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The simulation of the flow of polymer melt in lomolding

Dymond, Jacques Andrew Dryden (2004-12)

Thesis (MScIng)--University of Stellenbosch, 2004.


ENGLISH ABSTRACT: Lomolding is a new process similar to injection moulding. In this thesis a numerical model of the polymer flow into the cavity is presented. The model is used to compare the two processes with each other. Lomolding and injection moulding were modelled numerically with the finite element method. The model was an axisymmetric model and takes phenomena such as generalised Newtonian flow, free surfaces, moving boundaries and solidification into account. The processes’ characteristics that were compared are the cavity pressure, shear rate and shear stress. Improvements in these characteristics will result in lomolding having smaller machines, less fibre breakage and a better potential for in-mould-decoration. The thesis shows that lomolding has substantially lower shear rates and shear stresses than injection moulding. The model was also used to investigate certain machine design aspects, and to gain a better understanding of the polymer flow in lomolding.

AFRIKAANSE OPSOMMING: Lomoldering is ’n nuwe proses soortgelyk aan inspuitgiet. Hierdie tesis beskou ’n numeriese model van die polimeervloei soos dit in die gietholte invloei. Die model word gebruik om die twee prosesse met mekaar te vergelyk. Lomoldering en inspuitgiet is numeries gemodeleer met die eindige-elementmetode. Die model is aksiaal-simmetries en neem verskynsels soos Newtoniese vloei, vrye oppervlakke, bewegende grense en stolling in ag. Die proses-karakteristieke wat vergelyk is, sluit die gietholtedruk, vervormingstempo en skuifspanning in. Verbeterings in hierdie karakteristieke sal meebring dat lomoldering kleiner masjiene nodig sal hê, minder veselskade sal veroorsaak en meer versoenbaar met in-gietholte-versierings sal wees, vergeleke met inspuitgiet. Die tesis toon dat lomoldering laer vervormingstempo’s en skuifspanning het, in vergelyking met inspuitgiet. Die model is ook gebruik om sekere masjienontwerpaspekte te ondersoek, en om die polimeervloei in lomoldering beter te verstaan.

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