US1808520A - Insulated conductor - Google Patents

Description

June 2, 1931.

D. R.l BRoBsT INSULATED CONDUCTOR Filed Nov. 10, 1925 Psfenied June 2, 1931 UNITED STATES PATENT OFFICE DAVID) R. IBROBST, F NEW YORK, N. Y., ASSIGNOR TO BELL TELEPHONE LAI-BORATORIES, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION 0F NEW YORK- msi-.mamma coNDfroron.

Application illed November 10, 1925. Serial No. 68,0578.l

This invention relates to electric conductors and particularly to iexible conductors and cables.

An object of the invention is to improve the insulation characteristics of conductors insulated with cellulose acetate.

Another object of the invention is to improve the Skinning characteristicsof fibrous covered conductors impregnated with cellulose acetate.

Another object of the invention is to eliminate air-gaps and interstices in theinsulation of a conductor.

Another object of the invention is to improve the quality and reduce the cost of lswitchboard cables.

Another object of the invention is to improve methds of impregnating fibrous covered conductors with cellulose acetate.

S0 Heretofore, it ha's been proposed to enamel bare conductors with cellulose acetate lacquers as well as to treat fabrics with cellulose acetate in order to produce a glossy 'finish. It has also been suggested to'impregn'ate fibrous covered conductors with cellulose acetate in order to improve the'insulation characteristics of such conductors. An example of such a method is that disclosed in a copending application of John H. White, Se-

' n ria1N0.750,718,med-November 19,1924.

Accordin to the method disclosed in Whites app 'caiton the fibrous insulation upon a conductor is impregnated with a solution of cellulose acetate and dried preferably without allowing moisture to come in contact with the impregnated conductor during the drying operation.y The result of this process is to produce a conductor provided with a glossy tube-like cover in which the '40, cotton fibres are enclosed in a solid matrix of cellulose acetate. Such an insulating cover also it has been found that the cellulose acetate solution does not readily replace thel air in the lowerlayers of the fibrous material unless special precautions are taken. Various methods of treating the fibrous material to overcome this difficulty have been developed but these have the objection ofadding an extra ste to the process. f

A thoroug penetration of cellulose acetate is particularly desirable in those cases where the impregnated conductor is to be subsequently skinned. When a thorough impregnation is not obtained the'fibrous coveringl `it is applied.

In accordancel with one of its features, the

invention provides a new, and improved method of treating the individual conductors of a cable such as a telephone switchboard cable with cellulose acetate in which the im.- pregnation iscarried out so that the cellulose acetate permeates the complete structure being treated. In this manner, all the individual fibres of the covering receive fa thorough coating of cellulose acetate, and all the elc- I ments of the covering will adhere together. Such a structurehas been found to materially enhance the electrical insulating characteristics and the Skinning characteristics of the impregnated conductor. Briefly, this is accomplished by impregnating the fibrous covered conductor with a solution ofy cellulose acetate, applying a potential between the conductor and the container holding the solution during the impregnation, and drying.

The result of this process is to produce a conductor provided with a glossy tube-like cover in which the cotton fibres are enclosed in a solidmatrix of cellulose acetate, and in which air-gaps are. substantially eliminated.

The various features and advantages of the invention'are described in detail with ple.

reference tothe accompanying drawings in which: Fig. 1 is a lsectional side view illustrating the method of treating an insulated conductor in accordance with the invention.

Fig 2 is a front view in section of the ap aratus shown in Fig. 1.

s shown in the figures, a conductor 1 1nsulated with cotton or 4other suitable `insu-A lating material is drawn from a supply reel 2 over a suitabley pulley or other guiding mea-ns 3 to lan impregnating tank 4 containing a cellulose acetate bath 5. The impregnating tank 4 is preferably composed of a suitable electricall conducting cellulose acetate-inert materia such as brass, for exams From the pulley 3 the conductor passes under the pulley 6, up and over the pulley 7 down andunder the pulley 8, u and out of the bath and tank and over t e pulley 9. From the tank 4 the conductor passes to an impregnatiuf tank 10, and drying chamber `11 to a suitable take-up reel 12.

