10 



THE INDIA RUBBER WORLD 



[October i, 1908. 



Growth of the Insulated Wire Industry. 



By Ira W. Henry. 



THE importance of rubber as an insulator for electric con- 

 ductors must be considered an ever growing factor in the 

 supply of and demand for this material. The constant in- 

 crease in the use of electricity, not only for lighting, heating, and 

 means of communication, but also for city transportation on street 

 railways, and latterly on trunk lines, calls for enormous quanti- 

 ties of copper conductors insulated in a manner that must make 

 them not only waterproof, but also flexible. Although many 

 substitutes, such as cotton, jute, and paper, on account of their 

 cheapness, are being applied as insulators, in every case where 

 specially good service is required the engineer insists on rub- 

 ber as a dielectric. 



The first authentic record we find in America of the use of 

 rubber as a dielectric is mentioned in the diary of Samuel F. 

 Morse, inventor of the telegraph, describing a cable he made in 

 1842 insulated with cotton surrounded by rubber. The telegraph 

 being the first commercial use to which electricity was applied, 

 naturally called for insulated wire, and continual experiments 

 were made by the Magnetic Telegraph Co., looking for a satis- 

 factory insulation for submarine wires for river crossings, un- 

 til finally a cable was laid across the Hudson from New York 

 to Fort Lee in 1843, manufactured by Day. 



This cable was followed in 1845 by another rubber cable made 

 by Charles Goodyear for Ezra Cornell. From this small be- 

 ginning the business of insulating wires naturally increased with 

 the growth of electricity, for the various purposes, and the names 

 of Day, Brixey, Habirshaw, Requa, and Reed are closely identi- 

 fied with the development and building up of the insulated wire 

 industry in America. 



The manufacturers of insulated wires and cables are now 

 using enormous quantities of the best Para rubber and the con- 

 stant increase in the demand for their products has led the more 

 far-sighted to closely investigate the supply from its fountain 

 head. One large wire corporation sent two of its experts to 

 South America to arrange for a constant supply direct from the 

 forests. The trip proved highly satisfactory and a large quan- 

 tity of rubber was purchased on the ground at a price that paid 

 the expense of the trip, though financial complications arose to 

 prevent a continuation of the business. 



The importance of the quality of the gum used in insulation is 

 hardly appreciated by manufacturers of mechanical goods. The 

 rubber must not only be uniformly elastic, but of such a quality 

 that it will constantly stand the strain of the electric current. 



The importance of quality can better be appreciated when it 

 is recalled that our battleships are literally managed, the guns 

 pointed, loaded and fired by electricity, all controlled from a 

 central point over rubber insulated wires. The United States navy 

 specifications are very rigid and state that the compound shall 

 contain from 39 to 44 per cent, by weight of fine Para rubber. Any 

 deviation from these specifications, which they detect by chemi- 

 cal analysis, means a rejection of the entire length of conductor. 



The United States signal corps, which controls and operates 

 all the telegraph and telephone lines owned by the government, 

 has at the present time over 2,524 miles of rubber insulated deep 

 sea cables in the Alaska territory. There is a similar system 

 connecting the islands of the Philippine group operating over 

 1,572 miles of rubber cables in various circuits. The army, 

 using as it does such a large amount of cable, and having con- 

 stantly in mind the trying conditions under which it must be laid, 

 has carefully mapped out a set of specifications calling for a 

 compound containing 40 per cent, of pure Para rubber, by chemi- 

 cal analysis, mixed with dry mineral water only. 



The specifications laid down by the government have natur- 



ally been made use of by electrical engineers for commercial 

 work, as with the ever increasing voltage used power trans- 

 mission the quality of the conductors must be improved to stand 

 the break-down test. Rubber cables are to-day carrying suc- 

 cessfully 20,000 volts pressure on underground lines and one 

 plant now being constructed will use twelve miles of underground 

 conductors under a working pressure of 28,000 volts. 



Telephone companies are also very large users of rubber in- 

 sulation. Every telephone is connected from the point where the 

 service cable enters the building with wire direct to the instru- 

 ment, made under the rigid specifications of the American Bell 

 Telephone Co. Requirements as rigid as the National Board of 

 Fire Underwriters are insisted upon and all wire is tested by 

 the engineering representative of the telephone company before 

 delivery. 



During the past few years some of the manufacturers have 

 attempted to use guayule in combination with higher grade rub- 

 bers. Results, however, have been anything but satisfactory as 

 not only mechanical, but electrical conditions have to be consid- 

 ered in an insulator. Electro-chemical effects are constantly tak- 

 ing place in a rubber compound that is not properly mixed, and 

 9n excessive amount of free sulphur not only causes the in- 

 sulation to deteriorate, but in many cases has corroded the wire 

 itself so that ruptures have taken place and the resulting arc 

 from the electrical current has started fires. 



African, Madagascar, and other cheaper grades of rubber have 

 been experimented with, but owing to the strict specifications 

 of engineers they will probably never make much headway in 

 this industry, as years of tests have proven that only Para rub- 

 ber, when properly compounded, will meet all the conditions to 

 which a wire is subject and carry a current without loss to the 

 desired distributive point. 



Rubber wires have been in use in buildings in New York 

 city for over twenty years. A sample of the original conductor 

 with which the Fifth Avenue Hotel was wired in 1888, on being 

 taken out during the destruction of that building this year, was 

 in as good condition as when originally installed. This wire had 

 not been placed in conduits, as is the present practice, but it had 

 been strung on insulators between the floors separated only by 

 fireproofing material from other wires. It had been subjected 

 to extreme heat in fact ; met the most trying conditions imagin- 

 able, but is still as elastic as on the day it was installed, and 

 the density of the compound shows that the insulation is in no 

 way impaired. 



There are two methods employed in the insulating of wire with 

 rubber. In the older or "cut" process, the rubber compound is 

 first calendered in sheets, then cut in narrow strips and placed 

 on the wire lengthwise, the edges of the strips being pressed to- 

 gether by roll cutters, making two longitudinal seams the whole 

 length of the conductors, which are sealed in vulcanizing. The 

 other process is known as the "seamless method" whereby the 

 compounded rubber is forced through a die around the conduc- 

 tor, thus making a uniform or seamless surface. This system, it 

 will readily be seen, does not depend on the heat of vulcanizing 

 to form the compound into a homogeneous mass. Both methods 

 have their advantages, the latter or "seamless" process being speci- 

 fied by the government for their submarine cables, owing to the 

 fact that a conductor laid in the bottom of the sea must stand 

 enormous water pressure, and it is thought that a seamed insula- 

 tion might open under this strain, thus destroying the insulation 

 of the cable. 



One of the greatest aids to the industry was perfected a few 

 years ago when the Wire Manufacturing Engineers' Association 



