Abstract: A supporting belt (3) for ribs (7), carrier belts (6) for the ribs (7) arranged adjacent to the supporting belt (3), a feed (8) for the ribs (7), and a fusion welding device (11) (laser beams, electron beams) which welds half-tubes (10) with the ribs (7) contacting the outer sides of the latter (10) proceeding from the inner sides are used to provide tubes with ribs. After providing the half-tubes (10) with ribs, the latter are connected with additional ribbed half-tubes (10) by means of welding the longitudinal edges (27) to form exchanger tubes. These exchanger tubes can then be galvanized individually or in bundles as heat exchangers.

Abstract: A heat exchanger includes exchanger tubes which are narrow in flow direction of an outer exchanger medium. Always two adjacent exchanger tubes are connected to each other by fins which are either U-shaped individual or are components of a meander-like fin strip. The tube sides are connected to bases of the individual fins or to contact portions of the fin strips by welding, particularly by fusion welding on the inner surfaces of the tube sides. The exchanger tubes are formed by two tube shells which are welded together at the longitudinal edges thereof after two adjacent tube shells have been connected to each other by the fins. The ends of the tubes are placed in tube plates. The resulting heat exchanger is completely galvanized and does not require support structures.