Patent GB-1436132-A (GB)
Title: Apparatus and method for extruding and moulding plastic material
IPC: B29C48/305
Filed: 1973-08-20
Abstract: 1436132 Extruding and moulding glass sheet COMPAGNIE FRANCAISE DE RAFFINAGE 20 Aug 1973 [23 Aug 1972] 39337/73 Heading C1M [Also in Division B5] The attenuation in thickness of a flat or profiled sheet of glass in plastic condition, e.g. of greater than 1 mm. thickness, during intermittent vertically downward extrusion and delivery for further moulding, is counteracted during the extrusion to maintain a constant thickness by progressively increasing the corresponding thickness dimension of the orifice from which the sheet is extruded. The further moulding may comprise, blowing, stamping or vacuum forming. The orifice thickness dimension may be varied by displacement of one, or both, die lips defining the orifice, and this may be effected by hydraulic, pneumatic or mechanical means, and either manually or automatically. In addition, the width of the orifice may be periodically increased to produce increases in sheet thickness at locations to compensate for thinning during the further moulding. In the Fig. 1 embodiment, the glass is supplied from a screw extruder, and via an inlet 19, to an accumulation chamber 16 from which it is intermittently extruded, by a piston 3, at an orifice 20 defined between die lips 10, 12. The chamber 16 is filled at atmospheric pressure, or under a counterpressure of the piston 3, and whilst the orifice 20 is obturated by the die lips 10, 12, or by a valve 8 which is either manually, or pneumatically, or hydraulically actuated by means 9. Electrical resistance and steam heating means 7a and 7b are controlled by a thermocouple 17 and insulation 18 is provided. The piston 3 may be circular but is preferably rectangular and extends across the width of the chamber 16 and orifice 20. The progressive increase in width dimension is obtained by displacement of one or both lips 10, 12, by a jack and lever system 15, 14. The orifice 20 defined by the lips 10, 12 may be rectangular; may comprise one planar side and one rectilinearly undulating side, Fig. 2a (not shown), or may be arcuate, Fig. 2b (not shown) and defined between opposed convex and concave lips to reduce thickness variations in stamping or blowing of the sheet. The displacement of one or both lips may alternatively be effected by a wedge mechanism, Fig. 4 (not shown), or by each lip being fixed to a rotatable shaft, Fig. 6 (not shown) located in a die groove extending across the entire die width to facilitate cleaning of the lips. In the Fig. 7 embodiment an orifice is provided in each of a pair of die heads 51, 52 each orifice being defined by a displaceable and a fixed lip 53, 55, and 54, 56, the extruded sheets from each orifice being brought together as a composite sheet due to the relative inclination of the orifices. The thickness of each sheet may additionally be varied by the extrusion rate, by the lips 53, 54, or by obdurators 57, 58, e.g. at locations serving as hinges in the moulding. The composite sheet may be reinforced by an intermediate mat 60, and one or both external surfaces may be provided with a reinforcing or decorative material 61, or a coating from a spray 63. In the Fig. 8a embodiment, at least one displaceable lip 70 is provided, and the sheet is held by means 76 which may also comprise cutters prior to the further moulding effected by mechanically, hydraulically, or pneumatically actuated plungers 74, between mould 72 and cavities 83 of moulds 77 which are provided with coolant ducts 79, and air channels 78 which may alternatively be connected to vacuum. In this embodiment, the lip is displaceable to produce periodic thickness of the sheet 75 at locations at which the plungers 74 engage, Fig. 8b. The cutters 76 may be formed of circular or polygonal shape and between which the sheet 75 travels, or may comprise independent cutter bars which may be straight or profiled. The moulded articles may comprise gear casings, suitcases, or automobile or ship bodies. The sheet may be displaced from the die by roller means.