Patent ID: 6458311
Filing Date: 2002-10-01
Classification: B29C,B29L

Abstract:
A method for the continuous manufacture of a twin-wall pipe (10) having a pipe socket (41) and consisting of a smooth internal tube (39â€²) and an external tube (37â€²), which is welded together with the internal tube (39â€²) and which is provided with transverse grooves (38), comprising the following method steps:extruding a first mass flow of melt of plastic material per unit of time and forming an external tube (37) having an inside and an outside; providing the external tube (37) with a corrugation of transverse grooves (38) and corrugation troughs (40) by an over pressure acting from the inside to the outside; extruding a second mass flow of melt of plastic material per unit of time and forming an internal tube (39) into the external tube (37); pressing the internal tube (39) against the corrugation troughs (40) of the external tube (37), thereby welding together the internal tube (39) with the external tube (37); expanding the external tube (37) at given intervals and by the application of the over pressure acting from the inside to the outside to form a substantially smooth-walled, approximately cylindrical pipe socket (41) and a transition section between a corrugation trough (40) and the pipe socket (41); expanding the internal tube (39) during expanding the external tube (37) and pressing the internal tube (39) outwards against the socket (41); keeping constant the first and second mass flow of melt of plastic material per unit of time during providing the external tube (37) with a corrugation of transverse grooves (38) and corrugation troughs (40); and modifying at least one of the first and second mass flow of melt of plastic material per unit of time independently of the other one of the second and first mass flow of melt of plastic material per unit of time during the forming of the pipe socket (41) and the transition section.