WO1998021801A1

WO1998021801A1 - Composite material splice closure for electrical cables

Info

Publication number: WO1998021801A1
Application number: PCT/US1997/003399
Authority: WO
Inventors: William G. Allen; Russell P. Smith
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1996-11-15
Filing date: 1997-03-05
Publication date: 1998-05-22
Also published as: AU2526997A

Abstract

A composite material closure for an uninsulated portion of a cable (24) in which two composite sheets (10) containing a meltable material are provided. Each composite sheet (10) includes a relatively rigid portion (12) which provides mechanical protection for the cable (24) and relatively flexible end portions (14, 16) that are bonded to the cable (24). The corresponding longitudinal margins of the sheets (10) are bonded together to render the closure air tight and water tight.

Description

COMPOSITE MATERIAL SPLICE CLOSURE FOR ELECTRICAL CABLES

Background of the Invention This invention relates to electrical cables and, more particularly, to a composite closure for protecting spliced portions of electrical cables.

Electrical cables, such as power cables, communication cables, and the like, usually are formed by electrical conductors or optical fibers surrounded by an outer jacket of an insulative material to provide a protective barrier to moisture or other damaging contaminants. However, portions of the outer insulating jacket often have to be removed from the corresponding portion of the conductor for various reasons. For example, when two or more cable ends are spliced together when extending a cable, tapping into an existing cable, or repairing a severed cable, the outer insulating jacket must be removed around the splice area. Generally, it is necessary to provide a closure for such splices to protect the splice against harmful environmental influences, regardless of whether the cable is above-ground or buried.

One problem in the use of splice closures involves the need for a complete seal about the splice. Many prior art splice closures accomplish sealing by providing a complex array of nuts and bolts, clamps, gaskets and heat shrink (thermoelastic) tubing, as well as potting gels and resins, in various combinations. Besides the fact that these closures require significant assembly time, the closures still often suffer leaks or ruptures, particularly along their seals. This problem is even more acute at the sealing of the closure to the cable jacket (the outermost layer of the cable), where even the slightest defect can result in the migration of moisture along the jacket or the inner surface of the closure. Such moisture progresses into the splice area and adversely affects the electrical connections therein, often even when heat shrink tubing is used, since such tubing provides a relatively weak adhesive bond to the cable jacket. The use of heat shrink tubing in the construction of splice closures is further limited by the usual requirement of an open flame, which in many cases (e.g., splices in trenches or manholes) can be very dangerous due to the possible presence of explosive gases.

Leakage at the seal between the closure and the cable may be somewhat reduced by the use of special closure designs such as so-called clamshell designs which include a hinge integrally molded with the top and bottom halves of the closure. One such exemplary closure is illustrated in U.S. Patent No. 4,810,829, which is referred to as a SliC splice closure (SliC is a trademark of Minnesota Mining and Manufacturing Co.). Nevertheless, moisture migration is still possible along the longitudinal seal of such a closure, as well as at the end caps or seals to the cable jacket. A lack of a complete (hermetic) seal can also be particularly detrimental for pressurized closures.

Although these seals may be strengthened by the use of adhesives, the adhesive bonds formed are relatively weak due to the low surface energy of the material of the closures and cable jacket, which is typically polyethylene.

In addition to the problems set forth above, splice closures of the above type often do not provide adequate mechanical protection for the splice. Also, some of the closures do not restore the mechanical integrity of the cable, and/or are not adaptable to a wide range of splice bundle diameters, cable diameters and number of cables.

Therefore, what is needed is a splice closure which is strongly bonded to the cable splice, which is air tight and water tight, and which provides mechanical protection for the splice. Also needed is a splice closure of the above type which restores the mechanical integrity of the cable and is easily adaptable to a wide range of splice bundle diameters, cable diameters and number of cables.

Summary of the Invention The present invention, accordingly, provides a closure for extending over an uninsulated portion of an electrical cable and a method of enclosing the latter portion, in which two composite sheets containing a meltable material are provided that enclose the uninsulated portion and some of the insulated portions of the cable. Each composite sheet includes a relatively rigid portion which provides mechanical protection for the cable and relatively flexible end portions that are bonded together and to the cable. The corresponding longitudinal margins of the sheets are also bonded together to render the closure air tight and water tight.

Advantages are achieved according to the present invention since the splice closure of the present invention provides a very strong bond, is air tight and water tight, and provides mechanical protection for the cable. Also, the closure of the present invention restores the mechanical integrity of the cable, and is easily adaptable to a wide range of splice bundle diameters, cable diameters and number of cables.

