US1648443A

US1648443A - Electric cable

Info

Publication number: US1648443A
Application number: US39886A
Authority: US
Inventors: Cawthon Samuel Clifton
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1925-06-27
Filing date: 1925-06-27
Publication date: 1927-11-08
Anticipated expiration: 1944-11-08

Description

Nov. 8,l 1927.

S. C. CAWTHON Filed June 27. 1925 MUM /n Ven 70/ Jmae/W/a Patented Nov. 8, 1927.

UNITED STATES 1,648,443 PATENT OFFICE.

SAMUEL CLIFTON CAWTHON, OF WESTERN SPRINGS, ILLINOIS, ASSIGNOR TO WEST- ERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRIC CABLE.

Application led .Tune- 27, 1925. Serial No. `39,886.

This invention relates to electric cables, and more particularly to improvements in submarine cables and methods of making them.

In one type of submarine cables a plurality of conductors having paper or similar fibrous insulation are stranded together to form a cable core which is thereafter sheathed with a metal sheath, such as a lead alloy, preferably applied thereto in a substantially solid state by an extrusion press. This protective sheath is of great importance in submarine cables since it forms a seal for the core against the lentrance of water. It has been found in practice that the more nearly continuous the operation of extruding the lead sheath around the core with a minimum of interruption in the operation of the prelss the more etiicient and durable is the sea The usual practice in making submarine cables having paper or similar fibrous insulation is to provide a relatively large amount of insulation which is compressed as much as is mechanically possible without injuring the insulation during the stranding process. This compact form is used in order that as much resistance as possible may be offered to the flow of water in the event of a break in the sheathing and that the cable may be taken up and repaired before a substantial length thereof is ruined.

It has been suggested that by inserting plugs at intervals in under-water cables, the same effect can be obtained. The value of a plug lies chiefly in the fact that with its use a much more efiicient cable may be designed and constructed, for except at the actual plugging point, the cable may be made much less compact and therefore more efficient from a transmission standpoint than the type above mentioned. The cable can also be made with less insulating paper and of smaller diameter than is ordinarily possible.

The primary object of this invention is to produce a submarine cable having an im.- proved plug of this type the efficiency of one portion of which increases upon the failure of another portion, upon a break occurring in the cable, to positively seal the adjacent portion of the cable from the entrance of water.

Another object is to produce a plug of this type wherein the method of fabrication is such that it permits the subsequent sheathing ofthe. cable core to be accomplished with a minimum of interruption in the operation of .the extrusion press, in consequence of which a more durable and efiicient sheath is produced.

'In accordance with the general features of this invention, a section of the stranded cable core is first treated with a relatively thin water-proofing compound which will thoroughly impregnate and water proof the paper insulating material. The section is then subJected to a relatively heavy water proofing compound which will fill all the interstices between the individual strands constituting the core. Thereafter the impregnated section is bound very tightly by an elastic rubber tape for a portion of its length then loosely for another portion, and then tightly again for the balance of the impregnated section. A wrapping of strand. for instance, a cotton thread is then applied with sufiicient tension at the beginning and ending of each bound portion of the impregnated section. The cable core is then inserted in a suitably heated baking oven for a suitable period to remove any moisture which may be contained in the insulation of the cable core. Thereafter the diameter of the bound section is built up to the diameter of the adjacent portions of the cable core with a material of such a character that the heat of the lead covering when applied is sufficient to cause the material to flow into a homogeneous mass to completely fill the space between 'the core and the sheath.

Where plugs are inserted in a cable as hereinbefore mentioned, one method has been to bind a section of the cable core which has been previously impregnated with `a waterproofing compound having a comparatively low flow point with elastic rubber tape to give it a reduced diameter at a single portion of the impregnated section`I so that upon the subsequent binding thereof it will provide a certain degree of flexibility. This has the disadvantage that the impregnating compound at the baking temperature will tendy to flow from the center of the plug or the reduced portion toward either end and into other portions of the cable on account of the low flow point thereof, thereby reducing the effectiveness ofthe plug. If the plugs are inserted after the baking operation and during the covering of the cable core with a lead Sheath, for instance, the time of inserthe press is idle and consequently the outputv the accompanying drawing, in which conductorsllO are covered in the usual manner with paper insulating material. A section 11 of the cable core, preferably of from twelve to twenty-four inches in lengthisimpregnated with water-proofing compounds of the type fully described in copending application of F. S. Malm, Serial No. 630,201, filed April 6, 1923, with the exception that in the second impregnation a compound is used having a slightly higher flow point than thaty described in the aforementioned application which permits the plug to be fabricated before the baking operation, since the compound at the baking temperature will not tend to flow from the impregnated section into they adjacent sections of the cable core and thereby reduce the efficiency of the plug. It suffices tosay that a section of the cable core is first treated with a relatively thin Waterproofing compound composed of a mixture of rosin oil and rosin and the section is then subjected to a relatively heavy waterproofing compound composed of rosin oil, rosin and asphaltum in which the asphaltum is the major ingredient so as to give the impregnating compound a sufiiciently high flow point. Y

After impregnatingthe section of the core which is to form the plug with the water- .p proofing compounds above referred to, this section of the core is preferably wrapped one or more times with elastic rubber tape 12 with sufficient tension accumulatively .applied to the tape to bind the cable core into a very compact mass along two portions thereof indicated by the

numerals

13 and 14.

