Cable-shielding Material

Abstract

A cable-shielding material is shown to comprise annealed, low carbon steel and aluminum layers of selected thicknesses arranged and metallurgically bonded together in selected positions relative to each other to provide novel and advantageous properties of strength, weight, volume, electrical conductivity, magnetic permeability corrosion resistance, and formability, whereby the cable-shielding material can be economically manufactured and easily formed around a cable to provide the cable with suitable electrical and electromagnetic shielding while further providing the cable with suitable protection against sharp objects, rodents and corrosion. Such a cable-shielding material having a layer of copper thereon for facilitating soldering of the material is also shown.

Parent Case Text

This application is a continuation-in-part of copending applications Ser. No. 591,801 and Ser. No. 591,827, filed Nov. 3, 1966, by the inventors hereof now abandoned.

Description

Cable-shielding materials are known to serve a variety of functions including shielding the cable from the effects of lightning and electromagnetic fields and protecting the cable from sharp objects, rodents and effects of corrosion. On the other hand, the cable-shielding materials add significantly to the weight and size of the cable and, including the basic cost of the shielding material as well as the cost of their application, add significantly to the cost of shielded cables. In fact, primarily because of cost factors, it has been conventional to use one of three different cable-shielding materials depending upon the requirements of the particular application. For example, one widely followed specification requires use of copper cable-shielding material, the specification requiring copper of 0.005 inch thickness to meet the electrical conductivity requirement of the specification but further requiring use of copper of 0.010 inch thickness to provide sufficient strength in the cable-shielding material. Alternately, where the strength requirements of the specification can be waived in a particular application, an aluminum cable-shielding material of 0.008 inch thickness is used to meet the electrical conductivity requirements of the specification. Alternately, where stringent electrical requirements do not have to be met, steel cable-shielding materials can be used to provide physical protection for cables. In all of these applications, the cable-shielding material is preferably in annealed or easily formable condition to permit economical application of the shielding material to a cable. Further, in these known shielding materials, the thickness of the material is preferably kept in the range from 0.010 to about 0.014 inches in order to limit the bulkiness or volume factor in a shielded cable formed with the shielding materials.

It is an object of the invention to provide a novel and improved cable-shielding material which is characterized by suitable strength, low-weight, small volume, high electrical conductivity, and suitable magnetic permeability; to provide such a material which displays good corrosion resistance; to provide such a material which is easily formed; to provide such a material which is easily soldered; and to provide such a material which is economically manufactured and applied in cable construction.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings in which several of the various embodiments of the invention are illustrated:

FIG. 1 is a view illustrating a typical application of our new multilayered shielding material to form an improved cable, said material being shown diagrammatically by single lines;

FIG. 2 is an enlarged fragmentary cross section taken on line 2--2 of FIG. 1, illustrating a two-layered form of the invention;

FIGS. 3-5 are views similar to FIG. 2 showing three-, four- and five-layered forms of the invention, respectively; and

FIG. 6 is a view similar to FIG. 2 illustrating an alternate five-layered form of the invention.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. The drawings are illustrative and are not to exact scale, the small thicknesses of the layer involved being exaggerated.

It is desirable, if possible, to avoid or to minimize the use of copper in a cable-shielding material because of the high cost of copper and the fact that copper sometimes is in short supply. Nevertheless, the benefits of high conductivity, strength, light weight, small volume and good formability as well as good corrosion resistance and magnetic permeability can be obtained in a cable-shielding material or sheath employing only aluminum and steel according to the arrangements hereinafter specified, or employing such aluminum and steel layers together with a very thin solderable layer of copper as is hereinafter specified, the composite sheath thickness being on the order from 0.010 to 0.014 inches and preferably being on the order of 0.010 to 0.012 inches.

Referring now more particularly to the drawings, there is shown at numeral 1 a typical conductive core of a cable or like construction to be shielded. At numerals 3 and 5 are shown the usual inner and outer nonmetallic flexible or resilient insulating sleeves that are employed in cable construction. Between these sleeves 3 and 5, our composite shielding material or sheath 7 is employed as is described below. A strip of such shielding material 7 made according to the invention is wrapped around the inner sleeve 3 in the usual manner, as suggested at 9 in FIG. 1, with or without transverse corrugations as illustrated at 11 in FIG. 1. The corrugations improve flexibility of the cable construction but are not always necessary. In the alternative, particularly where used without corrugations, the strip 7 may be applied helically to the cable in known manner (not shown). In FIGS. 2-6, various different forms of our new composite shielding material are illustrated on an exaggerated scale of thickness in order to clearly show the component layers.

Referring now to FIG. 2, an improved shielding material 7 is shown to be composed of a comparatively thick layer 13 of aluminum having a thickness in the range of 0.008 to 0.010 inches, and a comparatively thin layer of steel 15 of a thickness in the range from 0.002 to 0.004 inches, these layers 13 and 15 being interfacially and metallurgically bonded together, preferably by solid-phase bonding methods as set forth, for example, in U.S. Pat. Nos. 2,691,815 and 2,753,623 The thickness of the layers 13 and 15 are also preferably established with respect to each other so that the total thickness of the composite material 7 is kept within the range from 0.010 to 0.012 inches. It should be understood that methods for metallurgically bonding the composite layers 13 and 15 together are not restricted to those described in the noted patents, but that the solid-phase bonding methods of said patents are believed to be superior for forming the composite material 7.

