GB2113903A

GB2113903A - Cable manufacture

Info

Publication number: GB2113903A
Application number: GB08200849A
Authority: GB
Inventors: Lyndon Reginald Spicer
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-01-12
Filing date: 1982-01-12
Publication date: 1983-08-10
Also published as: AU9154882A; GB2113903B

Abstract

A cable comprises a central electrically insulating string (5) in whose periphery a plurality, four in the case of a quad, of electrical or optical conductors (6) are at least partially embedded. A polyethylene sheath (7) is extruded over the string (5). The quad may be made by heat softening the string (5) and pressing the conductors (6) thereinto by means of a tool (Figures 3, 4 and 5) which ensures the desired spacing and configuration of the conductors relative to one another, necessary for high quality quads of electrical conductors in order to have low crosstalk, is obtained. The cable construction is considerably simpler than previous constructions and can be manufactured with a minimum of process stages at high throughput speeds. <IMAGE>

Description

SPECIFICATION Cable manufacture This invention relates to cable manufacture and in particular but not exclusively to the manufacture of quads of electrical conductors for telecommunications cables.

High quality quads of electrical conductors, that is quads with good crosstalk levels, for example, of the order of 80 dB at 1 KHz, are conventionally manufactured by a multi-stage, and therefore expensive, process. There may be up to ten different operations required to manufacture a quad by the conventional method.

Basically the conventional method comprises manufacture of a central insulating string; manufacture of conductor wire; manufacture of four separate insulated wires from the conductor wire; rewind and water test the insulated wires for insulation defects; formation of a quad subassembly from the insulated wires by stranding them about or laying them up with the central string; and sheathing of the quad sub-assembly with extruded plastics material.

According to one aspect of the present invention there is provided a cable for telecommunications purposes comprising a central string member in whose outer periphery a plurality of spaced-apart electrical or optical conductors are at least partially embedded, the conductors being at least partially maintained in a desired configuration and at a desired spacing relative to one another by the central string, and comprising an electrically insulating sheath member extending over the string member and the conductors embedded therein.

According to another aspect of the present invention there is provided a method of manufacturing a cable for telecommunication purposes including the steps of embedding a plurality of electrical or optical conductors at least partially in the outer periphery of a central string member such that the conductors are spaced apart by the central string member, which also serves to at least partially maintain the conductors in a desired configuration relative to one another, and extruding an electrically insulating sheath member over the string member and the conductors embedded therein.

According to a further aspect of the present invention there is provided a tool for use in the manufacture of a cable of electrical or optical conductors for telecommunication purposes and by means of which a plurality of electrical or optical conductors may be embedded at least partially into the periphery of a central string member, whilst the latter is in a heat-softened state, such that the conductors are maintained at a desired spacing and in a desired configuration relative to one another, which tool comprises a body with a central longitudinal bore for receiving the central string and a plurality of guides for the conductors, which guides, one for each conductor, comprise respective cylindrical bores adjacent the inlet end of the tool, the axes of which bores extend at angle relative to the longitudinal axis of the central bore whereby the four bores converge towards a point external of the tool and at the outlet end thereof, which cylindrical bores merge with the central bore adjacent the outlet end of the tool and define conductor guide slots thereat, the central bore having a larger diameter at the outlet end of the tool than the inlet end.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a cross-section through a conventional quad construction; Fig. 2 shows a cross-section through a quad manufactured according to an embodiment of the present invention; Fig. 3 shows a longitudinal section through a tool employed in the manufacture of the quad of Fig. 2; Fig. 4 shows an inlet end view of the tool of Fig. 3, as seen looking in the direction of arrow 'A'; Fig. 5 shows an exit end view of the tool of Fig.

3, as seen looking in the direction of arrow 'B'; Fig. 6 shows, schematically, the use of the tool of Figs. 3, 4 and 5 in the manufacture of a quad with parallel conductors, and Fig. 7 shows, schematically, the use of the tool of Figs. 3, 4 and 5 in the manufacture of a quad with helically applied conductors.

In Fig. 1 a conventional quad is seen to comprise a central string or filler 1 about which are arranged four electrical conductors 2 having insulation 3. The conductors may be parallel to the length of the string 1 or arranged helically with respect thereto. A sheath or jacket 4 is extruded over the laid up or quad insulated conductors. The insulated conductors may be arranged around an initially circularly sectioned string, the string material having a lower softening point than the insulation, which subassembly is then heated to soften the string and the insulated conductors pressed together to deform the string to the shown cross-section, as disclosed in our co-pending British Application No. 8005614 (Serial No. ) (L. R.Spicer 23).

A quad in which the conductors are arranged relative to one another with the same if not greater precision in order to minimise crosstalk may, however, be produced by means of the present invention with a greatly reduced number of separate processing steps, as will be described hereinafter.

The embodiment of quad whose cross-section is shown in Fig. 2 may be produced by the tool shown in Figs. 3, 4 and 5. This quad comprises a central string or filler 5 of an electrically insulating material, for example, polyethylene in whose outer periphery four uninsulated electrical conductors 6 are embedded as a result of deformation of the string. An outer jacket or sheath 7 of, for example, polyethylene is provided over the central string 5 and conductors 6. As can be seen by comparison of Figs. 1 and 2, the conductors of both quads are arranged with the same spatial relationship therebetween, but the Fig. 2 arrangement is considerably simplified in comparison with the known Fig. 1 arrangement.

