Tablet hardness is one of the most important characteristics of the tablets during the compression process.If the required hardness of the tablet is not achieved it will result in various issues during transportation and tablet coating process.
Despite the fact that tablet hardness is a non-official or non pharmacopoeial test it has great importance for the product quality.
Our ultimate goal during the tablet compression process is to maintain the required hardness level along with weight uniformity. What will be the first solution if the required level of tablet hardness is not achieved for a given batch of product?
Case Study
Suppose that we are going to compress the batch of a product ‘A’ and its required hardness level is 10 to 15KP.In routine compression process this hardness is achieved at 30 rpm of turret speed but for this batch the operator is facing the issues with tablet hardness.
At 30 rpm the tablet hardness is 7 KP and the operator tries to increase it by increasing the main compression pressure but he is not able to increase the tablet hardness.
He discussed this issue with his shift in-charge and he asked him to reduce the speed of the tablet compression machine from 30 rpm to 22 rpm.When the operator reduced the compression machine speed and again checked the tablet hardness it was increased from 7 KP to 12 KP.
Now a common question comes to mind, how does the speed of the tablet compression machine impact the tablet hardness?
Science
The phenomenon involved for this concept is known as dwell time meaning the impact of speed on tablet hardness has a scientific justification and it is due to the dwell time concept.
What is dwell time?
The amount of time spent by the punch head under main pressure rollers is known as dwell time.
The time for which the punch head and pressure rollers remain in contact with each other is known as dwell time.
Relation of dwell time and hardness
We are familiar with the concept of dwell time and now we will try to learn how dwell time impacts tablet hardness.
When the speed of the tablet compression machine is high the dwell time will be low meaning the punch head will come in contact with pressure rollers for short duration or stay time of punch head under pressure rollers will be less.
Due to short contact time the less pressure from rollers will be transferred to the punch head or due to too high speed the pressure may not be precisely distributed and that is why we may face the issue of low hardness at higher tablet compression machine speed.
So now let’s understand how tablet hardness is increased when we reduce the speed of a tablet compression machine?
Due to reduced speed the dwell time is increased meaning by reducing the tablet compression machine speed we increase the stay time of punch head under the pressure rollers or in simple words we are increasing the contact time of punch head with main pressure rollers.
When the punch head spends more time under the pressure rollers it will receive more force and this force or pressure will be uniformly distributed to the powders and granules and tablet hardness is increased after compression.
Conclusion
There is a technical relationship between the tablet hardness and compression machine speed.It is observed that some time required hardness is not achieved at higher machine speed and we have to reduce the speed of tablet compression machine to get the required hardness.By reducing the speed we are basically increasing the dwell time which results in increased tablet hardness.
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