The basic principal employed in the heat treating process is to create an initial condition of surface and edge compression. This condition of surface and edge compression. This Condition is achieved by first heating the glass. then cooling the surfaces rapidly. This leaves the center glass thickness and then cools, it forces the surfaces and edges into compression.
In the “heat –treatment” process the key element is a 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 sustains the quench long enough to prevent reheating of the glass surface from the still-hot glass core.
A quenched condition becomes stable when the glass is reduced to a temperature of approximately 400-600 °F.
Tempered glass is used traditionally in place of other glass products in application requiring increased strength and reduced likelihood of injury in the event of breakage. The building industry, motor vehicle industry and certain manufacturing industries fine tempered glass effective and economical in a wide range of application.
Tempered glass can also be used for applications as doors, side lights, shower and tub enclosure, and interior partitions. It is also used in storm doors. Patio –door assemblies And stairway balustrades. As a glazing product, it is used in windows and in spandrel areas, sloped glazing, racquetball courts, skylights and solar panels. Manufacturing industries use tempered glass in refrigerators, furniture, ovens, shelving, and fireplace screens.