The conductors 6 may be of a solid or stranded construction, and comprise copper, aluminium or aluminium alloys, for example.

In order to manufacture high quality quads with the cross-section shown in Fig. 2, the conductor spacing and symmetry must be reliably and precisely achieved. One such tool for enabling this to be achieved is shown in Figs. 3, 4 and 5, which tool may be employed either for quads with parallel conductors or for quads with helical conductors, as will be described in more detail hereinafter. The conductors 6 are embedded in the periphery of the string 5, which is initially circular in cross-section, by forcing them thereagainst and thereinto whilst the string is softenedl by the effect of heat. The tool 8 of Figs. 3, 4 and 5 ensures that the conductors are precisely positioned with respect to one another and the central string.

The tool 8 has a central bore 9 which for the majority of its length is of a uniform circular crosssection 10. Adjacent the outlet end of the tool however the bore gradually widens (at 1 1 ) to a larger circular cross-section 12 for a certain length. The tool 8 also has four conductor guides 13. These guides converge towards a point external of the tool 8 as is apparent from Fig. 3.

For the majority.of their length the passages comprise circularly sectioned bores 14, however adjacent the outlet end of the tool they become part-circularly sectioned slots merged with the large cross-sectioned part 12 of bore 9 to form a single outlet 1 6 with the cross-section shown in Fig. 5. Thus the tool 8 has a separate inlet for each of the members defining the "inner" part of the quad, namely the central string and the conductors, but a single outlet. The tool, which should be very accurately machined, serves to reliably and precisely embed the conductor in the periphery of the string.

Two specific methods of use of the tool of Figs.

3 to 5 will now be described in greater detail. In Fig. 6 the tool 8 is used to provide a quad with parallel conductors. Central string 5 from a supply reel 1 7 is threaded through the central bore 9 of tool 8. In order to heat the string for softening purposes the string may be passed through a heater tube 18, or otherwise heated, prior to entry to the tool 8. Four conductors 6 (only two of which are shown in the drawing) from supply reels 1 9 are threaded through respective guides 1 3 of the tool 8. In order to provide additional heat for softening the string the conductors may be heated prior to entry to the tool, for example by a Bunsen flame, as indicated at 20.The conductors 6 together with string 5 are hauled through the tool 8 and a subsequently arranged plastics sheath extruder 21 by means, for example, of a drivertake-up bobbin 22. Due to the softening of the string by means of heater tube 18, with or without supply of heat from the conductors themselves, the conductors become at least partially embedded in the periphery of the string during passage through the tool 8. The subsequently extruded sheath 7 provided by extruder 21 maintains the conductors in position.

The sheath 7 may or may not become bonded to the remaining periphery of the string, in dependence of the materials and temperatures employed.

In Fig. 7 the tool 8 is used to provide a quad with helically laid conductors. In this application the tool 8 is mounted for rotation about its longitudinal axis, that is the longitudinal axis of bore 9, and act both as a die and a rotating lay plate. In a conventional wire strander 23 are arranged with provision for rotating a supply reel 24 of central string 5 and four supply reels 25 for the conductors 6. The conductors 6 and string 5 are threaded through the tool 8, being pulled therethrough during quad manufacture by a capstan or take-up bobbin. Sheath 7 may be extruded onto the quad sub-assembly directly after the tool 8 are described with reference to Fig. 6.The heat required to soften the string may be supplied by passing the elements (5 and 6) emerging from the wire strander 23 through a heated zone prior to passage through the tool, as indicated schematically by arrows 'H', with or without direct flame heating as indicated at 26.

As a result of passage through the rotating tool 8 the conductors are helically embedded in the periphery of the string. Helical embedding may alternatively be achieved with a stationary die 8 by, for example, also rotating the take-up reel 22 about an axis perpendicular to its axis of rotation for take-up purposes.

Thus manufacturing quad as shown in Fig. 2 requires basically only three steps, that is manufacture of the central string, manufacture of the conductors if appropriate, for example by stranding, and a process in which the conductors are embedded in the string and then sheathed, although sheath extrusion may be performed as a separate operation if required. The tool such as 8 employed to embed the conductors in the string is critical in as much as it must ensure that the four conductors are held in almost perfect symmetry with respect to one another to give good crosstalk levels. The speed of production of quaded conductors using such a cross-section and tool is very fast in comparison with conventional quading methods and much simpler with resultant cost savings, particularly in plant and energy requirements.

Whereas the invention has so far been described with reference to cables having quads of electrical conductors, it is equally applicable to the manufacture of cables having other conductors, for example, eight conductors, with suitable modification of the tool 8 in order to provide eight guides 13 etc. In this case crosstalk considerations may not apply. Cables can thus be provided with any number of conductors maintained in a desired configuration and at a desired spacing with respect to one another by a manufacturing process involving a minimum number of operations. The invention is not restricted solely to cables with electrical conductors 6 since it can equally well be applied to cables incorporating optical fibres (optical conductors) instead of electrical conductors 6.

