FR2605019A1 - Method and device for cladding a filament, in particular an optical fibre - Google Patents

Abstract

The cladding of a filament 10, such as an optical fibre, is obtained by means of a die 36, through which the filament 10 can be moved vertically, a tank 68 being provided in order to supply the die with a coating material in the liquid state. The die 36 is supported by a float 34 of general annular shape which surrounds the filament 10, and which is placed at the surface of a fluid medium 32 such as water.

Description

Method and device for sheathing a wire, in particular an optical fiber.

The invention relates to a method and a device for sheathing a wire, in particular an optical fiber.

Processes of this kind are already known in which the wire is moved vertically through at least one die supplied with a coating material in the liquid state, for example a resin capable of forming a plastic sheath.

One of the typical applications of these methods is the sheathing of optical fibers, that is to say an operation consisting in applying a protective sheath around the optical fiber which is already made up in itself by a core. surrounded by a sheath.

The purpose of this protective sheath is in particular to improve the mechanical strength and the corrosion resistance of the optical fibers and also to facilitate the connection of the optical fibers to each other.

This protective sheath is usually applied during an operation, known as a "fiberizing operation", consisting, starting from a preform, of drawing a wire continuously by means of a traction device of the capstan type, the preform being brought to an appropriate temperature to allow it to be stretched hot.

During its stretching, the wire is moved vertically up and down, and it is on this vertical displacement path that the sheath is applied around the wire being stretched.

For this, at least one die is used through which the wire is passed, this die being supplied with a suitable coating material, for example a photocrosslinkable resin.

The optical fiber thus coated with this sheath then passes through a drying oven to allow the hardening of the coating material, for example the crosslinking of the resin, around the fiber, and thus obtaining the sheath.

The optical fiber provided with its sheath is then wound on spools for storage.

One of the major problems posed by the sheathing operation is that of obtaining a correct centering of the sheath around the wire.

In the particular case of optical fibers, it has been observed that a defect in centering the sheath has a very harmful influence on the mechanical strength, the corrosion resistance and the connection of the fibers to each other.

Various solutions have already been proposed in the prior art with a view to obtaining correct centering of the sheath around the wire.

One of the known methods consists in very precisely defining the fiberizing axis, that is to say the vertical axis of displacement of the optical fiber during stretching, then positioning the die so that in the absence of coating material, the fiber is centered exactly in the axis of the nozzle of the die, and then to put the coating material in the die at a controlled and constant temperature to obtain a known and stable viscosity .

This known method makes it possible to obtain suitable centering of the sheath around the fiber, but it requires particularly sophisticated equipment.

Indeed, to precisely define the fiber axis, the fiber axis, which will be the fiber axis, is noted at three points along two orthogonal axes, using networks of photodiodes lit by beams luminous. The fiber drawings appear on oscilloscope screens, which makes it possible to record the position of the fiber using cursors.

When the fiberizing axis has been raised, you must position both the preform support and the die so that they are correctly aligned on the fiberizing axis.

This alignment requires the use of micromotors controlled by a microcomputer.

 It should be noted that another drawback of this known method lies in the fact that a periodic inspection of the fiberizing axis must be carried out in order to ensure that the die is always correctly aligned on the fiberizing axis. .

In another known method, part of the means for implementing the preceding method is used. This process consists of adjusting the position of the preform and prepositioning the die on a stable support.

This process does not give constant satisfactory results. In addition, it has the disadvantage of requiring to withdraw the die at the end of each fiberizing operation for cleaning, so that one can not be assured with certainty that the die will then be returned to its original location.

Another method has been proposed for overcoming anomalies resulting from a variation in the position of the fiberizing axis, during the fiberizing operation, caused by a non-rectilinear preform. This known method uses a second die which is arranged above the die carrying out the sheathing operation, in order to constitute a fixed point through which the fiber must pass before the sheathing operation.

This known method has the drawback in particular of requiring the dismantling of the two dies at the end of each fiberizing operation with a view to cleaning them. Again, it cannot be guaranteed with certainty that the dies will then be returned to their original positions.

