PURPOSE: To obtain a heat-shrinkable tube which possess desired diametral dimensions and a high draw ratio by a method wherein a resin film wound up multiply round the external circumference of a heat pipe type mandrel is made into a cylindrical body by melting and integrating the film and cooled after secondary orientation of the same through expansion by pressing gas into the same.
CONSTITUTION: When a processing part 6 is heated at a temperature of at least the melting point of a primarily-oriented film 16 after the tape 16 is wound up round the esternal circumference of the processing part 6 of a heat pipe type heating mandrel 2 until the film attains a fixed thickness, the multiple tape 16 melts, unifies and becomes a cylindrical body 16' of a uniform thickness. Then a high-frequency induction coil 9 is removed, cool air is blown against a heating and cooling part 5 through a blower 10 and the mandrel 2 is cooled. After removal of a press tape 17 of the external circumference of the cylindrical body 16' and an expansion control pipe 3 is fitted to the external circumference of the mandrel 2 to which only the cylindrical body 16' is clad. When the cylindrical body 16' is heated up to a fixed temperature and softened, air is pressed into a space between the cylindrical body 16' and the external circumference of the mandrel 2 and when the cylindrical body 16 is secondarily oriented and expanded up to a fixed outside diameter, it is cured through cooling.
MOCHIZUKI MASATAKA
MASUKO KOICHI
