METHOD AND APPARATUS FOR FORMING A SHIELDED ELECTRIC CABLE

Abstract: A method for forming a shielded electric cable from a core including a center conductor and a first insulating layer surrounding the center conductor comprises the steps of applying a first electrically shielding tape lengthwise along and circumferentially around the core, and activating a first heat-activated adhesive no later than immediately after the applying the first tape step to bond the first tape around the first insulating layer to form a first shielding member. The method can be used as the basis to form a coaxial cable, a triaxial cable, or other types of cables. A related apparatus is also disclosed.

Description: METHOD AND APPARATUS FOR FORMING A SHIELDED ELECTRIC CABLE Background of the Invention The present invention relates to a method and apparatus for forming shielded electric cables for transmission of signals through the cables, and more particularly relates to an improved method and apparatus for rapidly, economically, and uniformly manufacturing such cables. It is common practice to provide a shielded cable for transmitting signals. A shielded cable usually includes a core of one or more insulated conductors enclosed within at least one conducting layer. The shielding of the conducting layer resists signal leakage from the core and eliminates or reduces the interfering effects of extraneous electrical fields. One type of shielded electric cable used consists of a center conductor having a foam dielectric extending therearound to form a core. A first shield is provided by a tape wrapped around the core. The tape comprises an elongated metallic ribbon. It is also possible to provide a second metallic shield formed from copper or aluminum braid around the metallic tape. An outer cover or jacket of non-metallic material is then extruded around the second metallic shield. Shielded electric cables of the foregoing type are usually provided for use with standard electric connectors, so the cables have a standard diameter selected to accommodate the connectors. Braided shields, because of the spaces between the wire braids, have the disadvantage of providing less than 100% coverage and thus less than 100% shielding of the core. Additionally, the braided shields .re difficult to cut and attach to standard electrical connectors, thus increasing i nstallation time and costs. Other shielded electric cable designs have been proposed, including those disclosed in U.S. Patent Nos. 5,321 ,202, 5,414,213, and 5,521 ,331 , to overcome the deficiencies of such braided cables. In some of the shielded electric cable designs disclosed in these patents, a core including an insulated conductor is provided, along with a first shielding member formed from an elongated ribbon of insulating material and a pair of elongated metal foil strips arranged in a parallel relationship with the ribbon. The strips are bonded to opposite sides of the ribbon. The first shielding member is applied longitudinally to the core and wrapped circumferentially around the core in a generally parallel relationship forming two concentric substantially closed shielding layers. A layer of insulating material surrounds the first shielding member, and a second shielding member surrounds the insulating layer, the second shielding member being capable of being formed of non-braided metallic material of various kinds. The shielded electric cable is provided with an outer jacket of nonconductive material over the second shielding member. The above patents also describe various methods for making such shielded, nonbraided electric cable, the methods varying depending in some cases on the form of the component parts of the cable. As disclosed in U.S. Patent Nos. 5,321 ,202, 5,414,213 and 5,521 ,331 , it may be desirable to have at least some bonding between layers of such shielded electric cable to minimize or prevent migration of moisture between surfaces of the layers. To provide bonding between such layers in a triaxial cable, the above three patents disclose using a tape with an adhesive backing for the first shielding member to bond the first shielding member to the core. The latter two of the above three patents also disclose using either: a) a heat-activated adhesive added to the insulating layer, activated upon the extrusion of the outer jacket over the second shielding member, or b) a coating of adhesive on mating surfaces to bond the layer of insulating material to both shielding members. The latter two of the above three patents also disclose that the outer jacket may be bonded to the second shielding member. The shielded electric cable and the manufacturing methods disclosed in the above patents work well for their intended purposes. However, once capital investment has been made in facilities and equipment for manufacturing shielded electric cable, a slow line speed at which the cable can be manufactured (measured in feet of cable manufactured per second or minute) can negatively impact the efficiency of manufacturing the shielded electric cable. For example, braided shielding layers cannot be applied to electric cables at a rate faster than about 10 feet per minute. However, even if unbraided shielding layers are used thereby allowing faster line speed, various imperfections can be introduced due to difficulty in assembling component parts of cable at the greater line speed. Further, if a manufacturing line is set up to manufacture shielded electric cable at such a higher rate of speed, any imperfection induced will cause a correspondingly larger production of defective cable that must be discarded. Thus, there is a need for a rapid, efficient, and uniform method of manufacturing shielded electric cable. Summary of the Invention In accordance with the invention, a method is provided for forming a shielded electric cable from a core including a center conductor and a first insulating layer surrounding the center conductor, the method comprising the steps of applying a first electrically shielding tape lengthwise along and circumferentially around the core, and activating a first heat-activated