GB886233A - Improvements relating to glass melting by electric heating - Google Patents

Abstract

886,233. Electric glass furnaces. ELEMELT Ltd. June 20, 1958 [June 20, 1957], No. 19403/57. Class 39(3) In heating glass and other vitreous material in which glass melted or refined in a furnace chamber passes to a feeder chamber from which glass is withdrawn for working, the glass flows from the furnace to the feeder chamber through a feeder duct in which the glass is heated uniformly over its transverse cross-section by A.C. between electrodes spaced longtitudinally in the glass and supplying current over the cross-section of the duct over a sufficiently large area to promote uniform heating over that area. The electrodes border the bottom and side walls of the duct and are constructed to allow easy passage of a substantial part of the molten glass flow; as shown, they comprise a mesh 23 of wires or strips of molybdenum supported by vertical end rods 18 passing through the top or bottom of the feeder duct 11 and attached to current supply terminals. The glass may fill the duct wholly or partly and in the latter case the top of the duct is heated by fuel burners extending through openings 25 in the side walls of the duct. The rods 18 may be of nickel chromium alloy, of molybdenum sheathed with platinum or with ceramic to prevent oxidation above the glass level .When the rods 18 extend through the bottom of the duct, they may be supported as in Specification 664,121 and may have external fins cooled by an air blast. When the rods extend through the roof of the duct, they may be internally water-cooled. in a modification, the electrode comprises narrowly spaced vertical molybdenum rods threaded into a bar extending across the base of the feeder duct and firmly attached to end rods 18 extending through the roof of the duct. In another modification, the electrode comprises a vertical plate of a height equal to about 40% of the depth of the glass and supported adjacent the base of the duct by vertical end plates adjacent the side of the duct and supported through the roof the duct by rods internally water-cooled. The viscosity of the glass in the furnace chamber is preferably maintained at 1À5 X 10<SP>2</SP> poises and in the feeder chamber at 10<SP>3</SP> poises. The glass in the furnace and feeder chambers is heated by passing current therethrough or externally e.g. by fuel burners, and one furnace chamber may be connected to several feeder chambers. One or more transverse electrodes may be mounted between the electrodes at the inlet and outlet ends of the feeder duct and may be connected to supply greater current flow along parts of the duct to exercise greater control over the rate of cooling or heating of the glass passing through the duct. The current is supplied from separate transformers or from secondary windings of a single transformer with means for adjusting the voltages.