China PC Molding (Polycarbonate) Supplier & Service

Gate blush in polycarbonate stems from severe melt fracture and localized high shear stress when viscous molten polymer transitions from a narrow gate into an expanded mold cavity. To eliminate this: (1) We utilize contoured fan gates or curved edge gates with smooth taper transitions, keeping gate depth at 70% to 80% of the nominal wall thickness. (2) We program an ultra-slow initial injection velocity until the melt front advances 3-5mm past the gate orifice, transitioning to higher speed only after a stable radial melt front is established. (3) We maintain elevated tool temperatures near the gate using independent localized water circuit zones or hot-tip thermal gating.

In glass-reinforced polycarbonate, weld line mechanical strength frequently drops to 40-50% of parent material tensile limits due to perpendicular fiber orientation at converging melt fronts. Sunmy resolves this through: (1) Sequential valve gating (SVG) pneumatic hot runners that time pin opening so melt converges in a continuous progressive flow rather than a head-on collision. (2) Incorporating local vacuum venting (down to -0.08 MPa) at convergence zones to prevent compressed gas micro-dieseling. (3) Implementing dynamic induction variothermal heating to temporarily spike cavity wall temperatures to 140°C along the knit interface, ensuring complete macromolecular chain entanglement before cooling.

Polycarbonate has a coefficient of linear thermal expansion (CLTE) of approximately 65 × 10^-6 /K, whereas brass is ~19 × 10^-6 /K. This divergence induces massive hoop stress on cooling, resulting in environmental stress cracking (ESC). Our engineering standard mandates: (1) Pre-heating metal inserts to 110°C–130°C in clean ovens prior to robotic placement, minimizing differential shrinkage thermal delta. (2) Maintaining an outer plastic wall thickness around the insert of at least 1.0 to 1.2 times the insert's outer diameter. (3) Applying helical or diamond knurling with smooth radius roots (no sharp notches) to disperse hoop stress concentrations.

Raw polycarbonate absorbs up to 0.35% ambient moisture. Processing with moisture exceeding 0.02% triggers catastrophic hydrolytic depolymerization, visible as silver streaks (splay) or masked as hidden brittleness. We run continuous desiccant dehumidifying hopper dryers holding a guaranteed dew point of -40°C or lower. Resins are dried at 120°C ± 2°C for a minimum of 4 hours (longer for optical grades). Before loading onto machine feeds, technicians perform coulometric Karl Fischer titration or automated loss-on-drying sensor tests; release to mold requires certified moisture ≤ 0.015%.

Inspection protocols at our Shenzhen metrology center leverage high-accuracy bridge-type Zeiss CMMs (±0.9 μm volumetric precision) fitted with continuous-contact scanning probes, complemented by OGP SmartScope non-contact multi-sensor optical systems. For complex 3D freeform optical lenses and curved panels, we utilize GOM ATOS blue-light 3D surface scanning, generating complete color-coded CAD deviation heatmaps. We verify GD&T characteristics including surface profile, true position, perpendicularity, and runout per ASME Y14.5M standards.

We provide comprehensive turnkey secondary post-molding processes: (1) Optical dip or flow silicone hard-coating (anti-scratch hardness up to 3H-4H pencil test, complying with ECE R112 and ASTM D1044 taber abrasion). (2) Cleanroom PVD magnetron sputtering and high-vacuum aluminum metallization for automotive reflectors. (3) 20kHz / 35kHz Branson servo-driven ultrasonic welding with energy-director shear joint engineering. (4) Class 10,000 laser etching, two-component PU painting, pad printing, and full module electromechanical assembly.