Research On Float Mechanism Of Li₂O-Al₂O₃-SiO₂ Flat Glass

(LAS) glass-ceramics have many excellent properties, widely used in many fields, which are produced by holding technique currently. Float process is the best way to produce flat glass, therefore introducing float process to the production of LAS glass-ceramic was considered. The regularity of polishing and flatting process of LAS glass was studied. The float polishing mechanism of LAS system plate glass was investigated, providing theoretical support for the production of float LAS glass-ceramics.In this paper, by testing high temperature viscosity, surface tension and density, the variation of high-temperature viscosity, surface tension, density and temperature of LAS glass was investigated. The variation relation of thickness of the different components of LAS glass with temperature and time was measured. The depth of field microscopy was used to analyze polishing effect. The flatting process of LAS glass was analyzed theoretically. The effect of different thermal history on the crystallization of LAS float glass was studied by DTA, XRD and SEM. Besides, effect of crystallization on the viscosity, density, surface tension and surface polishing effect was also investigated.The results showed that the equilibrium thickness of LAS glass containing nucleating agents was about 7.24-7.26mm. The equilibrium thickness of LAS glass excluding nucleating agents was about 7.12-7.22mm. The equilibrium thickness of LAS glass thickness decreased slightly with temperature increasing.The thickness of LAS glass containing nucleating agents reaching equilibrium needed 8-10min, about 4min for LAS glass excluding nucleating agents. Glass polishing process reflected the micro effect of surface tension/viscosity ratio, and the flatting process was the embodiment of the macro effect of surface tension/viscosity ratio.The surface tension and density of LAS glass excluding nucleating agents increased linearly as the temperature decreased, which achieved a good polishing effect at 1250℃, while LAS glass containing nucleating agents needed above 1340℃.The theoretical flatting time of LAS glass excluding nucleating agents shortened with increasing temperature, which was about 31s at 1308.1℃(103.7dPa·s), approximately 101s at 1236.4℃(104.2dPa·s). In order to realize the float forming of LAS glass, the surface tension/viscosity ratio should be controlled within the range of 96 to 108(10-5Ncm-1dPa·s), considering the viscosity and surface tension to adjust the composition of LAS glass.As the temperature increased, the crystalline phase of different components of LAS glass appeared crystalline transformation, transition fromβ-quartz solid solution toβ-spodumene solid solution. Not only temperature influenced crystal phase of the LAS glass, the time of isothermal heat treatment was also an important factor.From low temperature to high temperature, LAS glass occurred crystallization, while still being glassy state during high temperature to low temperature heat treatment process. The crystallization of LAS glass increased polishing temperature of glass required, and reduced the polishing effect.