Patent GB-418059-A (GB)
Title: Improvements in and relating to annealing towers for flat drawn glass
IPC: C03B25/12
Filed: 1934-05-23
Abstract: 418,059. Glass manufacture. CLEMO, F. A., 9, Kingsway, London.-(Naamlooze Vennootschap Hollandsche Maatschappij voor de Vervaardiging van Glas; 104, Wetering- schans, Amsterdam.) May 23, 1934, No. 15405. [Class 56.] Relates to the method of making sheet glass in which a flat sheet of glass is drawn vertically upwards from a mass of molten glass and passes through an annealing tower. The invention consists in providing an annealing tower in which the loss of heat from the glass is retarded in the lower part of the tower and is increased in the upper part of the tower where the temperature of the glass is below the lower annealing temperature. The tower, shown in section in Fig. 1, is divided into three sections, between the levels 4 and 5, 5 and 6, and 6 upwards, respectively. Annealing is effected in the first two sections and the glass is cooled in the uppermost section to a temperature convenient for handling. The coolers 7, which are placed as usual just above the origin of the sheet 1, are deeper at the middle than at the ends in order to obtain as uniform a temperature as possible across the width of the sheet by cooling the hotter, central portion more than the edges. The ends of the cooler are also covered with heatinsulating material to diminish the cooling- effect. In the first section of the tower, the spaces between successive pairs of drawing rollers 9 are filled with blocks 11 composed of heatinsulating material enclosed in a casing 13, Fig. 2, of heat-resisting metal. Preferably, a space 14 is left between the material 11 and the inner portion of the casing 13, and electrical heating-elements 15 are provided in this space. Blocks 16 of insulating material are also arranged close to the drawing-rollers, and other blocks are fitted around the shafts and ends of the rollers. Baffles 19 are fitted above the blocks 11 to minimize the upward current of air. By these means, loss of heat from the glass by radiation and convection is reduced, and may be regulated as desired by means of the electric heaters 15, or by gas heaters. On the second section of the tower between the levels 5 and 6, the temperature of the glass is allowed to fall more rapidly, but the loss of heat is still retarded by the provision of baffles 24, Fig. 1, which are pivoted and counterweighted. When the baffles are in the position shown in full lines, they close ports 27 which open into the surrounding air. In the position shown in dotted lines, the baffles are inclined and allow the clearance of broken glass through side doors in the usual manner. By adjusting their inclination, the loss of heat in the section can be regulated by allowing the passage of air through the ports 27. In the upper section of the tower, the glass is cooled by means of water circulated through pipes 30. These pipes are bent and, by rotating them, they can be moved to or from the glass sheet to control the rate of cooling. Preferably, the drawing-rollers in the second and upper sections are rotated at a slightly higher speed than those in the lowest section in order to increase the tractive force on the glass in the lowest portion of the sheet.