Ceramics-Silikáty 52 (4) 225-239 (2008)

GLASS MELTING AND ITS INNOVATION POTENTIALS: BUBBLE REMOVAL UNDER THE EFFECT OF THE CENTRIFUGAL FORCE

L. Němec, V. Tonarová

The fining process may be enhanced by an additional force on bubbles in the glass melt. This study deals with the behaviour of a single bubble in the glass melt by a centrifugal force obtained in a rotating discontinuous cylinder. A model for bubble movement and size changes (growth or dissolution) for a single bubble in a glass melt exposed the combined gravitational and centrifugal fields has been developed and calculations of the bubble behaviour in a glass melt contained in a vertical rotating cylinder have been performed for a TV panel glass. The crucial factor of the removal of a bubble from the melt appeared to be its partial or complete dissolution in the molten glass, governed by the number of different gas species present, their concentrations in the bubble, as well as by their physical or chemical solubility and diffusion coefficients in the molten glass. The results of the calculations have shown that the bubble-separation (removal by moving the bubble to the glass melt surface) mechanism should be preferred to dissolution. The recommended bubble removal/separation conditions can be derived from the general found dependencies between the bubble-removal times and the cylinder-rotation velocity for different glass types, temperatures and cylinder dimensions. The minimum separation time, dependent on the applied temperature, rotation rate, filling level, size of cylinder, will direct to the most effective bubble separation conditions and appears to be a guide for practical applications. The position of the minimum in the curve of separation time versus cylinder rotation velocity and these bubble-separation times depend on the temperature, external pressure, the initial actual bubble radius (bubble radius changes if the rotational velocity is changed) and composition of the bubble, composition of the molten glass (gas properties in the given glass), the cylinder radius and the degree to which the cylinder is filled with glass.

Keywords: Glass melt, Bubble removal, Centrifugal force, Modelling, Rotating cylinder