Tube expanding method for heat exchanger tubes and tube expanding apparatus for heat exchanger tubes

Abstract

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 tubesthat pass through a fin layerprotrude from an upper end surface of the fin layer, hairpin portionsof the heat exchanger tubesprotrude from a lower end surface of the fin layer, and tube expanding billetsare inserted into each opening portion of the heat exchanger tubesto carry out primary tube expansion that expands the diameter of each straight tube portionof the heat exchanger tubesto integrate the heat exchanger tubesand fins. The primary tube expansion ends with each tube expanding billetinserted into a boundary between the straight tube portionand the hairpin portionof a heat exchanger tubeor the vicinity thereof. The tube expanding billetsare then held at the positions where the primary tube expansion ended and flare punchesare inserted into the opening portions of the heat exchanger tubesthat have been subjected to the primary tube expansion to form flare portionsin front end portions of the heat exchanger tubes