Method to reduce air center middle margin turnaround for folded tube applications

A method of making a folded fin air center having a reduced height middle margin turnaround for use in a heat exchanger core, said method including the steps:

• providing a pair of form rolls, each form roll being of the type comprising a plurality of form discs abutted one to the other and having a plurality of star-like teeth thereabout, points of the star-like teeth defining a major diameter of the form roll and valleys between adjacent ones of the star-like teeth defining a minor diameter of the form roll, and further including at least one stripper disc having no teeth therearound and interposed between at least two of the plurality of form discs, wherein the stripper disc has a diameter less than the minor diameter of the form roll, and wherein the form discs abutting the stripper disc are modified form discs having modified star-like teeth therearound, points of the modified teeth defining a major diameter of the modified disc to be less than the major diameter of the form roll;
• rotating the form rolls in opposite directions in a manner to cause the star-like teeth of one form roll to intermesh with the star-like teeth of the other form roll;
• feeding a blank strip of heat conductive material between the rotating form rolls;
• allowing the teeth of each form roll to engage the blank strip;
• forming the blank strip over the point of an opposing tooth to form a tip radius adjoining legs of a folded fin;
• causing the strip to be further drawn over the point of the opposing tooth to form a leg having a height at a middle margin turnaround in the region over the modified discs and the stripper disc less than the height of the remainder of the leg over the region of the plurality of form discs.