MXPA00010652A - Shielded cable and method of making same - Google Patents

Abstract

The present invention provides a non-braided shielded drop cable that can be easily attached to a standard connector. The cable comprises a cable core including a center conductor and a dielectric layer surrounding the center conductor, a first electrically conductive shield surrounding the cable core and bonded thereto, a second electrically conductive shield surrounding the first shield, and a cable jacket surrounding the second shield and bonded thereto. An interstitial layer is located between the first and second shields and is composed of axially displaceable elongate strands and is typically composed of helically served yarns or metal wires. The present invention also includes a method of making a shielded cable.

Description

ARMORED CABLE AND METHOD TO DO THE SAME FIELD OF THE INVENTION The invention relates to a shielded cable and more in particular, to a non-stranded down cable for the transmission of RF signals.

BACKGROUND OF THE INVENTION In the transmission of RF signals such as cable television signals, a downlink cable is generally used as the final link when bringing signals from a trunk and distribution cable directly into a subscriber's house. Conventional drop cables include an isolated center conductor that carries the signal and a conductive shield that surrounds the center conductor to prevent signal leakage and interference from external signals. In addition, the down cable generally includes a protective outer sleeve to prevent moisture from entering the cable. A common construction for lowering cable includes an insulated center conductor, a laminated tape formed of metal and polymer layers surrounding the center conductor, a layer of braided metal wires, and an outer protective sheath. One problem with conventional braided lowering cable is that it is difficult to connect to standard connectors. In particular, the shielding Braided is difficult to cut and connect to a standard connector and should normally be folded back, over the cable sheath during cable connection As a result, the metal braid increases the time and installation costs Also, form the metal braid it is generally a time-consuming process and limits the speed at which the cable can be produced. Therefore, there have been attempts in the industry to eliminate the braid of the conventional drop cable. For example, US Pat Nos. 5,321,202, 5,414,213, and 5,521, 331 from Hillburn teach replacing the outer braided shield of conventional construction with a foil shield or laminated metal foil shield and adding a layer of plastic between this shield and the internal shielding tape. Although this construction eliminates metal braids, creates other connection problems Specifically, when the connectors are connected to these wires, it it requires a special cut-off and core-cutting tool to prepare the cable so that the connector is connected to the cable. This requires additional time during the connection of these cables. Also, the detachment force of the cable without braid, ie the force required to detaching the cable connector, is undesirably reduced compared to the braided cables German applications DE 3931741 A and DE 3141636A describe alternative cable constructions In particular, DE 3931741 A describes a cable that includes an internal conductive core, surrounding insulation the inner conductive core, and an external conductor that surrounds the isolation. The external conductor comprises two unilaterally metallized films with conductive wires disposed therebetween. DE 3141636A describes a cable that includes a copper conductor, a plastic cover that surrounds the copper conductor, a copper mesh that surrounds the plastic as an internal shield, wires arranged side by side that surround the internal shield, a metallic sheet that surrounds the wires, and a second copper mesh that surrounds the metallic sheet as an external shield.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides an unbraided lowering cable which can be easily connected to a connector and which can appropriately fix a connector to prevent connector detachment once the cable is connected. In addition, the present invention provides a drop cable with sufficient shielding to prevent signal leakage and interference from external signals. These characteristics are provided by a shielded non-stranded cable that includes a cable core comprising a central conductor and a dielectric layer surrounding the central conductor, a first electrically conductive shielding surrounding the cable core and attached thereto, a second shielding electrically conductive