The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Skilled artisans will recognize the embodiments provided herein have many useful alternatives that fall within the scope of the invention.
The invention provides a cable shield for communications cable that includes a protective layer bonded between inner and outer copper or copper alloy cladding layers, in which the inner cladding layer is thicker than the outer cladding layer. By providing an inner cladding layer that is thicker than the outer cladding layer (i.e., an asymmetric clad design), more copper can be positioned in the area between the conductor wires and the shield in order to provide high conductivity as well as sufficient standoff distance to minimize signal attenuation. Use of an asymmetric clad design can also be used to provide cable shielding in which the overall amount of copper used can be decreased while maintaining the same, or greater, copper thickness in the area near the conductor wires to provide the desired electrical performance. Note that the terms cable shield and cable shielding have the same meaning and are used interchangeably herein.
A perspective view of an exemplary embodiment of a communication cable with cable shielding of the invention is provided by
To provide an asymmetric relation between the inner and outer cladding layers, the inner cladding layer should be thicker than the outer cladding layer. However, various embodiments of the invention may use specific ratios of the inner and outer cladding material to provide particular levels of performance and cost. For example, the inner cladding layer 22 may be twice as thick as the outer cladding layer 24. In further embodiments, the inner cladding layer 22 may be four times, eight times, or even twelve times as thick as the outer cladding layer 24. For example, for a 5-mil thickness cable shield, the outer cladding layer 24 could have a thickness of about 0.5-mil, the protective layer 20 a thickness of about 2.5-mil, and the inner cladding layer 22 a thickness of about 2-mils.
The inner cladding layer 22 and the outer cladding layer 24 are preferably composed of copper or a copper alloy. Preferably, the copper or copper alloy used has an international annealed copper standard (IACS) value of 90% or more. For example, pure annealed copper has an IACS value of 101%. Copper alloys may include various other metals in addition to copper, such as nickel, lead, tin, iron, silver, cadmium, tellurium, and zirconium. Typically the inner and outer cladding layers will be composed of the same copper or copper alloy. However, different copper or copper alloy materials can be used for the two cladding layers if desired. Examples of specific copper alloys that may be used include, for example, C10100, C10200, C10300, C10400, C10500, C10700, C10800, C10910, C11000, C11100, C11300, C11400, C11500, C11600, C12000, C12100, C12500, C12510, C12900, C14300, C14500, C14530, C14700, C15000, C15100, C15150, C15500, C15715, C16200, C18135, and C18700. See the Copper Development Association webpage maintained online for further details on various copper alloys and their compositions.
Between the inner and outer cladding layers is a protective layer 20. The protective layer includes a different material from that used in the cladding layers, thus providing a composite cable shielding material. Various amounts of material can be used to form the protective layer 20. The protective layer 20 should have sufficient thickness to provide the mechanical strength needed for the cable shielding 14, while not being so thick as to overly hinder formability. In some embodiments, the protective layer 20 should have sufficient strength to protect the cable from attack by rodents such as gophers. Accordingly, the protective layer 20 should be composed of a material that is strong, formable, and retains these characteristics when provided as a thin sheet. For example, the protective later 20 can be made of steel or a variety of steel alloys. A preferred steel for use in making the protective layer 20 is low carbon steel, which is relatively inexpensive. Examples of low carbon steel that may be used include 1006, 1008, and 1010 low carbon steel. Preferably, low carbon steel with a carbon content no greater than that provided by 1010 low carbon steel is used. Alternately, stainless steel or steel alloys may be used. Examples of steel alloys include steel alloyed with nickel, cobalt, titanium, aluminum, and copper.
While the thickness of the protective layer 20 may vary depending on the materials used, the protective layer 20 should have a thickness sufficient to provide the desired mechanical strength to the cable. Preferably, the thickness of the protective layer 20 is about equal to or greater than the thickness of the inner and outer cladding layers combined. For example, the thickness of the protective later 20 may vary from about 100% to about 300% of the thickness of the combined inner and outer cladding layers, with an intermediate value of about 200%.
The asymmetrical cable shielding 14 of the invention includes a protective layer sandwiched between two cladding layers. The three layers together preferably have a thickness ranging from about 3 to about 5 mils, and provide a material that has properties that are well suited for use as a cable shield. However, for applications where additional protection is desired (e.g., rodent protection), a thickness of about 5-10 mils may be used. The thickness of the various layers may vary as described above. For example, in one embodiment the percentage thickness of the outer cladding layer is about 5-10%, the protective layer is about 45-65%, and the inner cladding layer is about 30-50%, such that the percentage thickness of all three layers combined is 100%.
