Toughened glass forms small granules when broken.
Toughened glass is made from annealed glass via a thermal tempering process. Producing toughened and heat strengthened glass begins with the feeding by conveyor of cut-to-size annealed sheets of glass (with minimum arrised edges) into a furnace.The glass oscillates back and forth on ceramic rollers to an approximate temperature of 620ºC.Under computer control, the glass moves into the quench where it is rapidly cooled by high pressure cool air. This 'snap' cooling or quenching induces compressive stresses to the glass surface, while the centre remains in tension. Although the physical characteristics remain unchanged, the additional stresses created within the glass increases its strength by 4–5 times (for toughened glass) compared to that of annealed glass of equal thickness.
Features and applications:
Safety – Toughened safety glass is manufactured to AS/NZS2208 and 2080 and is a Grade A safety glass as per AS1288;
Stronger – Up to 500% stronger than annealed glass and therefore is more resistant to thermal breakage and can withstand greater wind loads. Can be used within a temperature range of minus 70°C to plus 250°C (surface temperature should not exceed 250° C if other surface is lower than 0°C ambient);
Frameless – Allows reduction of framing members to produce a cleaner frameless look;
Ease of handling – Standard arrised edge makes handling easier;
Matching – Ease of matching tinted toughened Safety Grade A glass and tinted annealed glass;
Delivery – Plastic wrapped or papered to avoid scratches during delivery;
Thicknesses – Available 12mm Grade A Safety Glass and 15–25mm toughened glass. Flat automotive and marine toughened is available in 4–12mm;
Applications – Recommended for door, side and low lites, frameless entries, balustrades with handrails, shower enclosures and furniture. Toughened glass furnace.
Design and glazing notes
Surface treatments – Toughened glass cannot be drilled or edgeworked in any manner. Sand blasting and other surface treatments should be carried out prior to toughening. Deep sand blasted patterns greater than 1mmare not permissible;
Templates – For toughened glass ordered to templates refer to our template processing guidelines;
Minimum edgework – Finish on toughened glass up to 12mm is a standard arrised edge. Minimum edge work on greater thicknesses will be a flat ground edge;
Bowing – Slight distortion or bowing may occur after toughening but is largely controllable. It will vary with substance, tint, surface treatment, size and shape of the glass. Ceramic painted, sand blasted or reflective coated glass has a greater tendency to bow and special tolerances would be advised. Flatness will be measured when the glass is standing on edge with a straight edge placed along the full length of the panel and a wedge measurement taken at the centre position;
Visual distortion – The furnacing of glass panels can produce slight corrugated distortion or roller waves. This visual effect is in the form of distortion bands 250–300mm apart. It is more noticeable in tinted and reflective toughened glass. It is recommended that the roller wave run horizontal on the glass subject to the sizing constraints of the toughening furnace. Less visual distortion is evident with a heat strengthened glass. Talk to our staff about specific optical requirements;
Quench pattern – During the quenching phase of the toughening process, the glass is rapidly cooled by high velocity blasts of air. Inevitably this results in slightly higher levels of compression at those areas adjacent to the air nozzles. The consequence of this is the occasional appearance of a strain pattern or iridescent spots or darkish shadows. This effect is referred to as the quench pattern as it occurs in the furnace quench. Typically, the pattern is only visible at times of polarised light (polarised sunglasses) or by viewing the glass from the inside at acute angles. Similarly, the thicker and more reflective the glass, the more obvious the pattern will be;
Plastic wrap on toughened glass is used to protect the glass during transport. The plastic wrap should be removed no later than one month after exposure to sunlight.
On rare occasions, toughened glass can break for what seems to be no apparent reason. A variety of contaminants in the raw stock can lead to problems either during or subsequent to the toughening process. Investigation into some instances of spontaneous breakage has identified an impurity in theglass called nickel sulphide as the cause. Most often however, breakage is usually due to surface damage or excessive loading on toughened glass.
Toughened Glasses can be made for following purposes and category:
- Clear Toughened Glass
- Door Panels
- High Performance
- Low E