Powder flow behavior

With an understanding of powder flow behavior and flow properties, segregation can be considered. Ultimately, as material is handled, stored, and transferred, the flow pattern that occurs will dictate how segregated the material will be when fed to downstream equipment. 

Spheroidization and lubrication—In the first step, the entire bicone is tumbled to spheroidize the powder granules through abrasion and the adhesion of fine powder particles, further improving the powder flow behavior. In some processes, a lubricant is also added to enhance the flowability of the powder during future handling steps. 

Characterization of powder flow behavior with the Flexible Wall Biaxial Tester... 

The purpose of this paper is to use the Flexible Wall Biaxial Tester to get more insight in powder flow behavior. This has been done by preparing powder samples and shearing them with constant volume and with eight different types of deformation. Anisotropy is occurring in these samples due to the structure in the powder. It was seen that stresses on opposite walls differ which means that there are shear stresses. It is thought that these are at least partially caused by the powder and not by the tester. This would mean that the principal axes of stress are not in the same direction as the principal axes of strain. 

One fundamental assumption about powder flow behavior is that powder is isotropic. For example the procedure that Jenike developed [1,2] for the characterization of powder flow does only look at strain, stress and porosity or bulk density. The point contact structure of the particles is not included. Feise showed in an overview article [3] that the exclusion of structure can have large influences on the characterization of powders. 

Flow behavior of powders is also of interest in direct compression. It is generally accepted that the flow rate initially increases with particle size, achieves a maximum in the range of 100-400 /um, and then decreases [85]. An excipient that has been well characterized is lactose, which undergoes particle fragmentation when compacted. For a-lactose monohydrate, it has been shown that the... 

In situations where a complete description of the physical behavior of a system is unknown, scale-up approaches often involve the use of dimensionless groups, as described in Chapter 1. Unlike flow behavior in a blender, the flow behavior of powder through bins and hoppers can be predicted by a complete mathematical relationship. In light of this, analysis of powder flow in a bin or... 

In scaling the flow behavior of powders, it is better to rely on first principles and material flow properties, as opposed to reliance on observations or data gleaned from the initial scale. 

Often the production of new materials such as composite materials heavily involves processes at interfaces. Thin films on surfaces are often dominated by surface effects. Examples are latex-films, coatings, and paints. The flow behavior of powders and granular media is determined by surface forces. In tribology, wear is reduced by lubrication which again is a surface phenomenon. 

Improve the flow properties. Powders, especially some food powders, show a poor flow behavior. Often these powders are sticky, hygroscopic and may contain fats, all of which have a negative effect on the powder flow properties. By agglomeration of the powders, the flow properties usually improve substantially. 

Particle sizes combined with shape factors have been the subject of many of the recent studies regarding flow of solids. Sphericity, circularity, surface-shape coefficient, volume-shape coefficient, and surface-volume-shape coefficient are some of the most commonly used shape factors. It is generally accepted that the flowability of powders decreases as the shapes of particles become more irregular. Efforts to relate various shape factors to powder bulk behavior have become more successful recently, primarily because of the fact that shape characterization techniques and methods for physically sorting particles of different shapes are... 

Lee, Y.S.L. Poynter, R. Podczeck, E. Newton, J.M. Development of a dual approach to assess powder flow from avalanching behavior. AAPS Pharm. Sci. Tech. 2000, 1 (3), 1-14 Article 21 (http //www.pharmscitech.com). Taylor, M.K. Ginsburg, J. Hickey, A.J. Gheyas, F. Composite method to quantity powder flow as a screening method in early tablet or capsule formulation development. AAPS Pharm. Sci. Tech. 2000, 1 (3), 1-21 Article 18 (http //www.pharmscitech.com). 

All the behaviors described above have the same effect in varying degrees to result in powder that is compacted more than it would otherwise be. Powders that are particularly susceptible to these influences are ones that are fine and very compressible. Compacted powder can attain higher cohesive strength, and become more difficult to handle. The compacted powder can also become much more prone to adverse two-phase flow behaviors, due to the decrease in permeability that accompanies an increase in density. 

There are three common modes of flow with respect to two-phase (powder interstitial gas) flow behavior ... 

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