GB2232423A

GB2232423A - Making moisture-impermeable electric cable

Info

Publication number: GB2232423A
Application number: GB9001520A
Authority: GB
Inventors: Josef Brunner
Original assignee: Phillips Cables Ltd
Current assignee: Phillips Cables Ltd
Priority date: 1989-01-23
Filing date: 1990-01-23
Publication date: 1990-12-12
Anticipated expiration: 2010-01-23
Also published as: GB8901378D0; CA2008229A1; GB9001520D0; GB2232423B

Abstract

To make moisture-impermeable, multi-wire electric cable, a viscous, semi-conductive, moisture-impermeable compound is applied to an advancing cable core to coat the core with uniform thickness. Wires are helically wound on the advancing coated core. The thickness of the coating is such that each of the interstices in the winding is filled with compound. The core runs from inlet 5 through compound in chamber 2 to carbide die 7. Piston 3 pressurises the compound. Sensor 8 senses the piston position and controls a pump to refill chamber 2. Heater 10 heats the compound. The core may pass through successive coaters, one for each wound layer. <IMAGE>

Description

Moisture-Impermeable Stranded Electric Conductor This invention relates to electric cables of the kind having one or more than one electric conductor comprising a plurality of wires or other flexible elongate elements of metal or metal alloy stranded or otherwise assembled together, the or each conductor being surrounded by at least one extruded layer of plastics material. For convenience, all such flexible elements of metal or metal alloy hereinafter will be included in the generic term "wires".The plastics material of the extruded layer immediately adjacent the outermost layer of wires of the or each conductor substantially fills interstices between the wires of the outermost layer of wires and is usually, but not necessarily, semi-conductive because it is the normal practice for the extruded layer of plastics material immediately adjacent the conductor to constitute a conductor screen.

With a view to substantially reducing risk of moisture penetration along interstices within a conductor consisting of a plurality of wires stranded or otherwise assembled together, it is common practice for the interstices wholly bounded by the wires of the conductor to be substantially filled with a semi-conductive moisture-impermeable compound throughout substantially the whole length of the conductor.

It is an object of the present invention to provide an improved method of manufacturing a substantially moisture-impermeable multi-wire electric conductor by means of which the conductor can be manufactured and rendered substantially moisture-impermeable in a single operation.

According to the invention, the improved method comprises causing a flexible elongate core of metal or metal alloy to travel continuously in the direction of its length; applying viscous semi-conductive moisture-impermeable compound to the advancing core to form around the core a longitudinally and circumferentially continuous coating of the compound of a predetermined substantially uniform overall diameter throughout the length of the core; and helically applying a plurality of wires to the advancing coated core to form a layer of helically extending wires around the core, the radial thickness and overall diameter of the coating of viscous semi-conductive moisture-impermeable compound having regard to the number and cross-sectional areas of the interstices bounded by the advancing core and wires of said layer being such that each of said interstices is substantially filled with viscous semi-conductive moisture-impermeable compound throughout the length of the conductor.

Preferably, the coating of viscous semi-conductive moisture-impermeable compound of predetermined substantially uniform overall diameter is formed around the advancing core by causing the core to travel into a chamber substantially filled with viscous semi-conductive moisture-impermeable compound maintained at a substantially constant pressure and temperature and out of the chamber through a die.In order to maintain the viscous, semi-conductive moisture-impermeable compound in the chamber at a substantially constant pressure, the volume of the chamber is automatically gradually reduced as the quantity of compound in the chamber falls; when the volume of the chamber has been reduced to a predetermined value, viscous semi-conductive moisture-impermeable compound is automatically introduced into the chamber and the volume of the chamber is automatically gradually increased to accommodate the additional compound; and, when the value of the chamber has been increased to a predetermined value, introduction of additional compound into the chamber is automatically stopped and this sequence of automatic operations is repeated as required.

The chamber which is substantially filled with viscous semi-conductive moisture-impermeable compound and whose volume is automatically gradually decreased or increased as required preferably is constituted by the bore of a cylinder in which works a pneumatically or hydraulically operated piston, operation of the piston being controlled by means which automatically senses the position of the piston within the cylinder, and hence automatically senses the volume of the chamber, and which also automatically activates and de-activates a pump for introducing viscous semi-conductive water-impermeable compound into the chamber.

The semi-conductive moisture-impermeable compound periodically introduced into the chamber is supplied from a source at which it is maintained at a temperature sufficient to ensure that the compound is of the desired viscosity. The compound within the chamber through which the flexible core continuously travels is maintained at a substantially constant temperature sufficient to ensure that the compound is of the desired viscosity by means of heating means which is associated with the chamber and which can be automatically controlled to maintain the compound in the chamber at the desired substantially constant temperature.

