6 Dynamic Process Models for Fine Grinding and Dispersing
213
To sum up, the conveying into the gap for both shearing and rolling motion is
evident, leading to increased capturing probabilities. A complete statement about the
type of contact is not yet possible due to limited computing capacity, an evaluation
of the capture probability is however possible [12].
3 Measuring Material Function of Fine Particles
For the calibration of a flow sheet simulation, quantitative knowledge about the breakage function of product particles and aggregates as well as about the specific breakage energy is required. Although there are ways to determine the breakage energy
distribution of single product particles via microcompression, this method is very
time-consuming due to sufficient statistics necessary for a representative database.
Moreover, a breakage function can only hardly or not be determined. Therefore,
this method is not suitable for industrial application due to high investment costs and
extreme high measurement time. In addition, it delivers limited information about the
resulting fragment size distribution. Another method stated in literature is the backcalculation of model parameters from the results of mill experiments. However, the
use of literature model equations for the breakage function is limited for ultra-fine
comminution and the results achieved by back-calculation are often restricted to the
test mill. Furthermore, this method is unsuitable for industries like pharmaceutics
where often only very small product samples are available for testing.
In order to connect these, a breakage tester was constructed, based on the working principle of an EXAKT-three-roll-mill (E-line) with a precise roller to bearing
clamping unit. It allows the investigation of a small but still reasonable amount of
particle breakage to guarantee the required statistical significance. In addition, the
fraction size distribution of an initial narrow particle size distribution can be measured after the stressing between the rolls. For this purpose, only two of the three rolls
are used for particle breakage. The gears are modified to set counter-rotating motion
of identical velocity, and only the normal pressure is applied and shearing between
the rolls is prohibited. The breakage tester can be seen as a scheme in Fig. 10 and as
the real device in Fig. 11.
The gap between the rolls can be adjusted in the range of 5–180 μm with an
accuracy of one micrometre depending on the bearing clearance, the parallelism of
the rolls, the fine-adjustment of the gap as well as the simultaneous measurement of
the low compression forces and torques. In addition to the original construction of
the three roller-mill, a torque meter is added to the third roll, which is not directly
involved in the crushing of the particles.
The particle deposition is carried out via a vibration conveyer on top of the devise
which allows for a defined velocity and the deposition of a specified particle mass of
a limited number of particles. The tailor-made feed platforms allow the deposition
along the entire width of the rolls according to the required distribution patterns.
Under the rolls, a removal unit enables the particle uptake. For torque measurements,
the direct contact of the removal unit to the rolls was prohibited.
213
To sum up, the conveying into the gap for both shearing and rolling motion is
evident, leading to increased capturing probabilities. A complete statement about the
type of contact is not yet possible due to limited computing capacity, an evaluation
of the capture probability is however possible [12].
3 Measuring Material Function of Fine Particles
For the calibration of a flow sheet simulation, quantitative knowledge about the breakage function of product particles and aggregates as well as about the specific breakage energy is required. Although there are ways to determine the breakage energy
distribution of single product particles via microcompression, this method is very
time-consuming due to sufficient statistics necessary for a representative database.
Moreover, a breakage function can only hardly or not be determined. Therefore,
this method is not suitable for industrial application due to high investment costs and
extreme high measurement time. In addition, it delivers limited information about the
resulting fragment size distribution. Another method stated in literature is the backcalculation of model parameters from the results of mill experiments. However, the
use of literature model equations for the breakage function is limited for ultra-fine
comminution and the results achieved by back-calculation are often restricted to the
test mill. Furthermore, this method is unsuitable for industries like pharmaceutics
where often only very small product samples are available for testing.
In order to connect these, a breakage tester was constructed, based on the working principle of an EXAKT-three-roll-mill (E-line) with a precise roller to bearing
clamping unit. It allows the investigation of a small but still reasonable amount of
particle breakage to guarantee the required statistical significance. In addition, the
fraction size distribution of an initial narrow particle size distribution can be measured after the stressing between the rolls. For this purpose, only two of the three rolls
are used for particle breakage. The gears are modified to set counter-rotating motion
of identical velocity, and only the normal pressure is applied and shearing between
the rolls is prohibited. The breakage tester can be seen as a scheme in Fig. 10 and as
the real device in Fig. 11.
The gap between the rolls can be adjusted in the range of 5–180 μm with an
accuracy of one micrometre depending on the bearing clearance, the parallelism of
the rolls, the fine-adjustment of the gap as well as the simultaneous measurement of
the low compression forces and torques. In addition to the original construction of
the three roller-mill, a torque meter is added to the third roll, which is not directly
involved in the crushing of the particles.
The particle deposition is carried out via a vibration conveyer on top of the devise
which allows for a defined velocity and the deposition of a specified particle mass of
a limited number of particles. The tailor-made feed platforms allow the deposition
along the entire width of the rolls according to the required distribution patterns.
Under the rolls, a removal unit enables the particle uptake. For torque measurements,
the direct contact of the removal unit to the rolls was prohibited.