TELEPHONE CABLE SPLICES

Abstract: A splice between ends of a pair of telecommunications cables is encapsulated in a thermoset foam. To encapsulate the splice it is positioned within a mold with the cables extending through apertures in the mold. At the apertures the cables are wrapped with an open cell foam material to block the cavity ends. Chemical reagents which undergo a foaming reaction, before solidifying, are then mixed, the mixture is deposited within the mold, and the mold closed. The mixture them foams to fill the mold with a closed cell foam which rapidly cures. The resulting joint is light, durable, waterproof and can be made re-enterable.

Description: TELEPllONE CABLE SPLICES This invention relates to a method for making a closure for telecommunications cable splices and to an encapsulated splice produced by the method. In the installation, extension or repair of telephone cables, there is frequently a need to splice individual conductors of one cable to conductors of another, contiguous cable. In order to protect the conductors and connectors at the splice site from water and other contaminants, the spliced conductors must be encapsulated or otherwise protected. In one known encapsulating technique, a thermosetting elastomer is used. After splicing the conductors, adhesive tape is wound onto the cable ends to form rigid collars and a mold is positioned to extend between the collars and surround the splice site. Unreacted thermosetting elastomer is then injected into the mold cavity and is allowed to cure. The amount of encapsulant used makes this technique expensive and operation time is long since elastomers having desired encapsulation properties are slow curing. Moreover the encapsulated joint produced is heavy and difficult to re-enter since the elastomer fuses with the material of both the cable sheath and insulation surrounding individual conductors of the cables. Another protective covering technique uses heatshrink, a plastic material that has been rendered dimensionally unstable during manufacture. A tube of heatshrink surrounding a splice site shrinks appreciably to tightly embrace the underlying joint when heated by a torch. Although splice closure is achieved very quickly using heatshrink, it is a relatively expensive material and requires the use of an open flame which is not desirable if splice closure is taking place in a duct where gaseous build-up can occur. Moreover, although providing excellent radial protection for the joint, a heatshrink tube does not prevent water from seeping towards the splice site along the interior of one or other of the cables. Finally, the technique is somewhat craft sensitive and produces a joint which is not as physically durable as might be desired. A technique is now proposed which overcomes these problems of knon closures. According to one aspect of the invention there is provided a method of protecting a telephone cable splice comprising disposing a mold around the splice and around ends of cables joined at the splice, blocking ends of the mold where the cable ends enter the mold thereby to define a mold cavity, mixing together a plurality of chemical reagents and depositing the mixture within the mold cavity, the reagents being such as to undergo a foaming action and thereby fill the mold cavity with a closed cell foam which subsequently solidifies. Splice connections can be encased in a secondary encapsulant, such as a bag of grease or urethane, and the splice wound with a protective film of material before being encapsulated within the foam. The chemical reagents can react together to produce a blowing agent which appears as tiny bubbles within the reaction product, the bubbles being locked in place when the foam solidifies. For a thermosetting reaction product the reagents preferably react exothermically. The reagents are thoroughly mixed in order to prevent large voids and unreacted sections in the solidified foam. The ends of the mold at which cable entry occurs are preferably blocked with a flexible, open cell foam material which permits venting of pressure built up by the expanding foam and also serves to create a skin by puncturing the cells of the expanding foam at the boundary thereof. The foam can also deform to accommodate any excess encapsulant in the mold. According to another aspect of the invention there is provided a closure for a telephone cable splice, the splice and end portions of cables extending from the splice being encapsulated within a closed cell plastics foam. The foam is preferably formed within a mold of, for example, a copolymer of polyethylene and polypropylene. The mold can have a cylindrical body portion and truncated end zones apertured for cable entry. The mold can be a multiple-part structure hinged in a longitudinal plane. An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a longitudinal sectional view through an encapsulated splice according to the invention; Figure 2 is a perspective view of a mold housing for use in the closure method of the invention; Figure 3 is a perspective view of an alternative mold housing; and Figure 4 is a schematic cross-sectional view through an encapsulated splice using an alternative mold housing. Referring in detail to the drawings, Figure 1 shows in longitudinal cross-section, a pair of cables 10, individual conductors of which are spliced to one another by connectors 12. Groups of connectors are tied into urethane filled bags for connector protection. At