How to Remove Agglomerates: Sifter for Micron-Size Particles
The process is effective because every particle has inherent structural weak points. “When exposed to the proper aerodynamic conditions, the particle will fracture at its weakest point,” says Glass. “The air pressure within the vortex chamber oscillates from extremely high to extremely low within a matter of micro-seconds, creating a pressure differential inside and outside the particle that causes it to crack. The process continues until each particle reaches its strongest crystalline structure.”
Because the process relies on pressure differential rather than abrasion, the hardness of the material has no significant effect on its ability to fracture.
How to Micronise Heat Sensitive Products
“Materials that soften with heat can be micronized without external cooling since no exothermic heat is generated by friction,” says Glass. “In fact, the process is slightly endothermic and works well for materials that are sensitive to heat and would otherwise require cryogenic cooling. Materials that contain water of hydration within their crystalline structure can be milled with no detrimental drying effect, while the process yields an extremely narrow particle size distribution.”
Centrifugal Force Prevents Agglomeration
Once the particles have been micronized, they are transported by compressed air up a pneumatic line into a product collector from which they are metered through a rotary airlock into the inlet spout of the centrifugal sifter. A feed screw directs the material into the cylindrical sifting chamber, where rotating helical paddles propel the particles through apertures in a 25 mesh (700 µm) stainless steel screen. The paddles never make actual contact with the screen.