FR2775115A1 - HIGH FREQUENCY TRANSMISSION CABLE TO TWO GROUPS OF CONDUCTORS - Google Patents

Abstract

The cable has a constriction (84) of a retaining sheath (8) located longitudinally between two groups of individually insulated electrical conductor wires, such as fourth stars (1a, 1b), and between two concave longitudinal portions (82, 83) of the retaining sheath (8) and having a width (LR) of between one (D) and two diameters of the wires (2a-5a, 2b-5b). The concave portions keep the quarters and the symmetry separate in each pair of yarns, and are obtained by adjusting a vacuum in the sheath during extrusion.

Description

High frequency transmission cable with two groups of conductors La

  The present invention relates to a transmission cable for high frequency, telephone and / or data processing and video signals (voice, data, images). The cable is of substantially flat shape and comprises at least two groups of individually insulated electrical conductor wires surrounded by a collective holding sheath. Each group comprises at least one symmetrical pair of insulated electrical conductors, for example a four-star star consisting of two pairs of insulated conductors arranged at the top of a square, the two insulated conductors of the same pair being

  arranged along a diagonal of the square.

  The relative positioning of the insulated conductor wires forming a quarter star is essential to maintain perfect symmetry of the quarter. Any defect in the symmetry of the fourth results in parasitic couplings causing transmission errors which can only be corrected depending on the speed of the information transmitted in the

fourth.

  French patent application FR-A-2709859 proposes a cable, the retaining sheath of which is divided into two portions, each surrounding one of the

  two groups of insulated electrical conductors.

  The retaining sheath portions are half-opened opposite one another along the cable so as to form two independent sheath tongues which can be substantially contiguous and which extend longitudinally between the two groups of wires

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  insulated electrical conductors. The tongues delimit between them a constriction having a width less than the diameter of the insulated electrical conductor wires. The objective targeted by the characteristics of this known cable is to provide easy stripping without special cutting tools, by breaking or tearing or cutting at least one of the tongues in order to open the retaining sheath and access the groups of insulated electrical conductors. In this cable, each group of insulated electrical conductors is a pair of conductors, or includes four conductors arranged freely, or assembled by tapes in

two separate pairs.

  The French patent application FR-A-2709859 does not address the maintenance of the symmetry of the insulated electrical conductors in at least two groups such as quartes, and does not disclose any

  method of manufacturing the retaining sheath.

  The objective of the present invention is to provide a retaining sheath between at least two groups of insulated electrical conductors comprising symmetrical pairs so as to maintain symmetry in each pair and to maintain a constant distance between the groups in order to attenuate any crosstalk between the groups and keep a constant impedance along the cable, while allowing a sheath manufacturing

  holding in a single extrusion operation.

  To this end, a high-frequency transmission cable according to the invention comprising two groups of individually insulated electrical conductor wires and a surrounding sheath

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  together and now separated longitudinally the two groups, is characterized by a narrowing which extends longitudinally between the two groups of conductors and between two concave longitudinal portions of the retaining sheath and which has a width comprised between a diameter and two wire diameters

insulated electrical conductors.

  The concave longitudinal portions of the retaining sheath forming a narrowing thereof between the groups of insulated electrical conductors maintain the groups at a constant distance and push them against the convex lateral portions of the retaining sheath which prevents any movement of the groups towards each other. The width of the narrowing between one and two diameters of the insulated electrical conductor wires, maintaining a relatively large space between the two groups, gives the cable sufficient flexibility during various manipulations of the cable, for example during manufacture, pulling or laying the cable. The shrinkage is easily obtained by a single extrusion operation of the retaining sheath, as

  this will appear in the subsequent description of the

  method of manufacturing the cable according to the invention.

  Each cross section of each concave longitudinal portion of the retaining sheath is applied against one of the insulated electrical conductors in one of the groups and one of the insulated electrical conductors in the other group located on either side. other of the narrowing. The retaining sheath, although not completely wrapping each group of wires, keeps it in place at a constant position in section

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  transverse to the other group of wires, this

  which gives a very low level of crosstalk.

