US 2118630 A
Description (OCR text may contain errors)
May 24, 193s. C. www@ M3263@ ELECTRIC CABLE Filed, l5, 19358 (APS) INVENTOR Buhl,
`COMM/Groff.; 60A/9mm? M445 Z5/WHW @5M/SNT @amg/V7* AT1 ORNLLYS Patented May 24, 1938 PATENT OFFICE ELECTRIC CABLE Richard C. WaldromClifton, N. J., assignor to The Okonite Company, Passaic, N. J., a corporation of New Jersey Application January 15, 1936, Serial No'. 59,204
This invention relates to an improvement in electric cables particularly adapted for vertical suspension as for example in the exploration of oil wells, and has for one of its objects the provision of a cable which is so constructed as to limit or restrict the elongation of the cable conductors. In previous cables for vertical suspension diillculty is experienced with elongation of the conductor of the cable to such an extent that upon contraction of the cable, i. e., restoration of the cable to its original length, the conductor buckles, repetition causing the conductor to break. This difficulty is eliminated in the present construction.
One of the objects of the present invention is the provision of an electric cable construction in which stretching of the conductor is so controlled that the cable can be elongated and restored to its original length without buckling and breaking of the conductor, my copending application Serial No. 58,475, tiled January l0, 1936, showing a construction inwhich the conductor will stretch and contract with the cable without deformation.
More specifically the present invention'provides a cable construction in which the conductor is applied helically about an extensible, incompressible core at a critical lay, the lay of the conductor about the core being such that upon initial elongation of the cable the conductor is elongated to a predetermined degree, elongation of the conductor being so controlled and restricted by the core and the lay of the conductor about the core that upon the tension being removed from the cable the 'cable can be restored to its original length without buckling of the conductor.
Comparing the cable of my invention with prior cables, and assuming the same certain desired percentage elongation of the cable in both instances, in prior cable structures the conductor is stretched to such an extent that upon return of the cable to its original length the conductor buckles, repetition resulting in breaking of the conductor; with my improved cable the conductor is so laid up about the core that the stretch or elongation of the conductor is materially reduced, and as a consequence, although the percentage of elongation of the cable is the same in both instances, my cable can be elongated and contracted repeatedly without buckling and breaking of the conductor. l
In addition to all of the foregoing in my improved construction the lay of the conductor is sufiiciently long so that the cable cannot be stretched without the conductors pulling down on the core and being deformed. As a consequence my construction adds the iullstrength of the conductor to the core due to the conductor pulling down on the core. It will be appreciated that this is of advantage in manufacture and avoids breakage of the core in manufacturing the cable.
Referring to the drawing: Fig. i is a part sectional View of a bodying my invention; l
Fig. 2 is a cross section of the cable of Fig. l; Figs. 3 and 4 are cross sectional views illustrating the relative positions of the cable conductor and core at different stages of elongation of the cable;
Fig. 5 shows one strand of the unstretched cable conductor about a core of extensible sub cable emstantially incompressible material ;V
Fig. 5A is an end view of thestructure of Fig. 5;
Fig. 5B is a development of a cylinder Whose O diameter is the pitch diameter of the strand of Fig. 5 and whose length is the length of lay of the strand of Fig. 5;
Fig. 6 shows the core and strand of Fig. 5 in stretched position;
Fig. 6A is an end view of Fig. 6;
Fig. 6B is a development of a cylinder whose diameter is the pitch diameter of the stretched strand of Fig. 6 and Whose length is the length of lay of the strand of Fig. 6; 30
Fig. 7 shows the condition ofthe conductor strand after the strand and core of Fig. 5 have been elongated and then allowed to contract;
Fig. '7A is an end view of Fig. r1;
Fig. 7B is a development of a cylinder whose diameter is the pitch diameter of the strand of Fig. 7 and whose length is the length of lay of the strand of Fig. 7;
Fig. 8 shows one type of conductor which may` be employed in the practice of my'invention;
Fig. 9 shows another type of conductor; and Fig. 10 still another type;
Figs. 11 and 12 are views of modified embodiments of my invention wherein multi-conductor cables are shown instead of the single conductor 45 cable of Fig. 1.
