Powder Flow Properties


The initial and very basic requirement for the existing pharmaceutical and additive manufacturing (AM) industries are powders. Powder properties affect the packing dynamics/efficiency and flowability. Therefore, the recent and new techniques developed by GranuTools for the measurement of flow properties have draw attention nowadays. Few such flow properties and techniques are powder spreadability, dynamic and static angle of repose, packing, flowability, and electrostatic charge.


Flow properties of powders are basically mechanical properties. The behaviors of bulk powders are very much similar to the non-Newtonian fluids due to its plastic flow and dilatancy. The iteration of particles is influenced by the attractive forces, such as van der waals, particle size, shape, porosity, moisture content and bulk density.


Very fine particles possess attractive forces such as van der waals, electrostatics, surface tension etc. and resulting cohesion of powder and poor flow properties. As particle size increases, flow of the powders also increases and after certain level works as free flowing. Appropriate blend of coarse and fine particles or in other words selection of particle size distribution improves the flow properties.


Smooth surface of particle increases the flow properties, however the rough surface is the reason of poor flowability due to friction.  Flat and elongated particles give high porosity and low flow property. In contrast, high density and low porosity provide good flow property. Powder flow properties can be improved by processing the granules in spherical shape.


The higher the amount of moisture, greater the risk of cohesion and adhesion. The GranuMidity is one such instrument, which can help to understand the influence of moisture on the powder flow properties such as electrostatic charge. Incorporating optimum flow additive, such as magnesium stearate, talc etc. improves the powder flowability.


GranuTools has developed instruments, which help to quantify the powder flow properties.

For free flowing and cohesive powders, the GranuDrum and the GranuHeap instrument measure the Angle of Repose. The flowing angle is influenced by a wide set of parameters: the friction between the grains, the shape of the grains, the cohesive forces (van der Waals, electrostatic and capillary forces) between the grains. The beauty of these instruments is that GranuDrum measures the dynamic angle of repose and GranuHeap measures static value.


The same two instruments (the GranuDrum and the GranuHeap) measure the dynamic and static values of cohesive index.


In addition, the GranuDrum helps to quantify the powder based on the spreadability parameter.


The GranuPack is an instrument, which help to know the free to tapped bulk density (compressibility) of different powders. Packing of powders is a quasistatic process and it is related to the flow rate, cohesiveness, and particle size of the powders. Carr Index (Cr) and Hausner ratio (Hr) are two parameters, which can also be calculated by this instrument.


For flowability of powder, GranuTools has developed an instrument named the GranuFlow, which measures the powder flow through different aperture and help us to quantify the Dmin.


The beauty of the GranuTools instruments is that they provide a wide range of data set for each measurement. For an example, the GranuDrum provides cohesive index and Angle of Repose for each rpm, which ranges from 2-70 rpm. Similarly, the GranuPack provides tapped density after each and every tap, up to the desired number of taps.

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