10 Dynamics of Separation Characteristics of Sieving and Flow …
351
air
Air
eff
Effective
f
Fines
G
Coarse
A
Feed
25
Particle size related to T(x) = 0.25
50
Mean particle size
75
Particle size related to T(x) = 0.75
3
Mass-weighted
t
Cut particle size related to T(x) = 0.50
v
Volume equivalent
area-equivalent
Projection area equivalent
perimeter-equivalent Projection perimeter equivalent
r
Rebound
i
Approach
0
Initial
imp
Absolute normal impaction
rad
Radial
tan
Tangential
rel
Relative
w
W a l l
kin.
Kinetic
1 Introduction
Dry classification processes are employed in powder technology for the separation
of outsize particles (e.g. following milling) as well as for the production of narrow
fractions. They can be divided into flow and sieving classification processes. In this
chapter, the classification processes of deflector wheel separation for fine particles
and sieving for coarser particles are treated. In spite of their broad use, the physical principles, which need to be taken into account for an optimized layout of the
processes, are still not completely understood.
In sieve classification, the collision processes take place between the sieve wires
and the particles of the collective. With the successful transport of the particles
across the meshes a fractionation in two or more specific size classes is obtained.
The passing probability depends in particular on the particle properties (e.g. size,
form, orientation), sieve geometry (mesh size and form, sieve inclination) and operational parameters (loading, frequency, amplitude), respectively [1]. For the steady
state sieve classification process models have been presented by Plitt [2], Rogers [3],
Molerus [4] and Trawinski [5] while for the instationary process additional models
were provided by Soldinger [6], Deghani [7], Nakajima and Whiten [8, 9] and Hatch
351
air
Air
eff
Effective
f
Fines
G
Coarse
A
Feed
25
Particle size related to T(x) = 0.25
50
Mean particle size
75
Particle size related to T(x) = 0.75
3
Mass-weighted
t
Cut particle size related to T(x) = 0.50
v
Volume equivalent
area-equivalent
Projection area equivalent
perimeter-equivalent Projection perimeter equivalent
r
Rebound
i
Approach
0
Initial
imp
Absolute normal impaction
rad
Radial
tan
Tangential
rel
Relative
w
W a l l
kin.
Kinetic
1 Introduction
Dry classification processes are employed in powder technology for the separation
of outsize particles (e.g. following milling) as well as for the production of narrow
fractions. They can be divided into flow and sieving classification processes. In this
chapter, the classification processes of deflector wheel separation for fine particles
and sieving for coarser particles are treated. In spite of their broad use, the physical principles, which need to be taken into account for an optimized layout of the
processes, are still not completely understood.
In sieve classification, the collision processes take place between the sieve wires
and the particles of the collective. With the successful transport of the particles
across the meshes a fractionation in two or more specific size classes is obtained.
The passing probability depends in particular on the particle properties (e.g. size,
form, orientation), sieve geometry (mesh size and form, sieve inclination) and operational parameters (loading, frequency, amplitude), respectively [1]. For the steady
state sieve classification process models have been presented by Plitt [2], Rogers [3],
Molerus [4] and Trawinski [5] while for the instationary process additional models
were provided by Soldinger [6], Deghani [7], Nakajima and Whiten [8, 9] and Hatch