adhesive no later than immediately after the applying the first tape step to bond the first tape around the first insulating layer to form a first shielding member. The first activating step may comprise heating at least one of the core, the first tape, and the first heat-activated adhesive prior to, during, or immediately after the applying the first tape step. The method may include the step of applying the first heat-activated adhesive to the core or first tape prior to or after the first activating step, and may also include the step of providing a core having the first heat-activated adhesive within the first insulating layer prior to the first activating step, or of providing the first tape including the first heat-activated adhesive prior to the first activating step. The method may further comprise the steps of applying a second insulating layer surrounding the first shielding member, and activating a second heat-activated adhesive to bond the second insulating layer to the first shielding member. If so, the second activating step may comprise heating at least one of the first shielding member, the second insulating layer and the second heat-activated adhesive prior to the applying the second insulating layer step. The method may also further comprise the steps of applying a second insulating layer surrounding the first shielding member, applying a second electrically shielding tape lengthwise along and circumferentially around the second insulating layer, and activating a third heat-activated adhesive no later than immediately after the applying the second tape step to bond the second tape around the second insulating layer to form a second shielding member. The third activating step may comprise heating at least one of the second tape, the second insulating layer, and the third heat-activated adhesive prior to, during, or after the applying the second tape step. The method may further comprise the step of applying the third heat- activated adhesive to the second tape or the second insulating layer prior to or after the third activating step, and may also include the step of providing the second tape including the third heat-activated adhesive prior to the third activating step, or the step of providing the second insulating layer including the third heat-activated adhesive. The first activating step preferably includes heating the exterior of the core to about 65-125GC, and more preferably includes heating the exterior of the core to about 80-1 OOϋC. The third activating step preferably includes heating the second insulating layer to about 65-135i;C, and more preferably includes heating the second insulating layer to about 80-1 OOLC Preferably, the applying the first tape step includes applying the first and/or second tape at a speed of at least about 50 feet per minute, and more preferably at a speed of at least about 200 feet per minute. Preferably, the steps of applying the first and second tapes include tensioning the tapes to about 10 pounds or less, and more preferably, 1 pound or less. In accordance with another aspect of the invention, an apparatus is provided for forming a shielded electric cable from a core including a center conductor and a first insulating layer surrounding the center conductor, the apparatus comprising a first tape applying assembly for applying a first electrically shielding tape lengthwise along and circumferentially around the core, and a first heating assembly located no further downstream than immediately downstream of the first tape applying assembly for activating a first heat-activated adhesive to bond the first tape around the first insulating layer to form a first shielding member. The first heating assembly may comprise a heating station located upstream from the first tape applying assembly for heating at least one of the core, the first tape, and the first heat-activated adhesive, a heated tape die forming a part of the first tape applying assembly, or a heating station located immediately downstream of the first tape applying assembly. The apparatus may further comprise an insulation assembly downstream of the first tape assembly for applying a second insulating layer to the first shielding member, a second tape applying assembly downstream of the insulation assembly for applying a second electrically shielding tape lengthwise along and circumferentially around the second insulating layer, and a second heating assembly located no further downstream than immediately downstream of the second tape applying assembly for activating a second heat-activated adhesive to bond the second tape to the second insulating layer to form a second shielding member. Preferably, the apparatus further comprises a cooling assembly located between the insulation assembly and the second heating assembly. The second heating assembly preferably includes a heating station located upstream from the second tape applying assembly for heating at least one of the second insulating layer, the second tape, and the second heat- activated adhesive, a heated tape die forming a part of the second tape applying assembly, or a heating station located immediately downstream from the second tape assembly. Preferably, the first and/or second tape applying assemblies include a tape folding tool and a tape die. Accordingly, the invention has the advantages of providing a method and related apparatus allowing a rapid, efficient, and uniform manufacture of shielded electric cable of various designs. Additional advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned from practice of the invention. Brief Description of the Drawings Fig. 1 is a perspective view of one embodiment of a shielded electric cable manufactured in accordance with the present invention, having a portion thereof partially removed for illustration of the construction of the cable; Fig. 2 is a longitudinal sectional view of the shielded electric cable taken along line ll-ll in Fig. 1 ; Fig. 3 is a perspective view of another embodiment of a shielded electric cable manufactured in accordance with the present invention, having a portion thereof partially removed