GB2049263A

GB2049263A - Method and apparatus for manufacturing telecommunication cable

Info

Publication number: GB2049263A
Application number: GB8014614A
Authority: GB
Original assignee: Industrie Pirelli SpA; Pirelli SpA
Current assignee: Industrie Pirelli SpA; Pirelli and C SpA
Priority date: 1979-05-18
Filing date: 1980-05-02
Publication date: 1980-12-17
Also published as: DK147629C; BR8003012A; FI801266A; CA1147935A; IT7922770A0; NZ193716A; DE3018902A1; GB2049263B; ES492066A0; ES8101806A1; FR2456998B1; FI71629C; DK182980A; FR2456998A1; AU535216B2; DK147629B; IT1166829B; CH637786A5; FI71629B; AU5766380A

Abstract

In manufacturing a telecommunications cable which comprises a plurality of insulated conductors enclosed within a sheath and with the interstices between the conductors filled with powder of a material which expands if it absorbs water (to form a blockage against passage of any ingressing water along the cable), the individual conductors 2 pass through a tapering cavity to converge and become stranded together and the powder is thrust towards the narrower, exit end of the cavity by a helical screw 20, thus forcing the powder in-between the conductors. In another embodiment (Fig. 5 not shown) the cavity does not have a helical screw but the feed hopper does. <IMAGE>

Description

SPECIFICATION Method and apparatus for manufacturing telecommunication cables The present invention relates to a method and apparatus for manufacturing telecommunication cables comprising a bundle of insulated conductors.

In this specification, the term "conductor" means a conductor provided with insulation, and "powdered expansible material" means a powdered material which expands when subjected to absorbing water. This invention relates to telecommunication cables in which such material is disposed between the conductors themselves and between the conductors and an enclosing sheath of the cable, so as to swell out, in the event of ingress of water into the cable due to accidents, to form a block against any such water spreading throughout the entire cable. As an example of these materials, mixtures of various powders can be briefiy cited-such as those disclosed in U.S. Patent Number 4 002 819-or for example carboxymethylecellulose or bentonite.

Certain known manufacturing methods are based upon causing a bundle of conductors, already cabled or stranded together, to pass into a container having an internal diameter corresponding to that of the bundle, and injecting a mixture of powders, by means of pressurised air, towards an annular passage of the container through which the conductors pass, in such a way as to force the powdered material in-between the conductors. Then, certain tapes are wound around the cable core thus formed, for preventing loss of the powders, and finally a protective sheath is applied by extrusion.Unfortunately, during the cabling together of the conductors-which is carried out before these enter the container, a canal can be formed between the conductors; successively, when the conductors pass into the container, there is the drawback that the air under pressure (at times up to 10 atmospheres) can pass along this canal to the outside of the container, and this tends to expel the powders that are already introduced in between the conductors.

Another known process comprises applying the powdered material electrostatically to the conductors before stranding them together.

This has the drawback of being rather slow, and moreover of being unsuited to the standard cabling or stranding machines used for the manufacture of telecommunication cables.

Moreover, the powder disposed on the conductors is in certain cases less than the quantity that is desired, and a further operation of pre-disposing oil on the surface of the conductors, for aiding the adherence of the powders in the succeeding electrostatic phase, brings about (as is known) damage to the conductor insulation, due to the presence of the oil, when the cable is in electrical tension.

As seen from one aspect, in accordance with the present invention there is provided a method of manufacturing a telecommunication cable, which comprises a bundle of conductors enclosed within a sheath and powdered expansible material disposed in-between the conductors and between the sheath and conductors, said method comprising: a) advancing the conductors through a tapering cavity whilst maintaining the conductors separated at the wider, entrance end of the cavity and with the conductors converging towards the narrower, exit end of the cavity and becoming stranded together; b) feeding expansible material in powder form into the cavity and thrusting it under pressure towards said exit end of the cavity so as to force it in-between the conductors passing through the cavity; and c) applying a sheath to the stranded conductors after they have left said cavity.

In embodiments to be described herein, the powder is guided and mixed under pressure within a helicoidal canal, from whence the powder issues by means of a mechanical thrust and this causes the powder to be welldistributed around and in-between the conductors. In one embodiment, the powder advances between the entry and the exit ends of the cavity along a helicoidal course disposed all around the conductors, and moves from the helicoidal course towards the centre of the cavity, and around the conductors themselves.

As seen from a second aspect, in accordance with the present invention there is provided an apparatus for manufacturing a telecommunication cable which comprises a bundle of conductors enclosed within a sheath and powdered expansible material disposed in-between the conductors and between the sheath and the conductors, said apparatus comprising a tapering cavity, means for feeding expansible material in powder form into said cavity and thrusting said material towards the narrower end thereof, and guiding the conductors separately into the cavity at its wider end and passing the conductors through the cavity and out at its narrower end, the conductors converging towards said narrower end and becoming stranded together.

