High-speed post-forming line developed
PHOTO: Battenfeld co-extrusion line with a flat die
POST-forming is the efficient answer to producing single-shell PVC gutter profiles at speeds of up to 25m/min. Battenfeld Extrusionstechnik GmbH of Germany and the Italian company B-TEC have developed a complete line for this purpose.
For cost-efficient manufacturing of PVC gutters at high speed, a flat-sheet die with a small roller calender is connected to the plasticising unit to start producing PVC sheet. This sheet is formed into the desired gutter profile by a downstream forming tool.
In conventional extrusion lines with three vacuum pumps, speeds of 5 to 8m/min are normal. The special line, with only one vacuum pump, reaches up to 25m/min with a high output. For profiles with similar peripheral dimensions, an exchange of the forming tool is sufficient to cause a product changeover.
The system can be laid out as a co-extrusion line to extrude a high-quality, UV-resistant, weatherproof surface coating applied to the visible parts of the gutter. Small gutter profiles can be produced by a twin-strand process.
To produce the complete line, a choice of two extruder combinations with an output of up to 1000 kg/h is available. As the main extruder, either the BEX 2-110-28 V parallel twin-screw extruder or the extruder model BEX 2-135-28 V may be used, combined with the conical BEX 2-54 CC or the BEX 2-72 CC as co-extruder.
The flat-sheet die, equipped with interchangeable co-extrusion plates, is highly flexible. Efficient cooling of the sheet to about 120°C following extrusion is provided by the polishing stack with two temperature-controlled polishing rolls and two to four chill rolls that are also temperature-controlled. The contour forming tool has been integrated into the 4m calibration table.
Standardised tool holding fixtures on the cooling water tank allow for rapid exchange of the calibration and cooling units. The calibration unit is followed by a combined belt/roller haul-off, which provides smooth removal of the profiles that are open to one side. Because of the twin rollers which can be shifted on their shafts, this haul-off is also suitable for twin-strand extrusion. A sub-surface knife cutting device is installed at the end of the line which ensures swarfless and accurate cutting of the profiles.