Study Set Content:
26-31
Poor
>= 38
Very very poor
1-1.11
Excellent
1.12-1.18
Good
1.19-1.125
Fair
1.35-1.45
Poor
1.26-1.34
Passable
>=1.60
Very very poor
1.46-1.59
Very poor
A bulk powder is somewhat analogous to a non-Newtonian liquid, which exhibits plastic flow and sometimes dilatancy, the particles being influenced by attractive forces to varying degrees.
Fluidity
Powders may be
free-flowing or cohesive
Factors affecting flow properties:
Particle size • Shape • Surface tension
With relatively small particles (less than 10 µm), particle flow through an orifice is restricted because the cohesive forces between particles are of the same magnitude as
gravitational forces.
Poor flow may result from the presence of moisture, in which case drying the particles will reduce the
cohesiveness.
Elongated or flat particles tend to pack, albeit loosely, to give powders with a
high porosity
Particles with a high density and a low internal porosity tend to possess
free-flowing properties.
Measure the frictional forces in a loose powder.
Angle of Repose:
Maximum angle possible between the surface of a pile of powder and the
horizontal plane.
The rougher and more irregular the surface of the particles, the (blank) will be angle of repose.
higher
With increasing departure from the spherical, the angle of repose increased while the bulk density and flowability
decreased
