GB747738A - Improvements in or relating to method and apparatus for surfacing glass - Google Patents

Abstract

747,738. Surfacing glass. PITTSBURGH PLATE GLASS CO. July 8, 1953 [July 15, 1952; June 22, 1953], No. 18937/53. Classes 56 and 60 A method of surfacing glass includes dissolving a portion of the glass surface with an acid solution of a bifluoride to form a silicofluoride precipitate which masks the glass against further attack by the acid solution and continuously removing the precipitate in the presence of the solution from only the high portions of the glass. When the size and spacing of the particles of the precipitate permits the bifluoride to attack the'glass around the edges of the particles a frosted surface is produced, while when the particles are greater in number and smaller in size, an improved quality of surface is obtained. The particle size may be controlled by varying the degree of supersaturation of the acid solution and the solvent power of the solution for the precipitate. Solutions for the production of frosted surfaces may consist of ammonium bifluoride in water and/or phosphoric acid, the. proportion of phosphoric acid determining, together with the degree of supersaturation, the particle size. To produce non-frosted surfaces the solvent power of the solution for the precipitate is reduced by the addition of an organic radical, such as aliphatic or aromatic amines and hydrazines, or an inorganic cation, such as potassium. Alternatively, such cations, for example those of barium, lead, potassium and aluminium may be supplied by the glass. Liquids, such as acetic acid and higher molecular weight alcohols, and solids, such as sucrose, may also be employed to reduce particle size. Alcohol solutions, instead of aqueous solutions, may be used to dissolve the glass and these may also be modified by the addition of organic radicals which are not suitable for use with the aqueous solutions. To increase the power of the solution to dissolve the glass, organic and inorganic acids which are not a solvent for the precipitate may be added to the solution while various salts which will hydrolize and not form a fluorine complex of insoluble fluoride with that of the solution may also be employed. Figs. 6 and 7 show apparatus for producing a frosted surface on separate glass sheets 1 mounted in plastic beds or on a continuous sheet supported by rollers, the glass being traversed beneath tools 2 having serrated faces with portions 3b into which the solution is directed by members 4 which may be supplied either by separate pumps P or a common pump. The tools apply a pressure of about 2lbs./sq. in. to the glass and the spaces between them are flushed with water. Apparatus employing rotary felt-faced tools mounted on spiders or of a diameter large enough to extend across the glass and operating on one or both faces thereof is also described. The solution may be fed centrally to the tools which are separated by squeegee members to enable the glass to be washed as it passes between them or it may be fed to the glass by conduits arranged between the tools. To assist the action of the tools in removing the precipitate from the high portions of the glass, the solution may contain 10 per cent of abrasive, such as rouge, tin oxide, chromium oxide, barium sulphate or mixtures thereof.