image of multi-station press

Tablet Press

In Tableting Machines by Calistus OziokoLeave a Comment

Tablet press also referred to as tableting machine, pharmaceutical tablet press, tablet compressing machine or tablet punching machine is a mechanical device that compresses powders into tablets of uniform size, shape, and weight containing approximately the same quantity of Active Pharmaceutical Ingredient (API) and excipients. Apart from its use in the pharmaceutical industries for manufacturing varieties of tablets, it can also be used to manufacture illicit drugs, cleaning products and cosmetics. All tablet press employ the same basic principle of compression. The development of tablet press has been a continuous process. In the past, we have hand driven tablet press which have been modernized to electrical driven tablet press.

Reason for continuous development of tablet press

  • Increased rate of production resulting from increased demand, multiplication of disease conditions and exponential increase in population.
  • Development of newer technology in tablet production e.g. development of direct compression technology.
  • Development of stringent standard of cleanliness to comply with Current Good Manufacturing Process (CGMP).
  • The introduction of automation and continuous monitory of production process.

Types/Classification of Tablet Press

Tablet press in current use can be classified into;

  • Single punch/single station/eccentric presses.
  • Multi-station/rotary presses.

Single Punch

tablet press-image of a single punch tablet press

Single punch tablet press also known eccentric press or single station press is the simplest machine for tablet manufacturing. This machine uses single set of station tooling (a die and a pair of upper and lower punches). The compaction force on the fill material is exerted by only the upper punch while the lower punch is static; such action equivalent to hammering motion and as a result, the single punch press is referred to as stamping process. The single punch tablet press produce about 60-85 tablets/min e.g. Manesty F3.

Components/ functional parts of a single punch tablet press

parts of a tablet press

 

  • Hopper – This is connected to the feed shoe and it is where the granules/powder mixtures are poured into prior to tableting or compression. The hopper can be filled manually or by using mechanical equipment during subsequent tableting.
  • Die cavity – The die cavity is where the powder granules are compressed into tablet. The die determines;
    • The diameter of the tablet
    • The size of the tablet
    • To some extent the thickness of the tablet.
  • Punches – This comprises upper and lower punch and they compress the powder into tablets of various shapes within the die.
  • Cam truck – This guides the position/movement of the punches.
  • Tablet adjuster – This is used to adjust the volume of the powder to be compressed and so determines the weight of the tablet.
  • Ejection adjuster – This facilities the ejection of the tablet from the die cavity after compression.

In the production of tablet using single punch, the upper punch compresses the powder into tablets while the lower punch ejects the tablet.

The sequence of events involved in the formation of tablet.


The events involved in tablet production can be divided into 3 stages;

  1. Filing
  2. Compression
  3. Ejection

image of the sequence of events involved in tablet formation

Filing

  • Position 1 – The upper punch is raised and lower punch drops to create a cavity in the die.
  • Position 2 – The feed shoe moves over the die cavity and granules fall into the die cavity under the influence of gravity from the hopper.

Compression

  • Position 3 – The feed shoe moves out of the way and the hopper punch descends to compress the granules/powder mixture into tablets by progressive reduction of the porosity of the die content and forcing of the particles into close contact with one another.

Ejection

  • Position 4 The upper punch retracts and the lower punch moves upwards too to eject the compressed tablet. The whole events repeat over and over again unit the feed material is exhausted.

Advantages of Single Punch Tablet Press

  • The single punch structure is rational and small.
  • Easy to operate and it operates at a high utilization ratio.
  • It can manufacture odd shaped products with a diameter of up to 20mm.
  • It is ideal for development of tablets and small batch production.
  • Single punch tablet press utilizes a high amount of pressure to reduce weight variations between tablets while maintaining a low noise level at the same time.

Multi-Station PressTablet press-image of a rotary tablet press

Multi-station press is a mechanical device that unlike the single punch tablet press has several tooling station which rotates to compress granules/powder mixture into tablet of uniform size, shape (depending on the punch design) and uniform weight. It was developed to increase the output of tablets. In rotary 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 Press

parts of a multi-station tableting machine

  • 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 is compressed into tablets and it determines.
    • The diameter of the tablets.
    • The size of the tablets.
    • To some extent the thickness of the tablets.
  • 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.
  • Pre-compression 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 tablet.
  • Ejection cam– Guides the lower punch upwards facilitating the ejection of tablet 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 multi-station press

Multi-station 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 are to be used with. A tooling set comprises the die and its associated punches. Basically, there are two types of toolings:

  1. “B” type
  2. “D” type

The above type of configuration constitutes a majority of the tool configuration used today.

“B” Type

The “B” type configuration has a normal, punch barrel diameter of 0.750in. (19mm). The “B” type can be used with two types of die or can be said to have two different die sizes:

  1. The “B” dies with a diameter of 1.1875in. (30.16mm), suitable for all tablet sizes up to the maximum for the “B” punches.
  2. The smaller “BB” dies (small “B” die) that has a diameter of 0.945in. (24mm). This die type is suitable for tablets up to 9mm diameter or 11mm maximum.

“D” type

This type has larger nominal barrel diameter of 1in. (25.4mm) and a die diameter of 1.500in. (38.10mm) and thus is suitable for tablets with maximum diameter or maximum length of 25.4mm.

Tablet press 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 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.

 

REFERENCES

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