Hardened glass is made of unpolished, polished or figure glass sheets on a special hardening plants. All of necessary cutouts and holes are made before hardening, as well as chamfering, because after hardening it’s prohibited to carve, drill or subject to other kinds of mechanical processing the glass.
Glass hardening rather like, not unlike tempering. Firstly, glass is heated above the softening temperature and then rapidly cooled in the air jets. During cooling, first harden the surface layers of glass. Upon cooling of the inner layers, residual compressive stresses accumulate on the surface. That’s why hardened glass is so durable and heat-resistant.
Strength of hardened glass on a bend and hit a 5-6 times greater than the strength of ordinary glass, and both the heat resistance of its significantly higher. Broken hardened glass breaks into small sharp shards. What is more, such fracturing is regulated by the requirements of quality standards. At the test check hardened glass is struck by an acute hammer weighing 75 grams and must fracture on at least 40 shards if it’s 50×50 mm size and on at least 160 shards if it’s 100×100 mm size. The most vulnerable part of hardened glass is its edge. When installing the structures it’s necessary to protect its end faces against impact, scratches and other damage.