Referring to the drawing in detail and first of all to the construction illustrated in Figs. 1 to 7B, inclusive. I designates the core of my improved cable. This core is of pliable, exten- 50 sible, substantially incompressible material such as rubber. A brous material may be employed for the core if desired, such as silk or cotton thread, for example, which may be twisted together so as to provide a core which is sufliciently 55 incompressible and yet at the same time s ciently extensible and pliable for iny purpose.
About tlrls extensible, substantially incon sible core apply the conductor il. This conductorniay be composed of copper strands liellcally applied in parallel relation with a predetermined lay about tbe core l as will be brought ont in detail hereinafter. Directly over the conductor 2 'i apply insulation 3. This may be the usual rubber or rubber compound insulation commonly employed in electric cable Work.
About insulation 3 l apply a fabric cover-- ing l which may be in the form of a fabric tane saturated with oil and moisture impervious inam terial such as .rvel which is an acid condensa- 'tion product made from the oil obtained from cashew nnt shells.
designates a supporting armor consisting o-rnv stranded steel `wires. These wires are the as commonly employed in steel wire rope and' may be laid up in any of the methods common to wire robe manufacture.
.as cointed ont at the outset of tliis desert on, one oi the objects of my invention is the provision oi an electric cable wherein a construction is provided by which detrimental stretching of the conductor is avoided, tbe present construction providing that the elongation o the cable conductor shall be limited to apoint or degree where tbe cable a `whole may elongate and contract tvltbont detrimental buckling and eventual brealring oi the cono `,ctor. This construction is nrovided Under the present invention by applying the conductor the extensible, incompressible core oi the ca 1le with predetermined lay, which li term the c cal" lay. li the angle of lay of the conductor about the core is too long then npon elongation of the cable the inside diameter of the helix provided by the conductor decreases too fast as compared with the decrease in the outside diameter of tbe core andupon desiredelon gation oi the cable the conductor will be excessively stretched. On the other hand, the. lay is too short then the outside diameter of the core decreases too tast as compared with the decrease `in the inside diameter of the helix provided by the conductor and the conductor adds no strength to the core. ln accordance with the lpresent invention the conductor is laici about the core at such an angle that initially were the cable compressed, i. e. shortened, the core would increase in diameter faster than the conductor, and on elongation of the cable the conductor tends to pull down on the core.
With reference to the showing in Figs. 5 through 7B of the drawing, Figs. 5 and 5a show the initial position of each conductor strand.
da=the diameter of the core l d :the diameter of each strand of the cable condnctor D:pitch diameter of each strand or the con'- ductor :da-Hi L :length of lay of each strand of the conduc- In Fig. 6 I have illustrated the core and strand of Fig. 5 in stretched position. Here do:the diameter of the core l under the assumed conditions Di :the pitch diameter of the conductor strands a' :length or conductor strand for one complete about the core l i :'sercentage elongation which the cable is designed decimal) e l the cable has l een elongated and then allowed to contract and here f""n:t" diameter of tbe core 6:62@ lli :tne T oitclo diameta the conductor strand The lay of the condnctor il enen that initially, as .chown ir about and in contact 'w n the cable is allowed t e. 7, to origi cl le' dnctor i, however, o conductor has bee conductor -will again decrease outside diameter o'4 the core l niaiiininn elongati of the reached conductor :vill agaii l but Without further stretching oi tne c toi'. ieese conditions exist only tor a @erin critical lay", of the conductor the formula that vv `1 cable ln tbis oi cable the conductor ma" terially to the tensile strength or" the core will be appreciated inasmuch as the permitted elongation of the conductor is less 'than possible elongation of the core before breaking. is an advantage in manufacture in that it gives additional strength to the core.
