What is flowability of powder?
2023-02-22WIKI
Flowability is used to describe the flow properties of the powder under gravity. The flowability can be simply evaluated using only one parameter, such as the angle of repose, compressibility, and angle of spatula. However, flowability is a property related to various indices, which can be expressed more rigorously as the weighted sum of many parameters associated with powder characterization.
Carr indices method based on the angle of repose, compressibility, angle of spatula, uniformity, and cohesion is a more comprehensive method to evaluate the powder flowability. Uniformity can be calculated by dividing D60 by D10. Cohesion is determined by measuring the mass of powder on each sieve after the vibration of the sample for a specific period of time.
The Carr indices chart of flowability is shown below:
Carr Indices Chart of Flowability
|
Angle of Repose |
Compressibility |
Angle of Spatula |
Uniformity* |
Cohesion* |
|||||||||||
|
Degree |
Index |
Valve |
Index |
Degree |
Index |
No. |
Index |
% |
Index |
||||||
|
≤25 26-29 30 31 32-34 35 36 37-39 40 41 42-44 45 46 47-54 55 56 57-64 65 66 67-89 90 |
25 24 22.5 22 21 20 19.5 18 17.5 17 16 15 14.5 12 10 9.5 7 5 4.5 2 0 |
≤5 6-9 10 11 12-14 15 16 17-19 20 21 22-24 25 26 27-30 31 32 33-36 37 38 39-45 ≥45 |
25 24 22.5 22 21 20 19.5 18 17.5 17 16 15 14.5 12 10 9.5 7 5 4.5 2 0 |
≤25 26-30 31 32 33-37 38 39 40-44 45 46 47-59 60 61 62-74 75 76 77-89 90 91 92-99 ≥99 |
25 24 22.5 22 21 20 19.5 18 17.5 17 16 15 14.5 12 10 9.5 7 5 4.5 2 0 |
1 2-4 5 6 7 8 9 10-11 12 13 14-16 17 18 19-21 22 23 24-26 27 28 29-35 ≥35 |
25 24 22.5 22 21 20 19.5 18 17.5 17 16 15 14.5 12 10 9.5 7 5 4.5 2 0 |
- - - - - - - - - - - ≤6 6-9 10-29 30 31 32-54 55 56 57-79 ≥79 |
- - - - - - - - - - - 15 14.5 12 10 9.5 7 5 4.5 2 0 |
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|
Evaluation of Flowability |
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|
Degree |
Very Good |
Fairly Good |
Good |
Normal |
Not Good |
Bad |
Very Bad |
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|
Sum of Indices |
90-100 |
80-89 |
70-79 |
60-69 |
40-59 |
20-39 |
0-19 |
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Determination of using uniformity or cohesion is based on mean bulk density and sieve diameter of the powder sample.
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