Electric glass melting with low-frequency current

Abstract

Molybdenum electrodes are considerably corroded when melting lead glass by electricity. A theory concerning the corrosion of metal electrodes influenced by alternating current is presented. According to the present knowledge the corrosion increases with decreasing frequency of the alternating current. The new results demonstrate that the dependence of the decrease of electrode radius and of the amount of precipitated lead on frequency exhibits a more complicated course: with decreasing frequency both parameters grow to a maximum, then with further decreasing frequency they decrease to a minimum, which may be lower than the value corresponding to the zero current loading of the electrode. Only at very low frequency the corrosion grows again. An explanation of this behaviour is given. This new knowledge may be used to suppress the corrosion processes which occur in the electric melting of lead glass in a furnace equipped with molybdenum electrodes. A frequency converter for converting the main frequency into a required lower one, as well as the results of several years application of this method to the melting of 24 % PbO crystal glass in a furnace with a capacity of 12 t glass/d are described.