WCA January 2019

❍ ❍ Figure 3 : Cable 3 DSC curve

❍ ❍ Figure 4 : Cable 4 DSC curve

These compounds are formulated to be more robust, making them a higher-performance solution for speciality cables used in harsh environmental conditions. The cable evaluation methods developed at Mexichem have been critical in the determination of LSHF cable cracking failures. Understanding the cause(s) for cracking failure leads to the solution for the processor to manufacture a product less susceptible to thermal stress cracking. As the market of LSHF compounds continues to grow into various cable designs and environments, and cable manufacturers are faced with improved field performance and optimised processing techniques, a supplier with in-depth knowledge about available polymer types and analysis methods is an invaluable tool to help answer the widening demands of the wire and cable marketplace.

The process engineer for the cable manufacturer noted that just prior to the cable failure, a water chiller had been installed to boost line speed. In order to achieve commitment to higher line speed, an additional water trough was installed so the cable would run through heated water to cooler water to achieve gradient cooling. After the production line was modified, the same lot of compound utilised to make the “failed” cable was run at the faster line speed and sent to Mexichem Specialty Compounds for analysis. This is referred to as Cable 4. Cable 4 was analysed by DSC to determine if the stress level had been reduced. Figure 4 shows that Cable 4 has no significant frozen-in stress, as the first and second heating curves are very close. Cable 4 was then subjected to a thermal cycling test to determine if it would crack if exposed to harsh environment. Cable 4 passed all the requirements of crack resistance testing. Based on DSC analysis of Cables 3 and 4, which were of the same construction and made with the same lot of LSHF compound, processing made the difference between “good” and “failed” cable. 4 Conclusions Differential scanning calorimetry (DSC) analysis is a useful tool in determining if cables contain frozen-in stress due to processing and are therefore more prone to thermal stress cracking. This method of analysis is also helpful to define if process changes in the manufacture of cables have affected the level of frozen-in stress, which could lead to cables cracking and failing in the field. Besides having the ability to help pinpoint optimal processing techniques for these polymer types, Mexichem Specialty Compounds designs low-smoke halogen-free (LSHF) materials that are more resistant to thermal stress cracking.

Mexichem Specialty Compounds Leominster, Massachusetts, USA Tel : +1 978 840 2134 Email : mark.jozokos@mexichem.com Website : www.mexichem.com Mexichem Specialty Compounds Melton Mowbray, Leicestershire, UK Tel : +44 166 450 2203 Email : tanya.artingstall@mexichem.com Website : www.mexichem.com

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Wire & Cable ASIA – January/February 2019