CONTROL METHOD FOR THE MANUFACTURE OF ORIENTED PLASTICS TUBES

摘要

A method of expanding a tube of plastics material is disclosed in which a longitudinally travelling tube (10) is progressively diametrically expanded by internal fluid pressure in an expansion zone (20) between an upstream plug (24) and an expandable downstream plug (26). Expansion of the tube is controlled in response to parameters whi ch directly or indirectly indicate variation in the relative velocity at which material is delivered to and removed from the expansion zone, such as detecting upstream tube velocity (38), early expansion diameter (36), axial force (39) on a sizing device (28) or the tube diameter (41) just before the expansion zone.