Patent ID: 8769990

Claim:
A method for tempering a glass sheet, comprising: a heating step of preheating the glass sheet to a temperature close to the softening point of the glass sheet; a quenching step of blowing a cooling medium to both surfaces in the thickness direction of the heated glass sheet; a pre-quenching step performed between the heating step and the quenching step when a vicinity of a center portion in the thickness direction of the glass sheet has a temperature different from surfaces of the glass sheet; and an internal heating substep of selectively heating the vicinity of the center portion in the thickness direction of the glass sheet, relative to the surfaces, at least in the quenching step, wherein initiation of the internal heating substep is set to be within a period from an intermediate time point in the pre-quenching step to an intermediate time point in the quenching step, and termination of the internal heating substep is set to be at an intermediate time point in the quenching step, such that in the quenching step, when the temperature in the vicinity of the center portion in the thickness direction of the glass sheet is close to the tempering point of the glass sheet, the temperature at the surfaces in the thickness direction of the glass sheet is not higher than the annealing point.