Granulation of Fine Eggshell Powder to Produce Feedstock Powder for Binder Jetting Additive Manufacturing: Effects of Spraying Pressure and Slurry Feed Rate

ABSTRACT: Eggshell powder is a sustainable calcium carbonate-based material with potential as a feedstock for binder jetting additive manufacturing. However, its irregular particles exhibit poor flowability and powder spreading characteristics. Although spray freeze drying granulation has previously been shown to improve the properties of eggshell powder, the influence of process variables on the resulting granules remains insufficiently understood. This study investigates the effects of spraying pressure and slurry feed rate on the properties of granulated eggshell powder. One-factor-at-a-time experiments were conducted to identify feasible ranges of these process variables, and a full factorial design of experiments with two replications was employed to evaluate the main and interaction effects of spraying pressure and slurry feed rate on particle size and flowability of granulated eggshell powder. Spraying pressure had a statistically significant effect on particle size, whereas slurry feed rate did not significantly affect particle size within the investigated range. Increasing spraying pressure resulted in smaller granules. Powder flowability was evaluated using both the Hausner ratio and repose angle. Both measures showed a significant interaction between spraying pressure and slurry feed rate, indicating that powder flowability depends on the combined effects of these two variables. The findings suggest that spraying pressure is the key variable governing particle size, while the combined influence of spraying pressure and slurry feed rate must be considered when controlling powder flowability. The resulting process–property relationships provide a basis for selecting spray freeze drying conditions for converting eggshell waste into more suitable granulated feedstock for binder jetting additive manufacturing.