The take-up reel 12 is preferably formed of an electrlcally conducting material so .o that it may be employed as one ofthe elec-- trodes for applying the potentialbetween the conductor and the bath containing the conductor during the impregnation treatment. When used in'this manner, the conductin core of the conductor being treated is attac ed tothe metallic core of the take-up reel 12.

A suitable binding post is attached to the impregnating chamber 4 vsuch as at 13.

The insulated conductor 1 may be preheated to remove moisture before the impre nating process though this step is not consi eredessential to the'invention. An number of layers of fibrous insulation may e employed.

For example', the conductormay be insulated y with a single layer of cotton yarn of suicient through the impregnating tank 4, a potential.

-coarseness to secure tlae desired separation between the conductors of the cable to keep down the capacity therebetween. It is also preferable to'employ cotton yarn which is preferably not too highly hylgroscopic avoidmg the use of cotton which as been .bleached or otherwise treated in such a wa as to increase its hygrosco ic properties. f desired,

either before or a er bein spun into yarn, the cotton may be tested an if found to contain an undesirable quantity of soluble hygrosco ic and saline materials, it may be put throug a treat-ment of pure-hot water to remove such materials.

During the passage of the conductor is applied in accordancewith the' invention between suitable electrodes,`such as metallic reel 12 to which the conductin core of the conductor is attached andthe inding post 13, the reel 12, that is,'the conductor, being preferably made the anode or positive electrode. With the application of such a. po-

erably have. such 'a composition, however,

that its viscosity will be such that with the rate of motion of the conductor, the temperature of the bath, and the potential employed a thorough penetration will be pro'- duced. For general use, however, it may be -said that the proportion of cellulose acetate to solvent in the bath'may be varied over Wide limits. Solutions prepared for example, by dissolvingabout 150 grams to 300 grams of dry ing a. specific gravity of 0.797 at 60 F. have cellulose acetate pulp in a 'United States-gallon of refined acetone havbeen found suitable. This solution is preferably allowed to settleV and the clear supernatant liquor drawn olf for use in the impregnating-tank 4 while the gray undissolved sludge, if such remains, is rejected.

The insulated conductor ispassed through the tank 4, containing the cellulose acetate v solution prepared in the manner described above, any number of times desired so as to become thoroughly penetrated with the solution. In thel drawings the conductor.v is

shown as being given four passes thoroughy thebath in the tank 4.

' After passing through the 'tank 4 it has been. found that the conductor covering is thoroughly impregnated with cellulose acctate. i 'In order to produce a satisfactory finish, however, it has been found preferable to pass the initially impregnated conductor -through a plurality of additional impregnation steps without the application of'a po-l tential. In order to carry out'this object,

the conductor after leaving the tank 4 is drawn under a suitable guide reel 14 through a cellulose acetate bath 15 contained in e tank 10. The distance between the outlet of tank'4 and the impregnating bath 15 and the speed of the conductor 4arevfpreferably such as to prevent the deposition of moisture, on the conductor before" it reaches the bath 15. The conductor then' asses Vthrou h the d ing chamber ll'whic may be, or examp e, an electric furnace comprisingy a. refractory core 16 wound with suitable resistance wire 17- and enclosed within a second refractory tube 18 over which suitable h the' `chamber 11 1s preferably so regulate that heat'insulating material 19 is placed'. vThe passage of the conductor throu v chamber 11.

The subsequent impregnation treatments may be continued throughout an number of steps tol produce the desired thickness of to producesatisfactorycharacteristics. However, this set of conditions cannotbe said to after the initial ste-p insulation and the desired smooth and polished appearance of the conductor. Inv the figure, the conductor is shown asbeing given four passes through the impregnating bathb employing the potential difference.

It has been found that when the insulated conductor is first passed through an impregnating process employing a potential difference between the conductor and the container holding the bath the insulated conductor is thoroughly impregnated down to the wire and the iaws heretofore encountered are obviated.

