METHOD FOR PRODUCING CROSS-FIN TUBE FOR HEAT EXCHANGER, AND CROSS FIN-TYPE HEAT EXCHANGER

It is an object of the invention to provide an advantageous method of manufacturing a cross fin tube in which evaporation performance and condensation performance are not lowered, when expanding an internally grooved heat transfer tube is are externally expanded in accordance with a mechanically tube-expanding operation and is integrally fixed to heat dissipating fins, and a cross fin type heat exchanger including the cross fin tube obtained in accordance with the manufacturing method. A tube-expanding plug 18 has cutout-forming protuberances 28 which are formed on an outer circumferential surface thereof with a number of 60-160 per circumference such that the cutout-forming protuberances 28 extend in a direction which intersects primary grooves 20 which are previously formed on an inner circumferential surface of a heat transfer tube 10, and at the same time when the heat transfer tube 10 and plate fins 12 are fixed integrally to each other in accordance with the mechanically tube-expanding operation, secondary grooves 24 which are cross grooves with respect to the primary grooves 20 are formed to have a depth (d2) which is held in a range of 10-40 % of a depth (d1) of the primary grooves 20.