surrounding the first shield, and a cable sheath surrounding the second shield and attached thereto. Agree With the invention, an interstitial layer is placed between the ppmer and second shields and is composed of elongated strands disposed between said first and second shields to be able to move freely and axially while also serving to separate the first and second shields from each other. preferred embodiment of the invention, the first and second shields used in the cable are laminated metal-polymer-metal laminated ribbons that extend longitudinally of the cable and have longitudinal edges that overlap to produce 100% shielding coverage of the central conductor. Preferably, the first shielding tape is an aluminum-polyolefin-aluminum laminated tape and the second shielding tape is an aluminum-polyester-aluminum laminated tape. The threads of the interstitial layer are typically wound helically around the first tape. of shielding and are formed of metal wires and / or textile threads. Preferably, these are ras are metal wires that cover less than 30 percent of the surface of the first underlying shielding tape. The metal wires may be provided as more than one layer having different orientations such as two layers having opposite helical orientations (e.g. , counterclockwise and clockwise) The threads for the interstitial layer typically cover less than 50 percent of the surface of the first shielding tape and are selected from the group consisting of threads of polyester, cotton and aramid and mixtures thereof The layer interstitial may include both wires and metal wires disposed along the wires, and may also include a water blocking material. The present invention also provides a method for making a shielded cable. In the manufacture of these cables, a cable core which it comprises a central conductor and a dielectric layer surrounding the central conductor is advanced and an electrically conductive shielding tape is wrapped longitudinally or "wrapped like a cigar" around the cable core. The interstitial layer is applied to the first cable of the cable. shielding typically wrapping the strands helically around the first shielding tape A second shielding tape is then wrapped longitudinally over the interstitial layer and a cable sheath is extruded onto the second shielding tape to produce the cable Preferably, the method It also includes connecting the shield tape to the cable core and a the second shielding tape to the sheath The shielding tapes are preferably bonded metal-polymer-metal laminated ribbons having longitudinal edges that are placed in an overlying relationship. These laminated ribbons also preferably include an adhesive on a metal surface. the same, including the first shielding tape an adhesive on the surface that is inwardly adjacent to the cable core and the second shielding tape including an adhesive on the outwardly facing surface on which the outer sheath is extruded to provide the desired junctions in the shielded cable The shielded cables of the invention are easy to connect to standard connectors Specifically, because the shielded cable is not stranded, the problems related to braids are not experienced during the connection of the shielded cable of the invention Likewise, the interstitial layer in the cable of the invention is composed of strands that can be moved axially and therefore do not require cutting before the connection In addition, these strands that can be moved axially help to fix the connector on the cable, thus increasing the resistance to cable detachment BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will be apparent from the following detailed description of the invention taken in conjunction with the drawings, in which Figure 1 is a perspective view of a shielded cable according to the invention having portions of the same partially removed for purposes of illustration, figure 2 is a partial cross-sectional view of the shielded cable of figure 1 taken along line 2-2, figure 3 is a schematic illustration of a method for making a cable armored according to the invention, Figure 4 is a perspective view of a shielded cable according to the invention connected to a standard one-piece connector and with separate portions for purposes of illustration; and Figure 5 is a longitudinal cross-sectional view of the connected cable of Figure 4 taken along the line 5-5-.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Referring now to Figures 1 and 2, there is shown a shielded cable 10 according to the present invention. Shielded cable 10 is generally known as a down cable and is used in the transmission of RF signals such as cable television signals.

