WO2006061555A1

WO2006061555A1 - Tube assembly accomodating optical fibres and method of manufacturing same

Info

Publication number: WO2006061555A1
Application number: PCT/GB2005/004290
Authority: WO
Inventors: George Henry Platt Brown; David John Stockton
Original assignee: Emtelle (Uk) Limited
Priority date: 2004-12-07
Filing date: 2005-11-07
Publication date: 2006-06-15
Also published as: GB0426798D0

Abstract

A tube assembly (2) for accommodating optical fibres comprises: - at least one hollow tube (4); and a water-resistant layer (6) surrounding at least one said hollow tube (4). The water-resistant layer (6) comprises a metal layer bonded to a first support layer.

Description

TUBE ASSEMBLY AC COMODAT ING OPTICAL FIBRES AND METHOD OF MANUFACTURING SAME

The present invention relates to an improved tube assembly for the installation of optical fibres, and a method of manufacturing such a tube. The invention relates particularly, but not exclusively, to a tube assembly for accommodating optical fibres used to provide telecommunications, internet services and the like, and to a method of manufacturing such a tube assembly.

Optical fibre cables carry data at very high speeds and as the demand for Broadband Internet access grows, there is an increasing requirement for optical fibre cables providing high-speed connection to be deployed either directly into individual homes or business premises.

Increasingly, optical fibre networks are constructed by setting up a network of tubes, and then subsequently installing the optical fibre cables into the tube network usually by means of blowing and/or pushing. The optical fibres are blown into tubes by employing the fluid drag of air, or another suitable gas, passed at high velocity through the tubes, as is described in European Patent No. 0 108 590 for example.

It is often the case that individual tubes for use in the construction of a tube network are assembled either as tube bundles or individual tubes . Figures 1 to 7 illustrate typical prior art tube assemblies containing between one and twenty-five tubes.

As can be seen from Figures 1 to 7, it is common practice to surround tube bundles 100 with an aluminium layer 102, which is then typically over-coated with at least one layer 104 of a thermoplastic material such as polyethylene. The aluminium layer 102 is over-coated with the thermoplastic layer 102 by means of an extrusion process .

The purpose of the aluminium layer is to reduce .the rate at which water permeates into the tube assembly. Most materials allow the permeation of water to some degree, and whilst polyethylene is a good water-proofing material, it has been found that a thin layer of aluminium is approximately 1000 times better at reducing the rate of permeation of water than a substantially thicker layer of polyethylene.

The aluminium layers used in prior art tube assemblies typically have a thickness of 150 microns, and incorporate a layer of heat sensitive adhesive on at least one side thereof. The aluminium layer is wrapped around the tube bundle with the adhesive layer outermost so that when the hot thermoplastic over-coating is applied, the adhesive is activated by the heat, as a result of which the aluminium layer is bonded to the polyethylene. The bonding of the aluminium to the polyethylene provides the benefit of reducing voids between the thermoplastic over-coating and the aluminium layer. It is common practice to provide an overlap joint on the aluminium layer so that water does not permeate into the tube assembly. However, the overlap joint does not always provide a perfectly watertight joint.

To overcome this problem, it is known to weld the aluminium joint along the length of the tube assembly. However, the welding equipment necessary to carry out this process is expensive, and the process is slow. In view of this, the problems associated with an un-welded overlap joint are generally accepted.

The aluminium layer is generally supplied as a flat tape on rolls of adequate width sufficient to completely surround the tube bundle and provide some overlap. The length of a roll is typically 4000 m. The overlap is typically between 5 mm and 10 mm. The aluminium layer is 150 microns thick so that when it is wrapped around the tube assembly with some back tension applied, it holds its shape and does not ripple.

The existing tube assemblies suffer from the drawback that aluminium is very expensive and the cost of the 150 micron thick aluminium layer of prior art tube assemblies amounts to a significant percentage, typically up to 20%, of the total raw material cost of the tube assembly. However, a thin layer of aluminium has low tear strength, and it is important that the aluminium does not tear during the manufacturing process. Whilst it is common to use an aluminium layer having a thickness of 150 microns as discussed above, in order to reduce manufacturing costs, it is also known to use an aluminium layer having a thickness of as low as 80 microns. However, this can create manufacturing difficulties and care has to be taken to ensure that the edges of such a thin aluminium layer are not damaged in any way as a very slight fault can cause a tear to propagate.

A further disadvantage of using an aluminium layer is that it is supplied in discrete lengths, whilst the overcoating is applied to the assembly by means of a continuous extrusion process. In view of this, the length in which tubes assemblies may be manufactured is therefore limited to the supply length for the aluminium layer, which is typically 4000 m. It is possible to laser weld successive lengths of aluminium together but this is difficult and expensive, particularly in terms of the machinery required for the welding operation. The aluminium has to be very precisely cut and butt welded to the next length using laser welding equipment.

One further disadvantage of using an aluminium layer is that it conducts electricity. This is a particular problem when optical fibres are installed in a building in that there is a risk that faulty electrical equipment inside the building could come into contact with the aluminium layer of the tube assembly with potentially hazardous consequences for personnel involved.

Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.