  In order to increase the insulation between the groups, a flat longitudinal strip, or cylindrical, or with any other suitable profile, of insulating material can be accommodated in the narrowing between the groups of insulated electrical conductors and pinched between the concave longitudinal portions of

the retaining sheath.

  The cable may comprise a tearing cord extending between one of the convex lateral portions of the retaining sheath and the respective group of insulated electrical conductor wires. The pulling of one of the ropes tears the retaining sheath during a draw of one of the groups

  without necessarily drawing the other group.

  An at least partially metallic screen can surround the retaining sheath, and an electrical continuity wire and / or a tear-off wire can extend between the two concave longitudinal portions of the retaining sheath and the screen, which gives a regular oval profile to the cable despite the concave longitudinal portions of

the retaining sheath.

  Each group of insulated electrical conductors can be a fourth star. More generally, more than two groups of insulated electrical conductor wires can be juxtaposed substantially flat in the holding sheath and separated in pairs by narrowing each delimited by two respective concave longitudinal portions of the holding sheath.

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  The invention also relates to a method for manufacturing the high-frequency transmission cable of the invention, by means of an extruder comprising an inlet conduit extended coaxially by a conduit of a tubular punch having a

  tapered front end surrounded by a die.

  The method is characterized by guiding the groups of insulated electrical conductor wires in the front end of the punch conduit to keep them juxtaposed in an axial plane with a predetermined spacing corresponding to the narrowing in the holding sheath, by a suction created by a extraction pumping means communicating with the inlet duct to generate a vacuum in the extruded retaining sheath leaving the die in front of the tapered front end of the punch, and by adjusting the extraction pumping means so that the depression deforms the longitudinal portions of the retaining sheath between the groups of insulated electrical conductor wires and attracts them towards each other at a distance equal to the width of the narrowing for

  forming the concave longitudinal portions.

  The pumping extraction means of the process is adjusted to a suction pressure of between 102 and 105 pascals approximately so that the narrowing has a width of between one and two diameters of wires for a cable having a thickness of a few millimeters. The cross sections at the front ends of the punch and die conduits may have similar oblong or elliptical profiles and substantially larger than the contour of the retaining sheath, which requires a lower vacuum than that with die ends

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  and conventionally cylindrical punch, but to the detriment of a more specialized extruder tool. When an insulating loop forming a partition between two groups is provided, the method comprises guiding a flat longitudinal strip, or cylindrical, or with any other suitable profile, of insulating material between the groups of insulated electrical conductor wires in the conduit of the punch and pinching of the strip by the concave longitudinal portions of the retaining sheath

  drawn to each other by depression.

  Other characteristics and advantages of the present invention will appear more clearly on

  reading the following description of several

  preferred embodiments of the invention with reference to the corresponding accompanying drawings in which: - Figure 1 is a cross section of a two-quarter cable according to a preferred embodiment of the invention; Figure 2 is a cross section of a two-quarter cable according to another embodiment of the invention; - Figure 3 is an axial sectional view of an angle head extruder for extruding the cable holding sheath according to Figure 1 or 2; - Figure 4 is a more detailed schematic axial sectional view of the die and the front end of the punch in the extruder of Figure 3; - Figure 5 is a schematic front view of the cylindrical front face of the die and the punch at the front of the extruder;

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  - Figure 6 is a schematic front view of the oblong front face of the die and the punch at the front of the extruder, according to another embodiment and - Figure 7 is a cross section of the cable according to Figure 1 completed by a screen of

  shielding and an external protective sheath.

  According to the embodiment illustrated in FIG. 1, a high frequency transmission cable CAl comprises two groups of individually insulated electrical conductor wires 1a and 1b. In the rest of the

  description, similar items or items

  relating to similar elements in the two groups la and lb will be designated by the same reference numerals followed by the letter a and b respectively. Each group of conducting wires 1a, 1b is a twisted star quadrant made up of four individually insulated electrical conducting wires 2a to a, 2b to 5b. Each insulated electrical conductor wire consists of a solid conductor or a strand of fine annealed copper wires 6 and an individual insulating sheath 7 surrounding the solid conductor 6, for example made of solid polyethylene or polypropylene, or cellular, or cellular and massive. Seen in cross section, the four insulated electrical conductors 2a to 4a, 2b to 4b in a quarter la, lb are arranged at the vertices of a square and are symmetrical two by two with respect to the axes and the diagonals of any square of section transverse along the twists of the fourth so as to avoid any defect in the symmetry of the fourth which could induce

parasitic couplings.

