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.

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.

Made available in DSpace on 2014-12-17T15:14:59Z (GMT). No. of bitstreams: 1 GustavoOGR.pdf: 1907199 bytes, checksum: 6e8ae03d1bfaa0251b60dc88e9c5a9fb (MD5) Previous issue date: 2006-03-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / We study magnetic interface roughness in F/AF bilayers. Two kinds of roughness were considered. The first one consists of isolated defects that divide the substrate in two regions, each one with an AF sub-lattice. The interface exchange coupling is considered uniform and presents a sudden change in the defects line, favoring Neel wall nucleation. Our results show the interface field dependence of the threshold thickness for the reorientation of the magnetization in the ferromagnetic film. Angular profiles show the relaxation of the magnetization, from Neel wall, at the interface, to reoriented state, at the surface. External magnetic field, perpendicular to the easy axis of the substrate, favors the reoriented state. Depending, of the external magnetic field intensity, parallel to the easy axis of the AF, the magnetization profile at surface can be parallel or perpendicular to the field direction. The second one treats of distributed deffects, periodically. The shape hysteresis curves, exchange bias and coercivity were characterized by interface field intensity and roughness pattern. Our results show that dipolar effects decrease the exchange bias and coercivity / Estudamos os efeitos de rugosidade magn?tica em interfaces F/AF. Dois tipos de rugosidade foram considerados. O primeiro consiste de defeitos isolados que dividem o substrato em duas regi?es, cada qual com uma sub-rede do antiferromagneto. O acoplamento de troca, atrav?s da interface, ? considerado uniforme, o campo efetivo de interface apresenta uma mudan?a s?bita de sentido na linha de defeitos, favorecendo a nuclea??o de uma parede de N?el. Nossos resultados indicam que h? um limiar de espessura, dependente da intensidade do campo de interface, para o qual a magnetiza??o do filme ferromagn?tico se reorienta na dire??o perpendicular ao eixo f?cil do AF. Perfis angulares mostram como a magnetiza??o relaxa, espacialmente, do estado de parede de dom?nio de N?el, na interface, para o estado de reorientado, na superf?cie. A presen?a de campo aplicado perpendicular ao eixo de anisotropia do AF, favorece o estado reorientado. Para campo aplicado ao longo do eixo de anisotropia do AF, o perfil de magnetiza??o pode evoluir de uma parede de N?el, na interface, para o estado uniforme perpendicular ou paralelo ao campo aplicado, na superf?cie. O segundo trata defeitos distribu?dos, periodicamente, na forma de ilhas quadradas. Fizemos uma caracteriza??o das curvas de histerese, do deslocamento da histerese e da coercividade como fun??o da intensidade do campo de troca e do padr?o de rugosidade da interface. Nossos resultados indicam que efeitos dipolares, nesse padr?o de rugosidade na interface, diminuem o deslocamento da histerese e coercividade