GB2439756A

GB2439756A - Electrical Cable

Info

Publication number: GB2439756A
Application number: GB0613401A
Authority: GB
Inventors: Mark Billows
Original assignee: LINKRANCH Ltd
Current assignee: LINKRANCH Ltd
Priority date: 2006-07-05
Filing date: 2006-07-05
Publication date: 2008-01-09
Also published as: GB2441565A; GB0614745D0; GB0613401D0

Abstract

An electrical cable 1 has twisted pairs 3, 4, 5, 6 of conductors 3a, 3b, 4a,4b, 5a,5b,6a,6b extending along its length. The respective twisted pairs of conductors are spaced and held in a respective tube-form space provided in a cable jacket 2. The cable jacket is tubed onto the twisted pairs of conductors such that a discrete tube-form boundary wall 9 is present and an air gap 10 exists between the tube-form boundary wall and the respective twisted pair of conductors. A die (14, fig 2) and an extruder body (18, fig.2) are used to form the cable. Preferably the external profile 12 of the cable jacket is in the form of a cross shape having limbs provided with transverse 'hammer head' terminations 15. Additionally, chalk may be used as a lubricant between the boundary wall and the conductor pairs.

Description

Electrical Cable The present invention relates to electrical

cables.

The invention will be applicable to data cables, audio video power cables and other cables intended for other general or specialist applications.

Developments are being made in electrical cable technology to minimise undesired effects such as near end crosstalk' (NEXT) PSNEXT PSELFEXT return loss, insertion loss and other performance reducing effects. W02005/027148 and W02003/075287 disclose electrical cables designed to have technical features addressing these problems. Other examples of electrical cables designed to address crosstalk and other performance issues are disclosed in US 6297454 and W02001/54139. Improvements are particularly desired in relation to the ability to increase bandwidth capacity for cables.

An improved electrical cable and manufacturing technique and apparatus has now been devised.

According to a first aspect, the present invention provides a flexible cable comprising a plurality of twisted pairs of conductors extending along the length of the cable, the respective twisted pairs of conductors being spaced and held in a respective tube-form space provided in a cable jacket, the cable jacket being tubed Onto the twisted pairs of conductors such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall and the respective twisted pair.

Beneficially, the cable jacket comprises an insulator material and may be a PVC based Thermoplastic material. Thermoplastic elastomer materials have been found to be particularly

suitable.

In one embodiment, it is preferred that the respective tube form spaces for holding the twisted conductor pairs are s provided in limbs which extend outwardly from the axis of the cable jacket. Desirably, the respective tube-form spaces for holding the twisted conductor pairs are provided in head portions which project transversely outwardly with respect to I_-A'....

Desirably, the cable jacket provides a central or core portion of the cable.

It is preferred that the tube-form boundary wall is a Continuous boundary around the respective twisted pair. More preferably, tube-form boundary wall is without steps, apexes or projections interstitially of the conductors in a respective twisted pair.

A lubricant or separation layer or material is preferably provided between the tube-form boundary wall and the respective twisted pair. The lubricant or separation material may be provided in powder form. In a preferred embodiment, the lubricant or separation material comprises chalk.

It is preferred that the cable, including the cable jacket, is helically twisted along its length. Beneficially, for data cable, the lay length of the twisted cable jacket is in the range 100mm to 140mm.

In one embodiment there are four sets of twisted conductor pairs spaced about the axis of the cable.

According to a second aspect of the invention, there is provided a method of manufacturing an electrical cable comprising a plurality of twisted pairs of conductors extending along the length of the cable, the respective twisted pairs of conductors being spaced and held in a respective tube-form space provided in a cable jacket, wherein the cable jacket is tubed onto the twisted pairs of conductors such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall and the respective twisted iv Beneficially, the tube-form boundary is already formed before tubing onto the respective twisted conductor pair.

It is preferred that the solid jacket is formed upstream of a point at which the cable jacket is tubed onto the conductor pair.

Typically the cable jacket will be formed by extrusion, typically of Thermoplastics material.

In one realisation, the twisted conductor pairs pass through extrusion apparatus and the cable jacket is extruded and tubed on around the conductor pairs.

Beneficially, a lubricant or separation layer or material (such as chalk) is introduced between the tube-form boundary wall and the respective twisted pair. Following extrusion, the cable, including the cable jacket, is preferably helically twisted along its length. The cable may then be wound for storage in a Conventional manner.

