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3117 > flow_3 > Flashcards

flow_3 Flashcards

1
Q

flow testing methods

A
  1. angle of repose
  2. orifice flow
  3. tap density
  4. avalanche flow
  5. powder rheometer
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2
Q

reason for poor powder flow

A
  1. surface forces
  2. inter-particle friction
  3. interlocking of particles
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3
Q

what are cohesion and adhesion due to

A
  1. non-specific van der waals forces
  2. moisture
  3. electrical charge
  4. particle size
  5. contact sites
  6. time of contact
  7. crystalline bridges
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4
Q

cohesion

A

sticking together of particles of the same substance

adhesion

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5
Q

adhesion

A

sticking together of dissimilar particles or surface

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6
Q

overcoming flow issues

A
  1. container (hopper)- improve design
  2. conveyance- paddle, auger, suction: type and design
  3. formulation- add glidant, lubricant
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7
Q

powder flow problems

A
  1. arching (bridging)

2. ratholing

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8
Q

what is arching

A

an arch-shaped obstruction forms above discharge outlet and prevents flow. It may be due to mechanical interlocking of large particles forming an arch, or a cohesive arch when particles bond together

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9
Q

potential problem of arching

A

will be significant when outlet is less than 6-10 times the maximum particle size of particles

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10
Q

what is ratholing

A

occurs when discharge takes place only in central flow channel located above the outlet, the cohesive material outside channel will not flow and may cake or agglomerate

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11
Q

what are gildants

A

additives that are added to improve flowability of powders or granules; require a certain concentration range for optimal activity, excess may be detrimental

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12
Q

mechanism of action of glidants

A
  1. ball bearing effect : correct surface irregularity and rolling action
  2. reduce interparticulate friction
  3. reduce surface change
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13
Q

how does ball bearing effect work

A

associated with the rolling effect of small spherical particles, decreasing friction due to rough surfaces by physical separation (eg. starch)

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14
Q

effect of reducing friction

A

fine gildant powders will coat larger host particles thereby increasing separation distance between the large particles and hence, reduce interparticulate attractive forces (van der waals forces) (eg. fumed silica)

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15
Q

angle of repose

A

angle of inclination of a heap of powder carefully built up by dropping material (usually through an appropriate sieve), through a funnel onto a horizontal plate

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16
Q

angle of fall

A

angle of repose of a heap of material obtained after the application of certain shock (eg. tap 3 times)

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17
Q

angle of difference

A

difference between the angle of repose and angle of fall

18
Q

angle of spatula

A

angle of slope made by a powder heap formed on a spatula when inserted into a powder bed and lifting up

19
Q

relationship of angle of repose to flow

A

lower angle, better flow

< 35 degree: free flowing
>45 degree: poorly flowing

20
Q

Factors to consider during measurement

A
  1. no vibration at measurement site
  2. ensure elvel and horizontal plane
  3. conditioned surface characteristic of base
  4. funnel type and diameter (no arching)
  5. constant material moisture content
  6. controlled ambient humidity
  7. no particle fragmentation
  8. accurate of measurement (< +2%)
21
Q

volumetric flow

A

using a fixed volume of powder

22
Q

gravimetric flow

A

using a fixed weight of powder

23
Q

orifice flow

A

flow of known quantity of material through an orifice of known opening size

24
Q

how is flowability reported with orifice flow

A

reported as time required for known quantity (mass or volume) of material to flow through orifice

25
Q

tapping method

A
  1. sieve powder into cylinder
  2. remove excess, level
  3. weigh
  4. put on tapping machine
  5. tap to constant volume
26
Q

how does tapping reflect flow

A

the lower the hausner ratio/ carr index , the better the flow

27
Q

how to count hausner ratio

A

tapped density/ bulk density

28
Q

how to find carr index

A

measure compressibility index

(tapped -bulk density) / tapped density x 100

29
Q

how to eradicate powder history

A

conditioning process involves gentle loosening and slight aeration of powder. this is to disturb and gently drop each particle in order to construct a homogenously packed powder bed, removing any precompaction or excess air and ensure the results from the following test are independent of powder hx

30
Q

basic flowability energy BFE

A

is a measure of the powder’s flowability when forced to flow, such as through a screw feeder or in an active feed frame

  • measured during the downward blade movement
  • forced/ confined flow
31
Q

specific energy SE

A

measure of the powder’s flowability when unconfined, such as during low stress filling, or low shear blending

  • resistance to flow is measured as blade transverse from bottom to top
  • slow stress/ unconfined flow
32
Q

revolution powder tester

A

determine avalanche flow characteristics

33
Q

what can the revolution measure

A
  1. flowability of powders in low stress situations
  2. study how powder behaves once it is flowing
  3. determine the condition of powder as it moves through process
34
Q

shear cell

A

splits horizontally, forming shear plan between lower stationary base and upper moveable portion and could provide information regarding flowability via a number of indices

35
Q

shear cell data

A

measure flow factor, more suitable for cohesive material

36
Q

schulz rotational shear cell tester

A

annular type, well established test method

37
Q

brookfield rotational shear cell tester

A

annular type

  • most recent commercial shear tester
  • most automated with minimum operator contact
38
Q

FT4 rotational shear cell tester

A
  • rotational type shear tester
  • relatively new equipment
  • equipment has other capabilities for bulk characterization
  • quick operation
39
Q

what are particles responsible for?

A
  • flow
  • packing
  • mechanical strength
  • solubility
40
Q

methods of size reduction

A
  1. hammer mill
  2. pin mill
  3. cone mill
  4. fluid energy / jet mill <10 micrometer
41
Q

particle production methods

A
  1. crystallization
  2. milling
  3. spry drying/ spray congealing
  4. compact and mill
  5. fluid bed coating

3117 (15 decks)

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