PC Hollow Sheet Line

The annealing furnace is a critical downstream component that eliminates internal stress created during the extrusion and vacuum sizing process. Polycarbonate is particularly susceptible to residual stress accumulation because its high melt viscosity (typically 10–20× higher than PP at processing temperature) and rapid cooling rate in the vacuum sizing tank “freeze” molecular orientation into the sheet. This residual stress causes warping, dimensional instability, and reduced impact strength in the finished product. The multi-zone annealing furnace operates at 120–135°C (below PC’s glass transition temperature of ~147°C), allowing polymer chains to relax while the sheet is supported on a zero-tension conveyor. Post-annealing warpage is reduced to ≤0.5 mm/m versus 2–5 mm/m without annealing. The wind cooling unit then returns the sheet gradually to ambient temperature to prevent thermal shock.

These two stations serve complementary functions — corona treatment prepares the sheet surface for the end application, while film coating protects that prepared surface during delivery. Corona treatment increases the PC sheet surface energy from approximately 30 dynes/cm to 48–56 dynes/cm, which is essential for adhesion of anti-drip coatings (greenhouse), UV protective lacquers, screen printing inks, and laminating adhesives. Without corona treatment, these coatings and inks will bead, delaminate, or fail peel tests. The film coating unit then immediately applies protective PE film to both sheet surfaces — preserving the corona-activated surface and preventing scratches, dust, and handling damage during cutting, stacking, storage, and transportation. The protective film is peelable at the installation site without adhesive residue.

Standard configuration delivers 200–500 kg/h at sheet widths up to 2,100 mm (expandable to 2,200 mm). A verified reference installation in Algeria operates at 500 kg/h producing 2,200 mm wide PC hollow sheets in continuous production. Actual output depends on sheet structure (2-wall vs multi-wall), wall thickness, rib geometry, and material formulation — more internal ribs or thicker walls increase die head pressure and melt residence time, reducing throughput. Higher output configurations can be engineered upon request. Jwell’s process engineering team analyzes the customer’s target product mix to specify the optimal extruder size, screw design, and die configuration.

The screw is manufactured from 38CrMoAlA alloy structural steel with gas nitriding treatment achieving 0.5–0.7 mm case depth. Surface hardness reaches HV≥940 in the nitrided layer (base material hardness HV≥740). The screw features a 33:1 L/D ratio with a barrier section designed specifically for PC — the barrier flight separates solid bed from melt pool, improving plasticization uniformity and preventing unmelted material from reaching the die. The nitrided surface provides three key benefits: (a) abrasion resistance against mildly corrosive PC melt at 280–320°C, (b) reduced polymer adhesion preventing material degradation and black specks, and (c) extended service life of 3–5 years continuous production versus 1.5–2 years for non-nitrided alternatives. The melt pump between extruder and screen changer decouples extruder RPM from die head pressure — essential for consistent internal rib fill in multi-wall sheet production.