Online Stress Calculation in Tempering Process Based on Measured Process Data

Abstract

Optical stress measurement in tempered glass has its challenges. Stresses can be measured optically based on the optical anisotropy behavior of the glass. For example, the stress profile can be measured only offline, or stresses can be measured online at the edge. However, with an online stress calculation in the tempering line based on measured process data, the stress profile can be solved, and more information about tempered glass can thus be obtained. This information about stress level is important for glass processors because it provides information about glass strength and fragmentation which are important values for safety glass that meets the standards. To solve the residual stresses of tempered glass, it is important to know the glass material and the thermal history of the glass. The thermal history of the glass can be solved based on the information measured from the process and use this data with a heat transfer model. Time-dependent temperature profile is therefore used with thermo-elastic models to solve the stresses. The physical models and the measured data for calculation are presented in this study. The calculation model is then compared to offline stress measurements to find the accuracy of the results. The possible source of errors is also discussed.