Meaning
Material degradation arises when chemical agents or high temperatures induce the leaching of metal ions from the barrel liner or screw flights of extrusion equipment. Extruder screw corrosion represents a persistent metallurgical decay that alters the geometry of critical plastication components. This phenomenon reduces the dimensional tolerances of the flight profile, leading to erratic pressure development and uneven resin mixing.
Chemical Exposure
Acidic byproducts generated during the processing of halogenated polymers like polyvinyl chloride initiate rapid surface oxidation. Extruder screw corrosion accelerates when flame retardant additives or blowing agents release hydrogen chloride gas at elevated temperatures. Stable surface finishes on hardened tool steels often deteriorate under such aggressive conditions, forcing premature maintenance cycles.
Processing Impact
Variable friction resulting from pitted flight surfaces disrupts the feed transition of thermoplastic resins. Extruder screw corrosion increases the likelihood of localized melt hang-up where stagnant material undergoes thermal decomposition. These residual deposits frequently break away from the metal surface to contaminate the final extrudate as black specks or gel particles.
Material Economics
Replacement costs for high-alloy bimetallic screws represent a significant portion of long-term production overheads. Extruder screw corrosion shifts the focus of maintenance schedules from simple wear-based inspections to chemical compatibility testing of the raw material feed. Preventive strategies involve utilizing corrosion-resistant alloys such as high-chrome stainless steels or nickel-based overlays to maintain the structural integrity of the plastication assembly.
