US 3558378 A
Description (OCR text may contain errors)
3,558,378 ARMORED CABLE AND METHOD oF MAKING THE SAME- l. H. MARANTZ Jan. ze, 19171 z'sheetsfsheei 1 Filed ,my` 3.2.I 1.95?
INVENTOR sf/rs1. H. MAQAA/rz TN Tm TM] TW Jan. 26, 1971 l. H. MARANTZ 3,558,373
` ARMORED CABLE AND METHOD oF MAKING THE' SAME Filed Julyv 12. 1967 2 sheets-sheet A YINVENTOR. ure/:5L H. MfmvnA/rz M/ A a Arran/ver United States Patent 3,558,378 ARMORED CABLE AND METHOD 0F MAKING THE SAME Israel H. Marantz, Forest Hills, N.Y., assignor to C0- lumbia Cable & Electric Corporation, Brooklyn, N.Y.,
a corporation of New York Filed July 12, 1967, Ser. N o. 652,815 Int. Cl. H01b 13/06 U.S. Cl. 156-54 2 Claims ABSTRACT 0F THE DISCLOSURE This invention relates to an improved armored cable and to the method of making the same.
The invention is directed to a conductor for an armored cable wherein a central conductive portion is surrounded by a thermoplastic insulating sleeve, the thermoplastic sleeve, in turn, being disposed within a web of stretchable paper or the like, the axis of which is disposed in parallelism with the axis of the conductor, the web being convoluted so that the outer marginal edge thereof overlaps the inner marginal edge of the web. A hot melt adhesive secures the outwardly lapping edge to overlapped portions of the web.
SUMMARY OF THE INVENTION The present invention relates to armored electrical cable and particularly cable of the type customarily referred to as BXv cable. Armored cables of this sort are well known in the art and may generally be stated to comprise two or more conductors, suitably insulated from each other, within a steel jacket, the steel strip dening the jacket being helically wound to provide a ilexible convoluted sheathing.
Prior to the middle 19505 the insulating material for the conductors typically comprised rubber. The use of thermoplastic insulating materials for -the conductors had been proposed. However, such insulation typically presented the drawback that, under heating conditions, the insulation would tend to flow clear of the conductor, with the attendant danger of short circuits of the conductors to each other or to the jacket of the cable.
In order -to make the use of thermoplastic insulating material practical, the prior art employed a wrapping, such as wax impregnated kraft paper or the like, wrapped helically about the insulator, the primary function served by the wrapping being to maintain the insulation about the conductor notwithstanding temporarytinsulation melting influences.
The helically wound insulator construction has been found to be disadvantageous in certain respects. The helical wrap depends upon the pitch of the web and if there is not 100% overlap there would be resultant gaps, with the result that the insulating material could leak from within the Wrapping under conditions which induce flow in -the insulation. In addition, the process of helical- 1y wrapping kraft paper or webs of other materials is inherently slower than the speed at which the conductor may be extrusion coated with the insulating material, since a greater length of web is helically wound about a lesser length of conductor. As a result, it was necessary, in the methods of making insulated conductors heretofore known, appreciably to slow down the extrusion process of encapsulating the conductor in the thermoplastic insulation, below the speed at which such operation could be accomplished, so as to keep pace with the time-consuming helical wrap forming operation.
In accordance with the present invention, the speed of production has been greatly increased and the quality of ICC the product has been augmented by wrapping the web about the thermoplastic conductor while maintaining the web axis in parallelism with the axis of the conductor during the wrapping step. The web is thus longitudinally Wrapped, as opposed to helically wrapped, a hot melt adhesive being introduced into the nip dened between the outermost marginal edge of the web and the outer surface of the web just prior to iinal overlap.
The thus covered conductor is pulled through a radial pressure bushing and the hot melt adhesive is permitted to harden or cure or congeal at temperatures below the melt lpoint thereof.
