Ceramics-Silikáty 52 (4) 217-224 (2008)

Challenge to improve glass melting and fining process

M. Kawaguchi, T. Kato, Y. Imamura, N. Yoshida, S. Aoki

In this paper, two fundamental factors, such as preparation of uniformly mixed fine batch and acceleration of fining, are addressed and will be discussed. The glass melting furnace can be considered as a physically and chemically mixing reactor at an elevated temperature, typically higher than 1500°C. To enable glass manufacturing process at lower temperatures, a better preparation of glass batch close to a physically uniform condition is required. Therefore, it has been investigated whether a glass forming raw material batch pulverized with a ball mill could improve the melting behavior. Analysis of the gases released during the batch reactions and evaluation of the residual silica with XRD analysis have shown that the pulverization facilitates the batch reaction and lowers the vitrifying or fusion reaction temperature. These results suggest that the pulverization of batch could improve the melting and fining behavior and decrease the melting temperature. The application of helium gas may enhance the fining process during a glass melting process. The fining effect by diffusion of helium through the surface of the glass melt into this glass melt by application of a helium atmosphere has been investigated both by a laboratory experiment and in a pilot scale test. These results have indicated that helium dissolution in glass melt is very effective to eliminate seeds. However, this diffusion method of helium entering through the glass melt surface from a helium atmosphere is considered only suitable to a small scale production in which the glass melts can be in direct contact with the helium atmosphere for a long time. To increase helium dissolution into glass melt, helium bubbling in glass melt is considered effective as a pre-conditioning step, especially in tank furnaces with large throughputs. A laboratory experiment on helium bubbling through the molten glass has indicated that this helium bubbling in the glass melt has both merit and demerit. The merit is that a large amount of helium could be dissolved in the glass melt, resulting in expansion of seeds. The demerit is that a lot of new blisters could be introduced into the melts and a certain amount of fining gas could be lost from the glass melt by the helium stripping effect. Therefore, a optimum design of the bubbling process by helium gas should be developed.