Frequently Asked Questions..
What is Glass Strengthening ?
In order to improve the tensile strength characteristics it is possible to
"pre-load"
the surfaces of the glass with compressive stresses. This can be done either by
heat strengthening, heat tempering or chemically strengthening the glass. When
a glass plate is bent, the convex surface is placed into tension while the
concave
surface is compressed. By adding compressive stress to the glass, the
compressive force must be overcome before the surface becomes tensile in
nature. This can dramatically improve the amount of bending force that may be
placed on a plate of glass before it breaks.
What is Heat Tempered Glass
Heat tempered glass, or sometimes referred to as "tempered glass," is the name given to glass products that have been strengthened by heattreating the glass to increase the surface compression and/or edge compression beyond a specified level. When the surface compression introduced is above 10,000 psi (69 Mpa), it may be considered "Kind FT" per ASTM C 1048. In order to prevent confusion, the term "Heat Strengthened" is normally used to define glass heat-treated to a level below 10,000 psi surface compression.
Process of Heat Tempered Glass
Heat tempering of glass is achieved by
increasing the temperature of the glass to a point slightly below the
softening point of the material and then
immediately and quickly quenching the glass - generally by blowing volumes
of cooler air on the surfaces. Because the glass is expanded in the heating
process, the quick quench causes the external surfaces to cool suddenly
while the interior of the glass is still hot and expanded. The
surfaces become compressed and the interior mass of the glass is placed into
a state of tension. Since the outer surfaces are in compression and
the interior mass is in tension, the glass will release the tension when the
surface compression layer is penetrated. This tensile stress release causes
the glass to fracture into small fragments when the glass is broken. This
phenomenon is called dicing.