| 摘要 |
PURPOSE:To form fins in the desired position of a tube by juxtaposing a die for forming a finned part and a die for forming a non-finned part in an extruding direction. CONSTITUTION:A die 3 for forming a finned part and a die 4' for forming a non-finned part on the rear side of an extruding direction are dividedly retreated and a die 4 for forming a non-finned part on the front side of the extruding direction is joined thereto. A mandrel 6 is inserted into a blank material and the blank material is pushed in the arrow direction to form the cylindrical non- finned part at the front end of a tube 1. The die 4 is then retreated and the die 3 is joined thereto. The finned part projected with fins 2 on the outside circumference of the tube 1 is formed by the die 3 in succession to the non-finned part. The die 3 is finally retreated and the die 4' for forming the non-finned part on the rear side is joined thereto to form the cylindrical non-finned part at the rear end of the tube 1. The finned tube which is not projected with the fins 2 at both ends of the tube 1 is thus formed. |
