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Publication numberUSRE30715 E
Publication typeGrant
Application numberUS 05/957,046
Publication dateAug 18, 1981
Filing dateNov 1, 1978
Priority dateNov 1, 1978
Publication number05957046, 957046, US RE30715 E, US RE30715E, US-E-RE30715, USRE30715 E, USRE30715E
InventorsLeo V. Woytiuk
Original AssigneeNorthern Telecom Limited
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Water blocked electric cables
US RE30715 E
Abstract
An electric cable having a multi-stranded core of insulated conductors and a jacket, in which the spaces between and around the conductors are at least partially filled with a mixture which forms a blockage to the penetration of water. The mixture comprises water repellant treated calcium carbonate and high molecular weight polyacrylamide resin which do not react with each other or when in contact with water. Preferably the individual conductors are coated with a hydrophobic liquid such as a low viscosity paraffinic oil.
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Claims(10)
I claim:
1. An electric cable having a core of a plurality of insulated conductors and a jacket, the interstices between the conductors and within the jacket being at least partially filled with a mixture of water repellant treated calcium carbonate and at least one high molecular weight resin rapidly hydratable to form a viscous solution.
2. A cable as claimed in claim 1 in which the calcium carbonate is surface coated with a water repellant long chain fatty acid or modified fatty acid selected from the group consisting of lauric acid, myristic acid, palmitic acid, stearic acid and arachidic acid.
3. A cable as claimed in claim 1 in which the resin is an anionic polyacrylamide resin with an average molecular weight between 2.5106 and 7106 and with between 12% and 28% acrylamide groupings which have been chemically converted to acrylic acid groupings.
4. A cable as claimed in claim 1 in which the resin is a polyacrylamide resin which has been crosslinked by irradiation.
5. A cable as claimed in claim 1 in which the resin is irradiated cross-linked polyethylene oxide.
6. A cable as claimed in claim 1 in which the resin is a hydrolized starch graft polymer of polyacrylonitrile.
7. A cable as claimed in claim 1 in which the mixture fills between 30% and 95% of the total volume of the interstices.
8. A cable as claimed in claim 1 including a core wrap and a metal sheath located between the conductors and the jacket, the mixture being also interposed between the core wrap and the metal sheath.
9. A cable as claimed in claim 1 in which the conductors are each coated with a hydrophobic liquid.
10. A cable as claimed in claim 9 in which the hydrophobic liquid is a low viscosity paraffinic oil.
Description

.Iadd.This application is a continuation-in-part of my copending application Ser. No. 556,294 filed Mar. 7, 1975, now U.S. Pat. 4,004,077 issued Jan. 18, 1977. .Iaddend.

This invention relates to electric cables protected against the entry and migration of water.

Cables for use underground where water is present in the environment are now manufactured by filling the interstices between and around the conductors with a jelly or greaselike material to protect the polyolefin insulated conductors against contact with water entering the cable and to prevent any water which does come into contact with a conductor from excessively migrating along the conductor. For effective water blockage such a cable must be filled almost 100% which requires a large amount of filler material. Also, the jelly or greaselike material is difficult to remove from the conductors during splicing and terminating the cable. It is often necessary to apply the filling compound hot and this tends to degrade the insulation on each conductor. The jelly or grease like material also sometimes imparts stiffness to the cable which hampers installation, especially at low temperatures. A further disadvantage is that such materials are flammable.

It has been proposed to replace the jelly or greaselike material with a powder filling which will react with water to form water blockage materials. An example is disclosed in U.S. Pat. No. 3,538,235 issued Nov. 3, 1970 to Ilse Arendt et al assignors to Siemens AG. However, the powder mixture of the Arendt cable swells on contact with water and alters the mutual capacitance of the cable to an inacceptable degree. If a lower concentration of powder mixture is used the swelling of the resin by itself is not sufficient for adequate water blockage.

