PIPE WITH SPIRALLY GROOVED INNER SURFACE, METHOD FOR MANUFACTURING SAME, AND HEAT EXCHANGER

摘要

The purpose of the present invention is to provide a pipe that has a spirally grooved inner surface and is devoid of orange peel generation and has excellent outer-surface and inner-surface properties, a method for manufacturing the pipe with a spirally grooved inner surface, and a heat exchanger. The present invention is a method for manufacturing a pipe with a spirally grooved inner surface in which: an extruded raw pipe or a pipe with a spirally grooved inner surface is drawn while being twisted immediately before being placed in a drawing die, is reduced in diameter in the reduced-diameter portion of the drawing die, and is drawn, and the drawing and the twisting process are performed at the same time, the extruded raw pipe or the pipe with a spirally grooved inner surface being produced by processing into a coil shape an aluminum extruded raw pipe having a plurality of straight grooves formed on the inner surface in the longitudinal direction at intervals in the circumferential direction and fins formed between the straight grooves, then stretching the pipe material to give a twist to the pipe material, and then drawing the pipe material; the method for manufacturing a pipe with a spirally grooved inner surface being characterized in that the average crystal grain diameter of the pipe with a spirally grooved inner surface obtained after annealing is no greater than 120μm, and that the average crystal grain size of the extruded raw pipe used for manufacture is no greater than 80μm. In addition, the present invention is a pipe with a spirally grooved inner surface manufactured by processing into a coil shape an aluminum extruded raw pipe having a plurality of straight grooves formed on the inner surface in the longitudinal direction at intervals in the circumferential direction and fins formed between the straight grooves, then stretching the pipe material to give a twist to the pipe material, and then drawing the pipe material, the pipe with a spirally grooved inner surface being characterized in that the metal structure of the pipe is wholly a fibrous structure in the longitudinal direction of the pipe, or is a recrystallized structure solely in the surface layer, and is wholly a fibrous structure outside of the surface layer.