Bulk Powder Properties

Question 1

What are ‘Loosely packed powders’

Answer 1

They contain a maximum of airspace between particles and minimum of contact points

Question 2

What are ‘tightly packed powders’

Answer 2

Minimum air entrapped & maximum interparticulate contact

Question 3

What does porosity mean

Answer 3

Relative amount of air entrapped between particles

Question 4

What does porosity depend on ?

Answer 4

Shape and size

Question 5

Determination of Tapped Density

Answer 5

• Powders placed in cylinder on tapping volumeter
• Tapped until Volume constant
• Rotating Cam at base lifts cylinder then drops it down
• During the fall particles will have all interparticulate forces removed and rearrange position
• Final Volume = Minimum bulk volume or ‘tapped Volume’ = Vt
• recipricol values will be ‘maximum bulk density’ or
  ‘tapped density’ ρt.
  use to measure dynamic powder packing i.e. monitor change of packing density with time (no. of taps)

Question 6

What is the equation for Carr’s Compressibility Index?

Answer 6

Carr’s compressibility index (%) =
(Tapped density – bulk density) x100
————Tapped density————

Aka: (Initial volume – final tapped volume) x100
—————Initial volume—————

Question 7

What do Interparticulate forces give?

Answer 7

• Larger difference between poured and tapped densities
• increase in number of taps required to give tightest packing state

Question 8

What does Carr’s Compressibility Index and Hausner Ratio use to estimate what?

Answer 8

• use powder packing data to estimate powder flow

Question 9

What is the Equation for Hausner Ratio.

Answer 9

Tapped Density
——Powder Density——

Question 10

What does a value less than 1.25 Indicate?

Answer 10

Indicates Good flow = 20% Carr

Question 11

What does a value greater than 1.5 Indicate?

Answer 11

Indicates poor flow = 33% Carr

Question 12

What does the angle of repose apply to?

Answer 12

Applies to only free flowing materials

Question 13

The rougher and more irregular surface of particles means what?

Answer 13

Higher the angle of repose

Question 14

What do lower values of angle of repose indicate

Answer 14

They indicate better flow Characteristics

Question 15

What are the angles and what kind of flow does it have?

Answer 15

Less than 20 degrees = Excellent Flow
20-30 degrees = Good Flow
30-34 degrees = Pass Flow
Greater than 40 Degrees = Poor Flow

Question 16

What are the two main types of flow through orifice from hopper?

Answer 16

-Funnel Flow
-Mass Flow

Question 17

Describe Funnel flow

Answer 17

• some powder remain stationary
• Rat holing occurs
• Typical in hoppers with shallow angle of orifice
• Stagnant powder may cause segregation & powder remains in hoppers