In accordance with this invention, the composite cable-shielding material 7 is annealed in order to provide the material with sufficient formability to permit economical application of the shielding material to a cable in the manner illustrated in FIG. 1.

In this construction, it is found that a minimum thickness of aluminum of 0.008 inches in the composite material 7 provides the cable-shielding material with suitable electrical conductivity to meet the requirements of most applications and of most widely used cable-shielding specifications and standards. That is, this minimum thickness of aluminum assures that the cable shielding material has the current-carrying capacity required to ground currents induced by lightning strokes that may reach the cable. The use of aluminum as a current-carrying member in the material 7 significantly reduces the cost of the material below the cost of the solid copper shielding material previously used in high electrical conductivity applications.

In this construction, it is also found that, while too great a thickness in the steel layer 15 of the composite material 7 would unduly increase the weight and bulkiness of the cable-shielding material and would tend to reduce the formability of the material, a minimum thickness of 0.002 inches for the steel layer provides the composite material 7 with the strength which is required for most cable-shielding applications and which is required for meeting most widely used cable-shielding specifications and standards. That is, this minimum thickness in the steel layer provides the composite material with the strength to withstand blows from sharp objects and to shield a cable from rodents. The steel layer further provides the composite material 7 with abrasive-resistance properties which make it preferably to locate the steel layer on the outer surface of the material when applied to a cable. This minimum thickness of the steel layer also provides the cable-shielding material 7 with adequate magnetic permeability for shielding the cable from the effects of electromagnetic fields. Most important it is also found that this minimum thickness of the steel layer 15 is also required to permit annealing of the steel layer 15 while metallurgically bonded to the aluminum layer 13 without formation of aluminum-iron intermetallic compounds at the interface between the aluminum and steel layers. That is, it is found that where the thickness of the steel layer 15 is less than about 0.002 inches, embrittling intermetallic compounds tend to form at the interface between the steel and aluminum layers in the composite, these intermetallics tending to reduce the formability and electrical conductivity of the composite material and tend to cause delamination or separation of the aluminum and steel layers within the composite material.

In this latter regard, to permit easy annealing of the steel-aluminum composite material 7, the aluminum material embodied in layer 13 preferably incorporates from 0.7 percent to 3.0 percent by weight of silicon. Similarly, for avoiding intermetallic formation during annealing, the steel material embodied in layer 15 of the composite material preferably incorporates not more than about 0.08 percent by weight of carbon, not more than about 0.017 percent by weight of aluminum and from about 0.003 percent to 0.009 percent by weight of uncombined nitrogen. When such materials are utilized, the composite material 7 is easily annealed at temperatures in the range from 950 .degree. F. to about 1050.degree. F. without significant formation of aluminum-iron intermetallics at the interface.

In this construction, it can be seen that the composite material 7 combines the desirable electrical conductivity and strength characteristics of a variety of prior art materials in a single cable-shielding material while achieving these desirable results at lower cost in a lightweight low-volume material which is easily formed.

In FIG. 3 is shown another form of the invention in which there is bonded to the aluminum layer 13 a steel layer 15 having a range of thickness from 0.002 -0.004 inches. Bonded to the steel layer 15 is another aluminum layer 17 of thickness in the range from 0.0002-0.0015 inches. The total combined thickness of layer 13 together with the thickness of the layer 17 again should be in the range of 0.008 to 0.010 inches in order to provide the composite material with suitable electrical conductivity. As will be understood, the aluminum layer 17 provides corrosion protection for the steel layer 15 while also tending to reduce the "notch effect" for increasing the strength of the steel layer. That is, layer 17 of the composite shields the steel layer 15 from scratches which would tend to cause breaking of the thin steel layer. In this form of the invention it is preferable that the thicker layer of aluminum 13 shall be inside of the steel layer and that the thinner layer of aluminum 17 shall be outside of the steel layer when applied to a cable although this arrangement may also be reversed. Alternatively, where soldering of the composite material 7 shown in FIG. 3 is desired, the layer 17 of the composite material can be formed of copper within the scope of this invention. As the layer 17 is extremely thin, this use of a copper layer 17 dies not unduly increase the cost of the composite material and slightly increases the electrical conductivity of the material.

In FIG. 4 is shown a four-layered form of the invention in which the aluminum layer 13 has bonded on its opposite sides steel layers 19 and 21, each of which has a thickness in the range of from 0.0002-0.004 inches. Bonded to the steel layer 19 is a thinner aluminum layer 23, of thickness in the range from 0.0002 -0.0015 inches. The total thickness of the layer 13 together with the thickness of the layer 23 is again preferably also, the range of 0.008 to 0.010 inches. Preferably also, the total thickness of the composite material 7 illustrated in FIG. 4 is kept within the range from about 0.012 to 0.014 inches. In this case it is preferable that the steel layer 21 be inside of layers 13 when applied to the cable and the aluminum layer 23 on the outside if the cable is to be located in corrosive surroundings. This arrangement gives the steel layer 19 some protection against corrosion by reason of the outside position of the aluminum layer 23. The arrangement may, however, be reversed for use in noncorrosive surroundings. Alternatively, where solderability of this composite material is desired, the layer 23 of the laminate material can be formed of copper within the scope of this invention for the purposes noted above.