According to an aspect of the present invention there is provided a tube assembly for accommodating optical fibres, the assembly comprising: -

at least one hollow tube; and

a water-resistant layer surrounding at least one said hollow tube, wherein the water-resistant layer comprises a metal layer bonded to a first support layer.

This provides the advantage that a thin layer of aluminium may be used to waterproof the tube assembly, whilst still providing a high tear strength for the water-resistant layer as a result of the support layer. In a preferred embodiment, the metal layer includes aluminium.

Preferably, the assembly further comprises a further layer surrounding said water-resistant layer.

Preferably, the support layer comprises a polymeric material .

This has the benefit of providing the water-resistant layer with a high tear strength.

Alternatively, the support layer is made from paper.

This provides the advantage of preventing any heat generated by the application of the further layer from being transferred through the metal layer to the tubes and possibly damaging the tubes.

The assembly may further comprise a second support layer disposed on a side of the metal layer remote from the first support layer.

Preferably, the second support layer comprises a polymeric material.

Alternatively, the second support layer may be made from paper.

This provides the advantage that both sides of the aluminium layer are coated, and in this way, the risk of an electricity supply accidentally coming into contact with the aluminium layer is significantly reduced. The advantage is also provided that if the water-resistant layer is provided with a compatible polymeric support layer on both sides, then it may be easily welded along the overlap joint, along the complete length of the tube assembly. This can be achieved simply by either heat welding or ultra-sonic welding, whereby the overlapping polymer layers are fused together.

Preferably, the tube assembly further comprises a bedding layer disposed between at least one said hollow tube and the water-resistant layer.

This provides the advantage of providing a regularly shaped support surface for the water-resistant layer, so that deformation of the water-resistant layer is reduced when it is formed over the tubes of the tube assembly.

The bedding layer may comprise a foam material.

According to another aspect of the present invention, there is provided a method of forming a tube assembly for accommodating optical fibres, the method comprising the step of wrapping a water-resistant layer comprising a metal layer bonded to a support layer around at least one hollow tube to form a water-resistant sheath around the or each said tube.

The support layer may comprise a polymeric material.

Alternatively, the support layer may be made from paper.

Preferably, the method further comprises the step of forming a further layer around the water-resistant layer. In a preferred embodiment, the method further comprises the step of forming a bedding layer providing a regularly shaped support surface for the water-resistant layer between at least one said hollow tube and the water- resistant layer.

The bedding layer may comprise a foam material .

A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: -

Figure 1 shows a prior art tube assembly comprising one tube;

Figure 2 shows a prior art tube assembly comprising two tubes;

Figure 3 shows a prior art tube assembly comprising four tubes;

Figure 4 shows a prior art tube assembly comprising seven tubes;

Figure 5 shows a prior art tube assembly comprising twelve tubes;

Figure 6 shows a prior art tube assembly comprising nineteen tubes;

Figure 7 shows a prior art tube assembly comprising twenty-five tubes; Figure 8 shows a tube assembly embodying the present invention;

Figure 9 shows a cross sectional view of a portion of a water-resistant layer of the assembly of Figure 8; and

Figure 10 shows an apparatus for manufacturing the tube assembly of Figure 8.

With reference to Figure 8, a tube assembly 2 comprises four hollow tubes 4a, 4b, 4c and 4d, surrounded by a bedding layer 5 which is in turn surrounded by a water- resistant layer 6. The water-resistant layer 6 is surrounded by a further layer 8.

As can be seen from Figure 9 in particular, the water resistant layer 6 comprises an aluminium layer 10 bonded to a polymer support layer 12. The polymer support layer 12 provides adequate strength compatible with the manufacturing process. An example of such a water- resistant layer 6 is product code 2AAHOBD supplied by Polifibra Spa, 20041 Agrate Brianza (MI) Via Marconi, 74, Italy. Such a water-resistant layer 6 is a 7-micron thick aluminium foil laminated to a 12-micron thick layer of polyester. The cost of this product per square metre is approximately 15% of the cost of the 150 micron thick aluminium layer of prior art tube assemblies . In using such a water-resistant layer, the cost of manufacturing tube assemblies is significantly reduced.

One difficulty in using a water-resistant layer 6 including an aluminium layer having a thickness of only 7 microns is that unlike prior art water-resistant layers where the aluminium is 150 microns thick, the water- resistant layer 6 does not hold its shape once it is formed. This creates a problem when manufacturing a tube assembly containing four tubes for example, as shown in Figure 3, in that the water-resistant layer 6 is likely to collapse producing a very irregularly shaped tube assembly which is not commercially attractive. In order to overcome this problem, the tubes 4a, 4b, 4c and 4d are surrounded by the bedding layer 5, which provides a substantially solid and regularly shaped support surface for the water-resistant layer 6. A suitable bedding layer 5 for the tube assembly 2 is made from flexible polyvinylchloride, which may also be doped with a suitable blowing agent such as baking powder in order to create a foam structure and thus reduce the cost and weight of the bedding layer 5.

It is to be appreciated that the problem of deformation of the water-resistant layer 6 does not generally exist if the assembly comprises only one tube, since the single tube has a round profile, and therefore provides adequate support to allow over-coating with the further layer 8 without causing deformation of the water-resistant layer 6.

