Glass is heat-treated by heating annealed glass to a temperature of
approximately 1,150°F (621°C), then rapidly cooling it. The glass is cooled
by a carefully controlled airflow (also known as quenching), which uniformly
cools all glass surfaces simultaneously. High airflow rates produce tempered
glass and much lower airflow rates produce heat-strengthened glass.
Characteristics
Fully tempered glass is approximately four times stronger
than annealed glass of the same thickness and configuration. When it is
broken, tempered glass fractures into small fragments that reduce the
probability of serious injury as compared to annealed glass. Tempered glass
meets all safety glazing standards including the federal safety glazing
standard. Because tempered glass fractures into many small pieces, it tends
to vacate the opening, when broken, more than heat-strengthened and annealed
glass does.
Applications
Tempered glass is used when the strength requirements exceed
the capabilities of heat-strengthened glass, and for all safety glazing
applications. Tempered glass is commonly used in sliding doors, storm doors,
atriums, partitions, windows, storefronts, display cases, bath and shower
enclosures and all-glass doors and entrances. Tempered glass should not be
installed in areas where it is exposed to temperatures greater than
approximately 400°F because it will begin to lose its degree of temper
(reverting back to annealed glass).
