Profile dies | machinery feature
Sophisticated simulation software can help to make profile die development more accurate. Lou Reade reports
Going with the flow
The business of perfecting an extrusion die can be tricky. Profiles, in particular, can be very intricately shaped, meaning that the die may need to be re-worked several times – often through trial and error. However, sophisticated modelling software can help
designers to model polymer flow through the die, which can cut the amount of re-working. Mahesh Gupta, a professor at Michigan Technological
University in the US, has modelled the effects of polymer viscosity on the final shape of co-extruded profiles. “The main goal in designing a die for extrusion of a
complex profile is to get a uniform velocity distribution at the die exit,” he said. If the velocity on exiting the die is different in
different portions of the profile, the polymer is redistrib- uted until a uniform velocity is obtained away from the die. The thickness of the profile usually increases at those locations with larger velocity, and decreases at low velocity locations. As well as a change in thickness, redistribution of the polymer can also cause significant distortion of the profile’s shape. Balancing a complex profile die is difficult at the best of times, but is made even harder when multiple polymers are involved – such as in a co-extrusion. Gupta simulated bi-layer flow in the die – using a mesh partitioning technique – which included predic-
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tions in post-die profile shape. He also runs a spin-off company, Plastic Flow, which
has developed the PolyXtrue software used to perform the simulations. He says that the traditional finite element mesh is not modified or regenerated with this software, which allows simulation of highly complex co-extrusion systems. The test was performed by modelling two extrusion
resins: an ABS from Dow and a polystyrene from BASF. Simulations for a number of flows were compared. Flow through two particular sections of the die – one ‘J’ shaped, the other ‘C’ shaped – was analysed. When using ABS as the substrate and PS as the cap
PolyXtrue software was used to simulate the flow of two resins through a profile die
Greiner’s
co-extrusion tooling cuts
vacuum energy
consumption by 80%
May/June 2012 | PIPE & PROFILE EXTRUSION 15
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