TEMPERED AND HEAT-TREATED GLASS

MANUFACTURING PROCESSES

In the "heat-treatment" process the key procedure is application of a rapid air quench immediately upon withdrawal of hot (approx. 1200 ° F) glass from the "tempering furnace." The immediate and sustained application of an air quench produces the temper. As air direction against hot glass from arrays of fixed, reciprocation or rotating blast nozzles, it is important to extract heat uniformly from both surfaces (uneven heat extraction may produce bow or warp) and to sustain the quench long enough to prevent reheating of the glass surfaces from the still-hot glass core. A quenched condition becomes stable when the glass is reduced to a temperature of approximately 400-600 ° F.

There are two principal manufacturing methods for producing heat-treated glass. One process heat treats the glass in a horizontal position while the second method moves the glass through the furnace in a vertical position with each light of glass held by metal tongs.