The dry granulation process

Dry granulation is a systematic process. That means it occurs through a series of steps starting from the preparation of the material to the final blending of the granules. In each step, there are control measures used to ensure that the technique works as expected. Let us learn more about these steps.

Preparing the Material

One thing to keep in mind is that dry granulation is not only used in the pharmaceutical industry but also across multiple industries. It is just that pharma is among the pioneers of the technique. Also, this article primarily focuses on dry granulation in the pharmaceutical industry

The process starts with the preparation of the dry powder that will be fed into the compressor or compaction unit. A lot can go on in this preparation.

To start with, the active ingredient in the powder is mixed with excipients - inert compounds that facilitate dry granulation.

After the active ingredients and the excipients are mixed, they are blended in special grinders to produce a homogeneous powder. This powder is then fed into the specific machine for the agglomeration to occur.

Feeding the Compaction Unit

Compaction is defined as the use of force to pack matter tightly. This is the step in the process that matters the most.

Dry granulation can be carried out using various techniques. The most widely used in pharma are slugging and roller compaction.

Slugging and roller compaction are initial steps that produce large tablets that will then be milled in the next step to produce the individual granules. In slugging, the large tablets are typically referred to as slugs. They measure about 20 mm in diameter and 15 mm in thickness.

Roller compactors form long ribbons using two rollers that rotate in opposite directions. We will elaborate more about how this works in another section of the article.

Milling Process

The actual granulation of the dry powder occurs in this step. Milling involves the breakdown of the slug and the long ribbons into small granules.

In most cases, the machine that mills the compacted powder into granules is the same that makes the ribbons and slugs. This means that the machines usually have multiple functions. This design decision is made to maximize efficiency and promote productivity.

Final Blending

At the milling step, most of the work is usually done. However, in some cases, a final blend is needed. This blend can involve the addition of other excipients in the granules. It is meant to improve the qualities of the granule compounds.