· Toughened or tempered glass is a type
of safety glass processed by controlled thermal or chemical treatments to
increase its strength compared with normal glass.
·
Tempering puts the outer surfaces
into compression and the inner surfaces into tension. Such stresses cause the
glass, when broken, to crumble into small granular chunks instead of
splintering into jagged shards as plate glass creates. The granular chunks are
less likely to cause injury.
·
As a result of its safety and
strength, toughened glass is used in a variety of demanding applications,
including passenger vehicle windows, shower doors, architectural glass doors
and tables, refrigerator trays, as a component of bulletproof glass, for diving
masks, and various types of plates and cookware.
·
The term tempered glass, in addition
to meaning glass that has been heat treated to increase toughness, can refer to
glass that has been treated with hydrofluoric acid or other acid. The acid
etches away surface scratches and imperfections to increase strength.
·
Toughened glass is physically and
thermally stronger than regular glass. The greater contraction of the inner
layer during manufacturing induces compressive stresses in the surface of the
glass balanced by tensile stresses in the body of the glass.
·
It is this compressive stress that
gives the toughened glass increased strength. This is because any surface flaws
tend to be pressed closed by the retained compressive forces, while the core
layer remains relatively free of the defects which could cause a crack to
begin.
·
The strain pattern resulting from
tempering can be observed with polarized light or by using a
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