for illustration of the construction of the cable; Fig. 4 is a longitudinal sectional view of the shielded electric cable taken along lines IV-IV in Fig. 3; Fig. 5 is a flow chart diagrammatically showing manufacturing steps and pieces of apparatus according to the present invention useful to manufacture either of the shielded electric cables shown in Figs. 1 through 4, or other shielded electric cables; Fig. 6A is a schematic representation of the cable core supply and tape supply indicated in Fig. 5; Fig 6B is a schematic representation of the tape lubricant supply indicated in Fig. 5; Fig 6C is a schematic representation of one heating station indicated in Fig. 5, the heating station being representative of the others indicated in Fig. 5; Fig 6D is a schematic representation of one tape applying station indicated in Fig. 5, the tape applying station being representative of the other indicated in Fig. 5; Fig 6E is a schematic representation of one extruding station indicated in Fig. 5, the extruding station being representative of the others indicated in Fig 5; and Fig 6F is a schematic representation of one cooling station indicated in Fig. 5, ,he cooling station being representative of the others indicated in Fig. 5. Description of the Preferred Embodiments Reference will now be made in detail to the presently preferred embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be used on another embodiment to yield yet another embodiment. It is intended that the present invention include such modifications and variations. Figs. 1-4 show two examples of shielded electric cables that can be manufactured according to the present inventive method and apparatus. It should be understood, however, that other variations in design of cables resulting from the inventive method and apparatus are possible within the scope of the invention, depending on the specific properties of the desired cable and the corresponding method steps and apparatus portions selected. As broadly depicted, Figs. 1 and 2 show a shielded electrical cable 10 including a number of layers. Cable 10 is a coaxial cable, as will be described below. Figs. 3 and 4 show a triaxial snielded electrical cable 10a having a number of elements in common with coaxial cable 10. Common elements between cables 10 and 10a are given common reference numerals for ready identification. Cable 10 includes a center conductor 12 and an insulating layer 14 surrounding the center conductor. Together, center conductor 12 and insulating layer 14 comprise a core 16 of cable 10. A first shielding member 18 surrounds core 16, and a jacket 20 surrounds first shielding member 18. Center conductor 12 may be made of any suitable conductor material. Typically, copper clad steel is used, but other metals or other materials could be used as center conductor 12 within the scope of the invention. Insulating layer 14 preferably comprises a foam dielectric material such as a thermoplastic foamable polymer. For example, polyolefins such as polyethylene and polypropylene, and fluoropolymers, such as fluorinated ethylene propylene polymer or perfluroro alkoxy copolymer, or various mixtures thereof, may be used. First insulating layer 14 may be extruded onto center conductor 12 to thereby create core 16, as is commonly known. First shielding member 18 preferably comprises an electrically shielding tape suitable for forming an electrical shield around core 16. As shown in Fig. 2, first shielding member 18 comprises a single-layer tape made of a metallic material and extending lengthwise along and circumferentially around core 16. First shielding member 18 may comprise a tape made of an elongated aluminum foil strip, or may be made of copper or other metallic material suitable for providing shielding of core 16. Alternatively, first shielding member 18 may comprise a multi-part tape. Such tapes often include at least three layers: a central strip of insulating material and a pair of outer strips of metallic material. Such tape, when wrapped around core 16, provides two concentric, substantially closed shielding members, each being formed by one of the respective metallic strips. Use of such tape in such application is described for example in U.S. Patent No. 5,321 ,202, the description of which is incorporated by reference herein. One commercially-available multilayer tape is APA tape, available from Facile Technologies of Patterson, NJ It should be understood that first shielding member 18 may have other constructions within the scope of the invention. Applicants have merely discussed two examples of potential materials for use as first shielding member 18 herein in connection with Figs. 1 and 2 to provide some background for the inventive method and apparatus discussed below. Similarly, the joint along the edges of shielding member 18 has been depicted as an overlap joint. However, other types of joints are possible within the scope of the invention. For example, a butt joint, a Z-fold, or a shorting fold such as a single fold, double interlocking fold, etc. may also be employed within the scope of the invention. Jacket 20 is formed of a non-conductive material. Preferably, jacket 20 is made of an extruded polyethylene, polyvinyl chloride, or some other suitable non-conductive material. The material chosen for jacket 20 should be selected so as to be suitable for the intended application of cable 10. For example, depending on whether the cable is to be used indoors or outdoors, above ground or underground, etc., the jacket material may be selected from various suitable materials. Cable 10a, shown in Figs. 3 and 4 is substantially similar to cable 10 shown in Figs. 1 and 2, except that cable 10a is a triaxial cable. Thus, cable 10a includes center core 16, first shielding member 18, and jacket 20, all as described above regarding cable 10. Additionally, cable 10a includes a second insulating layer 22 and a second shielding member 24. Second insulating layer 22 may be constructed of any of the materials or mixtures thereof mentioned above regarding first insulating layer 14. Second insulating layer 22 may be made of the same