Typically, the diameter on the sheath of the cable 10 is between about 0.61 cm and 1.04 cm. The cable 10 includes a cable core 12 comprising an elongated central conductor 14 and a dielectric layer 16 surrounding the central conductor. A first shield preferably formed of a first shield band 18 surrounds the cable core 12 and is bonded thereto. A second shielding preferably formed of a second shielding tape 20 surrounds the first shielding tape. The first and second shield tapes 18 and 20 prevent leakage of the signals being transmitted by the center conductor 14 as well as interference of external signals. An interstitial layer 22 is placed between the shield tapes 18 and 20 and separates the tapes of shielding one from the other. A cable sheath 24 surrounds the second shielding tape 20 to protect the cable from moisture and other environmental effects and is attached to the second shielding tape. As mentioned above, the center conductor 14 in the shielded cable 10 of the invention is generally used in the transmission of RF signals such as cable television signals. The central conductor 14 is preferably formed of copper-coated steel wire but another conductive wire (eg, copper) can also be used. The dielectric layer 16 can be formed of either a foamed or a solid dielectric material. Preferably, the dielectric layer 16 is a material that reduces attenuation and maximizes the propagation of signals such as a foamed polyethylene. In addition, solid polyethylene can be used. The cable 10 further includes a first or internal shielding tape 18 surrounding the cable core 12 and attached to the cable core by an adhesive layer 25. The longitudinal edges of the first shielding tape 18 are typically overlapped so that the first Shielding tape provides 100% shielding coverage. The first shielding tape 18 includes at least one conductive layer such as a thin sheet metal layer. Preferably, the first shield tape 18 is a bonded laminated tape that includes a polymer layer 26 with metal layers 28 and 30 bonded to opposite sides of the polymer layer. The polymer layer 26 is typically a polyolefin film (eg, polypropylene) or a polyester film. The metal layers 28 and 30 are typically layers of thin aluminum foil In order to avoid cracking of the aluminum when folded, the aluminum foil layers can be formed of an aluminum alloy which generally has the same tensile and elongation properties as the polymer layer Cintas having this construction are available under the Neptco HYDRA® trademark. Also, the shielding tape 18 preferably also includes an adhesive on a surface thereof to provide the adhesive layer 25 between the first shield tape and the cable core. typically form an ethylene-acphc acid (EAA), ethylene-vinyl acetate (EVA), or ethylene-meta-plate (EMA) copolymer or other suitable adhesive. Preferably, the first shielding tape 18 is formed from a laminated tape of aluminum-polypropylene-aluminum joined with an EAA copolymer adhesive A second shielding tape or external 20 surrounds the first shielding tape 18 and also provides shielding of the central conductor 14 The longitudinal edges of the second shielding tape 20 are typically overlapped and the second shielding tape is preferably attached to the cable sheath 24 The second tape of shield 20 includes at least one conductive layer such as a thin metal foil layer and preferably is a bonded laminated tape that includes a polymer layer 34 with metal layers 36 and 38 attached to opposite sides of the polymer layer as shown in FIG. described above Nonetheless, to provide resistance and connector retention added to the shielded cable 10, the second shielding tape 20 is preferably a laminated aluminum-polyester-aluminum laminate tape Furthermore, to avoid cracking of the aluminum upon being bent, the second shielding tape 20 can include aluminum alloy sheet layers having in general the same tension and elongation properties as the polyester as described above with respect to the first shielding tape 18 The second shielding tape 20 typically also includes an adhesive on a surface thereof that forms an adhesive layer 40 to provide a bond between the second shielding tape and the cable sheath 24 Preferably, the adhesive is a copolymer EAA for polyethylene covers and an EVA copolymer for pohvinyl chloride sleeves Between the first shielding tape 18 and the second shielding tape 20 an interstitial layer 22 is provided which separates the shielding tapes from each other The interstitial layer 22 it is composed of elongated strands 42 disposed between the ppmera shielding tape 18 and the second shielding tape 20 The elongated strands 42 are placed and arranged between the straps 18 and 20 in such a way that they can move freely and axially. As described in more detail below, this allows the strands 42 to be displaced when the cable 10 is connected to a standard connector. In the illustrated embodiment , this is achieved by arranging the strands loosely between the straps 18 and 20 without any binding to one another or to the tapes. Alternatively, a bonding agent or adhesive could be used to stabilize the strands during manufacture, provided that When the joint is relatively weak and allows axial movement of the strands during the The strands 42 forming the interstitial layer 22 are preferably arranged helically around the