Production of toughened sheet glasses of thin nominals

Abstract

An experimental apparatus for forming thin nominals glass by vertical drawing has been developed. The character and duration of transients in the area of sheet glass molding with thickness less than 2 mm in the stability of their geometri c parameters and physicochemical properties have been researched. The time-temperature regimes of drawing of thin nominals sheet glass have been determined. It was found that their molding should be carried out in the temperature range of 840–850°C (glass viscosity 10{4.8}–10{5} Pa · s), since the detaching effect of surface tension forces does not lead to significant narrowing ribbon of the glass. According to the parameters of glass surface quality, glass drawn in this temperature range resembles float glass to some extent. However, it is characterized by the lower thickness (0.5 mm). The temperature increase to 900–950°C (in the active forming zone) causes the decrease of the surface quality and a significant narrowing of the glass ribbon at the expense of forces of surface tension. Being formed in the temperature range of 800–750°C on the roller drawing device the glass ribbon requires more effort high. It reduces the efficiency of the process. The researches of toughness of thin nominals sheet glass demonstrate that the low-temperature ion-exchange treatment in the KNO 3 melt at the temperature of 400–500°C causes significant increase of strength, microhardness and glass heat resistance. The concentration of K {+} ions exercises a decisive impact on glasses properties in this temperature range. Being processed the K{+}ions diffuse to a depth of 10–15 µm of a surface layer of the glass and cause high values of compressive stress.