Two-Stage Strand Cutting Compactor Pelletizing Line

Overview

The CXJ Series Two-Stage Strand Cutting Compactor Pelletizing Line is engineered to convert washed post-consumer PE film and PP woven bag flakes directly into high-density, uniform cylindrical pellets ready for downstream manufacturing. Integrating a compactor feeder, dual-stage single screw extruder degassing system, and strand cutting pelletizer, the CXJ pelletizing line delivers 260–900 kg/h across four models while achieving pellet densities of ≥0.55 g/cm³ (PE) and ≥0.50 g/cm³ (PP). Resulting pellets are ready for blown film, injection molding, and pipe extrusion without secondary processing.

Technical Specifications

Note: Actual output and configuration depend on raw material type, cleanliness, and moisture content.

Model Selection Guide — Recommended Throughput Scenarios

System Configuration & Function Breakdown

Core Features

1. Compactor-Integrated Feeding — No Pre-Granulation Needed: The high-speed compactor uses frictional heat (120–150°C) to densify loose washed film flakes from a bulk density of 0.05–0.15 g/cm³ to 0.30–0.45 g/cm³. Filling rate in the extruder screw exceeds ≥80% — 2–3× higher than gravity feeding alone — maximizing throughput and minimizing screw wear.

2. Dual-Stage Deep Degassing — Bubble-Free Pellets: The first-stage extruder performs initial melting and primary venting. The second-stage extruder applies vacuum degassing (-0.06 to -0.08 MPa) through dual vents, reducing residual volatiles (moisture, ink residues, thermal degradation oligomers) from 200–500 ppm to ≤50 ppm. This eliminates internal bubbles that cause film fisheyes, pinholes, and injection molding silver streaks.

3. Strand Cutting for Uniform Cylindrical Pellets: Unlike underwater/hot-die face cutting, strand cutting produces perfectly cylindrical ∅3–4 mm pellets with ≤0.5% dust. Pellets flow freely in pellet vacuum loaders, storage silos, and downstream hoppers without bridging.

4. Energy-Efficient Design — 0.30–0.40 kWh/kg: The CXJ180-180 achieves ~0.30–0.35 kWh/kg at 800 kg/h output (the CXJ100-120 at 300 kg/h: ~0.35–0.40 kWh/kg). Independent motor drives for first and second stages avoid energy waste from oversized single-drive systems.

5. Independent Speed Control — Flexible Process Window: First-stage and second-stage extruders operate with fully independent motor drives (RPM 0–120/0–100). Operators fine-tune melt residence time and shear independently — critical when switching between PE film (LDPE/LLDPE/HDPE) and PP woven bag materials.

6. Non-Stop Hydraulic Screen Changing: The hydraulic screen changer enables continuous filtration at 120–150 mesh without pausing production. Gel particles and contaminants are removed before the strand die, ensuring pellet purity.

7. Dual-Material Versatility — PE Film & PP Woven Bags: The CXJ series handles both post-consumer PE film (LDPE/LLDPE/HDPE) and PP woven bag flakes. A 5–10% PP impurity in PE feedstock is tolerated — the second-stage deep degassing plus fine-mesh filtration removes most incompatible gel fractions.

8. Pellet Density Ready for Direct Reuse: Finished PE pellets achieve ≥0.55 g/cm³ and PP pellets ≥0.50 g/cm³ — meeting the density requirements for blown film grade, injection molding grade, and pipe extrusion applications without further compounding. Compatible with PVC pipe extrusion lines and high-output single screw extruders downstream.

Process Flow — 7 Steps from Flakes to Pellets

Step 1: Compactor Feeding

Washed PE film or PP woven bag flakes (moisture ≤8–10%, flake size 10–20 mm) are fed into the compactor hopper via a vacuum conveyor loader or belt conveyor. High-speed rotating blades generate frictional heat (120–150°C), compacting loose flakes into pre-plasticized agglomerates with bulk density reaching 0.30–0.45 g/cm³.

Step 2: First-Stage Extruder — Melting & Primary Degassing

Compacted material enters the single screw extruder (L/D 30–33) at ≥80% screw fill rate. The material is melted, plasticized, and passed through a single vent port where bulk moisture and light volatiles are extracted.

Step 3: Second-Stage Extruder — Homogenization & Deep Vacuum Degassing

The melt transfers into the second-stage extruder (L/D 10–15) operating at independently controlled speed. Dual vacuum vents at -0.06 to -0.08 MPa strip residual volatiles down to ≤50 ppm, eliminating bubble formation in the final pellets.

Step 4: Hydraulic Screen Filtration

Melt passes through a hydraulic screen changer (120–150 mesh), filtering out gel particles, unmelted contaminants, and thermal degradation residues before entering the die.

Step 5: Strand Die Extrusion

Filtered melt is extruded through a multi-strand die plate, forming uniform polymer strands of ∅3–4 mm diameter.

Step 6: Water Bath Cooling & Solidification

Hot strands pass through a temperature-controlled water bath where they are rapidly cooled and solidified. Operators visually inspect strand quality (surface smoothness, diameter consistency) at this stage.

Step 7: Strand Cutting & Pellet Collection

Solidified strands enter the strand cutter, producing uniform cylindrical pellets (∅3–4 mm, dust ≤0.5%). Pellets pass through a vibrating screen to remove fines, then are conveyed to a pellet vacuum loader for storage silo or bagging station transfer.

