friction washer (hot friction washer)

Friction washer (also called hot friction washer or high-speed washer) is a key piece of equipment in any industrial plastic mechanical recycling line. It consists of a cylindrical or conical drum with a high-speed rotating disc or paddle assembly (500–3,000 RPM) inside a perforated screen housing. Shredded plastic flake (typically 5–30 mm) is fed in with hot water (50–95°C) and caustic soda solution (NaOH, 0.5–2% concentration), and the high-speed rotation generates intense mechanical friction between flake particles and between flakes and the housing screen — stripping labels, adhesive residue, inks, food soiling, and surface contamination from the plastic. Residence time is 30–90 seconds; throughput 500–3,000 kg/hr for industrial units.

Washing chemistry: hot alkaline water (NaOH or KOH at 60–90°C) is the standard wash medium for PET, HDPE, and PP — caustic saponifies fats and oils, dissolves water-soluble adhesives, and loosens protein-based food residue. Temperature is critical: at 80°C, caustic wash removes 95%+ of residual contamination from PET flake; at 50°C, efficiency drops to 75–80% for similar residence time. For PVC-containing streams, hot caustic must be used carefully — PVC above 60°C with NaOH begins HCl desorption. Surfactant addition (anionic surfactants at 0.1–0.5%) improves inking and adhesive removal for printed film streams. Wastewater from the friction washer is the primary effluent in plastic recycling: BOD 500–5,000 mg/L, COD 1,000–10,000 mg/L, turbidity high — requires ETP (Effluent Treatment Plant) treatment to CPCB general discharge standards before disposal.

Equipment costs in India: domestic friction washers (Gujarat, Rajkot manufacturers) for 500–1,000 kg/hr throughput: Rs 8–20 lakh; 1,000–3,000 kg/hr: Rs 20–50 lakh. Imported European equipment (Herbold, NGR, Erema) is 3–5x higher cost with superior wear life on abrasive streams (agricultural film, sandy MRF material). Running cost: caustic soda at Rs 18–25/kg, hot water heating (steam or electric), and screen replacement (Rs 50,000–2,00,000 per year depending on abrasive feedstock). A friction washer processing 500 kg/hr of contaminated PET flake runs approximately Rs 0.8–2.0/kg processing cost excluding labour.

For Indian recyclers designing a washing line, the friction washer is the equipment where cutting corners has the highest cost downstream: under-washed flake results in poor pellet colour and quality, customer rejections, and yield loss from reprocessing. Specify screen hole diameter correctly for your flake size (1.5–3x the shredder output size), size the hot water heater for continuous 80°C operation at full throughput (many Indian lines undersize the hot water heater and lose washing efficiency during peak production), and install a caustic dosing pump with automatic control rather than manual batch addition.