FR2525349A1 - Optical fibre cable with fibre resin reinforcement - the reinforcement being under tension to ensure all force on the optical fibre is absorbed - Google Patents

Abstract

An optical fibre transmission cable includes at least one longitudinally extending glass fibre/resin reinforcing strand which is under permanent tension. The strand has a modulus of (4-6)x 10 power 6 psi, an ultimate tensile strength of 70,000 to 200,000 psi, and a flex modulus of (1.0-5.7) x 10 power 6 psi. Pref. it is 60-80% by wt. of glass fibres and the resin is pref. a polyester. The strand being under tension allows any elongation forces before they are applied to the optical fibres.

Description

 OPTICAL FIBER TRANSMISSION CABLES WITH REINFORCEMENT.

 The present invention relates to optical fiber transmission cables provided with armatures; it also relates to the armatures of such cables and the method of manufacturing cables and armatures.

 According to the prior art, optical fiber transmission cables generally comprise one or more optical transmission fibers provided with one or more sheaths or sheaths of synthetic resin.

 In addition, in order to provide them with the necessary mechanical resistance, such cables are also provided with mechanically resistant elements forming reinforcements.

 In particular, optical fiber transmission cables are inevitably subjected to voltage charges during their manufacture, handling, installation and, in many cases, during the service life of these cables. For example, when such cables are stretched in suspension between two pillars or towers or the like, or when they are installed in galleries or channels, it is necessary to exert on them significant traction forces. Tensioned and suspended cables are also subjected to tension loads resulting from the weight of the cables themselves but also from atmospheric conditions, such as wind, ice, etc.

 To this end, the cables for transmission by optical fibers are provided with reinforcements taking charge of these tension forces so as to avoid breaks, relatively weak optical fibers on the mechanical level.

 Providing such reinforcements presents various difficulties.

For example, if the armatures must be of an electrically nonconductive nature to avoid a danger due to lightning when the cables are suspended in the atmosphere, armatures made of electrically conductive metals such as aluminum or steel are not suitable. .

It has also been proposed in the prior art to provide optical transmission cables with non-mechanical reinforcing elements, in the form of helical polyaramide wires, for example such as those known in the art under the brand KEVLARe from the firm DuPont from Nemours, covered with polytetrafluoroethylene tape (see for example "Modern Plastics,
July 1978, p. 38-41, and "Design Engineering", March 1979). A sheath or a sheath of one or more layers of suitable material such as polyethylene is then provided around the reinforcing elements.

 However, one of the advantages in the use of KEVLARX type polyaramid fibers lies in the fact that these fibers are made of highly oriented polyaramid filaments and, consequently, are flexible, and such flexible fibers are inconvenient when used for he reinforcement of optical fiber transmission cables lies in the fact that, when they are associated with a sheath made of synthetic resin material, the latter shrinks during heat treatment or vulcanization.

This retraction causes a tendency of the reinforcements to buckle.

Consequently, when the cable is subjected to a tension load, the load is not immediately supported by the reinforcements. In fact, there is a delay until the reinforcements return to normal and take over the stresses, so that part of the load is supported during this delay by the optical fiber or fibers of the cable.

 The object of the present invention is to avoid these drawbacks by resorting to prestressing of the reinforcements and, in particular, to permanent tensioning of fibers, so that at the time of use, the tension loads are immediately recovery without delay by the reinforcements.

 The present invention therefore relates to optical fiber transmission cables provided with new and improved cable frames.

 According to a preferred embodiment of the invention, a fiber optic transmission cable is provided with a special reinforcement system and comprises a bundle of glass fibers maintained or embedded in synthetic resin heat treated or vulcanized and maintained under tension by the synthetic resin which is thus prestressed by the beam. The reinforcements used preferably have a tensile modulus of 2.8 to 4.2.106 N / cm2.

 According to a preferred embodiment of the invention, the reinforcements can, for example, extend parallel to the longitudinal axis of the cable and be linked to an extruded sheath.