Brief Description of the Drawings Fig. 1 is an isometric view of a composite sheet of the present invention. Fig. 2 is an exploded sectional view depicting several sheets of material that make up a composite sheet of Fig. 1. Fig. 3 is an isometric view of two spliced cables to be treated in accordance with the present invention.

Fig. 4 is an isometric view depicting two composite sheets of Fig. 2 forming an closure for the cables of Fig. 3.

Fig. 5 is a view similar to that of Fig. 4, but depicting an alternate embodiment of the present invention.

Fig. 5a is a view similar to Fig. 5, but depicting another alternate embodiment of the present invention.

Fig. 5b is a view similar to Fig. 5, but depicting a further alternate embodiment of the present invention. Description of the Preferred Embodiment

Referring to Fig. 1 of the drawings, the reference numeral 10 refers in general, to a composite sheet of the present invention. The sheet 10 consists of a first sheet 12 formed of a relatively rigid, high melting material, such as a high density polyethylene. Two additional sheets 14 and 16 extend from the respective ends of the sheet 12 and are formed of a relatively softer, lower melting material, such as a low density polyethylene or polyethylene copolymer such as offered by Dupont Dow under the trademark "Engage".

A pair of strips 18 and 20 extend over the respective distal ends of the sheets 14 and 16 and are preferably formed of a material that is stronger than the sheets 14 and 16 and has a higher melting temperature than that of the latter sheets. For example, the strips 18 and 20 can also be formed of a high density polyethylene.

The length of the sheet 12 is greater than the corresponding dimensions of the sheets 14 and 16 and the strips 18 and 20, while the widths and thicknesses of the sheets 12, 14 and 16, and the strips 18 and 20, are the same.

As a non-limiting example, the sheet 12 is approximately 20 inches long and approximately 7 inches wide and the sheets 14 and 16 extend approximately 2 inches from the respective ends of the sheet 12 and also have an approximate 7 inch length which coincides with the 7 inch width of the sheet 12. The strips 18 and 20 extend approximately 0.25 inch from the respective distal ends of the sheets 14 and 16, respectively and also have a length of approximately 7 inches.

All three sheets 12, 14, and 16, and both strips 18 and 20, are approximately 0.1 inch thick.

The composite sheet 10 is formed by fusing the sheets 12, 14 and 16 and the strips 18 and 20 together in a manner better described with reference to Fig. 2. More particularly, the sheets 14 and 16 are laid over the respective end portions of the sheet 12 with approximately one-half the actual length of the each sheet 14 and 16 overlapping the corresponding end portions of the sheet 12. Therefore, in the example referred to above, the actual length of each sheet 14 and 16 would be 4 inches, with 2 inches overlapping, and the other 2 inches extending from the respective ends of the sheet 12, as specified above.

The overlapping portions of the sheets 14 and 16 are then fused to the respective end portions of the sheet 12. The strips 18 and 20 are then laid over the respective distal end portions of the sheets 14 and 16, with approximately one-half the actual width of the each strip 18 and 20 overlapping the corresponding end portions of the sheets 14 and 16. Therefore, in the example referred to above, the actual width of each strip 18 and 20 would be 0.5 inch, with 0.25 inch overlapping, and the other 0.25 inch extending from the respective ends of the sheets 12 and 14, as specified above. The overlapping portions of the strips 18 and 20 are then fused to the respective end portions of the sheets 14 and 16, to form the composite sheet 10 shown in Fig. 1. The fusing technique used in accordance with the foregoing can be any one of several techniques, such as fusion bonding, thermal forming, injection molding, blow molding, or the like. Since all of these techniques are well known in the art, they will not be described in detail.

The main portion of the sheet 10, which is formed by the sheet 12, is relatively rigid since the sheet 12 is formed by a relatively high density material. The end portions of the sheet 10, which are formed by the relatively low density sheets 14 and 16, are relatively flexible, with the exception of the extreme ends of the sheet 10 which are relatively rigid by virtue of the strips 18 and 20 being formed by a high density material. The reasons for this particular configuration of the sheet 10 will be apparent from the following.