material as first insulating layer 14, or may be made of a different material for certain applications. Similarly, second shielding member 24 may be made of any of the materials discussed above as suitable for first shielding member 18, and second shielding member 24 may be of the same or different construction as first shielding member 18. It is also possible, within the broadest scope of the invention, for second shielding member to comprise a braided metallic shield, as described above, or some structure other than a tape. Use of such a braided metallic shield or other structure for the second shielding member would provide certain benefits of the invention regarding the claimed method and apparatus. However, it is preferable that second shielding member 24 comprise some sort of tape more rapidly applicable to cable 10a than is a metallic braid in order to enjoy the full scope of the invention. Cable design options other than coaxial or triaxial cables are also possible within the scope of the invention, such as those commonly called messenger cable, Siamese cable, etc. Fig. 5 is a flow chart outlining the claimed methods for forming shielded electric cable using the claimed apparatus according to the present invention. Options are set forth on Fig. 5 for manufacturing a coaxial cable such as cable 10 or a triaxial cable such as cable 10a. It should be understood that further modifications are possible to the methods outlined in Fig. 5 for making variations of such cables within the scope of the invention. As shown in Fig. 5, the method for forming a shielded electric cable from a core begins with a core supply, identified as reference numeral 30. As mentioned above, such core 16 is typically made by extruding an insulating layer 14 over a center conductor 12. Core supply 30 is (schematically) also shown in Fig. 6A. As also indicated in Figs. 5 and 6A, a tape supply or tape feed 32 is provided for supplying a first electrically shielding tape 18a to be used to form first shielding member 18. As schematically indicated in Fig. 6A, tape supply 32 may include a reel 34 from which a supply of tape 18a is paid out through tensioning rollers 36. Tape 18a is preferably tensioned at 10 pounds or less, and more preferably at 1 pound or less. Such tension levels reduce the possibility of damage to tape 18a that could negatively impact the ability of shielding member 18 to provide uniform shielding. Other guide and drive rollers may be provided if desired, along with control and feedback systems (not shown). As shown in Figs. 5 and 6B, an optional lubricant application station 38 may be provided including rollers 40 for guiding the tape 18a used to form first shielding member 18 across a lubricant wick 42 or other lubricant applying element. Lubricant is used to reduce friction on tape 18a as it passes to and through the tape applying assembly, as will be described below, to thereby maintain uniformity along cable 10 and increase line speed. The lubricant may be dehydrogenated mineral oil or other similar substances. As stated, lubricant station 38 is optional. If desired, a lubricant may be placed on one or both sides of tape 18a during its manufacture, thereby eliminating the need for station 38. Also, no lubricant need be used, although such would reduce the speed of manufacture and increase wear on component parts and tape 18a itself, possibly also impairing shielding of shielding member 18. In accordance with the invention, a heating assembly is used in a first activating step to activate a heat-activated adhesive to bond the first tape around the first insulating layer to form the first shielding member. This first activating step occurs no later than immediately after the step of applying the first tape. The term "immediately after" is defined below. One embodiment of the heating assembly is a heating station 44, which is schematically indicated in Fig. 6C and may embody several forms and have several locations. Preferably, heating station 44 comprises an elongated enclosed housing 46 including an inlet 48 and outlet 50 through which an element or portion of cable 10 such as core 16 passes. A number of heating elements 52 are located within housing 46 and may take a number of forms. For example, heating elements 52 may comprise electrical, ceramic, gas, or any other type of heating element in accordance with the invention. Options for placing heat-activated adhesive in position to form a bond between core 16 and first shielding member 18 are discussed below. Heating station 44 may be optionally located upstream of the tape applying assembly, with either first tape 18a or core 16 passing through it. Thus, either first tape 18a or core 16 would be heated and the first heat- activated adhesive be activated, prior to the first tape being applied to the core. Alternately, two such heating stations could be provided, one each for heating first tape 18a and core 16 prior to application of the tape to the core. Also, heating station 44 may be located immediately downstream of the tape applying assembly, thereby heating all of first tape 18a (first shielding member 18), core 16, and the first adhesive simultaneously. "Immediately downstream" means downstream of the tape applying station and upstream of any other cable manufacturing assemblies for adding to or modifying layers or other portions of the cable being manufactured. Immediately downstream therefore means prior to a downstream extruder, if used, so that a downstream heating station 44 provides heat apart from that provided by a downstream extruder. An immediately downstream heating station 44 beneficially can provide controlled heating at desired temperatures, durations, etc., that a downstream extruder likely cannot. Thus, any extruder downstream of the first tape applying station does not comprise part of the first heating assembly for activating the first heat-activated adhesive to bond first tape 18a around first insulating layer 14 to form first shielding member 18. A second embodiment of the heating assembly is a heated portion of the tape applying assembly. That heated portion will