| 摘要 |
PURPOSE:To reduce the central tensile stress and surface compression stress and prepare a glass plate without the self propagation of a breaking line nor breaking into fine fragments, by heat-treating the glass plate under specific conditions. CONSTITUTION:A glass plate, e.g. a window glass, of 10-15mm. thickness is introduced into a roll hearth 2 and heated at 600-660 deg.C by a heating apparatus 4 while conveyed by rolls 3 in the hearth 2. The glass plate 1 taken out of the roll hearth 2 is then transferred to a gap between the opposite top and bottom hot air blowing holes 5 and cooled to 200-450 deg.C by blowing hot air at 50- 300 deg.C. The cooled glass plate 1 is then cooled to ordinary temperature in the atmosphere to give the aimed glass plate having 85-200kg/cm<2> central tensile stress (sigmat) and 1.5-2.0 ratio (sigmac/sigmat) between the surface compression stress (sigmac) and the central tensile stress (sigmat) without breaking into fine fragments even on the occurrence of cracks. |
