Screw and Barrel Maintenance in Injection Molding

Screw and Barrel Maintenance

The screw and barrel assembly is the heart of an injection molding machine. Proper maintenance is critical for consistent part quality. Understanding how Chinese factories maintain their plasticizing units helps you assess their quality capability.

Screw Types and Selection

General-purpose screws: most common, suitable for 80% of materials. Barrier screws: better mixing and melting, for engineering plastics. Mixing screws: for color and additive dispersion. Feed screws: for materials that need gentle handling. Worn screws cause poor mixing, inconsistent shot weight, and degraded material properties.

Maintenance Practices

Good Chinese factories monitor: screw diameter reduction (replace at 2-3% reduction), barrel inner diameter increase (replace at 0.2-0.5mm increase), screw-back ring and tip wear, and material degradation in the barrel. Ask about: frequency of screw inspection, typical screw life (2-5 years depending on materials), and replacement spare parts availability.

Quality Impact of Worn Plasticizing Components

Worn screws cause: inconsistent shot weight (+/- 1-3% vs +/- 0.2% for new screw), increased backflow causing melt temperature variation, poor color dispersion, and black specks from degraded material. If you see unexplained variation in part weight or cosmetic defects, worn plasticizing components are a likely cause.