| 摘要 |
A foil strip composed of several layers is continually rolled up around an axis extending in its longitudinal direction to form a tubular body (38) in such a way that the two edges (42, 44) overlap. To effect welding, the overlapping edges are pressed together between two strips (16, 18) which are driven in a circulating manner in the longitudinal direction. The inner strip (16) which passes inside the tubular body (38) is provided with a longitudinal groove (40) which at least partly receives the region of the overlapping edges (42, 44). The longitudinal groove (40) forms the region of the seam of the tubular body (38) which is facing inward, and prevents the plastic material which is liquefied for welding from expanding as a result of the application pressure. In this way it is ensured that the material of the two edges (42, 44) is fully welded together, so that no pressed-out edge regions of liquid material cool prematurely and therefore do not adhere to the opposed material layer. |
