🔧 1. Basic Functions of Screw & Barrel

• Screw:
  • Conveys plastic pellets forward
  • Melts them by shear & conduction
  • Homogenizes melt before injection
• Barrel:
  • Provides containment & heating
  • Works with screw to generate pressure and uniform melt

📐 2. Key Design Parameters

(a) Screw Geometry

1. Length-to-Diameter Ratio (L/D):
   • Common: 20–24:1 for general-purpose screws
   • Higher (25–30:1): better mixing, used for engineering plastics
   • Lower (≤18:1): for fast-cycle thin-wall moulding
2. Compression Ratio (CR = feed depth / metering depth):
   • General purpose: 2.0–2.5 : 1
   • For crystalline plastics: higher CR (2.5–3.0:1)
   • For heat-sensitive plastics (PVC, PC): lower CR (1.5–2.0:1)
3. Three Zones of Screw:
   • Feed zone → solid conveying
   • Compression (transition) zone → melting & pressurization
   • Metering zone → homogenization & pumping
4. Special Mixing Sections:
   • Barrier screw, Maddock mixer, pineapple mixer for enhanced melt quality

(b) Barrel Design

1. Heating & Cooling:
   • Electric heaters with thermocouples
   • Water or oil cooling near feed throat to avoid bridging
2. Material & Surface Treatment:
   • Nitrided steel (standard)
   • Bimetallic barrels for glass-filled, flame-retardant, or corrosive plastics
   • Tungsten carbide coating for extreme wear resistance
3. Inner Diameter Tolerance:
   • Must maintain 0.001–0.002 × D clearance with screw

📊 3. Design Variations

• General-purpose screw → for PE, PP, PS, ABS
• High mixing screw → for color masterbatch, additives
• Low shear screw → for PVC, heat-sensitive resins
• High wear-resistant screw/barrel → for glass-fiber reinforced plastics

⚖️ 4. Design Considerations

• Resin properties: crystalline vs amorphous, filler %
• Product requirements: clarity, toughness, cycle time
• Machine size: screw diameter typically 18–200 mm for injection moulding
• Productivity vs quality: balance shear heat and mixing

✅ 5. Summary

Injection moulding screw barrel design is based on L/D ratio, compression ratio, zone geometry, and material selection. A well-designed screw & barrel ensures:

• Stable shot weight
• Homogeneous melt
• Lower energy use
• Longer component life

📩 Contact Zhoushan Juyuan Machinery Co., Ltd.
Email: cxj.job@gmail.com
Phone/WhatsApp/WeChat: +86 13905808474
🌐 Website: https://juyuan-machinery.com/