GB953953A - Improvements in or relating to an electric glassmaking furnace - Google Patents

Abstract

An electric glass-making furnace of the type having a trough defining an inner chamber and melting electrodes and further comprising a refining device disposed in the hottest region of the inner chamber, comprises means for withdrawing in the course of a continuous glass-making process a portion of the molten glass in said region and thus removing it from the large movements of the molten glass due to convection currents in said, chamber, means for rapidly raising the temperature of said portion so as to diminish its viscosity and increase the size of the bubbles which are thus separated from the fine glass, means for discharging outside the trough as production proceeds the fine glass just obtained, and means for returning to the inner chamber the bubbles thus separated. A furnace, Fig. 1, comprises a copper trough 5, with a bottom aperture 6, an inner zirconia alumina lining 8, and copper tubes 7 brazed on its outer surface for circulation of cooling fluid. Three adjustable molybdenum melting electrodes 9 terminating in segments 11 are connected to copper electrode carriers 9a which extend through insulating sleeves 10. A refining device 13 comprises upper and lower molybdenum discs 14 and 15. The upper disc 14 forms an electrode and is connected to a molybdenum bar 18 carried by a carrier 18a adjustably supported by an insulating sleeve 19 threaded through a nut 20 supported by a fixed plate 21 carried by pairs of rails 22. The rails 22 also support carriages 23 carrying auxiliary starting electrodes 24. The upper <PICT:0953953/C1/1> <PICT:0953953/C1/2> <PICT:0953953/C1/3> <PICT:0953953/C1/4> disc 14 has an axial passageway 25 and radial passageways 26, Fig. 5. The lower disc 15 forms a second electrode and is connected to a molybdenum rod 27 with an axial passageway 28, Figs. 3, 5, through which fine glass is extracted. The rod 27 passes through a platinum sleeve 36 with a skirt 37 and is secured by three coaxial sintered alumina members 29, 30, 32. The sleeve 36 terminates in a circular head orifice 36b. An electrode carrier 40 is connected by a molybdenum bar 38 to the rod 27 at 39, Fig. 1. In use, after starting up the furnace, molten glass within the furnace which is overlaid by a glass raw material composition P is kept molten and further composition P melted by current supplied to the melting electrodes 9. As molten glass is drawn off from the bottom of the passageway 28, more glass flows in to the refining device 13 from the main body of glass in the furnace through the annular gap between the discs 13, 14. Current supplied to these discs 13, 14 rapidly raises the temperature of the glass lying between them reducing its viscosity and expanding any air bubbles that may be present in it so that the air bubbles rapidly rise and pass back into the main body of glass in the furnace through the passageways 25, 26. In one modification the member 32 is extended radially inwards to support the molybdenum rod 27. In another modification, to assist the return of surplus heat in the refined glass as it is drawn off to the main body of glass in the furnace; a heat exchanger 45, having a cross-section as shown in Fig. 8, is secured between the rod 27 and the refining device 13. Two further constructions of the refining device 13 are also described and illustrated.