` In the embodiment illustrated in the drawing, only one tape l2 is shown applied to the core. Preferably a single tape 12 is applied helically to the core, beginning at either end of the section 11, and if this section is twelve inches in extent, it is first bound very tightly for four inches, then loosely for another four inches' along a 'portion 15 intermediate the

portions

13 and 14, and then very tightly again for four inches, the intermediate por.` tion 15 being bound tightly enough to reduce the diameter thereof as compared to the portions of the cable core adjacent the ends of the section 11, but not as tightly as the porduring service and. wat r under pressure should pass either of the ightly bound portions 13v and V14 thereof, the compound in the center portion which is more or less mobile due to its character and its comparative freedom to move in opposite directions, the latter being due to the loose binding of the center portion lq'as compared to the

adjacent portions

13 and 14, will be forced into the other` tightly bound portion thereby increasing the effectiveness thereof and pro viding a perfect seal for the adjacent portion of the cable core for preventing .the entrance of water thereinto. A wrapplng of some' suitable strand, for instance cotton thread, is then applied helically to the core with suflicient tension at the beginning and ending of each bound portion of the impregnated section as indicated by the numerals 16 to retain the tape in position. The cable core is then inserted in a suitably heated baking oven where it is heated for a period sufficiently long to expel any moisture which may be contained in the insulation ofthe cable core. A filling material is used to build up the diameter of the core to approximately that desired. The filling material may be of any suitable type which will beof a character to seal the space between the outside ofthe tape 12 and the inside of a lead sheath 17 when the sheath is applied thereto and is preferably applied just previous to the sheathing operation and after fthe baking operation. Although this requires the stoppage of the press, it is of small consequence since the filling material may be applied very quickly compared to the method hereinbefore referred to wherein the entire plug is inserted during the stoppage of the press. Preferably, I employ for this purpose material of the type described and fully llt) disclosed in the copending application of F. S. Mahn, Seria'l'No. 331,360 filed April 11, 1923,` to which reference may be had for a disclosure as to the particular ingredients thereof. This material is composed of a .mixture of a plastic gum, such as crude rubber, an adhesive material which will soften t-he gum, such as a mixture of resin-and rosin oil, and a fibrous' filling material, such as asbestos fibers, and is of such a character that the heat of the lead sheath 17 when applied is sufficient to cause the Jsaid material', indicated in the drawings by the reference numeral 18,.to flow' into a homogeneous mass to completely fill the space between 'the core and the sheath. When the lead sheath 17 is in place, a hemp coverin 19, a steel armor 20, and an outer jute co ering 21 are applied in the usual manner.

By constructing a plug in accordance with be apparent.

the method hereinbefore described, a sealing compound having a maximum resistance to flow may be used for impregnating that section of the cable core to be plugged, and still retain a given amount of flexibility, due to the loose binding of the portion 15 as compared to the binding of the

portions

13 and 14 at either side thereof, as will readily Also with the use of such a compound a plug is provided which may be inserted in the cable core before the baking operation, and consequently the subsequent cable core sheathing operation may be accomplished with a minimum of interruption to the operation of the extrusion press, in consequence of which a more durable and efficient sheath is produced.

What is claimed is:

1. The method of making a submarine cable, which consists in assembling into a cable core a plurality of insulated conductors, impregnating a section lof said cable core and compressing spaced portions of said section to form seals and to confine therebetween a mobile body of impregnating material whichl is forced toward one portion to increase the effectiveness thereof upon the failure of the other portion to protect the cable.

2. The method of making a submarine cable, which consists in assembling into a cable core a plurality of insulated conductors, impregnating a section of said cable core and compressing spaced portions of said section and a portion therebetween whereby one portion effectively functions in the event of failure of the other portion to protect the cable.

3. The method of making a submarine cable, which consists in assembling into a cable core a'plurality of conductors having a fibrous insulation, impregnating a section of said cable core, compressing a portion of said section, and further compressing to a greater degree the portions at either side thereof, whereby .one portion effectively functions in the event of failure of another portion to protect the cable.

4. The method of making a submarine cable, which consists in assembling into a.v

cable core a plurality of conductors having a fibrous insulation, impregnating a section of said cable core, and compressing a portion of said section in such a manner that the diameter is Ireduced at a plurality of portions, an intermediate portion being greater in diameter than the other reduced portions but smaller than that portion ofthe core not Lreduced in diameter, whereby one portion effectively functions in the event of failure of another portion to protect the cable.

5. The method of making a submarine cable,v which consists in assembling into a cable core a plurality of conductors having a fibrous insulation, impregnating a section of said cable core, compressing spaced portions of said section `and aportion therebetween whereby one portion effectively functions in the event of failure of the other portion to protect the cable, subjecting the cable core thereafter to a drying medium to remove any moisture contained therein, thereafter building up the compressed portions of said cable core to the size of the uncompressed portion thereof andsubsequently applying a sheath to the cable core.

6. In a submarine cable, a core comprising a plurality of conductors having a fibrous insulation, said core having an impregnated section, and a tape applied -to said section so that portions of said section at either side of a central portion thereof are compressed whereby one portion effectively functions in the event of failure of the other portion to protect the cable.

7. In a submarine cable, a core comprising a plurality of conductors havingv a fibrous insulation, said core having an impregnated section, and an elastic rubber tape applied helically to said section so that the diameter is reduced at a plurality of portions, an intermediate one of said portions being greater in diameter than the other reduced portions but smaller than the remainder of the core whereby one portion effectively functions in 4the event of a failure of the other portion to protect the cable.

In witness whereof, I hereunto subscribe my name this 16th day of June A. D., 1925;

SAMUEL CLIFTON CAWTHON.