MANUFACTURE OF HEAT TRANSFER TUBE WITH INNER SURFACE GROOVE AND MANUFACTURING APPARATUS

PROBLEM TO BE SOLVED: To extend the service life of a roll-forming roll for roll-forming slant fins on a metallic plate or rod material by relatively shrinking the outer diameter of pair of the roll-forming rolls or receiving rolls in a range faced to a range finally forming individual fin on the metallic plate or rod material accompanied with the rotation of the roll-forming roll. SOLUTION: The roll-forming rolls 24 for fin, are provided with the roll bodies 24B-24E having the same diameter parallel disposed in the same axis and one pair of side rolls 24A having the almost same diameter, fixed to the same axis at both sides thereof. On the outer peripheral surfaces of the roll bodies 24B-24E, many spiral fin roll-forming grooves 25 are parallel formed in the same pitch over these whole surfaces, and the fin roll-forming grooves 25 in the adjacent roll bodies are formed as a plane symmetry with the mating surfaces of these roll bodies as the boundary. The diameters in the outer peripheral surfaces of the roll bodies 24B-24E are not fixed, and the outer diameters of the roll bodies 24B-24E are shrunk near the mating surfaces of the roll bodies 24B and 24C, 24D and 24E, and the recessed parts 46 are formed over the whole circumferences.