Investigations on the mechanical strength of enamelled glass

Abstract

Enamelled glass has been used for many years in architectural applications. It is well known that ceramic frits have a weakening effect on the mechanical strength of thermally toughened glass. This fact is addressed in the relevant European product standards for thermally toughened (with or without heat soak test) and heat strengthened glass. In EN 12150-1 the minimum bending strength of thermally toughened enamelled glass is given with $$\upsigma _\mathrm{bB} = 75 \hbox {N}/\hbox {mm}^{2}$$ and in EN 1863 for heat strengthened glass the value is given with $$\upsigma _\mathrm{bB} = 45 \hbox {N}/\hbox {mm}^{2}$$ . The values are valid independently of the colour tint and the manufacturing process of the enamel coating. As the experimental data for the current values were determined decades ago and the background of these investigations is not available anymore, a recent research project examined influences of glass type, colour tint and the manufacturing process of the enamel by performing four point bending tests according to EN 1288-3. To compare the results with the non enamelled glass types the glass samples were taken from a single float glass batch. The test results show the strength is mainly dependent on the colour scheme, the thickness of the enamel and the temperature sequence of the fusing process itself. In the paper some of the results will be presented especially the influence of different parameters on the mechanical strength. Furthermore the results will be compared with the current values of the minimum bending strength given in the product standards.