Healing of Crack in Glass by Thermal Tempering Method

Abstract

The aim of the present work is to find the applicability of thermal tempering method for healing of the glass surface crack. The crack in the glass surface has been generated by Vicker’s Hardness Instrument with 1KgF load and dwell time of 10 sec. It is that the healing of the crack may be due to the viscous flow at the glass surface at the temperature greater than glass transition temperature. The driving force for this healing may be the surface roughness around the crack. All the samples were heat treated at 650°C and 700°C with a heat treatment time 2 hours, 4 hours and 6 hours. After the heat treatment for a specific temp and time, all the samples were rapidly quenched so that a surface compressive stress can be as we have experienced in thermal temp process. After rapid quenching, it has been observed that with an increase in dwelling time of the heat treatment the crack length decreases significantly. It has also been found that rapidly quenched glass not only closes the crack but also been observed a significant increase in surface compressive stress and flexural strength.