Cellulose Acetate Treatment for Textile Insulation - Engineering Development

transmission required THE improved standards of have greatly increased for present-day telephone communication the importance of improved electrical characteristics for telephone central office wire insulation. At the same time the tremendous growth of telephone systems, together with the increase in complexity of central office equipment due to the introduction of dial switching apparatus, has increased the quantity of insulated wires required to such an extent that the use of comparatively cheap materials is a matter of large economic importance. Silk and cotton yarns applied in the form of wrappings or braidings have been the standard materials for telephone central office wire insulation for many years. These materials in proper combinations and supplemented in certain cases by enamel and impregnating waxes provide sufficient dielectric strength to withstand the comparatively low voltages employed to operate telephone apparatus. This type of insulation also fulfills certain controlling mechanical requirements, in that it occupies small space, is not easily damaged by normal handling and can be applied in a large number of color combinations. On the other hand, there are disadvantages attendant upon the use of textile insulation, the most serious of which is the wide variation in insulating properties of such materials under different conditions of atmospheric humidity and temperature, caused mainly by changes in the moisture content of the materials. The efforts which have been made to improve textile insulation in this respect have had a two-fold objective, namely, to provide at moderate cost a super-quality insulation for use where it is important to have the best electrical characteristics obtainable, and to improve 213