 According to another preferred embodiment of the invention, the reinforcements can, for example, be arranged along the axis of the cable in the central position, a serine of optical fibers being distributed uniformly all around the central axis and spaced radially of the axial reinforcements.

In this case, the sheath can be formed with grooves or external longitudinal depressions in which the optical fibers are placed, a second synthetic resin sheath then being applied around the assembly formed by the optical fibers and by the first sheath. .

According to a preferred variant of the invention, the reinforcements can be wound in a helix around a central core comprising one or more
optical transmission fibers and sheathing.

The present invention also relates to a method of manufacturing a reinforcement for a fiber optic transmission cable comprising the
following phases: - tensioning of glass fibers, - coating of the glass fiber bundle in a liquid synthetic resin, - passage of the glass fiber bundle thus coated in a hole provided
in a plate to remove excess synthetic liquid resin
found on the surface, - heat treatment of the liquid synthetic resin, - while the bundle of glass fibers is kept under tension, - while a reinforcement or special reinforcements are created in
which the beam is kept in pretension by the resin
synthetic.

 To better understand the technical characteristics and advantages of the present invention, we will describe the embodiments, it being understood that these are not limiting as to their mode of implementation and the applications that can be make it.

We will refer to the following figures which schematically represent:
Figure 1, a side view of a fiber optic transmission cable whose components have been successively torn off.

 Figure 2, a sectional view along line II-II of the cable shown in Figure 1.

 Figure 3, a production line for the manufacture of the cable as shown in Figure 1.

Figures 4 to 6, the various elements of Figure 1 during the successive phases of the manufacturing process; and
Figures 7 to 10, sectional variants of cables according to the present invention.

The fiber optic transmission cable shown in Figures 1 and 2 according to a preferred embodiment of the invention is generally
indicated by reference 10.

The core or heart of the cable 10 is formed by a longened reinforcement
line and continuous 11 constituted by a bundle of glass fibers embedded in heat-treated polyester resin.

In what follows and for simplicity, we will use the expression
"heat treatment" or those derived therefrom to denote both
simple heat treatments as neighboring treatments such as vulcanization.

 The frame 11 extends axially inside a sheath 12 of heat-treated synthetic material, the frame 11 and the sheath 12 being linked together as will be described below.

 The periphery of the internal sheath 12 has eight longitudinal grooves or depressions 14 in which eight optical transmission fibers 15 are placed.

 An external sheath 16 of synthetic resin envelops the assembly constituted by the optical fibers 15 and the internal sheath 12.

 FIG. 3 shows the successive stages in the manufacture of the cable 10 shown in FIGS. 1 and 2.

 As shown in FIG. 3, a bundle of glass fibers 18 is unwound from a supply reel 19 and passes into a bath indicated as a whole by the reference number 20.

 The guide rollers 21 are provided for guiding the bundle 18 through the bath 20 and, more particularly, through the liquid polyester resin 22.

 At the exit from the bath 20, the bundle 18 embedded and coated in the liquid polyester resin 22 passes through a plate 24 whose circular orifice corresponds to the shape of the coated bundle so as to remove the excess liquid polyester resin 22 at the network area 18.

The bundle 18 and the remaining liquid polyester resin 22 coating the bundle 18 then pass through the heat treatment oven 25 which hardens the polyester resin, so that at the end of this manufacturing phase, the bundle 18 and the polyester resin heat treated constitute a set of reinforcements, the circular section of which is shown in the
Figure 4.

 The bundle 18 is drawn through the bath, the perforated plate 24 and the heat treatment oven 27 by traction rollers 26 acting on the assembly 11. A tension or braking system 27 is provided between the supply coil and the bath 20 for energizing the beam 18.

 Consequently, during its passage through the bath 20, the pierced plate 24 and the oven 25, the beam 18 is kept under tension by the system 27, on the one hand, and by the perforated plate 24, on the other hand, and this tension which can reach in practice for example 100 to 200 g is maintained during the heat treatment of the synthetic resin.

