TUBE WITH GROOVES FORMED IN INNER SURFACE THEREOF, METHOD OF PRODUCING THE TUBE, AND GROOVED PLUG

摘要

A tube having grooves formed in its inner surface. The grooves are formed in a reverse trapezoidal cross section, and the corners at the root of each groove have a circular arc shape and the ratio (R/d) of the radius R (mm) of each corner to the width d (mm) of the groove is not less than 0.10 and not more than 0.25. A grooved plug having ridges and grooves formed on the outer peripheral surface of the plug is inserted into a blank tube, and the outer peripheral surface of the blank tube is pressed. This causes a blank tube material to flow into the grooves of the plug to form grooves in the inner surface of the blank tube. In this process, the blank tube material can easily flow into the grooves of the plug, so that cracks of the grooves and fins can be prevented.