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  The holding cable CAl also comprises a thin insulating holding sheath 8 which together surrounds the two quarters 1a and 1b. The retaining sheath 8 is made of a thermoplastic material extruded according to the method of the invention, the thermoplastic material preferably being transparent so as to distinguish the different colors of the individual sheaths 7 from the insulated conductive wires in each of the two quarters. For example the sheath of

  holding has a thickness between 0.1 and 1 mm.

  The thermoplastic material of the retaining sheath such as, for example, polyethylene, polypropylene or PVC, has a low dielectric constant and sufficient mechanical characteristics to ensure the maintenance of the

  qualities and flexibility of the cable.

  Cross-sectional view as shown in FIG. 1, the holding sheath 8 of the cable CAl is symmetrical with respect to a median longitudinal plane YY passing between the two quarters la and lb and dividing the sheath into two portions 81a and 81b which are substantially in the shape of horseshoes, the ends of which are joined together in pairs. The pairs of joined ends of the retaining sheath portions 81a and 81b constitute two longitudinal central portions 82 and 83 which are concave, that is to say which have convex internal surfaces which are symmetrical with respect to each other to a longitudinal plane with trace XX in Figure 1, perpendicular to the YY plane and passing through

the central axes of the two quartes.

  A space 84 located inside the sheath 8 between the two quarters la and lb constitutes a narrowing with respect to the thickness E of the portions of the holding sheath 81a and 81b which

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  only partially surround the quarters la and lb respectively; indeed, portions of the individual sheaths 7 of two adjacent conductive wires 2a and 3a of the fourth quarter and of two adjacent conductive wires 2b and 3b of the fourth quarter are in pairs directly opposite and separated by the narrowing 84. Each portion of retaining sheath 81a, 8lb partially surrounds the respective quarter la, lb, without the insulated conductive wires 2a to 5a, 2b to 5b being embedded in the portion

  of respective retaining sheath 81a, 81b.

  As will be seen in the manufacturing method according to the invention, the concave curved sheath portions 82 and 83 are obtained by hot "drawing" of the thermoplastic material extruded from the holding sheath so that each sheath portion 82, 83 is constantly applied against an electrically conductive wire insulated from the first quarter la, in this case the insulated conductive wire 2a, 3a according to the section of the cable CAl illustrated in FIG. 1, and against an electrically conductive wire insulated from the second quarter lb , in this case the insulated electric conductor wire 2b, 3b according to the section of the cable CAl illustrated in FIG. 1. Each quarter being twisted, each insulated electric conductor wire occupies in successive transverse sections of the quarter, a position which turns progressively around the center of the quarter as we move along the axis of a twist of the quarter. The concave portions 82 and 83 of the retaining sheath are in contact successively for example with the electric conductor wires 2a and 3a, then 3a and 4a, then 4a and 5a, and finally 5a and 2a and so on at each twist period in the fourth, insofar as the direction of the twists is not changed. The

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  horseshoe portions 81a and 81b of the retaining sheath 8 are in contact with the two other conductors in the respective quarters la and lb, in this case the insulated conductive wires 4a and 5a in the first quarter la and the conductive wires insulated 4b and 5b in the second quarter lb according to the cross section of the cable CAl shown in FIG. 1. The constriction 84 has a width LR comprised between a diameter D and two 2D diameters of the

  insulated electrical conductors 2a to 5a, 2b to 5b.