 The frame 11 is thus manufactured in the prestressed state.

 If desired, this frame 11 can, at this stage of the process, be returned on a reel for storage or transport, for example to another factory. However, to facilitate understanding, Figure 3 shows the armature 11 passing directly from the treatment furnace 25 to the extrusion machine 28, although, as has just been said, the extrusion can be carried out in the machine 28 in a unit different from that of the heat treatment oven 25.

 In this extrusion machine 28, an internal sheath 12 is produced around the central frame 11, this sheath having grooves or longitudinal pressures 14, as shown in FIG. 5. As it cools, this sheath 12 hardens and its constituent material tends to retract on the frame.

 A connection between the sheath and the frame therefore essentially occurs due to the retraction of the material constituting the sheath on the frame 11.

 Furthermore, when the armature is manufactured as a corm, it has been described above by pulling the bundle of coated glass fibers through the orifice, and by treating the assembly thermally, the armature does not, in practice , a smooth outer surface and a uniform circular section but, on the contrary, has a rough surface and an irregularly shaped section when considered along its length. This rough surface and its variations in section increase the liaisosentre the sheath and the frame.

 Experience has shown that very satisfactory results are also obtained by manufacturing the reinforcement by the well-known method of tensile extrusion instead of the passage of the fiber bundle through an orifice, and that according to this method obtains a good connection between the cladding and the reinforcement, which in this case has a smooth surface and a uniform section.

 Again here, the frame 11 coated with the sheath 12 can, after this manufacturing phase, be returned for storage or transport, for example to another factory. However, still to simplify the understanding, FIG. 3 shows the assembly constituted by the armature and the internal sheathing carried out directly towards the next phase of manufacturing the cable according to the invention.

 Referring again to Figure 3, during this new phase of the manufacturing process, the optical transmission fibers 15 are unwound from supply coils 29 and guided by the rollers 30 to be inserted in the grooves 14 or equivalent system presented by the internal sheath 12, as shown in FIG. 6.

The assembly thus formed then passes through a second extrusion machine 31 where a new external sheath 16 is extruded around the assembly formed by the transmission fibers 15 and the sheath 12 provided with its armature.

The sheath 16 is then cooled and hardened thereby.

 The cable 10 thus obtained is then guided at 33 to be returned at 34.

 The armature 11 has sufficient tensile strength to protect the optical transmission fibers 15 from any tensile load during the manufacture, installation and commissioning of the optical fiber transmission cable.

 This is why, according to a preferred embodiment of the invention and for this purpose, the armature 11 is manufactured with a tensile modulus of the order of 2.8 to 4.2.106 N / cm2, and a resistance tensile strength 49,000 to 140,000 N / cm2. The tensile modulus and tensile strength of the reinforcement 11 are as high as possible so as to minimize the quantity of reinforcement required, which reduces the cost price. and the space occupied.

To this end, experience has shown that excellent reinforcement with a diameter of the order of 9/10 mm can be produced. However, the invention is in no way limited to the choice of this diameter, since excellent results have been obtained with other diameters ranging in particular from 5 to 18 / 10ths of a mm. We can even go beyond this range and reach, for example, a diameter of the order of 3 mm.

 The characteristics and the bending required for the reinforcement depend on the type of construction which has been chosen for the cable, as well as on the dimensions and the materials constituting the cable. However, in general, the reinforcement must have a sufficient stiffness to resist the tendency to loop during the cooling of the internal extruded sheath 12, but this reinforcement must also be flexible enough to allow the winding and installation of the cable. .

 The stiffness of the frame can easily be defined by an appropriate choice of the percentages of glass fibers and of synthetic resin in this frame and by the choice of the type of synthetic resin used to coat the glass fibers or to drown them.

 It has been determined that satisfactory results were obtained when the entire finished reinforcement had a flexural modulus of 0.7 to 4.106 N / Lm2 approximately, and a tensile strength at break of 17,000 to 100 000 N / cm2.

