Optimization of EPDM compounds for resistant insulators to electrical tracking

The efficiencies of two transition metal oxides (Fe/sub 2/O/sub 3/ and Co/sub 3/O/sub 4/), one hydrated filler (Al/sub 2/O/sub 3/3H/sub 2/O), and their mixtures as anti-tracking components in an EPDM (ethylene-propylene-diene monomer) compound have been investigated. Their concentration ranges varied between preestablished limits, 100-230 phr for Al/sub 2/O/sub 3/3H/sub 2/O and 0-23 phr for iron and cobalt oxides. The electrical tracking test was based on the modified IEC 587 method. Significant F test values at the 95% confidence level for weight loss and applied voltage vs. failure time integral values were obtained for the fit of quadratic and special cubic functions, respectively. An overlay of surface contour plots shows that the region of maximum tracking resistance coincides with that of minimum weight loss, thus easing the selection of optimal composition range. Due to the significant binary interactions between trihydrated alumina/iron oxide and cobalt oxide, the 159-210 phr Al/sub 2/O/sub 3/3H/sub 2/O, 3.5-11.5 phr Fe/sub 2/O/sub 3/, and 0-2.3 phr Co/sub 3/O/sub 4/ concentrations result in EPDM compounds with elevated electrical resistance and small polymer erosion.<
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