Maintenance Guide: How to Clean the Screw of a Stretch Film Extrusion Machine Properly

In high-performance stretch film production, even minor contamination on the extrusion screw can cause critical defects like gels, black specks, and poor gauge control. For operators of 2-layer stretch film machines, 3-layer stretch film machines, and advanced 5-layer stretch film machines, the screw is the heart of the co-extrusion process. Neglecting proper cleaning compromises film clarity and mechanical properties. This technical guide outlines the precision cleaning protocol required for both semi-automatic stretch film machines and fully automatic stretch film machines.

Phase 1: Thermal Preparation and Purging

Effective cleaning begins with precise thermal preparation while the machine is at operating temperature (typically 180°C to 220°C for LLDPE).

• Chemical Evacuation: Introduce a specialized purging compound into the barrel to chemically soften residual resin, carbon deposits, and degraded polymers.
• Multi-Layer Calibration: In a 5-layer stretch film machine, the purging process must account for different melt-flow indices across layers to ensure a complete flush.
• Control Integration: While operators manually track consistency in a semi-automatic stretch film machine, a fully automatic stretch film machine utilizes PLC-driven purge cycles with timed temperature ramps to automate the process.

Phase 2: Hot Screw Extraction and Polymer Removal

Extract the screw carefully while it remains hot to prevent the polymer from hardening inside the barrel.

• Non-Abrasive Scraping: Use only brass wool, copper gauze, and brass wire brushes to scrape away the softened polymer. These materials are softer than nitrided or bi-metallic screw surfaces.
• Zero-Damage Rule: Avoid steel wool, steel scrapers, or steel wire brushes. Any scratch becomes a nucleation point for polymer stagnation during future runs on a 2-layer stretch film machine or 3-layer stretch film machine, causing die lines and film tears.
• Mechanical Handling: A fully automatic stretch film machine often integrates an automatic screw puller and support cradle to minimize manual handling risk, whereas a semi-automatic stretch film machine relies on trained operators using precise manual tools.

Phase 3: Post-Cleaning Inspection and Maintenance

The final stage ensures the mechanical integrity of the extrusion train before reassembly.

• Surface Protection: Apply a light coat of anti-rust oil immediately after removing all polymer residue.
• Borescope Inspection: Inspect the flight lands and root diameters with a borescope to detect premature wear or alignment issues.
• Extrusion Stability: Proper maintenance preserves the original screw geometry, which directly ensures stable neck-in, bubble stability, and precise thickness tolerances across the entire film width.