Benefits of Controlled Benefits of Controlled Particle Reduction:Particle Reduction:

Particle size affects a number of characteristics in the manufacturing process. Controlling the particle size helps assure that the milled material will be consistent and repeatable with respect to:

Color - uniform particles assure batch-to-batch color consistency

Flow-ability - critical to packaging, tableting, weighing

Uniformity - consistent bulk density Density - helps control shipping costs and minimize dust

Reconstitution - assures the desired dissolution rate

Chemical reaction - vital for uniform, controlled chemical change

Taste - allows precise portion control for consistent taste

TYPES OF COMMINUTOR TYPES OF COMMINUTOR MILLSMILLS

a. Cutter mill.         b.  Roller mill.c.  Hammer mill.   d.  Ball mill.e.  Fluid energy mill.   f.  Colloid mills and homogenizers.

Understanding Comminutor Understanding Comminutor Cutting Mill OperationCutting Mill Operation The Comminutor operates by feeding material uniformly into a chamber in which a rotating blade assembly reduces the particles of the material by cutting or impacting them.

The material discharges through a screen which regulates final particle size at the outlet of the milling chamber.

The blade and screen act in conjunction to determine final product sizing.

Comminutor Cutting Mill Comminutor Cutting Mill OperationOperation

Feed ThroatFeed ThroatThe feed throat introduces material into the milling chamber.

There are several designs of feed throats.

A gravity feed throat introduces material tangentially to the rotation of the blades.

Other throats are available for milling machines, such as a metered feed throat, liquid inlet throat, etc.

Blade ProfileBlade ProfileThe type, quantity and shape of blade helps determine the degree of reduction achieved based on the material being processed. Some blade styles offer flexibility of knife on one side and impact on the other. Knife-edged configuration is for gentle granulation and impact-edged for more aggressive reduction. An optional bar rotor with rasping screen is available for low energy size reduction.

Feed RateFeed Rate Milling is accomplished most effectively if the product is fed uniformly to the throat.

Feed methods include metered feed from Variable Feed System (VFS), rotary valve, or gravity fed.

Manual feed pans are available where the operator is responsible for metering the material to the mill.

Rotor SpeedRotor SpeedThe Comminutors rotor speed directly affects the particle size range. As a general rule, and with all other variables remaining constant, the faster the rotor speed, the finer the grind:

Rotor speeds of 3000 to 7200 rpm are typically used with flat blades in fine grinding applications, while speeds of 1000 to 3000 rpm are typically used with sharp blades in coarse grinding applications. For general purpose applications, variable speed rotors are often specified to accommodate the physical characteristics of different materials.

SPEED OF ROTATIONSPEED OF ROTATION

ScreenScreenThe Comminutor sizing screen, located directly beneath the blades rotation arc, prevents particles from leaving the grinding chamber until they are at least as small as the screen holes.

These holes can have round or square perforations, diagonal or straight slots, or wire-mesh openings.

The screen thickness and the total open surface area of the screen also affect the comminuting operation.

The screen size (diameter of the screen holes) doesn't necessarily designate the particle size of the finished product.

The reason is that the impacted particles follow a tangential trajectory from the blades and approach the screen at a shallow angle.

Therefore, particles effectively see an opening as an ellipse.

The higher the rotor speed, the smaller the angle under which the particle approaches the screen and the smaller the screen openings appear to the particle.

The figure clearly shows that at higher The figure clearly shows that at higher rotor speeds only smaller particles will rotor speeds only smaller particles will pass through the screen. Also, the pass through the screen. Also, the thicker the screen, the smaller the thicker the screen, the smaller the particles must be to pass through the particles must be to pass through the screenscreen....

HAMMER MILL -is an impact mill HAMMER MILL -is an impact mill employing a high speed rotating employing a high speed rotating disc, to which are fixed a number disc, to which are fixed a number of hammer bars which are swung of hammer bars which are swung outwards by centrifugal forceoutwards by centrifugal force....

Centrifugal Impact MillsCentrifugal Impact Mills("CIM" or "Pin Mill“)("CIM" or "Pin Mill“)

"Pin Mill“"Pin Mill“Ideal for: Fine grinding of friable materials

Coarse grinding friable materials

De-agglomerating Conditioning of cellulose fibers Wet or dry materials Tight particle size control

OperationOperation Metered material is gravity fed through the centrally located inlet.

Centrifugal forces accelerate the material and launch it into the impact zone.

The action created by the stationary and rotating pins creates a "treacherous path" for material to pass through.

Varying the rotor speed between a few hundred rpm up to 5400 rpm provides the flexibility to use the machine as a coarse grinding or as a fine grinding mill an inexpensive, compact machine.

Fluid energy millFluid energy mill