Air classifiers (windsifters or pneumatic classifiers) separate materials by weight difference and aerodynamic behavior using controlled airflow. The light fraction (plastic films, paper, foams, textiles) is carried by the air; the heavy fraction (metals, stones, glass, dense wood) falls by gravity.
Operating principle
Shredded and classified material is fed onto an acceleration conveyor or into a free-fall zone. An airflow (suction or forced) passes through the material. Light particles are carried and directed to a collection point; heavy particles follow a ballistic trajectory to a second discharge point. More sophisticated machines allow separation into 2 or 3 fractions with adjustable air speed and deflector positioning.
Applications
Removal of films and light impurities from RDF before densification
Separation of heavy inerts (glass, stones) from organic or combustible fractions
Cleaning of organic compost by removing plastic contaminants
Pre-separation before shredders to remove light non-shreddable materials
Practical considerations
Efficiency is sensitive to moisture (wet materials stick together), particle size (extremes do not separate well), and feed uniformity. Air speed and splitter position adjustment is done on-site, observing actual behavior.
Simple in concept, but requires fine-tuning during installation.