NZ196207A

NZ196207A - Method of making a cable and resultant cable interstice between stranded conductors filled with hardened plastics material

Info

Publication number: NZ196207A
Application number: NZ19620781A
Authority: NZ
Inventors: L R Spicer
Original assignee: Int Standard Electric Corp
Priority date: 1980-02-19
Filing date: 1981-02-09
Publication date: 1984-10-19
Also published as: GB2069746A; AU543160B2; AU6732181A; GB2069746B

Description

1 96 2 0 7 Priority Datc(s): . "pT.?P. .... CosrspSete GpscS' St Class: t+Pi$7l P&, . ^'icatic-n Date: ....

P.O. Journal Ko: !0k3 ORIGINAL NEW ZEALAND THE PATENTS ACT, 1953 COMPLETE SPECIFICATION "COMMUNICATIONS CABLE" i*-Cl WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement I 9 6 0 7 This invention relates to communications cables, particularly, but not exclusively, electric communication cables.

It is known to provide a quad cable, that is to say a cable with four mutually insulated electrical conductors, by twisting four individually insulated conductors together. For general purposes such a cable is satisfactory in respect of crosstalk between the conductors but for some purposes it is desirable to reduce or minimise such crosstalk and it is one object of the present invention to provide a cable element construction which facilitates a reduction in crosstalk for electric cables although the invention is not limited to electric conductors.

According to the present invention there is provided a method of making a cable element, comprising the steps of providing a longitudinal member having an outer coating of a first plastics material, rendering said coating plastically deformable by heating, stranding at least three insulated conductors about the deformable outer coating, said insulated conductors being insulated by a second plastics material which is not rendered deformable by said heating, passing the longitudinal member together with the stranded said conductors through a die means arranged to cause the insulated conductors to deform the deformable outer coating to the interstice shape of the said conductors and fill the interstice therewith, the deformed outer coating 196207 holding said conductors in a desired juxtaposition relative to their physical and electrical spacing upon cooling.

Several such cable elements can be laid up to form a multi-element cable.

Preferably each element has a central strength member embedded in the longitudinal member.

In order that the invention can be more clearly understood reference will now be made to the accompanying drawings, in which:- Fig. 1 is a conventional cable stranding machine modified to incorporate a heating arrangement according to an embodiment of the invention.

Fig. 2 shows a cable element according to an embodiment of the invention laid up but prior to passing through the heating arrangement of Fig. 1 and Fig. 3 shows the cable element of Fig. 2 after it has passed from the heating arrangement of Fig. 1.

Referring to Fig. 1 the apparatus is shown in schematic form only and comprises a rotating bobbin support 1 carrying four bobbins such as 2 of plastics insulated conductors 3. A non-rotating bobbin 4 provides a longitudinal member in the form of a "string" 5 which lies in the centre of the wires 3 and acts as the strength member of the finished cable element 12 and includes plastics material which is heat softenable. The element is shown in radial cross section in ] o c ? r. 7 ! / <J L- Kj I Fig. 3.

Each wire 3 comprises a stranded compacted copper conductor 6 insulated with high density polythene 7. The "string" 5 comprises a monofilament strength member 8 of steel or 5 nylon over which has been extruded a sheath 9 of low molecu lar weight polythene having a lower melt temperature, i.e. it becomes soft and deformable at a lower temperature than the polythene 7.

The wires 3 and string 5 are drawn by a take-up capstan 10 10 a heater tube T and through a die 11 (Fig. 1). The low density polythene 9 is softened by hot air which is blown through tube T by a hot air blower B and is deformed at the die forming point so as to just completely fill the star-shaped interstice between the wires 3. The hot air is effec-15 tive to soften the low density polythene so that it becomes deformed at the die forming point, but the heat does not soften the high density polythene 7 which insulates the wires 6, at least not to such an extent that the high density would be deformed. There are various grades of polythene 20 which have different melt temperatures, the choice depends on the physical properties of the dielectric or insulant which is used on the copper conductors. As a general guide a 10°C difference in temperature between the melt temperatures (as hereinbefore defined) of insulating conductors 3 and the 25 string 5 is a minimum which should be maintained. The greater this difference the 196207 more reliable the process. The softened and plastically deformed low density polythene 9 is effective to hold the wires 3 in position in the element, the spiral grooves formed in the string keeping the insulated wires in correct juxtaposition relative to their physical and electrical spacing.