According to a further aspect, the invention provides extrusion apparatus for forming a cable, the apparatus including: a die having a die aperture; an extruder body having: a plurality of guide channels for guiding the passage of respective pairs of twisted conductors and a surface for guiding flowable material which solidifies to form a jacket about the respective pairs of twisted conductors; wherein the die aperture is not substantially spaced from the end of the extruder body, such that a solid cable jacket is formed on the extruder body upstream of a point at which the cable jacket is tubed onto the conductor pairs.

In one embodiment the extruder body has a plurality of projecting pipes defining the ends of the plurality of guide channels for guiding the passage of respective pairs of twisted conductors, the extruder body and die being so spaced to ensure formation of tube-form spaces in the jacket, with the tube-form boundary walls being formed on the projecting pipes.

The present invention will now be further described by way of example only, and with reference to the accompanying drawings, in which; Figure 1 is a schematic sectional view of an electric cable in accordance with the invention; figure 2 is a schematic sectional view of extrusion die apparatus for forming the cable of the invention; Figure 3 is facing view of the extrusion die point body of the apparatus of figure 2; Figure 4 is a side view of the the point body of figure 3; Figure 5 is schematic perspective view of a part of the cable of figure 1; Figure 6 is a is a schematic sectional view of extrusion die appardLus for forming a cable outside the scope of the invention; Figure 7 is a sectional view of a prior art cable formed with the apparatus of figure 6.

Referring to the drawings and initially to figures 1 and 5 there is shown an electrical cable 1 comprising a cable jacket 2 formed about twisted pairs of conductors 3, 4, 5, 6. Each of the twisted pairs of conductors comprises two respective conductors 3a, 3b 4a, 4c etc, each sheathed in a respective Thermoplastic insulator sheath 7. The cable jacket 2 is beneficially of flexible material enabling the tube to be twisted into a lay along its length and also give flexibility to the cable as will be described in detail. A suitable material for the jacket 2 is a PVC based Thermoplastic e].astomer.

The embodiment primarily described has four sets of twisted pairs of conductors 3, 4, 5, 6 however it is important to note that the invention has applicability where other numbers of twisted pairs of conductors are present. The invention is directed to minimise crosstalk and other effects (such as other interference effects) between pairs of conductors in the same cable and also between conductors in adjacent but discrete cables, such as so called alien crosstalk'. These effects and proposed solutions are described, for example in W02005/027148 and W02003/075287. The invention is applicable to power cables, data, audio and video cables and specialist cables to provide improved performance over Cat-5 type, Cat-6 type and Cat-7 type cables.

The twisted pairs of conductors, 3, 4, 5, 6 are twisted to be intertwined along their length as is common in the prior art and also as described in W02005/027148 and W02003/075287. An important feature of the invention is that in forming the io jacket 2, a receiving tube 8 for the relevant pair of twisted Conductors is formed, in such a fashion that the twisted conductor pair (e.g. pair 3a, 3b) is not embedded within the jacket 2. Rather that a discrete non fused tube boundary 9 and air gap 10 exists between the cable jacket 2 and the respective conductor sheaths 7 of each conductor in the pair.

This technical configuration and arrangement is different to the arrangements described for example in W02005/027].48 and W02003/075287 in which the twisted conductor pairs are embedded in the jacket by pressure type plastics injection moulding to embed the conductor pairs in the jacket. In these prior art arrangements described, there is no presence of a receiving tube for the relevant pair of twisted conductors formed, in such a fashion that the twisted conductor pair is not embedded within the jacket 2.These prior art disclosures do not disclose a discrete non fused tube boundary and gap existant between the cable jacket and the respective conductors.

In accordance with the present invention the desired result (the air gap 10 and separation boundary 9) may be achieved by a plastics moulding process in which the jacket is tubed on to the respective conductor pairs. This will be described in greater detail. In addition a separator or lubricant substance or layer may be introduced at manufacturing to enhance the boundary and separation effect between the non fused tube boundary 9 and air gap 10 existing between the cable jacket 2 and the respective conductor sheaths 7 of each conductor in the pair. In a technically realisable procedure chalk powder or dust may be utilised as the separator or lubricant. The tube boundary 9 of the tube formed in the jacket is without steps, apexes or projections interstitially of the conductors in a respective twisted pair.

The technical benefits realised by a cable construction according to the present invention, in which the twisted conductor pair (e.g. pair 3a, 3b) is not embedded within the jacket 2, but rather a discrete non fused tube boundary 9 and gap 10 exists between the cable jacket 2 and the respective conductor sheaths 7 of each conductor in the pair, include enhanced performance in terms of crosstalk reduction. This is believed to be due to the insulation properties of the air gap 10. Additionally enhanced performance has been found using twisting of the cable (including the cable jacket) along its longitudinal axis into a relatively tight helical lay-form.

