2 0 1 3 P R O D U C T G U I D E VIRACON PRODUCT GUIDE 2013 ...

HEAT TREATment
Heat Treatment Definitions
Heat-treated glass is a term used to describe glass that has been processed through a tempering furnace to alter its strength
characteristics. The process is done in order to provide greater resistance to thermal and mechanical stresses and achieve specific
break patterns for safety glazing applications as compared to annealed glass.
ANNEALED(AN)
Raw glass that has not been heat treated is annealed glass.
In a specification, the designation for annealed glass is AN.
HEAT STRENGTHENED(HS)
Heat-strengthened glass is twice as strong as annealed glass of the same thickness, size and type. If broken, heatstrengthened
glass will break into large shards similar to annealed glass.
The surface compression of heat-strengthened glass with thicknesses of 1/4” (6mm) and less is 4,000 - 7,000 psi. Surface
compression for 5/16” (8mm) and 3/8” (10mm) heat-strengthened glass is 5,000 - 8,000 psi. (Because of reader repeatability
and instrument tolerances, Viracon’s tolerance for heat-strengthened glass surface compression is +/- 1,000 psi.)
While improving the strength and resistance to thermal shock and stress, heat-strengthened glass does not meet safety
glazing requirements as outlined by the American National Standards Institute (ANSI) Z97.1 or the federal safety standard
Consumer Products Safety Commission (CPSC) 16 CFR 1201, and therefore should not be used in these situations.
In a specification, the designation for heat strengthened glass is HS.
FULLY TEMPERED(FT)
Glass with fully tempered surfaces is typically four times stronger than annealed glass and two times as strong as heatstrengthened
glass of the same thickness, size and type. In the event that fully tempered glass is broken, it will break into
fairly small pieces, reducing the chance for injury. In doing so, the small glass shards make it more likely that the glass will
become separated from the opening. The minimum surface compression for fully-tempered glass is 10,000 psi. In addition, it
complies with the safety glazing requirements as outlined by the American National Standards Institute (ANSI) Z97.1 and the
federal safety standard Consumer Products Safety Commission (CPSC) 16 CFR 1201.
In a specification, the designation for fully tempered glass is commonly abbreviated as FT.
HEAT SOAKING
Fully tempered glass may break without warning due to the expansion of nickel sulfide inclusions (NiS) present within float
glass. To avoid the risk of spontaneous breakage in fully tempered glass, a common practice is to avoid the use of tempered
glass whenever possible. Although the incidence of tempered glass breakage due to these inclusions is rare, greater publicity
of their occurrence has resulted in an increased awareness of this phenomenon. In fact, limiting the use of tempered glass in
commercial building applications has become the recommendation of a number of glass suppliers, including Viracon. In some
situations however, tempered glass is required to meet safety glazing requirements or for added strength. In these cases,
Viracon can perform a heat soak test to provide the added assurance that significant spontaneous breakage will not occur.
For more information, refer to our technical document Heat Soak Testing on our website viracon.com.
VIRACON // COMPONENTS & ENHANCEMENTS 031