Float Glass Forming

The process of float glass forming transforms a molten glass pool into a solid ribbon. The molten glass is conveyed on a molten tin bath and is stretched laterally by rolls to enhance ribbon width while it simultaneously cools and solidifies. The placement of overhead heating and cooling units is crucial to produce high optical quality (i.e., very uniform thickness).

Temperature distribution along the glass ribbon. At the beginning of the ribbon (left), the glass is exiting the furnace across a thin slit at a given temperature. At the end of the ribbon (right), after floating on the tin bath and being stretch both in the longitudinal and lateral directions by the numerous rolls located on the border of the ribbon, the thin, flat glass is cooled down and exits the tin bath at a much lower temperature with a small but uniform glass thickness.

The numerical simulation shows the evolution of the temperature, velocity and thickness of the glass ribbon while it is floating on the tin bath. Using this additional information, the glass designer can adjust the operating condition in order to further improve the production process, creating a glass sheet of higher quality.

Float glass forming was successfully modeled by Dr. Rajiv Tiwary and Dr. C.K. Edge of PPG Industries, Inc. using FIDAP. The simulation results provided insight into the float glass forming process, including width and thickness profiles, longitudinal and lateral stresses and residence times. Excellent agreement between the CFD results and plant measurements was obtained. The model was subsequently used for several parametric design studies.