Annealing of soda-lime-silica glass

Abstract

The production of decorative glass in Malta is carried out at the Malta Decorative Glass Factory. The process used is the following: Si O2, Na co3, Ca co3 and other oxides are mixed together in certain proportions by weight and fused in a furnace at about 1500°c. The melt is then used by skilled artisans to form decorative glass objects. If these objects are left to cool in air at room temperature, thermal stresses are set up in the glass and the glass may shatter. Therefore the glass objects are annealed, that is cooled at a controlled rate. At present this cooling process is taking forty eight hours and is thus limiting production to a certain amount of objects a day. The aim of this project is to show whether a faster rate of cooling is possible and also to work out an annealing time schedule after certain properties of the glass have been deter mined experimentally. It is also my intention to check this annealing schedule experimentally and also to see what is the effect of various different heat treatments on the glass. The time necessary to anneal the glass is going to be worked out by the Heat Transfer method. For this method the following properties of the glass have to be found experimentally. These are thermal conductivity and specific heat capacity. By conducting a certain number of tests I am also going to find the annealing range, that is the range of temperature between which annealing is most effective.