| 摘要 |
PURPOSE:To form recesses on the surface of a metal pipe so as to increase the bonding strength of concrete, by cooling the resin that has been extruded from an extruder to cover the outer surface of a metal pipe, and pressing a heated roll having projections onto the resin surface. CONSTITUTION:The outer surface of the metal pipe is covered continuously with a thermoplastic resin such as polyethylenes, and when the metal pipe 1 covered with the plastic is cooled, the heated roll 3 having projections is pressed onto the outer surface thereof so that the recesses are formed by the projections of the heated roll 3. A heat medium is circulated from a tank 8 via a heat medium circulation hose 7 into the inside of the cylindrical roll 3 to heat the roll 3. |
