A revision of BS EN 14179 Glass in building - Heat soaked thermally toughened soda lime silicate safety glass Part 1 Definition and description was issued in August 2016. The most significant change is to the temperature regime for the heat soaking process.
The holding temperature for the heat soak process is now 260+/-10°C. During the heating phase the temperature of the glass is not permitted to exceed 290°C and the time above 270°C is to be minimised. The minimum duration of the holding phase remains at 2 hours. This change has been implemented as it is believed that conversion of some combinations of NiS occurs at a temperature of about 290°C.
Other changes relate to tolerances and bring EN 14179 into line with the 2015 revision of EN 12150 Glass in building - Thermally toughened soda lime silicate safety glass and are as follows:
- new terms and definitions have been included in Clause 3 eg air cushion process, edge lift, roller wave distortion (previously referred to a local bow),
- additional nominal thicknesses have been included in Table 1,
- tolerance on squareness has been revised and is now expressed as the difference in diagonals,
- the section on flatness has been revised with different requirements for different production methods (horizontal, vertical and air cushion) and a reduced limit of 0.3mm for roller wave of uncoated float glass produced by the horizontal process (previously 0.5mm),
- the flatness section now includes a method of measuring edge lift,
- a new informative Annex dealing with an alternative method of measurement for roller wave distortion has been added,
- the informative annex Curved heat soaked thermally toughened safety glass has been deleted.