Page 88 - Glass-Technology International no. 4/2018

FURNACES

that is potentially subject to
HEAT SOAK breakage. All Tekno Kilns
TESTING furnaces are certified by an
The HST – Heat Soak Test External Body according to
– is a process carried out the European standard EN
on tempered glass, with the 14179-1.
aim of reducing spontane-
ous breakage of tempered CHEMICAL
glass sheets due to the TEMPERING
presence of nickel sulphide The flexibility characteris-
inclusions; thus avoiding tics of chemical tempered
costly substitutions on ex- glass are from five to ten
isting work. times higher than those of
During the Heat Soak thermal tempered glass.
Test, the glass must be Chemical tempering also
heated homogeneously up increases shock resistance
to 280°C, maintaining this of the glass.
temperature for two hours, Tests carried out with a
followed by controlled steel sphere, show that
cooling before removing thermal tempered glass has
the glass. Thanks to this more than twice the resist-
test cycle, defective glass ance compared to that of
sheets break, thus avoid- normal glass, while chemi-
ing the installation of glass cal tempered glass is more

86 Glass-Technology International 4/2018