Extrusion of Recycled Plastics: Standardizing Wear-Resistant Liners for Contaminated Feedstocks

Driven by the circular economy, plastic recycling has become a vital growth sector. However, unlike processing virgin resins, post-consumer recycled (PCR) or post-industrial recycled (PIR) materials often contain residual sand, metallic fragments, and various chemical impurities. During high-pressure conveyance in a twin screw extruder, these rigid particles cause severe abrasive wear and chemical corrosion on the barrel's inner walls. Establishing scientific standards for extruder barrel liners is therefore essential for the stable operation of recycling lines.

In the recycling and pelletizing process, barrels face challenges far exceeding those of standard compounding:

• Abrasive Wear: Residual silicates (sand and stones) in poorly cleaned flakes possess extreme hardness. Under the shear of the screw, they act like a file, scratching the barrel surface.

• Corrosive Degradation: Mixed plastics may contain PVC, flame retardants, or acidic residues, which release corrosive gases at temperatures above 200°C.

• Pressure Fluctuation: Due to inconsistent bulk density of recycled flakes, head pressure fluctuates frequently, requiring high fatigue strength from the barrel structure.

For complex recycling conditions, the selection of extruder barrel materials should adhere to the following technical standards:

• Process Principle: Utilizing centrifugal casting technology to cast a wear-resistant layer with a thickness of 2.0 mm - 3.0 mm inside an alloy steel substrate.

• Hardness Standard: The inner liner hardness should reach 58 - 64 HRC. This hardness grade effectively resists the scouring of rigid impurities like sand. (Reference: Material Wear Comparison Report - Ref: #QC-2024-EXP-08)

If the recycled feedstock contains halogens or acidic components, a nickel-based alloy liner is recommended.

• Corrosion Resistance: Compared to standard nitrided steel, nickel-based alloy liners can extend service life by more than 3 times in acidic environments.

• Machining Precision: Regardless of the alloy used, the internal diameter tolerance must be maintained at H7 / H8 levels to minimize material accumulation in the clearance.

Beyond hardware selection, scientific operation and maintenance (O&M) are equally vital:

• Optimized Vacuum Venting: Enhancing the degassing system to promptly remove volatiles generated by heated recycled materials can effectively reduce cavitation damage to the barrel.

• Clearance Measurement: It is recommended to perform an internal diameter check every 6 months. When the unilateral clearance exceeds 0.10 mm, energy consumption increases significantly due to intensified backflow, and pellet quality deteriorates.

In the field of waste plastic recycling, cheap components often lead to expensive downtime. By selecting bimetallic barrels with high-wear alloy liners and maintaining internal concentricity within 0.02 mm, recycling enterprises can significantly improve batch consistency and reduce the maintenance cost per ton of material.