PROCESS FOR THE MANUFACTURE OF PLATE GLASS WITH DESIRED SURFACE CHARACTERISTICS

1,151,853. Flat glass. PILKINGTON BROS. Ltd., D. G. LOUKES, and G. NIGHTINGALE. 8 July, 1966 [9 July, 1965], No. 29288/65. Heading C1M. A method of manufacturing flat glass comprising separately contacting the surfaces of the glass with bodies of molten electrically conductive material isolating the molten bodies from each other and passing a controlled electric current through the glass between the isolated bodies thereby modifying the surface constitution of the glass particularly so that metal enters the surface layer when molten metals are used. The molten electrically conductive material is confined on the upper surface of the glass by forming the margins of the glass ribbon as ridges thus laterally containing the molten pool. The forward and rearward movement of the molten pool is prevented by carbon barriers. In one embodiment the electric current is passed through the glass in a direction such that the molten pool acts as an anode and the top surface of the glass is modified. By reversing the electrode leads and including other metals in the bath, the bottom surface of the glass may be modified. In another embodiment both surfaces of the glass may be modified simultaneously by having two molten pools of electrically conducting material confined on the upper surface of the glass and separated by a distance such that the pools are electrically isolated from one another, passing electric current through the glass between the molten metal surface and the pools of molten metal in a direction such that one pool acts as an anode and the other as a cathode with respect to the molten metal surface, and an apparatus for use in such a process comprising a tank structure containing a bath of molten metal 10, means for delivering glass at a controlled rate to the bath and for advancing the glass along the bath as a layer of molten glass in ribbon form, thermal regulators 23 and 24 for controlling the viscosity of the glass so as to ensure that the glass is gradually cooled as it is advanced, means for maintaining a pool of molten material 39 on top of the glass and for preventing forward movement of the pool with the glass, electrodes arranged to dip into the pool of molten material and into the bath of molten metal, an electric current supply circuit connected to said electrodes, and edge shaping means 31 and 32 mounted relative to the tank side walls 7 for shaping the margins 36 of the ribbon of glass 37 so that the ribbon assumes a shallow trough-like format