Powder Characterization At Low Stress State

Flow and stress fields are drastically different in 3D printers, die filling processes, powder inhalers or at the bottom of a huge silo. Therefore, in the framework of an application, the powder characterization methods have to be selected cleverly among the wide variety of available geometries and applied stresses.

In powder bed based 3D printers, the confining pressure is low, the flow speed is relatively high and the free powder/gas interface plays an important role.

Moreover, the density of the powder bed must be well controlled.

Therefore, GranuDrum is a good candidate to perform flow characterisation in association with GranuPack to measure packing dynamics. The interest of GranuDrum instrument for additive manufacturing has been demonstrated in the framework of a collaboration between KU Leuven and ULiège [1].

The fast die filling process in tableting application requires a good powder flow. As shown by the recent publication of the University of Surrey [2], the laboratory silo GranuFlow is efficient to quantify this flowability.

Moreover, it has been shown previously [3] that our improved version of the repose angle measurement GranuHeap and of the tapped density measurement GranuPack are well adapted for fast and precise pharmaceutical powders characterization.

At the opposite, when the confining pressure is high like in a big silo, the characterisation method should simulate this stress condition and the shear cell is the historical method for such characterisation.

However, the packing dynamics measured precisely with GranuPack gives also valuable information about the powder behaviour when packed.

Moreover, a recent collaboration between Twente University and ULiege [4] have shown that GranuHeap, GranuDrum and shear cell measurements give coherent results from a fundamental point of view. In particular, stretching the shear cell at its lowest pressure and GranuDrum at its lower speed gives the same value for respectively the internal angle of friction and the flowing angle.

In these low confinement pressure conditions GranuDrum is a very versatile instrument giving values that can be connected to applications. For example, GranuDrum has been used by a company producing high quality limestone powders to quantify the dynamic fluidity of highly porous powdered slaked lime [5].

GranuTools offers a range of complementary instruments to cover the needs of all applications in powder technology.

 

Characterization at low stress state

REFERENCES

[1] Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants, G. Yablokova et al., Powder Technology 283 (2015) 199–209 (Ask us for a copy)

[2] Suction filling of pharmaceutical powders, A. Zakhvatayeva et al., Powder Technology 355 (2019) 438–448 (Link of the abstract)

[3] Linking flowability and granulometry of lactose powders, F. Boschini et al., International Journal of Pharmaceutics 494 (2015) 312–320 (Ask us for a copy)

[4] Stretching the limits of dynamic and quasi-static flow testing on cohesive limestone powders, H. Shi et al., Powder Technology 367 (2020) 183–191 (Open Access)

[5] Highly porous powdered slaked lime, Patent WO2017220775A1

Published by Granutools. All rights reserved.
©2020

Leave a Reply

Your email address will not be published. Required fields are marked *

ten + 9 =