|Adhesion study of thermosetting powder resin to metal surfaces
|Hong Kong Polytechnic University -- Dissertations
Metals -- Surfaces
Department of Applied Physics
|v, 51 leaves : ill. ; 30 cm
|The objectives of this study are to find out and investigate the various parameters that could affect the adhesions of thermosetting epoxy powder coatings to metal surfaces, in particular the steel lamination sheets used in micro motor armatures. The micro-motor industry manufactures small size motors for use in toys, household appliances, hand tools and automobile industries. To have higher efficiency and increased winding window for magnet wires over paper or plastic inserts, epoxy powder coating is widely used as insulation layer between motor armatures and magnet wires. To achieve functional characteristics and to satisfy safety requirement, these coating are usually in the range of 0.15 to 0.3 millimeter thick. Impact test is one of the widely used test methods in micro-motor industry to reflect powder resin coating quality. Over the last 30 years, powder coating industry had gone through some change. This includes coating method, curing method and process change due to environmental concerns. Reports on failures in impact test of powder epoxy coating are occasionally received in past three to five years. The timing was quite in line with the enforcement of the Montreal Protocol which suspense the use of ODC (Ozone Depleting Chemicals). It was suspected that this change could be one of the causes of impact failure due to cleaning process change. This study aims to understand whether cleaning process is essential to good adhesion of powder coating. Tests were carried on four different substrates with two cleaning for comparison and benchmarking purpose. Surface roughness, FTIR and contact angle measurement were used to characterize the substrate through different steps before powder coating. SEM, DSC was used to verify the coating was fully cured to achieve maximum functional properties. Microhardness and cross-cut tape test were carried out to understand coating adhesion after the powder coating process. Test results were analyzed to understand the correlation of these parameters to coating adhesion to steel substrates. Results in this study indicated that powder coating has reasonably good adhesion to metal substrates without the need of vigorous cleaning. Further works is suggested to focus on finding out the cause of impact failure. It also verified that different cleaning methods give different degree of cleaning consistence. It might be a good indication to industries where cleaning is a critical process.
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