 The glass fiber content of the entire frame is preferably of the order of 60 to 80, re by weight.

 Excellent results have been obtained with mixtures of resins for the reinforcement containing a rigid unsaturated isophthalic polyester resin modified by the addition of a flexible polyester resin containing a saturated aliphatic acid. The degree of flexibility of the finished reinforcement depends on the ratio between these polyester resins and, in fact, these blends can range from 100% of unsaturated isophthalic resin to 100% of resin containing saturated aliphatic acid. Particularly satisfactory results have been obtained with mixtures containing 20% of resin itself containing aliphatic acid.

 It is obvious that many thermosetting materials can be used, making it possible to achieve very diverse ranges of flexibility which depend essentially on their degree of crosslinking or bridging, so that the invention cannot be limited to resins which have been listed above.

 In order to reduce the differential thermal expansions or expansions of the armature 11 and the optical transmission fibers 15 and thus to reduce or even entirely eliminate the internal tensions due to variations in ambient temperatures, the glass fibers of the armature are chosen. preferably with a coefficient of linear thermal expansion as close as possible to that of the fibers 15 and, preferably, of the order of 5.X 10-6 / "C.

 The cable variant illustrated in FIG. 7 and indicated as a whole by, the reference number 40 has a central core constituted by the armature 41 similar to the armature 11 of FIGS. 1 and 2.

The sheath 43 of synthetic resin has a circular peripheral section and surrounds both the armature 41 and a certain radial distance from the latter of the optical transmission fibers 44.

 According to the variant shown in Figure 8, a single optical transmission fiber 50 constitutes the core of the cable and is embedded in the sheath 51 of synthetic resin, a series of frames 52 also being embedded in the sheath 51, these frames 52 being radially spaced from the optical transmission fiber 50 and being evenly spaced angularly about the axis. If necessary, the single optical transmission fiber 50 can be replaced by a series of such fibers or a bundle of such fibers.

 The cable shown in Figure 9 has similarities to that of Figures 1 and 2. However, in the case of the cable of this Figure 9, the core consists of an optical transmission fiber 61 surrounded by an internal sheath 62 corresponding substantially to the sheath 12 of Figures 1 and 2.

 Eight reinforcements 63 are arranged in the grooves where longitudinal external pressures of the periphery of the internal sheath 62 and an external sheath 64 of synthetic resin surround all of the reinforcements 63 and of the sheath 62.

 In each of the embodiments of the invention which is the subject of FIGS. 7 to 10, the reinforcement or each of the reinforcements is constituted by a bundle of continuous glass fibers, impregnated, embedded or coated in synthetic resin heat treated , as it is said in connection with Figure 3 or by the process of extrusion under tension and the reinforcement or each reinforcement is bonded to the adjacent synthetic resin constituting the sheaths, as described above.

 Figure 10 shows a cable indicated as a whole under the reference 70 having an axial optical transmission fiber 71 embedded in an internal sheath 72 of synthetic resin. In this case, eight reinforcements 73a, 73b are wound in a helix around the internal sheath 72 without being linked to it so as to form a weave around the sheath 72 and the optical transmission fiber 71 and to protect them against screen - during the cable installation. The nine plates 73a are wound helically in the opposite direction to that of the nine plates 73b.

 Two layers wound in opposite directions 74 of polyester adhesive tape are wrapped around the reinforcements and wrapped, in turn, by an extruded external sheath 75.

The tensile strength and the crushing strength of the cable shown in Figure 10 are defined:
a) by the flexibility of the reinforcements,
b) by the number of reinforcements, and
c) by the helix winding angles of the reinforcements around the
internal sheath.

 With regard to point c) above, when the helical winding angle is increased, the ability of the reinforcements to withstand tensile loads in the axial direction decreases.

 In this way, by a correlation and a predetermination of the factors a), b) and c), it is possible to predetermine the effective tensile strength and the crushing resistance of the reinforcements taking into account the requirements of the intended applications.

