| 摘要 |
<p>The following specifications discloses a flexible duct constructed from a spiral of channel-shaped metal with the legs of the channel facing inwards of the spiral. A strip of cloth or other flexible webbing material is formed into a spiral with its overlapping edges folded into the channel of the spiral with a cord or string filling the remainder of the channel cavity before the channel legs are crimped together to maintain the webbing strips edges fast together within its grip. The expansibility of the duct is increased by increasing the width of strip of webbing.</p> |
