| 摘要 |
PURPOSE:To make it possible to simply perform the production of a perforated pipe easy in laying construction and having high strength by extrusion molding, by drilling perforations to a ring shaped thin film in such a state that a part of a movable die and a part of a fixed die are contacted when the width of an operation space is narrowed to form the thin film. CONSTITUTION:A movable die 6 is moved up and down to make the width of an operation space S variable at definite cycles. When the width of the operation space is widened by upwardly moving the movable die 6, molten synthetic resin is extruded downwardly from an extrusion orifice 8 while a thick walled ring shaped rib 1 is formed and, when the movable die 6 is downwardly moved to narrow th width of the operation space S and a projection 7 is contacted with an operation surface, a ring shaped thin film 2 is extruded and perforations 3 are drilled to said ring shaped thin film 2. According to the up-and-down movement of the movable die 6, a perforated pipe A wherein the ring shaped ribs 1 each largely protruded to the inner peripheral surface side and the ring shaped thin films 2 having the perforations 3 drilled thereto are alternately and integrally continued at predetermined pitches is obtained. By this method, the perforated pipe can be molded only by moving the movable die in extrusion molding to be able to simply obtain the perforated pipe withstanding load in embedding and having the ring shaped thin films. |
