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Tempered Glass and Thermally Toughened Glass

The process of glass tempering consists of heating up the glass up to anything between 620 and 650°С and then rapidly cooling it. Both heating and cooling must happen in a controlled way in order to avoid breakage and achieve perfect flatness. The result is glass that is four to five times stronger than regular annealed glass, which is achieved by creating contained stress inside the glass. Tempered glass is considered to be safety glass. It can still be broken, but the break pattern consists of many small blunt pieces of glass that do not cut.

Thermally toughened glass  is a variation of thermally processed glass. It differs from the tempered glass in the way it is cooled. In thermally toughened glass the force and volume of the air used is much less thus reducing the stress on the glass. The result is a product that is about twice as strong as regular annealed glass. The break pattern consits of few bigger shards of glass. Thermally touhged glass by itself is not considerd safety glass. It can be used in laminatated safety glass in combination with tempered glass or another thermally touhged glass. The reason is that in case the glass breaks, the big remaining glass pieces will remain in one place until safely removed.  Thermally toughened glass is also used as part of insulating glass units where extra strenght is required. The biggest advantage of thermally toughened glass is that it is not prone to "spontaneous breakage”, while being stronger than regular glass.

Tempered and thermally toughened glass produced by "Bul-It Glass" Ltd.meets the requirements of standards EN 12150, EN 1863, EN 14072, ISO 3904, ISO 1095, ISO 3254. Tempering of glass with all colors and coatings is possible.

We are equipped with a Glaston FC500.


Technical specifications:

Glass thickness tempered glassfrom 4 to 19 mm.
Glass thickness thermally touchened glassfrom 4 до 10 mm.
Glass type
  • clear float
  • tinted float
  • with magnetron and pyrolise coatings                                                                                                                   
  • with low-e soft coating, double or tripple silver, suited for tempering
Minimal glass dimensions200 x 300 mm.
Maximum glass dimensions of 4 mm. glass1800 x 2800 mm.
Maximum glass dimensions > 4mm.2400 x 4800 mm.
Preprocessing requirementsPlease see conditions for successful tempering..




Comparison table between tempered glass, thermally toughened glass and annealed glass:

 Tempered glassThermally toughened glassAnnealed glass
Mass per mm. of thickness2.5 kg/m22.5 kg/m22.5 kg/m2
Resistance to temperature difference250°C130°C35°C (~ 50°C when edge is processed)
Temperature resistanceup to 300°Cup to 290°Cup to 150°C
Strength in comparison to annealed glassx5x2x1
Tension strength(8 mm. glass)150 N/mm280 N/mm240 N/mm2
Break patternMultiple small blunt pieces.Few large shards, sharp edges.Very few large shards with, sharp edges.
Considered safeYesNoNo
Option to process finished productNoNoYes


VIDEO: Heat-Treated Glass Processes. Credit: glassed.vitroglazings.com




"Spontaneous" breakage of tempered glass:

The manufacturing process of float glass involves usage of a wide variety of inclusions. One such inclusion is Nickel-Sulfide. In rare occasions small Nickel-Sulfide stones may end up in the mass of the glass. With size as small as 0.2mm. they are practically invisible to quality control and there is no known method to detect and avoid them. Being of metal nature these stones expand thermally in a different rate than glass. After tempering, the glass becomes internally stressed and such different expansion from the inside may cause a "spontaneous" breakage. This is a very rare occasion and may take place after any period of time depending on the conditions where the glass is installed. In most cases the cause of breakage of tempered glass ends up being caused by external factors such as installation mistakes, vandalism or natural causes such as a hit with a sharp object. To avoid a potential Nickel-Sulfide stone caused breakage there is a test called "Heat-Soak". During this test the tempered glass is heated up to 300 °C in order to provoke the expansion of potentially included nickel-sulfide stones and thus artificially force the breakage while still in production. Despite of that there is no 100% guarantee that Heat-Soak testing will prevent all potential "spontaneous" breakages. Nickel-Sulfide stone inclusions can not cause spontaneous breakage when the glass is thermally toughened, due to the fact that internal stress with this type of glass is much less.




VIDEO: Nickel Sulfide and Spontaneous Breakage. Credit: glassed.vitroglazings.com

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