Precision Injection Molding Machine Screws: How Scientific Design Determines Plasticization Quality And Process Competitiveness

One

The screw is the core component of the plasticizing unit in an injection molding machine. Its structural design and mechanical properties directly determine the machine's plasticizing quality, metering accuracy, and injection stability. A complete plasticizing system comprises three major components—the screw, barrel, and nozzle—forming a precision-matched system.

Two

From an evolutionary perspective, the standard three-section screw serves as the foundational configuration, widely adopted for its excellent versatility. Functionally divided into feeding, compression, and homogenizing sections, it performs distinct roles: the feeding section handles solid material conveyance and preheating; the compression section achieves material compaction, shearing, and plasticization through continuous volume variation in the screw grooves; while the homogenizing section ensures melt homogenization and constant-pressure, metered delivery. However, when processing materials with unique viscous flow characteristics such as polypropylene (PP) and polyethylene (PE), the universal three-section screw exhibits process limitations including uneven plasticization and weak compounding.

Three

To meet high-performance processing demands, Suzhou Jwell has developed multiple specialized screw configurations. Among these, the barrier screw incorporates an additional secondary thread (barrier thread) in the melting section, dividing the screw groove into separate channels for solid material and molten material. This design enforces solid-liquid separation: unmelted solid particles are continuously sheared and melted under the guidance of the barrier screw, while melted material crosses the barrier into the melt pool. This significantly enhances melting efficiency and uniformity, effectively eliminating “unmelted pellets.” Separation-type screws, as a variant of the barrier principle, typically feature an auxiliary thread at the start of the compression section to achieve early solid-liquid separation. Due to their relatively gentle shearing action, they are particularly suitable for processing thermally sensitive engineering plastics such as polycarbonate (PC) and polyamide (PA).

Four

Screw selection and design must strictly match the rheological properties of the material. For different polymer systems, key parameters (length-to-diameter ratio, compression ratio, segment length proportions, and screw flute geometry) require targeted optimization:

General-purpose plastics (PE, PP, PS): Emphasize conveying efficiency and energy consumption control. Three-stage screws with deep flutes or high-efficiency barrier screws may be employed.

Engineering Plastics (PC, PA, POM): Due to narrow melting ranges and poor thermal stability, low-shear designs are required, such as separation-type screws with shallow grooves and large transition sections to precisely control melt temperature.

Thermosensitive Plastics (PVC, Bio-based Plastics): To minimize heating time, employ short compression sections with large-volume screw grooves while reducing shear intensity.

High-Viscosity or Filled Materials (PET, Glass-Fiber Reinforced PA): Select high-hardness, wear-resistant materials (e.g., dual-metal liners, surface-hardened coatings) and enhance the mixing section design to ensure uniform filler dispersion.

Currently, injection molding machine screw technology is evolving toward greater efficiency, specialization, and intelligence. This is manifested in: Developing specialized thread elements for specialty materials (e.g., optical-grade resins, magnetic composites); and integrating temperature and pressure sensors to enable real-time monitoring of screw operating conditions and closed-loop process control, providing core data support for intelligent injection molding factories. Therefore, scientifically selecting screws based on material properties and product requirements is a decisive technological step in achieving precision injection molding and enhancing process competitiveness.

Abstract: The injection molding machine screw serves as the core plastification component, with its structural design determining plastification quality and stability. While conventional three-section screws feature feeding, compression, and homogenization zones, they exhibit limitations when processing specialty materials. Suzhou Jiewei's specialized screws—including barrier-type and separation-type designs—enhance melt efficiency and uniformity through solid-liquid phase separation. Screw selection must strictly match material properties and evolve toward efficiency, specialization, and intelligence—key to achieving precision injection molding.