| 摘要 |
<p>The flange and stiffener is formed from a strip of metal sheeting and comprises an initial straight horizontal portion (3). This has perpendicular wall (4), the top edge being folded over to form a bead (6). This section encloses the duct flange (14). This continues vertically downwards (7) and then outwards at an angle (8) to terminate in a turned-in hook (9) near the initial starting point. This hook is held elastically by a row of projections (17) punched into the ventilation duct sheet (2) by machine or using a hand tool.</p> |
