process simulation | CAE
Right: Finite element
method (FEM) is a 3D
technique to simulate local process
conditions, such as the
local distribu- tion of pressure and velocity
improve its 1D-SIGMA software through focused research projects. A mathematical model of fibre breakage in a twin- screw extruder is a recent example of such work. France-based Sciences
Computers Consultants (SCC) is a creator of both 1D and 3D software. SCC’s Ludovic 1D simulation program now has a simpler user interface, improved reliability, and new functionali- ties, such as one that allows users to input proprietary material behavior laws and customer-specific kinetic reactions and another that helps them interpret native Ludovic results. SCC recently released a software version designed
for simulating twin-screw extrusion of pharmaceutical products (so-called “hot melt extrusion” of excipients and active pharmaceutical ingredients). The company is also currently working on a new simulation program for co-kneaders called Lucomax. It is seeking industrial partners to further develop the program and hopes to release the first version by the end of this year.
Accuracy depends on data 1D simulation can predict key system parameters – such as specific energy, melt temperature, residence time, and pressure – that directly influence the quality of a compound, said Adam Dreiblatt, Director of Process
Technology for CPM Century Extrusion, in a presentation at the 2015 Compounding World Forum. Accuracy of 1D
simulation depends on the accuracy of the material
data. A model can be “calibrated” for a material, but may need to be adjusted if other components of the formula (such as lubricants, low-melting additives or other
polymers with low melt viscosity) change the way the material melts,
according to Dreiblatt. Even without accurate material data, however, simulations can be used to predict relative perfor- mance, such as how a material will perform in one screw configuration versus another or for scale-up from one machine size to another. “As long as the same material data file is used to compare different machines or different screw configurations, the results are valid. Material data files for simple blends can be quickly and easily created; using these placebo blends to approxi- mate the torque on the extruder (at the simulated operating conditions) will result in close approximation to the real-world situation,” Dreiblatt says. Conveying of powdered solids is one aspect of the
process that is highly affected by the properties of the raw materials (bulk density and particle size distribu- tion, for instance). And even with good material data, feed intake depends on many variables and can fluctuate, said Paul Anderson of Coperion Corp and Frank Lechner of Coperion Germany in a presentation at the Society of Plastics Engineers ANTEC 2016 conference. Actual process data, however, can be used to “train” a simulation and produce a better model, they reported.
Good material data is also crucial for modelling of
Sciences Computers Consultants’ Ludovic Pharma simulation software used to determine the design and operating space for a hot-melt extrusion process. The pink dot denotes the initial setting (rotation speed vs flow rate). The chart is the result of a Design of Experiment in a 12-mm twin screw extruder where speed is varied from 135 to 165 rpm and output is varied from 1.08 kg/h to 1.32kg/h. The plot presents a specific output, which is the time the material remains in the extruder at a temperature > 80°C. This can be related to a degradation ratio.
16 COMPOUNDING WORLD | March 2017
the polymer melting stage. Although distributive mixing of fillers can be modelled, simulations cannot yet adequately model dispersive mixing or the resulting crucial aspects of product quality, such as gels, agglomerates, and filler dispersion, says Coperion’s Schmudde. As a consequence, Coperion engineers do not rely solely on simulation to design an extruder setup or a screw configuration, he says, but combine simulation with experience and laboratory trials or use simulation to compare relative performance of screw configurations. Validation of simulation models is also important. After optimisation results are obtained from simulation, experiments on laboratory or commercial
www.compoundingworld.com
PHOTO: COPERION
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