Method and device for producing a double-walled thermoplastic corrugated pipe having a connecting sleeve

A method for producing an endless double-walled pipe made of thermoplastic material and having corrugated pipe sections and sleeve pipe sections, by extrusion of an outer tube, forming the outer pipe of the double-walled pipe, and of an inner tube, forming the inner pipe of the double-walled pipe, in a molding passage having at least one section with a corrugated molding surface and at least one section with a preferably smooth, cylindrical or slightly conical sleeve molding surface,

• wherein
• to shape a corrugated pipe section, the outer tube is extruded into the corrugated molding surface and is brought into contact with the corrugated molding surface, and the inner tube is extruded into the outer tube and is brought into contact with the outer tube, in contact with the corrugated molding surface, in the region of the corrugation valleys of the outer tube;
• to shape a sleeve section, the outer tube is extruded into the sleeve molding surface and is brought into contact with the sleeve molding surface, and the inner tube is extruded into the outer tube, 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 already in contact with the sleeve molding surface over the entire axial length of the sleeve molding surface,
• wherein a pressure (pa1) acting on the inner side of the outer tube is reduced to a pressure (pa2) just before or at the same time as the outer tube is extruded into the sleeve molding surface,
• wherein the pressure (pa2) acting on the inner side of the outer tube is increased to the pressure (pa1) as soon as the extrusion of the outer tube into the sleeve molding surface is completed,
• wherein a pressure (pi1) acting on the inner side of the inner tube is increased to a pressure (pi2) before or at the same time as the inner tube is extruded into the outer tube already in contact with the sleeve molding surface, and
• wherein a pressure (pi2) acting on the inner side of the inner tube is reduced to the pressure (pi1) as soon as the extrusion of the inner tube into the outer tube in contact with the sleeve molding surface is completed.