The improved ow resistance in the article of the present invention is occasioned, first, by the absence breaks or leak-prone areas in the covering material, where a longitudinal wrapping is employed and, second, by the absence of any flow inducing pressures exerted by a helically wrapped web against the insulation. Specifically, a helically wound wrapping, particularly where the web itself is stretchable to a degree, and is wound under any appreciable tension, tends, when the insulator material is heated to melting or flow temperatures, to exert pressures on the softened material, increasing the likelihood of a flow thereof, the flowing material in turn, causing a shifting of the helically wound layers, with a concomitant increase in the likelihood of interstitial leak spaces being formed between convolutes of the helical web.
It is, accordingly, an object of the invention to provide an improved insulated conductor particularly intended for use in armored cable.
A further object of the invention is the provision of a method and apparatus for making a conductor of the type described.
To attain these objects and such further objects as may appear herein or be hereinafter pointed out, reference is made to the accompanying drawings, forming a part hereof, in which:
FIG. 1 is a side elevational view, diagrammatic in form, showing an apparatus for making the device of the present invention;
FIGS. 2 to 6 comprise magnified vertical sections taken, respectively, on lines 2 2, 3 3, 4 4, 5 5 and 6 6 of FIG. 1, said figures showing progressive steps in the manufacture of the insulated conductor;
FIG. 7 is a sectional view taken along line 7 7 of FIG. l;
FIG. 8 is an isometric view of an insulated conductor formed in accordance with the invention;
FIG. 9 is an isometric view, on smaller scale than FIG. 8, showing the three strands of the conductor disposed within an armoring sheath; and
FIG. 10 is a section taken on the line 10 10 of FIG. 9.
In accordance with the invention, there is diagramatically and schematically shown in FIG. 1 an apparatus for manufacturing a wrapped conductor in accordance with the invention, the apparatus including a payout reel 10'on which is mounted a quantity of conductor wireA 11 to be insulated.
The wire is passed over support roller 12 into an extruder 13 of known construction which functions to apply to the wire a predetermined thickness of thermoplastic insulating material 13' of the type commonly used in the known helical wrap constructions. The plastic composition, which is immaterial to the present invention, is preferably comprised of a thermoplastic material having a melt temperature of about 360 F. The coated wire 14 passes from the extruder to an extended cooling trough 15 and thence one or more convolutions of the 'wire 14 are lwound about the periphery of a water cooling capstan 16, which also serves to draw the wire at a predetermined rate through the initial, i.e., extruding and trough cooling stations.
The wire 14, which is cooled by the capstan 16 to a degree at which the insulation coating 13' is no longer readily deformable, is introduced into a Wrapper device 17, which device functions to apply a double layer of web member 18 over the insulator layer 13 formed in the earlier stages.
The web 18, which is fed from rotatably mounted reel 20, preferably comprises a crinkled kraft paper strip of about 3 mil thickness, the material preferably being impregnated with a low melting wax such as paraine. The web is fed through slot 21 in a guide 21 in the folder device 17. The width of the web 18 is preferably about seven times the diameter of the insulated coated wire 14, which passes through a guide tube 19 below guide 21', to permit double coverage plus an overlap.
As the wire and web are advanced through the various stages depicted in FIGS. 3, 4, and 6, the web 18 is progressively caused to be convoluted longitudinally about the outer surface of the insulated wire 14 by a series of spiral or parti-spiral bent metal guide flanges 22, 23, 24 and 25, and guide channel 23. As the coated wire and web advance through these flanges, a rst A and, thereafter, a second B convolution of web are formed about the insulated wire 14, the emerging wrapped wire, as seen in FIG. 6, having the outermost marginal edge 26 extending beyond the inner edge 26. I is important to note that the web and wire are maintained and advanced in parallelism during the wrapping operation.
Certain advantages may be achieved by timing the process in a manner such that the residual heat in the insulation is sufficient to melt or soften the low melting wax components in the web. By this means a more intimate conformation of the web to the wire is achieved, and also the softened or melted Wax may serve as a lubricant when the web and wire pass through the web convoluting apparatus.
