Blow moulding molecularly oriented thermoplastic containers - to ensure uniform wall thickness from blanks extruded and heated unevenly

摘要

Hollow articles are produced from extruded blanks of thermoplastic material which are symmetrical around an axis and are closed at one end. The blanks are at a temp. which at least in parts in higher than that required for molecular orientation, and they have circumferential zones of different thickness, between which the temps. are also different. The temp. of these zones is reduced, whilst maintaining the differences in temp. to a value at which molecular orientation can be achieved, and these zones of different thickness are expanded to a different degree so that they lie against the walls of the mould. The wall thickness of the thicker zones is reduced more sharply than that of the thinner zones, so that the object produced is given a more uniform wall thickness. Risk of bursting when filled with a pressurised liq. is reduced.