Using this technique with electric conductors, it has been found possible to improve crosstalk levels within a quad by 10 to 20 db both when a multiquad electric cable is used in static or dynamic modes.

The element can be sheathed if required.

Several such elements can be subsequently laid up to form a multiquad cable and held together by an outer extruder plastics sheath.

The electric cable element described has a specific application where high tensile strength, provided mainly by the monofilament 8, and low crosstalk levels are required, such as for telemetering.

It is not essential to have four insulated conductors; there could be three or more. One or more of the conductors could be coated optical conductors, or they could all be optical conductors, in which case there would be no crosstalk problem although one of the problems with fibre optic cables, working 196 2 0 in the dynamic and hydrostatic modes, is the formation of microbends initiated by differential pressure points within a fibre optic cable. The embodiment described when the insulated wires 3 are replaced with optical fibres, would lead to an improvement in this respect owing to the support given by the deformed low-density polythene to the optical fibres, minimising the likelyhood of microbends. Once again the choice of coating and the plastics 9 depends on the softening point and a 10°C difference should be the minimum.

Claims

: ^ f- 0 ~ t y O <L vJ 1 What we claim is:-

1. A.method of making a cable element, comprising the steps of providing a longitudinal member having an outer coating of a first plastics material, rendering said coating plastically deformable by heating, stranding at least three insulated conductors about the deformable outer coating, said insulated conductors being insulated by a second plastics material which is not rendered deformable by said heating, passing the longitudinal member together with the stranded said conductors through a die means arranged to cause the insulated conductors to deform the deformable outer coating to the interstice shape of the said conductors and fill the interstice therewith, the deformed outer coating holding said conductors in a desired juxtaposition relative to their physical and electrical spacing upon cooling.

2. A method as claimed in claim 1, wherein the longitudinal member comprises a tensile strength member coated with said first plastics material.

3. A method as claimed in claim 2, wherein said tensile strength member is a filament of steel or nylon.

4. A method as claimed in any one of claims 1-3, wherein said first plastics material is a low density polythene and said second plastics material is a relatively high density polythene. - 7 - : r -v -7 i ✓ C C. ^ !

5. A method as claimed in any one of the preceding claims, wherein the difference in temperature at which said first and said second plastics material are rendered deformable is at least 10°C.

6. A method as claimed in any one of the preceding claims, wherein said conductors are electrical conductors.

7. A method as claimed in claim 6, wherein four said insulated conductors are stranded about the longitudinal member and held in a quad formation.

8. A method as claimed in any one of the preceding claims, wherein the conductors are stranded about the longitudinal member in a helical manner.

9. A method as claimed in any one of claims 1-5, wherein said conductors are optical waveguides.

10. A method as claimed in any one of claims 1-5, wherein said conductors comprise a combination of one or more electrical conductors and one or more optical waveguides.

11. A method as claimed in any one of the preceding claims, wherein said outer coating of first plastics material is rendered deformable by passing the longitudinal member through a chamber into which hot gas is blown.

12. A method of making a cable element, substantially as herein described with reference to Figs. 1-3 of the accompanying drawings.

13. A cable element manufactured by the method as claimed in any one of the preceding claims. - 8 - 6 i 96207

14. A multi-element cable arrangement comprising a plurality of cable elements as claimed in claim 13, stranded together and arranged within an outer protective sheath member. INTERNATIONAL STANDARD ELECTRIC CORPORATION i P.M. Conrick Authorized Agent 5/1/1223 - 9 - r r' /• .