Another example of a powder filling which swells on contact with water is disclosed in U.S. Pat. No. 3,803,339 issued Apr. 9, 1974 to Speekman where the interaction of the water with the powder also generates a gas which urges the expanded polymeric material into the voids within the sheath of the cable. Here again the composition and the configuration of the core are altered, which adversely affects the mutual capacitance of the core. More specifically the generation of a gas releases electrolytic ions which adversely changes the specific inductive capacity of the separating medium while swelling and gas pressure changes the geometric configuration of the core. Also, the gas-evolving materials may contain allergenic, toxic and hazardous components or they may produce harardous and objectionable by-products. In German Patent No. 2,007,163 dated Sept. 2, 1971 it has been suggested that polyvinyl alchol or polyacrylamide could be used as a swelling agent but certain of those synthetic resins do not swell rapidly enough in cold water to effect a satisfactory water block where the core is only partially filled with a powdered water blocking agent. Since synthetic resins of this type are expensive, it would be uneconomical to pack a cable core fully with such materials.

The present invention overcomes these disadvantages by providing an electric cable partially filled with a powder material which will block the ingress of water at low temperatures (i.e. ground temperatures). The invention further provides an electric cable having a filler which is non-flammable, non-allergenic and non-toxic and which does not produce deleterious by-products when heated.

In its broadest aspect the invention consists of an electric cable having a core of a plurality of insulated conductors and a jacket, the interstices between the conductors and within the jacket being at least partially filled with a mixture of water repellant treated calcium carbonate and at least one high molecular weight resin rapidly hydratable to form a viscous solution. Preferably the conductors are each coated with a hydrophobic liquid.

Example embodiments of the invention are shown in the accompanying drawings in which:

FIG. 1 shows a multi-stranded, jacketed electric cable filled according to the invention; and

FIG. 2 shows a multi-stranded, sheathed and jacketed electric cable filled according to the invention.

The example embodiment of FIG. 1 shows a cable 10 comprising a plurality of insulated conductors 12 stranded together to form a core enclosed in a jacket 14 of polyethylene or other material. The interstices between conductors 12 and jacket 14, and between the conductors themselves, contain a filler 16 comprising a mixture of a hydrophobic powder in the form of water repellant treated calcium carbonate and a hydrophilic powder in the form of at least one high molecular weight resin rapidly hydratable to form a viscous solution. Preferably the hydrophobic powder is a .[.long chain fatty acid coated.]. .Iadd.water repellant treated .Iaddend.calcium carbonate .[.such as that.]. .Iadd.which has a surface coating of a long chain fatty acid or modified fatty acid such as lauric acid, myristic acid, palmitic acid, stearic acid, or arachidic acid. Suitable such powders are .Iaddend.sold under the trade .[.mark.]. .Iadd.marks .Iaddend."Protaxulate" or "Protex E" by Pluess-Stauffer A.G. of France.[., and the.]..Iadd.. The .Iaddend.hydrophilic powder is a high molecular weight .Iadd.resin, and one such resin is a high molecular weight .Iaddend.polyacrylamide such as that sold under the trade mark "Separan" by Dow Chemical Corporation or "Magnifloc" by the Cyanmid Company. .Iadd.Other suitable resins may be a polyacrylamide which has been cross linked by irradiation, an anionic polyacrylamide having an average molecular weight between 2.5106 and 7106 and with between 12% and 28% acrylamide groupings which have been chemically converted to acrylic acid groupings. Additionally, the resin may be an irradiated cross-linked polyethylene oxide or a hydrolyzed starch graft polymer of polyacrylonitrile. .Iaddend.It should be noted that the manufacturers of such .[.hydrophilic.]. .Iadd.hydrophobic .Iaddend.powders specify compacting to achieve water blockage but it will be appreciated that tamping of the core filler in the production of a continuous cable would be very difficult to achieve.

The percentage composition of filler 16 should be between 95% and 70% by weight of the hydrophobic powder and between 5% and 30% by weight of the hydrophilic powder, depending upon the electrical characteristics required of cable 10. The more critical the electrical transmission requirements, the lower will be the percentage by weight of the hydrophilic powder. For instance a telephone cable would require a minimum amount of the hydrophilic powder, i.e. 5%.

Using filler 16 of the invention it is not necessary to substantially fill the voids in .[.claim.]. .Iadd.cable .Iaddend.10. It has been found that in certain instances cable 10 will be water blocked when filled only 33% by volume, because of the nature of the reaction of filler 16 to the ingress of water into the core of the cable. When such ingress occurs in sufficient quantity to break down the surface tension of the coated calcium carbonate the polyacrylamide will dissolve rapidly in the water to increase the viscosity of the water. The solution will travel only a short distance along the cable core, depending on the percentage by volume of the filler present in the core and the pressure of the water itself.

