GB956832A - Method and apparatus for producing films and flakes from heat softenable material - Google Patents

Abstract

In the manufacture of glass films or flakes, the glass 33 is melted in an annular chamber 12 from which it flows downwardly through an annular homogenizing chamber 14, in which it is heated substantially above the liquidus temperature of the glass for a time sufficient to melt any crystalline particles, and thence downwardly into contact with a cooling surface 16 of circular cross-section until cooled to a workable viscosity, the cylindrical glass film 18 so formed being pulled and attenuated downwardly while the glass is cooled rapidly through the liquidus range to prevent crystallization and the film fractured to form flakes, if required. Glass marbles 30 are fed in shoots 30, made of spaced metal rods 32, to openings 28 above the annular chamber 12 of platinum which is heated through terminals 20, 22 on opposite sides and aligned plates 58, 60 (not shown) between the wall 50 and a conical perforated screen 57 for retaining unmelted glass particles. The chamber 14, which is much narrower than chamber 12, is formed with a double wall 84, 86 and the space 88 between is filled with castable zircon or other material of high thermal conductivity. Air to maintain the cylinder 18 of glass expanded is passed through chambers 12 and 14 through a tube 114, with a flared lower end 116, surrounded by a casing 35 with a flare 110 so that the area of chamber 14 is lessened at its lower end, the space 120 between being filled with insulation material such as powdered alumina. The lower end of chamber 14 is closed by a plate 100 having an annular ring of orifices 102 through which the molten glass flows. In an alternative construction, particularly for glasses with high surface tensions, an annular slot may replace the orifices 102. The air through tube 114 is passed outwardly towards the cooling surface 16 by a baffle 130 comprising an annular plate 132 and an inverted core 138 secured thereto by wires 140. The surface 16 is formed by an inwardly inclined wall 106 and a cylindrical wall 108 arranged to be directly under the orifices 102 so that drops therefrom are received by the wall 108 and spread to form a film over the surface. In addition to cooling of the surface 16 by the ambient atmosphere, the wall 108 may be cooled by other, unspecified, means. The cylinder 18 of glass is pulled by rolls 36 perforated at 37 and having alternate suction and air under pressure sections 38, 40 so that the film is split into two parts held against the rolls by suction through pipes 44 and then broken into flakes by air from pipe 46, the flakes being collected in containers 48. Specifically, the apparatus may be used to form flakes of sodium silicate, which may then be backed to form silica flakes or of the following composition in percentages by weight: SiO2 53.73; CaO 12.94; MgO 8.96; BeO 7.96; ZrO2 1.99; TiO2 7.96; Li2O 2.99; Fe2O3 0.5. Specification 826,585 is referred to. <PICT:0956832/C1/1> <PICT:0956832/C1/2> <PICT:0956832/C1/3>