  For example, according to the embodiment shown in FIG. 1, the width LR of the constriction 84 is approximately 1.7D, while according to a second embodiment shown in FIG. 2, the constriction 84 has a width of 1.2D. The width LR of the constriction 84 is chosen according to the use and the cost of the cable. The narrower the narrowing 84, the more the quads 1a and 1b will be kept separate, and the more a suction pressure applied in the extrusion sheath according to the method of the invention will be high and therefore the more the shrinking will be difficult to achieve; however, tensile forces exerted laterally in opposition on the concave sheath portions 82 and 83 to stretch these will be all the greater as the width LR of the constriction 84 is small and the sheath portions 82 and 83 are thick. On the other hand, during stripping operations, the greater the width LR of the narrowing 84 and the thinner the sheath portions 82 and 83, the more the extraction of a quarter end 1a, 1b by the iron opening at horse of the respective portion 81a, 8lb between the concave portions 82 and 83 will be facilitated, possibly there 2775115 after incision or initiation of cutting of one or of the two concave portions 82 and 83. The cable CAl shown in FIG. 1 has a easier drawing

  quads than that of the CA2 cable shown in Figure 2.

  However, the cable CA2 has concave portions of sheath 82 and 83 whose facing internal surfaces are more pointed towards the center of the sheath so that the concave portions 82 and 83 have internal application surfaces against the conductive wires isolated 2a, 3a, 2b and 3b larger and therefore exert an effort to separate the

two-fourths higher.

  The cables of the invention are cables which are for example substantially flat, that is to say with an oval or elliptical or oblong cross section in which two or more quarters are juxtaposed. They are used in particular as telephone and / or data processing and / or video transmission cables for building cabling. Each quadrant star la, lb comprises two pairs of insulated conductive wires, each pair comprising two insulated conductive wires arranged along a diagonal of the square section of the quadrant. However, the invention is not limited to quarter cables. For example, the two groups of insulated conductors may each include more than two pairs of insulated electrical conductors, although the groups may have different numbers of insulated conductors. According to another example, the cable comprises more than two groups of insulated conductive wires; generally, when a cable comprises N groups of insulated conducting wires, N being an integer, the cable has (N-1) throttles 84 between the groups taken successively two by two. Others say

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  variants, the cable can be a mixed cable, with at least one of the groups comprising only optical conductors, such as optical fibers, protected individually or together, and / or with one of the groups comprising both wires individually insulated electrical conductors and

  individually sheathed optical conductors.

  According to a variant, a cable of the invention comprises three or four or more quarters arranged in

star in cross section.

  With reference to FIG. 3, the two quarters 1a and 1b are for example pulled through holes in one or more guide plates from two coils of twisted quarte followed by pulling drums, or from two parallel quarrying stations to penetrate continuously along arrow T through an inlet duct 10

  an EX square head extruder.

  The EX extruder shown in FIGS. 3, 4 and 5 conventionally comprises a cylindrical punch 11 of tube type extending along the main longitudinal axis of the extrusion head, and an extrusion screw 12 disposed perpendicularly to the punch 11. The extrusion screw 12 pushes the softened thermoplastic material, such as polyethylene, into conduits 14 at the front periphery of the punch 11. At an exit end of the extruder, a die 15 of tube type has a frustoconical bore 16 of which the small base is extended by a front orifice 17. The frustoconical bore 16 and the orifice 17 surround coaxially and in a substantially complementary manner a frustoconical portion 18 and a portion of revolution 19 of the end

before the punch.

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  To manufacture the cable of the invention, the cross sections of the orifice 17 of the die and of the portion of revolution 19 at the front end of the punch can be cylindrical as shown in Figures 4 and 5. The two quarters 1a and 1b after entering the inlet conduit 10, pass through a long axial conduit 20 of the punch 11 which gradually narrows at the front end of punch 18-19. The circular sections of the front bore 17 of the die 15 and of the front end 19 of the punch 11 have internal and external diameters substantially greater than the largest internal dimensions LI and external LE (FIG. 1) of the sheath 8 to be obtained , respectively. The quarters la and lb respectively pass through holes 21 in a guide 22 fixed transversely to the outlet of the conduit so as to keep the quarters la and lb juxtaposed in an axial plane, at their final spacing in the retaining sheath 8 at the outlet of the 'extruder. More generally, when the cable to be manufactured must contain N groups of wires, the guide 22 contains N orifices 21 juxtaposed in an axial plane with the punch, two by two distant from the definitive spacing of the groups in the cable at

  N-1 level shrinkage of retaining sheath.