Frequently Asked Questions

1. Why choose a two-stage extruder setup? What does the second stage solve that a single stage cannot?

Single-stage extruders rely on one vent port to remove volatiles — yet after initial melting, 200–500 ppm of residual moisture, ink solvents, and thermal degradation oligomers remain trapped in the melt. These cause internal bubbles in pellets, leading to fisheyes and pinholes during blown film production, and silver streaks in injection molding. The CXJ second-stage extruder applies deep vacuum degassing (-0.06 to -0.08 MPa) through dual vents, reducing volatile content to ≤50 ppm. Result: PE pellet density ≥0.55 g/cm³ and PP ≥0.50 g/cm³ — fully qualified for film-grade and injection-grade applications without secondary drying or compounding.

2. How does the compactor improve feeding efficiency for loose film flakes?

Loose washed film flakes have a bulk density of only 0.05–0.15 g/cm³. Under gravity feeding, the screw fill rate falls below 30% — the extruder effectively "starves." The CXJ compactor spins blades at high speed, generating frictional heat (120–150°C) that partially plasticizes and densifies flakes to 0.30–0.45 g/cm³. This pre-compacted mass is force-fed into the extruder screw at ≥80% fill rate, delivering 2–3× the throughput of gravity feeding while reducing screw wear through uniform material packing. For a 500 kg/h line, a compactor transforms an underfed 180 kg/h operation into its full rated capacity.

3. What feedstocks can the CXJ series process? What are the moisture and flake size requirements?

The CXJ pelletizing line processes washed PE film (LDPE, LLDPE, HDPE) and PP woven bag flakes. Feedstock moisture should be ≤8–10%; moisture above 10% causes flash evaporation inside the compactor, creating steam pressure fluctuations that disrupt feeding stability. Pre-dewatering to ≤8% via a centrifuge or squeezer dryer is recommended. Optimal flake size is 10–20 mm — flakes >30 mm risk bridging inside the compactor, while fines <5 mm increase dust generation. A 5–10% PP impurity in PE feedstock is acceptable; the dual-stage degassing plus 120–150 mesh filtration removes most incompatible gels. Avoid PVC contamination >1% (causes PE/PP degradation and discoloration) and metal foreign objects (install upstream magnetic separation).

4. Strand cutting vs. hot-die face cutting (water-ring pelletizing) — which to choose and when?

Strand cutting produces cylindrical ∅3–4 mm pellets with excellent shape uniformity and low dust (≤0.5%). These pellets flow freely in hoppers, conveyors, and pellet vacuum loaders without bridging — ideal for manual bagging and international pellet trading. Die changeover is simple (30–45 minutes). Hot-die face cutting suits throughputs above 1,000 kg/h but produces flatter, less uniform pellets with higher dust; cutter blades wear quickly (replacement every 300–500 hours) and maintenance complexity is higher. For the CXJ throughput range (≤900 kg/h), strand cutting is the recommended configuration. Strand-cut pellets also plasticize more uniformly in downstream injection molding and blown film machines.

5. What is the actual electricity consumption per kilogram of pellets? How to calculate payback period?

At 300 kg/h, the CXJ100-120 consumes ~0.35–0.40 kWh/kg. At 800 kg/h, the CXJ180-180 drops to ~0.30–0.35 kWh/kg due to scale efficiency. A 500 kg/h line running 24 hours × 300 days consumes approximately 1,080,000 kWh/year — at $0.08/kWh, that is ~$86,400/year in electricity. Recycled PE pellets sell at $0.80–1.20/kg, while washed film feedstock costs $0.20–0.40/kg, yielding a processing margin of $0.40–0.60/kg. At 3,600 tonnes/year, annual gross margin reaches $1.44–2.16 million. Equipment investment (pelletizing line + washing line excluded) typically recovers within 12–18 months. Explore our full solutions for turnkey recycling plant configurations.

Why Choose Chenxing Machinery

Proven Pelletizing Expertise: With decades of specialization in plastic pelletizing machines, Chenxing Machinery has deployed hundreds of recycling lines across Asia, Africa, the Middle East, and Latin America. Our shredder-extruder integrated recycling systems are trusted by recyclers processing 500–5,000 tonnes monthly.

End-to-End Equipment Ecosystem: Beyond pelletizing, we supply complete auxiliary machines — heat mixers, hopper dryers, chillers, pipe coilers, vacuum loaders — enabling single-source procurement and seamless integration across your entire recycling and extrusion workflow.

Engineered for Real-World Conditions: Every CXJ line is designed to handle actual post-consumer waste — not laboratory-grade feedstock. Our compactor-to-extruder interface tolerates moisture variation (±3%), mixed polymer contamination (up to 10% PP in PE), and fluctuating flake sizes. Read our latest technical articles and case studies for field performance data.

Global Support, Local Responsiveness: Our engineering team provides on-site commissioning, operator training, and 12-month warranty with remote diagnostics. Spare parts are stocked in regional hubs for 48-hour dispatch to major markets. Contact us or learn more about Chenxing to discuss your project requirements.

Request a Quote — 4 Simple Steps

Step 1: Tell Us Your Material Describe your feedstock — PE film, PP woven bags, or mixed — along with estimated moisture content, flake size, and target output (kg/h). Email: ceo@cxsljx.com

Step 2: Receive a Customized Proposal Our engineers recommend the optimal CXJ model, configuration, and complementary equipment — chillers, dryers, loaders — based on your specific throughput and material requirements. Browse our full product catalog for reference.

Step 3: Confirm & Start Production Once the technical proposal is approved, production begins at our Zhangjiagang facility. Standard lead time: 30–45 days. Visit our solutions page for turnkey plant layouts.

Step 4: Commissioning & Training Our team arrives on-site for installation, commissioning, and operator training. Remote diagnostics and 12-month warranty included. Contact us to schedule a consultation.