This white paper explains the basics of the dry granulation principle with a roller compactor.
Granulation is a process in which powder particles are made to adhere to each other, resulting in larger, multi-particle entities, so called granules. If such a process is performed without adding liquids, this is called dry granulation. In dry granulation, the powder blend is compacted by applying a force onto the powder, which in general causes a considerable size enlargement.
Principally there are two methods to obtain the compacts when using dry granulation: slugging and roller compaction.
If a tablet press is used for the compaction process, the term slugging is used. But since particles with a small particle size do not flow well into the die of a tablet press, the results are weight differences from one tablet (slug) to another. This in turn causes large fluctuations in the forces applied onto the individual slugs, with translates in variations of
the slug’s mechanical strength. Therefore, the properties of these granulates obtained by milling the slugs cannot be controlled well either. This is one of the main reasons why slugging is hardly used any more as a dry granulation method.
A Roller compactor generally consist of three major units:
- A feeding system, which conveys the powder to the compaction area between the rolls
- A compaction unit, where powder is compacted between two counter rotating rolls to a ribbon by applying a force
- A size reduction unit, for milling the ribbons to the desired particle size.