Articles with a cross-section varying in the longitudinal direction, e.g. corrugated pipes

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Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor (extrusion blow-moulding B29C49/04) > characterised by the shape of the extruded material at extrusion > Articles with a cross-section varying in the longitudinal direction, e.g. corrugated pipes