be described below in conjunction with the description of one embodiment of tape applying assembly, namely tape applying station 54. In this embodiment, the heat-activated adhesive that bonds first shielding member 18 to core 16 is activated during the application of first tape 18a to core 16. Thus, first tape 18a, core 16, and the adhesive are all heated to some extent simultaneously. A third embodiment of the heating assembly is a heated supply of heat- activated adhesive. Thus, adhesive supplying station 68, as described below, could also be heated, thereby providing activated heat-activated adhesive to either core 16 or first tape 18a prior to application of the tape to the core. The heat-activated adhesive that bonds first shielding member 18 to core 16 thus may be activated either prior to, during, or immediately after first tape 18a is applied to core 16 within the scope of the present invention. As shown in Figs. 5 and 6D, the tape applying assembly is provided downstream of core supply 30 and tape supply 32. At the tape applying assembly, core 16 is joined with first tape 18a to form a coaxial (non-jacketed) cable portion. As indicated in Fig. 5, whether it is intended to create a coaxial cable such as cable 10, a triaxial cable such as cable 10a, or some other type of cable based on either of these types, all methods and apparatus for manufacturing cable according to the present invention begin with and include at least the core supply 30, the tape supply 32, a heating assembly of some sort, and the tape applying assembly. One preferred form of the tape applying assembly comprises tape applying station 54, which preferably includes a tape folding tool 58 held by holders 60, as indicated in Fig. 6D. Tape folding tool 58 is preferably a thin piece of metal or some other material that at the upstream end 58a has a flat configuration that is continuously bent along the downstream direction to a circular configuration at the other end 58b. Tape folding tool 58 may have various other shapes according to the invention, and may be modified or augmented, for example, if a joint or fold other than the overlap joint shown in Figs. 1 and 3 is used. For example, a series of blocks (not shown) having openings of progressively smaller size could be substituted for folding tool 58. Holders 60 are shown schematically in Fig. 6D and may be adjustable in various directions to accommodate differently sized tools 58, cores 16, first tapes 18a, etc. As shown in Fig. 6D, if adhesive is applied to or supplied with first tape 18a, first tape 18a should be oriented so that such adhesive 18b is on the side of the tape facing insulating layer 14 prior to entry into tool 58. Any lubricant on first tape 18a should be on the opposite side facing the folding tool 58. Tape applying station 54 also preferably includes a tape die 62 including an orifice 64 disposed through a removable portion 66, through which the core 16 and first tape 18a pass to squeeze the first tape tightly onto the core to thereby seal them together via the heat-activated adhesive when activated. Also, orifice 64 can be precisely machined to ensure that core 16 and first shield member 18, which comprises first tape 18a, is precisely sized. If desired, orifice 64 may narrow slightly in diameter in the downstream direction to provide a smooth flow through tape die 62. Tool 58 and portion 66 may be replaceable with corresponding parts of different sizes for manufacture of different sizes of cable. As mentioned above, a portion of the tape applying assembly is preferably heated to provide additional activation of the heat-activated adhesive during the application of the first tape to the core. Accordingly, tape die 62 of heating station 54, may be heated, for example, by an electrical resistance heater (not shown). If so, heated tape die 62 would be considered at least a part of the heating assembly. Alternately, heated tape die 62 alone could comprise all of the heating assembly, avoiding the necessity of employing any other heating station 44, either upstream or downstream of tape applying station 54. However, for most applications, it is preferable for the heating assembly to include both an upstream heating station 44 for heating core 16 and heated tape die 62. As indicated in Fig. 5, tape applying station 54 may further include a temperature sensor 56 for monitoring the temperature of core 16 just prior to the folding of first tape 18a to ensure that the heat-activated adhesive is being properly activated by the heat within core 16. Such temperature sensor 56 is used where core 16 passes through an upstream heating station 44. Any commonly available temperature-sensing device may be employed as temperature sensor 56, such as an infrared sensor, etc. Point 70 in Fig. 5 denotes the point at which the methods and apparatus outlined for forming coaxial cable and triaxial cable depart. If coaxial cable such as shielded electric cable 10 is desired, the joined core 16 and shielding member 18 go directly along path 72 to a jacket applying station such as an extruder 76. If a triaxial cable such as shielded electric cable 10a is desired, the joined core 16 and shielding member 18 follow path 74 to additional intermediate stations prior to jacket applying extruder 76. It should be kept in mind that paths 72 and 74 are used only for schematic reference in Fig. 5, and are not intended to indicate that separate, optional feed paths are required for the practice of the inventive method and apparatus. As a practical matter, one could set up triaxial cable path 74 as a production line in a manufacturing facility and simply remove certain elements from the line to alter the end product to manufacture coaxial cable or other types of cable. The present invention thus provides ready adjustability in manufacturing and ready change out of manufacturing capability so that one production line can be easily altered to manufacture a number of different cable products. As shown in Figs. 5 and 6E, extruder 76 is disposed downstream of tape applying station 54 for applying an outer jacket 20 over the manufactured