Design of a sheet forming apparatus for overflow fusion process by numerical simulation

Abstract

The overflow fusion process is an important method for the manufacture of glass sheets and is currently used for the production of TFT/LCD display devices. The design of the forming apparatus is critical for obtaining very high surface quality glass to allow the successful application of semiconductor type materials. However, there is only little work presented in the literatures, because of difficulties and expansions in experiments. In this study, a numerical model for simulation of molten glass flow through an isopipe during the overflow fusion process was carried out. An explicit finite difference algorithm with the surface tracking method has been proposed. The effect of the geometry of the forming apparatus, flow rate and viscosity of molten glass on the flow patterns during overflow was investigated. It was found that the stability and flatness of the sheet glass was influenced by the design of the forming apparatus, and the flow rate and viscosity of molten glass flow. The tilt angle at the bottom the of a trough should be high enough (5–7°) to avoid the accumulation of molten glass. The smaller root angle (<50°) was better for recombination of two stream of glass. High flow velocity will induce an unsteady flow profile along the wall of the isopipe. A precise control of the working temperature was needed for maintaining an equal thickness along the isopipe.