GB771738A - Improvements in or relating to methods of manufacturing mouldings - Google Patents

Abstract

771,738. Moulding thermoplastic resin. NAAMLOOZE VENNOOTSCHAP PHILIPS GLOEILAMPENFABRIEKEN. Aug. 4, 1955 [Aug. 6, 1954], No. 22461/55. Class 87(2). A rod is moulded from polythene in a mould 1, which may be of glass, and which can be lowered into a tube 2 of larger diameter, which may also be of glass, filled with water which, when the mould enters, overflows into a tank 4. A heater 5 which, like the tube 2, is stationary surrounds the tube 1. With the lower end of the mould 1 in the heating range of the element 5, finely powdered polythene is introduced and after the polythene in the lower end of the mould has been liquified by the heat and air or other occluded gas has escaped the mould is lowered progressively, so that the polythene above is heated. At first a thin jet of liquid polythene emerges from a hole 6 in the bottom of the mould but, when the mould is lowered, a thin layer of solid polythene is formed on the bottom. Before the bottom of the mould is submerged in the water the aperture 6 is opened by breaking off the adhering thread of solid polythene so that, as the lowering progresses, the clear space due to the contraction of solidified polythene is filled with water, which supports the lower end of the moulded rod. The weight of the partly solidified rod is not therefore held solely by adhesion to the wall of the mould which might produce cracks, and long rods can be moulded. Instead of water, a liquid which does not act upon polythene may be used, e.g. glycerol or amyl alcohol. The aperture 6 may be larger and closed at the beginning of the process. The polythene may be introduced to the mould directly in the liquid state (the viscosity in some cases being reduced by adding liquids), necessary after de-gassing to remove air bubbles ; also, the mould may be partially evacuated to assist the removal of occluded gas bubbles. De-gassing, either in the mould or in a separate vessel, is of advantage in the moulding of high polymeric thermoplastic synthetic resins other than polythene. The moulds may be shaped to produce rods of different profiles, or to form tubes.