US 2690984 A
Description (OCR text may contain errors)
Oct 5, 1954 E. L. CRANDALL ET AL ELECTRIC CABLE JACKET Filed Jan. 25 1950 Inventors:
Eugene .B .CrandalL Vicen f f al bij l "Their` Atto egg.
Patented Oct. 5, 1954 ELECTRIC CABLE. JACKET Eugenev L.4 Crandall and Vincent. A. Shoals, Sche-- n'ectad'jg N. Y., assignors to General'. Electric Company, a corporation. ofv New York Application. January' 25, 19150,;'Seria1l No.. 1.405470 (Cl. 15d-27) 4' Claims.
This. invention relai-.esto a cable jacket and more. particularly to` a cable jacket for the pro.- tection of. electric cables in which a. metallic covering. such as a lead. sheath, ametallic. binding or shielding tape is employed over the cable insulation.
Inasmuch as a cablev jacket. is intended. to serve the dual function of reinforcing a lead sheath, for example, against internal cable pressures. andof protecting the sheath against corrosion and electrolysis encountered in connection witlrthe. usual underground service, primary consideration in the design ofa cable jacket is given to strength and corrosive resistant characteristics. The electrical properties of such jackets are. unimportant since the. Voltage encountered in stray currents are only of the order of a few volts. However, cable jackets. heretofore available have succeeded inV only partially performing the foregoing two important functions because the desired strength and corrosive-resistant properties combined with. a suitable long life have never been simultaneously present to the degree desired.
For example, it is common practice in the industry to employ a. jacket over. lead sheaths built up from a plurality of layers of tape comprised of a woven cotton fabric webv with. a calendered coating of a synthetic rubber-like material on one side thereof. Although the cotton fabric reinforces the jacket to a certain extent when the cable isinitially placedinservice, it has a certain degree of elasticity and sooner or later yields sufficiently to result, under fluctuating pressure conditions,4 in a loose relationship between the jacket structure proper andthe leadcable. sheath. Infact', such jackets have been known to. sleeve `or move with respect. toA the lead sheath even While still new when. the cable is. pulled into ducts upon installation.v Furthermore, under thesevere service conditions underground, cotton, not being a good corrosive resistant material, rots or deteriorates with the results that its. reinforcing value gradually diminishes and voidsare presented between the. jacket and lead sheath. into which moisture seeps or penetrates, as a. result 0f which the jacket, during subsequent heating and cooling cycles, swells to cause further separation thereof from the lead sheath. In addition, when cotton thus deteriorates, its reinforcing value, in preventing the lead sheath from swelling, due to internal pressure, is lost. This maybe followed by mechanical failure of the sheath and consequent electrical failure ofthe cable.
In an. effort to overcome these objections, the employment. of ber. glass has been considered as a. substitute for the cotton fabric currently employed. However, the employment of glass presents aproblem. in. that glass bers are brittle, easily broken when handled unprotected and when subjectedv to abrasion such as. would be experienced ifiber glass was positioned in direct contact with the lead sheath or other metallic covering of a cable or in direct contact with another ber glass body. In. addition, the glass fibers must be fabricated into such a structural form.. that their strength. properties will be realized and the bonding together of the material with which it is combined will. be facilitated. N evertheless,. it has been recognized that because of its superior inherentv strength, inelasticity, non-conductivity and corrosion resisting properties, the employement of glass could result. in a lead' sheathed cable protective jacket greatly superior to any other provided the foregoing objections to glass or the problems engendered thereby could be overcome.
Itis, therefore, an object of this invention to provide an improved electric. cable jacket having superior strength and protective properties and a length of' life commensurate with normal cable life.
It is also an object of this inventionto provide a cable jacket wherein glass is employed in such a manner that itis fully protected from damage both during the fabrication of the jacket and in the. finished. structure.
It is a further object of this invention to provide a new andv improved method for manufacturing an electric cable jacket.
Our invention will be better' understood from the: following description whentaken in connection withthe accompanying drawing andthe scope of our invention will be pointed out in the appended. claims. In the drawing, Fig. 1 illustrates. a partiall elevation. and sectional View of a. jacketed lead. sheathed cable embodying our invention as it would appear prior to the final completion step; Fig. 2. shows a plan view partly broken away of a tape employed to build up the jacket. structure of' Fig. 1; Fig.` 3 isy an enlarged section taken along the line 3 3 of Fig. 2 while Fig,y 41is. an enlarged section. taken along the line 4 4 of Fig. 2 and Fig, 5. illustrates an enlarged sectionalA view of. a portiony of. the. cable jacket asit would appear subsequent to nal comple.- tion..
