XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1085
some cases required. A roller press, either in a comminution
or agglomeration application, requires gap and pressure
measurements to be taken not only for control purposes
but to also ensure a safe operation. Furthermore, bearing
temperature, drive torque and motor current, as well as
vibration data, are also recorded. If screw feeders with vari-
able speed drives are installed, frequency measurement is
also used to better control feeding behavior.
In a typical production setting, process conditions can
vary such as the material, ambient temperature, or the mix-
ing of the fresh and recycled feed can fluctuate, depend-
ing on filling level of intermediate hoppers. Existing signals
can be utilized in combination with mathematical models
of the compressive behavior between the roller gap. This
creates multipurpose use-cases for the sensors as digital
helpers. Therefore, two important model approaches are
described below.
Maximum Compression Force Calculation
Schönert (1985) describes a simple way of calculating the
pressure curve along the angular distribution in high pres-
sure grinding rolls. Using the given roller dimensions and
the known applied force of the hydraulic pistons, the maxi-
mum pressure spot of the distribution profile, pmax, can be
obtained as follows:
pmax c DL
F 1
F 0 a =(1)
where:
cF =Material specific factor
α0 =Compression angle
F =Grinding /compacting force
D =Roller width
L =Roller length
cF is a material specific factor leveraging medium to highest
pressure. The angle, α0, is geometrically dependent on the
proportion of gap size to roller diameter and additionally
depends on the density of the material.
D
2s 1n
feed
flake
0 a t
t
=-d (2)
where:
s =Operating gap size
ρflake =Apparent flake density
ρfeed =Feed bulk density
Pressure Distribution in Angular Direction
For the detailed curve progression of the angular pressure
profile in roller presses, several works are available from work
conducted in the field of compaction. Hermann (1973)
gives an overview of several modeling methodologies. One
of the earliest formulations came from Katashinskii in
1966 and is based on experimental data concerning metal
powders. Another still commonly utilized approach was
described by Johanson (1965). Below, the model equa-
tions for the Johanson model will be shown briefly without
focusing on the derivation. The calculation is based on the
Jenike-Shield flow criterion and splits the compression in
the roller gap into two sections or zones, slip and no slip.
A graphical representation of the pressure gradient in both
zones is shown in Figure 5.
The first is the slip zone. The input parameters for the
model calculation consist of the angle of the internal flow,
φe, the wall friction angle, φR, and the compressibility
Figure 4. Schematic graphic of the axial pressure distribution
after Lubjuhn
Figure 5. Pressure gradient dependent on angular position
within the roller gap after Johanson (1965)
some cases required. A roller press, either in a comminution
or agglomeration application, requires gap and pressure
measurements to be taken not only for control purposes
but to also ensure a safe operation. Furthermore, bearing
temperature, drive torque and motor current, as well as
vibration data, are also recorded. If screw feeders with vari-
able speed drives are installed, frequency measurement is
also used to better control feeding behavior.
In a typical production setting, process conditions can
vary such as the material, ambient temperature, or the mix-
ing of the fresh and recycled feed can fluctuate, depend-
ing on filling level of intermediate hoppers. Existing signals
can be utilized in combination with mathematical models
of the compressive behavior between the roller gap. This
creates multipurpose use-cases for the sensors as digital
helpers. Therefore, two important model approaches are
described below.
Maximum Compression Force Calculation
Schönert (1985) describes a simple way of calculating the
pressure curve along the angular distribution in high pres-
sure grinding rolls. Using the given roller dimensions and
the known applied force of the hydraulic pistons, the maxi-
mum pressure spot of the distribution profile, pmax, can be
obtained as follows:
pmax c DL
F 1
F 0 a =(1)
where:
cF =Material specific factor
α0 =Compression angle
F =Grinding /compacting force
D =Roller width
L =Roller length
cF is a material specific factor leveraging medium to highest
pressure. The angle, α0, is geometrically dependent on the
proportion of gap size to roller diameter and additionally
depends on the density of the material.
D
2s 1n
feed
flake
0 a t
t
=-d (2)
where:
s =Operating gap size
ρflake =Apparent flake density
ρfeed =Feed bulk density
Pressure Distribution in Angular Direction
For the detailed curve progression of the angular pressure
profile in roller presses, several works are available from work
conducted in the field of compaction. Hermann (1973)
gives an overview of several modeling methodologies. One
of the earliest formulations came from Katashinskii in
1966 and is based on experimental data concerning metal
powders. Another still commonly utilized approach was
described by Johanson (1965). Below, the model equa-
tions for the Johanson model will be shown briefly without
focusing on the derivation. The calculation is based on the
Jenike-Shield flow criterion and splits the compression in
the roller gap into two sections or zones, slip and no slip.
A graphical representation of the pressure gradient in both
zones is shown in Figure 5.
The first is the slip zone. The input parameters for the
model calculation consist of the angle of the internal flow,
φe, the wall friction angle, φR, and the compressibility
Figure 4. Schematic graphic of the axial pressure distribution
after Lubjuhn
Figure 5. Pressure gradient dependent on angular position
within the roller gap after Johanson (1965)