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March 1, 2004

1 Min Read
Extrusion die design creates greenhouse roofing

A special extrusion-die design to process double-wall Lexan-brand PC sheet used as greenhouse roofing can save up to 30% in UV stabilizers coated on outside layers. The special coextrusion die reduces the amount of the outer skin melt, which includes the additive, to form a thinner, more even layer thickness than conventional dies, says Fabio Cazzani, managing director of Omipa Extrusion Machinery, the die's manufacturer.

It was developed for processor GE Structured Products Europe and IMAG, the Dutch Institute of Agricultural and Environmental Engineering, to produce ZigZag greenhouse roofing. This hollow panel retains 45% more heat than single glass sheet, but offers light transmission comparable to glass. GE says the high light-transmission secret lies in the multiwall panel's geometry, which reflects light back into the greenhouse to compensate for any loss due to the panel's double wall.

This helps produce energy savings of 20% to 40% for growers. Support profiles to hold the panels in place are unnecessary as ZigZag's weight is less than half (4 kg/m) of equivalent glass (10 kg/m). Inner sides are covered with a non-drip coating to dissipate moisture before it drops and damages plants, while the sheet's channels are extruded with an anticondensation additive to reduce algae growth.

The die has an output of 200 to 250 kg/hr. Cazzani says that although this problem has been solved, it was especially difficult to construct because its geometry made even melt distribution and flow difficult. ZigZag sheet has a width of 1.20m and length of 2.6m. GE Structured Products, Bergen op Zoom, the Netherlands, +31 164 292742; www.lexanzigzag.com; Omipa SpA, Morazzone (VA), Italy, +39 0332 461400; www.omipa.it

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