| 摘要 |
The method comprises extruding a tube from thermoplastic material, and subsequently forcing the tube over a mandrel (6) at an orientation temperature of the plastic material. The mandrel comprises an expanding section (8) which produces expansion in the circumferential direction of the tube. A tube speed controlling means (12) acts upon the tube upstream of the expanding section of the mandrel for exerting an axial force on the tube, and a pulling means (20) acts upon the tube downstream of the mandrel (6) for exerting an axial pulling force on the tube. Upstream of the tube speed controlling means (12) the plastic material in an outer layer of the wall of the tube, upon which layer the tube speed controlling means acts, is brought to a temperature which is below the orientation temperature, this layer being so thick that it can withstand the force exerted by the tube speed controlling means. |