.Iadd.The mixture may fill between 30% and 95% of the total volume of the interstices. .Iaddend.

To aid in the production of the filled cable core, and to inhibit the powders of filler 16 from falling out when cable 10 is cut, it is advantageous to wet the surfaces of the insulation of conductors 12 with a hydrophobic liquid which will not produce adverse characteristics to the cable such as stress cracking in a polyethylene jacket. A low viscosity paraffinic oil would be suitable for the purpose preferably with a high analine point.

In the embodiment shown in FIG. 2 of the drawings a shielded cable 20 is formed by applying a core wrap 22 and then a metal sheath 24 between conductors 12 and jacket 14. Before applying core wrap 22, filler 16 is introduced to occupy the voids between conductors 12 as before. After core wrap 22 has been applied a further amount of the same mixture of hydrophobic powder and hydrophilic powder is applied with metal sheath 24 to form a layer 26 interposed between the core wrap and the sheath.

In specific tests three different telecommunications cables consisting of 25 pairs of 19 gauge insulated conductors were filled in the interstices with varying amounts of powder comprising 80% by weight of water repellant treated calcium carbonate and 20% by weight of high molecular weight polyacrylamide resin. The resultant cables had the following characteristics:

______________________________________              Test ResultsDesired Nominal Level                (1)     (2)     (3)______________________________________Filling by bulk        60%         55      57    67densityAverage water flow        35 inches max.                    14      26    17in core after 22days with 3' headof waterAverage mutual        0.083  0.005                    0.080   0.079 0.079capacitance______________________________________
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3538235 *Nov 26, 1968Nov 3, 1970Siemens AgMethod of making telecommunications cables
US3711621 *Feb 18, 1971Jan 16, 1973Gen Cable CorpMoisture block in sheathed telephone cables
US3803339 *Dec 14, 1972Apr 9, 1974Philips CorpLongitudinally watertight cable
US3903013 *Oct 19, 1972Sep 2, 1975Int Standard Electric CorpWater blocking gel composition
US3915888 *May 9, 1973Oct 28, 1975Hoeppel Raymond WOil base gel having low viscosity before gelation and method for its preparation
DE2006359A1 *Feb 6, 1970Aug 19, 1971Siemens AgPlastics insulated signal cable
DE2007163A1 *Feb 17, 1970Sep 2, 1971Sichel Werke GmbhWatertight electric cable
DE2257133A1 *Nov 18, 1972May 22, 1974Aeg Telefunken KabelwerkeSystem zur uebertragung elektrischer energie
GB1116175A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US5072073 *Sep 19, 1990Dec 10, 1991In-Situ, Inc.Cable sealing method and apparatus
US5095176 *Jun 12, 1990Mar 10, 1992At&T Bell LaboratoriesAerial metallic shielded cable having waterblocking provisions
US5218011 *May 20, 1991Jun 8, 1993Waterguard Industries, Inc.Composition for protecting the contents of an enclosed space from damage by invasive water
US5256705 *Aug 28, 1989Oct 26, 1993Waterguard Industries, Inc.Composition with tackifier for protecting communication wires
US6326551Jun 4, 1999Dec 4, 2001Commscope Properties, LlcMoisture-absorbing coaxial cable and method of making same
EP0096123A1 *Jun 4, 1982Dec 21, 1983Northern Telecom LimitedPowder filled fiber optic cable
Classifications
U.S. Classification174/23.00C, 174/107
International ClassificationH01B7/288
Cooperative ClassificationH01B7/288
European ClassificationH01B7/288
Legal Events
DateCodeEventDescription
Dec 23, 1999ASAssignment
Owner name: NORTEL NETWORKS CORPORATION, CANADA
Free format text: CHANGE OF NAME;ASSIGNOR:NORTHERN TELECOM LIMITED;REEL/FRAME:010567/0001
Effective date: 19990429
Aug 30, 2000ASAssignment
Owner name: NORTEL NETWORKS LIMITED, CANADA
Free format text: CHANGE OF NAME;ASSIGNOR:NORTEL NETWORKS CORPORATION;REEL/FRAME:011195/0706
Effective date: 20000830