Cable having the separation air gap 10 (enhanced by lubrication) enables the twisting into lay-form to be consistently achieved with reduced damage to the respective twisted pairs such as kinking, buckling or stretching, all of which can adversely affect performance. This is because the twisted pairs are not fully embedded within the jacket 2.

Twisting cable having fully embedded twisted pairs such as described in W02005/027l48 and W02003/075287 will be prone to damaging effects such as kinking, buckling or stretching. The air gap 10 shown in figures 1 and 5 is pronounced, primarily for the purposes of explanation. In reality the air gap produced will more likely be of the order of 1mm or less. The tube boundary 9 is similarly shown as circular but in reality will become collapsed or flattened to an irregular ovoid form about the twisted conductors. The air gap, however small, exists because of the fact that there is a separate tube boundary 9 formed in the cable jacket 2.

Referring to figures 2 to 4, there is shown.extrusion apparatus for producing cable according to the invention having the air gap 10 and separation interface at the tube on boundary 9. The apparatus comprises an extrusion die 14 having a die aperture conforming to the external profile configuration of the cable jacket 2. In the case of the cable of figure 1, the external 0 profile 12 of the cable jacket 2 is in the form of a cross shape having limbs provided with transverse, hammer head' terminations is. In this case the die 14 aperture is correspondingly shaped in the form of a cross shape having hammer head' terminations.

An extruder point body 18 is Positioned upstream of the extrusion die 14 and has respective bores 23, 24 25 26 extending through the extruder point body 18 through which are fed respective twisted conductor pairs. In figure 2 only upper and lower bores 23 25 for twisted pairs 3 5 are shown, the twisted pairs being fed from the left hand side of the apparatus. The pairs of conductors pass out from the extruder point body 18 via respective cylindrical pipes 33,34,35,36 which have their respective downstream ends approximately co-terminal with the die aperture of the die body 14.

The molten Thermoplastic material to form the cable jacket 2 flows along a generally conical outer surface 43 of the extruder point body 18 an over and around the pipes 33, 34, 35, 36 and out through the die aperture. The flow of material has a set rate through the extruder point body 18 and die 14 and is not restricted, or choked. Because the flow rate is uniform through the die, the radial thickness of the jacket 2 can be maintained accurately via adjustments to the line feed speed.

The die aperture of the die 14 is large enough for the extruder point body 18 to be positioned within its periphery.

The solid jacket is formed on the pipes 33, 34, 35, 36 upstream of the point of insertion of the conductor pairs into the S jacket (via the ends of the pipes). In this way, the already formed jacket is tubed onto the twisted pairs of conductors ensuring that a discrete non fused tube boundary 9 and gap 10 exists between the cable jacket 2 and the respective conductor sheaths 7 of each conductor in the pair. The die 14 aperture is provided substantially level with the of the end of the extruder body 18, such that a solid cable jacket is formed on the extruder body upstream of a point at which the cable jacket is tubed onto the conductor pairs.

This is contrasted with the prior art techniques such as certain embodiments described in W02005/027].48 and W02003/075287 in which the extrusion point is behind the die aperture and the flow of material is restricted causing pressure build up and the extruded material to form about the twisted pairs themselves filling the interstices between the members of a twisted pair and fully embedding the pairs in the jacket.

Figures 6 and 7 show such a prior art technique falling outside the scope of the present invention, in which the downstream end of the extruder point body 118 is spaced upstream of the die aperture of the die 114 such that the molten Thermoplastic material of the jacket forms directly on the twisted conductor pairs 103 105 fully embedding the twisted pairs which then form an integral part of the Thermoplastic cable jacket. See figure 7 in which there is no gap equivalent to the air gap 10 shown about the twisted pairs of conductors. This latter extrusion technique is often referred to as pressure extrusion. The flow of material is restricted causing pressure to build up at the die 114. This ensures that the interstices between the conductor pair are filled with extruded material.

Particularly beneficial results have been achieved with cable in accordance with the present invention that has a longitudinal twist laid during manufacture. it has been found to be particularly technically beneficial to provide a cable having the combined technical features of a longitudinal cable lay twist and pairs of twisted conductors extending in a tube pre formed within a cable jacket so as to have discrete non-fused tube boundary 9 and gap 10 existing between the cable jacket 2 and the respective conductor sheaths 7 of each conductor in the pair. For data cables lay lengths of the order of 100mm to 140mm have been found to produce beneficial effects. Other preferred lay lengths for cables for other uses is and applications are envisaged.

