Investigations into all-electric melting of neutral glass with improved reboil behaviour

With regard to chemical stability, great demands are made on neutral glasses because of their pharmaceutical application, which requires a high standard of the quality parameters: bubble numbers, homogeneity, and reboil stability. Nowadays, acceptable results are only reached by fuel-fired special furnaces with very high specific energy consumption and engineering efforts. The economical and ecological advantages of all-electric glass melting could contribute to considerable cost cutting. At present, however, certain quality criteria are not within reach when using this melting technology. The main disadvantages are the comparatively high residual gas contents and bubble numbers. Up to now, efforts have been unsuccessful to melt neutral glass with sufficient glass quality all electrically. The possible advantages, however, are worth treating this problem further. The present conception is based on a separation in melting and fining basin. By using knowledge of all-electric melting of borosilicate glass 3.3, the disadvantages in respect of gas solubility and bubble numbers will be removed in a separate fining cell by use of bubbling. Various laboratory experiments led to the concept of a combination of chemical and physical refining. The parameters for optimizing the refining process have been investigated. As a result of this work, a technical realization is proposed.