GB1383495A - Manufacture of glass articles - Google Patents

Abstract

1383495 Tempering glass UNITED GLASS Ltd 30 March 1972 [30 March 1971 12 Nov 1971] 8140/71 and 52666/71 Heading C1M A glass article, e.g. a plate or jar, is toughened by immersing the article, after it has been heated to a temperature between its annealing and softening points, in a fluidized bed maintained at a temperature below the strain point of the glass the fluidizing medium being or comprising a gas having a thermal conductivity of at least 0À1 w./mk. Preferably the article is at a temperature of between 650‹ and 750‹ C. prior to immersion, while the bed is at least 150‹ C. below the strain point of the glass and is preferably in the range 20‹ to 100‹ C. The article is held in the fluidized bed for 5 to 30 seconds. The material forming the bed is preferably a material with good heat transfer properties such as iron or copper and is fluidized with a high thermal conductivity gas such as helium, although air or nitrogen may be used. A low thermal conductivity material such as sand, alumina or magnesia may be used particularly if the bed also includes from 1 to 5% by weight of a thermally sublimable solid such as ammonium chloride. When a hollow article is being roughened, the fluidization of that part of the bed enclosed by the internal surface of the article must be maintained either by having a secondary source of fluidized air in an upright article (Fig. 1, not shown) or having a suction tube within an inverted article (Fig. 2, not shown).