Method of making an internal grooved tube

摘要

An internal grooved tube according to the present invention comprises a large number of fine spiral grooves on the inside surface in parallel arrangement, wherein the grooves are formed to assure that the ratio of a groove width in the tube axial direction to a groove height is in the range of 1 to 2. A lead angle theta of the grooves to the tube axis is preferably limited to 26 to 35 degrees. A method of manufacturing an internal grooved tube according to the present invention comprises the steps of inserting a grooved plug into a blank tube rotatably, and then pressing the blank tube against the outside surface of the grooved tube with several balls revolving both around the circumference of the blank tube and on its axis in a location of the grooved plug inserted, while drawing out the blank tube longitudinally in one direction, wherein the number of balls is limited to 2 to 3.