Overview of Dry Granulation Processes and Equipment Design

With low-dose products, flow and compressibility are relatively minor issues since formulations are essentially placebos. The low percentage of active loading allows for the addition of ample amounts of excipient(s) that possess good flow 

TABLE 6.1 Dry Granulation Manufacturing Process Approaches (1) Blend Mill and (2) High Shear-Dry Blend 

Blend Mill for Dmg A High-Shear Dry Blend for Drug B 

One of the major flaws in dry granulation for low-dose products is the granulation efficiency is lower than wet granulation. The material that bypasses the rolls, referred to as bypass, is the source of the incomplete granulation by roller compaction. Equipment factors that affect bypass in the feed system, roller compaction system and mill system are the focus of the discussion below. 

The most common form of dry granulation is roller compaction. A roller compaction system consists of a feed system which conveys powder between two counterrotating rolls. The powder is drawn between the rolls where a specified force is applied causing the powder to compact into a briquette or a continuous ribbon. The compacted material can then be milled in-fine or collected and milled off-line in a separate processing step (i.e., screening mill). 

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