| 摘要 |
PURPOSE:To make a draft resistance of a conventional needle-shaped fin more uniform, and to improve an efficiency of heat exchange, by furthermore dividing the tip of a needle-shaped fin, formed by notching a metallic belt toward the inside from the outer peripheral part while leaving the base part of said belt in its longitudinal direction. CONSTITUTION:Needle-shaped fins 7 are respectively formed by providing notches 6, notched toward the inside of a fin part 11 from the outer peripheral part of it so that the base part is left, by a main cutting device 12. Next, each tip 14 of the needle-shaped fin 7 is divided in two parts and is enlarged into the Y shape with the aid of an auxiliary cutting device 13 so that the sufficient heat exchange is attained even by the divided tips. Accordingly, both draft resistance at the tip part 14 and the base part 4 of the needle-shaped fin 7 are made uniform, and the irregularity of the wind velocity is reduced. |
