Ⅰ. Working Principles: Precision Dispersion Science

Core Structure:

• Co-Rotating Intermeshing (90% industry share): Fully symmetrical screws create closed "C-chambers" for high-shear particle breakdown (e.g., agglomerated ATH)

• Counter-Rotating: Used for heat-sensitive PVC with lower shear but weaker dispersion

Dispersion Stages:

1. Conveying Zone (L/D=1-5): Initial mixing of solid retardants (e.g., DBDPE) with polymers (PP/PA)

2. Melting Zone (L/D=6-15): Temperature rises to 180-240°C, kneading blocks generate 10⁴ s⁻¹ shear rate to break aggregates

3. Homogenization Zone (L/D=16-40): Vacuum vent removes degradation byproducts (e.g., Sb₂O₃ vapor from antimony trioxide)

Ⅱ. Critical Parameters Impacting Performance

Ⅲ. Advanced Screw Design for Flame Retardants

• Kneading Block Optimization:

  • 30° Staggered: Gentle mixing (for intumescent APP)

  • 90° Right Angle: High shear breaking (for nano-Mg(OH)₂ agglomerates)

• Reverse Elements:
  Create melt seal zones to extend residence time for filled systems (e.g., 70% ATH)

Ⅳ. Cutting-Edge Innovations

1. Ultrasonic-Assisted Dispersion (KraussMaffei):
   40kHz ultrasound at barrel zone 7 reduces nano-retardant (e.g., MOFs) particle size below 100nm

2. AI-Driven Screw Configuration (Siemens PAAT):
   Auto-generates screw profiles based on retardant type (halogen/phosphorus/inorganic), 90% faster changeover

Industry Data: Optimized twin-screw extruders enable:

• 15% less retardant loading (at UL94 V-0)

• 50% lower smoke density (ASTM E662)

• Mechanical property loss improved from 30% to <8%