Granular discharge and clogging for tilted hoppers

We measure the flux of spherical glass beads through a hole as a systematic function of both tilt angle and hole diameter, for two different size beads. The discharge increases with hole diameter in accord with the Beverloo relation for both horizontal and vertical holes, but in the latter case with a larger small-hole cutoff. For large holes the flux decreases linearly in cosine of the tilt angle, vanishing smoothly somewhat below the angle of repose. For small holes it vanishes abruptly at a smaller angle. The conditions for zero flux are discussed in the context of a {\it clogging phase diagram} of flow state vs tilt angle and ratio of hole to grain size

Tailored granule properties using 3D printed screw geometries in twin screw granulation

Twin screw granulation is becoming increasingly relevant due to its compact size, continuous and robust mode of operation, customizable design, and flexible production capacity. This work describes the experimental study undertaken to understand the dependence of granule properties on the screw element design in a twin screw granulator. A CAD geometry analysis of the free volume in the granulator revealed that there is a direct quantitative correlation between the screw geometry and the maximum size and aspect ratio of the granules obtained using conveying elements. Conveying element geometries with different pitch lengths were 3D printed to generate cost-effective prototypes of the designs. Wet granulation experiments were performed using the 3D printed designs to test the hypothesis that the correlation between the granule shape and maximum granule size and the screw element geometry is predictable a priori. The feasibility of 3D printing method for fabricating new screw element designs is examined. Quality-by-Design strategies and scale-up criteria for twin screw granulation are discussed

Characteristics of Multi-Component Formulation Granules Formed using Distributive Mixing Elements in Twin Screw Granulation

This work examines the influence of pharmaceutical powder formulation characteristics on granule properties formed using distributive mixing elements (DMEs) in twin screw granulation. High and low drug dose formulations with three different active pharmaceutical ingredients (APIs) were considered. The type and concentration of the API in the formulation significantly affected the dry blend particle size distribution and the wet blend dynamic yield strength. However, despite the differences in blend properties, the granule size distributions were not significantly affected by the type of API used. The granule size distributions were solely functions of the liquid-to-solid ratio and the screw element geometry. However, the granule porosities were observed to be dependent on both the liquid-to-solid ratio and the dynamic yield strength of the blends. This work is the first to study the influence of drug loading and API type on the granule attributes produced using distributive mixing elements

Granule breakage in twin screw granulation: Effect of material properties and screw element geometry

© 2017 Elsevier B.V.This study is the first to explicitly measure the influence of material dynamic yield strength (DYS) and screw element geometry on the breakage process in twin screw granulation. Granule breakage is the key mechanism for controlling granule size within the Twin Screw Granulator. Novel experiments which isolated breakage from other granulation rate processes were performed using conveying and distributive mixing element configurations and 2 and 3 mm cylindrical pellets of model materials (DYS from 0.5 to 137 kPa). Daughter size distributions and survivor pellet shape visualization was used to infer that the breakage mechanism in conveying elements (CE) is primarily edge chipping whereas in distributive mixing elements (DME), breakage is a combination of chipping and crushing. The maximum size of granule that could remain unbroken (3.49 mm for CE and 3.18 mm for DME) was determined by the largest available gap size in the element as measured by an analysis of the screw elements' open volume geometry. Below the maximum size, breakage probability varied inversely with granule strength up to 9 kPa. For granules stronger than 9 kPa DYS, breakage characteristics are independent of formulation properties and depend only on screw element geometry. This helps explain why twin screw granulation is more robust with respect to formulation changes compared to high shear wet granulation. Implications for using the results for both optimizing screw element design and calculating kinetic parameters for population balance modeling are discussed