The critical step of wet granulation which is mainly affected by the speed of the impeller blades is kneading.
Keading is one of the most important steps of wet granulation which is performed for tablet manufacturing in pharmaceutical industries.
The kneading step is dependent on the expertise of the operator as well as background knowledge of the granulation process.
In this article, we will mainly discuss the effect of the impeller blades speed or the speed of agitator blades on wet granulation.
All the discussion in the article will be based on practical observations and I hope you will learn a lot after reading this article.
What Is Kneading?
The kneading process is also known as the wetting stage, in which a binder solution is added to the dry fine powders & these powders are converted into wet mass or granules.
Purpose of Kneading/ Wetting
The purpose of kneading in wet granulation is to convert fine powders into granules so that no fine powders are left behind.
This process of wetting or kneading is usually performed in a rapid mixing granulator (RMG) or high-shear mixer granulator where the fine powders are mixed and then a binder solution or solvent is added to make a wet mass.
Function Of Agitator Blades
The impeller blades or agitator blades perform the following functions,
- Mixing of powders before the kneading step.
- The agitator blades of RMG remain in continuous motion during binder addition, this motion of blades helps in mixing the binder solution with powders.
- The agitator blades of RMG ensure uniform spreading of binder solution or solvent into powder particles.
- Due to this spreading & mixing action of impeller blades the powders are converted into wet mass.
Structure Of Agitator Blades
Majority of Pharmaceutical industries have rapid mixing granulators where agitating blades are mounted to the bottom side meaning these are attached to the bottom side of the mixing bowl of RMG.
The number of blades and their shape may varry depending upon the model of the RMG but most of the RMGs have an agitator with 3 blades.
Impact Of Speed On Process
The speed at which Agitator blades revolve plays an important role in the endpoint achievement of wet granulation.
It is practically observed that if the speed of the agitator or impeller blades is high it results in rapid wetting and if the speed of the Agitator blades is slow it results in slow or smooth wetting.
High Speed Vs Moderate Speed
We should give preference to the smooth and moderate mixing of binder solution with powders because in this way our binder solution is uniformly mixed with the powders and there are no chances of overwetting.
If the agitator blades speed is very high it will result in fast mixing of the blinder solution with the powder due to rapid mixing & there are chances of overwetting because the end point at high speed is difficult to trace & over-wetting may occur within a fraction of a time.
How To Adjust Mixer Speed
To adjust the speed of the impeller blades of the RMG, first of all, run the RMG with dry powder and observe the movement of powder with different speeds of Agitator blades.
Example
First of all, observe the Powder motion before wetting at 50 RPM then increase it gradually like 60 to 70 & so on.
If you observe that the powder movement at 50 RPM is sufficient enough & it is very fast at 75 rpm then select 50 RPM for the Kneading process.
Now at 50 rpm, add a binder or solvent solution and observe the movement of powder under load ( as the binder solution is added the load is increased due to wet mass & movement may become slow).
If you observe that the speed is reduced and the mixing of binder is not uniform with powders then increase the speed to 60 rpm and continue the remaining process at 60 rpm till the endpoint is reached.
Important Note
- Sometimes the impeller blades are jammed under load if the speed is very low depending upon the product nature & type of binder solution used. So do increase the speed (if required) under load.For this you must have to continuously observe wet mass movement.
How To Obser Product Movement
The advanced type RMGs are equipped with sensors which do not allow the blades to run if the lid is opened due to safety reasons.
So powder movement & binder spreading process is observed through the viewport of the high shear mixer or rapid mixing granulator which is installed over its lid.
Also Read
- End point determination or wet granulation.
- Equipments used for Granulation.
- Working of Rapid Mixing Granulator.
- GMP vs cGMP and 21 CFR.