The composite sheet 10 of Figs. 1 and 2 is used to enclose uninsulated portions of a cable, or cables, for the purpose of protecting the uninsulated conductor of the cable from moisture and contamination. For, example, a pair of spliced cables are shown, in general by the reference numerals 24 and 26 in Fig. 3. The cable 24 comprises an electrical conductor 24a surrounded by a cylindrical jacket 24b formed of a conventional insulating material such as polyethylene, polypropylene or an inclusive polymer. The conductor 24 is spliced at 24c and, as a result, the portion of the insulating jacket 24b extending over the splice is removed.

The cable 26 comprises an electrical conductor 26a surrounded by an insulating jacket 26b identical to the jacket 24b of the cable 24. The conductor 26 is spliced at 26c with the portion of the jacket 24b extending over the splice being removed. The sheets 14 and 16, which form the flexible portions of the sheets 10 and 10' , have a lower melting temperature than the insulating jackets 24b and 26b of the cables 24 and 26, respectively, for reasons to be described.

Fig. 4 depicts the composite sheet 10 of Figs. 1 and 2 extending over the cables 24 and 26 of Fig. 3, and a composite sheet 10' extending underneath the cables 24 and 26. The sheet 10' is identical to the sheet 10 and therefore will not be described in any further detail. The sheets 10 and 10' extend over the spliced portions 24c and 26c of the cables 24 and 26, respectively, and for several inches along the lengths of the cables including portions of the insulating jackets 24b and 26b of the cables. The widths of the sheets 10 and 10' are also considerably greater than the distance D between the respective outer longitudinal portions of the cables 24 and 26, as shown in Fig. 4.

Various bonding methods can be provided to bond sheets 10 and 10' together. One example includes the use of a resistance wire connected to receive alternating current (AC) or direct current (DC). Another example includes a wire which functions as an antenna to receive radio frequency (RF) waves. A further example includes a bead or beads of suitable adhesive.

After the sheets 10 and 10' are respectively placed over and under the cables 24 and 26 as viewed in Fig. 4, the corresponding longitudinal marginal portions of the sheets 10 and 10' are bonded together. This can be done in any conventional manner such as, for example, by using two sets of electrically conductive resistance wires or strips 30 and 32, which may be of stainless steel or nickel-chromium or other suitable material. According to this technique, the strips 30 and 32 are placed between the sheets 10 and 10' and along their respective longitudinal marginal portions as shown in Fig. 4, and the latter portions clamped together in any known manner, such as by utilizing closure length bars and "C" clamps (not shown). The strips 30 and 32 extend for substantially the entire lengths of the sheets 10 and 10' , and their respective end portions are bent at right angles and project out from the sheets. Although not shown in the drawings for the convenience of presentation, it is understood that the strips 30 and 32 are connected in an AC or DC electrical circuit including a voltage source so that, upon the application of a predetermined amount of voltage, the strips are heated by the electrical energy. The sheets 10 and 10' thus melt slightly along their respective marginal portions, and, upon cooling, bond together along the latter portions. Since this type of bonding is well known in the art, it will not be described in any further detail.

The sheets 10 and 10' are also sealed around the cables 24 and 26. This also can be done in any conventional manner such as by using an external heater, such as, for example, a flexible silicone heater strap well known in the art. An example of the heating technique using this strap will be described as follows without reference to the drawings since the technique, per se, does not form any part of the present invention.

A heating strap is placed over the flexible portion of the sheet 10, that is, over that portion of the latter sheet formed by the sheet 14, and another heating strap is placed under the corresponding flexible portion of the sheet 10' . Two teflon sheets are positioned between the heater straps and the sheets 10 and 10' , respectively, to prevent melted material from the sheets from adhering to the heater straps. The outside of each heater strap is covered with a sheet of aluminum foil which, in turn, is covered by several layers of insulating fiberglass cloth. A thick foam strip is then positioned over the fiberglass, and an evenly distributed weight, such as 50 pounds, is then placed on top of the bond area to provide a bonding pressure. The temperature of the heater straps is raised to 350-375 degrees F. for a period of approximately 15 minutes.

As a result of the above melting process, the flexible portions of the sheets 10 and 10' formed by the sheets 14 melt and fill the voids between the sheets 10 ands 10' and the cables 24 and 26. The heating continues until the insulating jackets 24b and 26b of the cables 24 and 26, respectively, begin melting thus adhering to the above-described melted portions of the sheets 10 and 10' . The temperature is controlled so that the above melting of the insulating jackets 24b and 26b does not damage or adhere to the conductors 24a and 26a of the cables 24 and 26, respectively. The heating straps are then allowed to cool down, and the melted portions of the sheets 10 and 10' bond to each other and to the corresponding portions of the jackets 24b and 26b. The above procedure is repeated with the other flexible end portions of the sheets 10 and 10' formed by the sheets 16.

