Tempered Glass is safety glass. Tempered glass is made from plain annealed glass.
First, cut glass to finally required trim size out of a big annealed glass sheet (e.g. 3660×2440mm), next glass is heated to close to glass softening point 700 degrees in tempering furnace, then heated glass suffers from rapid homogeneous cooling to become tempered glass (usually 5 mm – 6 mm glass was heated for 240 seconds under 700 degrees high temperatures, cooling 150 seconds; 8 mm – 10 mm glass suffers from heating for 500 seconds under 700 degrees high temperatures, cooling time 300 seconds). Anyhow, the heating and cooling time depends on the thickness of glass.
After tempering processing, glass surface forms an uniform compressive stress, while the internal has tensile stress, which improves the bending and impact strength of the glass. Mechanical strength of tempered glass is about four times more than ordinary annealed glass.
One important aspect everyone should remember is that after tempering processing, tempered glass can’t be further cut, edge-grinded and other physical treatment. Tempered glass will get broken if the balance of external compressive stress is damaged.
The weak points of tempered glass lies in glass edges and corners, that’s why during long-distance transportation, glass edges and corners must be well packed and protected.
Following pictures show the different fragmentation status of tempered glass and annealed glass after breakage.