Why Die Flow Design Matters More Than Just "Matching the Shape"

• Restricted-Flow / Spider / Mandrel Design (for Hollow Profiles & Pipes): The mandrel (supported by spider legs in the die head) defines the internal void; its alignment relative to the outer die ring determines wall-thickness concentricity — critical for pressure-pipe spec compliance and hollow-profile symmetry.

• Land Length & Draw-Down Compensation: Die-land (the final straight-section before exit) is deliberately longer than the theoretical calibrator gap because PVC exhibits die-swell (typically 1.1–1.3× die gap). Junhui dies are cut with pre-compensated land-length so the extrudate, after vacuum-calibration and draw-down, matches the target ± 0.1–0.2 mm sectional tolerance.

• Distributive vs. Restrictive Zones: In complex multi-chamber profiles (e.g., thermal-break aluminium-clad PVC), the runner may incorporate choked/restricted zones to equalise pressure across thick and thin webs — preventing one leg from over-filling while another starves.

Key Specification Points (From Junhui Mold Product Page)

• Product Designation: Custom PVC Mold Plastic Steel Profile

• Die Body Material: Forged alloy steel — 40Cr (typical) or 45# steel; core/chase optionally in higher alloy (e.g., 3Cr13 / 4Cr13 stainless for corrosion-prone lines) on request

• Heat Treatment: Quench + temper → core hardness HRC 28–32; stress-relief anneal after rough machining → final finish-grind — minimises warping under sustained extruder barrel pressure & cyclic thermal load

• Machining Accuracy: ± 0.01–0.02 mm on critical profile-defining surfaces (die lip, mandrel OD/ID); surface roughness Ra ≤ 0.4 µm on flow-contact faces

• Cavity Configuration: Single-cavity (most profile work) or multi-cavity (for small symmetrical sections / pipe + ancillary strip); co-extrusion adapter blocks available for 2–3 layer cap/foam/core

• Runner / Flow Channel Finish: Mirror-polished or chrome-plated on request — reduces melt stagnation, eases carbon-buildup cleaning, improves surface gloss of dark-colour profiles

• Calibration / Cooling Sleeve (Optional Match): Vacuum calibration table inserts / water-cooling sleeves can be supplied to match die cross-section — ensures first 300–500 mm of profile sets correct shape before haul-off

• Custom Inputs Required:

• Full CAD drawing of profile cross-section (DWG / DXF / STEP)

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

• PVC formulation notes (CaZn vs. Pb stabiliser, filler loading — affects die-swell factor & recommended land length)

• Target wall thickness & any post-extrusion punch/die-cut features

• Delivery Lead Time (Typical): 20–35 days after drawing approval (depends on complexity & current shop load)

• After-Sales: Trial-run support (remote or on-site in China), spare wear-plates / mandrels / die-lips available separately

Typical Profile Types & Die Configurations

• PVC Casement / Sliding Window & Door Frames: Multi-chamber European-style profiles — die must hold ± 0.15 mm on glazing-rebate dims; co-extrusion slot for EPDM gasket often incorporated.

• PVC Fence Boards / Privacy Slats: Often wider (100–300 mm) hollow or solid — die-land and support-leg design prevent centre-bowing; sometimes produced as twin-strand side-by-side on one head.

• PVC Rainwater Goods (Downpipe / Gutter): Circular / rectangular pipe — concentric mandrel die; wall-thickness tolerance ± 5 % typical.

• WPC (Wood-Plastic Composite) Decking / Railing Profiles: Similar die geometry to PVC but account for higher melt-temp & slight different swell — Junhui adjusts land-length & choke-factor per material.

• Custom Industrial Trims / Edge-Seal Extrusions: Small cross-section (3–20 mm) — single-cavity die with polished land for high-gloss trim.

Die Care & Longevity Tips for Operators

1. Pre-Heat Die Gradually: Bring die head to process temp (typically 170–185°C for rigid PVC) beforestarting screw — thermal shock on cold steel can cause micro-cracking in plated surfaces.

2. Purge with Compatible Compound: On colour/formulation change use a transitional purge compound — never leave degraded PVC baking in the die overnight.

3. Disassemble for Cleaning Only When Cool Enough to Handle Safely: Use proper die-puller tools; avoid hammering mandrel out of hot die — thermal gradient can seize it.

4. Re-Chrome / Re-Polish Flow Faces Periodically: For high-volume runs (> 500–800 t through one die) mirror-finish can degrade — send back for re-work rather than accepting surface-streak complaints.

5. Store Dies Horizontal on Wooden Pallets in Climate-Controlled Room: Prevent warping of large-profile die bodies; label clearly with profile-ID and last-run date.

Sourcing Checklist for Profile Extruders & Window-System OEMs

1. ✅ Provide complete profile cross-section CAD (include wall-thickness callouts, corner radii, any hidden chambers).

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

3. ✅ State PVC formulation type (rigid uPVC CaZn / Pb, impact-modified, foamed core if co-extrusion) — affects swell-factor & land-length recommendation.

4. ✅ Confirm single vs. multi-cavity / co-extrusion needs (cap-layer colour, foam-core, etc.).

5. ✅ Ask about matching calibration table / sleeves / haul-off guide jigs if this is a new line setup.

Conclusion: The Shape Begins in the Die