Patent Grant
8674228
This invention relates to a device of and method for manufacturing shielded wire and cable. More particularly, the present invention relates to a device of and method for applying longitudinal shield tape to electronic wire and cable using an edge folder to enclose a drain wire in an edge of the shield tape.
Modern electronic wire and cable typically includes insulated electrical conductors, such as copper wire, bound together in a common protective jacket or sheath. The conductors are insulated from each other by coating them with an insulating material using an extrusion process, such as pressure extrusion or tube/sleeve extrusion. Under accepted industry standards, individual conductors are allowed to include a predetermined amount of defects or pin-holes in the insulation, which are measured by “spark” tests. Such imperfections are essentially unavoidable during the fabrication of the individual conductors and can result in “hi-pot” (high potential) test failures in cabled conductors if the current traveling through those conductors arcs with shield tape disposed around the conductors.
Shield tape is typically applied around cabled conductors to shield the conductors from the undesired effects of external influences, such as electromagnetic radiation. A variety of different constructions of shield tape have been applied around conductors in a number of different configurations to shield the conductors from such effects. Shield tape constructions generally include thin metallic foil layers, such as aluminum, laminated with a layer of insulating film, such as polyester, that form opposing sides of the shield tape. The layer of insulating film is provided to add strength and durability to the shield tape as well as to insulate the aluminum layer. A non-insulated grounding wire, or “drain” wire, is disposed on the aluminum side of the shield tape in electrical contact therewith to provide a low resistance electrical connection, or drain, to ground from substantially any point along the shield tape.
Shield tape is typically applied either helically wound around the conductors or longitudinally wrapped, i.e., “cigarette” wrapped, around the conductors. In both applications, the longitudinal edges of the shield tape generally must overlap one another by a relatively large amount, such as 25%, to prevent the shield from leaking radiation. The shield tape may be applied around the conductors either with the aluminum side facing outward away from the conductors and the drain wire disposed on the outside of the shield tape between the shield tape and the jacket or with the aluminum side facing inward toward the conductors and the drain wire disposed between the shield tape and the conductors. There are significant problems, however, with those conventional configurations of the shield tape and drain wire.
Shield tape is generally helically wound around the conductors to improve the flexibility of the cable. Helically wound shield tape, however, is prone to loosening and kinking at the overlapping edges when it is flexed during use or when drawn through various types of conduits during installation. Loosening and kinking of the shield tape may create spiral slots around the circumference of the shield that radiate interference rather than inductively coupling interference. The interference may radiate as much as 360° around the shield. Although it is also possible for slots to appear at the overlapping edges in cigarette wrapped shielding, those slots will be longitudinal and will radiate interference less effectively because they radiate interference only in the plane of the longitudinal slot. In addition, helically wound shield tape has a greater tendency to conform to the conductors than cigarette wrapped shield tape and is therefore less geometrically stable and more likely to form slots in the shielding.
Helically wound shield tape may be applied to the conductors during the cabling/stranding of the conductors. When shield tape is helically wound around the conductors during cabling/stranding, the shield tape is drawn over the conductors as the conductors rotate, or twist, together. To allow sufficient overlap of the shield tape edges and to ensure that the shield tape is tightly wound around the conductors, the twist lay length of the conductors must be short. Not only do short lay lengths require slower cabling/stranding speeds, they also require a greater amount of conductor material to make the same length of cable, which in turn results in a larger signal delay through the conductors. To apply helically wound shield tape around conductors with larger lay lengths with sufficient overlap and tightness, additional equipment must be used to rotate the shield tape around the conductors at a slower rate than the conductors are being twisted together. This extra machinery can be cost prohibitive.
Helically wound shield tape may also be applied to the conductors subsequent to the cabling/stranding of the conductors. When shield tape is helically wound around the conductors subsequent to cabling/stranding, the shield tape may be applied with sufficient overlap and tightness around the conductors irrespective of the conductors' lay length. This process, however, requires that the conductors be collected on a reel after cabling/stranding and then paid off that reel into separate machinery that applies the shield tape, which requires additional man hours and multiple staging areas and is overall less efficient and more expensive than applying shield tape during cabling/stranding.
As discussed above, the drain wire may be applied between the shield tape and the jacket or between the shield tape and the conductors for either helically wound or cigarette wrapped conductors, depending on the side of the shield tape that faces the conductors. When the shield tape is applied with the aluminum side facing downward toward the conductors, the drain wire must be disposed between the conductors and the shield tape. To prevent the drain wire and/or shield tape from arcing with defects in the conductors and to prevent the drain wire from damaging the insulation on the conductors, a barrier layer of insulating material is typically applied around the conductors so that the aluminum side of the shield tape is in contact with the barrier layer and the drain wire is disposed therebetween. Applying an additional layer of insulating material around the conductors, however, requires additional material and machinery and greatly adds to the costs of manufacturing the cable.
