Thermal stresses during annealing of a glass ribbon

Abstract

In order to avoid fracture and to keep transient and residual stresses within acceptable bounds, it is necessary to include in the continuous process of glass forming an annealing phase, during which the temperature of the sheet is slowly brought from approximately 600 °C down to 25 °C. An adequate control of the annealing gallery requests a good understanding of the stress generation during cooling. The problem is quite complex, since the prediction of stresses is intimately related to the thermo-viscoelastic character of glass. Moreover, stress relaxation is accompanied by structural relaxation, which is strongly dependent upon temperature history.