Patent GB-1211854-A (GB)
Title: Improvements in or relating to the production of glass having predetermined surface characteristics
IPC: C03B18/14
Filed: 1967-06-19
Abstract: 1,211,854. Treating glass surfaces. PILKINGTON BROS. Ltd., A. S. ROBINSON, D. G. LOUKES, and J. LAWRENSON. 20 March, 1968 [19 June, 1967], No. 28273/67. Heading C1M. In a method of producing glass having predetermined characteristics the temperature of the glass is regulated so that it is electrically conductive, and a body of molten electrically conductive material is maintained against the glass by causing the body to cling to a locating member adjacent the glass, an electric current is passed between the molten body of electrically conductive material and the glass and is regulated to cause controlled migration of an element from said molten material into the surface of the glass, thereby effecting a predetermined change in the characteristics of the glass. The method is preferably applied to the manufacture of float glass. A body 36 of molten electrically conductive material clinging to the underside of a bar-shaped electrode 31 is located against the upper surface of a glass ribbon. A second electrode 37 is located in the molten metal bath alongside the path of travel of the glass. The passage of current through electrode 31, glass ribbon 32, bath 10, electrode 37 is regulated in relation to the speed of advance of the ribbon to give accurate control over the intensity of the change in characteristic of the glass surface. The molten body 36 may be maintained by feeding in fresh material at the edges. In an alternative embodiment (Fig. 6) the electrode 31 is of hollow rectangular cross-section, the internal space 39 holding a pool of the molten material 36 by capillary action which spreads out beneath the sides of the electrode. Several other embodiments are illustrated in which the locating means is a thin foil stretched between two supports; two solid locating members spaced apart from each other either such a distance that the current passing must flow along part of its travel through the molten metal bath or such that the current merely flows along the upper surface of the ribbon; a hollow rectangular member in the internal space of which is a solid bar of the metal or a metal of the molten material for replenishing said molten material; and wherein the locating member is of a porous material, e.g. alumina, and is of such a form as to hold a quantity of a molten salt, which salt percolates through base to form a molten body 36. The molten material may be a molten metal or a molten metal alloy, the locating member being made of the alloy metal which migrates into the glass. If desired the molten alloy may comprise at least two metals which are to enter the glass, the alloy temperature and the current being selectively regulated to give the desired proportional migration of the two elements. In a further embodiment bodies of molten electrically conductive material are maintained against both surfaces of the ribbon. In this instance the ribbon may be at such a temperature as to be conveyed upon rollers without damage, the lower body of material being located between successive rolls. Suitable metals from which the electrodes may be made are platinum, palladium, ruthenium, rhodium, osmium, iridium, rhenium, silicon, titanium, manganese, chromium, iron, vanadium, cobalt, nickel, copper, silver and gold. The molten material may be molten tin, lead, bismuth, antimony, indium, zinc and thallium. The molten alloy may be of tin or bismuth or lead with a solute metal of lithium, sodium, potassium, zinc, magnesium, aluminium, silicon, titanium, manganese, chromium, iron, vanadium, cobalt, nickel, copper, silver, gold, antimony, indium and rhenium. The molten electrically conductive material may be a halide or mixture of halides of silver, copper, zinc, sodium, potassium, lithium, chromium, manganese, cerium, cobalt, neodymium and praeseodymium. The invention is useful for forming glass having coloured surfaces, especially for " antiglare " glasses, special reflectivity, or tempered. The colour or other surface characteristic may be finally developed upon exposure to a reducing atmosphere surrounding the ribbon during production.