cable. If following path 72, extruder 76 applies outer jacket 20 over shielding member 18 to form coaxial cable 10, shown in Figs. 1 and 2. Extruder 76 may be any commonly available extruder capable of extruding jacket 20 over shielding member 18. A heat-activated adhesive may also be used to bond shielding member 18 to jacket 20. Such adhesive may either be placed on shielding member 18 or extruded with jacket 20. As indicated in Figs. 5 and 6F, a cooling assembly such as a cooling station 78 is disposed downstream of extruder 76 for cooling and setting the extrudate from extruder 76 into jacket 20. As shown, cooling station 78 includes an elongated tray 80 having an inlet 82 and an outlet 84. Tray 80 is filled with water 86 that may be circulated into and out of the tray to remove heat transferred from the cable passing though the tray. If desired, a cleaning station (not shown) may be disposed at or near outlet 84 to remove any impurities or other extraneous materials from the finished cable. The cleaning station may clean the cable, for example, by wiping or passing it through an air current, or both, or by some other means. Alternately, the cooling assembly could employ an airflow such as chilled or room temperature air, or a liquid spray to cool the extrudate. The distance between the cooling assembly and the extruder should be selected so that any heat-activated adhesive employed may be sufficiently activated to bond shielding member 18 to jacket 10 before cooling occurs. A take up assembly of some sort (not shown) may be provided to wind the manufactured cable onto replaceable spools after leaving the cooling assembly. There are several options for selecting the type and placement of the heat-activated adhesive according to the present invention, all of which impact the point at which the heat-activated adhesive is activated. For example, the heat-activated adhesive may be formed on one or both sides of first tape 18a. Also, the heat-activated adhesive may be part of the extrudate used to form insulating layer 14 and/or jacket 20. The heat-activated adhesive could also be applied to any of first tape 18a, core 16, or shielding member 18 during manufacture, and could be so applied, for example, by wicking, wiping, electrostatic deposition, using a hot-melt adhesive such as by liquid adhesive bath, or any other method within the scope of the invention. Thus, optional adhesive applying station 68 is indicated in Fig. 5 as providing adhesive to either of core 16 or tape 18a, either in an activated condition or an unactivated condition for later activation. The adhesive selected should be a heat-activated adhesive that is activated at a temperature substantially lower than the melting temperature of insulating layer 14. Also, the adhesive selected should be chosen according to its ability to bind the relevant portions of the cable, and this factor may be determinative of the method of application. If the heating assembly includes an upstream heating station 44 for heating core 16, the heating station should not heat core 16 to the extent that insulating layer 14 begins to melt, degrade, or deform. Similarly, if the heating assembly includes a heating station 44 for heating first tape 18a, the heating station should not damage the tape. It is thus preferable that such heating stations 44 be placed upstream of and relatively close to tape applying station 54 to minimize or at least reduce cooling between heating station 44 and tape applying station 54, to thereby allow economically efficient activation of heat- activated adhesive. If a downstream heating station is used, similar concerns also arise regarding first shielding member 18 and core 16. The temperature of heating elements 52, the ambient atmospheric temperature within housing 46, the length of housing 46, and the size of inlet 48 and outlet 50 should all be selected, in conjunction with desired line speed, to bring the heat-activated adhesive to the desired temperature to effectively activate it. The thermal properties of center conductor 12, insulating layer 14, first tape 18a and the thermally-activated adhesive are all also relevant to the design of heating station(s) 44. If the heating assembly applies heat to core 16 through tape die 62, factors such as the temperature, dimensions, conductivity, etc. of tape die 62 may also affect activation of the adhesive. Further, the dimensions, spacing, and operating parameters of extruder 76, as well as those of cooling station 78, may also affect the activation of the adhesive. Thus, all of the above factors may cause certain adhesives to be better for certain applications or may require adjustment in order to manufacture certain types of cable. If a triaxial cable 10a is desired, optional path 74 may be chosen, as shown in Fig. 5. Fig. 5 indicates a preferable arrangement in which extruder 76a, cooling station 78a, and heating station 44a are disposed downstream of tape applying station 54. Extruder 76a may be any commonly-available extruder suitable for extruding second insulating member 22 around shielding member 18, and may be of the same type, or may be of a different type, as extruder 76. Similarly, cooling station 78a may be similar to or different than cooling station 78, and heating station 44a may be similar to or different than heating station 44. Also, adhesive station 68a may be similar or different than adhesive station 68. The placement, dimensions, and operating parameters of cooling station 78a, heating station 44a, and adhesive station 68a should be chosen according to the temperature of the extrudate used to form second insulating layer 22, the speed of the manufacturing line, the type and placement of adhesive, etc., and thus may differ from their upstream counterparts. As indicated in Fig. 5, a second tape applying station 54a and a second tape supply 32a may also be used, along with an optional lubricant station 38a, to attach second shielding member 24 to create a triaxial cable. Tape applying station 54a may be essentially similar to tape applying station 54, although the dimensions of the tape folding tool and