| 摘要 |
<p>A polygonal tube is produced from metal strip by forming rows of recesses (15) and projections (16) along opposite edges of the strip and then bending the strip until each projection is received in a corresponding recess to form the tube. The projections are then squeezed between opposed surfaces (26,28) one inside and other outside the tube. The surface inside the tube forms a groove (27) in the tube wall at the inside of the tube, spreads each projection to take up any clearance between edges of the projections and boundaries of the corresponding recesses. The surface outside the tube allows the tube to remain flat. <IMAGE></p> |