The cavity may comprise a frusto-conical casing provided with a hopper for feeding the powder into the casing, a hollow screw disposed within the casing and having a helical thread, the screw being rotatable around its own axis and comprising an external profile in the proximity and along the casing inner surface and an inner profile defining a frustoconical chamber through which the conductors pass, and means for rotating the screw.

Embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings, in which: Figure 1 is a view of one end of a telecommunication cable manufactured according to the invention; Figure 2 is a diagrammatic longitudinal view of an apparatus for manufacturing the cable of Fig. 1; Figure 3 is a longitudinal section of one embodiment of a powder-introducing apparatus of the apparatus of Fig. 2 for the introduction of the powders; Figure 3a shows enlarged detail of the apparatus of Fig. 3; Figure 4 is a view in the direction shown by the line IV-IV of Fig. 3; Figure 5 is a longitudinal section through a second embodiment of powder-introducing apparatus; Figure 6 is a section on the line VI-VI of Fig. 5.

The telecommunication cable 1 shown in Fig. 1 comprises a plurality of conductors 2, insulated for example with thermoplastic resins such as polyolefins or vinylic resins, two layers of helically wound, overlapped tapes 3, 4, an external sheath 5 and expansible material 6 in the form of powder disposed inbetween the conductors 2 and between the conductors and the tapes 3 and 4 underlying the sheath. For example, these tapes may comprise polyesther, the sheath polyethylene, and the powdered expansible material carboxymethylcellulose.

The inter-spaces between the conductors and around the conductors are filled at least partially, at a suitable dosage, with the powdered expansible material intended for forming a block against any penetration of water.

For example, this material might occupy 30% of the spaces present in the cable-core, and then, if there be any ingress or water, it swells out to block the water from spreading along the cable.

The apparatus 7 (Fig. 2) for the manufacture of cable 1 comprises a station 8 having a plurality of bobbins 9 around which are wound the conductors 2, a group 10 of guide-pulleys 11 for the conductors 2 during unwinding, an apparatus 1 2 for the application of the powdered expansible material, means 1 3 for applying the taper layers 3 and 4 around the cable-core, an extruder 1 4 for applying the sheath 5 to the core, a winching drum 15, and a drum 1 5' for collecting the cable.The drums 1 5 and 15' rotate around their own axes for pulling and collecting the cable, and simultaneously they also rotate around the axis A-A of the apparatus 7, for effecting in a known way the cabling or stranding of the conductors at the exit of the apparatus 1 2.

All components of the apparatus 7, except the powder introducing apparatus 12, comprise known devices and hence will not be described in any further detail.

One embodiment of powder introducing apparatus 1 2 is shown in Figs. 3, 3a and 4 and comprises means for helically urging the powder forward into a frusto-conical cavity and means for guiding the conductors 2 separately, one from the other, into the cavity.

These means comprise, respectively, an Archimedean screw 20 and by a die element 1 7.

The apparatus 1 2 comprises a frusto-conical casing 1 8 supported on a base 16, a hopper 1 9 for feeding the powdered expansible material into the casing 18, the screw 20 disposed within the casing and having a hollow helical thread rotating around its own axis 21 which coincides with the axis A-A of the manufacturing appearatus, and means 22 for rotating the screw. The narrower, exit end of the casing 1 8 is provided with a plug 18' preferably of stainless steel and having a central hole for the passage of the conductors.

The helical screw 20 is disposed with its outer profile 23 in the proximity of, and along the inner surface of the casing 1 8 and with its inner profile 25 defining a frusto-conical chamber 26, through which the conductors 2 pass, and which is in communication with the inter-spaces between the turns of the screw.

The means 22 for rotating the screw comprises an annular flange 27 integral with one end 28 of the screw 20 and disposed against the wider end of the casing, a hollow pulley 29 secured to the flange 27, and drive means 30 comprising a motor 31, a pulley 32 and a belt 33 trained around the two pulleys 32 and 29.

The screw 20 is supported and centered with respect to the casing by suitable supporting means which are comprised, in the embodiment shown of a plurality of rollers 34 carried by projecting arms 35 of the casing itself, with their axes parallel to the axis of the screw 20, and distributed around the running on the flange 27 (see Figs. 3 and 4). This plurality of rollers press by way of their own peripheries 36 within a complementary annular groove 37 formed in the flange 27, the rollers being brought into rotation by the flange 27 itself and preventing any misalignment of the screw 20 with respect to the casing 18.

The entry end of the casing 1 8 is closed by the die 17, which comprises a disc mounted on a structure 28 and provided with a plurality of holes 39, distributed around various circles concentric with the axis A-A, through which the conductors 2 pass.

