Sidelite / Backlite Edge Stress
Due to the tempering process, edge compression and associated tension of sidelites and backlites can be very intense. Therefore, they are very sensitive to details of the thermal process. Often, the ring that the glass sits on while formed and tempered robs or gives heat near the edge of the glass, so that small pockets of tension are created. This tension serves to diminish the compressive skin force developed in tempering. If these tension pockets reach sufficient values any contact or load will result in catastrophic failure.
Specimen 1 and Specimen 2 below are 27Mpa Hot Spot consistent