Hot Forming of Glass Ceramics

The parent glass melt is cooled down to the processing temperature in the fore hearth, homogenized and fed to the rolling machine via a nozzle. The glass flow is controlled by the size of the nozzle gap and the roller velocity. 

The reheating is concluded quickly due to further cooling of the glass strip via heat loss to the air and transport rollers (see Fig. 3.32). The glass becomes rigid and the shaping process is completed. 

The complex thermal processes during shaping in the rolling machine can be described as follows the heat flow between the glass and the rollers is by means of conduction, convection, and radiation. The course of heat flow across the circumference of a roller is reflected in the heat-flow diagram (see Fig. 3.33). 

The local temperature distribution and the change of the temperature on the surface of a roller with time can be viewed as the overlaying of a stationary temperature field with a field resulting from a temperature oscillation. The illustration shows the local heat-flow density in a roller as a function of the number of revolutions (see Fig. 3.33). 

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