| 摘要 |
PURPOSE:To obtain a welded tube having a welded part excellent in strength by coiling an upward-warping band-shaped sheet material into a spiral shape and joining the adjoining sheet materials so that their back sides are facing each other. CONSTITUTION:A band-shaped sheet material 3 coiled around a drum 2 is delivered from the drum 2 and is introduced to a corrugator 4, to warp upward its both ends of the width direction by the corrugator 4. Further, the sheet material 4 is coiled into a spiral shape at a spiral shape attaching part and its joining part is welded by a welder thereafter. Because the material 3 is welded at its joining part in a state that the back sides of adjoining sheet materials 3 are facing each other, the strength at the welding part of a welded tube is considerably high.
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