Today, let’s cover just one short but very peculiar question:
Yes, it is, but it is not recommended as there is no advantage when doing so.
You will more likely find yourself in trouble. This is because if the glass breaks in the furnace, it will shatter into small fragments more easily than during the first tempering.
Secondly, the optical quality will become worse. After the first tempering, the glass will have a certain amount of roller wave and edge lift, and then these will only become worse after the second tempering.
As comes to stresses, you won’t get any advantage if the process parameters don’t change. The stresses created in the first tempering will relax entirely, and the final outcome will be based on the settings of the second tempering.
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