Wet Milling During Granulation

Wet milling is one of the most important step of wet granulation and if you are not aware of the wet granulation process then read the following article

Tablet Manufacturing By wet Granulation

In this article we will only discuss one step of wet granulation and this step name is wet milling.

What is wet milling 

Wet Milling is also known as wet sieving and as the name indicates wet milling is the process where we break down the large lumps of the wet mass to reduce the particle size.

In simple words the passage of wet mass through a specified mesh number to reduce the particle size by using a specific equipment is known as wet milling or wet sieving process.

Wet milling

Why do we need a wet milling process?

Before going into details of the need of wet milling, first of all we must be familiar how wet mass is formed.A wet mass is formed when we add binder solution or solvent to the fine powder during wet granulation and when this wet mass is formed there are chances of formation of large lumps.

We perform the wet sieving process because of two reasons 

  • To break down the large lumps.
  • To increase the surface area

To break down the large lumps

If Large lumps formed during kneading process are not broken down and the wet mass is directly transferred to the fluid bed dryer the fluidisation will not be proper due to large lumps & heavy weight.Due to non uniform form fluidisation the drying time will be prolonged.

To increase the surface area

Large lumps have less surface area & drying time will be prolonged because less surface area of the particles is in contact with the hot air but when we use wet milling or wet saving the surface area of the particles is increased and it results in rapid drying.

Equipment Used For Wet Milling 

Two types of equipments are used for the wet milling process during the wet granulation in pharmaceutical industries 

  • Wet Mill
  • Wet Granulator

Wet Mill

Wet mill is an equipment which is available in two forms either it is installed with the rapid mixing granulator for the continuous granulation process or it is also available as a separate installed equipment.

Components Of Wet Mill 

In a wet mill there is a material charging chute from which wet mass is introduced into the wet sieving chamber of the wet mill. Then we have the moving blades or rotating blades and below the rotating blade a specified number of mesh is installed.

Working Of Wet Mil

The wet mass from the rapid mixing granulator is charged to the charging chute of the wet mill and when this material strikes with the rotating blades of the wet mill it breaks down the large lumps and the wet mass is pushed through the mesh installed around the rotating blades of the wet mill.The sieved wet mass is collected in a container or in case of continuous wet granulation process the wet mass is directly transferred by a pneumatic system through a transfer pipe to the fluid bed dryer.

Wet Granulator

Wet granulator is always available in the portable form and it is not attached to the rapid mixing granulator. 

It has similar functions like the wet mill mean we charge the wet mass from the charging chute and large lumps are broken down by the rotating blades and pass through the mesh installed around rotating blades.The sieved wet mass is collected in the container and then this material is charged to the fluid bed dryer for drying.

Image Credit

Image Source – Google | Image By – Hanningfield

Also Read

  1. Wet and Dry Granulation Techniques
  2. Difference between wet and dry granulation 
  3. End point of wet granulation
  4. Equipment Used For Wet Granulation
  5. Granulation Defects