Viscoelastic modelling of stresses in glass samples at the seal edge

The envelope of a CRT consists of three glass parts. Since glass is a brittle material these parts are sensitive to the stress level produced during processing and in use. Maximum stresses occur during safety impact tests. In order to improve the reliability of the frit process and later processes it is important to know the cause and magnitude of the stresses during and after the frit process. A viscoelastic simulation of the frit process of two blocks of glass has been carried out to obtain insight in the stress generation in screen and cone glass. The in uence on the stresses of various processing parameters is studied. Conclusions: Stresses occurring in the glass during the frit process are not only caused by di erence in thermal expansion coe cient but mainly by structural rearrangement at higher temperatures. A relatively simple elastic model of glass is not su cient to simulate the real frit process. Fritting with both higher and lower maximum oven temperature settings will decrease the absolute value of the residual stresses in the screen glass. c Philips Electronics N.V. 1998 iii UR 001/98 Unclassi ed Report Thermal history of the glass signi cantly in uences the stress evolution during the frit process. Reason for this e ect is the degree of compaction of the initial glass products; a rapid cooled `fresh' glass will be subject to high compaction during subsequent thermal processes such as the frit process. The di erence in frit crystallization dynamics near the maximum temperature of the frit process is negligible. Crystallization of the frit at lower temperatures causes the absolute values of the stresses to increase. The calculated residual stress is strongly dependent on the choice of the initial parameter initial ctive temperature and the frit process parameters oven temperature settings and frit crystallization dynamics. Therefore a careful validation of the boundary conditions and assumptions has to be made for reliable modelling. Comment: This work has been carried out as an orientational research project in the frame of a student practical training at the Nat. Lab. It has correlations with running projects at Disp. Comp. PPD `High surface compression' and `Prestressed seal edge' iv c Philips Electronics N.V. 1998 Unclassi ed Report UR 001/98