the orifice in the tape die will necessarily be slightly larger than in station 54 in order to accommodate the increasing diameter of the manufactured cable. To make triaxial cable, extruder 76a forms second insulating layer 22 around first shielding member 18, and cooling station 78a cools second insulating layer 22 in place. A heating assembly of some sort, as described above, may be employed in a second activating step to activate a second heat- activated adhesive to bond second insulating layer 22 to first shielding member 18. The activation may be accomplished by heating at least one of first shielding member 18, second insulating layer 22, and the second adhesive prior to extrusion. The second adhesive also may be applied to first shielding member 18. Preferably, the second adhesive is mixed with the extrudate used to form second insulating layer 22, and the adhesive is thus extruded into place and activated simultaneously. Second shielding member 24 is then applied to form a triaxial cable. Preferably, second shielding member 24 is bonded to second insulating layer 22 via a third heat-activated adhesive, and this bonding may be carried out in any of the ways set forth above regarding first shielding member 18 and first insulating layer 14. Preferably, a heating station 44 upstream of second tape applying station 54a applies heat to second insulating layer 22 to activate a heat-activated adhesive that is extruded along with that layer. In this case, the second and third heat-activated adhesives may actually be the same material. Also, preferably, a second heated tape die (not shown) also activates the third heat-activated adhesive. However applied, the third heat-activated adhesive should be activated no later than immediately downstream of the second tape applying assembly. Once second shielding member 24 is in place, jacket 20 is preferably placed on cable 10a by extruder 76. If desired, jacket 20 may be bonded to second shielding member 24 by a fourth heat-activated adhesive that may be applied to second shielding member 24 prior to extruder 76 or extruded along with jacket 20. The present invention thus provides improved methods and apparatus for manufacturing various forms of cable. If desired, bonding between many or all layers and members may be achieved. The following are examples of cables made according to the claimed method and apparatus by applicants corresponding to cables 10 and 10a discussed above indicating how and where bonding is achieved between layers. Example 1 The above example was manufactured with a line speed of 303 feet per minute using an upstream heating station maintained at a temperature of 800°C measured via an internal thermocouple to heat the core. At the first tape applying station, the exterior of the core was 95°C, measured via an infrared sensor. The tape die at the first station was heated to 88°C measured via a thermocouple. The first extrudate for the second insulating layer was a mix of thermoplastics and ethylene acrylic acid, and was extruded at about 400°C. A cooling station followed the first extruder. A second heating station maintained at 750°C measured via an internal thermocouple heated the second insulating layer to 88°C measured via an infrared sensor on the second tape applying station. The second tape die was heated to 88°C measured via a thermocouple. A second extruder extruded the jacket, which was a mix of low-density polyethylene and ethylene acrylic acid at about 465°C. A second cooling station followed. Example 2 The above example was manufactured with a line speed of 197 feet per minute using an upstream heating station maintained at a temperature of 700°C measured via an internal thermocouple to heat the core. At the first tape applying station, the exterior of the core was 95°C, measured via infrared sensor. The tape die at the first station was heated to 88°C, measured via thermocouple. The first extrudate for the second insulating layer was a mix of thermoplastics and ethylene acrylic acid, and was extruded at about 400°C. A cooling station followed the first extruder. A second heating station maintained at 595°C measured via an internal thermocouple heated the second insulating layer to 100°C measured via an infrared sensor on the second tape assembly. The second tape die was heated to 88°C measured via a thermocouple. A second extruder extruded the jacket, which was a mix of low-density polyethylene and ethylene acrylic acid about 400°C. A second cooling station followed. It should be understood all of the apparatus shown in Figs. 6A through 6F are commonly available apparatus that could be assembled by one of ordinary skill in the art or purchased from commercial providers. Applicants have claimed an inventive apparatus and related methods herein that relate to the arrangement of such apparatus and the usage of such apparatus in such methods. The representations of the apparatus shown in Figs. 6A through 6F are thus intended to be no more than representations, and are thus not considered to be limiting as to the form or design of the claimed apparatus or method. Further, as described above, various optional changes are possible to the inventive methods and apparatus within the scope of the invention. It is intended that these optional changes and additions to the inventive methods and apparatus be included within the claimed invention and its equivalents. It should also be apparent that control systems, feedback systems, and drive systems can be applied to or added to the above described method and apparatus by one skilled in the art to allow for precision operation of a manufacturing line according to the disclosed method and apparatus. Detailed descriptions of such systems have not been included herein as it is within the ordinary skill in the art to use such systems in concert with the present invention. Thus, it will generally be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope and spirit of the invention. It is intended that the present invention include such modifications and variations as come within the scope of the appended claims and their equivalents.

