the counter. The data
variability stemming
from these problems
resulted in having to
make unnecessary
adjustments to the
production parameters. Consequently,
before the Insitec
system was implemented, the process
parameters were
adjusted once or twice
per shift. Now, adjustments are made only
once or twice a day.
Moreover, after an
adjustment has been
made, it is no longer
necessary to wait two
hours to see its ef-
fect. The result is im-
mediately visible on
the time history log
that depicts the process variables (Figure 4). In
this example, the blue line representing the me-
dian diameter (D50), while within specification,
was a little low. Hence, the shift supervisor
decided to readjust the mill rotor speed, in-
creasing the median
particle size while
maintaining it within
specification. The
process change also
increased toner out-
put by 0.2 to 0.3%.
Even more interesting is Figure 5,
which represents the
most modern line
equipped with an
Alpine air-jet mill. In
this case the Dv(50)
upper specification limit was 10. 7 Oct.
μm and production 04
was controlled at
10.66 μm—that is,
just 0.3% below the
maximum limit. The
on-line system has
enabled the line to
achieve such tight
tolerance because it
has improved process
control. Maintaining
tight specifications
leads to important
energy savings and
higher production
throughput.
Figure 6 represents
the evolution of the
average particle size
before and after the Oct.
installation of the 04
on-line particle sizer.
With range limits
set between 10. 5
Figure 5: Screen capture of a time history log showing the most modern line with a
reduced standard deviation
and 11. 5 μm, the mean particle size achieved
using the particle counter was between 10. 8
and 11.1 μm. After the new system was installed, the average particle size achieved has
been between 11.2 and 11.35 μm, increasing
throughput of just-in-specification product.
As shown in Figure 7, this improvement was
made possible by reducing the particle size
standard deviation. While the standard deviation for the median diameter (D50) was
0.22 before on-line control, it was lowered
to 0.15 after the installation.
Overall, the factory has achieved a 1%
increase in toner output as a result of the
process control upgrade. In addition, line
blockages can be anticipated, and a threshold
has been established that warns of the need
for maintenance action. Finally, the on-line
system has enabled the shift supervisor to
detect process errors immediately, enabling
him to respond quickly to events that can
cause overgrinding.
transformed into a number distribution as pro-
vided by the counter.
Figure 1 shows that the correlation between
the two techniques is independent of the type
of product, process mill (NPK or Alpine), and
even the sampling point. The graph shows an
excellent correlation (0.97) for the median diameter (D50) between the Insitec and the counter.
Figure 2 shows the correlation for the
percentage of particles below 5 μm. At 0.93,
the correlation is still very good. Out-of-specification material is defined as less than
5 and greater than 20 μm. Which parameter
was the most relevant to control the classifier?
In fact, the 10% diameter (D10) is used to control the classifier and the 90% (D90) diameter
is used to control the air-jet mill.
The opportunity was also taken to compare
the correlation between the two Insitec particle
sizers at the Dieppe plant (Figure 3). At 0.9953,
the correlation was excellent, although one of
the two units belongs to an older generation.
Once the correlation with the counter was
established, it was possible to transform the
Insitec result into values equivalent to those
obtained in the past with the particle counter.
Toshiba expects to replace the counter measurement with an average value of the median
diameter obtained using the Insitec over the
total duration of the batch production.
The resulting reduction of sample measurement time in the laboratory has made it possible to release operators for production tasks.
Before the Insitec system was introduced, one
operator spent 70% of his time taking samples
and performing analyses. Reducing the number
of lab analyses was particularly valuable because of analysis times were expanding.
Malvern Instruments, Westborough, MA, is a
leading supplier of advanced analytical systems
that deliver particle, rheological, and chemical
composition data essential for characterizing a
wide variety of materials. For more information,
call 508-768-6400 or visit www.malvern.com.
D50 Monthly Average Particle Size (μm)
12.0
11. 8
11. 6
11. 4
11.2
11.0
10. 8
10. 6
10. 4
10.2
10.0
Sep.
04
Nov.
04
Dec.
04
Jan. Feb. Mar.
05 05 05
Month/Year
Apr.
05
May
05
Figure 6: Evolution of particle size distribution
Operating with On-Line Analysis
A direct result of integrating the particle sizer
has been to reduce the number of process
adjustments on the production line by a factor
of three. The sample dispersion problems had
a direct influence on the results obtained using
0.5
D50 Monthly Average Particle Size
Standard Deviation
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Sep.
04
Nov.
04
Dec. Jan. Feb. Mar.
04 05 05 05
Month/Year
Apr.
05
May
05
