. The Bell System technical journal . ese materialsin this test, and factory handling of cores confirms the general con-clusion. Flexibility: The flexibility of submarine cable insulation is importantbecause the core is subjected to considerable flexing during manu- 3 Hippensteel, Bell Laboratories Record, S, 153 (1928). PARAGUTTA, A NEW INSULATING MATERIAL 143 facture, laying and repairing and possibly at times during use, espe-cially where tidal currents may cause movement in the cable. Para-gutta and gutta percha cores have been subjected to slow and con-tinuous flexing at 0° and 25° C. for
. The Bell System technical journal . ese materialsin this test, and factory handling of cores confirms the general con-clusion. Flexibility: The flexibility of submarine cable insulation is importantbecause the core is subjected to considerable flexing during manu- 3 Hippensteel, Bell Laboratories Record, S, 153 (1928). PARAGUTTA, A NEW INSULATING MATERIAL 143 facture, laying and repairing and possibly at times during use, espe-cially where tidal currents may cause movement in the cable. Para-gutta and gutta percha cores have been subjected to slow and con-tinuous flexing at 0° and 25° C. for long periods and it was found thatboth materials will withstand millions of repeated flexures at smallamplitudes without failure. When the amplitude of flexure wasincreased to strain the conductor slightly beyond its elastic limit,the conductor always failed in advance of the insulation. Plasticity Tests: Laboratory tests were made to determine the rela-tive plasticity of paragutta and gutta percha, using both the Williams ^ 9 100. 40 60 COMPRESSION-PER CENT 100 Fig. 6—Comparative compression properties of paragutta and gutta percha at 25° C. and the Marzetti ^ type of plastometers. These tests are valuableguides but the final judgment of a material as regards thermoplasticitywas made by determining its workability on commercial gutta perchainsulating machines. Paragutta is somewhat more resistant to flowthan gutta percha at temperatures ranging from about 40° to 70° applied to the conductor, however, its greater resistance to flowat elevated temperatures can be taken as an advantage as it lessensthe danger of faults occurring if the core should be accidentally exposedto elevated temperatures or to conditions which might exist in con-nection with cable used in the tropics. * Williams, Jour. Ind. & Engg. Chem., 16, 262 (1924).^ Marzetti, Giorn. Chitn. Ind. Applicata, 5, 342 (1923). 144 BELL SYSTEM TECLINICAL JOURNAL Figure 7 shows the relative plasticities of cabl
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