  The extrusion material pushed between the die and the front end 1819 of the punch 11 first continuously forms a sheath with a frustoconical profile around the assembly of the two quarters 1a and 1b. This frustoconical sheath at the exit of the EX extruder naturally tends to stick to the lateral periphery of the quartes at the level of the horseshoe portions 81a and 81b and to collapse along the axis YY to pass to a smaller diameter. at the largest external dimension LE (Figure 1) but greater than

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  the thickness E of the sheath 8 to be obtained, as the extruded sheath cools down towards a cooling tank at the outlet of the EX extruder. According to the invention, the narrowing 84 is created by a depression DE inside the sheath 8 leaving the die 15 and mainly in the center of the latter between the two quarters 1a and 1b. DE depression is generated by the suction of a vacuum pump connected to a vacuum tube 23 opening into the inlet conduit 10 of the extrusion head, in front of a sealing ring 24 crossed by the quarter la and lb from coils or manufacturing stations. By adjusting the suction pressure of the vacuum pump, the vacuum DE is more or less high in the longitudinal duct 20 of the punch and particularly at the front end 19 of the punch where the two quarters la and lb come out. . This front end of the punch protrudes a few millimeters from the front face of the die so that the hot thermoplastic material does not come into immediate contact with the quads and begins to collapse naturally around all of the

fourths.

  The lower the DE depression, the less the sheath 8 is deformed. For example a DE depression of a few thousand pascals stretches towards the center of the sheath, central portions, substantially circular convex so that they are gradually deformed into concave portions 82 and 83 of a cable as shown in FIG. 1; a depression of the order of 10,000 pascals more consistently stretches the concave portions 82 and

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  83 so as to obtain a retaining sheath as

shown in figure 2.

  According to another embodiment shown in Figure 6, the tooling at the outlet of the extruder is somewhat modified. The cross sections of the duct at the front of the punch and of the front portion of revolution 170 of the die have oblong or elliptical profiles substantially larger than the oblong profile PO of the retaining sheath 8 to be obtained, without the concave portions 82 and 84, like

shown in figure 1.

  The DE depression necessary for the deformation by stretching of the concave portions 82 and 83 to bring them together according to this other embodiment is less

  higher than with the tools shown in Figure 5.

  As a variant, a longitudinal thin thermoplastic separating strip 24, as shown in dotted lines in FIG. 2, is interposed between the quarters 1a and 1b perpendicular to the concave portions of the holding sheath 82 and 83. The height of the strip 24 is at least equal to the width LR of the constriction 84, but has a thickness less than the distance between the two quarters. During the manufacture of the cable according to this variant, the thin strip 24 forming a partition between the two quarters 1a and 1b is drawn continuously between them and passes through a rectangular orifice 25 formed between the circular orifices 21 in the guide 22, as shown in Figure 6. At the exit of the EX extruder, the separation strip 24 is held between the two quarters 1a and 1b by pinching and adhesion exerted by the concave portions of retaining sheath 82 and 83. The strip can be flat or cylindrical, or having a profile suitable for the space between the quarters la and lb. The cable of the invention in practice contains the following elements, as shown in FIG. 7: - a tearing line 26a or 26b for the two quarters, or two tearing lines 26a and 26b respectively for the two quarters 1a and 1b; a tearing line 26a, 26b preferably being situated between the bottom of the respective convex lateral portion 81a, 81b of the retaining sheath 8 and the respective fourth la, lb in order to draw the quarters - a shielding screen 27 having at least a metallized face and surrounding the retaining sheath 8, for example by taping; - one or two electrical continuity wires 28 and 29 placed in small longitudinal volumes between the shielding screen 27 and the concave portions of retaining sheath 82 and 83, which gives a regular oblong profile to the screen and consequently cable; a tear line can be placed with each electrical continuity wire 28, 29 in said respective small longitudinal volume; and - an outer protective sheath 30 surrounding the metal screen 27, made of insulating material

  such as PVC, or in halogen-free flame retardant material.

