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In certain
occasion, tempered glass or its composite could meet the quest
of thickness and air-pressure for building facade, but it also
brings the threat, spontaneous breakage, when setting-up in high
buildings. But, fortunately, heat soak test make us out of the
risk with advanced technology.
There are two sakes of spontaneous
breakage: one is natural , and another one is made: the natural
one is caused of gaseous inclusions and other inclusions, include
nickel sulphide inclusion, and the making one is caused of the
deficiencies on corner or edge by neglect in process, or the failed
setting-up.
Strict quality control could solve problems of gaseous
inclusions, impurities of large particles, and deficiencies on
corner and edge, and the course of setting-up is control-able
as well, but nickel sulphide inclusion is invisible and hardly
examined, so after all of that, tempering processing and setting,
one could only seek his fortune away from the danger of spontaneous
breakage.
There are two types of nickel sulphide molecules, £\
and £], which would change its structures with temperature to cause
spontaneous breakage. But why not in lehr? For slowly cooling
process provides sufficient time for nickel sulphide inclusion
to transform from £\ to £], however, through tempering process over
380¢J, type £] turns into unstable type £\ "frozen" in
tempered glass when no time to turn back by rapid cooling, worse,
stress balance will be destroyed as type £\ is turning back to type
£] by any chance, then spontaneous breakage will occur. Heat soak
test prompts unstable type transforming and evoking spontaneous
breaking if any possibility.
In this case, heat soak test is for
selecting. According German DIN 18516, the process of heat soak
test is in 2 hours heating slowly close to 290¢J and keeping in
290¢J¡Ó10¢J through 8 hours and then to room temperature in 2 hours.
So that 99 percents above of nickel sulphide would be transformed
into stable type or failed glass would break caused of its blemishes.
Plus, there is tempering recession when heated above 300¢J, so rising
and keeping control of temperature is very important during whole
process. Tempered glass could be examined by specified equipments,
but none to examine weather heat soak test or not, so it is only
guarantee of reliable company . |
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