Study on the optical quality and strength of glass edges after the grinding and polishing process
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SI: CHALLENGING GLASS
Study on the optical quality and strength of glass edges after the grinding and polishing process Paulina Bukieda · Katharina Lohr · Jens Meiberg · Bernhard Weller
Received: 5 February 2020 / Accepted: 5 May 2020 © The Author(s) 2020
Abstract Glass edges result from cutting glass sheets and a further optional finishing. The mechanical interference into the brittle material glass causes flaws and cracks at the edge surface. Those defects have an influence on the strength of the whole glazing. Within the scope of a research project at the Institute of Building Construction from the Technische Universität Dresden, the grinding and polishing process is examined in terms of characteristic visible effects on the glass edge and the edge strength. Thereby a special focus of the research project is the impact of various polishing cup wheels for the chamfer surface of annealed glass. The article presents some basics about the processing steps of glass edges surfaces, introduces the considered grinding and polishing cup wheels and gives an overview of the performed experimental examinations. A microscopic analysis enables a characterisation of typical defects at the surfaces. Furthermore, four-point bending tests are performed to determine the bending tensile stresses at failure. The combination of both methods enables an analysis of the fracture-causing defect before destruction and a correlation between the optical surface quality and the bending tensile stresses. Additionally, the microscopy could be used to support the adjustment of a grinding machine and control reproducible edge qualP. Bukieda (B) · K. Lohr · B. Weller Technische Universität Dresden, Dresden, Germany e-mail: [email protected] J. Meiberg Artifex Dr. Lohmann GmbH & Co. KG, Kaltenkirchen, Germany
ities. The evaluation shows that a special development of polishing cup wheels for the chamfer can improve the surface quality and consequently increases the edge strength. Keywords Chamfer · Edge strength · Glass edge · Grinding · Microscopic analysis · Polishing
1 Introduction 1.1 Consideration of glass edge strength in the design The mechanical and thermal loads in window and facade constructions are growing with modern architectural demands and firm requirements for building physics. With increasing glass formats and complex glass structures, the superposition of mechanical and especially thermal loads can cause critical stresses particularly in the edge areas. According to the current design codes in various European countries, the design value of annealed glass needs to be reduced for dimensioning glass edges (Feldmann and Kasper 2014, p. 55). In case of the German and Austrian standard (DIN 18008-1 2019 and ÖNORM B 3716-1 2016) a reduction of 80 % of the characteristic bending strength of annealed glass is required. That reduction considers the high scattering of the edge strength due to the processing and represents a minimum level of the glass edge strength. The reduced resistance of the edge strength of annealed gla
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