a central zone of the splice, the bagged connectors and conductor ends are wrapped in a polyethylene film 14. The polyethylene film 14 is itself surrounded by a mass of closed cell thermoset foam 18 housed within a medium density polyethylene polypropylene copolymer mold 20. The mold has a cylindrical central zone 22 and truncated conical end zones 24 allowing cable entry. The thermoset foam 18 is confined at the ends of the molds 20 by collars 26 of open cell foam material such as polyurethane. In order to effect encapsulation of a splice, connector groups are initially manually inserted into bags filled with a urethane potting compound, "Z" Encapsulant (Trade name), and the central splice zone is wound with a film of polyethylene. Onto the sheathed cable ends is then wound a collar 26 of a highly flexible, open cell polyurethane foam tape having an adhesive backing. The size of collar 26 depends on the size of mold which is to encapsulate the splice. The collar 26 has a radial extent sufficient to contact the mold wall in the end zones but will not be so large that it has to be appreciably compressed in order that it will fit into the mold. As shown in Figure 2 the mold 20 is hinged into two parts 30 and 32 at an elongate weakened zone 28 in the mold wall. The splice is layed into the-central zone 22 of the mold part 30 and the cable ends, with sheaths abraded and then coated in an acrylic adhesive, are located in the end zones 26. For a mold having a mold cavity free volume V, a V/5.65 mixture of methyl diphenyl isocyanate and polyether glycol in a weight ratio of approximately 5:4 is produced, the reagents being thoroughly mixed for several minutes. These materials are available from Biwax Corporation of the United States. Once mixing is complete, the mixture is immediately poured into the mold part 30 and the mold parts 30 and 32 are fastened together by integrally molded clip formations 34 along the two outer edges of the mold part. Within a few seconds of mixing, the mixture begins to foam and expands to several times its original volume, reaction heat very rapidly causing the resulting closed cell foam to set. The reaction produces a solid urea in which are trapped tiny bubbles of water vapour and CO2, the water acting as a "blowing agent". Both the time taken for the various stages of the foaming reaction to take place and the nature of the foam obtained can be altered by adjusting the amounts or identities of the constituents used. is the foam material expands to fill the mold. 20, it both partially deforms, and permeates into, the open cell foam collars 26. Threads of tha collars 26 tend to puncture the closed cells so inducing a natural cm lapse at the boundary of the uncured foam as it presses into the co'lars. This action represents an inherent pressure valve, the collapsed cells also forming, in effect, a protective skin at the boundary of the foci. Because the foam collars are highly flexible they tend to compact somewhat and to be driven into the conical end zones 24 further relieving pres;ure within the mold cavity. The are however prevented from exiting the told 20 by the conical form of the mold wall at the end zones 24. Use of at adaptor collar 26 of highly flexible foam allows multiple cable entrl without the use of other adaptors or labour intensive cutting and shar ng. Referring to Figure 3 an alternative mold shown has a ceni al region 36 of semicircular cross section, this region having strcigthening ribs 38. Two arcuate section wing portions 40 are hinged to the ventral portion at weakened zones 42. In use, the central portion 38 is yield under the splice with flexible ties (not shown) anchored at holes 44 )unched through the wall of the mold. The ties extend around the sluice to leave the mold central portion suspended under the splice. The form mixture is then poured into the central portion-36, the wing portions 40 are folded in and tied into position and the foaming reaction takes place as described previously. Referring to the sectional view of Figure 4, as an alternative to the Figure 2 mold, the mold can consist of two flanking parts 50 hinged to a central part 51. This design has the advantage that the mold and foam reagents which, during operation, are contained with the central part 50, are more easily balanced when the mold is suspended from a cable splice shown schematically as 53. The mold is suspended at locations spaced along the mold by tie-wraps 54 which extend through anchoring brackets 52 adhering to the inner surface of the mold part 51. Brackets 52 are preferable to holes through the mold since the latter may suffer from moisture ingress. The anchors 52 are slightly below the center line of the mold tending to draw the splice into the bottom mold section 51. On the other hand, the anchors are inclined to a vertical plane and so, together with the relatively stiff tie-wraps 54, the splice will, in fact, tend to centralize within the mold. Once the splice is properly positioned within the mold, and-collars (not shown) have been fitted as previously described, the two flanking parts 50 are moved successively to cover the splice, one of the parts 50 covering the other part 50. The free edges of these two parts tend towards alignment longitudinally at molding distortions caused by the presence of hinge zones 55. After pouring the mold foam reagents into the part 51 and before foaming takes place, the various parts of the mold are clamped in