Cut edge of annealed float glass: crack system and possibilities to increase the edge strength by adjusting the cutting process

The edge strength of annealed float glass is an essential aspect in engineering design. A common problem in engineering applications is the failure of the edge due to thermally induced stresses. The edge strength of annealed glass is affected by cutting, further processing and handling. Thermally treated glass exhibits higher edge strengths, but may show optically negative effects such as anisotropy and roller waves. In case of covered edges, e.g. insulating glass covered by framing, an enhanced strength of the cut edge is desirable. This paper presents results showing that enhanced strength of the cut edge is feasible and reproducible using regular cutting technology. A large part of this contribution deals with the crack system resulting from the cutting process. A deep understanding of this is essential for the relationship between cutting parameters, damage and edge strength. In addition to optical microscopic analyses, confocal microscopy and indentation tests have been carried out. The influence of different cutting process parameters on the edge strength was investigated within the scope of extensive analyses by the Fachverband Konstruktiver Glasbau e.V. This allowed to adjust selected process parameters so that the edge strength could be reproducibly enhanced. In this contribution the latest results of these investigations are presented. In addition, the correlation between microscopic optical characteristics and the mechanical strength as expressed by the macroscopic fracture stress is described.