| 摘要 |
<p>For conforming to a circular cross-section the end of a metallic tube 1 of oblong cross-section for a heat exchanger, a single step is performed consisting in forcibly driving a punch 5 into the tube end. The punch 5 has a cylindrical body 13 of circular cross-section with a diameter equal to that desired for the inner surface of the tube end, connected to a head 8 of curvilinear quadrangular cross-section through an intermediate portion 14 of progressively varying cross-section. <IMAGE></p> |