The water-resistant layer 6 also includes a further polymer support layer 14 on the opposite side of the layer β to the support layer 12. This allows subsequent lengths of water-resistant layer 6 to be easily joined by a simple heat-sealing process. For example, two lengths of water-resistant layer 6 are laid one on top of the other, such that they overlap at their ends. The overlap is then heated such that the outer polymer layers 12 and 14 which are in touching contact with each other, bond together. This joining process is very quick and can be achieved in a time of around two seconds, which is significantly quicker and less expensive than the process of laser welding the aluminium layer of prior art tube assemblies .

Even at relatively high line speeds of 30 m per min, a joining time of two seconds only requires an accumulator to store 1 m of water-resistant layer 6 so that the water-resistant layer 6 can be stopped during the joining process whilst the process of manufacturing the tube assembly (see below) continues. In this way, production of the tube assembly can remain continuous.

Figure 10 illustrates an apparatus 15 for manufacturing the tube assembly, comprising a first pay-off reel 16, a second pay-off reel 18 and an accumulator 20. The accumulator 20 comprises upper and lower rollers 22 and 24 respectively.

A roll of water-resistant layer 6 is loaded onto each of the pay-off reels 16 and 18- The pay-off reels 16 and 18 are power driven but also provide an adjustable back tension to apply a constant tension to the water- resistant layer 6 during the manufacturing process. Such pay-off reels may be purchased from Nextrom Technologies, Route de Bois 37, CH-1024 Ecublens, Lausanne, Switzerland.

At the beginning of the process, the water-resistant layer 6 is drawn from pay-off reel 16 and is threaded through the accumulator 20 towards that part of the process (not shown but indicated by arrow Y) in which the water-resistant layer 6 is wrapped around the tubes 4a, 4b, 4c and 4d, and then over-coated by the further layer

The lower rollers 24 are free to move up and down. When the water-resistant layer 6 on pay-off reel 16 comes to an end, the layer 6 is clamped and cut, and the cut end is placed in the heat welding position indicated by A on Figure 10. The end 26 of the layer 6 from reel 16 is then heat welded to the end 28 of the layer 6 from reel 18. Whilst the joining of the layer 6 from reels 16 and 18 is taking place, the manufacturing process can continue, because the lower rollers 24 of the accumulator 20 rise up allowing water-resistant layer 6 to be fed to the next part of the manufacturing process.

As soon as the heat welding of the two ends 26 and 28 has been completed, the pay-off reel 18 allows sufficient layer 6 to be dispensed such that the lower rollers 24 of the accumulator 20 return to their initial position such that sufficient layer 6 is stored in the accumulator 20 so that the heat welding process can be repeated in a similar fashion when the water-resistant layer on pay-off reel 18 has almost come to an end. In this way, the manufacturing process as a whole can remain continuous, since the dispensation of the water-resistant layer to the next part of the manufacturing process whereby it is applied over the bedding layer, does not stop when the ends 26 and 28 of the layer 6 are being fused together.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alternatives and modifications are possible without departing from the scope of the invention as defined by the appended claims .

Claims

1. A tube assembly for accommodating optical fibres, the assembly comprising: -

at least one hollow tube; and

2. An assembly according to claim 1, wherein the metal layer includes aluminium.

3. An assembly according to claim 1 or 2 further comprising a further layer surrounding said water- resistant layer.

4. An assembly according to any of the preceding claims wherein the support layer comprises a polymeric material.

5. An assembly according to any one of claims 1 to 3 wherein the support layer is made from paper.

6. An assembly according to any of the preceding claims, further comprising a second support layer disposed on a side of the metal layer remote from the first polymer support layer.

7. An assembly according to claim 6 wherein the second support layer comprises a polymeric material.

8. An assembly according to claim 6 wherein the second support layer is made from paper.

9. An assembly according to any one of the preceding claims, further comprising a bedding layer disposed between at least one said hollow tube and the water- resistant layer.

10. An assembly according to claim 9 in which the bedding layer comprises a foam material.

11. A tube assembly for accommodating optical fibres, the assembly substantially as hereinbefore described with reference to Figures 8 to 10 of the accompanying drawings .

12. A method of forming a tube assembly for accommodating optical fibres, the method comprising the step of wrapping a water-resistant layer comprising a metal layer bonded to a support layer around at least one hollow tube to form a water-resistant sheath around the or each said tube.

13. A method according to claim 12, wherein the support layer comprises a polymeric material.

14. A method according to claim 12, wherein the support layer is made from paper.

15. A method according to any one of claims 12 to 14, further comprising the step of forming a further layer around said water-resistant layer.

16. A method according to any of the preceding claims, further comprising the step of forming a bedding layer providing a regularly shaped support surface for the water-resistant layer between at least one said hollow tube and the water-resistant layer.

17. A method according to claim 16 in which the bedding layer comprises a foam material.

18. A method of forming a tube assembly for accommodating optical fibres, the method substantially as hereinbefore described with reference to Figures 8 to 10 of the accompanying drawings .