| 摘要 |
<p>A twin-walled sheet (10) formed of plastics material has spaced planar walls (11) joined by parallel webs (12) extending between opposite parallel edges of the sheet to form tubular cavities. The walls are turned inwardly towards each other around the perimeter of the sheet and are welded together to form a generally round edge (in section) which thereby seals the cavities against contamination from externally. The sheet has rounded corners. A machine for forming the rounded edges has parallel belt conveyors (22) for transporting the sheet through the machine and heaters (31) adjacent said opposite edges. The heaters heat the edge of the sheet and a pair of pinch rollers (32) at each said edge squeeze the walls together at their edge and cause them to be welded together. A further heater (33) on each side and grooved rollers (34) form the welded edge around said corners.</p> |
