PROCESS FOR PRODUCING A LARGE CALIBRE PLASTIC PIPE AND AN EXTRUSION TOOL FOR THE PROCESS

摘要

A process for production of large calibre plastic tube, in which a hollow thermoplastic profile of rectangular cross-section is extruded and is coiled on a drum helically with contiguous turns with adequate deformability , and in which during the coiling operation the turns are welded together at t he contact surfaces by a butt-welded seam under axial pressure and heat. The hollow plastic profile is moulded in an extrusion tool to form a multi-cell profile having outer profile walls and cell-forming webs and at the same tim e and/or thereafter, by internal cooling of the outer profile walls and the cell-forming webs, is sized and given a design strength which is stable up t o a predetermined critical pressure. The calibrated mufti-cell profile is agai n heated at the contact surfaces to the welding temperature of the thermoplast ic material. The butt-welded seam between the turns is welded with an axial pressure below the critical pressure of the design strength. Extrusion tools for performing the process are also described.