| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for easily obtaining a perforated flat tube having a fin twisted in the tubular axial direction on an inner surface of each hole. SOLUTION: In a method where the metallic stock 1 is fed in a groove 3 of a rotating wheel 2, and fed into a collection chamber 5 in a shoe block in contact with an outer circumference of the wheel 2, and extruded from a die 6 part provided on the end of the collection chamber 5, the shoe block 4 is pierced, and groove parts 8 of a plurality of mandrels 7 having the groove parts 8 on the tip part are faced in a row with the prescribed intervals to the die 6 part, and a prescribed spiral fin is formed on each groove part 8 on the inner surface of each hole of a tube to be extruded by turning the mandrel 7 by the external drive when the tube is extruded. |
