Why Dedicated UV-Cap Co-Extrusion Manifold Matters for Door-Skin Longevity

• Cap-Layer Distributor (Upper Manifold): A restricted-flow, fish-tail or coat-hanger style manifold meters the UV-stabilised compound (typically TiO₂-loaded rigid PVC or ASA-capped PVC) to a uniform 0.3–0.8 mm thickness across the full width — verified by ultrasonic or micrometer check on start-up samples. This thin skin blocks UV-A/B penetration to the wood-fibre core, preventing greying and chalking on exterior-facing doors.

• Core-Layer Distribution (Main Manifold): The bulk WPC or foamed-PVC melt (often high filler-load, CaCO₃ 30–50 phr) is distributed through a larger-volume channel with choked/restricted zones to equalise pressure across wide sections — critical for 600–900 mm door blanks where edge-to-centre pressure variance can cause bow or cell-size gradient.

• Merge Zone Before Land: Cap and core merge just upstream of the die land — the interface is designed to avoid flow lines ("snakeskin" defects) while preserving cap integrity; land length is pre-compensated for PVC die-swell (1.15–1.30×) and foaming expansion.

Key Specification Points (From Junhui PVC WPC Door Die Page)

• Product Designation: PVC WPC Anti UV Moisture Soundproof Thermal Door Extrusion Die Mold

• Die Body Material: Premium alloy steel — 40Cr die steel (forged, quenched & tempered to HRC 28–32 typical); mandrel / core rods optional stainless (3Cr13 / 4Cr13) for corrosion resistance in WPC high-moisture lines

• Heat Treatment: Rough-machine → stress-relief anneal → finish-grind / polish — preserves dimensional stability under sustained 170–190°C barrel pressure & thermal cycling

• Machining Accuracy: ± 0.01–0.02 mm on profile-defining surfaces (die lip, mandrel OD/ID for hollow jamb); flow-channel surface Ra ≤ 0.4 µm (mirror-polish or hard-chrome-plate on request)

• Co-Extrusion Feature: Single or dual cap-layer manifold — supports UV-resistant cap, coloured ASA/PVC cap, or rigid-foam cap over foamed core

• Foaming Compression Ratio (Land Pre-Land): Tuned 2.5:1–4:1 (Celuka / semi-Celuka WPC door panels); free-foam variants use lower compression — Junhui adjusts per customer's WPC formulation (blowing-agent type & loading, cell-regulator)

• Calibration / Cooling Sleeve (Optional Match): Vacuum calibration block-set (multi-piece aluminium or stainless) contoured to die exit — ensures first 300–600 mm sets flatness and corner-radius fidelity; water-manifold cooling sleeves for hollow jamb extrusions

• Custom Inputs Required:

• Full CAD cross-section (DWG / DXF / STEP) of door panel or jamb — include wall-thickness, hollow chambers, embossed texture zones

• Extruder die-head mount flange (e.g., Ø 65 mm / Ø 80 mm conical twin-screw, clamp-ring or bolt pattern)

• PVC vs. WPC formulation notes (foaming yes/no, filler %, cap-layer material & thickness target)

• Desired co-extrusion layers (1-cap / 2-cap / none)

• Lead Time (Typical): 25–40 days after drawing approval (complex wide-door die may trend longer)

• After-Sales: Die-trial support (remote or on-site in China), spare mandrels / die-lips / restrictor bars available separately

Typical Door-Profile Applications & Die Configurations

• PVC / WPC Hollow or Solid Door Panels (Flat / Embossed): 600–1000 mm wide × 35–45 mm thick — die includes emboss-plate pocket (optional) and cap-coextrusion manifold; calibration block-set matches.

• Door Jambs / Architraves (Hollow Rectangular or L-Shaped): Mandrel-supported hollow die; wall-thickness tolerance ± 0.15 mm; often run as twin-strand side-by-side.

• Casement / Side-Lite Frames (Multi-Chamber): Complex internal ribbing — die land and pre-land choke-points tuned per chamber width to equalise fill; co-extrusion cap on exposed face only if specified.

• WPC Ceiling / Wall-Cladding Panels (Related): Same die-platform family — Junhui can adapt width/emboss for matching interior cladding runs.

Die Care & Surface-Preservation Tips for Long Runs

1. Pre-Heat Die to Process Temp Before Screw Start: 170–190°C for rigid PVC/WPC — avoids thermal shock to plated flow faces.

2. Use Compatible Purge Compound on Colour/Formula Change: Prevent cross-contamination; do NOT leave degraded WPC bake in die overnight (cellulose fibre chars → carbon build-up in corners).

3. Disassemble for Cleaning Only When Manageably Cool: Use proper die-puller; avoid hammering mandrel — thermal gradient can seize it.

4. Periodic Re-Chrome / Re-Polish: On high-volume runs (> 500–800 t through one die) mirror-finish degrades — return for re-work before surface streak complaints arise.

5. Store Dies Horizontal on Wooden Pallets in Climate-Controlled Room: Large door-die bodies can warp if leaned vertically long-term; label with profile-ID & last-run date.

Sourcing Checklist for WPC Door Mills & Profile OEMs

1. ✅ Provide complete door-panel / jamb cross-section CAD (include embossed texture zones, hollow chambers, wall-thickness callouts).

2. ✅ Specify extruder make/model & die-head mount flange (photo/drawing helpful).

3. ✅ State material system — rigid PVC / WPC (foamed Celuka / free-foam / solid) / co-extrusion cap-layer type & target thickness.

4. ✅ Confirm single vs. twin-strand / co-extrusion needs (UV-cap, ASA-cap, foam-core etc.).

5. ✅ Ask about matching vacuum calibration blocks / water-cooling sleeves / haul-off guide jigs if new line setup.

Conclusion: Mould the Performance Before the Profile Leaves the Die