| 摘要 |
<p>A method of manufacturing a roofing of sheet metal, where a sheet in a first step is preformed so as by a first cross-section perpendicular to its surface extension be given a portion, which is curved in waveshape, and the preformed sheet in a second step is provided with steps of a predetermined height by means of a pressing tool, which comprises at least one first and one second pair of tools movable to and from each other, the preformed sheet being held down by each tool pair, whereafter the tool pairs are moved relative to each other through a distance corresponding to the step height, so that the sheet by a second cross-section perpendicular to the surface extension of the sheet and to said first cross-section is given a step-shaped portion, whereafter the preformed sheet is advanced through a predetermined adjusted distance, and thereafter the next step is formed, and so on. According to the invention, said second tool pair, which are located at the discharge end of the pressing tool, are caused to hold down the sheet with a holding-down force so high that sliding movement between the sheet and the tool surfaces is prevented. Said first tool pair located at the feed end of the pressing tool are caused to hold down the sheet with a lower holdingdown force so adjusted, that sliding movement between the sheet and the tool surfaces of the first pair takes place when a tensile stress has been attained in the sheet by said relative movement of the tool pairs which is higher than the yield strength of the sheet.</p> |
