Browsing by Author "Roger, Ulrich"

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    Formation and oxidation of silicon in container glass melts
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Wischnat, Volker; Roger, Ulrich; Lenhart, Armin
    The input of recycled container glass is increasing continuously in container glass production, unfortunately also causing the rise of rejects because of inclusions. In the group of glass inclusions caused by recycled cullet small silicon spheres are the main problem due to their different thermal expansion coefficient in relation to soda-lime-silica glass. Aluminium is introduced together with the recycled cullet into the melting process. Silica is partly reduced by aluminium to metallic silicon which forms small spheres in the produced containers. The kinetics of formation and dissolution of these silicon inclusions was investigated over a long period with respect to the melting parameters in several plants. Single reaction steps were repeated in the laboratory. Aluminium metal introduced as foils or pieces reduces nearly the same amount of silicia in flint, green and amber glass melts. Between 800 and 1000 °C silicon formation starts as a brown powder with a great specific surface area. This silicon modification melts at temperatures over 1400 °C and crystallizes to metallic silicon spheres. The highly varying number of silicon inclusions in glasses of different colour is not directly proportional to the aluminium input. It depends on different dissolution velocities. Because of their small density the silicon phases rise up to the glass bath surface and are oxidized. This reaction is a function of temperature and residence time at the surface of the glass bath. In amber glass melts the oxidation velocity of the silicon inclusions is greater than in flint glass because of much higher surface temperatures compared with flint glass melts.
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    Glass conditioning by viscosity controi
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Roger, Ulrich; Hessenkemper, Heiko; Roth, Peter
    During the forming process of a glass melt the viscosity is the dominant process parameter. Up to now in the industrial Container glass production only temperature-controlled Systems have been used. With these control elements only thermally induced variations of the viscosity are visible. Variations in the composition, the redox State , the water and the SO₃ content in the melting process cause a shift in the viscosity Up to now these changes have not been detectable and therefore, it has not been possible to compensate them. A measuring device for t he continuous determinadon of the viscosity in the glass was developed and tested for several months in a Container glass plant. All measured variations of the viscosity can now be corrected by the existing control elements for the thermally controlled glass conditioning. Dependent on the posidon of the viscosimeter in the feeder Channel , a feedforward or feedback Controlling concept is practicable.
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    Validation of a mathematical glass tank model
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Bauer, Johannes; Roger, Ulrich; Simons, Philip
    In the past mathematical modelling of glass furnaces concentrated on the redesign and optimization of such aggregates. For the future, it is conceivable that such models will also be used for the control of glass furnaces. The present study showed that an increased occurrence of bubbles due to increased glass pull can be found in the results of the model, while a corresponding link between model and practice could not be found for solid inclusions. As a main cause for the limited correspondence between modelling and practice the dominating influence of recycled cullet and the frequent changes of the glass pull could be identified.