Safety tempered glass after suitable off-line Heat Soak Test

Abstract

Heating conditions of off-line Heat Soak Test have been investigated based on a lot of studies about nickel sulfide defect included in the tempered and heat-strengthened glass products. The temperature of the alpha-beta phase transformation is different with a change of the chemical composition (sulfur content) of the nickel sulfide crystal. In the case that the nickel sulfide includes higher than 35.3 wt % of sulfur component, the temperature of alpha-beta phase transformation continuously changes from 379 to 282 °C. There are several thermal conditions for the off-line Heat Soak Test of the tempered glass. The most reliable heat-treatment condition (260 °C+/−10 °C) has been established in ISO 2065 based on EN 14197-1-2016 in 2017. In the world, a lot of glass manufacturers adopt an old condition (290 °C+/−10 °C) of EN 14179-1-2005 in the off-line Heat Soak Test. In the off-line Heat Soak Test, we must maintain the furnace temperature lower than 270 °C that was specified in ISO 20657-2017 in order to raise the degree of beta-phase transformation of nickel sulfide.