Study On The Technique Principle Of Heat Shock Resistance Borosilicate Glass Formed By The Float

With the developing of electronics,biotechnology,security,new energy and aerospace fields,they have a higher demand to related flat glass.Borosilicate glass has a very high-performance,such as good thermal stability,chemical stability, mechanical properties,machine performance and optical properties,to meet these requirements.At the same time,flat glass producted by the float process have many well-known advantages,such as low cost,production,good surface quality and more variety,is the best technology for large-scale production of flat glass.And for a float flat glass production process,the forming process and the principle of the tin bath is one of its key technologies.In this study,high temperature viscosity,surface tension,electronic probe, atomic force microscope and other modern means of testing were used,mainly in borosilicate float glass forming process and the principle.The main work and conclusions are as follows:1.The flatting and polishing process were studied.The viscosity,the surface tension and the density of borosilicate glass at high temperature were measured,and differences between borosilicate float glass and sodium-calcium-silicon float glass were compared.The results show that:(1)Equilibrium thickness:The equilibrium thickness of borosilicate float glass is greater than that of sodium calcium silicon float glass.It is decreasing with temperature,about 7.46 mm at 1170℃,and about 7.10 mm at 1270℃.For borosilicate float glass,equilibrium thickness(T_h)and temperature(T)meet the empirical formula relationship:T₌12.25-0.00408 T(1170℃＜T＜1270℃). Introducing the ratio of surface tension to density of the test results,the theory of the formula can be extended.The equilibrium thickness(T_h)of borosilicate float glass can be judged through surface tension/density ratio(Φ)of glass.The relationship between them meet T_h=0.060Φ-2.423.(2)Polishing process:The polishing effect and flatting time were both determined by surface tension/viscosity ratio at high temperature.But there is no clear boundaries between them in the existing float forming theory.This article holds that the polishing process reflects the microcosmic effect of the surface tension/viscosity ratio,and the flatting process reflects the macroscopical effect of the surface tension/viscosity ratio.The surface quality of float glass in polishing process is not restricted by time,but by temperature.Borosilicate float glass can reach a good polishing quality at the temperature above 1230℃.(3)Flatting process:The flatting time of borosilicate float glass is shortening with the increase of temperature,about 109s at 1168.6℃and 35s at 1276.7℃.A new method is put forward to choose the polishing and flatting region of borosilicate float glass,i.e.combining surface tension/viscosity ratio(88～97)from 1168.6 to 1276.7℃and the needed temperature(＞1230.0℃)for polishing decided jointly. The tin bath regional temperatures of the borosilicate float glass were compartmentalized by this new method and supplemented by the viscosity curve.2.The effects of time,temperature and protection gas on penetration of tin into borosilicate float glass were studied by simulating the actual forming process of float glass.The similarities and differences between borosilicate float glass and sodium calcium silicon float glass were compared under the same experimental conditions. Finally,the borosilicate float glasses including different concentration tin were heated to demonstrate the critical value of tin concentration which bring on bloom.The results show that:(1)The tin ion penetration depth is about 25 to 40μm in borosilicate glass float, and tin concentration is about of 0.2 to 1.2 at%.The amount of tin in borosilicate float glass increased with the residence time of glass on tin liquid extended.The tin ions mainly entered into deep layer at high temperature and congregated at surface layer(＜7μm)at low temperature.The anomaly boron phenomena caused by temperature can induce an abnormal tin penetration profile,but it would disappear at lower temperature because of inverted penetration.(2)The tin penetration amount of borosilicate float glass was less than that of sodium calcium silicate float glass under the same conditions.(3)The critical value of tin concentration which bring on bloom to borosilicate float glass was about 0.81 at.%,and increasing the purity of protection gas was propitious to decrease the amount of tin penetration.3.The penetration of tin into the surface can change the property of borosilicate float glass.The possible phase transition and the effect of tin on borosilicate glass were studied.The results show that:(1)The borosilicate glass surface may crystallize SiO₂ crystal at about 750℃.(2)The tin ions penetration into the surface of borosilicate float glass can inhibit the extent of surface crystallization,and will not bring more bad effects.