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Powder Flow Testing with the FT4 Powder Rheometer

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The FT4 employs patented technology for measuring the resistance of the powder to flow, whilst the powder is in motion. A precision ‘blade’, or impeller, is rotated and moved downwards and upwards through the powder to establish a precise flow pattern. This causes many thousands of particles to interact, or flow relative to one another, and the resistance experienced by the blade represents the difficulty of this relative particle movement, or the bulk flow properties. The more the particles resist motion and the harder it is to get the powder to flow, the more difficult it is to move the blade.

Dynamic Methodology

As the blade moves through the sample, the FT4 measures both rotational and vertical resistances, in the form of Torque and Force respectively. It is important to capture both signals as it is the composite of these two values that quantifies the powder’s total resistance to flow.

 

Using the calculation of Work Done, it is possible to represent both the Torque and Force signals as a Total Flow Energy, the energy required to move the blade through the sample from the top to the bottom of the powder column. However, because the values of torque and force are constantly changing, it is necessary to calculate the energy for each small distance travelled. This is the calculation of Energy Gradient, the energy measured for each millimetre of blade travel, expressed in mJ/mm.

Calculating the area under the Energy Gradient curve provides the Total Flow Energy, representing the powder’s resistance to being made to flow in a dynamic state.

Energy Gradient is calculated directly from the measurements of Torque and Force.

Work Done = Energy = (Resistance x Distance travelled).

Energy Gradient = Energy per mm of blade travel

where ‘Resistance’ is the combined Torque and Force

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