Abstract: A multi-layer bell is formed from the outer shell of a multi-layer pipe in a secondary process, thereby allowing the extrusion process to be conducted at normal speeds. The bell may include a strain limiting membrane fused or mechanically secured between the outer shell extrusion layer and the inner liner extrusion layer, increased hoop or circumferential stiffness. This invention allows the extrusion process to be in its simplest form, with no adjustments to the corrugator or extruder speeds.

Abstract: A method and an apparatus for producing an endless double-walled pipe having corrugated pipe sections and sleeve pipe sections are described. The production is effected by extrusion of an outer tube (Sa), forming the outer pipe of the double-walled pipe, and of an inner tube (Si), forming the inner tube of the double-walled pipe, in a molding passage (10) having sections with a corrugated molding surface and a smooth cylindrical sleeve molding surface. To shape the sleeve section, the outer tube is extruded into the sleeve molding surface and is brought into contact with the sleeve molding surface. The inner tube (Si) is then extruded into the outer tube (Sa), already in contact over the entire axial length of the sleeve molding surface, and is brought in the process into contact with the inner side of said outer tube (Sa) that is in contact.

Abstract: A multi-layer bell is formed from the outer shell of a multi-layer pipe in a secondary process, thereby allowing the extrusion process to be conducted at normal speeds. The bell may include a strain limiting membrane fused or mechanically secured between the outer shell extrusion layer and the inner liner extrusion layer, increased hoop or circumferential stiffness. This invention allows the extrusion process to be in its simplest form, with no adjustments to the corrugator or extruder speeds.

Abstract: A method and an apparatus for producing an endless double-walled pipe having corrugated pipe sections and sleeve pipe sections are described. The production is effected by extrusion of an outer tube (Sa), forming the outer pipe of the double-walled pipe, and of an inner tube (Si), forming the inner tube of the double-walled pipe, in a molding passage (10) having sections with a corrugated molding surface and a smooth cylindrical sleeve molding surface. To shape the sleeve section, the outer tube is extruded into the sleeve molding surface and is brought into contact with the sleeve molding surface. The inner tube (Si) is then extruded into the outer tube (Sa), already in contact over the entire axial length of the sleeve molding surface, and is brought in the process into contact with the inner side of said outer tube (Sa) that is in contact.

Abstract: An apparatus for producing seamless plastic tubes comprises an injection head to which molten plastic material is fed by an extrusion device. The injection head has a plate-shaped distribution device 13a, 13b having an intake opening 20 into which the feed passage 17a, 17b for the molten plastic material opens. In the distribution device, distribution passages 14 extend in a star configuration from the intake opening 20 and extend perpendicularly to the axis of the injection head, wherein each distribution passage 14 has a straight radial passage portion 14r and three branch passages 14z which branch therefrom and which each go into arcuate passage portions 14k which, in the region of the periphery of the distribution device, communicate with the annular gap 25 of the injection head, with the adjacent ends at a respectively identical angular spacing, and they each introduce a respectively identical volume flow into the annular gap 25.

Abstract: This invention concerns an apparatus for producing seamless plastic tubes. It has an injection head to which molten plastic material is fed by an extrusion device. The injection head has a plate-shaped distribution device 13a, 13b having an intake opening 20 into which the feed passage 17a, 17b for the molten plastic material opens. In the distribution device, distribution passages 14 extend in a star configuration from the intake opening 20 and extend perpendicularly to the axis of the injection head, wherein each distribution passage 14 has a straight radial passage portion 14r and three branch passages 14z which branch therefrom and which each go into arcuate passage portions 14k which, in the region of the periphery of the distribution device, communicate with the annular gap 25 of the injection head, with the adjacent ends at a respectively identical angular spacing, and they each introduce a respectively identical volume flow into the annular gap 25.