US 3857996 A
Power cable such as pendant cable is found to have improved flex life when it combines propylene-ethylene copolymer insulation on the individual conductors with a polyurethane thermoplastic overall jacket.
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United States Patent 1191 Hansen et al.
[ Dec. 31, 1974 1 FLEXIBLE POWER CABLE  Inventors: Theodore E. Hansen; Floyd A.
Wilson, both of Marion, 1nd.
[731 Assignee: vThe Anaconda Company, New
' York, NY.
22 Filed: June 18, 1973 21 Appl. No; 371,320
2] US. Cl. 174/113 R, 174/116, 174/120 SR 1] Int. Cl. HOlb 7/02 8] Field of Search 174/116, 113 R, 120 AR,
174/120 SR, 110 R, 1 PM  References Cited UNITED STATES PATENTS 1/1950 Rapp 174/116X 1/1973 Hoeg ..174/120 AR OTHER PUBLICATIONS Avisun Corporation Bulletin, Gade TD-321D Gen- PROPYLENE-ETHYLENE COPOLYMER eral Purpose Electrical Insulating Polymer, 5-1966. Aamodt et al.. Propylene-Based Copolymers in Wire and Cable Application, 12th Annual Wire and Cabl Synposium, 12/63. 29 pages Rosato Electrican Wire and Cable Plastics What Ahead, in Wire & Wire Products, 3/70, pp. 49 and 56.
Jones, An Oil Extended Ethylene-Propylene Rubber for Cable lnsulations and jackets, in Wire 1l/66, pp. 1822-1826.
Prima1y'ExaminerE. A. Goldberg Attorney, Agent, or Firm-Victor F.'Volk ABSTRACT Power cable such as pendant cable is found to have improved flex life when it combines propyleneethylene copolymer insulation on the individual con ductors with a polyurethane thermoplastic overall jacket. 1
4 Claims, 1 Drawing Figure POLYURETHANE THERMOPLASTIC PAIENTEDHEB31|9?4 3.857. 996
POLYURETHA PROPYLENE- ETH THERMOPLAS COPOLYIVIE FLEXIBLE POWER CABLE BACKGROUND OF THE INVENTION Flexible electric cables, and particularly cables for use suspended in pendants where they are subjected to repeated folding and unfolding and where interruptions in service due to cable failure are costly and the failures themselves may be dangerous, are the objects of continuing research for means of improving their flex life. Cables in general use today greatly outlive the cables of a decade ago by reason of a number of cable improvements, each of which was the survivor of a number' of proposed improvements which did not test out. In one form of flex life test, or fatigue test, these cables are loaded with weights pulled back and forth over sheaves until conductors in the cable break or are short circuited. Clearly, the flex life performance of a proposed cable is unpredictable since, if it were not, such expensive, time-consuming, test programs would not be necessary. The elements of a cable interact in such a complex manner that no adequatetheory has ever been developed for the prediction of cable performance and each proposed new cable construction must be extensively tested in the laboratory and in field trials.
SUMMARY- We have invented an improved flexible cable which, as shall be shown, outlasts presently known constructions due to a synergism of the cable elements as now, for the first time, combined. Our novel, improved flexible power cable comprises, in combination, a plurality of copper conductors, each stranded from a plurality of wires. a heavy wall of propylene-ethylene copolymer insulation covering each of the conductors and a polyurethane thermoplastic jacket'surrounding the conduc- 4,100 pounds per square inch when tested according to ASTM test method D-638-6 IT, a 100 percent modulus of 1,170 pounds per square inch when tested according to ASTM test method D4 1 2, and a dilatometer melting point of 165C when tested according to ASTM test method D-785-60T. These values should, in any event, exceed 950 pounds per square inch for the 100 percent modulus, 3,700 pounds per square inch for the yield strength, and 155C for the dilatometer melting point.
Each of the conductors 11-14 covered with a layer 16 comprises a strand 17, 18, 19, 20 and the four strands are cabled together with about a three-inch right hand lay. Over the bunched conductors 11-14 and under the walls 16, we have applied a one-half mil longitudinal polyester tape 21. These are applied at the extrusion machine and prevent the extruded composition from penetrating the wire strands. It is known to stabilize the copolymer compositions against a poisoning effect of copper by incorporation of inhibitors such as oxanalide and the composition of walls 16 is so stabilized, but the tapes 21 add further protection against copper migration into the insulation. During the cabling operation, the cable core is rounded out conventionally by the inclusion of paper wrapped rayon fillers tors with their. walls of insulation. In a preferred embodiment of our invention, the insulated conductors are helically cabled together to form a flexible core. The polyurethane thermoplastic used for the jacket may advantageously be based on polytetramethylene ether.
BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows a section of a cable of our invention. 1
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT -32 l. The copolymer we have found suitable for insulations in our cable is distinguished from monomeric polypropylene in having a much lower brittle point when tested in accordance with ASTM D-74,6-57T.
The brittle point ofa selected insulation l,6 is l6C and a copolymer having a brittle point of at most -IOC should be used. The copolymer is essentially distinguished from monomeric polyethylene in having higher tensile strength, modulus and melt temperature. The copolymer of the walls 16 exhibits a yield strength of A thirty mil thick jacket 23 of polyurethane thermoplastic has been extruded over the cable strands l7-20. A suitable composition for the jacket 23 is commercially available from Uniroyal, Inc. under their trademark Roylar, designation XE-87- 101 which is based on polytetramethylene ether. This composition has the following unaged typical properties:
ASTM TEST METHOD Shore A hardness Tensile Modulus, psi
Ultimate Tensile Strength, psi 7c Elon ation 20071 ongation Set, Elon ation Set at Break 71 Bell rittle Point, F S cific Gravity elt Temperature award of Letters Patent as defined in the following claims.
We claim: l. A flexible power cable comprising, in combination.
A. a plurality of copper conductors, each being stranded of a plurality of wires, B. a heavy wall of propylene-ethylene copolymer insulation having a yield strength of at least 3,700 pounds per square inch and a dilatometer melting 3 I 4 point of at least 155C covering each of said congether to form a flexible core. ductors, and 3. The cable of claim 1, wherein said polyurethane is C. a polyurethane thermoplastic jacket surrounding based on polytetramethylene ether.
said conductors having said walls of insulation. 4. The cable of claim 2, wherein said polyurethane is 2. The cable of claim 1, wherein said conductors 5 based on polytetramethylene ether. being covered by said walls, are helically cabled to-