WO1997032710A1

WO1997032710A1 - Cable componentry

Info

Publication number: WO1997032710A1
Application number: PCT/AU1997/000127
Authority: WO
Inventors: Alan Stringer
Original assignee: Pacific Dunlop Ltd
Current assignee: Dunlop Olympic Ltd
Priority date: 1996-03-04
Filing date: 1997-03-03
Publication date: 1997-09-12
Anticipated expiration: 1998-09-04
Also published as: AUPN843596A0; ZA971762B; ID16449A

Abstract

A method of manufacturing reinforcing rods from plastics comprising extruding or pulltruding from a die cavity a plurality of sub-strips, and bonding the sub-strips together to produce a single strand of rod.

Description

TITLE

Cable Componentry

FIELD OF INVENTION

This invention relates to a method of producing reinforcement for cables. The invention also includes a method of producing cable.

DISCUSSION OF BACKGROUND ART

Non-metallic fibre optic cables are used in a variety of situations and frequently comprise a plurality of tubes that contain a loose bundle of optical fibres. The tubes are wound onto a central fibre reinforced plastics (FRP) rod that operates as a strength member. The tubes are then encased in an outer sheath. The FRP rod is usually of circular cross-section and is viewed as one of the more expensive components of the cable.

In some cables one or perhaps two tubes are used to contain the bundles of fibre optical cables. One way of producing cables of this kind is to wind the tubes around an FRP rod and fill the gaps around the circumference of the rod with spacer tubes or fillers. This construction is however considered unnecessarily bulky since much of the cable is constituted by filler material. Cable of this kind is also viewed as unnecessarily expensive. An alternative means of producing a cable that has one or two tubes containing optical fibres is to reinforce the tube or tubes on either side with a pair of small FRP rods. The tubes can either be wound onto the rods or the rods wound onto the tubes. This type of cable requires the need for FRP rods of smaller cross-section than would be the cross- section of a rod that is used centrally to support a plurality of tubes. It has been discovered that the cost of the FRP rods is more dependent on the manufacturing process than the material and thus simply reducing the cross-sectional area of the rod does not substantially reduce its cost. Thus, in a cable where there is a need to use two FRP rods of smaller diameter to reinforce a single optical fibre tube, the cost of the rods is effectively almost twice the expense that would be incurred in using a single larger rod centrally of the fibre optical tubes.

There is thus considered a need for FRP rods that are of smaller cross-section than the more conventional circular cross-sectional rod. However, these rods need to be proportionally cheaper so that two or more rods can be used as reinforcement in a cable without substantially increasing the cost of the cable. It has also been discovered that the production of cable using two or more rods of smaller cross-section has to be carefully controlled because of the necessity of accurately orientating the FRP rods during the cable manufacturing. This problem is particularly acute if the cross-section of the rods is not axially symmetrical.

It is these problems that have brought about the present invention which addresses both the manufacture of reinforcing rods as well as the manufacturing process of an optical fibre cable using such rods.

SUMMARY OF THE INVENTION

According to the first aspect of the present invention there is provided a method of manufacturing reinforcing rod from plastics comprising extruding or pulltruding from a die cavity a plurality of sub-strips, and bonding the sub-strips together to produce a single strand of rod. The rod is preferably fibre reinforced plastics and the sub-strips are usually identically shaped.

Preferably, the sub-strips are cured and then subjected to a bonding agent prior to bonding the sub- strips together to produce a single strand of rod.

Preferably, the single strand of rod is wound onto a take- up roll.

According to a further aspect of the present invention a method of producing an optical fibre cable comprises de-bonding rod of the kind described above, separating the rod into a plurality of sub-strips and adding the sub-strips to an optical fibre core to form a cable.

According to a still further aspect of the present invention there is provided an optical fibre cable made from the method described above.