 The reinforcements 73a, 73b are made as described with reference to FIGS. 1 to 9 and are wound under tension on the sheath 72.

After the winding operation, the reinforcements are kept under tension by the sheathing.

 Also, the helical winding angle of the reinforcements 73a is equal but opposite to that of winding the reinforcements 73b for reasons of symmetry.

 In the embodiments of the invention described above, polyethylene sheathings are preferably used. However, any other suitable material can be used, for example thermoplastic elastomers.

 Of course, the present invention is in no way limited to the embodiments described and shown; it is susceptible of numerous variants accessible to those skilled in the art, depending on the applications envisaged and without departing from the spirit of the invention.

 In the foregoing, the expression optical fiber taken in its general sense may contain a set or a bundle of unit fibers.

The same goes for glass fibers.

Claims (30)

 1.- Fiber optic transmission cable comprising: - at least one optical fiber, and - at least one continuous and elongated reinforcement, characterized in that the reinforcement comprises a bundle of glass fibers coated in a heat-treated synthetic resin or vulcanized and maintained in a pretension state only by the synthetic resin, said reinforcement having a tensile modulus of 280 to 420,000 bars, and said cable comprising at least one sheath of synthetic resin extruded around the assembly formed by the optical fiber and said frame.  2.- transmission cable according to claim 1, characterized in that said annature has a tensile strength of 4,900 to 14,000 bars.  3.- transmission cable according to claim 1 or 2, characterized in that the armature has a flexural module from 70,000 to 400,000 bars.  4.- transmission cable according to any one of claims 1 to 3, characterized in that the frame comprises 60 to 80% by weight of glass fibers.  5. Transmission cable according to any one of claims 1 to 4, characterized in that the resin is a polyester-based resin.  6. Transmission cable according to any one of claims 1 to 5, characterized in that the coefficient of thermal linear expansion of the armature is substantially equal to that of the optical fiber.  7.- transmission cable according to claim 6, characterized in that the armature has a coefficient of linear thermal expansion of the order of 2 x 10-6 / C.  8.- transmission cable according to any one of claims 1 to 7, characterized in that the armature extends along the axis of said cable and that the optical fiber is constituted by a series of unitary optical fibers distributed uniformly around the axis and radially spaced from the central frame.  9. A transmission cable according to claim 8, characterized in that said sheathing is constituted by a first sheath surrounding said reinforcement and having a series of grooves or longitudinal external pressures receiving the optical fibers, a second sheath of synthetic resin surrounding l 'all optical fibers and the first sheath.  10.- transmission cable according to any one of claims  1 to 7, characterized in that the optical fiber is arranged axially on  the cable and that the reinforcement consists of a set of reinforcements in  dividends distributed uniformly around the central optical fiber  and radially spaced from the latter.  11.- transmission cable according to claim 10, characterized in  what the cladding consists of a second sheath surrounding a first  sheath which, in turn, surrounds the optical fiber, said first sheath pre  feeling at its periphery a series of grooves or longitudinal depressions  receiving said optical fibers thus inserted between the two sheaths,  said first sheath being made of synthetic resin.  12.- transmission cable according to claim 8 or 9, characterized  in that the optical fibers and the armatures are embedded in the sheathing.  13.- Fiber optic transmission cable, characterized in that it includes  a continuous slender frame, said frame being made of heat-treated or vulcanized synthetic resin,  a bundle of glass fibers coated in said synthetic resin and placed  in a pretensioning state only because of said resin, - said frame having a tensile modulus of 280,000 to 420,000 bars, - a first sheath of synthetic resin, - a series of optical fibers distributed around the first sheath, and - a second sheath of synthetic resin extruded around the assembly  consisting of optical fibers and the first sheath.  14.