Dry Granulation : an overview

Flow consistency is very critical for some industries, especially those having to very quickly transform a powder, for example in a tabletting machine in pharma industries, or a molding machine in plastics industry. Larger particles tend to flow better and more reliably than fine powder, thus the interest in some applications to granulate the powder, which means enlarging the particle size. Different processes can achieve that but one solution quite simple and worth to consider is dry granulation.

1. What is dry granulation ?

In dry granulation, the particle size of a bulk solid, is increased thanks to a dry compaction step. This compaction is typically done on a roller press.

The powder to granulate is fed through a dosing equipment, for example a screw conveyor, to a roller compactor which is applying a very high pressure to the powder allowing to gain some strength (you can know more about How does the powder stick together when going through a press through this link). At the outlet of the compactor, the material takes the shape of sheets or briquettes.

It is then necessary to reduce the size of those agglomerates in order to have granules of a size significantly larger than the original powder, with higher strength, while being suitable for easy bulk solids handling.

The agglomerates are thus dropped to a granulator which is breaking them down to the desired size. The granules are then classified, the ones having the correct sizes are sent to the new process stage, for example tabletting in the case of a pharmaceutical process, while fines and over-sized are recirculated back to the compactor in order to be granulated again.

The recycling can be done mechanically or with a small pneumatic conveying system.

2. Applications of dry granulation

• Pharmaceutical industry : this is the industry of choice for granulation. Granulation techniques are indeed very often used to reduce the risks of segregation and to facilitate the flow of the bulk solids to a tablet press for instance.

• Plastics industry : similarly to the tabletting in pharma factories, having a reliable flow of materials to molds is critical to make sure the part will be produced as per specification. Dry granulation can bring a simple solution for plastic parts manufacturers.

3.1 Dry Granulation in the Pharmaceutical Industry

Dry granulation is a very important process within the pharmaceutical industry, where precision and consistency are key, where this technique is widely employed to transform fine powders into granules with controlled properties. One significant advantage of the dry granulation process in pharmaceutical applications is its ability to reduce the risk of segregation, ensuring uniform distribution of active pharmaceutical ingredients (APIs) and excipients. This is particularly crucial in tablet manufacturing, where the even distribution of pharmaceutical powders directly affects the quality and efficacy of the final product. By creating granules of controlled size and strength through the dry granulation process, pharmaceutical engineers can facilitate smooth powder flow, enhancing the efficiency of downstream processes like tablet pressing. Dry granulation also minimizes the need for moisture, which can be detrimental to certain pharmaceutical formulations.

3.2 Dry Granulation in the Plastics Industry

In the plastics industry, where precision molding processes have gained a lot of importance, maintaining a consistent flow of material to molds is critical. By granulating plastic powders using the dry granulation process, manufacturers can achieve better control over the flow properties of their materials. This translates to more predictable and reliable molding processes, ensuring that each plastic part meets precise specifications. Whether it's injection molding or extrusion, the granulation of plastic powders enhances their handling characteristics and diminishes the likelihood of issues like bridging or erratic flow.

Source

Preconditioning process powders with dry granulation, Johnson, PBE, 1987