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Packing Dynamics
Packing of particles has application in various fields. Therefore, its study is of great importance...
Introduction
Packing of particles has application in various fields. Therefore, its study is of great importance.
The packing dynamics achieved through compaction can characterize powder-forming processes. The packing dynamics is well expressed by the packing density.The packing behavior of powders can be strongly influenced by inter-particle attractive forces of different types, such as adhesion, cohesion etc. The relevance of the different types of attractive interactions for the packing density of powders of different materials and particle size distributions (PSD) is, however, largely uncertain. Therefore, it is a challenging problem to predict the packing density of a certain granular system specified by the particle size distribution and the material properties of the particles (Parteli et al., 2014).
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Characteristics of Packing Dynamics
In powder metallurgical processing techniques, the characteristics of particle packing are of great interest, since the final density obtained depends critically on the initial packing.
The experimental study of random packing was started in early 1960’s by Bernal, with a collection of monosized spherical particles, putting into the cylindrical container [Yen and Chaki, 1992].
Calculation of packing density
The free bulk density and the ability of a powder to increase its density are important parameters for storage, transportation, caking, etc.
The packing density is calculated by the ratio of the mass of particles and volume of the container occupied by the particles.
Formula : Packing density = mass of particles / volume of container occupied by the particles
Tapped density
In order to tightly pack the particle or to increase the packing density, the vessel containing the particles is vibrated by tapping. During tapping, the particles collide with the wall and with the neighboring particles as well, they rebound within the container. The friction coefficients between the particles and between the particle and the wall are used to be different.
According to Scott and Kilgour, the maximum packing density of large vibrated stacks of monosized spheres is 0.639. Such assemblies are called random close packed structures. In practice the fine powders have packing densities less than the random packed structure (rpack<0.639).
Based on above discussion, we can understand that measurement of packing dynamics is a simple test.
However, it has three major drawbacks :
- This measurement is operator dependent because the initial powder volume is influenced by the filling method.
- The volume measurements by naked eyes induce strong errors on the results.
- We completely miss the proper measurement of packing dynamics between the initial and the final value, with this simple method.
An automated tool for packing density measurement (GranuPack)
To eradicate these issues an automated and improved tapped density instrument is developed, which is named as GranuPack. The GranuPack is developed based on the recent fundamental research results. The beauty of this instrument is that it provides repeatable results and the behaviour of the powder is analysed at each successive taps.
For detailed description and principle of the instrument please go through the list of our products (GranuTools products).
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References
[1] Parteli, Eric JR, et al. “Attractive particle interaction forces and packing density of fine glass powders.”, Scientific reports 4 (2014): 6227.
[2] Scott, G. D., and D. M. Kilgour. “The density of random close packing of spheres.”, Journal of Physics D: Applied Physics2.6 (1969): 863.
[3] Yen, K. Z. Y., and T. K. Chaki. “A dynamic simulation of particle rearrangement in powder packings with realistic interactions.”, Journal of Applied Physics 71.7 (1992): 3164-3173.