The die through which the advancing core emerges from the chamber preferably is constituted by a carbide wire drawing die.

Where the conductor is a stranded conductor consisting of seven wires, the flexible core will be constituted by a single wire around which the six other wires of the conductor will be helically applied after the longitudinally and circumferentially continuous coating of viscous semi-conductive moisture-impermeable compound has been applied to the single wire.

Where the conductor is a stranded conductor consisting of nineteen wires, filling of the interstices within and wholly bounded by wires of the stranded conductor preferably is effected in two operations carried out in tandem, in the first of which a stranded conductor of seven wires with the interstices within the conductor substantially filled with viscous semi-conductive moisture-impermeable compound is formed as hereinbefore described and, in the second of which, the flexible core will be constituted by the stranded conductor of seven wires around which the twelve other .wires of the conductor will be helically applied after the longitudinally and circumferentially continuous coating of viscous semi-conductive moisture-impermeable compound has been applied to the seven-wire conductor.

Expressing the preferred method described in the preceding paragraph in more general terms, where a stranded conductor consists of a multiplicity of wires in n layers, the wires of the innermost layer being helically applied around a single wire and the wires of each succeeding layer being helically applied around the preceding layer, filling of the interstices within and wholly bounded by wires of the stranded conductor preferably is effected in n operations carried out in tandem.

The invention also includes apparatus for use in the manufacture of a substantially moisture-impermeable multi-wire electric conductor as hereinbefore described.

The invention further includes a moisture-impermeable multi-wire electric conductor manufactured by the improved method hereinbefore described.

The invention is further illustrated by a description, by way of example, of the preferred method of manufacturing a substantially moisture-impermeable multi-wire electric conductor comprising a single central wire and six wires helically applied around the central wire with reference to the accompanying diagrammatic drawing which shows a side view, partly in section and partly in elevation, of preferred apparatus for applying a longitudinally and circumferentially continuous coating of viscous semi-conductive moisture-impermeable compound to the central wire.

Referring to the drawing, the preferred apparatus for applying a longitudinally and circumferentially continuous coating of viscous semi-conductive moisture-impermeable compound to the central wire of the multi-wire conductor comprises a cylinder 1 having a bore 2 in which works a pneumatically operated piston 3 having an associated pneumatic compression cylinder 4.

The bore 2 of the cylinder 1 constitutes a chamber to be filled with viscous semi-conductive moisture-impermeable compound which will be maintained at a constant pressure and temperature and through which the central wire (not shown) of the multi-wire conductor will be caused to travel via an inlet 5 and an outlet 6. A carbide wire drawing die 7 is disposed immediately adjacent the outlet 6, the internal diameter of the die being such that the coating of viscous semi-conductive moisture-impermeable compound on the central wire emerging from the chamber 2 will be of the desired overall diameter and hence radial thickness.

Operation of the piston 3 is controlled by a sensor 8 which automatically senses the position of the piston within the cylinder 1, and hence automatically senses the volume of the chamber 2, and which automatically activates and de-activates a pump (not shown) for introducing through an inlet port 9 into the chamber viscous semi-conductive water-impermeable compound from a source (not shown) at which it is maintained at a temperature sufficient to ensure that the compound is of the desired viscosity. Compound within the chamber 2 can be continuously maintained at a constant temperature sufficient to ensure that it is of the desired viscosity by means of an electric heater 10.

Excess viscous semi-conductive moisture-impermeable compound flowing from the drawing die 7 can be collected in a reservoir (not shown) positioned beneath the die, where the excess compound can be pumped back into the source of compound.

In use, the central wire of the multi-wire conductor to be formed is caused to travel in the direction of its length through the chamber 2 via the inlet 5 and outlet 6, the chamber being filled with viscous semi-conductive moisture-impermeable compound so that, on emerging from the drawing die 7, the wire has a longitudinally and circumferentially continuous coating of the compound of a predetermined uniform overall diameter, and hence radial thickness, throughout the length of the wire. As the quantity of compound in the chamber 2 falls the piston 3 continuously working in the cylinder 1 automatically gradually reduces the volume of the chamber so that the pressure of the viscous semi-conductive moisture-impermeable compound in the chamber is maintained constant.When the volume of the chamber 2 has been reduced to a predetermined value, the position of the piston 3 is sensed by the sensor 8 which automatically activates a pump to introduce viscous semi-conductive moisture-impermeable compound via the inlet port 9 into the chamber 2 from the source of compound (not shown). When the volume of the chamber, which is now automatically gradually increasing to accommodate the additional compound, has been increased to a predetermined value, the position of the piston 3 is sensed by the sensor 8 which automatically de-activates the pump to stop introduction of further compound into the chamber. This sequence of automatic operation is repeated as required during manufacture of the multi-wire conductor.

