(57) Improved method and apparatus for making finned tubing from difficult-to-work materials
such as titanium and stainless steel uses spaced sets (26, 28) of finning discs on
a plurality of arbors to form a tube (11) against a mandrel having different diameters
(14, 16) under each set of discs. By forming the tips of the fin turns (11') to their
final O.D. in the first disc set (26) and by deepening their roots to bring the fin
turns to their final height in the second disc set (28), tubes with higher fin turn
counts and or higher fin heights can be achieved than were formerly possible. The
process of separately cold working the tips and roots also permits tubes to be made
which are dimensionally identical to prior art tubes but with higher quality and productivity
since tube stresses are greatly reduced. An improved titanium tube is also disclosed
which has at least a fin turn per mm (26 fins per inch), a fin height of at least
0.86 mm (0.034") and an outside to inside surface area ratio of at least 3.0.
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