| 摘要 |
Process for producing a hollow body with non-circular cross-section from a thermoplastic by extruding a tube and subsequently inflating it in an intermediate mould to give a parison (intermediate moulding) which has a circular cross-section and is reshaped to form the hollow body in a final blow mould. For reasons of material economy it is desirable to achieve a substantially uniform wall thickness of the hollow body with, at the same time, the least possible amount of material to be pinched off. To this end the tube is extruded from the extruder nozzle directly into the intermediate mould, it being sealed at an early stage by pinching its lower end, preblown to a slightly pear-shaped form approximately when it reaches a third of its length and blown to give the parison after completion of extrusion, said parison being designed such that its circumference is the same as, or if necessary a few per cent smaller than, the circumference of the hollow body that is to be produced, said hollow body being then subsequently produced in the final blow mould without significant further stretching of the parison. The device for carrying out the process comprises a blow moulding machine with reciprocating screw extruder and an extruder nozzle having a channel for inflation air, a split intermediate mould being disposed below said extruder nozzle, whose cylindrical mould cavity has a circumference the same as or at the most a few per cent less than the circumference of the hollow body that is to be produced. The unsplit base of the intermediate mould is height-adjustable with respect to the mould halves so that the neck shape and wall thickness in the neck area can be influenced. An analog-controllable compressed air solenoid valve is provided in the compressed air line to the extruder nozzle, since the blowing operation must be controlled very precisely.
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