According, to our invention. wev provide; an im.- provedv cable. jacket` comprising, generally speaking, a homogeneous layer of a rubber or rubberlike material such as neoprene having glass fiber threads imbedded therein and bonded thereto. To produce such a jacket we preferably iirst provide suitable tapes which are wrapped around the cable and subsequently vulcanized into a solid jacket body.
Although our invention is equally applicable to multi-conductor cables, we have shown in Fig. l, for illustrative purposes, a single conductor cable comprised of a stranded copper conductor l electrically insulated in any conventional manner by insulation Il which is in turn protected by a lead sheath l2. The lead sheath is covered by a protective jacket built up by layers of tape generally indicated by the numeral i3 which, in accordance with our invention, includes glass fibers but which is so fabricated that the previously existing disadvantages associated with the use of glass nbers have been overcome. Generally speaking the tape E3 consists of the combination of a body of glass bers and a rubber or rubber-like bonding material such as neoprene. In order to realize maximum strength, glass ber threads or yarn, constituting the body or web of the tape are preierably woven into a fabric. For a purpose which will subsequently be apparent, the glass fabric is woven so as to have an open weave providing interstices between the threads thereof having dimensions several times the diameter of the threads, as more clearly illustrated by Figs. 2 and 3. To fully and completely protect the glass web, it has been calender coated on one side with a layer or coating of neoprene i5 and on the opposite side with a similar coating of neoprene l. In the application thereof these two coatings are made to strike through the open weave of the web and bond to each other as shown in Fig. 4 to form an integral or homogeneous neoprene structure with the Woven glass fabric buried therein. To set the weave, to protect the glass fibers from abrasion against each other where the threads cross each other, to prevent distortion of the weave in subsequent handling of the tape and to provide an adhering surface for the calender coatings which assures bonding of the neoprene to the glass, it has been found desirable to apply to the woven glass fabric, prior to calendering, a thin surface covering of a suitable coating material such as neoprene cement.
The jack proper is built up by the application of one or more layers of such tape to the lead sheath of the cable. For the purpose of illustration we have shown in Fig. 1 three layers of tape il', 2S and iS each of which is spirally applied with close butt joints all in the same direction with a suitable break or tape joint to give an optimum leakage path consistent with mechanical strength. It should be noted that because of the particular manner in which the glass fabric has -been protected in the individual tapes, the glass web in the under layer l'l is isolated from the lead sheath I2 and in addition, the glass webs in each of the respective tape layers are isolated from each other. Thus, the possibility of damage to the glass fabric by abrasion is thereby eliminated. A combination cotton fabric and neoprene tape 2D comprised of woven cotton 2l calender coated on one side with neoprene 22 is applied overall. This tape. spirally applied in the opposite direction with a slight lap and with the neoprene coating toward the cable core serves as a protective tape to protect the finished jacket from damage while the cable is pulled into ducts. The jacket thus constructed is finally subjected to heat so as to vulcanize and cure the neoprene compound and bond all of the tapes together. In this operation the outer cotton tape also serves to prevent successive turns of coiled cable from sticking together before and during curing.
The resulting structure, as illustrated by Fig. 5, comprises a plurality of concentric layers of glass fabric and an outer concentric layer or coating of cotton fabric spaced from each other and from the lead sheath by alternate layers of neoprene compound bonded together through the open weave of the fabrics to form a completely integral or homogeneous neoprene structure reinforced by the glass fabric layers. By way of example, the glass fabric may be woven of 0.005 inch diameter yarn with 17 by 17 threads per inch resulting in a breaking strength of approximately '75 pounds per inch width. The thickness of the calendered neoprene may, for example, be 0.009 inch on each side of the fabric resulting in a thickness of neoprene between the layers of glass of 0.018 inch in the finished jacket.