position by independent ring clamps 56 instead of by interacting mold formations such as those shown in Figure 2. The clamps 56, which can be attached and detached by hand, are available in a range of inside diameters from Cole Parmer Instrument Company under the specification No. C-6832-76. The mold shown in Figure 4 may be vacuum formed from a sheet of 120 gauge polyethylene. The vacuum formed sheet is weakened to produce the hinge zones 55 by slicing part of the vacuum formed material away once it is rigid. Before being encapsulated in foam, the splice connections are placed into a sock of open cell foam material which is, in turn, placed within a urethane filled bag. The entrance to the bag is tied and taped. Subsequently, the bag is manipulated to encourage this secondary encapsulant to penetrate between adjacent conductors and connectors. The thermosetting foam used is quite rigid and can take a compressive stress of the order of 15 kg/cm2 without deforming. Most importantly, the foam, being a closed cell material, is inherently waterproof, and can be made adherent to polyethylene so forming an effective waterproof seal with the cable and conductor sheath portions which it contacts. An advantage of the foam closure is that the cable joint can be made re-enterable. In a first re-entry method, a steel wire lanyard is laid the length of the splice and, except for an end portion, is sealed within the foam during the foaming reaction. Subsequently if access to the joint is required, for example, for repair purposes, then after removing the mold 20, the lanyard is pulled to cut the foam capsule along its length. In a second method a special blowing agent for example, an azobisisobutyronitrile is incorporated into the foam and decomposes into carbon and nitrogen when the foam is heated by torch to about 25O0C. This causes spontaneous rupture of the individual cells, the foam falling away from the underlying splice. Care must be taken in order not to release toxic gases when heating the foam material; from this point of view a silicone based foam may be preferable. The spliced conductors within the joint are free of foam since the splice is wrapped in polyethylene film before the foaming operation is performed. The polythene wrap has another function when encapsulating splices using grease filled cables. If the foaming reaction is exothermic it will melt the grease. If the melted grease is not kept away from the foaming reagents, the reaction product will be found to be at least partly open-cell which is undesirable. It has been estimated that the materials used in foam closures are half the cost of the heatshrink tube and a third of the cost of the necessary amount of thermosetting elastomer for a comparable encapsulating operation. Moreover, foam encapsulating is comparable in installation time with heatshrink and takes considerably less time than potting the splice in a thermosetting elastomer. In fact, the closed joint can be buried or replaced in a duct immediately after the foaming action is complete. As indicated previously the resulting closure is waterproof, durable, re-enterable and is not craft sensitive. A further advantage of the closures described is that they are relatively lightweight compared with an elastomer encapsulation. The weight of materials for encapsulating a 50 pair splice of 24 AWG wire is about 1Kg. Although the invention has been described only in terms of splicing one cable to an identical cable, the same method and equipment can be used for encapsulating the joint between, for example, a 50 pair cable and two 25 pair cables. The only variation in the method described is to apply the open cell foam collars to the cable sheath end portions in a slightly different manner to that described for the illustrated embodiments. Thus In the example chosen, the two 25 pair cables are initially separately wound with the open cell foam and then are wound as a single unit so that an essentially oval collar is eventually produced around the two aligned, smaller cables. This will distort to circularity when the mold is fitted. A service wire cut out of the main cable is treated in a similar manner. The open cell foam is initially wound around the main cable, the service wire is positioned alongside the main cable and open cell foam is subsequently wound around both the cable and the service wire. The only change then is in the way in which the open cell foam strip is applied. The mold itself and the foaming reagents are versatile and can be used in diverse applications. A splicing encapsulation kit which can be carried easily to splice sites consists of a mold, the wraps and anchors, open cell foam tape, foaming reagents, and outer clamps. The amounts of foaming reagents in the kit are selected so as to fill the mold, any slight excess then penetrating into the open cell foam collar. The nature of the collar, that is, its flexibility and permeability, is important. The properties of rigid, sealing collars used when potting splices in thermosetting elastomers by prior art methods, are quite unsuitable for use with the foaming technique described here. Although the invention has been described only for the application of encapsulating splices between grease packed cables, the technique can be used for encapsulating joints between powder filled cables and between optical fiber cables. Also the encapsulation techniques can be used where the splice is to be aerially suspended or buried.

