METHOD FOR MANUFACTURE OF COEXTRUDED MULTILAYER PIPE, DEVICE FOR ITS REALIZATION AND PIPE SO PRODUCED Russian patent published in 2002 - IPC

FIELD: manufacture of pipes, applicable for manufacture of metallo-polymeric pipes with a heat-insulating coating. SUBSTANCE: the method consists in formation a metal pipe with a polymeric coating by coextrusion of polymeric material coating by coextrusion of polymeric material on its inner and outer surfaces at tube movement and cooling. After cooling a porous layer is additionally formed around the pipe with a polymeric coating by extrusion of the polymeric material with the foaming agent on the outer surface of the external polymeric coating of the metal pipe at its movement inside the extrusion head. The head has a caliber of the outer surface of the pipe, provided with a cooling jacket. Use is made of an extrusion head at least with a single duct for formation of the porous layer. The cross-section of the duct at the outlet in the point of its conjugation with the calibrating duct is similar in shape to the longitudinal section of the calibrating duct formed by the outer surface of the metal pipe with the polymeric coating and the inner surface of the caliber of the outer surface of the pipe under production. Cross-section area S of the outlet of the duct for formation of the porous layer is bound up with cross-section area S of the calibrating duct by expression s=S/n, where n - the quantity of ducts. Polyolefin with blowing agent is used as a polymeric material with a foaming agent for the porous layer, the density of polyolefin being within 900 to 960 kg/cu.m, with the gas number of blowing agent being within 200 to 220 ml/g and the temperature of decomposition within 180 to 200 C. Extrusion is carried out at a temperature within 135 to 180 C. The thickness of the wall of the caliber of the outer surface of the pipe under production between the cooling jacket and the outlet of the duct for formation of the porous layer is made smaller than the thickness of the wall of the caliber of the outer surface of the pipe under production under the cooling jacket. Described also is the device for realization of the method and coextrusion of the multilayer pipe. EFFECT: provided continuous manufacture of metal pipes with polymeric and heat-insulating coatings that can be bent without breaking of the heat-insulating coating. 28 cl, 7 dwg