Milling Process in Pharmaceutical Industry

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Milling is a mechanical process of breaking particles into smaller pieces via one or more particle size reduction mechanisms.


Types of Milling

  • Impact: Particle size reduction by applying an instantaneous force perpendicular to the particle/ agglomerate surface. The force can result from particle-to-particle or particle-to-mill surface collision.
  • Attrition: Particle size reduction by applying a force in a direction parallel to the particle surface.
  • Cutting: Particle size reduction by applying a shearing force to a material.


Milling Operation Principles

  1. Fluid Energy Milling: Particles are reduced in size as a result of high speed particle-to-particle impact and/or attrition; also known as micronizing.
  2. Impact Milling: Particles are reduced in size by high-speed mechanical impact or impact with other particles; also known as milling, pulverizing, or comminuting.
  3. Cutting: Particles are reduced in size by mechanical shearing.
  4. Tumble Milling: Particles are reduced in size by attrition utilizing grinding media.
  5. Screening: Particles are reduced in size by mechanically induced attrition through a screen. This process commonly is referred to as milling or de-agglomeration.


Milling Equipment Classifications

1. Fluid Energy Mills

Fluid 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.

  • Tangential Jet
  • Loop/Oval
  • Opposed Jet
  • Opposed Jet with Dynamic Classifier
  • Fluidized Bed
  • Fixed Target
  • Moving Target


2. Impact Mills

Impact mill subclasses primarily are distinguished from one another by the configuration of the grinding heads, chamber grinding liners (if any), and classifiers.

  • Hammer Air Swept
  • Hammer Conventional
  • Pin/Disc
  • Cage


3. Cutting Mills

Although cutting mills may differ from one another in whether the knives are movable or fixed and in the classifier configuration, no cutting mill subclasses have been identified.


4. Tumbling Mills

Tumbling mill subclasses primarily are distinguished from one another by the grinding media used and by whether the mill is vibrated.

  • Ball Media
  • Rod Media
  • Vibrating


5. Screening Mills

Screening mill subclasses primarily are distinguished from one another by the rotating element.

  • Rotating Impeller
  • Rotating Screen
  • Oscillating Bar


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