In view of at least the above-identified problems, it is preferable to manufacture shielded cable by applying shield tape around the conductors in a cigarette wrapped configuration with the aluminum side of the shield tape facing outward away from the conductors. Even this configuration, however, creates several problems. For example, the dies used to fold the shield tape suffer significant wear when the aluminum side of the shield tape faces outward away from the conductors because the aluminum side of the shield tape is thereby placed in frictional contact with the dies as the shield tape moves through the dies. Although those dies are typically coated with a protective material to protect against excessive wear, the shield tape will still wear through the protective material when drawn through the dies at higher speeds. And, although pre-lubricated shield tape may be purchased, such shield tape can be cost prohibitive.
In addition, when the aluminum side of the shield tape faces outward away from the conductors, the drain wire must be disposed on the outside of the shield tape so the drain wire will be in electrical contact with the shield tape. Placing the drain wire outside the shield tape, however, creates a bulge in the otherwise flat surface of shield tape surrounding the conductors. If the cable jacket is pressure extruded over the assembly, the jacket will fill in around the drain wire and cause a groove to form on the inside of the jacket and/or a ridge to form on the outside of the jacket. And, if the jacket is tube/sleeve extruded over the assembly, the cable jacket will stretch around the drain wire and cause a ridge to form on the outside of the jacket. A groove on the inside of the jacket compromises the integrity of the cable by creating a thinner portion of jacket extending the length of the jacket, and a ridge on the outside of the jacket will compromise the integrity of the cable by not only adversely affecting the aesthetics of the cable, but also by making it more difficult to draw the cable through various types of conduits during installation.
Accordingly, there is a need for a device of and method for manufacturing shielded cable that allows the conductors to be shielded in a cigarette wrapped configuration, allows the drain wire to be on the outside of the shield tape without forming a ridge, and minimizes the amount of leakage in the shield. Further, there is a need to manufacture such a cable without causing excessive wear to the folding dies and while reducing the amount of additional cable material, man hours, work space and machinery required to shield the cable.
Accordingly, to solve at least the above problems and/or disadvantages and to provide at least the advantages described below, a non-limiting object of the present invention is to provide a shielded cable and device of and method for making same that includes a first folding die configured to fold a first edge of a shield tape a first direction from a central portion of the shield tape and to fold a second edge of the shield tape a second direction opposite to the first direction from the central portion of the shield tape, a second folding die configured to wrap the shield tape around at least two insulated conductors to apply a fold to the first edge of the shield tape so as to fold the first edge back over onto the central portion of the shield tape to form a receiving area, a third folding die configured to tighten the shield tape around the plurality of conductors while positioning the receiving area to receive a drain wire, a wire guide configured to install a drain wire in the receiving area, and a closing die configured to close the shield tape around the plurality of conductors and the drain wire to form an enclosure around the plurality of conductors with the second edge overlapping the receiving area at an outside surface of the enclosure.
These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description, taken in conjunction with the accompanying drawings.
Reference will now be made in detail to non-limiting embodiments of the present invention by way of reference to the accompanying drawings, wherein like reference numerals refer to like parts, components and structures.
Turning to the figures,
The first folding die is adapted to apply a Z-fold to the shield tape 114. The second folding die 104 is adapted to pre-form the shield tape 114 by beginning to tighten the shield tape 114 around the insulated conductors 116 and beginning to crease part of the Z-fold where the drain wire 118 is installed. The third folding die 106 is adapted to position the shield tape 114 for installation of the drain wire 118, to tighten the shield tape 114 further around the insulated conductors 116, and to maintain the orientation of the shield tape 114 so it closes properly after the drain wire 118 is installed. The wire guide 108 is adapted to install the drain wire 118 in the J-fold 306 (
As illustrated in
As illustrated in
The upper lip portion 212 prevents the upward fold 216 from extending too far upward into the upward folding portion 208 by providing a physical barrier beyond which the first edge 226 of the shield tape 114 cannot extend. The lower lip portion 214 prevents the downward fold 218 from extending too far downward into the downward folding portion 210 by providing a physical barrier beyond which the second edge 228 of the shield tape 114 cannot extend. Accordingly, the upper lip portion 212 and the lower lip portion 214 work in conjunction to maintain the shield tape 114 substantially centered in the first folding die 102 as the shield tape 114 is drawn through the first folding die 102.