first shielding tape 20. Preferably, the strands 42 are metal wires or textile yarns. Metal wires are especially preferred as they impart more resistance, provide a conductive bridge between the shielding layers, and increase the strength of the connection between the cable and the connector. Examples of wires include copper or aluminum wires having a generally circular cross section and a diameter of up to about 0.025 cm. The metal wires can be applied in a layer having a predetermined helical orientation or in more than one layer (e.g., two layers) each layer having alternate alternating helical orientations. For example, a first layer of wires can be applied in a clockwise orientation and a second layer of wires can be applied in a counterclockwise orientation. In any case, the metal wires are applied in such a way that they can move freely and axially and therefore are not interlocked in the manner used to make braided wires. For this purpose, the metal wires preferably cover less than 30 percent of the surface of the underlying shielding tape 18, and most preferably between about 10 and 20 percent of the surface of the underlying shielding tape. As mentioned above, the strands 42 may also be composed of textile yarns. Examples of yarns include yarns of polyester, aramid and cotton, and mixtures thereof. Preferably, the yarns are continuous multi-filament polyester yarns. The threads can also be semiconductor or contain filaments or conductive fibers to provide a conductive bridge between the shield tapes 18 5 and 20. The threads can adequately provide less than 50 percent coverage of the underlying shielding tape 18 and, for example, they can cover between 20 and 40 percent of the surface area of the first shielding tape. The threads are preferably arranged helically around the first shield tape 18 and can be used alone to form the layer interstitial 22 or can be combined with metal wires. For example, metal wires and wires may be disposed along one another to form interstitial layer 22 or in separate layers as described above. The interstitial layer 22 may also include a material water block to trap any moisture that may enter the cable 10 and prevent corrosion of the metal layers in the cable. The water blocking material may, for example, include a powder that swells with water such as a polyacrylate salt (e.g., sodium polyacrylate). This water blocking powder can be supplied in threads used as threads in the interstitial layer 22, applied to the strands in the interstitial layer, or provided on the surface of the first or second shielding tape 18 or 20 adjacent to the interstitial layer.

As shown in Figures 1 and 2, the cable 10 generally also includes a protective sheath 24 surrounding the second shielding tape 20. The sheath 24 is preferably formed of a non-conductive material such as polyethylene or polyvinyl chloride. Alternatively, a low smoke insulation such as a fluorinated polymer can be used if the cable 10 is to be installed in air chambers that require compliance with UL910 requirements. Figure 3 illustrates a preferred method for making the shielded cable 10 of the invention. As shown in Figure 3, the cable core 12 comprising a central conductor 14 and surrounding the dielectric layer 16 is advanced from a reel 50. As the cable core 12 is advanced, a first conveyor belt 12 shield 18 is supplied from a spool 52 and is wrapped longitudinally or "wrapped like a cigar" around the cable core. As mentioned above, the first shielding tape 18 is preferably a bonded metal-polymer-metal laminated tape having an adhesive on a surface thereof. The first shielding tape 18 is applied with the adhesive surface positioned adjacent the underlying cable core 12. If an adhesive layer is not already included in the first shielding tape 18, an adhesive layer can be applied by suitable means such as extrusion before longitudinally wrapping the first shielding tape around the core 12. One or more guide rollers 54 direct the first shielding tape 18 around the cable core with the longitudinal edges of the first tape. of overlapping shielding to provide 100% shielding coverage of the cable core 12. Next the wrapped cable core is advanced to a creel 56 which coils or helically "supplies" the strands 42 around the first belt of shield 18 to form the interstitial layer 22. The creel 56 preferably includes as many reels 58 as are necessary to provide the desired coverage of the first shielding tape 18 described above. The creel 56 rotates either clockwise or counterclockwise to provide winding helical of the strands 42. Additional creels (not shown) can also be included to produce more than one layer of strands 42 in the interstitial layer 22. Also, if a water blocking material is not provided in the strands 42 or over the surface of the first or second shielding ribbons 18 or 20, a powder that swells with water can be applied to the interstitial layer 22 by means of suitable means (not shown) to prevent migration of moisture into the cable 10. Once the interstitial layer 22 has been applied, a second shielding tape 20 is provided from a spool 60 and is wrapped longitudinally around it. the interstitial layer. As mentioned above, the second shielding tape 20 is preferably a bonded metal-polymer-metal laminated tape having an adhesive layer on a surface