Experimental and numerical investigation of warpage of branched polyethylene in rotational moulding
| Title |
Experimental and numerical investigation of warpage of branched polyethylene in rotational moulding |
| Publication year |
2003 |
| Language |
English |
| Author |
Glomsaker, Terje |
| Co-Authors |
Andreassen, Erik - Larsen, Åge - Ommundsen, Espen (Norner) |
| Source |
PPS Europe-Africa Conference. Athens, Greece, 14-17 september, 2003 |
| Abstract |
Warpage of semi-crystalline polymers in rotational moulding appears due to asymmetrical cooling. The outer wall is in contact with the mould and is therefore cooled faster than the inner wall, where the heat loss is nearly vanishing. This creates a solidification front moving from the outer wall towards the inner wall and thus the volume contraction due to crystallisation induce asymmetric residual stresses and warpage of the final product. We have in this work developed an experimental technique that is able to quickly rate different materials with respect to warpage under typical rotational moulding conditions. The technique is based on melting of pressed plates which is subsequently cooled from only one side. The technique has been applied to create reproducible results for a range of different LLDPEs in order to rate the materials as warpage versus stiffness. We have also developed a numerical simulation model that is able to simulate the induced residual stresses and warpage of a uniformly cooled plate. The model includes a non-isothermal kinetic crystallisation model fitted to DSC measurements at a range of different cooling rates and is used to discuss various models for the mechanical properties after the liquid-solid transition and adhesion to the substrate. |