Edge strength: Crack system and possibilities of increasing the strength

The edge strength of annealed glass is an essential aspect in design. A common problem is the failure of the edge due to thermally induced stresses. The edge strength of annealed glass is affected by cutting and further processing. Thermally treated glass exhibit higher edge strength, but these products may show negative effects such as anisotropy and roller waves. In case of covered edges, e.g. insulating glass, an enhanced strength of the cut edge would be desirable. This paper presents results that show that enhanced strength of the cut edge is feasible and reproducible. Initially, the cutting process and the resulting crack system is explained. It is shown how different the cut edge can appear and which optical properties can be defined. In addition to photomicroscopic examinations, confocal microscopie and indentation tests were carried out. Furthermore, results will be presented which have been obtained within the scope of extensive investigations of the Fachverband Konstruktiver Glasbau e.V.. The influence of different cutting parameters on the edge strength was examinated with more than 1500 tests. This allowed to adjust selected parameters so that the edge strength could be reproducibly enhanced. In addition, the correlation between microscopic characteristics and the strength is described.