All of these known solutions have in common the use of complex means for carrying out the sheathing and of frequently requiring adjustments, in particular at the start of a new manufacturing operation.

The invention aims in particular to avoid these drawbacks.

It is one of the objects of the invention to provide a method and a device making it possible, with very simple means, to obtain the correct centering of a sheath around a wire, such as an optical fiber.

It is another object of the invention to provide such a method and such a device, in which the centering can be obtained automatically, without the need for complicated adjustments.

According to a first aspect, the invention relates to a method for the sheathing of a wire, in particular an optical fiber, in which the wire is moved vertically through at least one die supplied with a coating material to the liquid state, characterized in that said die is fixed to a float of generally annular shape which surrounds the wire and which is placed on the surface of a fluid medium.

The use of a floating die allows the latter to self-center around the fiber, that is to say to make the axis of displacement of the yarn coincide, or fiberizing axis, and the axis of the sector. This self-centering is obtained thanks to the restoring force obtained by the reaction of the fluid medium on which the float attached to the die is placed.

 According to the invention, the wire can be advanced either through a single die or through a double die. The use of a double die appears to be more advantageous since it makes it possible in particular to eliminate the bubbles liable to form in the coating material applied in the liquid state around the wire.

According to another characteristic of the invention, the die is supplied by a vertical cylindrical flow of the coating material in the liquid state, this flow being centered approximately around the axis of movement of the wire and flowing from '' a supply tank placed above the die.

According to another aspect, the invention relates to a device for implementing the method. This device for sheathing a wire, in particular an optical fiber, comprising at least one die through which the wire is vertically movable, as well as means for supplying the die with a coating material in the liquid state, is essentially characterized by the fact that it comprises a float of generally annular shape suitable for surrounding the thread and for supporting the die, and a receptacle suitable for containing a fluid medium on the surface of which the float is placed.

In a preferred embodiment of the invention, the container has a generally annular shape and contains a liquid medium such as water.

The float is advantageously constituted by a one-piece element, for example obtained by molding a plastic material such as dense polystyrene, this one-piece element comprising an annular body on which a frustoconical wall depends internally, the upper edge of this wall being attached to the body and its lower edge forming a support for the die.

Advantageously, the die is arranged in such a way that the center of gravity of the float-die assembly, when the die is filled with the coating material in the liquid state, is practically at the level of the water line of the float.

In a preferred embodiment of the invention, the means for supplying coating material in the liquid state comprise a supply tank equipped with a positive displacement pump and means for maintaining the coating material at a determined temperature. , support means being provided to maintain the reservoir in a fixed position above the die.

In the description which follows, given only by way of example, reference is made to the appended drawings, in which - FIG. 1 is a schematic view of an installation for manufacturing optical fibers, in which a sheathing device is provided according to the invention; - Figure 2 is a vertical sectional view of a double die cladding device according to the invention; and - Figure 3 is a detail, on an enlarged scale, of Figure 2.

First of all, reference is made to the installation shown in FIG. 1 which makes it possible to manufacture an optical fiber 10 by hot stretching from a preform 12. This preform 12 is heated by means of an oven 14 to allow stretching the optical fiber to an appropriate temperature. The fiber being stretched is moved vertically, from top to bottom, passing around a return pulley 16 and a capstan 18 suitable for exerting traction on the fiber. This fiber is then wound up. The fiber being stretched, after leaving the oven 14, is provided with a sheath by means of a sheathing device 20 according to the invention. On leaving said device 20, the sheathed wire passes through an oven 22 intended for drying the coating material which has been applied around the fiber 10. Reference is now made to FIG. 2 which shows the structure of a device for cladding that can be used with the installation described above.

This sheathing device comprises a container 24, of generally annular shape, capable of containing a fluid medium, in the example a liquid such as water.

The container 24 is limited by an external cylindrical wall 26, an internal cylindrical wall 28, concentric with the wall 26, and an annular flat bottom 30.

