US 3824330 A
This electrical cable construction has an insulated center conductor with a metal strip longitudinally folded around the insulated conductor, and with the strip having corrugations extending in directions at a substantial angle to the edges of the strip. The shield formed by the metal strip may serve as a shield or as the outer conductor of a coaxial cable. Since the major stiffening caused by corrugations is in the direction in which the corrugations extend, this invention makes the corrugation shield bend more easily around the insulated conductor; and the greater ease in folding the strip around the conductor is an important advantage with small wires. In the preferred embodiment, corrugations extend at acute angles and come together at a mid region in a herringbone pattern. The invention is useful for CATV drop cords with the shielding serving as the outer conductor.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 1 Lang I [111 3,824,330 [451 July 16, 1974 I CORRUGATED SHEATH CATV DROP WIRE 75 Inventor: Fred Lang, Hillside, N.J.
 Assignee: General Cable Corporation, New
 Filed: May 25, 1973  Appl. No.: 363,814
 US. Cl. 174/102 D, 174/107  Int. Cl. 1101!) 7/18  Field of Search 174/102 D, 106 D, 107, 174/110 PM, 36; 138/122, 121; 156/53, 54,
 References Cited V UNITED STATES PATENTS 3,681,515 8/1972 Mildner 174/107 FOREIGN PATENTS OR APPLICATIONS 1,048,462 11/1966 Great Britain .174/102 D Primary Examiner-A. T. Grimley 5 7 ABSTRACT This electrical cable construction has an insulated center conductor with a metal strip longitudinally folded around the insulated conductor, and with the strip having corrugations extending in directions at a substantial angle to the edges of the strip. The shield formed by the metal strip may serve as a shield or as the outer conductor of a coaxial cable. Since the major stiffening caused by corrugations is in the direction in which the corrugations extend, this invention makes the corrugation shield bend more easily around the insulated conductor; and the greater ease in folding the strip around the conductor is an important advantage with small wires. In the preferred embodiment, corrugations extend at acute angles and come together at a mid region in a herringbone pattern. The invention is useful for CATV drop cords with the shielding serving as the outer conductor.
12 Claims, 15 Drawing Figures PRIOR ART l CORRUGATED SHEATH CATV DROP WIRE BACKGROUND AND SUMMARY OF THE INVENTION Metal shields are commonly applied over insulated conductors by folding the metal strip longitudinally around the insulation, and the strip is often corrugated with the corrugations extending at right angles to the edges of the strip in order to give the final'conductor construction greater flexibility when the conductor has to bend.
Although the corrugations make the final product more flexible, it also has the effect of stiffening the strip transversely so that it is hard to fold the strip around the insulated conductor, particularly with small wires. Where the shield has to bend with a small radius of curvature, it is difficult to apply; and on very small wires the corrugated strip cannot be bent sharply enough without damaging the corrugations.
This invention makes the corrugations extend in directions having a component that is in the direction of the length of the conductor instead of extending at right angles to the length of the strip as in prior art constructions. By having the corrugations extend angularly, the stiffness resistance to the folding of the shield around the insulated conductor is reduced.
In the preferred construction, corrugations that are nearer to the opposite edges of the strip slope in different directionswith respect to the edges and these differently sloping corrugations meet in a region, between the edges of the strip, with a herringbone pattern.
The metal strip that is folded around the insulated conductor may be for the purpose of providing conductivity and it may constitute the outer conductor of a coaxial cable, as previously pointed out; or it may be used for mechanical strength, corrosion protection, flexibility, or electrical shielding.
A bare metal strip can be used for this invention; but if the metal is one that corrodes in the environment where it is used, then .it is necessary to apply a corrosion-resistant coating to the outside and preferably to both sides of the metal shield. The term strip is used herein to designate a metal strip whether bare orlaminated with coating of plastic on either the inside or the outside surface of the strip, or on both sides; or a laminated strip having two or more layers of metal with or without plastic coating.
Some cables of substantial size have shields that are corrugated with the corrugations helical, the pitch of the helix being substantially equal to the width of the corrugation. The component of the direction of extent of the corrugation that is lengthwise of the cable is much too small in such a construction to accomplish the purposes of the present invention. The slope of the corrugations with respect to the strip edges must be larger than such helical corrugations, as will be explained in connection with the drawings.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.
