Method for producing heat exchanger tubes

In a method of producing metallic heat exchanger tubes having a heat exchange surface that is increased by fins, whereby a rotating tube has helically wound about its outer surface a strip that forms said fins, with said strip being fed to the surface of said tube under tension, and with the bottom edge of said strip being welded to said tube, the improvement comprising the steps of:

• fusing the contact surface that exists between said tube and the bottom edge of said strip, and that extends helically on the surface of said tube, exclusively at the surface of said tube via a laser beam that is directed in the region where said strip runs onto the surface of said tube, and that fuses a portion of said tube surface that in the axial direction of said tube corresponds at least to the width of said bottom edge of said strip and in the circumferential direction of said tube corresponds approximately to the same amount;
• at the same time fusing with said laser beam said bottom edge of said incoming strip exclusively in the region where said strip runs onto the surface of said tube;
• and
• joining said two fused surface areas of said tube surface and said bottom edge of said strip in a gap-free manner as a consequence of said tension that is exerted upon said incoming strip as the same runs up on said tube surface, whereupon during subsequent cooling these two fused surface areas are connected to one another in such a way that a continuous, residual-gap-free welding of said helically wound strip with said tube results.