Preferably, the composite formed by combining the protective and cladding layers provides a material with a tensile strength in the range of 35-55 thousands of pounds per square inch (ksi), a yield strength in the range of 25-45 ksi, a percent elongation of 11% (minimum), and an electrical conductivity of 40% IACS (minimum). More preferably, the composite cable shielding 14 provides a tensile strength of about 44 ksi, a yield strength of about 38 ksi, a percent elongation of about 18%, and an electrical conductivity of about 53% IACS. An example of a asymmetrical cable shielding that provides these properties is cable shielding in which the ratio of thickness for the outer cladding, protective, and inner cladding layers is, respectively, 5/55/40, and further in which 1008 low carbon steel is used for the protective layer and commercially pure copper is used for the cladding layers.
The cladding and protective layers that make up the cable shielding 14 can be bonded to one another using techniques known to those skilled in the art. Briefly described, the process includes first obtaining sheets of material (e.g., coiled sheets) for use in making the protective layer and the cladding layers. The sheets of protective material and cladding material are prepared for roll bonding by chemical and/or mechanical cleaning. The cleaned protective material is then sandwiched between two or more layers of cleaned cladding material. The sandwiched sheets of material are then passed between a pair of bonding rolls in a conventional roll bonding mill. Preferably, lubrication is applied between the bonding rolls and the outer surfaces of the metal layers. The sandwiched package is rolled in one pass with sufficient force to reduce the package thickness by over approximately 40%, or preferably between approximately 50-70%, with the cladding material and the protective material reduced in thickness simultaneously in about the same proportion to provide cladding layers and a protective layer. A solid-state bond is thus created in the roll-bonded material at the interfaces between the protective layer and the cladding layers.
Optionally, the inner or outer layer of the roll bonded material can be identified by marking during the final rolling pass through the rolling mill. This can be done by creating a pattern on a work roll via processes such as etching, grit blasting, or machining. Because the “mark” has been rolled into the surface, it is durable enough to remain during additional finishing processing steps such as annealing and/or slitting without a significant degradation in visual appearance. Use of a mark on one side of the cable shielding material makes it easier to distinguish one side from the other in the asymmetric finished material.
The solid-state bond in the composite material may be further strengthened with an elevated temperature sintering and annealing cycle. The temperature of annealing should be controlled so as to not impart excessive inter-diffusion amongst the layers. Excessive diffusion can result in a degradation of the electrical properties the shield, resulting in, for example, a decrease in bulk electric conductivity. Further information on the preparation of solid-state bonded composite material may be found in U.S. Pat. No. 6,475,675, which is hereby incorporated herein by reference.
After bonding the layers, the roll-bonded material is then edge trimmed, if needed, to remove edge cracks and then continuously rolled to provide the desired finish gauge. The finish rolled material is then edge trimmed, if needed, and then cut to a size appropriate to provide cable shielding 14. Once formed, the asymmetric cable shield 14 can be used as is (i.e., without corrugation) to surround and protect the central core 12 of a communication cable 10. For example, in some applications where rigid or extra-heavy cable shielding is desired, it may be preferable to use cable shielding that has not been corrugated. However, for most applications the cable shield material is corrugated before being used to form a sheath around the central core 12. Corrugation involves altering the sheet of cable shield material such that it includes, for example, alternating ridges and grooves, and may be carried out using a conventional corrugation mill. An example of a corrugation pattern can be seen in
As shown in
Asymmetric cable shielding is a lower cost alternative to the other cable shielding designs, such as non-composite or composite symmetrical shielding, that are used to provide shielding in non-rodent resistant buried communication cable (e.g., telecommunication cable), primarily as a result of the significantly lower volume percentage of copper used. The protective layer of the asymmetric cable shielding also provides better forming characteristics for the cable shield of the invention relative to other cable shielding due to its low yield strength and high work hardening characteristics. While the asymmetric cable shielding described herein is ideal for use in non-rodent resistant buried communication cable, asymmetric cable shielding can also be used for a variety of other communication cable applications. For example, use of thicker shielding may provide the cable with rodent resistance, while still minimizing the cost of the materials being used relative to other shielding alternatives.
While various embodiments in accordance with the present invention have been shown and described, it is understood the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.
The present application claims priority from U.S. Provisional Application No. 60/808,990 filed May 26, 2006, the disclosure of which is hereby incorporated by reference herein.
Number | Date | Country | |
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60808990 | May 2006 | US |