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Wet granulation and dry granulation are two most commonly used methods for tablet manufacturing in pharmaceutical industries.
We are familiar that the conversion of powders into large agglomerates or granules is known as granulation.
How Granules are formed In wet granulation?
In wet granulation the powders are converted into large agglomerates or granules by adding the binder solution or solvent into the pre-mix of powders.
When we add solvent or binder solution into the pre mix of powders a wet mass is formed which undergo size reduction by wet sieving and then it is dried by using fluid bed dryer or tray dryers.
Now the dried mass is passed through a suitable sized sieve to get the granules of desired size.Every one of you is familiar with this method of granules manufacturing but majority of the freshers working in pharmaceutical industries are not aware of how granules are manufactured during dry granulation.
How Granules are Manufactured In Dry Granulation?
We can understand from the name that this method of granules manufacturing does not require any solvent or solution so a confusion question comes to mind how we will prepare granules in dry granulation without using any solution or solvent.
The one word answer to this question is ‘By pressure’.
Explanation
Pressure is the main factor which is used for converting fine powders into granules during the process of dry granulation.
In dry granulation we may apply pressure by two methods
- Slugging Method
- Roller Compaction
Slugging Method
In the slugging method pressure is applied by using a compression machine where we compress large size tablets from fine powders at higher weight and pressure.
These tablets are then crushed by using an oscillating granulator or cutting mill where granules of desired size are obtained by installing a suitable size mesh or sieve to the oscillating granulator or cutting mill.
Roller Compaction
In roller compaction the pressure is applied by a set of rollers where fine powder is fed to the pair of rotating rollers.
The pressure is controlled by the distance between these two rotating rollers and due to the pressure fine powder is converted into powder sheets which are then crushed to get the granules of desired size.
Conclusion
In the dry granulation method we are restricted to use any kind of solvent or binder solution so powders are converted into granules by applying pressure either by slugging method or by the roller compaction process.