On the surface of the fluid medium 32 contained in the container 24 is placed a float 34, of generally annular shape, which surrounds the wire 10 and which supports a die 36 intended to sheath the optical fiber 10.

The float 34 is a one-piece element produced, for example, by molding a plastic material such as dense polystyrene. The float comprises an annular body 38, of generally rectangular cross section, on which depends internally a frustoconical wall 40 which widens from the bottom to the top. The upper edge 42 of this frustoconical wall is attached to the upper edge of the body 38, while its lower edge 44 serves to support the die 36. More particularly, the internal face of the frustoconical wall 40 has, at the level of the lower edge 44 , an annular shoulder 46 on which the die 36 rests.

As can be seen from the drawing, the dimensions of the float and the container are chosen such that the cylindrical wall 28 of the container is in the annular space delimited by the body 38 and the frustoconical wall 40 of the float 34 .

In the example shown, the die 36 is a double die. This die comprises a cylindrical base 48 extended by an annular edge 50 suitable for coming to rest on the shoulder 46 of the float 34. The base 48 and its edge 50 are formed in one piece with a conical wall 52 which internally limits a reservoir. upper 54 for the coating material in the liquid state. The bottom of the conical wall 52 is pierced with a calibrated orifice 56 forming a die nozzle. The orifice 56 communicates with a spherical reservoir 58, or lower reservoir, delimited on the one hand by a hemispherical cavity 60 formed by the base 48 and on the other hand by another hemispherical cavity 62 formed by a hemispherical cap 64 coming from adapt to the base 48. The hemispherical cap 64 is pierced with a calibrated orifice 66 also forming die nozzle. The calibrated orifices 56 and 66 are aligned vertically when the float 34 rests horizontally on a fluid medium.

In the example, where the diameter of the bare optical fiber, that is to say without its protective sheath, is of the order of 125 micrometers, the diameter of the calibrated orifice 56 is 1.7 millimeters , while the diameter of the calibrated orifice 66 is 300 micrometers.

Advantageously, the constituent elements of the die 36 are made of brass, which makes it possible to obtain a very light die.

The float 34 and the die 36 are determined in such a way that the center of gravity of the thread float assembly, when the die is filled with the coating material in the liquid state, is practically at the level of the water line of the float 34.

 The use of a double die is particularly advantageous in that it makes it possible to eliminate the bubbles liable to form when a photocrosslinkable resin is used as coating material. The upper tank 54 serves as a bubble tank, that is to say to eliminate bubbles, while the lower tank 62 serves to obtain an overpressure of the resin, this overpressure facilitating the evacuation of the air bubbles entrained in the fiber drawing and also used for self-centering of the die, due to its spherical shape.

To allow the sheathing operation, the upper reservoir 54 of the die 36 is continuously supplied with coating material by supply means which will now be described.

These means include a supply tank 68 and support members 70 designed to hold the tank 68 in a fixed position above the die 66. The tank 68 consists essentially of two parts, namely an upper part 72 generally cylindrical and a lower portion 74 of generally frustoconical shape. The upper part 72 provides an annular surface 76 capable of cooperating with a cylindrical recess 78 formed by a horizontal support 80. This support is maintained in a fixed and adjustable position by means of two vertical axes 82 and 84, provided respectively with a nuts 86 and 88. These nuts are equipped respectively with knobs 90 and 92 used to hold the nuts at the desired height relative to the respective axes 82 and 84. Each nut, such as nut 88, is extended upwards by a threaded part 94 suitable for cooperating with a thumb wheel 96 to keep the support 80 tight against the nuts 86 and 88. For this purpose, the support 80 comprises two orifices 98 and 100 which allow the passage of the respective vertical extensions of the two nuts.

Thanks to the aforementioned support means, the reservoir 68 can be held firmly in position above the container 24 and at the desired height.

