GB2085324A

GB2085324A - Filling electric cables

Info

Publication number: GB2085324A
Application number: GB8033404A
Authority: GB
Original assignee: Pirelli General Cable Works Ltd; Pirelli General Cable Works
Current assignee: Pirelli General Cable Works Ltd; Pirelli General Cable Works
Priority date: 1980-10-16
Filing date: 1980-10-16
Publication date: 1982-04-28
Also published as: GB2085324B

Abstract

Telecommunication cables are fully filled with a water impervious medium by passage through first and second elongate tubes (1,2). Filling medium heated to liquid state is fed into the first tube (1) through line (5) and inlet (6), and filling medium in liquid or semi-liquid/semi-solid or solid state may be fed into the second tube (2). <IMAGE>

Description

SPECIFICATION Fully filled electric cables This invention relates to the manufacture of electric cables, particularly telecommunication cables, of the type which comprise a plurality of insulated conductors enclosed within a sheath with the interstices between adjacent conductors and between the conductors and sheath filled with a water impervious medium such as petroleum jelly. Cables of such type are known as fully filled electric cables.

The water impervious medium is primarily intended to prevent water seeping along the cable within the sheath should the sheath ever be ruptured. The filling medium is such that it will not drain from the cable in the event of sheath rupture, but it will allow the necessary relative sliding movement of the conductors during such bending of the cable as occurs during its manufacture and installation.

Petroleum jelly is a preferred filling medium and such filling mediums upon cooling do not solidify at a distinct temperature but pass from liquid to solid states over a range of temperatures.

The effectiveness of filling telecommunication cables is related to the size of the interstices between adjacent conductors and the pressure differential between the interior and exterior of the cable (which factors depend upon the design of cable) and the viscosity of the filling material.

Known methods of filling a cable comprise passing the cable conductors, laid-up together, longitudinally of themselves through a tube to which the filling medium in liquid state is fed under pressure.

The enclosing sheath is applied subsequently. Different particular designs of cable and different particular filling media tend to require different filling procedures and criteria in carrying out this method.

In some cases the method can give rise to imperfect filling, owing to some of the liquid medium subsequently dripping from the cable conductors, shrinkage of the medium as it cools, and incomplete initial deposit of material within the interstices.

In accordance with this invention, there is provided an apparatusforfullyfilling an electric cable with a water impervious medium, comprising a first elongate tube for a plurality of insulated conductors, laid-up together, to pass through longitudinally of themselves, means for heating water impervious filling medium to liquid state and feeding it into said first elongate tube, a second elongate tube for said conductors to pass through after passing through said first elongate tube, and means operable to feed water impervious filling medium in liquid semiliquid/semi-solid or solid state to said second elongate tube.

This apparatus may be operated with one or other or both of the two elongate applicator tubes in use.

For example, especially for a large diameter cable with small diameter conductors so that the interstices are small and difficult to fill, the first elongate tube may effect an initial filling with liquid filling medium (under pressure) and then the second elongate tube subjects the liquid-filled cable to semi-liquid/semi-solid or solid medium under pressure. With the second tube sufficiently long and close-fitting about the laid-up conductors, sufficient pressure is built up within the second tube for the filling medium fed thereto to penetrate considerably into the cable in the radial direction, to the extent of refilling to a considerable depth with the cooler medium. The previous liquid filling may be forced further towards the centre of the cable to fill interstices to which liquid filling medium may have failed to penatrate in the first applicator tube.Also, because a considerable proportion of the cable diameter will now be filled with the cooler filling medium, there will be less subsequent shrinkage of the filling medium. Moreover, the cable issues from the second applicator tube with filling medium in viscous condition filling not only the peripheral interstices but also several layers at least of interstices radially inwards of the peripheral ones, so that there is no risk of medium dripping from the cable.

For a cable of small diameter and large interstices, for example, satisfactory filling may be achieved using only the second applicator tube, fed with semi-liquid/semi-solid medium. The laid-up conductors then pass through the first applicator tube on their way to the second, but no feed of medium is made to the first tube.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawing, which is a diagram of an apparatus for fully filling a telecommunication cable with electricaliy insulating, water impervious filling medium such as petroleum jelly.

The apparatus comprises first and second elongate applicator tubes 1,2 disposed one after the other on a straight line path for a plurality of insulated conductors, laid-up together, to pass through the first tube and then through the second tube. An extrusion head for applying an enclosing sheath to the fully filled conductors may be disposed downstream of the second tube 2. Both tubes are a close fit about the laid-up plurality of conductors, such that only a small clearance exists around these conductors, and each has a length at least several times its internal diameter. Both tubes are provided with inlet and outlet seals 3,4 which embrace the laid-up conductors to prevent or minimise escape of filling medium from within the tubes and enable the required pressure of medium within each tube to be maintained.