The lay twist is applied following forming of the jacket 2 and positioning of the twisted conductor pairs in the respective tubes formed in the cable jacket 2, at a forming station provided downstream of the extrusion apparatus.

In tests the cable of the present invention having the separately formed tubed on cable jacket defining the air gap between the cable jacket and the twisted conductor pairs, has been found to be of improved performance in terms of reduced crosstalk effects and also bandwidth. This performance is enhanced by helically twisting the cable including the cable jacket once extruded. Additionally the use of a separator or lubricant layer or substance (such as chalk) at the interface of the tub boundary 9 and conductor pairs has been found to improve manufacturing and subsequent performance.

Claims

Claims: 1. An electrical cable comprising a plurality of twisted pairs

of conductors extending along the length of the cable, the respective twisted pairs of conductors being spaced and held in a respective tube-form space provided in a cable jacket, the cable jacket being tubed onto the twisted pairs of conductors such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall and the respective twisted pair.

2. A cable according to claim 1, wherein the cable jacket comprises an insulator material.

3. A cable according to claim 1 or claim 2, wherein the cable jacket comprises a Thermoplastics material.

4. A cable according to any preceding claim, wherein the respective tube form spaces for holding the twisted conductor pairs are provided in limbs which extend outwardly from the axis of the cable jacket.

5. A cable according to claim 4 wherein the respective tube form spaces for holding the twisted conductor pairs are provided in head portions which outwardly with respect to the limbs.

6. A cable according to any preceding claim, wherein the cable jacket provides a central or core portion of the cable.

7. A cable according to any preceding claim, wherein the tube-form boundary wall is a continuous boundary around the respective twisted pair.

8. A cable according to any preceding claim, wherein a lubricant or separation layer or material is provided between the tube-form boundary wall and the respective twisted pair.

9. A cable according to claim 8 wherein the lubricant or separation material is provided in powder form.

10. A cable according to claim 9, wherein the lubricant or separation material comprises chalk.

11. A cable according to any preceding claim, wherein the cable, including the cable jacket, is helically twisted along its length.

12. A cable according to claim 11 wherein the lay length of the twisted cable jacket is in the range 100mm to 140mm.

13. A cable according to any preceding claim wherein there are four sets of twisted conductor pairs spaced about the axis of the cable.

14. A method of manufacturing an electrical flexible cable comprising a plurality of twisted pairs of conductors extending along the length of the cable, the respective twisted pairs of conductors being spaced and held in a respective tube-form space provided in a cable jacket, wherein the cable jacket is tubed onto the twisted pairs of conductors such that a discrete tube-form boundary wall is present and an air gap exists between the tube-form boundary wall and the respective twisted pair.

15. A method according to claim 14, wherein the tube-form boundary is already formed before tubing Onto the respective twisted conductor pair.

16. A method according to claim 14 or claim 15, wherein the solid jacket is formed upstream of a point at which the cable jacket is tubed onto the conductor pair.

17. A method according to any of claims 14 to 16, in which the cable jacket is extruded.

18. A method according to claim 17 in which the twisted conductor pairs pass through extrusion apparatus and the cable jacket is extruded and tubed on around the conductor pairs.

19. A method according to any of claims 14 to 18, wherein a lubricant or separation layer or material is introduced between the tube-form boundary wall and the respective twisted pair.

20. A method according to claim 19, wherein the lubricant or separation material is chalk.

21. A method according to any of claims 14 to 20, wherein following extrusion, the cable, including the cable jacket, is helically twisted along its length.

22. Extrusion apparatus for forming a cable, the apparatus including: a die having a die aperture; an extruder body having: a plurality of guide channels for guiding the passage of respective pairs of twisted conductors and a surface for guiding flowable material which solidifies to form a jacket about the respective pairs of twisted conductors; wherein the die aperture is provided substantially level s with the of the end of the extruder body, such that a solid cable jacket is formed on the extruder body upstream of a point at which the cable jacket is tubed onto the conductor pairs.

23. Extrusion apparatus according to claim 22, wherein the extruder body has a plurality of projecting pipes defining the ends of the plurality of guide channels for guiding the passage of respective pairs of twisted conductors, the extruder body and die being so positioned to ensure formation of tube-form spaces in the jacket with the tube-form boundary walls being formed on the projecting pipes.