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What Happens To An Air Classifier When Moisture Levels Rise

Wednesday, 21st February, 2018

Air classifiers do a great job of removing undesirable fines from quarried crushed stone and heavy mineral sands in a dry process without using any water. In order to effectively remove the fine dust, the moisture in the stone sand must be very low, 1-2% is best but some fines can be removed even at 2.5-3%. Higher moisture reduces an air classifier’s efficiency and requires a larger machine. Excessive moisture can make air classification totally ineffective. Low surface moisture is an important point to stress when air classifying because it directly affects the final products that are being processed.

Sturtevant Moisture Levels w/ Air Classifier

Here is what happens when the moisture goes up:

  1. More fines remain in the dedusted product
  2. Since the fines stick to the coarse material a larger air classifier with more air flow may be necessary for the machine to be effective
  3. When the moisture of a material is excessive (3.5% or more), the water centrifuges out and also leads to equipment clogging


If the moisture levels rise, the following adjustments are necessary to improve the machine’s performance:

  1. First, remove some or all rejector blades to try to maintain the desired dedusted product
  2. Next, significantly reduce the feed rate to try to maintain the desired dedusted product
  3. Finally, monitor the machine for vibration and scrape off any build-ups on the blades and on the inner housing

Even with all the above adjustments, the maximum moisture allowed will depends on the % fines in the feed and the % fines allowed in the desired dedusted product.

So, to summarize, make sure the feed material that is being air classified has the lowest moisture possible.


About Sturtevant

Sturtevant, Inc. is the leading family-owned manufacturer of material processing equipment including its patented Micronizer® jet mill which produces sub-micron sized particles, FCM an air-swept impact mill with integral classifier, Simpactor® and Infestroyer, centrifugal, pin-type impact mills and three types of high performance air classifiers that separate fine and coarse particles with precision and accuracy. Founded in 1883, Sturtevant was an early pioneer in size reduction, jet milling, micronization and air classification. The company introduced early versions of the jet mill and air classification systems. Sturtevant custom engineers its mills to suit the widest range of applications, extending beyond the traditional mineral processing markets into chemical, pharmaceutical, cosmetic, pigment, food and aggregate industries.


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Article Courtesy of Sturtevant 

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