The apparatus comprises a source of petroleum jelly (not shown) provided with a heat to maintain that supply of petroleum jelly at such a temperature that it is liquid. A line 5 is provided to pass this liquid filling medium to an inlet6 provided mid-way along the first tube 1 and pumping means may be provided to pump the filling medium along this line 5 and into tube 1 under pressure. A line 7 is provided to pass the liquid filling medium through a heat exchanger 8, effecting cooling of the filling medium to a semi-liquid/semi-solid state, and to a reservoir 9, from which the filling medium may be pumped (by pump 10) into the second tube 2 via an inlet 11 mid-way along its length. An inlet 12 to the second tube 2 is also provided (intermediate its ends) and is connected to a source of filling medium maintained at a temperature at which it is solid.Thus either semi-liquid/semi-solid or solid filling medium may be pumped to the second tube 2.

The above described apparatus has considerable versatility in that one or other or both applicator tubes may be used, depending on the type and size of cable and its constituent insulated conductors and the type of filling medium being employed. If one or other applicator tube is idle, the conductors may simply pass through the tube without filling medium being fed to that tube, or instead the tube may be removed from the apparatus. For certain uses, such as a particularly large diameter cable with small interstices, filling medium in liquid state may be fed to both tubes to ensure filling: for the second tube, the liquid filling medium may be fed directly from line 5 or through line 7 with the heat exchanger inoperative.

The tubes and their inlet and outlet seals may be removable and replaceable by like tubes and seals of diameters appropriate to the different sizes of cables to be handled bythe apparatus. Alternatively, the tubes may remain the same for different sizes of cables to be handled the pumps feeding the filling medium to the tubes then being adjustable to ensure that sufficient pressure is still maintained within the tubes even for smaller diameter cables (and therefore greater clearances between cables and tubes): it may be still necessary to change the seals to match the cable diameter.

CLAIMS (Filed on 30/9/81) 1. An apparatus forfully filling an electric cable with a water impervious medium, comprising a first elongate tube for a plurality of insulated conductors, laid-up together, to pass through longitudinally of themselves, means for heating water impervious filling medium to liquid state and feeding it into said first elongate tube, a second elongate tube for said conductors to pass through after passing through said first elongate tube, and means operable to feed water impervious filling medium in liquid, semiliquid/semi-solid or solid state into said second elongate tube.

2. An apparatus as claimed in claim 1, comprising a pump for pumping the heated filling medium into the first elongate tube under pressure.

3. An apparatus as claimed in claim 1 or 2, comprising a pump for pumping the filling medium (in liquid, semi-liquid/semi solid or solid state) into the second elongate tube under pressure.

4. An apparatus as claimed in any preceding claim, comprising a heat exchanger for receiving and cooling the heated, liquid state filling medium and feeding it into the second elongate tube.

5. An apparatus as claimed in any preceding claim, selectively controllable to feed filling medium in liquid or semi-liquid/semi-solid or solid state into the second elongate tube.

6. An apparatus as claimed in any preceding claim, selectively operable with one or other or both elongate tubes in use.

7. An apparatusforfullyfilling an electric cable, substantially as herein described with reference to the accompanying drawings.

8. A method of fully filling an electric cable using an apparatus as claimed in any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. at a temperature at which it is solid. Thus either semi-liquid/semi-solid or solid filling medium may be pumped to the second tube 2. The above described apparatus has considerable versatility in that one or other or both applicator tubes may be used, depending on the type and size of cable and its constituent insulated conductors and the type of filling medium being employed. If one or other applicator tube is idle, the conductors may simply pass through the tube without filling medium being fed to that tube, or instead the tube may be removed from the apparatus. For certain uses, such as a particularly large diameter cable with small interstices, filling medium in liquid state may be fed to both tubes to ensure filling: for the second tube, the liquid filling medium may be fed directly from line 5 or through line 7 with the heat exchanger inoperative. The tubes and their inlet and outlet seals may be removable and replaceable by like tubes and seals of diameters appropriate to the different sizes of cables to be handled bythe apparatus. Alternatively, the tubes may remain the same for different sizes of cables to be handled the pumps feeding the filling medium to the tubes then being adjustable to ensure that sufficient pressure is still maintained within the tubes even for smaller diameter cables (and therefore greater clearances between cables and tubes): it may be still necessary to change the seals to match the cable diameter. CLAIMS (Filed on 30/9/81)

1. An apparatus forfully filling an electric cable with a water impervious medium, comprising a first elongate tube for a plurality of insulated conductors, laid-up together, to pass through longitudinally of themselves, means for heating water impervious filling medium to liquid state and feeding it into said first elongate tube, a second elongate tube for said conductors to pass through after passing through said first elongate tube, and means operable to feed water impervious filling medium in liquid, semiliquid/semi-solid or solid state into said second elongate tube.