This document discusses powder flow properties which are important for pharmaceutical manufacturing processes. It defines different types of powder flow and factors that affect flow properties, such as particle size and moisture content. Several methods for measuring flow properties are described, including angle of repose, Carr's index, and shear cell testing. Maintaining consistent powder flow is crucial for uniformity in tablet and capsule production. Proper control and understanding of flow properties can improve process efficiency and product quality.
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Powder flow testing and control
1.
2. Introduction:
Powder flowability is the ability of a powder to flow in a
desired manner in a specific piece of equipment.
Flow of powders may be:
Free-flowing
Non-flowing or Cohesive
Manufacturing of tablets, capsules, filling of powder in container
involves several powder handling steps, including blending,
transfer, storage, and feeding to a press or a dosator.
The inability to achieve reliable powder flow during these steps
can have a significant adverse effect on the manufacture and
release of a product to market.
3. Flow Patterns:
Two flow patterns developed when powder flow from container:
Funnel Flow
Mass Flow
Funnel Flow
• Side wall material
stagnant whereas flow
of funnel- shaped
material take place
• First-in-last-out
• Chance of powder
segregation
• Suitable only for free
flowing powder
Mass Flow
• All of the material is in
motion
• First- in-frist-out
• Minimize segregation
and prevent rat-holing
4. Factors Affecting Powder Flow Properties:
The specific properties of a powder that affect its flow are known as
flow properties.
These flow properties depend upon:
Collective
forces acting on
individual particles
Particle variable
Environmental
condition
Powder or Particle
variables:
• Particle size, Size
distribution, Shape, Surface
texture, Cohesively, Surface
coating, Particle
interaction, Wear or attrition
characteristic, Propensity to
electro-static
charge, Hardness, Stiffness, Str
ength, Fracture toughness
External Factors
influencing Powder
Behaviour:
• Flow rate, Compaction
condition, Humidity, Electro-
static charge, Aeration,
Transportation experience,
Container surface effects,
Storage time
5. Consideration of critical Factor:
Particle Size
Particle Nature
Porosity
Bulk Density
Moisture Content
Interparticle force
Van der Waals
Electrostatic
Surface tension
Interlocking
Friction, etc
During Storage and Transportation
Caking and bridging
Packaging condition
High to low aeration
De-aeration
Consolidation by tapping
6. Powder Flow Problem:
1. Rat-holing
2. Arching
3. Flooding
Prevention of flow problem:
Increased outlet diameter
Reduced filling height powder
Equipment capacity can be reduced
Reduced cohesive strength of powder
Agitation or mechanical assistance can be utilized
7. Measurement of Flow Properties:
1. Angle of repose:
The internal angle between the surface of the pile and the horizontal
surface is known as the angle of repose.
Angle of repose depends upon:
Density
Surface area
Shapes of the particles
The coefficient of
friction of the material
This angle is in the range
0 –90 .
Flow Property Angle of repose (Degrees)
Excellent 25–30
Good 31–35
Fair—aid not needed 36–40
Passable—may hang up 41–45
Poor—must agitate, vibrate 46–55
Very poor 56-65
Very, very poor ≥ 65
8. Angle of repose method used interparticulate friction or resistance
to movement between particles.
Experimental Variable:
Segregation of material
Consolidation
Aeration
Methods for determining the static angle of repose :
Fixed height method
Fixed base diameter method
Tilting box method
Methods for determining the dynamic angle of repose:
Revolving cylinder method
9. Avalanching Tester:
Used to determine dynamic angle of
repose.
MTA (mean time to avalanche)
determine and at the time of
avalanching image was captured.
Aero-Flow™ Automated
Powder Flowability
Analyzer
10. 2. Carr’s Compressibility Index And Hausner Ratio:
Both are determined by measuring the bulk volume and the
tapped volume of a powder.
Compressibility
Index (%)
Flow Character Hausner Ratio
≤10 Excellent 1.00-1.11
11-15 Good 1.12-1.18
16-20 Fair 1.19-1.25
21-25 Passable 1.26-1.34
26-31 Poor 1.35-1.45
32-37 Very poor 1.46-1.59
≥37 Very, very poor ≥1.60
11. 3. Flow Through an Orifice:
Useful only for free-flowing materials.
Two types of flow rate of powder determined:
Mass flow rate
Volume flow rate
Experimental variable:
The type of container
The size and shape of the orifice used
Height of the powder bed
General guidelines for dimensions of the cylinder are as follows:
Diameter of opening > 6 times the diameter of the particles
Diameter of the cylinder > 2 times the diameter of the opening
12. 4. Shear Cell Method:
In the shear cell method, the force necessary to shear the powder
bed by moving the upper ring is determined.