The particular operating conditions employed in any given instance will vary, of course, with the yworking conditions of the plant. A set of conditions which has been found satisfactory for impregnating, wire having a covering-of two servings of cotton yarn, one being No. 50 cotton yarn and the other being No. 30 two-ply yarn, has been found to be the potentialldife-rence of 250 volts, and a rate of motion of a conductor of 10 feet er minute, the conductor being subject to t e'action of the potential diierence while in contact with the cellulose acetate for approximately three minutes. The example given is one which has 'been found be preferred for all purposes over others but conditions intermediate those given or differing widely Ifrom them and yet within the limits deiined by the claim may be used to secure the advantages of the invention, the conditions employed depending upon the particular conditions stance.

It will be obvious that the terminals for applying the potential 'difference may be other than those represented in thegure of the drawings. For example, the cathode might be an electrode in contact with the hatrli instead of the container holding the The temperature of the cellulose acetate l bath which is employed, has not been found to substantially infiunce the results. obtained.

The use of an initial tem erature of the bath in the neighborhood ol room temperature has been found satisfactory. Asia. general rule, it has been found that the tenriperatureA ofthe bath increases materially with time as present in each iny, ance with the invention.. It has been found,

for example, that the AC mutual capacity Aand conductances between wires in a pair are both lowered and theDC insulation resistance and AC breakdown strength are materially increased. As an exainple 'of the increase in insulating characterlstics which is produced by treating an insulatingconductor in accordance with the invention, one insulated conductor'was given 5 passes through cellulose acetate as show in the drawings without applying'a potential difference and another conductor of the same type given the same treatment with the application of potential. The rate of motion ofthe conductor was approximately 17 feet per minute, applied potential difference between 230 and 250 volts and the length of time during which the conductor was subjected to-the potential d iiference approximately 11A, minutes. The fol-v lowing table gives the results obtained: i Capacity in micro-micro farads ,in 50 yfeet Tmp 85 85 85 85 Humidity 05% 75% 85% 90% 93% 75% 65% Conductor treated with applied potential 1,500 2,000 2,700 3,330 4,000 2,700 2,200 Conductor treated without applied potential...T 1,900 2,300 3,050 3,700 4,540 3,050 2,500 Percentage decrease-- 21% 1'3%11%% 10% 12% 11%% luo'omluctace in micro-mitos per 50.feet VN Conductor treated l with applied potenv Jini. 2.2 2.2 2.3 '8.3 6.0 2.4 2.2

Conductor treated A without applied po. l tentil i 2.2 2.2 2.3 14.0 10.1 2.6 ".3 Percentage decrease... 0.0 A 0.0 d 0.0 40.61' 40.6 8.0 5.0

Insulation resistance in megohms per 50 feet Temp- Humidity v potentreated appiled po- Percent e in insula g .due to tion show superiority over one given a simple Conductor treated :gli applied poten- Conductor` treated without applied potential..

Percentage increase duc to application of potential It will be noted that the insulating conductor prepared in accordance with the invenimpregnation with cellulose acetate particularly at the hi lier humidities and also shows a greater ten ency to recover rapidl `from the effects of humidity. The varying umidity conditions to which the conductors were subjected throuohout the test While severe, nevertheless indicate the conditions to which the switchboard cable maybe subjected in actual operating conditions.

While the invention has been described with particular reference to ,cotton covered conductors, it isy to be understood that it is equally applicable to conductors insulated with other materials.

The invention is also capable of other modifications and adaptations not specifically re-4 ferred to but included within the scope of the appended claim.

What is claimed is: s

The method of treating an insulated conductor which com rises immersing the conductor in a bath o? cellulose acetate, causing a ilow of electric current through the conductor and the bath, and subsequently in succession passing the conductor through a bath of cellulose acetate and through a drying chamber.

In witness whereof, I hereunto subscribe my name this Qndday of November A. D.,

DAVID R. BROBST.

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