| 摘要 |
An improved tube and fin heat exchanger and a method and apparatus for making the same is disclosed. The heat exchanger includes spaced end sheets and a stack of plate fins positioned therebetween. Hairpin tubes extend through the end plates and the stack of fins. The tubes are initially sized to loosely fit through the end sheets and fins and are expanded into tight heat exchange engagement therewith during manufacture. The end sheets are accurately positioned a fixed distance apart by a method and apparatus in which the end sheets are held a fixed distance apart during the expansion of the tubes. The bent ends of the hairpin tubes are moved upwardly through the adjacent end sheet and the fins ahead of the expansion bullets to compensate for the shortening of the tubes created by the expansion operation. In one embodiment, piston and cylinder actuators supply a force on the bent ends of the tubes which substantially balances the axial force produced by the expansion bullets and prevents distortion of the remote end sheet. In a second embodiment, a mechanical drive is provided to move the bent ends of the hairpins in response to movement of the slide which carries the expansion bullets.
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