thereof. The second shielding tape 20 is applied with the adhesive layer remaining outwardly away from the interstitial layer 22, i.e. adjacent to the cable sheath 24 One or more guide rollers 62 direct the second shielding tape 20 around the interstitial layer 22 with the longitudinal edges of the second overlapping shielding tape to provide 100% shielding coverage The cable then an extruder apparatus 64 is advanced and a molten polymer material is extruded at an elevated temperature around the second shielding tape 20 to form the cable sheath 24 If the second shielding tape 20 no longer includes an adhesive, an adhesive layer 40 can be applied to the second shielding tape by suitable means such as coating or extrusion or it can be extruded together with the cable sheath 24 The heat of the extruded molten product generally activates the adhesive layers 25 and 40 to provide an junction between the cable core 12 and the first shield band 18, and between the second shield band 20 and the sheath 24 Once the protective sheath 24 has been applied, the cable is extinguished in a cooling channel 66 to harden the sheath and the cable is wound on a reel 68 Figures 4 and 5 illustrate the shielded cable 10 of the invention connected to a standard connector 70 The connector 70 shown in Figures 4 and 5 is a one-piece braided connector of the type conventionally used in the cable television industry However, other types of connectors such as two-piece compression connectors could also be used according to the invention tion The standard one-piece connector 70 typically includes an inner sleeve or liner 72 and an outer sleeve 74. As shown in FIG. 5, for connecting the shielded cable 10 of the invention to the connector 70, the shielded cable is typically prepared by cutting an portion of the dielectric layer 16 and first shield tape 18 to expose a short length (e.g., 0.64 cm) of the central conductor 14 protruding from the dielectric layer. An additional short length is removed from the second shielding tape 20 and sheath 24 (e.g., 0.64 cm) by exposing the dielectric layer 16 and first shielding tape 18. The connector 70 is then connected to the cable 10 by inserting the liner 72 between the shield tapes 18 and 20 and inserting the outer sleeve 74 around the sleeve 24. The outer sleeve 74 is then folded down on the cable 10 using a suitable folding tool to complete the cable connection. Because the strands 42 forming the interstitial layer 22 can move freely between the two shield tapes 18 and 20, the strands are pushed back axially as the connector liner 72 is inserted. The insertion of the connector does not require special preparation or use of a core tool. As best shown in FIG. 5, a portion of the axially displaced threads 42 are housed or wedged between the connector liner 72 and the second shielding tape 20. These threads 42 serve to assist in attaching the connector liner 72 to the liner. cable 10 and thus increase the resistance to detachment of the cable, that is to say, the force necessary to detach the connector 70 from the cable.

The benefits of the invention can be demonstrated by determining the detachment force between standard cables and connectors using the test method described in Document IPS-TP-401 of the Society of Telecommunications Engineers by Cable (SCTE), issued on January 17. 1994 and called "Test Method for Axial / Cable Pull Connector". Using this method, RG6 cables with a diameter over the sheath of 0.691 cm were compared. Cable A was constructed using metal wires according to the invention and cable B was constructed using a layer of foamed polyvinyl chloride between the shielding tapes. The results are provided in Table 1 and demonstrate the increased shear strength of the cables according to the invention.

TABLE 1 In addition to providing ease of connection and resistance to improved connector detachment, shielded cable 10 of the invention can be produced at a better speed than braided cables conventional and at a lower cost. Also, the shielded cable sufficiently protects the RF signals carried by the center conductor. Accordingly, the shielded cable 10 of the invention overcomes many of the problems associated with prior art cables.

Claims (2)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A shielded cable (10) comprising: a cable core (12) comprising a central conductor (14) and a dielectric layer (16) surrounding the central conductor (14); a first electrically conductive shield (18) surrounding said core of cable (12) and attached thereto, said shield (18) comprises a laminated metal-polymer-metal tape attached longitudinally extending the cable (10) and has edges longitudinal overlapping; a second electrically conductive shield (20) surrounding said first shield (18) comprising a bonded metal-polymer-metal laminated tape extending longitudinally of the cable (10) and having longitudinal edges that overlap; a cable sheath (24) surrounding said second shield (20) and attached thereto; and an interstitial layer (22) placed between said first and second shields (18, 20), said interstitial layer (22) is composed of elongated strands (42) disposed between said first and second shields (18, 20) to be able to move freely and axially while also serving to separate said first and second shields (18, 20) from one another.
