Internal grooved tube and manufacturing method thereof

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 θ 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.

What is claimed is:  
     
         1 . An internal grooved tube, comprising: 
 a large number of fine spiral grooves formed on an inside surface in parallel arrangement;    wherein said grooves are formed to assure that the ratio of a groove width W in the tube axial direction to a groove height H is in the range of 1 to 2.    
     
     
         2 . An internal grooved tube according to    claim 1   , wherein a lead angle θ of said grooves to the tube axis is limited to 26 to 35 degrees.  
     
     
         3 . A method of manufacturing an internal grooved tube comprising the steps of: 
 inserting a grooved plug having a large number of fine spiral grooves on the outside surface into a blank tube rotatably; and    pressing the peripheral wall of the blank tube against the outside surface of the grooved plug 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.    
     
     
         4 . A method of manufacturing an internal grooved tube according to    claim 3   , wherein a lead angle θ of said grooves of the grooved plug to the axis is limited to 26 to 45 degrees.  
     
     
         5 . A method of manufacturing an internal grooved tube according to    claim 3   , wherein the direction of revolution of the balls is allowed to match the direction of rotation of the grooved plug.  
     
     
         6 . A method of manufacturing an internal grooved tube according to    claim 4   , wherein the direction of revolution of the balls is allowed to match the direction of rotation of the grooved plug.