1088 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
will allow for higher flake densities. Within the range of the
conducted experiments, the operating gap size is shown to
have a larger influence on flake density in comparison to
the compacting pressure.
This shows the importance of uniform operating pres-
sure and gap size, both of which must be monitored and
guaranteed within a fitting control system. One possibility
is to control the feeding system with a preset gap setting. A
PID controller is used to regulate the volumetric flow of the
bulk material via a screw feeder that pushes material into
the roller gap. In combination with the knowledge from the
spring curve of the hydraulic-pneumatic system, the roller
press can operate with the desired operating settings. IIoT
benchmarks are also used to compare various plant setups
and provide optimization background for machines operat-
ing under subpar process conditions.
pmax-Control
In comminution, Schönert’s compression theory can be
used for control purposes as well. In operation, the pmax
value is dependent upon the roller gap and compression
force (see equations (1) and (2)). Figure 9 shows two flake
samples under an x-ray scan. The samples were formed by
two different gap settings within a particle bed. Particle size
analysis of the product from the piston and die test shows
a higher concentration of fine particles in the smaller par-
ticle bed (Heinicke, Kühnel). This effect can be described
as the result of force action lines within the bulk material
bed, which lead the stress towards the edge of the gap, thus
reducing the applied force to the particles in the middle of
the roller. Therefore, the grinding effect is limited in this
area.
In general, it can be said that the gap formed in
between the rollers of high-pressure grinding machines is
linked to the applied pressure and the feed material. As the
feed material is not constant, fluctuations will occur thus,
changing the applied pressure to the material. Consequently,
a control loop is implemented focused on the pmax value,
and this enables consistent energy transfer from the main
drive into the material volume being processed within the
working gap. Additionally, the comparison via IIoT remote
data analysis for variable plant setup is a major tool for the
optimization of the grinding effects within the roller press.
With regards to the importance of roller surfaces and their
negative reaction to high applied pressures, which may lead
to material cracking on the surface, the pmax control can
be used in this regard to assist in the safe operation of the
machine. As mentioned previously, material abrasion will
contribute negatively to the wear of the roller surface, and
more specifically high pressure can lead to surface damage.
Utilizing the pmax control loop mitigates these effects while
maintaining safe operation of the machine.
Gap Oscillation for Glazing Detection in Roller
Compaction
Depending on the material properties and process settings,
undesirable effects can occur on the surface of the rollers
within potash compaction. One instance of this is known
as “glazing” of the roller surface, where undesired material
will stick to the surface of the roller. A layer of material
starts to cover the surface in one region of the profiled roller
and will continue to accumulate if action is not taken. This
process is mainly dependent on the material properties,
ambient temperature and the set compacting pressure. In
summer, for example, glazing is more likely to occur due
to higher ambient temperatures. With time, the sticking
material starts to cover more of the roller surface until it
eventually covers the entire compaction area. Because the
material layer has a certain thickness, the actual working
gap is now much smaller in the compression zone and is
Figure 9. Powder status in small and wide gap according to Heinicke
will allow for higher flake densities. Within the range of the
conducted experiments, the operating gap size is shown to
have a larger influence on flake density in comparison to
the compacting pressure.
This shows the importance of uniform operating pres-
sure and gap size, both of which must be monitored and
guaranteed within a fitting control system. One possibility
is to control the feeding system with a preset gap setting. A
PID controller is used to regulate the volumetric flow of the
bulk material via a screw feeder that pushes material into
the roller gap. In combination with the knowledge from the
spring curve of the hydraulic-pneumatic system, the roller
press can operate with the desired operating settings. IIoT
benchmarks are also used to compare various plant setups
and provide optimization background for machines operat-
ing under subpar process conditions.
pmax-Control
In comminution, Schönert’s compression theory can be
used for control purposes as well. In operation, the pmax
value is dependent upon the roller gap and compression
force (see equations (1) and (2)). Figure 9 shows two flake
samples under an x-ray scan. The samples were formed by
two different gap settings within a particle bed. Particle size
analysis of the product from the piston and die test shows
a higher concentration of fine particles in the smaller par-
ticle bed (Heinicke, Kühnel). This effect can be described
as the result of force action lines within the bulk material
bed, which lead the stress towards the edge of the gap, thus
reducing the applied force to the particles in the middle of
the roller. Therefore, the grinding effect is limited in this
area.
In general, it can be said that the gap formed in
between the rollers of high-pressure grinding machines is
linked to the applied pressure and the feed material. As the
feed material is not constant, fluctuations will occur thus,
changing the applied pressure to the material. Consequently,
a control loop is implemented focused on the pmax value,
and this enables consistent energy transfer from the main
drive into the material volume being processed within the
working gap. Additionally, the comparison via IIoT remote
data analysis for variable plant setup is a major tool for the
optimization of the grinding effects within the roller press.
With regards to the importance of roller surfaces and their
negative reaction to high applied pressures, which may lead
to material cracking on the surface, the pmax control can
be used in this regard to assist in the safe operation of the
machine. As mentioned previously, material abrasion will
contribute negatively to the wear of the roller surface, and
more specifically high pressure can lead to surface damage.
Utilizing the pmax control loop mitigates these effects while
maintaining safe operation of the machine.
Gap Oscillation for Glazing Detection in Roller
Compaction
Depending on the material properties and process settings,
undesirable effects can occur on the surface of the rollers
within potash compaction. One instance of this is known
as “glazing” of the roller surface, where undesired material
will stick to the surface of the roller. A layer of material
starts to cover the surface in one region of the profiled roller
and will continue to accumulate if action is not taken. This
process is mainly dependent on the material properties,
ambient temperature and the set compacting pressure. In
summer, for example, glazing is more likely to occur due
to higher ambient temperatures. With time, the sticking
material starts to cover more of the roller surface until it
eventually covers the entire compaction area. Because the
material layer has a certain thickness, the actual working
gap is now much smaller in the compression zone and is
Figure 9. Powder status in small and wide gap according to Heinicke