Bultmann's Roll Compaction-site
on Dry Granulation

GENERAL PRINCIPLES OF DRY GRANULATION

In the dry granulation process, powder is densified between usually two counter rotating rolls. This results in an (ideally) endless ribbon which is subsequently fed into an external or integrated granulation (milling) unit which mills the ribbons down to the desired granule size.

Figure: General layout of simple roll compactors. External milling equipment is required.

Since usually non free flowing powders are to be processed (otherwise there would not be any need for a dry granulation step and one would consider direct tabletting), the powder which is to be densified has to be conveyed to the area between the rolls (nip area) by a so called tamping auger.
The hardware layout of dry granulation systems can be improved, of course: A combination of two augers might be used, a powder bridge breaker (also known as agitator) can be inserted into the feeding hopper, a small amounts funnel might be attached in order to handle minimum quantities of powder (e.g. during early development) and a granulation unit can be included in the system in order to make the roll compactor a complete dry granulation system.

Figure: Main parts of an advanced granulation system (left: layout, right: production size compactor)