Rotary tablet press is a mechanical device that unlike the single punch tablet press has several tooling station which rotates to compress granules/powder mixture into tablets of uniform size, shape (depending on the punch design) and uniform weight. It was developed to increase the output of tablets.
In rotary tablet press, the compaction force on the fill material is exerted by both the upper and lower punches leaving the powder granules to be compressed in the middle. This is known as accordion type of compression. The capacity of a rotary tablet press is determined by the rotation speed of the turrent and the number of stations on the press.
Components/Functional Parts of a Rotary Tablet Press (Multi-Station Tablet Press)
Hopper- The hopper holds the granules/powder mixture (API plus excipient) that are to be compressed into tablets.
Die cavity – This is where the powder granules are compressed into tablets and it determines:
The diameter of the tablet.
The size of the tablet
To some extent the thickness of the tablet.
Feed paddle – Helps to force the feed/ the granules into the dies especially during faster rotation.
Punches – This comprises the upper and the lower punches. They move within the die bore to compress granules into tablets.
Lower cam track – This guides the lower punch during the filling stage so that the die bore is over filled to allow accurate adjustment.
Cam tracks – This guides the movement of both the upper and lower punches.
Dept of fill/capacity control – This adjusts the lower punch track during the latter part of the fill stage to ensure that the appropriate quantity of granules remains within the die prior to compression.
Recompression rollers – This roller gives the granules an initial compression force to get rid of excess air that might be entrapped in the die.
Main compression – This roller applies the final compression force needed for the formation of tablets.
Ejection cam– Guides the lower punch upwards facilitating the ejection of tablets from the die cavity after compression.
Take-off Blade – This is fitted in front of the feeder housing and it deflects the tablet down the discharge chute.
Discharge chute – This is where the tablet passes through for collection after being deflected by the take-off blade.
Classification of Rotary Tablet Press
Rotary tablet press can be classified into several ways but the most important of these classifications is based on the type of tooling with which the machine is to be used with. A tooling set comprises the die and its associated punches. Basically, there are two types of toolings:
The above type of configuration constitutes a majority of the tool configuration used today.
The “B” type configuration has a normal, punch barrel diameter of 0.750 inches. (19 mm). The “B” type can be used with two types of die or can be said to have two different die sizes:
The “B” dies with a diameter of 1.1875 inches. (30.16 mm), suitable for all tablet sizes up to the maximum for the “B” punches.
The smaller “BB” dies (small “B” die) that has a diameter of 0.945 inches. (24 mm). This die type is suitable for tablets up to 9 mm diameter or 11 mm maximum.
This type has larger nominal barrel diameter of 1 inch. (25.4 mm) and a die diameter of 1.500 inches. (38.10 mm) and thus is suitable for tablets with maximum diameter or maximum length of 25.4 mm.
Tabletting machines are designed to be used with either “B” or “D” tooling but not both. The compression force obtainable in a machine depends on the type of tooling used. Machines that are designed to “B” type tooling exert a maximum compression force of 6.5 tones and machines that use the “D” type configuration exert 10 tones compression force.
There are equally some special machines that are designed with the intention of exerting higher compression forces. The maximum force that can be exerted on a particular size and shape of tablet is governed by the size of the punch tip or the maximum force of which the machine is designed.
Individual manufactures of tablet press have sought to achieve higher output by;
Increasing the effective number of punches.
Increasing the number of station.
Increasing the number of points of compression.
Increasing the rate of compression turrent speed.
Each of the above approaches has its own advantages and limitations.
Advantages of Rotary Tablet Press (Multi-station tablet press)
High productivity can be gained with a minimal amount of labour while saving money.
Rotary press has an output of between 9000 – 234000 tab/hour thus saves time and meets up with the high demand of tablet dosage form.
The powder filled cavity can be automatically managed by a moving feeder.
Rotary press decreases waste of valuable formulation in non-specific tablets.
The machine allows independent control of both weight and hardness.
Bill Bennett and Graham Cole (2003). Pharmaceutical Production: An Engineering Guide. Institute of Chemical Engineers (IChemE), UK.
David, B. Troy and Paul, Beringer (2006). Remington: The Science and of Pharmacy. 21st edition. Lippincott Williams and Wilkins, USA.
Gilbert, S. B and Christopher, T. R. (2003). Modern Pharmaceutics. CRC Press, Taylor and Francis Group, LLC.