Glass Technology: European Journal of Glass Science and Technology Part A Volume 49 Number 1 February 2008 33 1. Introduction The progress and development of glass production are driven by new production ideas and by applica- tions where glass acts as a key material. The need of higher quality levels results in new requirements for the production processes. Innovations in the past were sometimes simple such as mechanical stirring of glass melts. However, high quality levels were a precondition for the production of glass components for the light-optical microscopy and other optical products (1) and they are still an issue of concern. (2) Some significant difficulties exist in controlling the melt flow during glass processing. Unavoid- able changes in melt properties are caused by their temperature dependence, fluctuations in chemical composition, or variations in the outlet flow which lead to irregularities and variations in the residence time and the chemical and thermal homogeneity of the glass melt. (2) Therefore the techniques of glass production have to be optimised in relation to the chemical composition of the glass and the required material properties of the product. This paper is organised as follows: Section 2 gives a short overview of existing possibilities for the optimi- sation of glass melting processes by various methods and their influence on the melt flow. Although from a historical perspective the influence and effect of elec- tromagnetic forces on the melt flow is not a new tech- nique, (3,4) it still has no industrial application and thus in Section 3 we evaluate the potential of the Lorentz forces followed by the description of the experimental set-up and parameters used here (Section 4). Then we report experimental results (Section 5) obtained from in situ measurements of temperature distribution during the electromagnetic stirring of glass melts; these include consideration of striae formation in the glass and the calculation of the velocities and the flow direction using temperature fluctuations. The summary of our investigations shows that external Lorentz forces provide an additional method for the optimisation of glass production. 2. Convection in glass melts In practice the manipulation of glass melt flow is mainly based on free convection, which is caused by density differences resulting from the inhomogeneous tem- perature distribution in the melt. Therefore, the effects of free convection are always interconnected with the direction of gravity and are optimised by the construc- tion of the melt system. Techniques of forced convection like bubbling, which acts as a local flow ‘barrier’ in tank furnaces, and direct electric heating via electrodes are mainly suitable for vertical melt flows. (5,6) In these cases the vortices that are produced in the melting system Electromagnetic effects on glass melt flow in crucibles U. Krieger, 1 B. Halbedel, D. Hülsenberg & A. Thess* DFG-research group Magnetofluiddynamik, TU Ilmenau, Germany Department of Inorganic Nonmetallic Materials, P.O. box 100565, D-98684 Ilmenau, Germany *Department of Thermo- and Magnetofluiddynamics Manuscript received 17 July 2006 Revision received 23 July 2007 Manuscript accepted 30 July 2007 Knowledge and control of the vortex flow in melting systems play an essential role in improving the homogenisation of glass melts. Although from a historical perspective the influence and effect of electromagnetic forces on the melt flow is not a new technique it still has no industrial application. This paper addresses this alternative method resulting from the application of Lorentz forces. So called external Lorentz forces are generated by the interaction of an electric current density and a magnetic flux density realised by direct electric heating via electrodes and an external magnet system. Experimental results on the electromagnetic modification of the flow in stacked melts in a crucible, using coloured and colourless glass are presented. In addition the temperature fluctuations enabled the calculation of the velocity and the direction of the flow in the melts by the application of cross-correlation. The results show an enhanced thermal homogeni- sation of the glass melts by the external Lorentz forces and provide possibilities for the optimisation of glass production using magneto-hydrodynamic effects. 1 Corresponding author. Email Uwe.Krieger@tu-ilmenau.de Now at: JSJ Jodeit GmbH, Am Nasstal 10, D-07751 Jena-Maua, Germany. Email service@JSJ.de Proceedings of the Eighth International Conference on Advances in Fu- sion and Processing of Glass, 12–14 June 2006, Dresden, Germany Proc. Eighth Advances in Fusion and Processing of Glass Glass Technol.: Eur. J. Glass Sci. Technol. A, February 2008, 49 (1), 33–40