June !.• 1911.] 



THE INDIA RUBBER WORLD. 



319 



The Manufacture of Insulated Wire. 



(By a Practical Man.) 



ONE of the great industries into which ruhher manufacture 

 divides itself is the insulation of electric wires. The half 

 hundred factories in various parts of the world, while 

 having in a measure their own processes and special machines, 

 still come near enough together in practice to make a general 

 description of one fit them all. The work of laying the rubber 

 upon the wire calls for two distinct operations that are accom- 

 plished by the use of the spewing machine and the strip machine. 



Spewing Machine Insulation. 



The spewing machines used for this branch of the business are 

 identical with the tubing machines common to all rubber fac- 

 tories, with the exception of the head, which is usually con- 

 structed so that the compounded rubber is emitted from the 

 side of the head upon the wire which passes through it at right 

 angles to the worm. It is true some machines are so constructed 

 that the wire passes through a hole drilled the length of the 

 worm, but this style is used only for small wire, and the manu- 

 facturer claims a speed of production for an 18 B. & S. wire of 

 12,000 feet per hour. The side delivery is, however, in more 

 extended use, as it is contended that this method of forcing 

 insulation upon wire gives it greater density, a most desirable 

 item in a body required to resist electric voltages. 



The compound containing rubber for spewing machine work 

 is prepared in the mixing mills in the manner employed for 

 mechanical stocks. "Bolivian fine" is extensively used, as well as 

 African and other sorts, and high and low-grade reclaimed 

 rubbers. It is conceded that the best insulation stocks are 

 secured by use of fine Para, and as a rule, specifications for the 

 very highest type of insulated wire and cables call for its use. 



While for ordinary "mechanicals" crude rubber requires but 

 little breaking down to render it fit for use in compounds, such 

 is its intractable nature, that before it can be successfully used 

 in the spewing machine, in mixings containing 20 per cent, to 

 40 per cent., its time in the breaking-down process consumes 

 from four to si.x hours. It is during this interval that, specifica- 

 tions permitting, paraffin, ozocerite and other substances known 

 to contribute to electrical resistance, are worked into the crude 

 rubber. As the electric fluid has a marked affinity for particles 

 of sand, metal and foreign substances in general, the greatest 

 care is observed in preparing the materials that compose the 

 mixings. The mineral powders are sifted through silk or brass 

 mesh sieves, and frequently the completed compound is passed 

 through a tubing machine, a special head for which is fitted with 

 No. 40 to 60 brass or steel mesh. 



Finally, after preparation in this painstaking fashion, the in- 

 sulation material is ready for the spewing machines. It goes 

 directly to these from the mixing mills, as, in order to work 

 successfully, it must be used while hot and tractable. It is cut 

 in strips from the mills, or passes through a scoring machine 

 that permits the spewing machine operative to tear it apart as 

 required. Hand feeding of these strips or pieces, however, 

 requires skillful manipulation to overcome the tendency of the 

 thickness of the insulation "to vary as each new piece of insula- 

 tion material is fed into the machine. Some factories adopt the 

 method, for light insulation, of passing the prepared compound 

 through the calender and cutting it into strips of a specified 

 width. Materia! thus prepared has the advantage of uniformity. 

 The feed is, also, practically automatic, requiring little or no 

 manipulation after the first end of the cut strip is in the machine, 

 as the revolutions of the worm draw it in steadily. By this 

 method, one man can frequently run the whole job, except where 



a layer-up of wire on a drum is required ; by the first method, 

 and also where the wire is to be coiled in a pan, from two to 

 four men are required. 



With insulation material in proper working order, the next 

 most important step is to secure its even and unvarying thick- 

 ness on the wire. This is gained by manipulation of parts called 

 the die and nipple, by means of set screws in the machine head. 

 Tliis centering is important, for insulation is only as strong as 

 its thinnest part. A grain of sand, or a minute sliver of wood 

 sticking in the die will throw the insulation out of center, or if 

 successful in passing through, remain as a weak spot for the 

 electric fluid to discover. 



With this smooth and symetrical cover, the wire glides swiftly 

 onward to pan or drum for vulcanizing. If intended for the 

 drum it passes in a double turn through a tank of cold water for 

 the purpose of hardening the msulation coat. If a pan is to be 

 used, the water bath is omitted. Pan curing is necessary for 

 most high-grade insulation for the reason that its soft composi- 

 tion would flatten if wound on a drum. Consequently pans are 

 bedded with talc, or soap stone, upon which the wire is coiled 

 by hand, and this material supplied between each layer. It is 

 a neat job calling for acquired skill, to lay the wire in absolutely 

 concentric circles without tangling, crossing or bruising. All the 

 operations connected with spewing machine work call for expert 

 manipulation. For example, white or red core is a type of in- 

 sulation used in vast quantities. The size commonly used is 14 

 B & S, and the wire receives two coats of insulation material : 

 the outer coat black, and the inner coat white or red. These two 

 coats are applied in one operation (the spewing machines being 

 run tandem), the wire receiving from the first machine the 

 colored core, and from the second, the black cover. Naturally 

 the speed of each machine requires accurate adjustment to secure 

 perfect work, yet 50,000 to 60,000 feet per day is ordinary pro- 

 duction. 



It is not uncommon, however, in high-grade insulation, for 

 specifications to call for three grades of composition. The 

 modern method is to set three machines in line, and apply all 

 three coats in one operation. The layer next the wire is fre- 

 quently pure, unadulterated Para rubber, or all three coats may 

 be compounded material. 



Not only are all sizes of single wire successfully insulated by 

 means of the spewing machine, but double and twisted conduc- 

 tors, and stranded cables. In short, the successful manufacturer 

 of insulated wire must have a genius for this branch of the rub- 

 ber manufacturing business, so varied and exacting are its re- 

 quirements. 



The insulation material, composed of costly ingredients, is 

 valueless until vulcanized. This is accomplished in various 

 types of vulcanizers by means of live steam, the length 

 of time and the temperature being carefully adjusted to 

 the requirements of each type and grade of insulation. Some 

 single wires and almost all sizes of stranded cables receive a 

 layer of rubber-coated tape before going through the curing 

 process. This is wound about them concentrically, special ma- 

 chinery being required for the purpose of preventing the swell- 

 ing of the rubber coat during this operation, and also to prevent 

 its flattening or injury in handling. 



Vulcanization, barring mechanical injury in process, for the 

 first time raises the insulation material to the dignity of insula- 

 tion; and having passed the voltage tests required of its grade, 

 or by the specifications under which it was produced, it is for 

 the first time commercially valuable. As a rule, however, it is 



