(58b) Predicting Process Performance in Screw Feeders Using Powder Flow Measurements

Authors: 
Freeman, T. - Presenter, Freeman Technology
Yin, J., Freeman Technology Inc
Monington, L., Freeman Technology
Buechi, D., Gericke AG
Weber, T., Gericke AG
Weinekotter, R., Gericke AG
Screw feeders are routinely used to ensure accurate and consistent feeding of powders between stages of a process. Despite widespread use, predicting feed rates typically relies on pre-existing performance information and extrapolation. This can result in the use of equipment that does not meet design requirements, often contributing to sub-specification operation and in extreme cases – complete process failure.

Automated, multi-variate powder characterisation tools provide reliable and comprehensive measurement of a powder’s response to process-relevant conditions. This data can then be correlated with process performance information to improve feeder efficiency and ensure high quality final products at the required rates.

Five powders were run through two different screw feeders, a DIWE-GLD-87 VR (a full flight single-screw feeder) and a DIWE-GZD (a flat-bottomed double-screw feeder) (Gericke AG, Switzerland). These materials were also tested using an FT4 Powder Rheometer® (Freeman Technology Ltd, UK) to evaluate their dynamic flow, bulk and shear properties. Multiple Linear Regression (MLR) analysis was then performed to evaluate the relationships between volumetric feed rate of the screw feeders and rheological properties of the powders.

MLR analysis demonstrated clear relationships between the GLD volumetric feed rate and two dynamic flow properties, Specific Energy (SE) and the Flow Rate Index (FRI). A correlation between GZD volumetric feed rate and Aerated Energy (AE) was also observed. The testing of two additional materials provided further support of these correlations and reinforced the models defined by the MLR analysis.

The two different screw feeders generate very different processing environments and therefore exhibited relationships with different rheological parameters. This emphasises the need for a multi-variate approach to powder characterisation.

This study shows the robust relationships that exist between powder flow properties and the volumetric flow rate delivered by different screw feeders and demonstrates how it is possible to generate a design and operating model that can be used to predict performance in order to optimise productivity.