CO-EXTRUDABLE MULTI-LAYER PLASTIC PIPE AND METHOD AND DEVICE FOR ITS MANUFACTURE Russian patent published in 2000 - IPC

FIELD: manufacture of pipes. SUBSTANCE: proposed pipe has one or more inner pipes surrounded by center layer made from softer material as compared with that of inner pipe and outer pipe enclosing the middle layer surrounding one or more inner pipes. Circular rigidity of inner pipe is higher than that of middle layer and compression of wall of middle layer is at least 1.5% of inner diameter of pipe. Compressed gas is introduced into polymer material in area of plasticizing of screw feeder for middle layer at point where polymer material is molten; gas is mixed polymer material and is extruded into cavity formed by inner pipe (pipes) and outer pipe. Calibrating device for simultaneously calibrating the outer surface and inner surface of multilayer pipe is mounted near nozzle of molding tool and part of foaming is ensured in this device. EFFECT: low cost of manufacture of pipe. 38 cl, 5 dwg