Granulator (granulator)

A granulator is a high-speed secondary size-reduction machine that follows a primary shredder, producing uniform 5-20 mm particles needed for clean downstream separation of metals, plastics and circuit fragments. While a primary shredder tears material apart with brute torque, a granulator cuts with sharpened rotor blades against fixed bed knives, achieving a calibrated particle size set by a perforated screen at the discharge.

The geometry matters. Open-rotor granulators (3-5 fly knives) run cooler and handle thick parts but produce more fines; closed-rotor designs give finer, more uniform output but require pre-cooled feed for elastomers. Rotor diameters of 400-800 mm and speeds of 400-800 RPM are typical; motor power runs 30-160 kW depending on throughput (0.5-3 TPH for e-waste and plastics).

Screen aperture is the master variable: a 10 mm screen produces flake suited to wash lines and float-sink tanks, a 6 mm screen gives the fine granulate needed for eddy current separator efficiency and for PCB metal liberation, while 4 mm and below begins to generate excessive fines that complicate air classifier work. Blade clearance — typically 0.15-0.30 mm between fly and bed knives — must be reset every 200-400 hours; loose blades produce stringy output, tight blades shatter on metal inclusions.

Trade-offs are real. Finer granulation improves metal-plastic liberation in mixed e-waste — copper trapped in cable insulation, gold deposited on PCB lands, aluminium bonded to plastic in casings — but raises blade wear cost (a complete blade set is Rs 80,000-2.5 lakh, lasting 600-1,500 hours), increases dust load on the bagfilter, and elevates kWh per tonne by 30-60% over single-stage shredding. Heat build-up at high throughput can soften PE, PP and ABS feed, gumming the screen — wash lines often dose chilled water mist; pyrolysis-bound feed avoids this since fines are tolerable.