Since the strips 18 and 20, which form the ends of the sheet 10 and 10' , respectively, have a higher melting temperature than that of the end portions of the sheets formed by the sheets 14 and 16, the strips 18 and 20 do not melt during the above process, but rather remain relatively rigid and keep the melted material of the sheets 14 and 16 from flowing out from the respective ends of the sheets 10 and 10' . The strips 18 and 20 are small enough not to compromise the flexibility of the end portions of the sheet 10 formed by the sheets 14 and 16 as well as the corresponding end portions of the sheet 10' .

The embodiment of Fig. 5 is similar to that of Fig. 4 and identical components are referred to by the same reference numerals. According to the embodiment of Fig. 5, the sheets 10 and 10' are replaced by a single sheet 40 which is formed by the sheets 12, 14, and 16, and the strips 18 and 20 in the same manner as the sheet 10 is formed as disclosed in the previous embodiment.

However, the sheet 40 has a width approximately twice the width of the sheet

10. In the non-limiting numerical example referred to above, the width of the sheet 40 would therefore be approximately 14 inches, and, is doubled over a fold line F, which could be a living (built-in) hinge, to define an upper portion 40a and a lower portion 40b, as viewed in Fig. 5, each of which has a width of approximately 7 inches. Thus, only one pair of longitudinal margins of the sheet portions 40a and 40b have to be bonded together using the strips 30 and 32 in the manner disclosed above. Otherwise, the closure formed by the doubled-over sheet 40 is identical to the closure formed by the sheets 10 and 10' .

In Fig. 5a, a loop of resistance wire 39 is also placed along each opposite end 41 of sheet 40 to seal around the cables 24, 26. This can be used as an alternative to replace the heater strip method mentioned above. Also in Fig. 5b, the previously described RF wire or bead of adhesive can be used for sealing. More specifically, a copper wire 39a, Figs. 5b and 5c, can be incased in a suitable thermoplastic or heat fusible material 39b containing susceptor composite flakes 39c, i.e. radio frequency power absorbing materials comprising a plurality of multilayered flakes made of thin film crystalline ferromagnetic metal layers, such as NiFe alloy, stacked alternately with thin film dielectric layers, such as SiO. This forms a susceptor composite coating including about 1 to 10 percent susceptor composite flakes 39c in a suitable binder 39b such as polyethylene. The use of the wire 39a provides a method of bonding ends 41a of sheet 40 to seal around the cables 24, 26, and bonding edge 41b using RF power at a frequency of about 5 to about 6000 MHz in the form of an oscillating magnetic field. The field intersects the susceptor composite flakes 39c or susceptor composite binder 39b so that heat is generated, melting and fusing the coating and bonding ends 41a and edge 41b of sheet 40 together. Alternately, a bead of a known low energy surface adhesive can be used to replace copper wire 39a in Fig. 5b. The term low energy surface adhesive refers to an adhesive based on standard acrylic monomers with organo borane/amine complexes, and may include a polyurethane, an epoxy, or a polyaziridine.

The closures, and the methods of forming same, of both of the above embodiments of the present invention have several advantages. For example, a strong bond is created between the respective marginal portions of the sheets 10 and 10' and between end portions of the latter sheets and the cable jackets 24b and 26b. Also, the closure thus formed is air tight and water tight, and the relative rigid portions of the sheets 10, 10' , and 40 formed by the sheets 12 provide mechanical protection for the spliced portions 24c and 26c. Also, the closure of the present invention restores the mechanical integrity of the cable, and is easily adaptable to a wide range of splice bundle diameters, cable diameters and number of cables.

It is understood that several variations can be made in the foregoing without departing from the scope of the invention. More particularly, the application of the closures and methods of the present invention is not limited to spliced cables, but is equally applicable to any electrical conductor at least a portion of which is uninsulated. For example, when the cable is to be connected to a terminal, or other component, the insulating jacket from the end portion of the conductor has to be removed to enable the conductor to be connected to the terminal or component. Thus, the closure of the present invention could be applied over this end portion of the cable. Also, the present invention is not limited to the particular materials specified above for the sheets 12-16 and the strips 18 and 20, since other materials are equally applicable as long as the basic features of the present invention are retained. Further, the sheet 12 could be eliminated and the sheets 14 and 16 combined into one sheet extending the length of the closure.

