Modeling And Simulation For Pre-controlling Toughened Glass Cooling Process

Tempering is able to eliminate or reduce the micro cracks on the surface of theglass, improve the mechanical properties, and increase the thermal stability. As the lastprocess of tempering, the cooling may produce spontaneous detonation of glass orsurface stress surface stress spot which can decrease the quality of tempered glass, sincethe each point cooling time length is different from each other and it is difficult toguarantee the cooling uniformity of plate during the cooling process. Therefore, it isnecessary to preview the cooling process to make sure the quality of toughened glass.The main work is listed as follows.The process control requirements during the cooling process control are analyzedand the cooling rate and cooling time are thus selected as the precontrol object. Basedon the Fourier law and the features of the glass stress relaxation and the structurerelaxation, the relationship model between the cooling rate and temperature field andthe temperature and the glass viscoelastic constitutive model are built. Furthermore, thechange relationship between cooling rate and residual stress is deduced, and theprecontrol mathematic model is built to control the cooling process accurately.Based onthe finite element analysis method, simulation model of temperature and stress changesin the toughened process of cooling process is established.After running precontrol model and multiple sets of simulation experiment, thefollowing results can be obtained. If the thick of glass is5mm and convective heattransfer coefficient is190w/(m2K), the glass should be cooling with by0.125℃/s2within the first40s and by0.125℃/s2between40s to80s, and thereby obtain the atemperature difference of151℃in the center of the glass in7s. The glass temperatureshould decease to below the transition temperature region within10s, to finalize thestructure of glass basically. The approximate parabolic distribution of residual stress isobtained, which can provide the pre-stressing force under stress. All the above resultsdemonstrate that the pre-control mathematic model has higher accuracy and reliability and it can be used in practice.