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Size Reduction [Milling]

Milling:

It is a physical phenomenon in which we can achieved desired particle size by the principle of cutting, attrition and impact depends on use of mills

     Common types of mills used in our API industry are:

  1. Multimill

  2. Cadmill

  3. Jet mill

Multi Mill

Multimill

Multimill :

Particle size reduction is done with the help of cutting and impact of the material through the blades assembly provided through some predefined speed (RPM) of Multimill.

There are the provision of VFD to some Multimills by which we can vary the RPM of the blades by setting the speed of machine on VFD panel depending upon the product requirement.

In case of belt driven Multimill, speed to be set by changing the position of belts on pulley.

Various screen sizes ranging from 0.3 mm (i.e. 300µm) to 12 mm (12000 µm) are available depending on requirement of particle size and accordingly we have to fix the screen to Multimill before milling operation. Milled material finally collected in a HMHDPE drum through discharge end.

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Major parts of Multimill:

  1. Base Plate: On which screen is to be fitted in grooves provided.

  2. Blade assembly: Number of blades provided to the shaft of Multimill through which by cutting and impact, desired particle size gets achieved.  

  3. Beater assembly: Present at the bottom below the blades to recollect the un-milled material again into flow.

  4. Feeder hopper: Through which material is to be fed depending on nature of material by using slide plate opening (25 % open: For free flowing/granular/crystalline material, 50 to 75 % open: For lumpy material).

  5. Discharge End: Through milled material is collected in HMHDPE drum.

Cad Milling

CAD (Commuting )Mill

Cadmill :

Cad mill is used for particle size reduction. Particle size reduction is done by milling through cutting and impact.

It consists of a stainless steel material feed pan through which the product slides into anComminutingchamber, moves to the cad mill blade assembly where it is milled with the help ofblades (with highest RPM of 4500) i.e. reduction in required size is done by cutting and impact. It is belt driven cadmill, speed to be set by changing the position of belts on pulley Screen size of 0.5 mm is used for the same. Milled material finally collected in a HMHDPE drum through discharge end.

 

Major parts of Cadmill:

  1. Material Feed Pan: From here material is fed to Comminuting chamber of cad mill assembly.

  2. Blade assembly: Number of blades provided to the shaft of Cadmill through which by cutting and impact, desired particle size gets achieved.  

  3. Comminuting Chamber: This is milling area. Where material is milled in between blades

  4. Discharge End: Through milled material is collected in HMHDPE drum.

Jet Milling

Jet Mill

Jet mill :

It operates, solely utilizing the energy of compressed air and reduces the particle size principally by attrition between the particles of the powder themselves.

It consists of a stainless steel hopper through which the product slides into an processing chamber, moves to the jet mill assembly where it is milled between collision of two air pressure i.e. ventury compressed air and grinding compressed air reduced to required size, fine particles finally collected in a collection bin.

The variable parameters include feed rate, main air pressure, ventury compressed air pressure and grinding compressed air pressure.

 

Break down of the large particles in to smaller particle in following way:

  1. Attrition due to two air pressure i.e. ventury compressed air and grinding compressed air pressure.

  2. Collision between the particles themselves.

 

Major parts of Jet mill:

  1. Charging hopper with screw feeder: From here material is fed to processing chamber of jet mill assembly.

  2. Jet mill Grinder Assembly: This is milling area where ventury air pressure line and grinding air pressure line provided.

  3. Collection bin: Where milled material is collected.

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