DESCRIPTION OF THE DRAWINGS

An embodiment to the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic side on view of the process line for manufacturing fibre reinforced plastics rod,

Figures 2a to f are cross-sectional views of fibre reinforced rod sub-strips manufactured according to the process of Figure 1,

Figure 3 is a schematic process line illustrating the manufacture of cable using the product manufactured in Figure 1, and Figure 4 is a cross-sectional view of the cable.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 is a schematic illustration of a process line for manufacturing fibre reinforced rod. The process line starts with a multi-die cavity 10, each cavity is split to produce a plurality of identically cross- sectionally shaped sub-strips 11, 12 of fibre reinforced plastics rod. Options for the cross-sectional shape of the rod sub-strips are shown in Figure 2. In Figure 2a the rod leaves each die in the form of semi-circular sub-strips 11 and 12. In Figure 2b the sub-strips 13, 14 form a hollow centre and in Figure 2b the rod has been split into four sub-strips 15, 16, 17, 18. Although the cross-section of each sub-strip is identical, it is understood that there could also be non-uniform sub-strips; for instance by also forming a central sub-strip in Figure 2c of circular cross- section. Other section of sub-strips 21, 22, 23 are shown in Figures 2d, e and f. The die cavity splits the rod into the desired number of sub-strips so that on reassembly, a single rod of axial symmetry is produced. As the fibre reinforced plastic is pulltruded from the die cavities 10 and split as shown in Figure 2 the split sub-strips 11, 12 of rod are then passed through a curing and/or coating station 20 during which the rod may be heat cured through a variety of means known to those skilled in this art. If the rod is of thermo-plastics, it is understood that the curing step would not be necessary. It is also understood that where necessary the rod could be subjected to suitable coating process that would also be well known to those skilled in this art. Polyethylene co-polymers are common coating materials.

After leaving the curing/coating station 20 a bonding agent in the form of a hot melt adhesive is applied to the surfaces of each portion of the rod sub-strip that would contact the surface of an adjacent sub-strip of the rod should the sub-strips be put together. After application of the bonding agent the rods are pulled through a combination station 30 which includes apparatus to cause the sub-strips of rod to be pressed into abutting contact to form a single rod. The apparatus would also include means to wipe off excess adhesives. The single rod then passes through a tβnβioning device 40 to be wound onto a take up drum 50. In a situation where there are a plurality of cavity dies 10 it will be understood that a plurality of take-up drums 50 will be provided to take-up individual single strands of combined sub-strips. Thus the process described above in effect forms a plurality of identical sub-strips of equal length which can then be subjected to a hot melt adhesive and combined to form a single symmetrical (usually circular) rod which is then wound onto a take-up drum for delivery to a cable manufacturing process. Figure 3 illustrates a schematic production line for a fibre optical cable. The cable 51 in completed form is shown in Figure 4 and comprises a single tube 60 containing a bundle of loosely held optical fibres 66. The tube is positioned centrally of a pair of diametrically opposed reinforcing rods 61, 62 that are wound onto the tube in a loose lay and the whole assembly is coated in an outer sheath 65 of plastics material. The reinforcing members 61 and 62 are of semi-circular cross-section and are manufactured of fibre reinforced rod produced by the method shown in Figure 1. The drum of composite sub- strips of FRP is wound into the cable manufacturing process 80 through a de-bonding or separation phase 70 during which the rod is subjected to heat which causes the hot melt adhesive to melt. Alternatively, the sub-strips can be simply pulled apart. The equipment is also designed to cause the sub-strips that make up the rod to be separated into separate strands which are then fed into the cable processing equipment 80 to produce an optical fibre cable 51 that is shown at the end of the line. The importance of this manufacturing technique is that by feeding a single composite rod into the line and de-bonding that rod into identical sub-strips of equal length, the alignment and orientation of the sub-strips relative to the cable can be carefully controlled so that the reinforced sub-strips can then be wound onto the optical fibre to produce a final cable without the need for complicated, sophisticated and expensive machinery to re- align, control and re-position the reinforcing rods that make up the cable.