Downstream of the drawing die 7, the central wire with the coating of compound thereon passes to a standard wire stranding machine where six wires are helically applied to the advancing coated wire to form a layer of helically extending wires around the central wire. The radial thickness and overall diameter of the coating of compound on the central wire having regard to the number and cross-sectional areas of the interstices bounded by the advancing central wire and the six wires of the layer are such that each of these interstices is filled with viscous semi-conductive moisture-impermeable compound throughout the length of the conductor.

The improved method of manufacturing a substantially moisture-impermeable multi-wire electric conductor has the important advantage that the conductor can be manufactured in a single operation irrespective of the number of wires of which the conductor is built up. The improved apparatus for use in the manufacture of a substantially moisture-impermeable multi-wire electric conductor has the important advantage that it is simple and inexpensive and can be readily used in tandem with a standard wire stranding machine.

Claims

Claims:

1. A method of manufacturing a substantially moisture-impermeable multi-wire electric conductor, which method comprises causing a flexible elongate core of metal or metal alloy to travel continuously in the direction of its length; applying viscous semi-conductive moisture-impermeable compound to the advancing core to form around the core a longitudinally and circumferentially continuous coating of the compound of a predetermined substantially uniform overall diameter throughout the length of the core; and helically applying a plurality of wires to the advancing coated core to.form a layer of helically extending wires around the core, the radial thickness and overall diameter of the coating of viscous semi-conductive moisture-impermeable compound having regard to the number and cross-sectional areas of the interstices bounded by the advancing core and wires of said layer being such that each of said interstices is substantially filled with viscous semi-conductive moisture-impermeable compound throughout the length of the conductor.

2. A method as claimed in Claim 1, wherein the coating of viscous semi-conductive moisture-impermeable compound of predetermined substantially uniform overall diameter is formed around the advancing core by causing the core to travel into a chamber substantially filled with viscous semi-conductive moisture-impermeable compound maintained at a substantially constant pressure and temperature and out of the chamber through a die.

3. A method as claimed in Claim 2, wherein the volume of the chamber is automatically gradually reduced as the quantity of compound in the chamber falls; when the volume of the chamber has been reduced to a predetermined value, viscous semi-conductive moisture-impermeable compound is automatically introduced into the chamber and the volume of the chamber is automatically gradually increased to accommodate the additional compound; and, when the volume of the chamber has been increased to a predetermined value, introduction of additional compound into the chamber is automatically stopped and this sequence of automatic operations is repeated as required.

4. A method as claimed in Claim 3, wherein the chamber is constituted by the bore of a cylinder in which works a pneumatically or hydraulically operated piston, operation of the piston being controlled by means which automatically senses the position of the piston within the cylinder, and hence automatically senses the volume of the chamber, and which also automatically activates and de-activates a pump for introducing viscous semi-conductive water-impermeable compound into the chamber.

5. A method as claimed in any one of Claims 2 to 4, wherein the semi-conductive moisture-impermeable compound periodically introduced into the chamber is supplied from a source at which it is maintained at a temperature sufficient to ensure that the compound is of the desired viscosity.

6. A method as claimed in Claim 5, wherein the compound within the chamber is maintained at a substantially constant temperature sufficient to ensure that the compound is of the desired viscosity by means of heating means which is associated with the chamber and which can be automatically controlled to maintain the compound in the chamber at the desired substantially constant temperature.

7. A method as claimed in any one of the preceding Claims, wherein the die through which the advancing core emerges from the chamber is constituted by a carbide wire drawing die.

8. A method as claimed in any one of the preceding Claims, wherein the flexible core is constituted by a single wire and six wires are helically applied to the advancing wire to form a stranded conductor consisting of seven wires.

9. A method as claimed in any one of Claims 1 to 7 in which the multi-wire electric conductor is a stranded conductor consisting of a multiplicity of wires in n layers, the wires of the innermost layer being helically applied around a single wire and the wires of each succeeding layer being helically applied around the preceding layer, wherein filling of the interstices within and wholly bounded by wires of the stranded conductor is effected in n operations carried out in tandem.

10. A method of manufacturing a substantially moisture-impermeable multi-wire electric conductor substantially as hereinbefore described with reference to the accompanying drawing.

11. Apparatus for use in the manufacture of a substantially moisture-impermeable multi-wire electric conductor substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

12. A moisture-impermeable multi-wire electric conductor manufactured by the method claimed in any one of Claims 1 to 10.