This method is dedicated specifically to hardened panes applied in building facades and all places exposed to direct solar radiation, where cracking and the falling of hardened glass from frames, may endanger persons being nearby or beneath glazing.
Tempered glass manufactured by Press-Glas ranks among the very top quality products.
Nevertheless, this state-of-the-art product shows a certain weakness characteristic of float glass: tiny nickel sulfide crystals (NiS) which may occur in molten glass during float glass production process.
When glass is heated during tempering, nickel sulfide impurities in the glass pane increase their volume; when the heated glass is rapidly quenched in the toughening process, the impurities, which need a certain amount of time to return to their original state, cannot do so and become “frozen”, producing additional local stress concentration. The mechanism resembles a delay-action bomb: when tempered glass containing nickel sulfide impurities is used in a structural glazing system on a building façade, it gets heated by sun rays, allowing frozen crystals to expand, and thus generating even more internal stress. With an inclusion in the core tensile zone, stress is highly likely to exceed the acceptable level, causing spontaneous fracture of the pane.