BRIEF DESCRIPTION OF DRAWING In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views:
FIG. 1 is a'fragmentary view of a portion of a cable shield having a helical corrugation;
FIG. 2 is a view of one side of the corrugated shield of FIG. 1 with the shield rolled out so that the circumference is a straight line but the corrugations remain in the metal shield, both FIG. I and FIG. 2 being representativeof the prior art;
FIG. 3 is a fragmentary view, partly broken away, showing a cable construction made in accordance with this invention;
FIG. 4 is a view of a portion of the length of a strip which is folded around the insulated conductor of FIG. 3 to form the shield shown in FIG. 3;
FIG. 5 is a sectional view taken on the line 5-5 of FIG. 3, and greatly enlarged;
FIG. 6 is an enlarged sectional view similar to FIG. 5 but showing a conductor construction where the radius of curvature is shorter in the region of the seam and in the region where the corrugations come together to form a herringbone pattern as shown in FIG. 4;
FIG. 7 is a view similar to FIG. 4 but showing a different corrugation pattern;
FIG. 8 is a sectional view taken on the line 88 of FIG. 7, a similar sectional view on FIG. 4 would appear substantially the same.
FIG. 9 is a sectional view taken on the line 9-9 of FIG. 4;
FIG. 10 is a diagrammatic view showing the folding of the strip of FIG. 4 or FIG. 7 around an insulated conductor; and
FIGS. 11 15 are diagrammatic sectional views taken on the lines 11-11 through 15-15, respectively, of FIG. 10.
DESCRIPTION OF PREFERRED EMBODIMENT Cable shields of the prior art have commonly had the corrugations extending at right angles to the longitudinal seam of a shield where the seam is parallel to the axis of the cable. Sometimes the corrugations have been helical; in which case a pattern is formed where the corrugation is similar to a screw thread.
FIG. I shows a cable 20 having a shield 22 with corrugations 24 which form a helix when the shield is longitudinally folded around the cable.
FIG. 2 shows the shield 22 with the circumference of the shield in a straight line. The corrugation 24 in FIG. 2 extends from a point a at one edge of the shield 22 to a point a at the other edge of the shield. The point indicated by the reference character b is the mid-point of the corrugation 24 of FIG. 2.
The points a, a and b are also shown in FIG. 1 where the shield 22 is enfolded longitudinally around a cable as indicated in FIG. 1 there is no uncorrugated area between corrugations 24 so the pitch of the corrugation is the distance from a to a. This pitch is, of course, the same for all. corrugations and it is indicated in FIGS. 1 and 2 by the dimension reference w.
Referringagain to FIG. 2, the circumference of the folded shield is indicated by the dimension reference C; and the circumferenceC is taken at right angles to the edges of the shield 22. It will be apparent, therefore, that the angle indicated by the double-headed arrow 23 is equal to are tan C/w.
In FIGS. 1 and 2, which represent examples of the prior art where the corrugations are not at right angles to the edges of a shield, the corrugations do have a component of direction which is parallel to the axis of the folded shield and to the edges of the strip from which the shield 22 is made. However, the angle of these corrugations with the edges of the strip are so close to being right angles that they do not facilitate the folding' of the strip around the cable core to obtain the improvement to which the present invention is directed. For example, the angle which the corrugations 24 make with the edges of the strip in FIGS. 1 and2 is greater than 84 whereas the present invention has corrugation angles which are substantially less than this and preferably between and 75.
FIG. 3 shows a conductor construction comprising a cable 30 having a center conductor 32surrounded by insulation 34 and with a shield 36 around the insulation 34. The shield 36 is surrounded by an outer plastic jacket 38. By using the shield 36 as one conductor of the cable 30, the construction illustrated can be used as a drop wire for CATV, since the construction provides a flexible coaxial cable.
FIG. 4 shows a strip 40 which is corrugated with corrugations 42 spaced from one another by flat uncorrugated areas 44. The corrugations, shown in FIG. 4, extend at an angle of approximately 45 to an edge 46 of the strip 40.
