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Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Jun. 11, 2022

Even before I explain how a roll compactor for dry granulation machine works, please have a quick overview of the image below:


Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Working principle of roll compactor for dry granulation


To be honest, the principle behind roller compaction technology is simple and straightforward.

As you now know, the process of dry granulation is one that transforms powders into granules without using liquid binders.

This process primarily works by compacting and densifying powders to form granules of desirable shapes and sizes.


But how does it do this?

Below is a step by step process of how roll compactor machines work;


Step 1: Particle rearrangement

The first step of roll compaction is ensuring that you have a perfect blend of powder for compaction.

Here, you’ll have to feed the powder simultaneously into the feeding unit while riding it off the displaced air.


How does this work?

You see, in roller compaction, the materialis often fed into the system using an auger system.

This is to help achieve large mass flow rates of the raw material into the roller system.


 Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Feeding material


Economically, this makes lots of sense.

Now, during compaction process, there is always displaced air that comes from the roller system.

This air cannot escape through the roller nip area.

The only way it can escape is through the feed hopper.

When this happens, it prevents the uniform flow of material into the roller system.

Due to this, most roll compactor machines come with a vent on the side of the feeding hopper.

This vent allows for displaced air to exit from the roller system without disrupting the free flow of material from the hopper to the roller system.


Step 2: Feed of raw material

In this step, raw materials are uniformly and efficiently fed into the feeder unit.

The material will flow from the hopper and into the roller system for compaction.

 

Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Feeding material to the rollers


Depending on the design of the feeding system, the raw powder will be forced down into the two pressure rollers either vertically or horizontally.

All this will depend on the design of the roller and feeding system.


Step 3: Air flows back along the feeding screw

As I have explained in step 1, during compaction, there is often release of air from the powders which have to exit one way or the other.

Since it can’t flow down, it flows back along the feeding screw and out through the displaced air vent as seen in the figure above.


Step 4: Material is forced through to the roller system

Again, there are various types of feeding systems.

Nonetheless, most roll compactor machines use screw feeders which secures a smooth flow of the material from the hopper to the roller systems.

 

Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Roller system


Because of its design, the screw kind of pre-compacts the material while getting rid of trapped air at the same time.

It then feeds the raw material into the nip area of pressure rollers.

Note that screw feeder systems have variable speeds.

This speed has a direct influence on the roller gap and thus on the compaction capacity of the roll compactor.


Step 5: Powder compaction

Here, the roller compactor compacts material that comes in from the feeder system into flakes, ribbons or sheets.

Please note that the surface of the rollers here has a significant influence on the feed characteristic of the product.

Likewise, the variable speed of the rollers also determines the retention time of the material within the compaction area.

So, we’ve said that compaction of powders happens at this stage and in the gap of the two pressure rollers.

The hydraulic system of the machine transmits intense pressure to the rollers, which then facilitates compaction.


Step 6: Crushing of the flakes/ribbons/sheets

Step 5 above produces compacted powder in the form of flakes, ribbons or sheets.

These then come onto the milling system that reduces the granule size and shape into what is appropriate.

Remember that the mill has a sieve.

This separates the powders into large, required and fine particles.

The large particles remain in the mill for further crushing; the required particles are sieved into the next section of the mill.

 

Roll Compactor Working Principle – A Step-by-step Dry Granulation Process

Granules from flakes


The fine particles move to the lower section of the mill where they will be recycled for further compressing.


Step 7: Transfer of the final compacted product

This is the last stage of roller compaction.

Here, the appropriate granule sizes are sieved into the next section of the mill and transferred to the discharge unit.

They are then collected and pack for distribution or for whatever process is next after roll compaction.

So basically, this is the working principle of roller compacter machines.

As you can see, it is not rocket science.

The best part?

Everything is automated.

All you have to do is go to the control panel, key in the appropriate production parameters and let the machine do its job.

 

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