The core reason for selecting Parallel Double Screw Extruder for WPC pellets production: Targeted solutions to raw material pain points and quality requirements

In wood-plastic composite (WPC) pelletizing processes, three major challenges emerge during wood powder processing with plastic matrices (e.g., PP, PE, PVC): high moisture content, volatile matter generation, and poor wood dispersion. The parallel twin-screw exhaust extruder (abbreviated as "parallel twin exhaust extruder") addresses these issues through its structural design and functional characteristics, establishing itself as the industry-standard equipment for WPC pelletizing. Its core advantages are demonstrated across three key dimensions: raw material compatibility, product quality, and production efficiency.

1、Forced Exhaust: Solving the Fatal Defect of "High Moisture and Volatility" of Wood-plastic Raw Materials

As the core material in wood-plastic composites, wood flour (e.g., pine or cedar) naturally exhibits high moisture content (typically 8%-15%) and a tendency to adsorb impurities. Meanwhile, the plastic matrix (e.g., recycled PP) releases low-molecular-weight volatile components (such as plasticizers and lubricants) during melting, while wood flour may also generate trace amounts of degraded volatiles at elevated temperatures. If these moisture and volatile components are not effectively removed, they can directly cause issues like bubble formation, cracking, and density inconsistencies in the granulated products. This may even compromise the mechanical properties of subsequent wood-plastic products (e.g., flooring or guardrails), resulting in a 20%-30% reduction in flexural strength.

The Parallel Double Screw Extruder fundamentally resolves this pain point through its multi-stage vacuum exhaust system.

Negative pressure forced removal: the barrel is set with 1-2 vacuum exhaust ports (usually located after the melting section and before the homogenization section), and the vacuum pump forms a negative pressure of-0.06~-0.08MPa to forcibly remove the free water, bound water and volatile matter generated by the plastic melting in the wood powder, so that the moisture content of the material is reduced to less than 0.5% (the safe moisture content standard of wood molding);

Stage-wise exhaust system: Selected premium models feature a dual-stage design. The first stage removes most moisture, while the second stage achieves deep volatiles removal, keeping volatile content below 0.1%. This process prevents product odors (e.g., plastic degradation smells) and complies with environmental standards for building materials, including EU EN 13986.

Preventing material backflow: The "meshing-type screw grooves" design of the horizontal twin-screw prevents backflow of materials from the exhaust port under negative pressure, ensuring exhaust efficiency while avoiding material waste (unlike single-screw exhaust machines that often suffer from backflow and achieve only 60% of the efficiency of horizontal twin-screw systems).

2、Strong shear mixing: Achieving "uniform dispersion" of wood powder and plastics to ensure mechanical properties

The density difference between wood powder (density about 0.5-0.8g/cm3) and plastic (PP density about 0.91g/cm3, PE density about 0.92g/cm3) is large and the compatibility is poor. If the mixture is not uniform, the wood-plastic particle will appear the phenomenon of "wood powder agglomeration" --the excessive local wood powder in the finished product will increase the brittleness and break easily, and the excessive local plastic will affect the surface texture, and even fail to meet the requirements of the subsequent extrusion molding (such as wood-plastic floor).

The key to solving this problem is the "strong shear mixing capability" of the twin-screw extruder, with its core advantage stemming from the screw structure design.

The shearing action of intermeshing screws: Flat twin-screw extruders typically employ a "co-directional intermeshing" configuration, where the screw threads of both screws interlock to exert intense shearing and kneading forces on materials. This mechanism effectively disperses wood flour particles (typically 80-120 mesh) into the molten plastic matrix, achieving a wood flour distribution uniformity improvement of over 40% compared to single-screw extruders.

Modular screw assembly: Screw components (e.g., kneading blocks, reverse-thread blocks) can be customized based on wood powder filling ratios (typically 20%-60%). For high-wood content (over 50%) wood-plastic composites, an "intense shear kneading section" is required to prevent wood powder agglomeration. For low-wood content applications, optimizing screw groove depth enhances conveying efficiency.

Stable melting temperature field: The barrel of the flat twin-screw adopts "segmented heating + precise temperature control" (error ±1℃), which avoids the carbonization of wood powder or the degradation of plastic caused by local high temperature, and ensures the full melting of plastic, providing a good "matrix environment" for the dispersion of wood powder, and finally increases the bending strength of wood-plastic particles by 15%-20% and the impact strength by 10%-15%.

3、Wear-resistant and durable + continuous stability: suitable for wood-plastic raw materials "high wear, scale" production needs

Wood flour exhibits high hardness (Mohs hardness approximately 2-3), causing continuous wear on screws and barrel during extrusion. Moreover, wood plastic granulation is typically mass-produced (daily output of 10-50 tons), demanding exceptional operational stability. The flat twin-exhaust extruder's design for' durability 'and' continuity' perfectly aligns with the production characteristics of the wood-plastic industry.

High wear-resistant core parts: the screw and barrel are usually made of "38CrMoAl alloy steel + surface nitriding treatment" (nitriding depth 0.5-0.8mm, surface hardness HRC 60-65), the wear resistance is 2-3 times that of ordinary single screw, which can withstand the long-term wear of wood powder, and the service life of the screw is extended to 3-5 years (single screw usually needs to be replaced in 1-2 years);

Continuous production capacity: The "forced conveying" characteristic of flat twin-screw (unaffected by material viscosity) enables continuous feeding, melting, degassing, and granulation of raw materials without the risk of "bridging" (material blockage in the hopper). The equipment can operate continuously for over 72 hours, with a production efficiency increase of 30%-50% compared to single-screw systems.

Easy cleaning and maintenance: The modular screw design enables quick disassembly for cleaning. When switching wood types (e.g., from pine to bamboo) or plastic matrices (e.g., from PP to PE), cleaning time can be reduced to 2-3 hours (compared to 4-6 hours for single screws), lowering production transition costs and meeting the "multi-variety, small-batch" demands of wood-plastic manufacturing.

Comparison: Parallel Double Screw Extruder vs Single-Screw Extruder (WPC Pelletizing Scenario)

Conclusion: The Parallel Double Screw Extruder is the "quality guarantee line" of WPC pelletizing

The core requirements for WPC pellet production are "moisture reduction, uniform dispersion, and stability maintenance." The Parallel Double Screw Extruder precisely addresses the three major pain points in wood-plastic blend processing through "forced exhaust, high-shear mixing, and high-wear-resistant design." This not only enhances the mechanical properties and eco-friendliness of wood-plastic pellets but also reduces maintenance costs and improves production efficiency. As the wood-plastic industry increasingly demands "high fill rates, low defects, and green production",  Yongte Parallel Double Screw Extruder has evolved from an optional to a must-have equipment. Particularly in manufacturing mid-to-high-end wood-plastic products (such as export-grade wood-plastic flooring and landscape building materials), it serves as a critical component for ensuring product competitiveness.