Thus the corrugations 42 extend in directions having substantial components parallel to the edge 46. This greatly facilitates the bending of the strip 40 around the longitudinal axis of the cable core on which it is used. The corrugations 42 do not resist bending of the strip around a cable with the same stiffness as is encountered with corrugations extending at right angles to the edges of the strip or at a very large angle approaching a right angle as in the case of FIGS. 1 and 2. One of the reasons for the easier bending is that the bend can be distributed over a greater length of the corrugation; and another reason is that with the corrugations extending in a direction having a substantial component parallel to the edge of the strip, the corrugation can twist to some extent to accommodate the bend required to fold the strip around the cable core.
In the preferred construction of this invention, there are other corrugations 42' spaced from one another by uncorrugated flat areas 44 and extending in a direction having a substantial-component parallel to the other edges 46' of the strip 40. These corrugations 42 and 42 meet at a mid-region 50 to form a herringbone pattern and there is very little resistance to folding of the strip longitudinally at the region 50.
The corrugations 42 may be said to slope at an acute angle toward the right with respect to the edge 46; and the corrugations 42 may be said to slope at an acute angle toward the left with respect to the edge 46. FIG. 5 shows the strip 40 folded around the cable core, comprising the conductor 32 and the insulation 34 to form the shield 36. The portion of the shield adjacent to the edge 46 overlaps the corresponding portion adjacent to the edge 46' to form a lap seam. Because of the difference in slope of the corrugations adjacent opposite edges of the strip 40 which isfolded longitudinally to make the shield 36, there will also be a herringbone pattern of the corrugations along the seam similar to that along the mid-region 50.
The longitudinal seam formed by the overlapping portions adjacent. to edges 46 and Y46 is indicated by the-reference character 54. The seam 54 can have substantial overlap or very little overlap and it can be formed withthe edges 46 and 46 in a butting relation but this requires closer manufacturing tolerances and the lap seam is preferred.
Unless the strip 40 is constrained to cause the corru gated portions to bend uniformly with the region 50 and the region of the seam 54, the strip will bend to a sharper radius of curvature at the region 50 and at the seam region as compared to the corrugated portions of the width of the strip. It is advantageous to maintain the shield 36 substantially cylindrical when using the invention for a drop cord for CATV circuits which operate most satisfactorily with coaxial cable. For other uses, the shield may form with more ofa polygonal contour as shown in FIG. 6 where the region at the middle of the herringbone is indicated by the reference character 50a; and the region of the seam is indicated by the reference character 54a. Other parts of the structure shown in FIG. 6 corresponding to structure shown in FIG. 5 is indicated by the-same reference characters with a letter a appended.
FIG. 9 is a sectional view on the line 99 of FIG. 4 and illustrates the corrugations 42 with the spaces 44 separating them from one another. It will be noted that the corrugations 42 are displaced from one side of the strip 40 but not from the other, this permits the strip to be folded as a shield more snugly around the insulation 34 (FIG. 3) of the cable core consisting of the insulation 34 and any conductor or conductors which are enclosed in the insulation of the cable core. The reference character 58 indicates the cable core in FIG. 3 and FIG. 10.
Although the herringbone construction of FIG. 4 is a preferred construction for this invention, it can be corrugated with parallel herringbone patterns to obtain increased flexibility to bending around'the circumference of a cable core; and such plural herringbone patterns would constitutea construction similar to FIG. 4 but with a zone of identical appearance located to the right of the edge 46 and constituting a part of the width of the strip 40. v
The invention can also be used with a strip 60, such as shown in FIG. 7. This construction can be the same as the, construction of FIG. 4 except that the corrugations 62 and the uncorrugated areas 64 between them, extend in directions having a substantial component parallel toan edge 66 of the strip without any herringbone pattern. In FIG. 7 the corrugation 62 extend continuously across the full width of the strip 60 from the edge 66 to an opposite edge 66'. In FIG. 7 the corrugations 62 make an acute angle with the edge 66 equal to approximately 60. Even larger angles can be used depending upon the radius of curvature to which the shield must be bent for cables of smaller diameter, a smaller acute angle of inclination of the corrugations with the strip edges; is desirable. The preferred construction of this invention has the slope of the corrugations at an acute angle to the edges between 30 and 60. As the angle slope of the corrugations approaches 30 and becomes less than 30, the corrugations impair the flexibility of the conductor construction in a lengthwise direction and this is particularly objectionable for drop wires.