As thus constructed a relatively non-elastic jacket is provided which prevents localized stress areas from forming in the lead sheath under cyclic movement due to temperature changes, and thereby adds to the life of the lead sheath by preventing bending fatigue cracks from developing. Moreover, the glass, being non-deteriorating, will not lose its strength and will permanently prevent swelling and bursting or' the lead sheath. Since glass fabric has a greater tensile strength than cotton fabric, it will, of course, be obvious that the thickness of a lead sheath protected by our jacket may be proportionately thinner than would otherwise be required for the same internal pressure conditions if a jacket incorporating cotton fabric were employed. Thus our invention provides a cable jacket wherein the desirable strength, corrosion and rot resisting properties of glass fibers are utilized to maximum advantage, but in which the undesirable breaking tendencies formerly associated with glass nbers due to abrasion and handling have been completely eliminated.
While we have, in accordance with the patent statutes, shown and described a particular embodiment of our invention, we do not desire our invention to be limited to the construction shown and described for it will, of course, be evident to those skilled in the art that changes and modifications may be made without departing from our invention. For example, in lieu of a plurality of concentric layers of glass threads fabricated into a woven structure with alternate layers of neoprene therebetween the alternate layers of glass may comprise glass threads spirally wound on a layer of neoprene or rubberlike material so as to be spaced from each other to facilitate the striking through and bonding of adjacent rubber-like layers. However, in this case also, care should be taken to provide for adequate bonding of the glass threads to the rubber-like material. We, therefore, aim in the appended claims to cover all such changes modiications as fall within the true spirit and scope of our invention.
What we claim as new and desire to secure by Letters Patent of the United States is:
1. In the method of providing an electric cable having a metallic sheath with an outer jacket comprising the steps of applying to a woven glass fabric having an open weave a thin coating of neoprene cement, of calender coating opposite surfaces of the coated glass fabric with an uncured neoprene compound so that the neoprene coatings will strike through the fabric openings and be bonded together through the glass fabric openings to form a flexible glass-reinforced tape, spirally winding a plurality of layers of said tape onto the metallic sheath of the electric cable and applying an outer protective cotton fabric tape thereover, thereby forming a built-up jacket structure, and then subjecting said built-up structure to heat sufficient to cure the neoprene, whereby said neoprene glass tape layers are bonded to each other and to said outer cotton fabric layer to form a unitary jacket body.
2. In the method of providing an electric cable v with an outer jacket comprising the steps of applying to a woven glass fabric having an open weave a thin coating of neoprene cement, calender coating opposite surfaces of the coated glass fabric with an uncured neoprene compound so that the neoprene coatings will strike through the fabric openings and be bonded together through the glass fabric openings to form a exible glass-reinforced tape, spirally winding a plurality of layers of said tape over the electric cable and applying an outer protective cotton fabric tape thereover, thereby forming a builtup jacket structure, and then subjecting said built-up structure to heat suiiicient to cure the neoprene, whereby said neoprene glass tape layers are bonded to each other and to said outer cotton fabric layer to form a unitary jacket body.
3. In a method as recited in claim 2 wherein the said cotton fabric tape is calender coated on its underneath side with a layer of neoprene before it is applied to form the outer covering of the cable.
4. In a method of providing an electric cable with an outer jacket comprising the steps of applying to a Woven glass fabric having an open weave a thin coating of neoprene cement, 5 of calender coating opposite surfaces of the coated glass fabric with an uncured neoprene compound so that the neoprene coatings will strike through the fabric openings and be bonded together through the glass fabric openings to form a flexible glass-reinforced tape, spirally winding a plurality of layers of said tape over the electric cable thereby forming a built-up jacket structure, and then subjecting said builtup structure to heat sufficient to cure the neoprene, whereby said neoprene glass tape layers are bonded to each other to form a unitary jacket body.
References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,183,811 Homan Dec. 19, 1939 2,315,736 Rosch Apr. 6, 1943 2,446,292 McConnell et al. Aug. 3, 1948 2,479,924 Gillis Aug. 23, 1949 2,483,404 Francis Oct. 4, 1949 2,496,279 Ely et al. Feb. 7, 1950 2,514,030 Swiss July 18, 1950 2,522,169 Frei Sept. 12, 1950 2,525,070 Greenwald et al. Oct. 10, 1950 FOREIGN PATENTS Number Country Date 520,246 Great Britain Apr. 18, 1940 558,033 Great Britain Dec. 16, 1943 OTHER REFERENCES Serial No. 275,250, Deppe (A. P. CL), published May 18, 1943.
G. E. Review, page 48, September 1949.