Improvements in or relating to tempered glazings and glass for use therein

Abstract

Glazing, thermally tempered to required standards, are produced more readily by tempering panes having a high coefficient of thermal expansion (greater than 93×10 per degree Centigrade) and for a low Fracture Toughness (less than 0.72 MPam ). Use of glasses selected according to the invention enables thin glazings (especially glazings less than 3 mm thick) to be tempered to automotive standard with improved yields using conventional tempering methods, and thicker glazings to be tempered at lower quench pressure than required hitherto. Suitable glasses include glasses comprising, in percentages by weight, 64 to 75% SiO , 0 to 5% Al O , 0 to 5% B O , 9 to 16% alkaline earth metal oxide other than MgO, 0 to 2% MgO, 15 to 18% alkali mental oxide and at least 0.05% total iron (calculated as Fe O )