Roll Compactor - A Complete Description

The engineering behind the making of tablets is dry granulation by Roll Compactor. Roll Compactor is an intergral part of pharmaceutical and bulk drug industry. Dry granulation is a process that forces the fine powder into solid compacts or sheets. This is done by a Roll Compactor by passing the fine powder between counter rotating rollers and press.

What is Dry Granulation?

Dry granulation is basically a dry process which does not involve the usage of any liquid. Granulation is nothing but the process in which fine particles i.e., powder are made to cling with each other to form large multi particles called Granules. Hence dry granulation is the process of making multi particle compacts from powder by applying force. This force is provided by the roll compactor.

Construction of Roll Compactor-

The major elements are compacting rollers, charging hopper, feed screw and a sieve. The function of each element of the roll compactor can be anticipated by the process taking place in a roll compactor. The basic aim is to get multi particle granules and sheets as product.

Process of Granulation-

First of all the fine particles or powder is fed to the charging hopper from where it is fed to the compacting zone. The feeding of the powder to the compacting zone is done with the help of vertical feed screw. Then at the compacting zone the compacting rollers press the powder. The compacting rollers force the fine powder into compacts or sheets, also known as chips or flakes. Further these chips or flakes are resized i.e., reduced to desired shape and size using sizing machine. The size of chips or flakes can be controlled by a sieve. Depending upon the sieve size with the help of which different final sizes of compacts can be achieved. A scrapper is provided in order to ensure that the powder is not sticking the rollers.

Now the doubt arises about the thickness of the flakes. As discussed above the lead screw feeds pre defined amount of fine powder in compaction zone. Though amount of powder fed is responsible for the size, gap between the two counter rollers is also a characteristic. Controlling the amount of powder is a bit difficult and hence the thickness of the flakes directly depends on the space between the rollers. On the basis of this gap, the roll compactors are classified into two categories, Variable Gap Roll Compactors and Fixed Gap Roll Compactors. Both of them are almost similar with a difference in the smallest distance between their rollers.

In Fixed Gap Roll Compactor the force applied on the power bed is not constant for every flake. This is because the amount of powder fed into the compaction zone may not be consistent. This results in the fluctuations of properties of the flakes.

In variable or floating gap Roll Compactors, the distance between the rollers keep on changing depending upon the amount of powder fed. This ensures the forces on the granules equal all the time, since thickness is important. Hence this minimizes the fluctuation in the properties of flakes.

Katharine Hurley works with Cemach Limited, The India based manufacturer and exporter of pharmaceutical machineries company offers Roll Compactor, Tablet Press Machine etc.