As above mentioned an object of my invention Upon stretching the conductor the strand length c is increased as can be shown by an analysis oi the equation Dol=dol+d ol: do 41+ IFT #1,015+ d) Upon return of the conductor to its normal length after this initial stretch we have which is obviously larger than D. The increase in D depends on the increase in a or on the stretch 1S.. If S is small, such es normally occurs in cables, the increase in D" will be small and no distortion of the strand will result.
In this analysis, we have assumed d constant. For some constructions this might not be justified but for the usual constructions and for S less than 1/6 the change in d is negligible.
It will be seen from all of the foregoing that the present invention provides an electric cable construction in which the conductor is applied about an incompressible but extensible core with such a lay which I have termed a critical lay, that the inside diameter of the helix provided by the conductor initially contracts or decreases just slightly faster than the outside diameter oi the core so as to control or restrict to a predetermined extent the elongation of the conductor with a given predetermined elongation of the cable, this stretch of the conductor, however, is
' not sufiicient to prevent the conductor contract" ing without buckling as the cable contracts, the conductor remaining out of contact thereafter with the core except on subsequent elongations of the cable wherein at the limit of elongation for which the cable is designed the conductor again is drawn into contact with the core. In
' other Words, the lay is such that the inside diameter of the helix provided by the core always decreases faster than the outside diameter of the core, the initial elongation of the cable causing the conductor to stretch permanently so that on subsequent elongations the conductor will elongate without stretching until it contacts with the surface of the core.
Various types of conductor may be employed in the practice of my invention and in Figs. 8, 9 and 10 I have illustrated types of conductor diierent from that shown in Fig. 1, 8a showing a conductor made up of a group of strands previously twisted together, 9b a tape and IIIe woven or braided tape.
The invention of this application may be embodied in multi-conductor cables.
In Fig. 11 I have illustrated a multi-conductor cable in which a plurality of single conductor cables of the same type as shown in Figs. 1 and 2 are assembled around a 'core of hemp or other suitable material, these cables being designated I and the core II.
In Fig. 12 I have illustrated another modification in which two cables I2 of the type shown in Flg. 2, for instance, but Without the supporting armor wire, are twisted together, a circular cross section built up with jute I3 surrounded by tape I0, and a. plurality of single conductor cables I of the type shown in Figs. 2 or 11 laid about this assembly.
What I claim is:-
l. An electric cable comprising in combination a core of extensible, substantially incompressible material, and a conductor helically applied about and in contact with said core with such a lay that initially were the cable compressed longitudinally the core would increase in diameter faster than the conductor, While on elongation the conductor would tend toy pull down on the core.
2. n. multi-conductor cable comprising in combination a plurality of single conductor cables twisted together and each composed of a core of extensible substantially incompressible material, a conductor helically applied about and in Contact With said core with suon a lay that initially were the cable compressed longitudinally the core would increase in diameter faster than the conductor, while on elongation the conductor would tend to pull down on the core, a plurality of similar single conductor cables laid up about said first mentioned cables, each o the last mentioned cables being enclosed in supporting Wires.
3. A multi-conductor cable comprising in combination a plurality of single conductor cables disposed about a central core, each single conductor cable comprising a core of extensible, substantially incompressible material, a kconductor helically applied about and in contact with said core with such a lay that initially were the cable compressed longitudinally the core would increase in diameter faster than the conductor, while on elongation the conductor would tend to pull down on the core, and armor supporting wire for each cable.
4. An. electric `cable comprising in combination a core of extensible, substantially incompressible material, and a conductor helically applied about and in contact with said core with such a lay that initially were the cable compressed longitudinally the core would increase in diameter faster than the conductor, while on elongation the conductor would tend to pull down on the core, insulation about the conductor and supporting wires about said insulation.
RICHARD C. WALDRON.