Characterising powder flow properties – the need for a multivariate approach

Despite their widespread and well-established use, powders are challenging materials to work with, as evidenced by the common problems encountered during storage and processing, as well as in the quality and consistency of final products. The diverse range of unit operations used to handle and manipulate powders subject them to extremes of stress and flow regimes; from the high stress, static conditions present in hoppers to the dispersed, dynamic state of a fluidised bed dryer. It is therefore possible for a powder to behave a certain way in a given unit operation, but entirely differently in another. Many existing powder testing techniques don’t deliver the required information as the test conditions do not represent the conditions in the process. Modern powder rheometers generate process relevant data by accurately measuring dynamic flow, bulk and shear properties. This approach enables a powder’s response to aeration, consolidation, forced flow and changes in flow rate to be reliably quantified thereby simulating the conditions which a powder will be subjected to in process. This paper provides an introduction to powder rheology, including a comparison with traditional techniques, and uses case studies to demonstrate how powder rheology can be applied to optimise production processes and enhance product qualit

Characterising powder flow properties – the need for a multivariate approach

Despite their widespread and well-established use, powders are challenging materials to work with, as evidenced by the common problems encountered during storage and processing, as well as in the quality and consistency of final products. The diverse range of unit operations used to handle and manipulate powders subject them to extremes of stress and flow regimes; from the high stress, static conditions present in hoppers to the dispersed, dynamic state of a fluidised bed dryer. It is therefore possible for a powder to behave a certain way in a given unit operation, but entirely differently in another. Many existing powder testing techniques don’t deliver the required information as the test conditions do not represent the conditions in the process. Modern powder rheometers generate process relevant data by accurately measuring dynamic flow, bulk and shear properties. This approach enables a powder’s response to aeration, consolidation, forced flow and changes in flow rate to be reliably quantified thereby simulating the conditions which a powder will be subjected to in process. This paper provides an introduction to powder rheology, including a comparison with traditional techniques, and uses case studies to demonstrate how powder rheology can be applied to optimise production processes and enhance product qualit

Correlating polyamide powder flowability to mechanical properties of parts fabricated by additive manufacturing

The research was carried out in collaboration with Freeman Technology Ltd. and Micromeritics UK. open access articleThis study investigates the relationships between the flow properties of five blends of polyamide 12, with the mechanical and physical characteristics of the fabricated components. The bulk properties and flowability of the powder blends were characterised using powder rheology. Absolute, or skeletal volume of 3D printed cubes were measured using helium pycnometry. The tensile behaviour and surface hardness of specimens fabricated from the five blends were determined. The mechanical properties of the samples were correlated with the flow behaviour of the powder used. Comparison of the powder flow measures with the mechanical properties of the fabricated parts allows for prediction of final product quality prior to printing. Understanding the relationships between these parameters helps to identify and develop powders that enhance both process efficiency and the mechanical properties of the final product

Correlating polyamide powder flowability to mechanical properties of parts fabricated by additive manufacturing

This study investigates the relationships between the flow properties of five blends of polyamide 12, with the mechanical and physical characteristics of the fabricated components. The bulk properties and flowability of the powder blends were characterised using powder rheology. Absolute, or skeletal volume of 3D printed cubes were measured using helium pycnometry. The tensile behaviour and surface hardness of specimens fabricated from the five blends were determined. The mechanical properties of the samples were correlated with the flow behaviour of the powder used. Comparison of the powder flow measures with the mechanical properties of the fabricated parts allows for prediction of final product quality prior to printing. Understanding the relationships between these parameters helps to identify and develop powders that enhance both process efficiency and the mechanical properties of the final product

The influence of roller compaction processing variables on the rheological properties of granules

This study is part of an ongoing project to enable the full specification of the Design Space for roller compactor systems and shows how the processing parameters influence the behaviour of the product granulate from a placebo formulation. Granulate was produced using a proprietary roller compactor by varying the compaction pressure and gap width, and the dynamic, bulk and shear properties of the resultant granulates were measured. The results demonstrate several rheological properties of the granulate, which have been shown to be closely correlated with variance in die filling and tablet strength, and are predictably influenced by the processing parameters