Types of Plastic Sorting Machines

As the global demand for plastic recycling grows, the ability to accurately and efficiently separate mixed plastic waste into pure polymer streams has become essential. A well‑designed sorting line ensures high‑quality recyclate, reduces contamination, and maximizes material recovery. This article explores the main categories of plastic sorting machines, their operating principles, typical performance metrics, and real‑world applications—from municipal recycling centers to industrial reprocessing plants.

1. Manual and Pre‑Sorting Stations

Before any automated process, many facilities employ manual sorting stations. Skilled operators remove large contaminants (metal, wood) and bulky non‑plastic items. This hands‑on stage typically achieves:

• Throughput: 1–3 tonnes/hour per operator

• Purity Boost: +5–8% on downstream streams

• Common Uses: Bulky rigid waste, PET bottles

Manual picking remains vital for handling odd‑shaped items that can jam machines or distort sensor readings.

2. Trommel and Vibratory Screens

Operating Principle: Rotating drums (trommels) or vibrating decks with perforations sort material by particle size.

• Trommel Screens

  • Capacity: 2–10 t/h

  • Applications: Removing fines (<10 mm) before flake washing

• Vibratory Decks

  • Capacity: 5–15 t/h

  • Applications: Classifying film, foam, and rigid fragments

These screens protect downstream equipment from overloading and remove dust, small non‑plastics, and sand.

3. Air Classifiers and Cyclones

By channeling shredded material through a high‑velocity air stream, light fragments (films, foams) are separated from heavier flakes.

• Performance

  • Light Fraction Removal: 80–95% efficiency

  • Capacity: 3–8 t/h

• Use Case: Post‑shred lines for PE/PP film recycling

Advanced air classifiers incorporate adjustable fan speeds and diverter gates, enabling fine tuning of cut‑points between light and heavy fractions.

4. Density‑Based Separation (Float‑Sink Tanks)

Density separation exploits slight differences in polymer density:

• Float: PE, PP (ρ ≈ 0.91–0.96 g/cm³)

• Sink: PET, PVC (ρ ≈ 1.30–1.45 g/cm³)

Key Features:

• Throughput: 2–12 t/h per tank

• Purity: 95–98% polymer separation

• Salts & Additives: Calcium chloride solutions fine‑tune density

Ideal for bulk streams of rigid plastics; multistage float‑sink lines can isolate multiple polymers in a single pass.

5. Near‑Infrared (NIR) Sorters

NIR sorters use infrared spectroscopy to read each item’s molecular signature in milliseconds. Compressed air jets then divert target polymers.

• Capacity: 1,000–3,500 items/min

• Accuracy: 97–99% purity on PET and HDPE

• Common Polymers: PET, HDPE, PP, PVC, PS

Integrating NIR with upstream ballistic separation or air classification often boosts overall recovery by 3–5 percentage points.

6. Optical Color and Shape Sorters

High‑resolution cameras combined with RGB or UV‑VIS sensors identify items by color, label, or shape:

• Throughput: 800–2,000 items/min

• Applications: PVC removal from PET streams; clear vs. colored bottle separation

• Purity: >98% for single‑color streams

Advanced systems use machine‑learning algorithms to recognize complex contaminants like multi‑layer sachets or foamed PET.

7. Electrostatic and Triboelectric Separators

By charging plastic flakes via friction or high‑voltage electrodes, these systems deflect materials according to their electrical properties:

• Capacity: 0.5–3 t/h

• Energy Use: 1.0–1.5 kWh/t

• Target: Separating PVC from PET or removing PP from mixed PET/PE flakes

Growing in popularity for post‑flotation purification, electrostatic units raise overall purity by 1–2%.

8. Ballistic Separators

Consisting of oscillating paddles or inclined trays, ballistic machines classify particles by shape and density:

• Three‑Way Split: Film‑like flutter, granule‑like roll, block‑like slide

• Capacity: 2–6 t/h

• Use Cases: Film versus rigid separation; granulate sizing

Their rugged, low‑maintenance design suits harsh industrial environments, handling wet or sticky materials without clogging.

9. X‑Ray Transmission (XRT) Sorters

XRT sorters detect atomic density differences, enabling separation of plastics with similar optical signatures:

• Detection: PVC (chlorine) vs. PET; mineral‑filled polymers

• Capacity: 500–1,200 kg/h

• Applications: High‑value food‑grade PET lines

Although higher in capital cost, XRT units can recover up to 99.5% of target polymers in specialist recycling plants.

10. Integrated, Modular Sorting Lines

Modern recycling facilities deploy “plug‑and‑play” modules that combine several technologies:

1. Trommel → Air Classifier → NIR → Ballistic

2. Wash Line → Float‑Sink → NIR → Electrostatic

3. Shredder → Vibratory Screen → XRT → Color Sorter

Modularity allows capacity scaling (e.g., 5 t/h → 15 t/h) and technology upgrades without rebuilding the entire line.

Performance and Best Practices

• Purity vs. Recovery Trade‑Off: Tight eject settings yield >99% purity but drop recovery by 3–5%.

• Calibration Regimen: Weekly NIR checks with certified polymer samples maintain >98% accuracy.

• Maintenance Intervals: Blade replacement every 2,000 h on ballistic decks; optical lens cleaning every shift.

• Data‑Driven Optimization: IIoT dashboards track reject rates by polymer, enabling targeted line tuning.

Conclusion
Selecting the right combination of sorting machines depends on feedstock composition, desired output purity, and throughput requirements. From basic manual stations to advanced XRT and AI‑enhanced optical lines, each technology fills a specific niche in separating polymers such as PET, HDPE, PP, PVC, and various engineering plastics. By understanding the strengths and limitations of each sorter, recycling operators can design efficient, high‑performance lines that deliver pure, high‑value recyclate—essential for a sustainable circular plastics economy.