US1987508A - Insulated cable - Google Patents

Description

Jan. 8, 1935. H, JOHNS ET AL 1,987,508

INSULATED CABLE Filed Feb. 7, 1951 Tic-.1.

Q uvsumrmm gmntozs Patented Jan. 8, 1935 UNITED STATES PATENT OFFICE Ohio, asslgnors,

by mesne assignments, to Sterling Cable Corporation, a corporation of Michigan Application February 7, 1931, Serial No. 514,240

9Claims In electrical installations it is well known that conductors employed for carrying currents, especially high tension and high frequency currents, are open to the objection, which it has been difficult to overcome, in that there is considerable electrostatic and electromagnetic leakage, producing loss of current, corrosion of the cable, and other undesirable effects. This is apparently due to the fact that it is extremely dimcult to obtain perfect insulation and shielding within reasonable limits of high tension current conducting cables, the leakage around such cables manifesting itself frequently as a static field, and being under certain conditions even visible as an area of glow discharge in the vicinity of the conductor. The efl'ect is also noticeable through the production of ozone which manifests itself by its characteristic odor.

The glow discharge, commonly known as oorona, breaks down the insulating properties of the surrounding air, thereby rendering the air conductive in a well defined area. This discharge takes place when the critical break-down voltage is exceeded and has many harmful and objectionable results, among the most important of which are the 10$ of power, and the deterioration of the insulation about the conductor through the oxidizing action of the ozone-containing atmosphere surrounding the cable.

It has now been discovered, however, that if the insulation of the conductor is itself covered with a flexible insulating coating carrying particles of conductor material interspersed therethrough, that the formation of this static field around the conductor is avoided, the conductive coating applied to the insulation serving as a shield or damper preventing such leakage. Experiments have also indicated that the shielding effect of such a coating is dependent upon-the quantity of conductor material contained in the coating, the static field being virtually eliminated if there be sufilcient particles in the coating to form a continuous layer with no open interstitial spaces between the conducting particles.

It appears that the best results are obtained by using as the flexible coating medium, nitrocellulose lacquers carrying metal powders or powdered graphite, as the pigment for the lacquer. For example, if the insulation on the cable is coated with such a lacquer carrying a sufllcient quantity of powdered aluminum to present a uniformly silvered appearance, the shielding effects will be very satisfactory, so that the conductors so insulated may be safely employed in the electrical systems of automobiles for example, without danger of the deleterious electrical effects now very often experienced, especially if by any chance water should come in contact with the cables. Furthermore, the utilization of aluminum powder as a shielding medium is very desirable since it imparts a distinctive color to the cables, and since the aluminum is not aifected as to its color by contact with the sulphur in the rubber insulation, the use of the aluminum will render the appearance of the cable permanent and free from tarnish. While aluminum is preferred, it will be understood that any other metallic powder such as bronze pigments for example can be employed to produce a shielding effect, and also powdered graphite may be employed for the same purpose. The shielding effect of the conductive particles is apparently enhanced by the microscopic film of lacquer which surrounds each individual particle of the conducting material; and since the lacquer employed is very elastic, the cables can be bent in any desired manner without danger of breaking the lacquer coating.

The invention will be more readily understood by reference to the accompanying drawing, in which- Figure 1 represents in elevation a fragment of an insulated cable provided with the conductor carrying coating such as above described.

Figure 2 is a longitudinal section through the cable and its surrounding insulation showing the additional coating applied to the usual insulation, taken on the line 2-2 of Figure 3, and

Figure 3 is a cross section of the improved cable taken on the line 3-3 of Figure 1.

Referring more particularly to the drawing, 10 represents the conducting cable provided with the usual insulation 11, the insulation 11 being surrounded by the usual cotton fabric braid 12, which braid may or may not be covered with a thin layer of insulation. The insulation 11 is usually the conventional rubber insulation. Applied to this braid 12 in accordance with this invention is the additional external layer 13, which layer carries thickly interspersed therein conductive particles so as to give a uniformly appearing surface.

This layer 13 is applied, as above mentioned, by applying in any well known manner to the insulation 11, a lacquer formed of a nitro-cellulose base in a suitable solvent and carrying as its pigment particles of powdered aluminum, powdered graphite, or bronze, or any other good conducting material so that there will be presented a homogeneous appearance when the lacquer coating has dried on the cable; and except for a microscopic layer of the lacquer surrounding each particle, the individual particles of the conductive powder are in substantially unbroken contact with each other.

