surface (either in a continuous or in a jumping‐like motion) is an important factor in determining the erosion behavior. A thermophysical model for the case of the continuous displacement of the arc spot in copper cathodes was presented earlier in 4. In this paper, a universal approach for both regimes of displacement of the arc spot, the continuous and the jumping‐like ones (or step‐wise regime) is given a further development.…”

mentioning

confidence: 99%

Erosion of the Cold Electrode as an Ablation Process in Unsteady Arc Spots^a

Annals of the New York Academy of Sciences

Sharakhovsky

Essiptchouk

1999

A simple macroscopic thermophysical model is presented for cold electrode erosion in unsteady arc spots. The model is based on the consideration of erosion as heat ablation characterized by an effective enthalpy of erosion of the electrode material. The unbalance between the arc spot heat supply and the heat removal by conduction into the electrode body provides the heat spent in the erosion process. Two modes of displacement of the arc spot are considered: continuous and step‐wise. An experimental coaxial setup with a magnetically driven arc has been used for conducting erosion measurements in copper cathodes. Good agreement between this experiment and those reported by other researchers has been obtained with the continuous and the step‐wise models. Electrical Discharge Machining experimental data in steel cathodes have also shown good agreement with our step‐wise erosion model.