Tube expanding bullet and method of expanding tube

Abstract

A tube expanding bullet is inserted into and expands a heat exchanger tube which has been pierced through collared fin holes of piled heat exchanging fins, so as to expand the fin holes and integrate the tube with the heat exchanging fins. The tube expanding bullet has a first part formed at a front part of the tube expanding bullet and a second part formed at a rear part of the tube expanding bullet whose maximum outer diameter is greater than that of the first part. The fin holes are firstly expanded by passing the first part of the bullet through the tube. The fin hole is secondly expanded by passing the second part of the bullet through the tube. A first rate of expansion of the fin hole by the first part of the tube expanding bullet is less than a second rate of expansion of the fin hole by the second part of the bullet.

Dependencies are inferred from the claim text.