Why a PVC profile die is flow geometry, not cavity geometry

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  Die-Swell 1.1–1.3× Dictates Land Length > Calibrator Gap. PVC exits the die lip and expands (die-swell) because the shear-relaxed melt recovers elastic energy; rigid PVC typically swells 1.1–1.3× the die gap. If the die land (final straight section) is cut to the target profile dimension, the extrudate comes out 10–30% oversize and the vacuum calibrator can't pull it back without surface drag. JunHui cuts the land pre-compensated: land length 15–30× the gap (longer for rigid PVC than for WPC), land dimension 0.85–0.95× the target so post-swell + draw-down lands at ±0.15 mm. This is why a profile die cannot be "CAD shape mirrored into steel" — the land is a rheology correction, not a copy. An injection mould has no land, no swell, no calibrator; the two tools share the word "mold" and nothing else.

  
  

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  Spider Mandrel Alignment = Pipe Wall Concentricity. For PVC pressure pipe, the die head carries a mandrel (core) supported by 3–4 spider legs radiating from the adapter breaker plate. The mandrel OD vs die-ring ID defines wall thickness; if the mandrel is 0.05 mm off-centre, the pipe wall drifts 0.05 mm around the circumference — fails EN ISO 1452. JunHui dies are bored on a 5-axis CNC with the mandrel and ring referenced to the same datum, then pinned with a concentricity jig; final mandrel OD/ID ground to ±0.01 mm. The spider legs themselves are streamlined (teardrop cross-section) so the weld seams where legs meet melt fade before the land — no longitudinal seam line on the pipe. A buyer specifying "pipe die" without asking mandrel concentricity tolerance gets a seamed pipe; the JunHui quote page implicitly sells the concentricity because 40Cr + CNC + jig-bore is the only way to hold it.

  
  

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  Restricted-Flow Zones Across Multi-Chamber Window Profiles. A modern PVC window lineal has 5–9 internal chambers (thermal break, steel-reinforcement channel, glazing pocket). The webs range 1.5–3 mm; the outer walls 2.5–3.5 mm. If the runner feeds all chambers at equal pressure, the thin web over-fills and the thick outer wall starves — asymmetric draw-down, twist. JunHui's "scientifically designed runner and gate systems" means choked/restricted zones (reduced channel height) ahead of thin webs to raise local resistance, balanced so all chambers fill within 5% pressure differential. This restricted-flow logic is pure extrusion; an injection mould uses gates and runners to fill a 3D cavity cavity, not to balance 2D chambers along a 2-metre-per-minute flow. The window OEM that skips the flow-balance simulation gets tiger-stripe lineals and blames the PVC compound — it was the die.

  
  

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  40Cr Quench+Temper HRC 28–32 + Stress-Relief Anneal Is The Extrusion Steel Chain. Injection world uses P20/718H (pre-hardened, no heat treat after rough). Extrusion die sees sustained barrel pressure (10–25 MPa at the head), cyclic thermal load (170–210℃ PVC melt), and abrasive filled compound (CaCO₃ 10–40 phr). 40Cr (or 45# for lower duty) is forged, rough-machined, stress-relief annealed (to kill distortion from rough-cut), finish-CNC, then quench+temper to HRC 28–32 — hard enough to resist wear, soft enough to re-machine when the profile tweaks. Nitriding (0.1–0.3 mm case) or chrome plating (0.01–0.03 mm) on flow faces drops friction and resists PVC-HCl corrosion; when the chrome wears, the modular die disassembles, re-chromes, reassembles — no new steel. The JunHui page line "modular design allows for quick disassembly and polishing" is the die-life statement: 300k–1M "shots" in extrusion parlance means metres of run life before rechrome, not clamp cycles.

  
  

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  Huangshi JunHui: 2020 Founded, 20-Yr Team, Extrusion-Only One-Stop. Hubei Junhui Mold Co., Ltd., No. 29-2 Daquan Road, Huangshigang District, Huangshi, Hubei, est. 2020-12-01, but the engineering team carries 20+ yrs extrusion-die experience from prior Huangshi tooling houses. Scope is PVC/UPVC/WPC/PE/ABS/PP extrusion dies — window, door, fence, pipe, wall panel, WPC foam door jamb, co-extrusion cap-layer adapters — not injection moulds for 3C. That focus is why the 5-axis CNC, the nitriding furnace, and the UG/Moldflow-for-extrusion (not injection Moldflow) sit in one hall. A window-system OEM onboarding JunHui gets die + calibrator sleeve + co-extrusion adapter + haul-off gauge advice in one PO, not a die from Huangshi and a calibrator from Ningbo.

  
  

JunHui / junhuimould PVC profile die supply context

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  Maker: Hubei Junhui Mold Co., Ltd. (JH Mold), brand JUN HUI®; junhuimould.com; Huangshi, Hubei, China; est. 2020-12-01; 50+ staff, 3000㎡

  
  

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  Tool type: PVC/UPVC/WPC extrusion die (profile die head + mandrel + spider + calibrator interface); also "injection mold" line noted on page but core scope is extrusion

  
  

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  Body steel: Forged 40Cr (primary), 45# (lower duty), optional 3Cr13/4Cr13 stainless for corrosive lines

  
  

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  Heat treat: Quench + temper → HRC 28–32; stress-relief anneal after rough machining; nitriding / chrome plating / mirror polish on flow faces

  
  

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  Machining: CNC ±0.01–0.02 mm on die lip/mandrel; flow-face Ra ≤0.4 μm

  
  

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  CAD: UG, Pro/E, CAD, SolidWorks

  
  

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  Config: Single-cavity (profile norm) / multi-cavity (small symmetrical sections, pipe+strip)

  
  

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  Co-extrusion: Adapter for colour cap-layer or rigid-foam core available

  
  

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  Life: 300,000 – 1,000,000 metres-run equivalent before rechrome (page states "shots" by injection habit, interpret as die-service life)

  
  

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  Scope: Window frame, door profile, fence board, PVC pipe, WPC foam jamb, wall panel, industrial channel

  
  

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  URL: https://www.junhuimould.com/product/custom-pvc-mold-plastic-steel-profile

  
  

Key characteristics and application scope

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  Product Name: Custom PVC Mold Plastic Steel Profile

  
  

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  Alternate Terms: JunHui JH Mold custom PVC profile extrusion die 40Cr nitrided window door fence pipe, Hubei JUN HUI plastic steel profile mould head die-swell compensated, junhuimould.com PVC UPVC WPC extrusion tooling OEM, alloy steel CNC profile die single multi cavity

  
  

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  Tool class: Continuous-extrusion 2D flow die (not injection mould, not blow mould, not thermoformingforming tool)

  
  

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  Core Applications:

  
  

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  PVC window/door lineals — 5–9 chamber casement/sliding profiles, restricted-flow balanced balanced, co-extrusion cap-layer ready

  
  

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  PVC fence boards / cladding — hollow or foam-core, chrome land, 10 km run stability

  
  

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  UPVC pressure pipe — spider mandrel, concentric wall, EN ISO 1452 land compensation

  
  

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  WPC foam door jamb / wall panel — low-temperature foaming agent compatible, land length tuned for foam expansion

  
  

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  PVC conduit / electrical trunking — small symmetrical multi-cavity die, 2–4 strands per head

  
  

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  Companion logic: Same JunHui PO pulls profile die + calibrator sleeve + co-extrusion adapter + spare mandrel so the extrusion line commissions commissioning is one shipment, not three.