(409b) Packing Dynamics of Polymer Powders at High Temperature

Powder characterization is of huge importance for process improvement. As an example, for Additive Manufacturing, methods based on selective layer melting preheat the powder bed higher than the ambient temperature to decrease the amount of energy needed for the laser irradiation to melt the powder. This is especially the case for polymer powders [1]. However, while environmental conditions are known to influence the powder characterization, measurements are rarely performed at constant humidity and temperature or at the same environmental conditions that the process undergone by the powder. This can lead to inconsistent characterization of the powder behaviours due to seasonal change or high differences between measurement and process conditions. For this reason, powder characterization at controlled environmental conditions would be relevant for process improvement [2].

Packing is a popular method to characterize powder density and flowability. In this work, we investigated how the temperature can influence the packing dynamics of plastic powders. We performed tap density measurement with the GranuPack high temperature. The experimental protocol is the following: a steel tube, in which is poured the powder, performs a succession of free falls of 1mm of height, called “taps”. After each tap, the height of the granular pile is measured by a laser and the bulk density is computed from the knowledge of the tube diameter and the mass of the powder. The bulk density curve as a function of the taps number is then obtained. The temperature of the tube is controlled by a surrounding electrical heating jacket which can heat from ambient temperature to 200°C.

Significative changes between bulk density curves are observed when temperature increases, affecting both the packing range and the packing dynamics. Indeed, we observed that the initial and tapped density after 500 taps, defined as ρ₀ and ρ₅₀₀ , decrease with the temperature. The packing kinematics is generally described by the Hausner ratio Hr=ρ₅₀₀/ρ₀ . We also observe a decrease of Hr as the temperature increases. These results indicate an evolution of particle properties and highlight the importance of temperature for powder characterization.

References

[1] Lumay, G., Francqui, F., Detrembleur, C. and Vandewalle, N., 2020. Influence of temperature on the packing dynamics of polymer powders. Advanced Powder Technology, 31, 4428-4435.

[2] Neveu, A., Francqui, F. and Lumay, G., 2021. Packing dynamics of powders at high temperature. In EPJ Web of Conferences, 249, 12001.