Method for producing a tubular object of polyethylene terephalate or

Abstract

An object is produced from a tubular blank (10,15,17) of thermoplastic material of the type polyester or polyamide, preferably of polyethylene terephthalate by reducing the thickness of amorphous material in one or several areas of the blank by means of one single or several consecutive re-shaping operations. A mechanical shaping device (23,29,71,81) moves a transitional zone (13,14,113) situated between thicker and thinner material along the blank and elongates simultaneously the blank in the moving direction of the transitional zone. After the last re-shaping operation the thinner material has preferably an oriented state. During the re-shaping operation the temperature of the material in the transitional zone (13,14,113) is controlled at a level which, immediately before the re-shaping operation, is within or close to the range of the glass transition temperature (TG). In one embodiment the reduction of the wall thickness of the material is begun in a track (12) in the wall of the blank and continues symmetrically around the track. Clamping devices (41,51,61) are used to maintain the axial position of the blank. The blank is suitable for re-shaping for instance into a container in which the mouth too consists of oriented material. The invention offers possibilities for materials savings by comparison with previously used methods, at the same time as the thermal and mechanical characteristics of the container are improved.