The apparatus 1 2 further comprises sealing means between the stationary die 1 7 and the rotary pulley 29 which it faces. This means may comprise any of various structures and may be secured to the pulley 29 or to the die 17, but such that, during rotation of the pulley, a sliding, sealing contact is achieved.

For example, this sealing means may comprise an elastomeric annular gasket 40 having an outer periphery 41 attached to the pulley 29, and forming a lip-seal contact with an annular protuberance 43 on the die 1 7.

The apparatus further comprises sealing means between the casing 1 8 and the opposed rotating pulley 27, for example, an annular elastomeric gasket 44 disposed (see Fig. 3a) in contact with circumferential surfaces of the casing and of the pulley, which preferably are chrome-plated for reducing friction to the minimum. Upstream and downstream of the apparatus 12, suitable containers may be disposed for receiving, if necessary, small quantities of powder which nevertheless emerge from the apparatus. The two above-described sealing means prevent the powder from escaping and thus eliminate the need for any subsequent operations to recover such material, and, more importantly, maintain the surrounding air free of great quantities of powder dispersed therein, so that the health of operating personnel is safeguarded.

Manufacturing apparatus functions as fol lows-The conductors 2 (Fig. 2) subjected to a pull exerted by the drum 1 5 are progressively unwound from the bobbins 9 and guided over pulleys 11 towards the apparatus 1 2 of Fig. 3. The conductors 2 are maintained separated one from the others by the die 1 7 as they enter the casing 18, then they pass through casing 1 8 to converge and become stranded together as they exit from the casing 18 through the plug 18'.

During their passage through the crew 20, the various conductors pass through the frusto-conical chamber 26, remaining within the helical canal defined by the turns of the screw 20 which is rotated arund its axis by the drive means 30 (Fig. 3).

The screw continuously urges towards the plug 18' (according to a helical course) the powdered expansible material which is loaded into the hopper 19, and as the powder gradually approaches the casing exit it is compressed into regions of smaller cross-section and as a consequence of this compacting the powder fully penetrates in-between the conductors. This action is further favoured by the conductors converging towards the exit end of the casing 18, thus pushing and more compactly enclosing the powders within the bundle.

When the bundle of conductors 2, containing the powdered material, issues from the cavity 18, there takes place the usual following phases for manufacturing the cable 1. The cabling or stranding of the conductors is carried out by rotating the drums 1 5 and 15' around the axis A-A. Then, the tapes 3 and 4, are applied by means 13, whereafter the sheath 5 is applied by the extruder 14. Finally, the cable is wound onto, the collecting drum 15'.

One particular advantage of the powder introducing apparatus just described lies in the possibility of filling-up the inter-spaces between the conductors with powder even when, for some reason or other, the feeding by means of the hopper is interrupted. In fact, inside the casing 1 8 the;e is deposited a certain quantity of powder having a volume that is higher than that instantly required by the bundle of cables on exiting from the apparatus. Consequently, the screw 20 is for a certain period able to advance this powder independently of the hopper feed, in this way guaranteeing (at least for a period sufficient for the hopper to be refilled again) a correct manufacturing of the cable.

Figs. 5 and 6 show a second embodiment of the powder introducing apparatus, comprising a first frusto-conical casing 45, resting on a base 45' which the conductors 2 enter separately, being dragged through this casing by appropriate pulling means (not illustrated) from the entry end, at which a die 46 is provided, to the exit end 47 of the casing.

The apparatus further comprises a second frusto-conical casing 48, inside which is disposed a rotatable frusto-conical screw 49, having a solid core 50 and a thread 51; this screw is rotated around its own axis 52 by a motor 53 driving an endless screw 54 meshed with gears within a casing 55 for rotating the shaft of screw 49.

This second casing is fed with powdered expansible material fed from a hopper 56 and comprising an outlet extension 57 the final portion of which lies between the conductors 2 of the bundle adjacent the exit 47 of casing 45, or at a more distant position (see Fig. 6), with variations in the load of the powder as a function of the position of the end portion of the extension with respect to the conductors, which converge towards the exit of the first casing.

The first casing further comprises means for emitting a portion of the powder when the pressure to which they are subjected inside this casing adjacent the exit 47 becomes excessive and may risk bringing about a rupture in the conductors themselves. For example, the apparatus could be provided with an exhaust valve that is set for a predetermined pressure value of the powder; otherwise, it could comprise a conduit between the first casing and the hopper-in such a way as to return a certain quantity of powder to the hopper, and in this manner to maintain the pressure of the powder adjacent the exit 47 at a correct functioning value.

In the apparatus of Figs. 5 and 6, the powder is forced to follow a helical course determined by the turns of the screw 49 and issue from the extension 57 under a mechanical thrust which guides them towards the narrower end 47 of the casing 45.