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Claims (8)

  1 - High frequency transmission cable comprising two groups (la, lb) of individually insulated electrical conductor wires (2a-5a, 2b-5b) and a retaining sheath (8) surrounding the two groups together and now separating them longitudinally, characterized by a narrowing (84) which extends longitudinally between the two groups of conductors (la, lb) and between two concave longitudinal portions (82, 83) of the retaining sheath (8) and which has a width (LR) included between a diameter (D) and two diameters (2D) of the wires   insulated electrical conductors (2a-5a, 2b-5b).   2 - Cable according to claim 1, wherein each cross section of each concave longitudinal portion (82, 83) of the retaining sheath (8) is applied against one (2a, 3a) of the electrically conductive wires insulated in the '' one (the) of the groups and one (2b, 3b) of the insulated electrical conductors in the other group (lb) located   on either side of the narrowing (84).   3 - Cable according to claim 1 or 2, comprising a longitudinal strip (24) of insulating material housed in the narrowing (83) between the groups of insulated electrical conductors (la, lb) and pinched between the longitudinal portions   concaves (82, 83) of the retaining sheath (8).   4 - Cable conforming to any of   Claims 1 to 3, comprising a rope of   tearing (26a; 26b) extending between one of the convex lateral portions (81a, 81b) of the sheath 18 2775115   holding (8) and the respective group (la, lb) of wires insulated electrical conductors.   - Cable conforms to any of   Claims 1 to 4, comprising at least one screen   partially metallic (27) surrounding the retaining sheath (8) and an electrical continuity wire (28) and / or a tearing cord (26a; 26b) extending between the two concave longitudinal portions (82,   83) of the retaining sheath (8) and the screen (27).   6 - Cable conforming to any of   claims 1 to 5, wherein each group of   insulated electrical conductors is a fourth star (la, lb). 7 Cable according to any of   claims 1 to 6, comprising more than two groups   insulated electrical conductor wires (la, lb) juxtaposed substantially flat in the retaining sheath (8) and separated in pairs by constrictions (84) each delimited by two respective concave longitudinal portions (82, 83) of the retaining sheath (8).   8 - Process for manufacturing the high frequency transmission cable according to one   any of claims 1 to 7, by means of a   extruder (EX) comprising an inlet conduit (10) extended coaxially by a conduit (20) of a tubular punch (11) having a tapered front end (18-19) and surrounded by a die (15), characterized by a guide (21, 22) of the groups of insulated electrical conductor wires (la, lb) in the front end of the conduit (20) of the punch (11) 19 2775115   to keep them juxtaposed in an axial plane with a predetermined spacing corresponding to the narrowing (84) in the retaining sheath (8), by a suction created by an extraction pumping means (23) communicating with the inlet conduit ( 10) to generate a vacuum in the extruded holding sheath (8) leaving the die (15) in front of the tapered front end (18-19) of the punch, and by adjusting the extraction pumping means (23) so that the depression (DE) deforms longitudinal portions of the retaining sheath (8) between the groups of insulated electrical conductor wires (la, lb) and attracts them towards each other at a distance equal to the width ( LR) of the narrowing (84) to form the portions longitudinal concaves (82, 83).   9 - Process according to claim 8, according to which the pumping extraction means (23) is adjusted to a suction pressure between 102 and about 105 pascals.   - Method according to claim 8 or 9, wherein the cross sections at the front ends of conduits (200, 170) of the punch (11) and of the die (15) have similar and substantially larger oblong or elliptical profiles   as the contour of the retaining sheath (8).   11 - Process according to any one of   Claims 8 to 10, comprising a guide (25)   a longitudinal strip (24) of insulating material between the groups of insulated electrical conductor wires (la, lb) in the conduit (20) of the punch (11) and a pinching of the strip (25) by the portions 2 0 2775115   longitudinal concaves (82, 83) of the retaining sheath (8) attracted towards each other by the depression.