Abstract: A method of manufacturing an internal grooved tube according to the present invention includes 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 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. A lead angle ? of the grooves to the tube axis is preferably limited to 26 to 45 degrees.

Abstract: 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 &thgr; 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.

Abstract: The present invention is an apparatus for manufacturing an internal grooved tube, in which has a rotary die and a working head having a plurality of balls retained inside in such a way as to rotate with play are provided along the drawing direction of a metal blank tube in order and in such a way as to rotate separately, which is constructed in such a way that multiple grooves are formed in the internal surface of the metal blank tube by pressing the metal blank tube where a plug and a grooved plug rotatably coupled to the plug are inserted against the outer surface of the grooved plug as the metal blank tube is put through the rotary die and the working head and drawn, and which has lubricating-oil feeding units and separatedly provided at upstream sides of the rotary die and the working head.

Abstract: The present invention is an apparatus for manufacturing an internal grooved tube, in which has a rotary die and a working head having a plurality of balls retained inside in such a way as to rotate with play are provided along the drawing direction of a metal blank tube in order and in such a way as to rotate separately, which is constructed in such a way that multiple grooves are formed in the internal surface of the metal blank tube by pressing the metal blank tube where a plug and a grooved plug rotatably coupled to the plug are inserted against the outer surface of the grooved plug as the metal blank tube is put through the rotary die and the working head and drawn, and which has lubricating-oil feeding units and separatedly provided at upstream sides of the rotary die and the working head.

Abstract: 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 &thgr; 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.