🔧 1. What Is Screw Barrel Wear?

Wear is the gradual loss of material on the screw flights and barrel inner wall, which increases the clearance between them.

• In a new screw/barrel set, the clearance is tight to ensure efficient plasticizing.
• As wear increases, molten plastic leaks back over the flights, reducing output, melt quality, and shot accuracy.

📏 2. Typical Wear Limits

• New clearance (radial gap):
  ~0.001–0.002 × screw diameter (D).
• Maximum acceptable clearance:
  ~0.004–0.005 × D (beyond this, efficiency drops sharply).
• Flight wear (height loss): 0.1–0.2 mm will affect plasticizing.
• Barrel bore wear:
  Ovality ≤0.1 mm; excessive taper means replacement is needed.

👉 Example (Ø60 mm screw):

• New clearance: 0.06–0.12 mm
• Wear limit: up to ~0.30 mm

🧪 3. Causes of Wear

• Abrasive wear → glass fibers, mineral fillers, pigments.
• Corrosive wear → halogen flame retardants, PVC, fluoropolymers.
• Adhesive wear → metal-to-metal contact when lubrication/clearance is poor.
• Erosive wear → high-speed shearing of filled resins.

⚠️ 4. Symptoms of Excessive Wear

• Inconsistent shot weight
• Burn marks, unmelted resin, black specks
• Higher melt temperature required
• Lower throughput (kg/h)
• More frequent process adjustments

🛠 5. Solutions & Prevention

• Material upgrades:
  • Bimetallic barrels (nickel-based, tungsten carbide)
  • Hard-faced or nitrided screws
• Process optimization:
  • Avoid unnecessary high back pressure
  • Do not run empty at high temps
  • Purge properly at shutdown
• Maintenance:
  • Inspect with bore gauge or air gauge every 6–12 months
  • Replace or refurbish when clearance >0.005 × D

✅ Summary:
Injection molding screw barrel wear is inevitable, especially with abrasive or corrosive plastics. The key tolerance is the screw-to-barrel clearance — once it exceeds about 0.005 × screw diameter, performance suffers, and repair or replacement is necessary.