Mechanism Dominating the Generation of Sink-Mark and Residual Stress in a Press-Formed Glassware from a Thermal Engineering Viewpoint

This paper deals with an experimental study on the generation of sink-mark and residual stress in a press formed glassware. Since both phenomena appear in the cooling process after pressing, it is considered that they were related with the growth of solidification layer on the press-formed surface. In this paper, the growth of solidification layer in a glassware and the generation of residual stress due to non-uniform shrinkage of glass, i.e. the generation of thermal tempering stress were numerically predicted, and the mechanism dominating the generation of sink-mark and residual stress frozen in a press-formed glassware was discussed by comparing the numerical results with those measured in actual glassware, which were press-formed in this study. The obtained results can be summarized as follows: (1) With elongating the pressing duration, both the sink-mark depth and the compressive residual stress at the pressed surface decrease while temperature at the pressed surface are little affected by the pressing duration. (2) The pressing-duration dependency of the sink mark and residual stress at the pressed surface is qualitatively explained well by a hypothesis that the thermal tempering stress starts to appear in the glass just after the deformation of the pressed surface, i.e. the generation of sink-mark stops due to the rigidity of solidification layer, and that the switchover timing becomes later as the pressing duration is elongated. (3) The compressive residual stress at the pressed surface is considered to consist of the thermal tempering stress due to non-uniform shrinkage of glass and the bending stress in the solidification layer due to sink mark generation.