초록 ▼

For heat-setting tubular articles (such as can bodies) of an at least partly biaxially oriented crystallizable polymer, preferably a saturated linear polyester such as polyethylene terephthalate, e.g. for thermally processable food containers, a tube of the polymer is fitted over a mandrel and clamp

For heat-setting tubular articles (such as can bodies) of an at least partly biaxially oriented crystallizable polymer, preferably a saturated linear polyester such as polyethylene terephthalate, e.g. for thermally processable food containers, a tube of the polymer is fitted over a mandrel and clamped at its ends to the mandrel at a temperature below the 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 into can body sections by knives engaging in circumferential grooves. Contact between the tube and mandrel is released, e.g. by forcing compressed air out through small holes in the mandrel surface to allow the tube and mandrel to be separated. Tubular bodies with one closed end can be heat-set on a mandrel with a correspondingly shaped end.

대표청구항 ▼

A method of making a thermoplastic tubular article which will be dimensionally stable up to a specific elevated temperature, comprising the steps of fitting an at least partly biaxially oriented tube of a crystallisable polymer having at least one open end over a mandrel whose temperature is below t

A method of making a thermoplastic tubular article which will be dimensionally stable up to a specific elevated temperature, comprising the steps of fitting an at least partly biaxially oriented tube of a crystallisable polymer having at least one open end over a mandrel whose temperature is below the glass transition temperature of the polymer and whose outer diameter is only slightly less than the internal diameter of the tube, clamping the tube to restrain axial shrinkage thereof, heating the mandrel internally to heat the tube to a temperature higher than the said specific elevated temperature so that, whilst restrained against axial shrinkage, the tube shrinks radially into contact with the mandrel but is restrained thereby from further radial shrinkage, maintaining the tube at said higher temperature for a time sufficient to ensure the required degree of dimensional stability, cooling the tube to a temperature below the said specific elevated temperature, releasing contact between the tube and mandrel by forcing fluid under pressure from inside the mandrel through a plurality of apertures in its surface to form a fluid cushion between the tube and mandrel, and removing the tube from the mandrel while the fluid cushion is in existence. Apparatus for making a thermoplastic tubular article of a crystallisable polymer which is heat-set so as to be dimensionally stable up to a specific elevated temperature, comprising a mandrel having a plurality of apertures in its surface; heating means for heating the mandrel internally and thereby heating the article to a temperature higher than the specific elevated temperature; clamping means for clamping an at least partly biaxially oriented tube of the crystallisable polymer to restrain axial shrinkage of the tube; and a pressurised fluid supply for supplying fluid under pressure from inside the mandrel through said plurality of apertures in its surface, to release contact between the mandrel and a tube shrunk thereon.