Dimensonally stable thermoplastic tubular articles.

摘要

For heat-setting tubular articles (such as can bodies) of an at least partly biaxially oriented crystallisable polymer, preferably a saturated linear polyester such as polyethylene terephthalate, e.g. for thermally processable food containers, a tube (26) of the polymer is fitted over a mandrel (101) and clamped at its ends to the mandrel at a temperature belowthe glass transition temperature of the polymer. The tube is then heated, e.g. by inserting a heater (28) into the interior of the mandrel, above the temperature to which it is to be heat-set (at least 60°C above for PET) whereupon it shrinks into contact with the mandrel but is restrained from axial or further radial shrinkage. The tube and mandrel are cooled to below the heat-set temperature and the tube may then be cut by knives engaging in circumferential grooves (22) into can body sections. Contact between the tube and mandrel is released, e.g. forforcing compressed air out through small holes (16) in the mandrel surface to allow the tube and mandrel to be separated.Tubularbodies with one closed end can be heat-set on a mandrel with a correspondingly shaped end.