Fluidized Energy mill, also known as micronizers, or jet mills is a type of mill that consist of a hollow toroid which has a diameter of 20-200mm depending on the height of the loop which can be up to 2m. It operates by particles impaction and attrition. A fluid or milling gas, usually air or inert gas is injected as a high pressure jet through nozzles at the bottom of the loop. The powder particles in the mill are accelerated to high velocity. The kinetic energy of the air plus the turbulence created causes inter particle (particle-particle collision) and particle-wall contact resulting in particle size between 2 and 10 micrometer. The fluidized effect transports the particles to a classification zone where the size classifier retains the particles until sufficiently fine to be removed. The particle size and share are determined by;
- The speed of air/inert gas
- Feed rate and size
- The configuration of the mill
- Design of the classifer
- The position of the nozzle
- The impact between the feed and air
Fluidized energy mill subclasses have no moving parts and primarily are distinguished from one another by the configuration and/or shape of their chambers, nozzles and classifiers. They include;
- Tangential jet
- Opposed jet
- Opposed jet with dynamic classifiers
- Fluidized bed
- Moving target
- Fixed target
- High pressure homogenizers
Pharmaceutical uses of Fluidized Energy mill
- Fluidized energy is used in milling thermolabile materials
- It is the choice of mill when higher degree of drug purity is required
- Fluidized energy mill is used for the fine grinding of frits, Kaolin, Zircon, titanium and calcium, alumina.
Advantages of Fluidized Energy mill
- The machine has no moving parts and thus the tendency of contamination due to wear of parts is minimize.
- The equipment is easily sterilized.
- Small particle size (between 2 and 10) is usually obtained at the end of milling.
- Thermolabile materials can be milled with little degradation since the heat produced by the process is nullified by the cooling effect of the expansion of the compressed gas.
Disadvantages of Fluidized Energy mill
- Tendency of forming aggregates or agglomerates after milling.
- Generation of amorphous content due to high energy impact.
- Formation of ultra-fine particles
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Wen-Ching Yang (2003). Handbook of Fluidization and Fluid-particle Systems. Marcel dekker, Inc., New York.