As also illustrated in
The second folding die 104 is adapted to pre-form the shield tape 114. As illustrated in
As illustrated in
The third folding die 106 is adapted to position the shield tape 114 for installation of the drain wire 118 and to tighten the shield tape 114 further around the insulated conductors 116 while maintaining the orientation of the shield tape 114 so it closes properly after the drain wire 118 is installed. As illustrated in
As illustrated in
The wire guide 108 is adapted to install the drain wire 118 in the J-fold 306. As illustrated in
In the alternative, as illustrated in
The guide block 110 is adapted to maintain the shield tape 114 wrapped around the insulated conductors 116 and the drain wire 118 as they travel from the wire guide 108 to the closing die 112. As illustrated in
As illustrated in
The closing die 112 is adapted to close the shield tape 114 around the insulated conductors 116 and the drain wire 118 prior to jacketing the wrapped assembly 120. As illustrated in
The receiving end 800 of the closing die 112 is of a substantially larger diameter than the tubular central portion 802 such that a stepped portion 808 is formed at the transition between the two respective diameters. The stepped portion 808 is adapted to interface with the cross-head tip of an extruder and connect the closing die 112 thereto. The tubular central portion 802 is of a sufficient length to extend through the cross-head tip so the wrapped assembly 120 can be jacketed as it exits the exiting end of the closing die 112. The closing die 112 is preferably formed from a low wear material, such as plastic, to prevent excessive wear from frictional contact with the conductive layer 232 of the shield tape 114.
As illustrated in
In operation, the shield tape 114 is drawn through the first folding die 102 where it receives a “Z-fold”. The width of the central portion 206 of the first folding die's 102 folding aperture 204 may be changed according to the width of the shield tape 114 to ensure the proper amount of overlap 810 of the edges 226 and 228 of the shield tape 114 when it is closed around the insulated conductors 116 by the closing die 112. For example, by centering the shield tape 114 as it passes through the first folding die 102 and sizing the central portion 206 of the folding aperture 204 to be about two thirds the width of the shield tape, a 25% overlap of the first edge 226 and the second edge 228 of the shield tape is ensured. That is because the upward fold 216 and the downward fold 218 will each be approximately one sixth the width of the shield tape's central portion 206 (⅙÷⅔=25%). By ensuring the proper amount of overlap, more efficient cable shielding is produced. Moreover, the amount of overlap can be adjusted to ensure that the first edge 226 extends beyond the second edge 228. In addition, the first edge 226 may be folded back onto the upward fold 216 and towards the second edge 228 to make contact therewith so as to maintain electrical contact between the two edges 226 and 228, which decreases leakage and further improves high frequency performance.
As the Z-folded shield tape 114 exits the first folding die 102, a plurality of insulated conductors 116 are brought into close proximity of the shield tape's central portion 206 on the side of the shield tape 114 on which the insulating layer 230 is disposed. The shield tape 114 and insulated conductors 116 then enter the second folding die 104, where the shield tape 114 is pre-formed around the insulated conductors 116 with the conductive layer 232 facing outward away from the insulated conductors 116. Because the shield tape 114 is wrapped around the insulated conductors 116 with the conductive layer 232 facing outward away from the insulated conductors 116, the shield tape 114 can be disposed between the drain wire 118 and the insulated conductors 116 so that no additional barrier layer is required between the shield tape 114 and the insulated conductors to protect them from failures, such as those measured by “hi-pot” (high potential) tests. The elimination of a need for an additional barrier layer reduces the manufacturing costs associated with shielding the insulated conductors 116.
The pre-forming tube 302 of the second folding die 104 pre-forms the shield tape 114 by folding the downward fold 218 over onto the shield tape's central portion 220 to create the J-fold 306 in which the drain wire 118 is subsequently installed. In addition to wrapping around the drain wire 118, the J-fold 306 ensures that neither the first edge 226 nor the second edge 228 of the shield tape 114 will come into electrical contact with or electrically arc with the insulated conductors 116. Because J-fold 306 folds the second edge 228 of the shield tape 114 back onto the shield tape's central portion 220, the second edge 228 is physically separated from the insulated conductors 116 by the shield tape's central portion 206, i.e., the shield tape's central portion 206 is disposed between the second edge 228 and the insulated conductors 116. And, because the first edge 226 overlaps the other side of the shield tape 114 when the closing die 112 closes the shield tape 114 around the insulated conductors 116 and drain wire 118, the first edge 226 is also physically separated from the insulated conductors 116 by the shield tape's central portion 206 when the closing die 112 closes the shield tape 114 around the insulated conductors 116. That configuration ensures that the insulated conductors 116 are surrounded only by the insulating layer 230 of the shield tape 114, which greatly reduces the risk of hi-pot test failures.
