Pre Compression Of Tablets

Tablets are compressed by using a compression machine in which powders or granules are filled in the die and are compressed by using a set of punches known as upper & lower punches.

All of you must be familiar with that tablets are compressed with the help of main compression rollers or that the compression pressure is applied with the help of main compression rollers & Very few may be familiar with the concept of pre-compression wheels which are installed in the compression machines.

In this article, we will discuss what is pre-compression. The role of Pre pre-compression & how pre-compression is beneficial in the tablet compression process.

What Is Pre-Compression?

As the name indicates pre-compression is the compression that is applied before the main compression.

Pre-compression is the compression force that is applied by a set of small wheels known as pre-compression wheels.

The Role Of Pre Compression 

Pre Compression functionality available in advanced compression machines is helpful for removing the entrapped air before main compression so pre-compression is also known as the deaeration technique in tablet compression.

As we know that entrapped air in powder or granules during the compression process may result in tablet compression problems like capping & lamination so by removing this entrapped air the issues of tablet capping & lamination are overcome.

Pre-compression is also helpful for the compression of layered tablets.

Pre-Compression Roller?

Pre-compression rollers are smaller than the main compression roller & are installed in the same sequence as the main roller, meaning one on the upper side is known as the upper pre-compression wheel or roller & one on the lower side is known as the lower pre-compression wheel.

For double feed rotary compression machines 2 upper & 2 lower pre-compression wheels are present.

Pre Compression wheels are installed before the main compression wheels where they slightly press the powder or granules after weight adjustment to remove the entrapped air.

How To Adjust Pre-Compression?

Generally, it is recommended that pre-compression should be 1/10 of the main compression values but as we know that the properties of all materials are not the same so Pre Compression value may  vary depending on the product nature.

For understanding, Pre-compression is the small amount of pressure that does not result in strong bonding of powders or granules; it is only for forming a soft tablet by removing the entrapped air.

Pre compression force is adjusted in such a way that the tablet formed must be ejected as in form of a tablet but when we take this tablet in fingers & press it, it must deform into powders or granules.

Important Note

The pre-compression force must not be too high because too high pre-compression may also result in capping or lamination.

During compression of layered tablets high pre-compression may result in layer separation.


Pre-compression is applied in the tablet compression process for removing entrapped air to prevent tablet capping or lamination problems.

Also Read

Stages and Mechanism of Tablet Compression.

Advancements in tablet compression machines.

Calculation of compression machine capacity.

How to reduce compression machine breakdown.

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