Laser ablation of silicone composites

Silicone rubber based composites are used widely for outdoor high voltage components such as bushings, cable strings and as weather resistant coatings. In adverse weather conditions, dry band discharges [1] can occur resulting in tracking and surface damage; this can ultimately result in dielectric or mechanical failure. Traditionally these components are filled with aluminium trihydrate (ATH) and other fillers, such as silica, to improve their tracking resistance and erosion performance [2]. It is important in designing such materials that good arc resistant composites are chosen in order to maximise lifetime and minimise downtime and maintenance costs. Inclined plane tracking tests [2] have proved useful in determining the relative resistance of different material formulations to surface damage and have indicated that materials having a high filler loading are beneficial up to the point where a good dispersion of the filler can be maintained. An alternative test method is to use a high power laser to apply a known amount of energy at a known power to a localised region of the sample. Recently, this technique has been successfully applied to the characterisation of several outdoor insulation materials [3], however in these experiments we have sought to compare different materials rather than a fixed material having different filler contents. In the current investigation we consider the role of the filler content on the ablation resistance of several silicone rubber based composites, a range of laser powers and energies were employed and the resulting surface damage was quantified by pit-depth and mass loss measurements supplemented by optical microscopy. The extent of ablation was correlated to the filler content and composition and pointers to improved materials provided