| 摘要 |
PROBLEM TO BE SOLVED: To enable brazing through a joining surface having a large area and to improve joining strength, corrosion resistance and air tightness by brazing the high part in the width direction with the bottom part in the width direction of a plated steel strip coiled in a spiral state to the high part of the same via the joining surface having a wide area obtained by superposing the high part in the width direction of the plated steel strip having a difference in level on the bottom part of the same. SOLUTION: A tube wall is composed by coiling in a spiral state a plated steel strip which is provided with a difference in level equivalent to the plate thickness at the central part in the plate width direction, and a cylindrical body P is obtained by superposing a (n+1)th round of high part T in the width direction on a nth round of bottom B part in the width direction. Thus, the joining surface F having a satisfactorily wide area is secured. When flux is coated on the joining surface F, brazing filler metal is coated or filled if necessary and the cylindrical body P is heated at a brazing temperature, since the bottom part B in the width direction is brazed to the high part T in the width direction through the side joining surface F, the steel tube having high-joining strength, excellent corrosion resistance and air tightness is obtained.
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