INFLUENCE OF THE ANODE MATERIAL ON AN ARGON ARC

The interaction between the are and the anode was experimentally studi ed by means of a transferred are burning in argon with copper, iron, o r steel anodes. Depending on the rate of anode cooling, a stable plasm a was obtained just above the anode, established either in pure argon (strong cooling) or in a mixture of argon with metal vapor, Temperatur e and metal concentration fields were deduced from spectroscopic measu rements. Two important results were reached: the are radius near the a node depends on the nature of the electrode, even without anode erosio n; and the presence of metal vapor leads to a cooling of the plasma. T he same arc configurations were theoretically simulated by a two-dimen sional model, The comparison between experimental and numerical result s allows a large proportion of the observed phenomena to be interprete d, in spite of partial discrepancies between predicted and measured va lues. The dimension of the are root at the anode depends on the therma l conductivity of the solid metal, whereas the cooling effect due to m etal vapor in the plasma is explained by the increases of electrical c onductivity and of radiative losses in the presence of the vapor.