Twin screw granulation using conveying screws: Effects of viscosity of granulation liquids and flow of powders

The effects of increasing viscosity of granulation liquid (amount of binder) at varying powder feed rates on properties of granules and surface velocity of powder in Twin Screw Granulator (TSG) with conveying screws only were studied. The surface velocities of the dry and wet formulation powders were obtained using Particle Image Velocimetry (PIV) and Discrete Element Modelling (DEM) simulation. Granulation at both high viscosity of granulation liquid and powder feed rate led to decrease in granule size, voids reduction, increase in strength and compressibility index of granules. The reverse was observed with lowering both viscosity of granulation liquid and powder feed rate. In the PIV study, the dry formulation powder possessed a higher velocity compared to the wet granules. The surface velocity increased with increasing viscosity of granulation liquid and decreased with increasing powder feed rates. The results helped to qualitatively understand the twin screw granulation process.

The powder velocity is higher in area TA than area TB. The powder in TA is pushed by the screw flight towards area I. In area I, the powder velocity drops due to the opposing force from the powder accumulated on the edge of the barrel. The powder from the area I enter TB and moves freely with higher velocity.Figure optionsDownload as PowerPoint slide