US 2089774 A
Description (OCR text may contain errors)
Aug. 10, 1937. M. A. wAcHsTElN I 2,089,774
MULTIPLE ELECTRIC CORD F'lled April 5, 1955 ATTORNEYS Patented Aug. 10, 1937 UNITED STATES PATENT GFFICE 11 Claims.
My present invention relates to electrical cords of the multiple conductor type.
It is among the objects of the invention to provide a cord of the above type substantially equal in performance to cords of more expensive construction, and which bears none of the external evidence of the longitudinal groove or cleft characteristic of the belts of certain low cost cords and which yet affords facility of longitudinal separation or bifurcation of the cord ends for terminal connection.
Another object is to provide a cord of the above type, involving but a single extruding operation, whether two or more conductors are to be imbedded in the rubber insulating composition, and involving but a single vulcanizing operation, all with the use of conventional manufacturing equipment.
Another object is to provide a cord of the above type which, though it aiords a substantially solid uninterrupted bridge of rubber between the entire thickness of the imbedded individual conductors, for maximum factor of safety against electrical failure, and though it is devoid of the added cost involved in the use of auxiliary tear strips, is yet readily split or bifurcated by simply drawing the constituent conductors apart from one end ofthe cord, without disturbance to the complete insulating jacket about each individual separated conductor end.
Another object is to provide a simple and expeditious method-"and rugged apparatus devoid of moving parts for executing said method to carry out the foregoing objects.
According to the invention the solid belt of flexible insulating compositiom preferably rubber mix, imbedding the two or more parallel conductors, either bare or covered, is devoid of any concavity crease or groove, but the material of the belt is weakened preferably by being severed at the surface along median planes between the successive conductors, without ei'ecting at the line of severance any gap or notch visible to the naked eye.
A preferred method, according to my invention, for producing the multiple electric cord, is to weaken or sever the belt by use of an appropriate penetrating tool after the cord has been vulcanized. The belt may thus be slit longitudinally from one or both faces thereof, the slit extending into the belt only to the desired extent, so as to leave substantially continuous the main body of the belt or that thickness of the belt intervening between the thicknesses of the individual conductors. Alternatively the weakening may be effected by a series of minute spaced perforations or piercings all in a median plane and through the thickness of the belt. If desired, a cnbination of slits and piercings may be resorte o. 5
Another feature is simple belt slitting apparatus comprising a thin cutting blade rigidly held in a chuck and protruding into a guide tunnel through which the multiple cord is pulled past said cutting edge or edges. l0
In the accompanying drawing in which are shown one or more of various possible embodiments of the several features of the invention,
Fig. 1 is a perspective view of a length of twin cord according to my invention shown bifurcated 15 at one end thereof,
Fig. 2 is a transverse sectional view on an enlarged scale, taken on line 2--2 oi Fig. 1,
Fig. 3 is a view similar to Fig. l showing the application of the invention in a somewhat modified embodiment illustratively shown on a triple cord,
Fig. 4 is a view similar to Fig. 1 of another modification,
Fig. 5 is a view in longitudinal cross-section of apparatus for executing the slitting method,
Fig. 6 is a plan view of the apparatus shown in Fig. 5, and
Fig. 7 is a fragmentary view in cross-section taken on line l--l of Fig. 5 and on a larger scale.
Referring now tc Figs. l and 2 of the drawing, there is shown a twin electric oord comprising two conducting wires i0 and ll, usually of copper, which may be solid, stranded, or braided, and enclosed in a belt l2 extruded thereabcut and therebetween and of flexible insulating composi tion, preferably a conventional rubber mix, which is vulcanized according to usual practice. The conductors may be protected by a coating I3 of tin or of cotton tape braid, or tape or of paper, regenerated cellulose, cellulose acetate, or any o equivalent material.
The belt has no visible groove or cleft, and in cross section, as shown in Fig. 2, presents no notch or depression, its periphery being oval. The periphery is convex along its narrower sides, u and since the belt is devoid of any concavity, it is designated in certain of the claims as convex throughout in periphery.
As shown in Figs. 1 and 2, the belt is longitudinally weakened along a. median plane be- 50 tween the conductors, preferably by severance of the belt along a line of cleavage Il extending inward from the surface, and preferably also from r the opposite face along a further line of cleavage l5 in the same plane transversely of the belt. 55
in Fig. A2, and suggested by dot-and-dash line |4 in Fig. 1, the line of cleavage is but a hair line severing the rubber composition stock, so that in the completed cord the edges exposed at opposite faces of the line of cleavage are in physical contact with each other to render said cleavage substantially invisible to the naked eye and to afford no suggestion that the continuity of the belt has in any way been interrupted.
