The standard industrial process to produce medium-voltage electric cables based on EPDM consists of cross-linking by peroxides with high-temperature steam (pressurized water vapor). Suboptimal material cross-linking is usually due to a decrease of the temperature along the vulcanization pipe. Temperature variations are connected to variations in steam pressure into pipe system. A combined numerical and experimental approach to optimize the production process of medium-voltage, rubber-insulated electric cables vulcanized with steam water is presented. The numerical part of this process is based on the use of finite elements and an optimization genetic algorithm (GA) and will be presented in Part 2. In Part 1, attention focuses on the experimental investigation. In particular, the final cross-linking degree is experimentally obtained by means of differential scanning calorimetry (DSC) determination of nondecomposed peroxide from the external layer to the core of the cable insulation. The final task is to minimize the difference between numerically predicted and experimentally determined cross-linking degree using a steam-temperature profile along the pipe to explain the variations. A preliminary evaluation of kinetic-reaction constants of rubber cured with peroxides is provided with the support of a comprehensive experimental investigation of the curing process by means of standard rheometer characterizations done at different curing temperatures. An existing mathematical, kinetic model is applied to the experimentally determined rheometer curves, allowing the determination of partial-reaction kinetic constants used in the finite-element computations

Increases in modulus, tensile strength, and swelling caused by reinforcing silicone rubber with silica filler were correlated with the thermoelastic parameter, fe/f. A new semiempirical equation of state, containing a generalized front factor, was derived to explain the experimental results. While the retractive force in pure gum elastomers is largely entropic in origin, reinforcement in silicone rubber‐silica systems appears to arise by greatly augmenting the deformational free energy change stored in energetic modes.

SynopsisLight-scattering and optical microscope observations of silica-reinforced silicone rubber have shown that the filler is dispersed in a complex manner. Much of the original material appears agglomerated into particles several microns in size. These particles apparently further cluster to form agglomerates of about 20 p in diameter. I n an earlier paper in this series it was shown that the thermodynamic function fe/f (the fraction of the retractive force due to internal energy changes) was a measure of the reinforcement level. It is now proposed that the corresponding physical mechanism of reinforcement may have its origin in the large amounts of energy required to deform the filler particle agglomerates.

Six homologs of the cellulose triester series were found to exhibit, in general, three second‐order transitions as determined dilatometrically. A parallel study of torsional modulus versus temperature revealed one glass–rubber transition, which allowed molecular assignment of one of the above. The dependence of the remaining two transition temperatures on length of the ester group permits some speculation with regard to their origin. The glass–rubber and secondary transitions exhibit an inversion for cellulose trivalerate and higher homologs, the two secondary transitions occurring at temperatures higher than the glass–rubber transition. A possible explanation for this anomaly in terms of side‐chain crystallization is discussed.

The vulcanization of medium and high voltage (M-H V) cables is an important industrial application where manufacturers use principally EPM/EPDM, crosslinked polyethylene (XLPE) and now also thermoplastic rubbers. In the present article, an EPDM compound for medium voltage cablesnormally distributed to producers in pellets and ready to be curedis considered and several experimental tests (rheometer curves and mechanical characterizations) are conducted changing controlled curing temperature, peroxide type and peroxide concentration. In particular, tests are replicated in a temperature range between 160 and 200 degrees C, with data provided every 20 degrees C, using two different peroxides, a mixture of three commercial peroxides at five different concentrations. A huge amount of experimental data (cure curves) is obtained (one for each temperature, peroxide used and concentration) and results are critically compared one each other, to have a quantitative insight into the most effective temperature and peroxide to be used during this kind of vulcanization, with the aim of maximizing vulcanization velocity, final torque reached and mechanical properties of cured rubber. The comprehensive experimental study proposed is finally assessed from a numerical point of view, utilizing a complex kinetic scheme constituted by reactions occurring in series and parallel, which allows estimating numerically the vulcanization degree by means of a single second order nonlinear differential equation, with unknown parameters determined through non-linear least squares fitting, with target data represented by experimental rheoemeter curves. The experimental fitting is almost perfect for all the cases analyzed and is aimed at predicting (without an expensive experimentation) the most suitable production parameters (e.g., curing time and temperature) to guarantee improved mechanical properties and a good aging resistance of the items. In addition, the numerical approach could allow finding the most suitable recipe, also in presence of mixtures of peroxides, able to provide items with a uniform vulcanization level