PROCESS AND APPARATUS FOR MANUFACTURING DRWAN SHEET GLASS,INCLUDING THE USE OF ELECTRIC HEATING INSIDE THE KILN

摘要

1375232 Drawing sheet glass GLAVERBEL 24 Jan 1972 [24 Feb 1971] 3279/72 Heading C1M In the continuous upward drawing of sheet glass from the surface of molten glass in a kiln, the flow of molten glass into the ribbon of glass from at least one part of the kiln either to the front or rear of the drawing zone is promoted, in order to improve the uniformity between glass currents feeding different parts of the ribbon by passing electric current through molten glass in that part or parts of the kiln between electrodes which are at different levels in the kiln. Preferably the mean direction of the current between them is at least 45 degrees to the horizontal and may be vertical. In a Pittsburgh machine with molten glass 4 in a kiln 1, 2, 3, with glass ribbon 7 drawn from meniscus 6 over a draw bar 5 and in which the glass for the ribbon is normally drawn only from the upper strata of the glass 4, electrodes 8, 9, extending the full width of the glass ribbon 7, are positioned at -the rear side of the ribbon and at levels approximating to the upper and lower depths of this strata. In a Liffey-Owens drawing machine with shallow kiln 29, 30, 31 in which glass ribbon 32 is drawn from meniscus 33 over roller 34 and in which the glass for the ribbon comes from the full depth of the kiln, the electrodes 35, 36 and 37, (37), 38 are positioned either side of the ribbon, the top electrodes 35, 37 being just below the top surface and the lower electrodes 36, 38 on the sole 29 of the kiln. The electrodes 37 extend either side of the ribbon. A number of different positions and constructions of electrodes are shown. The electrodes may be solid, as 8; 9, 35 and 37 or of molten metal or molten salts as 36, 38, and a molten salt of lower specific gravity than molten ' glass may float on the top of the glass between the rear wall and the ribbon of glass. Pairs of electrodes either side of the ribbon, to assist flow to the edges thereof, may be used, or a single lower electrode 38 extending right across the kiln with two upper electrodes 37. Materials suggested for the electrodes are, for solid electrodes, tin oxide, molybdenum, tungsten, platinum, graphite or other refractory noble metals or conductive metal oxides; for molten metals, tin: for molten salts, magnesium chloride for an upper electrode. Specifications 1,375,231 and 1,129,416 are referred to.