Paper Technology International 2020 - Journal - Page 78

PAPERTECHNOLOGYINTERNATIONAL
Besides predicting the output values which are various
consequences of operating the process, one can see the effects of
each of the input variables on the outputs in different kinds of plots.
Figure 7 shows a set of curves of burst index plotted against size
weight on bottom side for different size temperatures, while keeping
other input variables constant. It is easy to see that the higher the
size weight, the higher is the increase in the burst index, but a limit
is reached. Higher temperatures have a better effect.
Pairs of variables often have interaction (synergistic) effects,
which can be seen from this kind of plots, or from contour plots.
Figure 8 shows contours of SCT CD index on a plane of nip load
and basis weight, keeping other input variables constant. Higher
nip loads naturally lead to better sizing and the benefit is higher for
smaller basis weights since the size weights are constant. Surface
plots can also be prepared in LUMET systems.
Optimisation calculations
There could be several purposes of developing
mathematical models. In the beginning, one wants to use models
to design the process and its equipment. Once the process
equipment exists, it is natural to want to find out how best to
operate the process. In other words, the objective could be to derive
maximum production and quality with minimal costs and time. More
specifically, for sizing, the aim could be to derive more strength from
less starch.
Optimisation helps derive the maximum benefit from the
process. The objective of process development is usually to
determine optimal or near optimal process operation conditions.
Once we have the quantitative knowledge of the process in terms
of variables of interest to us in the form of equations, it becomes
possible to determine good operating conditions. We would often
like to derive a certain SCT CD index and burst index at minimal
cost, while taking into account constraints on various other variables.
Figure 7: Burst index plotted against size weight on bottom side for different sizing temperatures.
Figure 8: Contours of SCT CD index on a plane of nip load and basis weight.
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