| 摘要 |
PURPOSE:To form regular and uniform recessed and protruded steps on the surface of the plastic by a method wherein two sets and more of specified pressing rolls are pressed to a plastic film being wound around the steel pipe effecting a spiral rotation. CONSTITUTION:The plastic film 14 is wound in spiral around the steel pipe 11 being preheated during being transferred into the axial direction thereof under the condition of spiral rotation. The pressing rolls 29A, 29B, 29C being supported by moving frames 24 respectively are arranged mutually so as to be coincided with the spiral of the film 14 and are pressed against the surface of the film 14 by operating a cylinder 32. The central part of a section to be a protruded part is recessed into a V-shaped groove by the central protuberance 40 of the pressing roll 29A, subsequently, the central part of the section to be a protruded part is flattened by the pressing roll 29B and further the formed recessed section of the pressing roll 29C is pressed thereagainst, thereby forming the regular and uniform recessed and protruded parts. |