Claims: We Claim: 1. A method for forming a shielded electric cable from a core including a center conductor and a first insulating layer surrounding the center conductor, the method comprising the steps of: applying a first electrically shielding tape lengthwise along and circumferentially around the core; and activating a first heat-activated adhesive no later than immediately after the applying the first tape step to bond the first tape around the first insulating layer to form a first shielding member. 2. A method as in claim 1 , wherein the first activating step comprises heating at least one of the core, the first tape, and the first heat-activated adhesive prior to the applying the first tape step. 3. A method as in claim 1 , wherein the first activating step comprises heating the core, the first tape, and the first heat-activated adhesive during the applying the first tape step. 4. A method as in claim 1 , wherein the first activating step comprises heating the core, the first tape, and the first heat-activated adhesive immediately after the applying the first tape step. 5. A method as in claim 1 , further comprising the step of applying the first heat-activated adhesive to the core prior to the first activating step. 6. A method as in claim 1 , further comprising the step of applying the first heat-activated adhesive to the core after the first activating step. 7. A method as in claim 1 , further comprising the step of providing a core having the first heat-activated adhesive within the first insulating layer prior to the first activating step. 8. A method as in claim 1 , further comprising the step of applying the first heat-activated adhesive to the first tape prior to the first activating step. 9. A method as in claim 1 , further comprising the step of applying the first heat-activated adhesive to the first tape after the first activating step. 10. A method as in claim 1 , further comprising the step of providing the first tape including the first heat-activated adhesive prior to the first activating step. 11. A method as in claim 1 , further comprising the steps of: applying a second insulating layer surrounding the first shielding member; and activating a second heat-activated adhesive to bond the second insulating layer to the first shielding member. 12. A method as in claim 11 , wherein the second activating step comprises heating at least one of the first shielding member, the second insulating layer and the second heat-activated adhesive prior to the applying the second insulating layer step. 13. A method as in claim 11 , further comprising the step of applying the second heat-activated adhesive to the first shielding member prior to the applying the second insulating layer step. 14. A method as in claim 11 , further comprising the step of providing the second insulating layer including the second heat-activated adhesive. 15. The method of claim 1 , wherein the step of applying the first tape includes tensioning the first tape at about 10 pounds or less. 16. A method as in claim 1 , further comprising the steps of: applying a second insulating layer surrounding the first shielding member; applying a second electrically shielding tape lengthwise along and circumferentially around the second insulating layer; and activating a third heat-activated adhesive no later than immediately after the applying the second tape step to bond the second tape around the second insulating layer to form a second shielding member. 17. A method as in claim 1 , wherein the heat-activated adhesive includes ethylene acrylic acid. 18. A method as in claim 1 , wherein the first activating step includes heating the exterior of the core to about 65-125°C. 19. A method as in claim 1 , wherein the applying the first tape step includes applying the first tape at a speed of at least about 50 feet per minute. 20. A method as in claim 1 , wherein the applying the first tape step includes applying the first tape at a speed of at least about 200 feet per minute. 21. An apparatus for forming a shielded electric cable from a core including a center conductor and a first insulating layer surrounding the center conductor, the apparatus comprising: a first tape applying assembly for applying a first electrically shielding tape lengthwise along and circumferentially around the core; and a first heating assembly located no further downstream than immediately downstream of the first tape applying assembly for activating a first heat-activated adhesive to bond the first tape around the first insulating layer to form a first shielding member. 22. An apparatus as in claim 21 , wherein the first heating assembly comprises a heating station located upstream from the first tape applying assembly for heating at least one of the core, the first tape, and the first heat- activated adhesive. 23. An apparatus as in claim 21 , wherein the first heating assembly comprises a heated tape die forming a part of the first tape applying assembly. 24. An apparatus as in claim 21 , wherein the first heating assembly comprises a heating station located immediately downstream of the first tape applying assembly. 25. An apparatus as in claim 21 , further comprising: an insulation assembly downstream of the first tape assembly for applying a second insulating layer to the first shielding member; a second tape applying assembly downstream of the insulation assembly for applying a second electrically shielding tape lengthwise along and circumferentially around the second insulating layer; and a second heating assembly located no further downstream than immediately downstream of the second tape applying assembly for activating a second heat-activated adhesive to bond the second tape to the second insulating layer to form a second shielding member. 26. An apparatus as in claim 25, further comprising a cooling assembly located between the insulation assembly and the second heating assembly. 27. An apparatus as in claim 25, wherein the second heating assembly includes a heating station located upstream from the second tape applying assembly for heating at least one of the second insulating layer, the second tape, and the second heat-activated adhesive. 28. An apparatus as in claim 25, wherein the second heating assembly includes a heated tape die forming a part of the second tape applying assembly. 29. An apparatus as in claim 25, wherein the second heating assembly includes a heating station located immediately downstream from the second tape assembly. 30. An apparatus as in claim 21 , wherein the first tape applying assembly includes a tape folding tool and a tape die.

Inventors: DUGAN TIMOTHY V, HILLBURN RALPH D, DUGAN, TIMOTHY, V., HILLBURN, RALPH, D.
Applicants: DUGAN TIMOTHY V, HILLBURN RALPH D, OMEGA ONE COMMUNICATIONS LCC, DUGAN, TIMOTHY, V., HILLBURN, RALPH, D., OMEGA ONE COMMUNICATIONS, LCC
Application year: 1999
Main classification: H01B13
IPC codes: H01B13