- Transmission cable, characterized in that it comprises:  - at least one optical fiber,  - a first synthetic resin sheath formed around at least one  optical fiber, - a series of separate individual frames wound in a helix in  opposite directions and under tension around the first sheath, ~ said individual reinforcements each comprising a bundle of fibers  of glass under tension and a coating of heat-treated synthetic resin  or vulcanized coating said bundle and maintaining it in pretensioning state, - said reinforcements having a tensile modulus of 280,000 to 420,000 bars, ~ and a second sheath of synthetic resin formed around said  reinforcements and said first sheath.  15.- In a process for manufacturing optical fiber transmission cables comprising the contribution of the optical transmission fiber and a sheath of synthetic resin, the improvement is characterized by the following phases of the process: - impregnation or coating of the fiberglass bundle by resin  synthetic, - heat treatment or vulcanization of said synthetic resin, - beam under tension during heat treatment of  said synthetic resin to constitute a separate reinforcement consisting  by combining said bundle and said treated synthetic resin  thermally, said synthetic resin heat treated now  said beam in pretensioning state, and - combination of said armature with said optical transmission fiber  and said sheath.  16.- Method according to claim 15, characterized in that the phase of combining the optical transmission phase and the sheath with the armature comprises the extrusion of said sheath on said armature and the cooling of said sheath.  17.- Method according to claim 16, characterized in that a series of grooves under longitudinal external pressure circumferentially spaced on the surface of said sheath is formed, that there is in each of them an optical fiber and that the another synthetic resin sheath is formed around the assembly formed by the optical fibers and the first sheath.  18.- Method according to claim 15, characterized in that the phase of combining the optical transmission fiber and the sheath with said armature comprises the formation of said sheath around said optical fiber and then the helical winding of said reinforcement under tension around said sheath.  19.- Method according to claim 15, characterized in that it includes the passage of said bundle successively in a bath of synthetic resin to coat said bundle in an orifice to remove excess resin from said bundle and in a heat treatment oven resin remaining on said beam.  20.- A method according to claim 15, characterized in that the synthetic resin comprises a rigid unsaturated isophthalic polyester resin modified by addition of a flexible polyester resin containing a saturated aliphatic acid.  21.- A method of manufacturing a frame for an optical fiber transmission cable, characterized in that it comprises the following steps: - putting a bundle of glass fibers under tension, - coating said bundle of glass fibers with synthetic resin  liquid, - passage of said bundle of glass fibers coated with an orifice for  removing the excess of liquid synthetic resin which is formed therein, and - heat treatment of said liquid synthetic resin, while  the bundle of glass fibers is kept under tension to form  a separate individual frame in which said beam is  maintained in pretension state only under the effect of said resin  synthetic.  22.- Method according to claim 21, characterized in that the bundle of glass fibers constitutes 60 to 80% by weight of said frame.  23.- Method according to claim 21 or 22, characterized in that the synthetic resin, .comprends a rigid unsaturated isophthalic polyester resin modified by a flexible polyester resin containing a saturated aliphatic acid.  24.- Separate individual reinforcement for optical fiber transmission cables, characterized in that it comprises: - a bundle of glass fibers, and - a heat-treated or vulcanized synthetic resin coating said  beam, - said beam being kept under tension only under the effect of  said synthetic resin, said reinforcement having a tensile modulus of 280,000 to 420,000 bars.  25. Armature according to claim 24, characterized in that it has a tensile modulus of 70,000 to 400,000 bars.  26.- Reinforcement according to claim 25, characterized in that it has a tensile strength of 4,900 to 14,000 bars.  27.- Reinforcement according to claim 25, characterized in that it has a coefficient of linear thermal expansion of the order of 5 x 10-6 bars / C.  28.- Reinforcement according to claim 26, characterized in that it has a coefficient of linear thermal expansion of the order of 5 x 10-6 bars / C.  29.- Reinforcement according to claim 25, 26 or 27, characterized in that it comprises 60 to 80% by weight of bundle of glass fibers.  30.- Reinforcement according to claim 25, 26 or 27, characterized in that the synthetic resin comprises an unsaturated isophthalic polyester resin modified by addition of a polyester resin containing a saturated aliphatic acid.