Processed Toughened Glass

Toughened Safety Glass

Is up to five times stronger than annealed glass of the same thickness. Qualifies as a Grade 'A' Safety Glass and complies with AS/NZS 2208 and AS1288. Fractures into relatively small harmless particles when broken. Has a greater resistance to thermal stress. It can be subjected to temperatures ranging from 70°C to 290°C.

Heat Strengthened Glass

Is twice as strong as annealed glass of equal thickness. Does not qualify as a Grade 'A' Safety Glass. Has a greater resistance to thermal stress when compared to annealed glass. Typically breaks into large pieces which tend to remain in the opening.

Process

Heat-treated glass results from the controlled heating and cooling of annealed (float) glass. Firstly, annealed glass is heated inside a furnace to a temperature in excess of 600°C. The glass is then rapidly and uniformly cooled by blasting both sides of the glass with compressed air, a process known as quenching.

This 'snap cooling' or quenching action induces compressive stresses into the glass surface while the centre remains in tension. The cooling (or quenching) rate dictates how much stress is introduced into the sheet of glass. Toughened glass is cooled more quickly than heat-strengthened glass.

Hole and Cut Out Limitations

Holes:

  • Holes must be at least the thickness of the glass.
  • Holes must be at least 1.5 times the glass thickness from the glass edge for 4-6mm glass, and 2 times the glass thickness from the edge for 8-19mm glass. Otherwise a release cut will be required, with a minimum distance from the glass edge of holes in a corner must be at least 4 times the glass thickness from each glass edge.
  • The distance between holes must be at least 4 times the glass thickness.
  • Hole diameters must be less than 33% of the narrowest height / width dimension of the panel.

Cut Outs:

  • Centre cut outs must be at least 50% of the width or height of the cut out from the glass edge, with a minimum of 75mm for 4-6mm glass and 100mm for 8-19mm glass.
  • Side cut outs must be at least 80mm from the corner of the panel for 4-6mm glass and 100mm for 8-19mm glass.
  • The distance between centre cut outs must be at least 4 times the glass thickness.
  • Centre cut out height / width dimensions must be less than 33% of the narrowest height / width dimension of the panel.
  • Corner and side cut outs eg dog leg and t-piece panels, must not exceed 33% of the panel width / height.
  • Cut outs must have an internal radius corner of at least the thickness of the glass with a minimum of 8mm.