The cable manufacturing process is not described in detail herein as it is considered well known to those skilled in this art. Although in the preferred embodiment a hot melt adhesive is used to combine the FRP sub-strips into a single rod and then heat is used to release the hot melt adhesive during the separation phase, it is understood that other techniques may be used to complete both the combination and separation phases. Other adhesives and techniques such as ultrasonics are all possible ways to conduct the combination and separation phases. It is also understood that a component can be introduced to the plastics before the extrusion or pulltruding to ensure that the sub-strips can be bonded together. It is also understood that the rod may also comprise unreinforced plastics.

The processes described above provide a number of important advantages. In the first place the split cavity die and combination phase of the production line ensures that a plurality of identically shaped reinforcing sub- strips can be produced at about the same expense as producing a single circular section. Thus, the splitting of a single circular section into components parts is a considerably cheaper option than manufacturing separate FRP rods which then have to be wound onto the optical fibre core to form the cable. A further advantage emanates from the fact that since the single rod is fed into a separation phase and then applied to the cable, it is a much simpler matter to orientate and align the rod relative to the remaining parts of the cable than would be the case where individual rods are fed from drums into the cable manufacturing line. A further advantage that flows from the processes described above is that with careful selection of cavity dies it is possible to provide FRP rods of a variety of cross-sections and these cross-sections may vary depending on the shape and configuration of the cable. This process provides the manufacturers of reinforcing rods of plastics, especially fibre reinforced plastics, with a cost effective means of providing a wide range of rods of shapes or configurations that can be used in conventional cable manufacturing equipment.

Claims

CLAIMS :

1. A method of manufacturing reinforcing rod from plastics comprising extruding or pulltruding from a die cavity a plurality of sub-strips, and bonding the sub- strips together to produce a single strand of rod.

2. The method according to claim 1 comprising causing the sub-strips to be identically shaped.

3. The method according to either claim 1 or 2 wherein the sub-strips are fibre reinforced plastics.

4. The method according to claim 3 wherein the sub- strips are coated with an adhesive after leaving the die cavity.

5. The method according to any one of the preceding claims wherein the single strand of rod is wound onto a take-up roll.

6. A reinforcing rod for use in optical fibre cables manufactured by the method according to any one of the preceding claims.

7. A method of producing an optical fibre cable comprising unwinding reinforcing rod according to claim 6 from a take-up roll, de-bonding the reinforcing rod, separating the rod into a plurality of sub-strips and adding the sub-strips to an optical fibre core to form a cable.

8. An optical fibre cable made from the method according to claim 7.

AMENDED CLAIMS

[received by the International Bureau on 27 June 1997 (27.06.97); original claims 1, 5, 7 and 8 amended; remaining claims unchanged (1 page)]

1. A method of manufacturing reinforcing rod from plastics comprising extruding or pulltruding from a die cavity a plurality of sub-strips, and assembling and securing the sub-strips one to another to form a single element of composite rod that can be separated into the individual sub-strips.

2. The method according to claim 1 comprising causing the sub-strips to be identically shaped. 3. The method according to either claim 1 or 2 wherein the sub-strips are fibre reinforced plastics. 4. The method according to claim 3 wherein the sub- strips are coated with an adhesive after leaving the die cavity. 5. The method according to any one of the preceding claims wherein the single element of composite rod is wound onto a take-up roll.

7. A method of producing an optical fibre cable comprising unwinding reinforcing rod according to claim 6 when dependent on claim 5 from the take-up roll, separating the reinforcing rod into the individual sub-strips and adding the sub-strips to an optical fibre core to form a cabl .

8. An optical fibre cable made by the method according to claim 7. STATEMENT UNDER ARTICLE 19

The amendments that have been made to the claims of the PCT application are to further distinguish the claimed invention from the disclosure of the prior art cited in the International Search Report. The amendments to the claims emphasise that the sub-strips are assembled and secured to one another to form a single element of composite rod that can be separated into the individual sub-strips.