“Flowability” Measurement Terminology

Flowability:

• Defined as the movement of a powder from a stationary to a moving state.  Whereas a free-flowing powder moves consistently and steadily with particles moving independently of one another.

Angle of Repose

• Angle of Repose is the direct indication of the potential flowabilities of a powder sample.

Compressibility

• Compressibility is determined by the relative measurement of loose and packed bulk density.  Any powder sample having more than 20% compressibility may need additional measures to prevent bridge formation in a hopper and/or storage bin.

Angle of Spatula

• Angle of Spatula is an easily determined property that gives a relative angle to of internal friction of a dry powder sample.  A spatula is inserted into the powder heap parallel to the bottom and then lifted up and out of the powder sample.

Cohesion

• Cohesion is the natural attraction of dry powder particles to each other.  It is an indication of the “flowability” of the powder sample.  Care should be taken in designing feeders/hoppers and other handling equipment for powder samples having higher cohesion.

Uniformity

• Uniformity is defined as the ratio of particles of a given sample at the value points of d60 divided by the d10

Each measurement obtained using the Powder Characteristics Test can be converted into a corresponding index number using the Carr “Flowability” chart. The total of four (4) (using either Cohesion or Uniformity) index numbers will indicate the “Flowability” index as defined by RL Carr. Based on the “Flowability” index obtained from the chart the severity of either bridging or compaction of a material can be determined. How to eliminate the compaction of stored materials can be determined by the Flowability values. 

“Floodability” Measurement Terminology

Floodability:

• A floodable powder is characterized by unstable liquid-like flow.  Flooding is caused by the fluidization of a mass of particles by air or other stimuli.  This type of flow is typically uncontrollable and usually undesirable.

Flowability

• Flowability is obtained by using the total index value then converting the index value to a value that will be included in the total floodability value.

Angle of Fall

• Angle if fall is determined after the initial Angle of Repose is disrupted by a defined g-force giving the indication of the floodability of a powder sample.

Angle of Difference

• The Angle of Difference is the calculated difference between the Angle of Repose and the Angle of Fall.  A powder Sample will have a flushing characteristic when this value is great.

Dispersibility

• Dispersibility is the scattering/dusting and/or flushing of a dry powder sample.  In the event the dispersibility is greater than 50% the sample powder will have a HIGH uncontrollable flushing characteristic

Each measurement obtained using the Powder Characteristics Tester can be converted into a corresponding index number using the Carr “Floodability” Chart table. The total of four (4) (use either Cohesion or Uniformity) index numbers will indicate the “Floodability” index as defined by RL Carr.  Based on the “Flood three (3) measurement and the converted Flowability value the sample powder’s Floodability can be determined in addition it can also be determined if measurements to prevent the uncontrollable flushing of the powder will be required.