Claims: CLAIMS: 1. A method of encapsulating a telephone cable splice comprising disposing a mold around the splice and. cable ends adjacent the splice, blocking ends of the mold where the cables enter the mold to define a mold cavity, mixing together a plurality of chemical reagents and depositing the mixture within the mold cavity, the reagents being such as to undergo foaming and solidifying actions thereby to fill the mold cavity with a rigid closed cell foam (18). 2. A method as claimed in claim 1, further characterized in that a reaction between the reagents is exothermic and a reaction product is thermosetting. 3. A method as claimed in claim 1 or 2 further characterized in that the reaction between the reagents produces a blowing agent. 4. A method as claimed in any of claims 1 to 3, further characterized in that one of the reagents is a polymeric isocyanate. 5. A method as claimed in claim 2, further characterized in that another of the reagents is a high molecular weight polyol. 6. A method as claimed in claim 3, further characterized in that the blowing agent is water vapour. 7. A method as claimed in any of claims 1 to 6, in which the mold has a plurality of interconnected parts, the method further characterized in moving the parts (30, 32) to a mold open position to permit deposition of the fluid material therein and, subsequently, moving the parts (30, 32) to a mold closed position to define the mold cavity. 8. A method as claimed in any of claims 1 to 7, further characterized by blocking ends (24) of the mold (20) with a blocking means which yields under internal pressure in the mold cavity to alter an effective volume of the cavity. 9. A method as claimed in claim 8, in which the blocking means is a flexible open cell foam, the method further characterized by applying to each of the cable ends (10) a collar (26) of the open cell foam before disposing the mold (20) around the splice (15) and cable ends (10), whereby, when the mold (20) is so disposed, the mold (20) presses against the collars (26) to block the ends of the mold cavity. 10. A method as claimed in any of the claims 1 to 9, the method further characterized by, prior to foam encapsulation, laying a wire lanyard against a cable splice with a free end thereof projecting from the mold (20). 11. A method as claimed in any of claims 1 to 10, further characterized in that prior to foam encapsulation, a plurality of connectors (12) interconnecting individual conductors of the cables (10) are sealed intocontainers filled with a potting material for protection from contaminants. 12. A method as claimed in any of claims 1 to 11, further characterized in that the splice is wrapped with a plastic film before being encapsulated within the foam (18). 13. A closure for a telecommunications cable splice, the splice (15) and end portions of cables (10) extending from the splice being encapsulated, characterized in that the splice is encapsulated within a closed cell plastics foam (18). 14. A closure as claimed in claim 13, further characterized in that the foam is a reaction product of a plurality of chemical reagents. 15. A closure as claimed in claim 14, further characterized in that one of the reagents is a polymeric isocyanate. 16. A closure as claimed in claim 14 or 15, further characterized in that another of the reagents is a high molecular weight polyol. 17. A closure as claimed in any of claims 14 to 16, further characterized in that the reagents react to produce urea and a blowing agent. A A closure as claimed in any of claims 13 or i4; further characterized in that the foam (18) adheres to polyethylene. 19. A closure as claimed In any of claims 13 to 18, further characterized in that the foam is contained within a mold (20). 20. A closure as claimed in claim 19, further characterized in that ends of the mold (20) are apertured to permit cable entry, the apertures, intermediate the mold.and cables, being blocked by a blocking means which yields under internal pressure within the mold (20) to alter the effective volume of a mold cavity defined by the mold. 21. A closure as claimed in claim 20, further characterized in that the blocking means are collars (26) of open cell foam applied to the cable ends. 22. A closure as claimed in claim 21, further characterized in that the open cell foam of the collars is initially highly flexible but has parts deformed and rendered rigid on penetration by said closed cell foam (18). 23. Apparatus for encapsulatingsa telecommunications cable splice, the apparatus comprising a mold for surrounding the splice, the mold having apertures therein for entry of cable ends to the mold, blocking means for blocking the apertures around the cables whereby to define a mold cavity, the blocking means adapted to yield under internal pressure in a mold cavity to alter the effective volume of the cavity, and foam activating reagents for producing a rigid closed cell foam, the reagents present in a quantity sufficient that the rigid closed cell foam (18) produced thereby fills the mold (20). ' ' 24. Apparatus as claimed in claim 23, further characterized in that the blocking means comprises open cell foam tape. 25. Apparatus as claimed in claim 23 or 24, further characterized by a plurality of tie-wraps (54) and a plurality of anchor devices (52) for suspending the mold (20) from the cable splice (53). 26. Apparatus as claimed in any of claims 23 to 25 further. characterized in that the mold (20) has a central part (51) and two flanking parts (50), each of the parts being in the form of an elongate member of semicircular section, the members having truncated conical end parts. 27. Apparatus as claimed in claim 26, further characterized in that the mold has hinge zones (55) between adjacent ones of the members, the mold material being locally reduced in thickness at the hinged zones. 28. Apparatus as claimed in claims 22 to 27, further characterized in that the reagents react to produce urea and a blowing agent. 29. Apparatus as claimed in any of claims 22 to 28, further characterized in that the reagents react exothermically. 30. Apparatus as claimed in claim 27, further characterized in that one of the reagents is a polymeric isocyanateX 31. Apparatus as claimed in claim 29, further characterized in that one of the reagents is a high molecular weight polyol. 32. Apparatus as claimed in any of claims 22 to 31, further characterized in that the mold (20) is composed of vacuum formed high density polyethylene. 33. Apparatus as claimed in any of claims 22 to 32, further characterized in that the mold (20) has a plurality of parts (50, 51) movable relative to one another between an open mold position and a closed mold position. 34. Apparatus as claimed in claim 33, further characterized in a plurality of clamps which are hand attachable to the mold (20) to retain the mold (20) in said closed position.

Inventors: FINN, ROGER COLIN, JACKSON, CHARLES FRASER COHOE, TRUMBLE, WILLIAM PATRICK
Applicants: NORTHERN TELECOM LIMITED
Application year: 1982
Main classification: H02G15
IPC codes: H02G15, H02G1