Apparatus for measuring friction inside granular materials — Granular friction analyzer

• A new methodology to measure inherent friction of granular materials.
• ‘Hands-on’ design of a new apparatus for measuring inherent friction is presented.
• A new parameter, GFA-index to assess the inherent friction has also been introduced.
• A possible model to relate inherent friction with average particle size is introduced.

Flow of granular materials is a complex process but it is important to measure, because the flow of granular material during processing, handling and transportation strongly influences the quality of the final product and its cost. Flowability of granular materials depends on the characteristics of the material and on the conditions at which flow is occurring. Existing methods of measuring flowability of powders are described in this paper, and a new methodology is introduced to measure friction between granular materials under pressure induced with uniaxial compression. Apparatus also allows analysis of conditions at which granular material starts to flow when exposed to uniaxial compressive load, i.e., zero-rate flowability. We call the apparatus the Granular Friction Analyzer (GFA).The concept of the GFA was tested by measuring four different materials with different average particle sizes. It was observed that as the particle size decreases so does its zero-rate flowability. This is in agreement with powder literature. Therefore, it can be concluded that in general the GFA method can be a very useful tool to study friction between granular materials and conditions at which the granular material flow initiates, i.e. zero-rate flowability of powders under pressure. However, further improvements are required to increase its sensitivity and accuracy.

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