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A Study of Heat Transfer at the Cavity-Polymer Interface in Microinjection Moulding. The effects of processing conditions, cavity surface roughness and polymer physical properties on the heat transfer coefficient
Babenko, Maksims
Babenko, Maksims
Publication Date
2015
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The University of Bradford theses are licenced under a Creative Commons Licence.
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Accepted for publication
Institution
University of Bradford
Department
School of Engineering and Informatics
Awarded
2015
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Abstract
This thesis investigates the cooling behaviour of polymers during the
microinjection moulding process. The work included bespoke experimental
mould design and manufacturing, material characterisation, infra-red
temperature measurements, cooling analysis and cooling prediction using
commercial simulation software.
To measure surface temperature of the polymers, compounding of
polypropylene and polystyrene with carbon black masterbatch was performed to
make materials opaque for the IR camera. The effects of addition of carbon
black masterbatch were analysed using differential scanning calorimetry and
Fourier transform infrared spectroscopy.
Sapphire windows formed part of the mould wall and allowed thermal
measurements using an IR camera. They were laser machined on their inside
surfaces to generate a range of finishes and structures. Their topographies
were analysed using laser confocal microscope. The surface energy of sapphire
windows was measured and compared to typical mould steel, employing a
contact angle measurement technique and calculated using Owens-Wendt
theory. A heating chamber was designed and manufactured to study spreading
of polymer melts on sapphire and steel substrates.
A design of experiments approach was taken to investigate the influence of
surface finish and the main processing parameters on polymer cooling during
microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the
Battenfeld Microsystem 50 microinjection moulding machine.
A simulation study of polymer cooling during the microinjection moulding
process was performed using Moldflow software. Particular interest was paid to
the effect of the values of the interfacial heat transfer coefficient (HTC) on the
simulated cooling predictions. Predicted temperature curves were compared to
experimentally obtained temperature distributions, to obtain HTC values valid
for the material and processing parameters.
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Type
Thesis
Qualification name
PhD