In FIG. 5 is shown a five-layered form of the invention in which a thick aluminum layer 13 has steel layers 25 and 27 bonded to opposite faces thereof, the range of thickness of each of these layers 25 and 27 being in the range of 0.002-0.004 inches. Bonded on the outside of the steel layers 25 and 27 are aluminum layers 29 and 31, respectively, the thicknesses of which are in the range of 0.0002-0.0015 inches. Again the total thickness of the layers 13, 29 and 31 is preferably kept in the range of 0.008 to 0.010 inches and the total thickness of the composite material 7 illustrated in FIG. 5 is preferably kept within the range from 0.012 to 0.014 inches. As will be understood, one for both of the composite layers 29 and 31 can be formed of copper within the scope of this invention.

In FIG. 6 is shown an alternate five-layered form of the composite material of this invention in which a thin steel layer 33 has a pair of relatively thicker aluminum layers 35 and 37 metallurgically bonded to respective opposite faces thereof, each of the aluminum layers having a respective copper layer 39 and 41 bonded thereto. The thickness of the steel layer is in the range from about 0.002 to 0.004 inches and each of the copper layers has a thickness in the range from about 0.008 to 0.0015 inches, the total combined thickness of the copper and aluminum layers being in the range from about 0.008 to 0.010 inches and the total combined thickness of the composite material illustrated in FIG. 6 being in the range from about 0.010to 0.014 inches and preferably in the range from about 0.010 to 0.012 inches. In forming the material, the aluminum and steel layers are preferably solid-phase bonded as previously described and are then annealed in conventional manner. The copper layers are then electrodeposited by an conventional means.

In some cases it is desirable to employ, on one or both sides of the composites of FIGS. 2-6, a tough, insulating adhesive plastic (not shown) such as, for example, polypropylene, which will stick tenaciously to metal. Such an adhesive layer functions as a good bond with the insulating sleeve 3 and/or 5. It also provides protective barrier against corrosion in cases in which the cable is used in corrosive surroundings.

It will be understood that in certain applications of the invention corrosion of the steel or aluminum layers is not a problem and in such cases the use of the adhesive protective layer above described is not absolutely necessary. However, even in such cases, it provides a good bond with the insulating sleeves 3 and/or 5.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

We claim:

1. A composite cable-shielding material comprising at least one layer of steel metallurgically bonded to at least one layer of metal of relatively high electrical conductivity at least one of said layers of relatively high electrical conductivity being formed of aluminum metallurgically bonded to said steel layer, each of said steel layers having a thickness in the range from about 0.002 to 0.004 inches and being in annealed condition, the total thickness of said layers of relatively high electrical conductivity being in the range from about 0.008 to 0.010 inches, and the total thickness of said composite material being in the range from about 0.010 to 0.014 inches.

2. A composite material as set forth in claim 1 comprising one layer of steel and one layer of aluminum.

3. A composite cable-shielding material as set forth in claim 1 comprising one layer of steel, one relatively thick layer of relatively high electrical conductivity formed of aluminum, and one relatively thin layer of relatively high electrical conductivity formed of a material selected from the group consisting of copper and aluminum, said layers of relatively high electrical conductivity being metallurgically bonded to respective opposite faces of said steel layer.

4. A composite material as set forth in claim 3 wherein said relatively thin layer has a thickness in the range from about 0.0002 to 0.0015 inches.

5. A composite cable-shielding material as set forth in claim 1 comprising a relatively thick layer of relatively high electrical conductivity formed of aluminum, said relatively thick layer being sandwiched between and metallurgically bonded to two steel layers, and a relatively thin layer of relatively high electrical conductivity formed of a material selected from the group consisting of copper and aluminum, said relatively thin layer being metallurgically bonded to one of said steel layers.

6. A composite material as set forth in claim 5 wherein said relatively thin layer has a thickness in the range from about 0.0002 to 0.0015 inches.

7. A composite material as set forth in claim 6 having an additional relatively thin layer of relatively high electrical conductivity formed of a material selected from the group consisting of copper and aluminum, said additional relatively thin layer being metallurgically to the other of said steel layers.

8. A composite material as set forth in claim 7 wherein said additional relatively thin layer has a thickness in the range from about 0.0002 to 0.0015 inches.

9. A composite material as set forth in claim 1 comprising one layer of steel sandwiched between and metallurgically bonded to two layers of relatively high electrical conductivity formed of aluminum, and two relatively thin layers of relatively high electrical conductivity formed of copper, said relatively thin layers being bonded to said aluminum layers respectively.

10. A composite material as set forth in claim 9 wherein said relatively thin layers of copper each have a thickness in the range from about 0.0002 to 0.0015 inches.