As suggested in Fig. 1, when the cord is to be installed, a simple pull along the lines of the arrows will cause the belt to tear in the plane determined by the lines I4 and |5 of cleavage for in that plane as is clear, the effective cross-sectional area of the belt is abruptly reduced and a preferential tear line exists thereat through the thin web 6 between the inner edges of the slits. Thus, assurance is had that each of conductors Ill and remains completely imbedded in a rubber jacket determined by the contiguous portion of the rubber belt.
In Fig. 3, the invention is shown applied to a triple conductor cord having conductor elements 20, 2| and 22, there being a line of cleavage 23 extending inward from the face of the belt midway between conductors 20 and 2| and a similar line of cleavage 24 between conductors 2| and 22. Similar lines of cleavage 25 and 26 preferably extend inward from the opposite face of the belt. As in the embodiment of Figs. l and 2, these cleavage lines are invisible to the naked eye and the drawing is intended to show their position merely. In this embodiment there is preferably shown in addition to the lines of cleavage a series of hair line narrow slits 21 which may, if desired, penetrate or pierce the entire thickness of the belt in the cleavage planes and serve to assure the bifurcation of the belt throughout its thickness substantially precisely along the plane of cleavage. The end of the conductor is shown bifurcated, with all but one of the bifurcations removed, and the dotted lines indicate the edges of the various hair line slits, which determine the solid bridges 28 that become severed in bifurcating the cord ends. f
In the embodiment of Fig. 4, narrow hair line slits 28', similar to those of Fig. 3 are shown in the absence of the continuous line of cleavage. They are so minute in the direction transversely of the belt/as not to prevent the lateral walls of the perforations from contacting, thus rendering invisible the guiding tear line, shown on the drawing solely to indicate its position.
In these various embodiments, substantially none of the composition is removed in the slitting and/ or piercing operation. The walls of theslits or pierced slots are in contact with each other and preclude the objectionable ionization and eventual breakdown, encountered where, due to voids, air is imprisoned between conductors at different potentials. While the embodiment of Figs. 1 and 2 is preferred, especially in high voltage circuits, the pierced arrangement of the other embodiments does not materially increase the likelihood of breakdown when used in normal commercial circuits.
In a preferred method of producing the cord of Figs. 1 and 2, the parallel spaced conductors are embedded according to conventional methods into extruded composition to form the continuous end of the threaded stud 46 mounts a wing nut rubber belt therefor, the forming die being convex or oval to render the belt devoid of any groove or cleft. After the belt has been vulcanized it is longitudinally slit from one or both faces thereof, by use of appropriate thin cutting 5 tools to produce the structure of Figs. 1 and 2, or it is transversely perforated by the use of appropriate penetrating or piercing blades or needles to produce the structure of Fig. 4, or in the structure of Fig.f3 the belt is subjected to l0 both slitting and piercing operations. This slitting and/or piercing operation may be performed in any of a wide variety of ways that will readily suggest themselves to those skilled in the art. A preferred apparatus for performing the slitting 15 operation is shown in Figs. 5, 6 and 7 and will now be described. i
This apparatus comprises a pair of heavy base plates 30 and 3| rigidly bonded together in face to face relation, as by rivets 32. The base plates have matching grooves determining a guide or tunnel 33 extending substantially the entire length thereof and having the oval cross-sectional shape of the conductor belt and snugly housing the same. Chucks 34 and 35 are hinged about pins 36 in split jaws 31 integral with or rigidly amxed to the respective base plates 30 and 3| and extending into corresponding longitudinal grooves 38 in the base plates. Each chuck plate is made up of two leaves 40 and 4| which clamp therebetween a sharp cutting tool 42, such as an ordinary safety razor blade, screws 43 through a pair of the holes of said blade clamping the latter in place between the leaves of the chuck plates 40 and 4|. The blade 42 extends obliquely 35 with respect to the chuck with the extremity 44 of one cutting edge protruding into the tunnel 33 and along the median plane thereof.
