| 摘要 |
The present invention solves a problem with conventional tube expanding method for heat exchanger tubes that is susceptible, when carrying out tube expansion on U-shaped heat exchanger tubes that have a narrower diameter than in the past and forming flare portions in opening portions that have been subjected to tube expansion, to a buckling phenomenon at boundaries between straight portions and hairpin portions of the heat exchanger tubes or a vicinity thereof. Opening portions of U-shaped heat exchanger tubes 56 that pass through a fin layer 54 protrude from an upper end surface of the fin layer 54, hairpin portions 56b of the heat exchanger tubes 56 protrude from a lower end surface of the fin layer 54, and tube expanding billets 22 are inserted into each opening portion of the heat exchanger tubes 56 to carry out primary tube expansion that expands the diameter of each straight tube portion 56a of the heat exchanger tubes 56 to integrate the heat exchanger tubes 56 and fins 50. The primary tube expansion ends with each tube expanding billet 22 inserted into a boundary between the straight tube portion 56a and the hairpin portion 56b of a heat exchanger tube 56 or the vicinity thereof. The tube expanding billets 22 are then held at the positions where the primary tube expansion ended and flare punches 24 are inserted into the opening portions of the heat exchanger tubes 56 that have been subjected to the primary tube expansion to form flare portions 60 in front end portions of the heat exchanger tubes 56.
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