Types of shear cell method:
Cylindrical shear cell
Annular shear cell
Plate-type shear cell
4.1 Brookfield PFT
Choice of Test Options:
Flow Function
Time Consolidation
Test with Flow Function
Wall Friction
Data Output:
Flow factor Index
Arching Dimension
Rat-hole Diameter
Hopper Half Angle
Wall Friction
Bulk Density Curve
13. Flow factor index Flowability
ff<1 Non flowing
1<ff<2 Very cohesive
2<ff<4 Cohesive
4<ff<10 Easy flowing
ff≥10 Free flowing
The standard classification of powder
flowability uses the flow factor index (ff):
It is ideal for manufacturers who process powders daily and want to
minimize or eliminate downtime and expense that can occur when
hoppers discharge erratically or fail to discharge altogether.
Consolidation stress
14. 5. Cohesion Index:
Stable Micro Systems TA.XT Plus texture
analyzer used to determine cohesion
coefficient which is determined by
integrating the negative areas under
the force displacement curve.
Cohesion Index Flow behaviour
≥19 Hardened, extremely
cohesive
16-19 Very cohesive
14-16 Cohesive
11-14 Easy flowing
≤11 Free flowing
A low cohesion index is associated with
non-cohesive free-flowing powders.
15. 6. FT4 Powder Rheometer:
This methodologies allow measurement of:
Flow energy
Shear properties
Bulk properties
The forces causing the deformation and flow is measured.
FT4 flowmeter Downward testing mode Upward testing mode
Calibration and Data Analysis:
The variables are force, torque, height, and rotational and linear
velocities, flow properties determined via extrapolation.
16. Downward Test Mode:
It is used to measure the Basic Flow Energy (BFE)
Upward Testing Mode:
It is used to measure the Specific Energy (SE) which is the flow energy
per gram of powder tested.
17. 7. PTG-S4 Powder Characterization Instrument:
Features:
Fully USP <1174>, EP <2.9.36> and
ISO 4324 (12/83) compliant
Measure flow-time, cone angle,
flowability
PTG-ER stirrer included
Integrated analytical balance cell
Integrated dust protection bonnet
Built-in printer
18. 8. Penetrometry:
The pressure of penetration in Pascal was used
to estimate flow rate.
Particle size should be in the range of
0.250-0.630 mm.
Used for non-consolidated pharmaceutical
powder excipients: sodium chloride,
sodium citrate, boric acid, and sorbitol.
A polynomial quadratic equation was generated using the ratio of
penetration pressure to bulk density, from which the flow rates for the
group of all tested powders could be estimated.
19. Control of powder flow
1. Mucon Iris Diaphragm Valve
2. Powry Valve
3. Vacuum Assisted Powder Flow Nozzle
4. Funken Continuous Auto Feeder
5. Fluidizing Hopper Flow Control Valve
Mucon Valve
Powry Valve
20. Importance of Flow Properties in Pharmacy:
1. Tablet Manufacturing
2. Capsule Manufacturing
3. During Drug Delivery
4. During Mixing and Sieving
5. During Unloading of Packs
6. During Transportation Through Conveyers
7. During Filling of Powders, Dry Suspension and Dry Syrup
21. Conclusion:
Powder flow is a key requirement for pharmaceutical manufacturing
process.
An understanding of the fundamentals of powder flow can steer
one in the right direction to achieve reliable powder flow.
Continuous and even flow of powder during tablet and capsule
manufacturing reduced weight variation, content uniformity (also
hardness in tablet).
Powder flow is also crucial during mixing, packaging, and transportation
Reduction in process costs and maintaining the quality and consistency
of the final product
22. Reference:
1. Jenike, A.W., Storage and Flow of Solids (Bulletin 123 of the Utah
Engineering Experimental Station), 53 (26), (1964, revised 1980).
2. Prescott, J.K., and Barnum R.A., On powder flowability, Pharmaceutica
Technology, October 2000, pp. 60-84 and 236.
3. Prescott, J. K. and Hossfeld, R. J., Maintaining product uniformity and
uninterrupted flow to direct compression tablet presses.
Pharmaceutical Technology, 18 (6), 1994, pp. 99-114.
4. Baxter, Thomas J., “When Powders Flow Like Water: Addressing
Two-Phase Flow Effects in Tablet Press Feed System”, Tablets &
Capsules, March 2009, Volume 7, No. 2, pp. 26-32.
5. Barnum, Roger, Ebb and Flow: Understanding Powder Flow Behavior,
Pharmaceutical Processing, March 2009, pp. 18-21.