Integral or rigid with one leaf 40 of the chuck is a lug or ear 45 through which extends a threaded stud 46 lodged at its extremity 41 in a depression 48 in the corresponding base plate and surrounded by a coil spring 49 tending to raise the chuck about its hinge 36. The protruding 'tunnel accurately guides the belt so that as it passes the cutting edge or edges 44, the longitudinal slit is formed. It is obvious to those skilled in the art that for slitting the three conductor cord, the chuck plates would be made of three leaves with two cutting tools clamped at opposite faces of the middle leaf.
It will thus be seen that there are herein described methods and apparatus in which the several features of this invention are embodied, and which in action attain the various objects of the invention and are well suited to meet the requirements of practical use.
As many changes could be made in the above method and construction, and many apparently widely diierent embodiments of this invention could be made without departing from the scope thereof, it 'is intended that all matter lcontained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.
What I claim as new and desire to secure by Letters Patent is:
1. An electric cord comprising substantially parallel covered conductors, a belt of insulating composition intervening between and completely surrounding and embedding said covered conductors, said belt having interruptions at the exterior thereof along planes intervening between said conductors, said belt being substantially continuous in the region between the thicknesses of the conductors, said weakened areas having substantially sharp edges at the exterior of the belt so closely contiguous to each other as to be substantially invisible to the naked eye and to aiord 15 the appearance of a continuous, substantially uninterrupted and uncreased belt.
2. An electric cord comprising two or more parallel insulation covered electric conductors, a iiexible rubber belt extending between and completely encircling and closely embedding said conductors, said belt along certain transverse sections thereof being discontinuous along lines extending inward from the surface of the belt at an axis or axes midway between the conductors, said belt being continuous in the region between the thicknesses of said conductors.
3. An electric cord comprising two or more parallel insulation covered electric conductors, a flexible rubber belt extending between and completely encircling and closely embedding said covered conductors, said belt being convex along its entire periphery and being slit along longitudinal planes intervening between the conductors, said slits extending inward from the surface of the belt and substantially invisible to the naked eye.
4. An electric cord comprising two or more parallel insulation covered electric conductors, a exible rubber belt extending between and com- 40 pletely encircling and closely embedding said conductors, said belt having perforations therein extending substantially in a common plane between the conductors and of width so small as to be substantially invisible tothe naked eye.
5. An electric cord comprising a pair of parallel insulation covered electric conductors, a exible rubber belt extending between and completely encircling and closely embedding said conductors, said belt having minute transverse perforations 50 therethrough in a common plane midway between the conductors.
6. An electric cord comprising two or more parallel insulation covered electric conductors, a flexible rubber belt extending between and com- 55 pletely encircling and closely embedding said conductors, said belt having lines of cleavage longitudinally thereof in a plane or planes midway between the conductors and perforations transversely through the belt in the planes of said lines of. cleavage.
7. The method of fabricating electric cords which consists in extruding about two or more spaced and parallel electrical conductors a solid belt of rubber, convex in cross-section throughout its periphery, vulcanizing said belt and then severing the vulcanized structure at the exterior along a plane or planes intervening between the conductor pairs.
8. The method of fabricating electric cords, which consists in extruding rubber composition about and between two or more parallel spaced electrical conductors to form a belt therefor, convex throughout its periphery, vulcanizing the structure and then penetrating the belt with a sharp tool to sever the material along selected regions in a common plane midway between and perpendicular to the common plane of the pairs of conductors.
9. The method of fabricating electric cords, which consists in extruding rubber composition about and between two or more parallel spaced electrical conductors to form a belt convex throughout its periphery, vulcanizing the structure and then slitting the belt at one or both sides of the belt, with a thin sharp blade along a line or lines longitudinally thereof and in a plane or planes substantially midway between and perpendicular to the common plane of the successive conductors, the material of the belt between the thicknesses of the conductors remaining substantially continuous.
10. The method of fabricating electric cords, which consists in extruding rubber composition about and between two or more parallel spaced electrical conductors to form a belt thereabout convex throughout its periphery, vulcanizing the structure and then transversely piercing the material of the belt in a series of minute perforations in a common plane or planes substantially midway between and perpendicular to the common plane of successive conductors.
11. The method of fabricating electric cords, which consists in extruding rubber composition about and between two or more parallel spaced electrical conductors to form a belt therefor, convex throughout its periphery, vulcanizing the structure and then longitudinally slitting the material of the belt along lines in planes substantially midway between successive conductors and also transversely piercing the material in the plane or planes of said slits.
MAURICE A. WACHSTEIN.