machinery feature | Modelling software “In-die curing is unusual for silicone extrusion, but
would enlarge the possibilities for extruded geometries and the use of special silicones,” said the Miriam Haerst, in a presentation at the Antec conference. “For future process improvements, the calculation method helps to estimate the influence of various parameters.” The calculation model used by the researchers
covered four different cases: extrusion with and without a mandrel, and both before and after the onset of curing. The respective equation systems for each case were solved in Matlab using a trust region dogleg method. Physical experiments were carried out at die
temperatures up to 200°C, and VFD frequencies of no more than 2Hz – and these were plotted against mass flow rates of the silicone. The researchers concluded that the calculation model gave a “small hint” on the effects of several process parameters, and could be used for future estimations in LSR extrusion, but said: “It will not replace experimental testing.”
Graphic detail Researchers at the University of Minho in Portugal have used graphics processing units (GPUs) to improve the process of designing profile extrusion dies with complex geometry. The research was published in International Polymer Processing. The time needed for this type of calculation is
normally long, but the researchers parallelised the numerical code in the GPU using a simple programming approach, that required no complex memory manipula- tion. To verify the method, simulations were performed in three benchmark problems. Afterwards, the code was used to design two real-life
extrusion dies – to make a medical catheter and a wood-plastic composite decking profile.
One of the main challenges in extrusion die design is
to achieve balanced flow at the flow channel outlet, said the researchers. Numerical codes can help to overcome this, by cutting the amount of trial and error that is normally required. These types of simulation tool can help the designer to improve die channel geometry – through using either numerical-based trial and error procedures, or automatic algorithms that search for an optimised geometry. Medical catheters can comprise several channels
(‘lumens’) with different diameters that run along the length of the profile. The catheters have a constant cross-section, and are extruded from medical grade materials. The researchers made a five-channel catheter from
Targor’s Novolen PPH 2150 PP homopolymer. Several different locations were chosen for the lumens, in order to balance the outlet flow. Each computation took around 17 hours to run on a conventional central processing unit (CPU), but less than three hours on the GPU. The flow balance for the WPC die was also optimised,
and computation times were reduced from around 7.5 hours to 1.25 hours. As the full optimisation took five runs, the total time was cut from 38.5 hours to 5.5 hours. Results showed that, even with simple parallelisa-
tion, computation times could be reduced significantly for both types of die. “It is important to note that these results were
obtained without any complex memory management on the GPU, and therefore there is room for additional future improvements,” said the researchers.
Cooling simulation At last year’s Antec event in the US, Kenny Saul of SHS Plus told delegates how the company’s Chillware simulation program can be used to diagnose the problem of sagging or collapsing of pipe ends.
Software helps design new screws
Twin screw extruder maker Entek has developed a new software program that it claims “will enable customers to quickly and easily design screw and barrel layouts for their specific applications”. Key built-in features of the software include: drag and drop functionality on all components that need to be specified, such as barrel sections, screws and metallurgy; automatic calcula- tion of the remaining space on the screw shafts; safeguards to prevent certain elements being placed where they do not belong; simpler part ordering; and easy saving within the programme or export to an Excel file once a design is complete. ❙
http://screwdesign.entek.com
16 PIPE & PROFILE EXTRUSION | March 2017
www.pipeandprofile.com
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