FIG. 8 is a sectional view taken on the line 8-8 of FIG. 7 and shows a construction which is quite similar to FIG. 9. l
FIG. 10 is a diagrammatic view showing the way in which .the strip 40 is folded longitudinally around the cable core 58. The strip 40 advances first through corrugating rolls 71 and 72 which form the corrugations of 42. Beyond the corrugating roll pass, the corrugated strip 40 passes through a breakdown pass where rollers 74 and 75 provide the initial transverse bending of the strip 40 with the strip 40 partially bent to form the shield 36, the core 58 is introduced into the forming shield by a roll 78 which is preferably grooved to center the cable core 58 in the forming shield 36.
The shield 36 is further folded in another roll pass comprising rolls 80 which rotate about parallel vertical axes; and the folding of the shield 36 is completed in another roll pass between rolls 82 and 83.
FIG. is diagrammatic, and so are the enlarged sectional views of FIGS. 11 15. The forming apparatus of FIGS. 10 15 is conventional and can be used effectively for bending the novel shielding strip of this invention around a cable core and confining the shield to a substantially cylindrical contour, even though the strip has the herringbone pattern of FIGS. 3 and 4 and the resulting reduced stiffness to bending along the center of the herringbone. For example, the rolls 74 and 75 of FIG. 13 impart the same radius of curvature to the strip 40 at the center of the herringbonev and at regions of the strip on both sides of this center.
In FIG. 15, the rolls 80 substantially contact with one another at the bottom of the forming shield 36so that the mid-region along the center of the herringbone is not bent to any sharper curvature than the faces of the shield that contact with the concave circumferential faces of the rolls 80.
The preferred embodiment of the invention has been illustrated and described, but changes and modifications can be made, and some features can be used in different combinations without departing from the invention as defined in the claims.
What is claimed is:
1. An electrical cable construction including a center conductor, insulation surrounding the conductor, and a metal shield surrounding the insulation, said shield comprising a strip folded longitudinally around the insulated conductor and with corrugations in the shield extending at acute angles to the longitudinal edges of the strip. said angles being substantially less than are tan C/w, where w is the pitchof longitudinal advance of each corrugation within the width of the strip, and C is the width of the strip.
2. The electrical cable construction described in claim 1 characterized by the angle of the corrugations to the longitudinal edges of the strip being less than 60.
3. The electrical cable construction described in claim 1 characterized by each of the corrugations extending at a slope to the longitudinal edges of the strip, which slope advances the corrugations longitudinally of the cable and within the circumference of the cable for a distance substantially greater than the width of the individual corrugations.
4. The electrical cable construction described in claim 3 characterized by the strip having uncorrugated portions between successive corrugations.
5. The electrical cable construction described in claim 4 characterized by the uncorrugated portions of the strip being flat in the original strip and lying in a common plane, and the corrugations being displaced in the same direction from said plane and being entirely on one side of said plane.
6. The electrical cable construction including a center conductor, insulation surrounding the conductor, and a metal shield surrounding the insulation, said shield comprising a strip folded longitudinally around the insulated conductor and with corrugations in the shield extending in a direction having a substantial component in the direction of the length of the cable and characterized by some of the corrugations extending in directions that make an acute angle toward the right with respect to an edge of the strip and others of the corrugations making an acute angle toward the left with respect to the edge of the strip.
7. The electrical cable construction described in claim 6 characterized by the folded strip having a longitudinal seam, and some of the corrugations sloping toward the right with respect to the seam and others of the corrugations sloping toward the left.
8. The electrical cable construction described in claim 7 characterized by the corrugations that slope in different directions coming together at a region which extends parallel to the seam of the shield, the radius of curvature of the shield being shorter at said region and at the seam whereby the shield is bent less sharply at the corrugations.
9. The electrical cable construction described in claim 6 characterized by the corrugations toward different edges of the strip sloping in different directions with respect to the seam and meeting in a herringbone pattern.
10. The electrical cable construction described in claim 9 characterized by the corrugations meeting along a line that extends parallel to the seam and at a region substantially midway between the edges of the strip and on the opposite side of the conductor from the seam, the seam edges having one side extending across the other to form a lap seam.
11. The electrical cable construction described in claim 1 characterized by the construction being a CATV drop wire, the shield constituting a conductor of the drop wire, and an insulating plastic jacket enclosing the shield.
12. The electrical cable construction described in claim 1 characterized by the corrugations being at an acute angle to the edges of the strip, said acute angle being between 15 and