| 摘要 |
A curved connecting pipe for ducts is proposed which can be manufactured at low cost. It is made by rolling spirally a long metal strip having wide portions and narrow portions alternately so that the wide portions will meet at one edge of the strip and the narrow portions will meet at the other edge. A single flange formed along one edge is received in a double flange formed along the other edge. An apparatus for making the connecting pipe is disclosed. In another embodiment, a flat edge of the strip is rested on a recessed edge and welded together.
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