| 摘要 |
PROBLEM TO BE SOLVED: To prevent a trouble wherein a pipe external layer part becomes easy to melt by a method wherein a plastic pipe is heated, and after the temperature is raised to the vicinity of a dummy melting point wherein the tensile stress drastically reduces accompanying the temperature ascent, the temperature is heated to a specified temperature range, and a diameter contracting process is performed. SOLUTION: A plastic pipe 2 made of a polyethylene resin containing a cross-linking agent, which is extruded from an extrusion die 1, is cooled to, e.g. 60 deg.C or lower by a cooling device 3, and then, the plastic pipe 2 is passed through a first heating device 4 (the temperature of hot water is, e.g. 98 deg.C) for a specified period of time, and its temperature is raised to, e.g. 80-98 deg.C, and the temperature is raised to the vicinity of a dummy melting point wherein the tensile stress drastically reduces accompanying this temperature ascent. After cross-linking by this, the plastic pipe 2 is sent to a hot air dryer 5, and is heated to 100-130 deg.C, and the diameter is contracted by crushing the plastic 2 with a circular cross section by a diameter contracting device 6, and then, is cooled to a normal temperature by a cooling device 7, and is taken up by a take-up device 8 under the diameter contracted state while keeping the shape. Thus, the temperature raising is performed in two stages. |
