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What is flowability?

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, the compressibility, or the 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, the compressibility, the 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.

 

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

Evaluation of Flowability

Degree

Very Good

Fairly Good

Good

Normal

Not Good

Bad

Very Bad

Sum of Indices

90-100

80-89

70-79

60-69

40-59

20-39

0-19

* Determination of using uniformity or cohesion is based on mean bulk density and sieve diameter 
of the powder sample.

 

 

 

Download-Beginner-Guide-to-Particle-Analysis

Struggling to grasp particle analysis concepts? Our new Beginner's Guide to Particle Analysis is here to help you grasp these concepts in the most accessible manner possible. Download it as a PDF to read on the train, on the plane, or wherever else there’s no internet.

 

 

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In laser diffraction particle size analysis, inaccurate results can be caused by particles agglomerating in the suspension, especially when they are fine. Therefore, a full dispersion of the sample prior to measurement is essential.

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Samples that either dissolve or agglomerate in a wet medium or react with the medium are usually analyzed using the dry dispersion method.

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