The pre-forming tube 302 of the second folding die 104 also pre-forms the shield tape 114 by beginning to remove the first crease 222. As the second folding die 104 begins to curve the shield tape's central portion 220 around the insulated conductors 116, the shield tape's central portion 220 begins to move into the same plane as the upward fold 216 at the first crease 222. Although the definition of the first crease 222 is substantially reduced by the second folding die 104, the internal stresses imparted on the shield tape 114 at the first crease 222 when it was Z-folded by the first folding die 102 act to prevent the first edge 226 from folding over onto the insulated conductors 116 prematurely so that the J-fold 306 can be folded under the first edge 226 by the closing die 112 after the drain wire 118 is installed therein.
After the pre-formed shield tape 114 and partially wrapped insulated conductors 116 exit the second folding die, they enter the folding aperture 404 of the third folding die 106. The folding aperture 404 of the third folding die 106 further tightens the shield tape 114 around the insulated conductors 116. While further tightening the shield tape 114 around the insulated conductors 116, the guide lip 406 of the third folding die 106 positions the J-fold 306 for installation of the drain wire 118 while maintaining the proper orientation between the first edge 226 and the J-fold 306 so that the first edge 226 will overlap the J-fold 306 when the shield tape 114 is closed by the closing die 112.
After the third folding die 106 further closes the shield tape 114 around the insulated conductors 116 and properly positions the J-fold 306, the wire guide 108 installs the drain wire 118 in the J-fold 306 as the shield tape 114 and insulated conductors 116 are drawn past the wire guide 108. The drain wire 118 is drawn through the cable shielding device 100 with the shield tape 114 and insulated conductors 116. When the drain wire 118 is installed in the J-fold 306, it is disposed between the conductive layer 232 of the downward fold 218 and the conductive layer 232 of the shield tape's central portion 220. By surrounding the drain wire 118 with conductive material in this manner, the drain wire 118 makes better electrical contact with the shield tape 114 than conventional drain wires that are merely installed between the shield tape and an insulating layer, such as the cable jacket.
With the drain wire 118 installed in the J-fold 306, the shield tape 114, the insulated conductors 116, and the drain wire 118 are all drawn through the guide block 110, which maintains the shield tape 114 wrapped around the insulated conductors 116 and the drain wire 118 as they travel from the wire guide 108 to the closing die 112. As the shield tape 114, insulated conductors 116, and drain wire 118 are drawn through the closing die 112, the shield tape 114 is closed around the insulated conductors 116 and the drain wire 118. And, because the guide block 110 may have a guiding aperture 704 that is substantially conical with a diameter that decreases to at least as small as the diameter of the closing orifice 806, much or all of the closing of the shield tape can be performed by the guide block 110 prior to the shield tape 114, insulated conductors 116, and drain wire 118 entering the closing die 112. As the shield tape 114 is closed around the insulated conductors 116 and the drain wire 118, a smooth transition is created over the drain wire 118 when the first edge 226 of the shield tape 114 is moved over to overlap the J-fold 306. The smooth transition of shield tape 114 over the drain wire 118 substantially removes any ridge that would otherwise be created on the wrapped assembly 120 if the drain wire 118 were disposed on the opposite side of the shield tape 114 from the insulated conductors 116. By removing the ridge from the outside of the wrapped assembly 120, problems with jacketing and installation can be eliminated.
The closing die 112 can be inserted directly to an extruder cross-head so that the wrapped assembly 120 is jacketed as it exits the closing die 112. As the extruder jackets the wrapped assembly 120, a rip cord (not shown) can be installed between the wrapped shield tape 114 and the jacketing so that the jacketing can more easily be removed from the wrapped assembly 120 in the field. Alternatively, a rip cord may be installed between the insulated conductors 116 and the shield tape 114.
Accordingly, the cable shielding device 100 of the present invention can be utilized in tandem with an extruder and other cabling equipment, such as an inside-out cabler, in a continuous process. And, because the cable shielding device 100 is able to wrap shielding on insulated conductors that have already been cabled/stranded, it can be installed between a cabling/stranding machine and an extruder, thereby reducing what would otherwise be a two-step process into a one-step process. Thus, the present invention allows a single operator to complete an entire cabling/stranding, shielding and jacketing process without having to place cabled/stranded conductors on a reel and pay them back off through the shielding device 100 and/or an extruder.
The foregoing description and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not intended to be limited by the preferred embodiment. Numerous applications of the invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. For example, although the shield tape 114 preferably includes an insulating layer 230 and a conductive layer 232, the shield tape 114 may be only a single layer that is either dielectric or conductive; or, alternatively, the shield tape 114 may be more than two layers of insulating and conductive material in any suitable arrangement.
The present application is a divisional application of co-pending U.S. application Ser. No. 12/354,876, filed Jan. 16, 2009, which claims the benefit of U.S. Provisional Application No. 61/061,037, filed Jun. 12, 2008, the entire disclosures of which are hereby incorporated by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20100326695 A1 | Dec 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61061037 | Jun 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12354876 | Jan 2009 | US |
| Child | 12875027 | US |
