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It works by injecting the material stream to be sorted into a chamber which contains a column of rising air. Inside the separation chamber, air drag on the objects supplies an upward force which counteracts the force of gravity and lifts the material to be sorted up into the air. Due to the dependence of air drag on object size and shape, the objects in the moving air column are sorted vertically and can be separated in this manner.
Air classifiers are commonly employed in industrial processes where a large volume of mixed materials with differing physical characteristics need to be separated quickly and efficiently. One such example is in recycling centers, where various types of metal, paper, and plastics arrive mixed together and need to be sorted before further processing can take place.
- US patent 1629594, Stebbins, Albert H., "Air Classifier", issued 1927-05-24
- US patent 3734287, Jager, Heinz, "Air Classifier Assembly", issued 1973-05-22, assigned to WEDAG Westfalia Dinnendahl Groppel Aktiengesellschaft
- US patent 4869786, Hanke, Ernst W., "Air Classifying Process and Air Classifier", issued 1989-09-26, assigned to Pfeiffer, Christian
- Bell Crowe, Patricia; Peirce, J. Jeffrey (March–April 1988). "Particle Density and Air-Classifier Performance". Journal of Environmental Engineering. 114 (2): 382–399. doi:10.1061/(ASCE)0733-9372(1988)114:2(382). Archived from the original on 2011-07-16.
- Wang, Xiaoyan; Ge, Xiaoling; Zhao, Xuehua; Wang, Zhiwen (August 1998). "A model for performance of the centrifugal countercurrent air classifier". Powder Technology. 98 (2): 171–176. doi:10.1016/S0032-5910(98)00040-0.
- Yang, G.; Zheng, D.; Zhou, J.; Zhao, Y.; Chen, Q. (August 2002). "Air classification of moist raw coal in a vibrated fluidized bed". Minerals Engineering. 15 (8): 623–625. doi:10.1016/S0892-6875(02)00057-2.
- Aghasaryan, Abgar (Jun 2010). "Classifying the Best Solution". World cement: 77–80.