Rheological Investigations of Glass

This report focuses on how the glass industry is supported by high temperature rheometers like the FRS 1800 from Anton Paar. The measured viscosity, as it depends on temperature, is important for process engineering in glass manufacturing and for the development of new materials with ever new characteristics and applications. By characterizing glass compositions using a rheometer, glass manufacturers like SCHOTT AG gain a deeper knowledge about the temperature-, deformation- and time-dependent behaviors of a glass melt. Understanding of these properties is then transferred to the later production process (e.g. by modelling) to increase product quality or production output. This application report details a specific case by the glass company, SCHOTT AG, which has used Anton Paar rheometers for several years.


The glass industry is facing many challenges today. CO2 reduction targets combined with increasing energy costs and a growingly competitive global market is driving the need for companies to characterize the processed materials upfront in more detail than ever before. Only by knowing the exact behavior of the sample materials at specific conditions (such as temperature and shear rate) can the production processes be optimized to consistently reach production targets (costs, quality, and output). But not only production benefits from a proper characterization of raw materials. In addition, research and development needs detailed information about the behavior of new blends of raw materials at certain boundary conditions in order to consider this behavior during the design of a new material.

The most important characteristic in glass production is the viscosity of the material as it relates to temperature. Viscosity values of glass melts range over several orders of magnitude between the fully molten state and the glassy state. Because there is currently no single device available that can measure the viscosity over temperature ranges of about ten orders of magnitude, it is common and necessary to use multiple devices and measurement approaches, where results are not always consistent and comparable.

Within this report the focus was on the upper end of the temperature range, where the viscosity can be measured using a Searle-type rheometer like the FRS 1800. This temperature region is of special interest for the processing steps during production in which the glass exists in a molten state. 

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