Machining-free LP compressor shaft bumper bearing repairs

• Main Author: Chiang, Chao-wei
• Other Authors: Ng Bing Feng
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Aeronautical engineering
• Online Access: https://hdl.handle.net/10356/136836
• Institution: Nanyang Technological University

Bumper bearings are made of carbon fibre composite and can be found in all Rolls-Royce Trent series aero-engines. The bumper bearing, which is attached to the Low Pressure Compressor (LPC) shaft, acts to prevent this lower speed shaft from being in-contact with the Immediate Pressure Compressor (IPC) shaft during service. The existing repair on bumper bearing which includes machining is time consuming and repair quality is not consistent. The filament fraying and delamination resulted from in-service operations have caused safety concerns. Therefore, this thesis has focused on a feasibility study to develop a different repair work to replace the existing repair method in industry by introducing Resin Transfer Moulding (RTM) and Vacuum Assisted Resin Transfer Moulding (VARTM) manufacturing processes to deliver near net-shaped bumper bearing components. Six different trials with RTM and VARTM features were conducted to fabricate a thick composite of 150 mm x 30 mm x 13.2 mm. The process parameters such as resin viscosity, pressure, resin inlet positions, vacuum outlet positions, vacuum dwell time and number inlet tubes were parameterised in order to achieve the complete wetting of fibres. The temperature and flow pattern of resin appeared to play critical role in fibre wetting percentage as suggested by experiment results. Initial trials showed poor wetting of fibres due to fibre compaction by the vacuum bagging and high resin viscosity. This was therefore mitigated by conducting resin transfer at elevated temperature, pressuring resin and changing mould design to solid metallic moulding which included positive-pressure resin infusion, and the overall wetting percentage increased accordingly in later trials. However, complete wetting of fibres in the core region was still difficult to obtain within all six trials by this moment; nonetheless the data and basic knowledge collected in this thesis could serve as a good baseline and can be cross-referenced to future projects addressing composite repairs on aero-engine components.