IMPROVEMENTS IN OR RELATING TO TOUGHENED GLASS SHEETS AND METHOD FOR THEIR PRODUCTION

摘要

Thermally toughened glass sheets of thickness 2.5 mm to 4.0 mm for use as motor vehicle side or rear windows, are produced by quenching producing an average central tensile stress in the range 62 MN/m2 to 44.0 MN/n2. At least one gas jet is directed at the glass sheet to augment toughening stresses and produce at least one strip-shaped region of more highly toughened glass. The central tensile stress in the strip-shaped region is in the range from 2 MN/m2 to 5 MN/m2 greater than the average central tensile stress in the glass sheet. There are major and minor principal stresses in the strip-shaped region acting in the plane of the glass sheet. The difference between the major and minor principal stresses is in the range 5 MN/m2 to 25 MN/m2.