Working and Principle of Tablet Compression Machine

Tablets are being formed by compressing the granules by using the compression machine. Tablet formed in compression machine by pressing the granules in die with lower and upper punch. Tablet formation takes place by the combined pressing action of two punches (lower and upper) and a die.
Now it is possible to produce more than 500,000 tablets per hour due to different’s innovations to tablet compression machines.
Principle of Tablet Compression Machine:
In the tablet compression machine main principle is compressing of the upper and lower punch in a die hole, the hydraulic pressure plays a key role. This pressure is transmitted unreduced through the static fluid. Any externally applied pressure is transmitted via static fluid to all the direction in same proportion. It also makes it possible to multiply the force as needed. If we increase the hydraulic pressure more compressing force on tablet then it becomes more hard.


Different Stages of Tablet Compression Process:

Tablet compression process is divided into four distinct stage. These stage including filling, metering, compressing and ejection.

Tablet compressing stage

Filling                          Formulation is overfilled at the compressing station
Metering                      Overfill is removed
Compression             Tablet is formed by pressure of punches within die
Ejection                      Tablet is ejected from die


1.  Filling: The filling stage of tablet compression process involves transfer of raw materials into position for tablet compression. These raw materials have undergone prior processing by wet granulation, dry granulation (roller compaction), sizing or other process. The final formulation is then blended to yield a homogeneous blend. The blend then flows to the compressing machine punch-die cavity. The punch die cavity is composed of punch die and lower punch. The position of lower punch within the die determines the volume of the punch-die cavity. This volume must be appropriately sized for the weight of granulation to be compressed into tablets. The granulation is overfilled on the die table (turret) to ensure complete filling of the punch-die cavity volume.
2. Metering: The metering stage of the tablet compressing process involves removal of excess granulation from the compressing machine. This stage enables the exact weight (volume) of granulation to be compressed into tablets. The exact weight of granulation is controlled by the height of the lower punch in the die. The height of the lower punch is controlled by the metering cam (also called the dosage cam). The lower punch is raised to the appropriate level in the die to provide the exact weight of granulation in the punch-die cavity. The excess granulation is scraped from the surface of the die table. The metering stage is similar to the method used to measure flour when baking a cake. A measuring cup is first over-filled with flour; then a knife is used to scrape off the excess. The exact amount of flour is then left in the measuring cup.
3. Compression: The compression stage of the tablet compressing process forms the tablet. This stage involves bringing together the upper and lower punches under pressure within the die to form the tablet. As the punches enter the compressing stage, the upper and lower punches move between two large wheels called pressure rolls. These pressure rolls push the punches together to form the tablet. The distance between the upper and lower punches determines the thickness and the hardness of the tablet. When the punches are close together, a thin and hard tablet is created. When the punches are farther apart, the tablet made is softer and thicker. The proper balance of thickness and hardness determines the optimum roll distance for any specific product. These adjustments are made while keeping the tablet weight constant.
4. Ejection: The ejection stage of the tablet compressing process involves removal of the tablet from the lower punch-die station. In this stage, the upper punch retracts from the die cavity and rises above the turret table. Then the lower punch rises in the die, which in turn pushes the tablet upward to the top surface of the die table and out of the die cavity. A scraper (also called takeoff scraper or tablet rake-off) then pushes the tablet off the die table away from the compressing machine into the collection container.