Silicone Rubber and EPDM Micro Composites Filled with Silica and ATH

Since the 1970's two basic polymer compositions have been in use for outdoor electrical insulation applications as an alternative to porcelain and glass; these compositions are based on silicone rubber (SiR) and Ethylene Propylene Diene Monomer (EPDM) and a mixture of these two compositions, called an alloy, is also in use. To impart erosion and tracking resistance under dry band arcing to these compositions when used for outdoor electrical insulation, various fillers such as alumina trihydrate and various silicas, natural and synthetic, are used. This paper discusses the effect of the addition of inorganic microfillers into silicone and EPDM compositions. Two types of microfillers were used in this study; namely, ATH and micro silica. The inclined plane test, according to ASTM D2303, was used to evaluate the tracking and erosion resistance of the micro filled composites. For SiR composites, at the same filler loading, no clear distinction could be found between the two types of fillers in the prevention of erosion in the inclined plane test. However, it became quite clear that EPDM composites with ATH filler are less prone to erosion than EPDM composites with silica filler.