Aluminum is the preferred material for use as the shielding substance, since it imparts a permanent characteristic appearance to the cable,

I whereas other materials such as bronze, may tarnish in time through the action of sulphur contained in the rubber insulation. However, the shielding effect of these various conductors is good, one of the essential factors for electrostatic shielding being that the material possesses high electrical conducting properties; graphite is found to be very effective, although, of course, it does not present any particularly characteristic appearance. The lacquer coating being elastic will conform to any curvature imparted to the cable without breaking, so that an efiective shielding action is obtained, which is especially desirable in the electrical circuits of automobiles, for radio circuits, and for shielding radio apparatus from the effects of high tension currents, as for instance where the apparatus is installed in automobiles. It has also been found that when the present cable is employed in the wiring systems of automobiles or elsewhere where the cables are exposed to the action of oil and heat, the ductility and flexibility of the lacquer film is increased by the presence of the metal particles; and this is true whether the lacquer has been plasticized by resin or by oil. This action appears to result from a chemical reaction between the plasticizers or the gum content of the lacquer and the metal, leaving the film together and less brittle after it is subjected to the effects of heat and oil. By varying the amount of metal in the lacquer film, various degrees of flexibility can be produced.

The metal coating may be applied in various ways, for instance, by suspending the powder in the lacquer as a pigment; or the metallic film can be sprayed on the surface of the insulated cable immediately after it has received a coat of lacquer, there being thereby produced a smooth and even film, the metallic particles clinging to the lacquer surface as the lacquer dries. It is to be understood that the term lacquer as used in the specification and claims means a lacquer which includes a nitro-cellulose base or the equivalent thereof in a suitable solvent.

It will be apparent that variations in the specific details of this invention may be made without departingfrom the inventive concept. It will be understood, accordingly, that it is intended to embrace within the scope of this invention such modifications and changes as may be necessary to adapt it to varying conditions and uses.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States, is

1. An insulated electrically conducting cable having applied thereto an exterior coating comprising a cellulose lacquer having uniformly interspersed therein a finely divided electrically conductive material, the individual particles of which are separated by thin layers of lacquer,

and the conductive material being in such proportion as to provide a conductive static and ma netic shield about the cable.

2. An insulated cable for use in high tension electrical circuits, having applied thereto a coat- 5 ing of finely comminuted electrically conducting material interspersed in a cellulose lacquer, the characteristic of said lacquer being such as to render the coating flexible, and the conducting material having its particles separated by layers of lacquer of microscopic thickness, but being present in such quantity to provide a conductive static and magnetic shield about the cable.

3. An insulated electric cable provided with a homogeneous coating of a conductive powder carried by a cellulose lacquer, the individual particles of the powder being separated by films of the lacquer, but being present in such quantity to provide a conductive static and magnetic shield about the cable.

4. An electrical conductor cable comprising a conductor, a layer of insulation surrounding the conductor, a braid surrounding the insulation, and a shielding coating comprising finely divided aluminum carried by a cellulose lacquer applied to 25 the braid and forming a substantially continuous sheath of even thickness serving as a conductive shield against electrostatic and electromagnetic fields.

5. An electrical conductor cable comprising a 30 conductor, a layer of insulation surrounding the conductor, and an elastic coating on said insulation comprising a cellulose lacquer having interspersed therein finely comminuted electrically conductive material, the said conductive material 35 being in such proportion as to increase the flexibility of the elastic coating when subjected to heat and providing a conductive static and magnetic shield about the cable.

6. In an electrically conducting cable having 40 insulation thereabout, a coating of cellulose lacquer extending about said insulation and carrying finely divided electrically conductive material in such proportion to form a conductive static and magnetic shielding layer.

7. In an electrical cable having insulation thereabout, a coating of cellulose lacquer extending about said insulation and carrying finely comminuted aluminum in such proportion to form a conductive static and magnetic shielding layer.

8. A sheath for electric conductors having a coating of cellulose lacquer with metallic powder incorporated therein, the individual particles of the powder being separated by films of lacquer but being present in such quantity as to provide a conductive static and magnetic shield about the cable.

9. A flexible sheath for insulated electric conductors, comprising a coating with metallic powder interspersed therein in sufiicient quantity to produce an electrical shielding effect, said coating being of a substance which protects the metal particles and is resistant to attack. by oil, gasoline or the like.

HAYS JOHNS.

VERNE F. DOBBINS.

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