The conversion of powders or granules filled in the die cavity into solid unit mass by application of pressure is known as tablet compression process.
Tablets are manufactured in the pharmaceutical industry by the process of compression using the tablet compression machines.
If you are not familiar with the basic principle and components of the tablet compression machine, read the following article to learn all about the tablet compression machine because in this article we will only discuss the tablet compression process.
Tablet Compression Process
The tablet compression is a cyclic process and is completed into four different stages mean this procedure continues in a cyclic manner from stage one to stage four and when stage four is completed then again stage one is started and this process continues until the completion of the whole batch.
Stages Of Tablet Compression Process
There are four stages or steps of the tablet compression method and these four stages also known as compression cycle are given as below
- Feeding
- Weight Adjustment
- Compaction
- Ejection
- Feeding Stage
Stage one of the tablet compression process is the feeding stage or filling stage.
As the name indicates, in this first stage of feeding or filling the powders or granules are fed or filed into the dye cavities.
Explanation
- To start the compression operation we add powders or granules into the hoppers of the compression machine and then these powders or granules flow from the hopper to the feeder of the compression machine.
- The feeder of the compression machine has various housings and when dies pass below these feeder housings the powders or granules are filled into the cavities.
- The feeding of the powders/granules to the die bore or die cavity is known as the feeding stage or filling step of the tablet compression process.
The die cavities in this step are overfilled, meaning powders or granules are filled extra to ensure uniform weight of the tablets.
The feeding mechanism of compression machines may be of two types one is the conventional type which is known as gravity feed system where we feed powder or granules under the influence of gravity.This method is used in slow speed or conventional types of the compression machine.
Second type of feeding system is the force feeding system where fan-like structures are installed into the feeder and these fans rotate to ensure uniform filling of the die cavities.
This force feeding system is installed in the high speed tablet compression machines to ensure uniform filling of the die cavities.
To ensure smooth flow of powders or granules from the hopper the vibratory mechanism or rotating rod in the hopper may also be installed.
- Weight Adjustment
The second step of the tablet compression cycle is the weight adjustment stage or metering stage.
In the weight adjustment or metering stage the weight of the tablet is adjusted as per the specifications mentioned in the BMR or batch manufacturing record.
Weight adjustment cam & lower punch tip position in the die cavity play a significant role in the weight adjustment stage.
The position of the lower punch tip in the die bore die cavity can increase or decrease the filling capacity of the die cavity by altering the filling depth of the die cavity.
When the tip of the lower punch in the die cavity moves in upward direction the filling depth will be reduced and less powders or granules will be filled in the die cavity so as a result the tablet weight will be decreased.
When we pull the tip of the lower punch in downward direction the filling space inside the die cavity is increased and more powders or granules are filled so tablet weight is increased.
Explanation
- To understand the science involved behind the weight adjustment or metering stage we will take the example of conventional weigh adjustment system installed in the conventional compression machines.
- In conventional compression machines the weight of the tablet is increased or decreased by rotating the weight adjustment knob or dial in the clockwise direction or anticlockwise direction.
A simple question comes to mind, how weight is increased or decreased by just rotating the weight adjustment knob or dial in a clockwise or anticlockwise direction.
- The weight adjustment cam is attached to the weight controller knob through the rotating road.
- Suppose when we rotate the weight controller knob in clockwise direction the road pulls the weight adjustment cam in downward direction & when head of lower punch passes over the decreased height of weight adjustment cam the tip of lower punch comes down due to which die filling capacity is increased and weight of tablet is increased.
- When we rotate the weight controller knob in anticlockwise direction the road pushes the weight adjustment cam in upward direction & when lower punch head passes over this increased height of weight adjustment cam the tip of lower punch moves upward and die filling space is decreased so weight of tablet is also reduced.
- The excessive powder in the die cavity is removed with the help of tail over die during the weight adjustment stage.
- Tail over die is the scraper like structure which is adjusted over the dies to remove the excessive powder during the second stage of tablet compression cycle.
Auto Weight Controller (AWC)
In advance compression machines the auto weight controller system is installed where instead of rotation the weigh controller knob we can increase or decrease the tablet weight by just changing the value on HMI.
In advance type of compression machine the upward and downward movement of the weight adjustment cam is controlled by the servo motors by giving the feed on HMI of compression machine.
- Compaction Stage
The third stage of the tablet compression method is the compaction or compression.In this stage we apply pressure over the powders or granules filled in the die cavity to compress the tablet.
This pressure is applied by the compression pressure rollers and transmitted to the powders or granules through the punches.
Single feed compression machines have one main upper compression roller and one main lower pressure roller and for double feed compression machines we have two upper and two lower main pressure rollers or wheels.
Upper roller is fixed, meaning it is free to rotate but can’t move upwards or downwards to adjust tablet hardness.
The lower compression roller is attached with a lifting system by which we can increase or decrease the hardness by lifting the lower main compression rollers upward or downward by
rotating the hardness controller knob or dial.
In conventional compression machines the pressure controller is attached to the lifting system of lower main pressure rollers through the rotating rod.
By rotating the hardness controller clockwise or anticlockwise we can lift the pressure wheel upward or downward.
When we rotate the hardness controller to clockwise direction the lifting system push the pressure roller to upward direction & when punches pass through the compression rollers more pressure is applied and hardness of the tablet is increased.
When we rotate the hardness controller to the anticlockwise side the lifting system brings the lower pressure roller to the downward direction so less pressure is applied and hardness of the tablet is decreased.
In advance type of compression machine this lifting system is controlled by the servo motors.
- Ejection Of Tablet
The last stage of the tablet compression method is the ejection stage.In this stage the tablet compressed in the die cavity is removed out of the die cavity.
As we discussed at the start of the article that tablet compression operation is the cyclic process so when the tablet is ejected from the die cavity the empty die cavity is again ready to fill with powders or granules to continue the cyclic process.
The stem or tip of the lower punch and the ejection cam play an important role in the ejection of the tablet from the die cavity.
We have observed that the stem of the lower punch is always longer than the upper punch because the long stem is used to remove the tablet out of the die cavity after compression.
The ejection cam is like a slope and when the lower punch head rides over the ejection cam after the third stage the tip of the lower punch starts to move upward in the die cavity.
When the head of lower punch reaches at the maximum height of the ejection cam the stem or tip of the lower punch push the tablet out of the die cavity and this tablet strikes with the swipe of blade and is collected in the container.In this way the single tablet compression cycle is completed and this cyclic process continues until compression of the whole batch.