Insulator surface features resulting from cutting techniques

Summary form only given, as follows. The surface structure of insulators and barriers play a significant role in inhibiting and enhancing surface flashover. Experimental studies show that cutting similar plastic-metal laminate geometries using two different cutting techniques (water jet cutting and machine tool cutting) leads to significantly different voltage hold-offs. The surface characteristics of similar insulator geometries before and after breakdown are examined with a scanning electron microscope (SEM). Both secondary electron emission (SEE) and backscattering electron emission (BSE) are used to image and differentiate insulator surface structures. The insulator surface without and with gold coat were compared using the SEM. Low level electron beam currents and accelerating voltages were applied in the former case preventing charge up and surface damage. General surface features appeared unaltered by sample preparation. The machine cut piece exhibited the following surface characteristics: overall uneven cut, plastic surface extended 5 to 15 mm beyond the metal edges of the laminate, degassing due to material (possibly cutting oil?) trapped in the surface, pitting and galling, chatter marks and plastic melt on the aluminum edge, and slivers of aluminum separated or partially separated from the metal plate. The water jet cut piece exhibited the following surface characteristics: a uniform staircase-like cut, gouging in plastic and smoothed over corners on aluminum edge on the water jet side of aluminum, plastic fragments lodged against aluminum/plastic interface, fragments of a foreign material sparsely distributed over plastic surface, possible stress damage on the side of the aluminum plate, and erosion as a result of turbulence (evidence of Strouhal eddies in wake) on the leeward side of the aluminum plate. Both insulator geometries exhibited some material imperfections as well as striations formed by pitting. These characteristics are examined based on t- e processing techniques used.