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Author
Date
2021Type
- Doctoral Thesis
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Abstract
Pultrusion is a rapid and cost-effective manufacturing technology for continuous fibre reinforced polymer composite profiles. One of the main applications of pultruded profiles are large cross-section solid rods made from glass fibres and low viscosity thermosetting polymers used for high voltage composite insulators.
%With increasing energy demands worldwide, higher voltages will require longer and larger diameter insulator profiles than those currently available.
However, manufacturing increasingly large composite profiles to satisfy the requirements for higher transmission voltages is difficult due to the exothermic curing behaviour of thermosets.
%When not carefully controlled, the temperature gradients during curing result in stresses that can lead to the formation of cracks on the surface of the profile, delamination and warpage, or thermal degradation.
In contrast, thermoplastic composites offer reaction and solvent-free processing, while possessing a virtually infinite shelf life as well as being reshapable, weldeable and recyclable. This thesis therefore aims to substitute the thermoset matrix by a thermoplastic material in a collaborative research project between Pfisterer Switzerland AG and CMASLab of ETH Zürich. To achieve this goal, a thermoplastic pultrusion process must be developed capable of manufacturing large cross-section thermoplastic rods that fulfil the requirements for high voltage insulator core applications.
The suitability assessment of Ø 10 mm composite rods pultruded from commingled yarns consisting of glass fibres and different thermoplastic polymers shows that PET constitutes the most promising material for insulator core applications, passing all test standards according to IEC 62217 and IEC TR 62039. To successfully scale the manufacturing process to larger diameters, a two dimensional finite element model is used to simulate the heat transfer and fluid flow physics of the pultrusion process for increasing diameters from Ø 5 - Ø 40 mm. To facilitate the experimental validation, a novel batch-wise pultrusion concept is introduced in which the impregnation process is observed in-situ using a transparent die. The investigation of pulling forces that were incorporated in a regression model showed a quadratic response for increasing diameter and decreasing temperature as well as a linear dependency of the pultrusion speed. The void content investigation showed that with proper process design, thermoplastic pultrusion is able to deliver consistent, high quality (void content < 2 %) profiles up to at least Ø 40 mm. A multistage pultrusion concept consisting of multiple dies consecutively adding material around an initially pultruded rod allowed to manufacture single- and multi material profiles with low void content and good interface between both stages. The model-based optimisation predicted a speed improvement of up to 21% for a two stage set-up compared to a single stage approach.
Ø 18.57 and Ø 40 mm insulator prototypes were manufactured in collaboration with Pfisterer Switzerland AG using semi-crystalline PET, that exhibited the best adhesion to the silicone housing. The Ø 18.57 mm prototypes passed the tensile tests but failed the dye penetration test due to hollow channels in the delivered glass fibres, highlighting the need of a reliable supply chain. In spite of the high porosity of the glass-fibre, insulators using ECR (E-Glass Corrosion Resistant) glass fibres with semi-crystalline PET and pultruded above 250 °C consistently passed the final voltage test, successfully demonstrating that pultruded composite rods are a suitable material for high voltage insulator cores. Their performance can be further improved through the use of seed-less glass fibre as well the optimisation of the interface between silicone rubber housing and composite through a suitable primer or injection moulding procedure. Although this work is aimed at high voltage insulators, the developed manufacturing technology in this thesis will provide the benefits of thermoplastic materials to other sectors such as wind energy and civil engineering, where large cross-section Show more
Permanent link
https://doi.org/10.3929/ethz-b-000555669Publication status
publishedExternal links
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Contributors
Examiner: Ermanni, Paolo
Examiner: Wong, Joanna C.H.
Examiner: Arreguin, Shelly
Examiner: Schmuck, Frank
Publisher
ETH ZurichSubject
Pultrusion, thermoplastic polymers, composite, thermoplastic composite, high voltage, insulation materials, insulators, micrographsOrganisational unit
03507 - Ermanni, Paolo (emeritus) / Ermanni, Paolo (emeritus)
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