| 摘要 |
PURPOSE:To prepare a glass plate without breaking into fine fragments even on the occurrence of cracks, by heating the glass plate to a specific temperature, and annealing the heat-treated glass plate at a different temperature of cooling zone and a different heat-treating time according to the plate thickness. CONSTITUTION:A glass plate 1, 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. The glass plate 1 is then transferred to an annealing zone 5, annealed to 300-350 deg.C surface temperature and then cooled in a gap between cooling air blowing holes 6 by blowing cooling air thereon. The annealing in the annealing zone 5 is carried out by setting the temperature of the cooling zone 5 and retention time in the cooling zone at the following values according to the thickness of the glass plate 1: 50-150 deg.C and 2-15min for 10- 11mm. thickness, 80-200 deg.C and 3-17min for 11-13mm. thickness and 100-300 deg.C and 3-20min for 13-15mm. thickness. Thus, the aimed glass plate having 85- 200kg/cm<2> central tensile stress (sigmat) and 1.5-3.0 ratio (sigmac/sigmat) ratio between the surface compression stress (sigmac) and the central tensile stress (sigmat) is obtained. |