The sheets 14 and 16 can also be formed of a low melt flow material, such as a blow -mold grade of polyethylene, in which case the strips 18 and 20 would not be needed. It is also understood that the sheet 12 can be provided with reinforcing ribs or strength metal inserts, such as a metal frame, to increase its mechanical integrity. Further, other types of bonding techniques can be employed within the scope of the present invention, such as, for example, the application of radio frequency (RF) energy, or a bead or beads of adhesive. Also, the aforementioned heating strap can be built into the closure 10 rather than applied separately, as discussed above. Still further, other means, such as rubber air bladders, or the like, can be used to apply a uniform pressure over the heating strap and the sheets 10 and 10' during the bonding process discussed above. It is understood that other modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

ClaimsWhat is claimed is:

1. A closure for a cable including a conductor having an uninsulated portion and an insulating jacket extending over another portion of the conductor, the closure comprising a first sheet and a second sheet of meltable material for enclosing the uninsulated portion of the conductor and a portion of the jacket, at least two of the corresponding longitudinal margins of the sheets being bonded together and the respective end portions of the sheets being bonded to the jacket to render the closure air tight and water tight.

2. The closure of claim 1 wherein each sheet comprises a relatively rigid sheet and two relatively flexible sheets respectively attached to the ends of the rigid sheet to form the end portions of the sheets.

3. The closure of claim 2 wherein the longitudinal margins of the sheets are bonded together by melting the margins and wherein the end portions of the sheets are bonded to the jacket by melting the end portions.

4. The method of claim 3 wherein the end portions are also bonded to each other.

5. The closure of claim 4 whereby the melted end portions fill the voids between the cable and the sheets.

6. The closure of claim 2 wherein each sheet further comprising two relatively rigid strips disposed at the respective ends of the sheet for preventing the melted material of the flexible sheets from flowing out from the sheets.

7. The closure of claim 6 wherein the relatively flexible end portions of the sheets are fused to the relatively rigid sheet, and wherein the strips are respectively fused to the relatively flexible end portions of the sheets.

8. The closure of claim 1 where the sheets are formed separately and two opposite longitudinal margins of one sheet are respectively bonded to two corresponding opposite margins of the other sheet.

9. The closure of claim 1 wherein the sheets are formed by doubling over a single sheet and bonding the corresponding margins of the sheets thus formed.

10. A method of enclosing a cable including a conductor having an uninsulated portion and a insulating jacket extending over another portion of the conductor, the method comprising the steps of forming two sheets, disposing the cable between the sheets, bonding at least two of the corresponding longitudinal margins of the sheets together, and bonding the respective end portions of the sheets to the jacket.

11. The method of claim 10 wherein each sheet is formed by the step of fusing at two relatively flexible sheet to the respective ends of a relatively rigid sheet to form the end portions of the sheet.

12. The method of claim 11 wherein the longitudinal margins of the sheets are bonded together by the step of melting the margins, and wherein the end portions of the sheets are bonded to the jacket by melting the end portions.

13. The method of claim 12 wherein the end portions are also bonded to each other.

14. The method of claim 13 wherein the melted end portions fill the voids between the cable and the sheets.

15. The method of claim 12 wherein the step of melting comprises the step of applying electrical energy to the at least one flexible sheet.

16. The method of claim 12 further comprising the step of fusing two relatively rigid strips to the respective end portions of the sheets for preventing the melted material of the flexible sheets from flowing out from the sheets.

17. The method of claim 16 wherein the strips have a higher melting temperature than the end portions of the sheets.

18. The method of claim 10 where the sheets are formed separately and wherein the first step of bonding comprises bonding the opposite longitudinal margins of one sheet to the two corresponding opposite margins of the other sheet.

19. The method of claim 10 wherein the sheets are formed by doubling over a single sheet and wherein the first step of bonding comprises the step of heat bonding the corresponding margins of the sheets thus formed.

20. A closure for a cable including a conductor having an uninsulated portion and an insulating jacket extending over another portion of the conductor, the closure comprising a folded sheet of meltable material including a first sheet portion folded over a second sheet portion for enclosing the uninsulated portion of the conductor and a portion of the jacket, a margin of the sheet being bonded together along edges of the folded first and second sheet portions to render the closure air tight and water tight.