Air Classification can separate materials across particle sizes that are too fine to screen, and can improve the efficiency of mills.
When are air classifiers used?
Air Classifiers are normally used when the particle size that needs to be separated is too fine to screen. The air classified product can be the granular Coarse discharge with very little Fines/Dust or the Fines discharge with very little Coarse/Grit. Air Classifiers eliminate the blinding and breakage issues associated with screens.
How dry does the feed need to be?
In order to effectively remove fine powders, the surface moisture of the feed must be very low, less than 1 – 2% is best, but some fines can be removed even at 2.5-3%.
Can air classifiers be used for abrasive materials?
Yes. Air Classifiers do not operate at the high speeds that pulverizers do and wear protection liners can be used to economically process even abrasive
powders, like silica, fly ash and ceramics.
How fine can air classifiers cut?
Air Classifiers can separate powders as coarse as 80 mesh (180 microns, 0.180 mm) or as fine
as 2-3 microns.
Can air classifiers separate by density?
Yes and No. While density does play a role in Air Classifier separation, the internal air currents are mostly affected by the overall mass/weight of the particles in the feed. Lighter/Smaller particles are removed by the airflow, while Heavier/Larger particles are not entrained in the airflow. However, it must be noted that Large Particles with Low Density can have a similar mass/weight as Small Particles with High Density. This can reduce the effectiveness of an air classifier’s density separation.
How do you control the fineness of air classified products?
The fineness of Air Classified products is controlled by the quantity of rejector blades, the speed of the rejector blades, the velocity of the airflow and the feed rate.
Do air classifiers require cyclones or baghouses?
Air classifiers are categorized as Internal Fan Models and External Fan Models. Internal Fan
models re-cycle the air and do not require cyclones or baghouses to collect the separated fines. External Fan Models require cyclones or baghouses to collect the separated fines.
Do air classifiers fracture materials and generate additional fines?
In most cases, Air Classifiers do not fracture materials because they do not operate at the high speeds that pulverizers do and much of the feed never even makes contact with the rotating parts. However, in cases where the feed powder consists of extremely soft agglomerates, some minor fracture can occur.
Can air classifiers be used with mills?
Yes, in fact, Air Classifiers commonly operate in closed-circuit with a mill. This maximizes the capacity of the mill and reduces the mill’s energy cost because the mill does not have to be the sizing device.
Can air classifiers be fed pneumatically?
Yes. Air Classifiers can be fed pneumatically and, in some cases, this offers the opportunity to install the classifier in a pneumatic conveying line. However, it should be noted that the particles in a pneumatic fed process enter the Air Classifier at much higher velocity than gravity fed particles. Particles that approach the rejector blades at higher velocities are more likely to pass through, which requires a higher rejector speed to stop the oversize particles. Generally, this results in higher wear and lower fines removal efficiency.
