| 摘要 |
PURPOSE:To make bonding of foamed resin to a metal tube firmly and improve resistance to torque and screw thread cutting property by coextruding bonding resin from a cross head die provided on the periphery of the metal tube transferred in the longitudinal direction to the metal tube surface side and foaming thermoplastic resin to the outside of said surface side and coating the metal tube outer surface while foaming thermoplastic resin. CONSTITUTION:A cross head die 2 is disposed on the periphery in the longitudinal direction of a steel tube 1, and both of said resins are introduced from a foaming thermoplastic resin extruder 3 and a bonding resin extruder 4 to the die 2. The foaming thermoplastic resin 6 and the bonding resin 7 are introduced into the die 2 in a manner that the resin 7 is on the steel tube 1 side, and both resins are joined 8 in the die 2 and bonded together sufficiently. After that, both resins are coextruded and plastic resin 6 is foamed 9 and then bonded on the outer surface of the steel tube 1. A heat-insulated coated steel tube 5, therefore, is constituted of foamed resin 9 bonded firmly to the outer surface of the steel tube 1 through a bonding resin layer 7. |
