Working and Principle Of Tablet Compression Machine

Manufacturing of tablets in pharmaceutical industries is done by using a machine which is known as a compression machine. In the old era, single-punch compression machines were used but nowadays more advanced & sophisticated compression machines are used which are known as rotary compression machines.

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 that tablets are compressed with the help of main compression rollers or that the compression pressure is applied with 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 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.

Reasons and solutions of tablet capping.

Raking In Fluid Bed Dryer

Fluidization is the main principle by which FBD or fluid bed dryer works. The fluid bed dryer is frequently used in the drying process due to its reduced drying time & increased capacity means it can dry more volume of product in a short period as compared to the tray dryer.

Raking Process

Raking is the process that is routinely performed by all the operators in FBD during the drying process but we don't use this technical term in a routine so most of you are not familiar with this word Raking.

Raking is the manual process in which we remove the product trolley & manually mix the granules with gloved hands or with the help of stainless steel spatula & break large lumps formed in the FBD product trolley to ensure that all the material in the product trolley will be lifted uniformly & result in uniform drying 


Why We Need Raking

One of the main contributory factors of FBD for uniform drying of products is that it should lift all the product volume equally from all areas of the FBD product trolley but sometimes the uniform lifting is not achieved & the drying process is not uniform.

So to ensure uniform drying we use the process of Raking.

Factors Resulting Non Uniform Drying In FBD / Product Lifting Issue

Following are some factors that may result in non-uniform drying due to lack of uniform product lifting in the product trolley of FBD & require Raking after specified time intervals.

  • Fan Motor Speed

  • Product Load

  • Filter Blocking

  • Dutch Woven Sieve Blocking

Fan Motor Speed

The speed of the Blower Fan is responsible for increasing or decreasing the air velocity which is required for fluidization.If the speed of the blower fan is not proper it will not lift the product properly so drying will not be uniform & large lumps will be formed which will further hinder the drying process.

So removing the product trolley & performing the Raking process means breaking the large lumps & mixing all the granules in the product trolley manually & increasing the speed of the blower motor for proper fluidization will result in proper lifting and uniform drying.

Product Load

If the product trolley of FBD is overloaded than its recommended capacity, it will result in non-uniform drying due to product lifting issues.

Remove excessive load, perform Raking & dry the product in lots if the product load is higher than the recommended capacity.

FBD Filter Blocking

If the filters of FBD are choked or blocked, the required suction will not be produced & air velocity will be low so the product will not be lifted uniformly.

It is practically observed that on the filter choking product from one side is lifted & other remains unlifted & contains lumps. 

Remove the product trolley, perform Raking & replace or wash the filter to ensure proper suction for uniform lifting & drying.

Dutch Woven Sieve Blocking

The screen or mesh of the FBD product trolley is known as Dutch Woven Screen & if this screen is blocked the product is not lifted uniformly & lumps are produced.

Remove the product trolley, perform the Raking activity & clear or clean the dutch woven screen for uniform product lifting & drying.


Drying in FBD is not always smooth & uniform. Sometimes product lifting issues are observed which results in non-uniform drying so to avoid the issue of non-uniform drying in FBD or fluid bed dryer we use the manual technique which is known as Raking in which we manually mix & break the lumps.

Also Read

Working of fluid bed dryer.

Size Of FBD Mesh

Critical Process Parameters Of FBD

Kevlar Rope For FBD

Application of tray dryers in pharmaceuticals.

Kevlar Rope For FBD

Vertical FBD or fluid bed dryers are frequently used in the pharma sector for drying purposes during wet granulation.