Supposing that the casing 45 is half-filled with powdered expansible material, then the continuous rotation of screw 49 produces a further inflow of powder from the hopper 56 and directed from the outlet of the extension 57, in such a way as to continually pressurise and fill the upper free space in the proximity of the exit 47 of the casing 45, thus causing a compacted mass of powder, in the form of a frusto-conical block through which the conductors pass.

The embodiments of the present invention described above prevent the formation, in the powders accumulated adjacent the exit of the casing 1 8 or 45, of canals, created by the passage of the conductors, and having the characteristic of walls delimiting areas having sections that are greater than the transversal dimension of the conductors. This situation, if it should arise, would be extremely unfavourable since the conductors would pass through the canals without receiving or dragging the powders along with them. The embodiments illustrated in the Figs. 3 and 5 eliminate these drawbacks. In fact, the continuous inflow of fresh quantities of powder-pushed by the screw 20 (Fig. 3) or by the screw 49 (Fig.

5)causes a collapse and continuous re-mixing of the canal walls which tend to form by the passage of the conductors and this guarantees a contact and entrainment of the powder with the conductors. The screw 20 or 49 have a multiple thread instead of the single thread shown.

Claims

1. A method of manufacturing a telecommunication cable which comprises a bundle of conductors enclosed within a sheath and powdered expansible material disposed in-between the conductors and between the sheath and conductors, said method comprising: a) advancing the conductors through a tapering cavity whilst maintaining the conductors separated at the wider, entrance end of the cavity and with the conductors converging towards the narrower exit end of the cavity and becoming stranded together; b) feeding expansible material in power form into the cavity and thrusting it under pressure towards said exit end of the cavity so as to force it in-between the conductors passing through the cavity; and c) applying a sheath to the stranded conductors after they have left said cavity.

2. A method according to Claim 1, in which the powder advances between the entry and the exit of the cavity along a helical course disposed all around the conductors and is moved from the helical course towards the centre of the cavity and around and between the conductors themselves.

3. A method according to claim 1 or 2, comprising the step, after step (b) and before step (c) of winding tape around the conductors.

4. An apparatus for manufacturing a telecommunication cable which comprises a bundle of conductors enclqsed within a sheath and powdered expansible material disposed in-between the conductors and between the sheath and the conductors, said apparatus comprising a tapering cavity, means for feeding expansible material in powder form into said cavity and thrusting said material towards the narrower end thereof, and means for guiding the conductors separately into the cavity at its wider end and passing the conductors through the cavity and out at its narrower end, the conductors converging towards said narrower end and becoming stranded together.

5. An apparatus according to claim 4, in which said feeding means comprises a hopper for feeding the powder to the casing interior, a hollow screw within the casing and having a helical thread an outer profile of which is adjacent and along the casing inside surface, and an inner profile of which deimits a frustoconical chamber through which the conductors pass, and means for rotating the screw.

6. An apparatus according to claim 5, in which said means for rotating the screw comprises an annular flange secured to an end of the screw adjacent the entry end of the casing, an internally hollow pulley connected laterally to the flange, means for supporting the flange, and drive means for rotating the pulley.

7. An apparatus according to claim 6, in which said supporting means for the flange comprises a plurality of rollers carried by arms projecting from the casing and having their arms parallel to a central longitudinal axis of the casing, said rollers being distributed around the flange with their peripheries engaged with a complementary groove formed around the flange.

8. An apparatus according to claim 6 or 7, comprising sealing means between the rotating pulley and an element which is fixed facing the pulley and constitutes an entry die for the conductors entering the casing.

9. An apparatus according to claim 8, in which the sealing means comprises an annular gasket of elastomeric material made fast with the pulley and in sliding contact, when the pulley turns, with a pointed projection on and extending circumferentially of said fixed element opposite said pulley.

10. An apparatus according to any one of claims 4 to 9, in which the means for separately guiding the conductors into the frustoconical cavity comprises, adjacent the entry end of said cavity, a disc provided with holes for the passage of respective conductors.

11. An apparatus according to claim 4, in which said feeding means comprises a first frusto-conical casing through which the conductors pass, entering separated one from the others and converging towards the narrower, exit casing end, a second frusto-conical casing within which a solid core frusto-conical screw turns, said second casing being connected at one extremity to a hopper, and comprising at its opposite end an extension the end of which is disposed between the conductors which pass through the first casing and is directed towards the exit end of the first casing.

1 2. An apparatus according to claim 11, in which the conductors are guided into the first casing by respective holes in a disc which is secured to the entry end of the first casing.

1 3. An apparatus according to claim 11 or 12, in which the end of said extension is disposed adjacent the exit end of the first casing.

14. A method of manufacturing a telecommunications cable, said method being as claimed in claim 1 and substantially as herein described.

1 5. An apparatus for manufacturing a telecommunications cable, said apparatus being substantially as herein described with reference to Figs. 1 to 4 or Figs. 1, 2, 5 and 6 of the accompanying drawings.