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We make use of different strengthening processes in order to adapt glass, as a versatile, high-tech material, to its respective intended use.
Tempered safety glass consists of a single, specially thermally treated panel. The glass is heated to ca. 600 °C and then cooled suddenly. The center of the glass pulls back from the glass surface, which is being compressed. This process gives TSG an increased resistance to shocks and impacts. It is not sensitive to large changes in temperature and breaks into small, blunt pieces when exposed to extreme pressure. This reduces the risk of injury.
Thermal tempering: Semi-tempered glass (STG)
STG is exposed to a thermal tempering process just like TSG. However, the cooling process is slower, which results in less of a tension difference in the glass between the center and the surface. The resistance to bending lies somewhere between that of standard float glass and tempered safety glass. If broken, the resulting pieces resemble those of normal, non-hardened float glass.
If glass is exposed to a defined salt bath treatment, the resulting exchange of ions within a thin surface layer creates strong compressive stress that significantly improves the resistance properties of the glass. The chemical strengthening process is used primarily to strengthen thin glass up to 3 mm in thickness. The chemical strengthening process is ideal because the surface retains its flatness while also becoming more resistant to scratching.
Properties of tempered glasses
| Properties | FLOAT Glass Untreated | TSG Tempered Safety Glass | STG Semi Tempered Glass | CSG Chemically Strengthened Glass |
|---|---|---|---|---|
| Stone impact resistance | No change | No change | No change | ~ +40 % |
| Flexural strength | ~ 45 N/mm² | ~ 120 N/mm² | ~ 70 N/mm² | > 150 N/mm² |
| Temperature shock resistance | ~ 40 K | ~ 150 K | ~ 100 K | > 200 K |
| Cutting capability | Yes | No | No | Conditional |
| Appearance of fracture | Splitting | Friable structure | Splitting | Splitting |
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