| 摘要 |
PURPOSE:To improve quality of grooved tube by forming continuous inside grooves on the internal surface of a material tube and crushing the crest of the groove in order through a floating plug and a die. CONSTITUTION:A grooved plug 22 and a floating plug 23 are set in the material tube 20 and the plug 22 is rotatable through a bearing 43. The plug 22 has a groove forming part 25 provided with projections 24 and the outside diameter d1 of the plug 22 is somewhat larger than the inside diameter d2 of the tube 20. The plug 23 is provided with the head 26 of the maximum diameter and a taper part 27. The tube 20 is expanded by the plug 22 and the inside grooves are formed by the groove forming part 25 and rotating rollers 30. The tube 20 is drawn by a die 36 and the bearing part of the plug 23 so that crests rising along the inside grooves 5 of a tube 37 are crushed in order. The method increases heat transferring functions and improves the quality including dimen sional accuracy of a grooved tube 29.
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