2. 2. The shielded cable according to claim 1, further characterized in that said first shield (18) comprises a ribbon laminated aluminum-poholefin-aluminum and said second shield (20) comprises a laminated strip of aluminum-polyester-aluminum 3 - The shielded cable (10) according to any of claims 1-2, further characterized in that said interstitial layer ( 22) is formed from a first plurality of metal wires arranged helically around the first shield 4 - The shielded cable (10) according to claim 3, further characterized in that said interstitial layer (22) further comprises a second plurality of metal wires arranged helically around the first plurality of metal wires and having a helical orientation opposite the orientation of the plurality of metal wires 5 - The shielded cable (10) according to claim 3 , further characterized in that the first plurality of metal wires covers less than 30 percent of the surface of the first sub-shield. ace (18) 6 - The shielded cable (10) according to any of claims 1-2, further characterized in that said interstitial layer (22) is formed from threads arranged helically around the ppmer shield (18). - The shielded cable (10) according to claim 6, further characterized in that the threads are arranged in a single layer and they cover less than 50 percent of the surface of the first underlying shield (18). 8. The shielded cable (10) according to claim 6, further characterized in that said wires are selected from the group consisting of polyester, cotton and aramid yarns and mixtures thereof. 9. The shielded cable (10) according to claim 6, further characterized in that said interstitial layer (22) further includes metal wires disposed along said threads. 10. The shielded cable (10) according to any of claims 1-9, further characterized in that said interstitial layer (22) further comprises a water blocking material. 11. A method for making a shielded cable (10) comprising the steps of: advancing a cable core (12) comprising a central conductor (14) and a dielectric layer (16) surrounding the central conductor (14) ); longitudinally wrapping a first metal-polymer-metal laminated shielding ribbon attached (18) around the cable core (12) and overlaying the longitudinal edges of the shielding tape (18); joining the first shielding tape (18) to the cable core (12); applying an interstitial layer (22) composed of axially movable elongated strands (42) around the first shield tape (18); longitudinally wrapping a second laminated metal-polymer-metal laminated shield tape (20) around the interstitial layer (22) and overlapping the longitudinal edges of the shielding tape (20); extruding a cable sheath (24) around the second shielding tape (20); and joining the cable sheath (24) to the second armor belt (20). 12. The method according to claim 11, further characterized in that said step of applying an interstitial layer (22) comprises spirally wound elongated strands (42) around the first shielding tape (18). 13. The method according to claim 12, further characterized in that said step of wrapping in helical manner comprises spirally wrapping a first plurality of metal wires around the first shielding tape (18). 14. The method according to claim 13, further characterized in that said helical wrapping step further comprises helically wrapping a second plurality of metal wires around the first plurality of metal wires in a helical orientation opposite to the orientation of the first plurality of metal wires. 15. The method according to claim 13, further characterized in that said helical wrapping step comprises helically wrapping the first plurality of metal wires on less than 30 percent of the surface of the first underlying shielding tape. (18) 16. - The method according to claim 12, further characterized in that said step of wrapping helically comprises spirally wrapping a first plurality of yarns around the first shielding tape (18). 17. The method according to claim 16, further characterized in that said helical wrapping step comprises helically wrapping the first plurality of yarns on less than 50 percent of the surface of the first underlying shielding tape (18). ). 18. The method according to claim 16, further characterized in that said helical wrapping step comprises spirally wrapping a first plurality of yarns selected from the group consisting of polyester, cotton and aramid yarns and mixtures of the yarns. same. 19. The method according to claim 16, further characterized in that said helical wrapping step further comprises spirally wrapping metal wires around the first underlying shielding tape (18) and arranged along the first plurality of threads.