GB994551A - Method and apparatus for bending and annealing glass sheets - Google Patents

Abstract

<PICT:0994551/C1/1> <PICT:0994551/C1/2> In a method for bending and annealing glass sheets on a skeleton mould, heating means carried by the mould within the confines of its shaping surface is operable to heat preselected areas of the sheet during engagement of the bent sheet with the shaping surface. A three-part mould 11 comprises substantially continuous sloping rails 13 and, within the confines of the rails 13, a substantially continuous strain bar 15. The strain bar 15 comprises centre sections 36 and end sections 37, each section carrying an electric resistance heater which is connected to the heaters of its adjacent sections by flexible conductors 46. One of the sections 36 of the strain bar 15 has a gap 45. Two coupling means 41 (Fig. 4), are mounted, on either side of the gap 45, on a rack 12 that supports the mould 11 and are connected by flexible conductors 43 to the electric heaters on their respective sides of the gap 45. Each coupling means 41 includes a wheel 47 with an outwardly-opening groove 48 journalled on a rod 49 in one end of an arm 50. The other end of the arm 50 is supported by a pin in a clevis bracket 52. Each arm 50 trails behind the rack 12 as it travels through a tunnel furnace and is raised to the position shown in Fig. 4, from its initial position shown by dotted lines in Fig. 4 and determined by abutment surfaces 54, when it meets and rides up upon one of two generally rectangular bus-bars 40 mounted within and along part of the length of the furnace. Heating of the strain bar 15 is commenced while the mould 11 is in the bending zone and is discontinued at a point within the annealing zone of the furnace, the timing and duration of the heating being determined by the positioning along the length of the furnace and the length respectively of the bus-bars 40. The use of the heated strain bar 15 intensifies and permits more accurate control of the differential cooling of a bent glass sheet effected by the use of a conventional strain bar, and similarly produces areas of tension and compression in the bent sheet so that when subsequently pattern-cut the peripheral edge of the cut bent sheet is in compression. The heat supplied to different parts of the strain bar 15 may be varied by the suitable choice of resistance values for the individual heaters. The resistance heaters may be mounted on the top or bottom surfaces of the strain bar 15 or alternatively, may be disposed within a hollow strain bar. The strain bar 15 may also carry conventional heat shields. Other means for heating the strain bar 15 include directing flames on it or constructing it in the form of a conduit through which a heating fluid is passed.