The fibres may be primary coated or secondary coated fibres, the latter being presently preferred.

In the case of optical fibres the string would be preheated to approximately 850C by a hot air tube. For optical fibres the lay angle for helically embedded fibres would be of the order of 5 , whereas for electrical conductors the lay angle would be of the order of 17 to 25 degrees.

The central string 5 can, for example, comprise low density, for example grade 70, polyethylene, or grade 70 polyethylene extruded around a central strength member filament, such as nylon or Kevlar, in order to ensure the diameter of string 5 remains constant even under the tensions the string will experience during cable manufacture.

Such a strength member is particularly necessary for optical fibre cables. The sheath 7 may be extruded from high density polyethylene in which case it would bond easily to a string 5 of grade 70 polyethylene. Such a high density polyethylene outer sheath would provide electrical insulation, mechanical protection and moisture protection.

However, other sheath materials may be employed and it is not necessary that string and sheath bonding occurs. The conductors need only be partially embedded in the string material since they are protected by the outer sheath material.

Claims

1. A cable for telecommunications purposes comprising a central string member in whose outer periphery a plurality of spaced-apart electrical or optical conductors are at least partially embedded, the conductors being at least partially maintained in a desired configuration and at a desired spacing relative to one another by the central string, and comprising an electrically insulating sheath member extending over the string member and the conductors embedded therein.

2. A cable as claimed in claim 1, wherein the string member is of polyethylene.

3. A cable as claimed in claim 1 or claim 2 wherein the conductors are electrical, uninsulated and of copper, aluminium or aluminium alloys.

4. A cable as claimed in claim 1 or claim 2, wherein the conductors are secondary coated optical fibres.

5. A cable as claimed in any one of the preceding claims, wherein the sheath is of polyethylene.

6. A cable as claimed in any of the preceding claims, wherein the embedded conductors extend in parallel with the longitudinal axis of the central string.

7. A cable as claimed in any one of claims 1 to 5, wherein the embedded conductors extend helically with respect to the longitudinal axis of the central string.

8. A cable as claimed in any one of claims 1 to 7, wherein there are four or eight conductors.

9. A method of manufacturing a cable for telecommunications purposes including the steps of embedding a plurality of electrical or optical conductors at least partially in the softened outer periphery of a central thermoplastic string member such that the conductors have a predetermined lay and are spaced apart by the central string member, which also serves to at least partially maintain the conductors in a desired configuration relative to one another, and extruding an electrically-insulating sheath member over the string member and the conductors embedded therein.

10. A method as claimed in claim 9, wherein the string member is of a heat softenable material and wherein the conductors are pressed thereagainst and at least partially thereinto whilst the string member is in a heat softened state.

11. A method as claimed in claim 10, wherein the embedded conductors extend in parallel with the longitudinal axis of the central string.

12. A method as claimed in claim 10, wherein the embedded conductors extend helically with respect to the longitudinal axis of the central string.

13. A method as claimed in any one of claims 9 to 11 including the step of pulling the central string and the conductors through a bored tool, which tool serves to progressively guide the conductors towards the head softened string, whilst maintaining them in a desired configuration relative to one another, and progressively embed them at least partially into the periphery of the string member whilst still maintaining the desired relative configurätion.

14. A method as claimed in claim 13 as appendant to claim 12, wherein the tool is rotated about the longitudinal axis of the central string during passage of the string and conductors therethrough.

15. A method as claimed in claim 13 or 14, including heat softening the string by passing it through a heater tube prior to entry to the tool.

1 6. A method as claimed in claim 13 or 14, wherein the conductors are electrical and are heated prior to entry to the tool whereby to facilitate embedding in the string.

1 7. A tool for use in the manufacture of a cable of electrical or optical conductors for tele communications purposes and by means of which a plurality of electrical or optical conductors may be embedded at least partially into the periphery of a central string member, whilst the latter is in a heat-softened state, such that the conductors are maintained at a desired spacing and in a desired configuration relative to one another, which tool comprises a body with a central longitudinal bore for receiving the central string and a plurality of guides for the conductors, which guides, one for each conductor, comprise respective cylindrical bores adjacent the inlet end of the tool, the axes of which bores extend at an angle relative to the longitudinal axis of the central bore whereby the bores converge towards a point external of the tool and at the outlet end thereof, which cylindrical bores merge with the central bore adjacent the outlet end of the tool and define conductor guide slots thereat, the central bore having a larger diameter at the outlet end of the tool than the inlet end.

18. A cable of electrical or optical conductors for telecommunications purposes substantially as herein described with reference to Fig. 2 of the accompanying drawings.

1 9. A method of manufacturing a cable of electrical or optical conductors for telecommunications purposes substantially as herein described with reference to Figs. 2 to 5 in conjunction with Fig. 5 or Fig. 7 of the accompanying drawings.

20. A tool for use in manufacturing a cable of electrical or optical conductors for telecommunications purposes, substantially as herein described with reference to and as illustrated in Figs. 3, 4 and 5 of the accompanying drawings.