The material passes from the linal wrapping stage 25 (FIG. 6) to an adhesive applying station 27 which includes an applicator 28 which functions to extrude a small quantity of thermoplastic bonding material or glue into the nip between the marginal edge 26 and the outer surface of the convolution B of the web 18 as shown in FIG. 7.
While the specific composition of the bonding material employed is not critical, it is preferred that the melt temperature thereof be about 450 F., the solidified bonding material, at ambient temperatures, being highly flexible.
In the illustrated embodiment, the bonding initially comprises a coiled strand 29 of hot melt compound which is liquited in the applicator 28, it being understood that conventional glue applying apparatuses may be satisfactorily substituted for the illustrated device.
The wrapped conductor `30 passes from the station 27 t a compression bushing 30' which presses the marginal edge 26 against the outer surface of the convolution B, the bushing tending to distribute increments of the still liquid or deformable bonding material to the areas immediately adjacent the marginal edge portion 26 of the web.
The nished conductor 30 is stored on a powerized take-up reel 31 which also functions to draw the Wire through the folder mechanism and the adhesive applying station.
The finished conductor 30 is shown in FIG. 8 to comprise a tightly wrapped, longitudinally extending double layer A, B of web 18, the free marginal edge 26 of which has been adhesively secured to the underlaying layer of the web. It Iwill be noted that as the longitudinal axis of the web during the wrapping stages, was maintained in parallel With the axis of the wrapped wire, that the noted parallel arrangement exists in the finished conductor.
In FIG. 9 there is shown a section of finished armored cable 32, including a flexible armor jacket 33 enclosing three strands of finished conductors |30.
From the foregoing it will be appreciated that there is disclosed an improved conductor strand for incorporation within an armored cable or the like. Unlike helically wound conductors, wherein the wrapper material tends to unravel when severed, there is no such tendency in the longitudinally wrapped conductor material of the prese-nt invention.
Production in accordance with the apparatus and method disclosed is expedited since the web is advanced at the same rate as the advancing wire as it is being covered by extruding a plastic insulation, in contrast to helical wrapping devices and methods wherein the speed with which the web is applied must be considerably greater than the advance speed of the wire.
The apparatus is relatively simple as contrasted with helical Winding devices wherein the wrapper must be fed from complex planetary feed reel means which orbit the longitudinal axis of the wire.
A further advantage in the wire of the present device lies in the fact that even sharp bends formed in the wire are not likely to cause the formation of spaces or seams between progressive layers, as is the case with a helical wrapping, such bends, in the parallel wrapped conductor beig accompanied by a stretching of the crinkle paper rather than a shifting of helically wound layers.
As many changes could be made in the above method, article and equipment, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:
1. The method of producing an insulated conductor having improved resistance to breakdown under overheating conditions, comprising advancing a conductor wire from a bulk supply, progressively applying an insulating coating of thermoplastic material to said advancing wire at a temperature sufficiently high to melt said material, partially cooling said advancing coated wire, progressively applying to said partly cooled, coated wire a web of stretchable paper material impregnated with a low temperature melting wax while said coating of said wire is at a temperature above the melting point of said wax and while said wire and said web are advanced with the axis of said wire maintained in parallelism with the longitudinal axis of said web, progressively wrapping said web about said coated wire while maintaining said Wire and web axes in parallelism, to form at least one full convolution of said web about said coated Wire, and thereafter adhesively securing the free marginal edge of said web against an outer surface of said convolution.
2. The method of claim 1, including the step of applying inward radial pressure to said coated and wrapped wire, after application of said adhesive but before complete curing thereof.
References Cited UNITED STATES PATENTS '2,065,561 12/1936 Boyle et al. 156-54 2,426,413 8/ 1947 Pollett 156-56 2,948,647 8/1960 Lorch et al 156-56 3,340,113 9/1967 Burr 156-54 VERLIN R. PENDEGRASS, Primary 'Examiner