The upper part 72 of the reservoir 68 is provided with a lateral tube 102 which serves to supply the reservoir with coating material, as represented by the arrow
F1. The bottom of the upper part 72 is pierced with several orifices 104 which provide communication between the interior of the upper part 72 and the interior of the lower part 74. From the bottom of the upper part 72 depends a cylindrical well 106 which s 'extends vertically upwards and extends beyond the upper annular edge 108 of the part 72. On the edge 108 rests a cover 110 provided with a central opening 112 for the passage of the well 106. This cover 110 is part of a positive displacement pump whose blades 114 move in rotation in the annular space limited inside the upper part 72. The displacement of these blades makes it possible to force the circulation of the coating material towards the lower part of the tank by passing to through the holes 104.

The lower part 74 of the tank 68 has a frustoconical wall 118 forming the bottom wall of the tank 68, the upper edge 120 of the wall 118 cooperating by screwing with the part 72 of the tank and the lower edge 122 delimiting a circular opening 124 (Figure 3).

The wall 118 is of double thickness and provides a chamber 126 for the circulation of a fluid which penetrates into said chamber by an inlet pipe 128 and which emerges therefrom by an outlet pipe 130, as shown respectively by the arrows F2 and F3. It is thus possible to circulate a fluid, such as water, at a suitable temperature to maintain the coating material at a temperature suitable for the sheathing operation.

The reservoir 68 serves as a support for a vertical cylindrical tube 134, provided with an external coating 135, the lower end of which passes through the circular opening 124 thus providing an annular opening allowing the flow of the coating material. along the tube 134 and in the direction of the die 36. The tube 134 constitutes a distributor tube by means of which the die is supplied by a vertical cylindrical flow of the coating material in the liquid state.

The distributor tube 134 is housed inside a tube holder 136 which comprises an intermediate part 138 with external thread 140 adapted to cooperate with an internal thread 142 formed by the well 106. The tube holder 136 ends at its part lower by a bevel 144, the adjustment of the axial position of the tube holder relative to the well making it possible to adjust the flow rate of the coating material flowing along the distributor tube 134 (FIG. 3). To allow this adjustment, the tube holder 136 ends, at its upper part, with a wheel 146 which projects above the cover 110. The screwing or unscrewing of this wheel allows, as will be understood, to modify the vertical position of the tube holder with respect to the tank and, consequently, to modify the dimensions of the annular passage section around the distributor tube.

As shown in FIG. 2, it is advantageous for the lower end of the distributor tube 134 to penetrate slightly inside the upper reservoir 54 of the die 36.

In the case where one uses, instead of a double die, a single die, it suffices to place the hemispherical cap 64 -on the shoulder 46 of the float 34 and to modify the adjustment of the device so that the ex - lower end of the distributor tube 134 penetrates inside the tank delimited by the cap 64.

A sheathing device according to the invention, using a single die or a double figure, allows excellent centering of a coating sheath around a wire, such as an optical fiber, as shown by the two. following examples
Example 1.

In this example, a simple die is used, consisting of a hemispherical die analogous to the cap 64 shown in FIG. 2. This hemispherical die of very light weight (8 to 10 grams) pierced with a hole calibrated to 300 micrometers) is positioned on the annular float 34 floating in the container 24 filled with water.

As soon as the fiber leaving the fiberizing oven reaches a diameter of 110 micrometers, it is threaded through the die and stretched to the capstan. At the start of the test, the running speed of the fiber is approximately 6 meters per minute, this speed being insufficient for the die-float assembly to be able to center correctly around the fiber.

The supply tank of the device is then supplied with a photocrosslinkable resin having a viscosity of 6200 mPas at 250C.

As soon as the coating of the fiber begins, the fiber drawing speed is brought to 10 meters per minute and immediately the die-float assembly self-centers in the fiber axis. The fiber drawing speed is then accelerated to a value of 50 meters per minute, the diameter of the fiber being maintained at 125 micrometers. The die-float assembly stabilized perfectly as soon as the fiber drawing speed reached a value of 25 meters per minute.

 During the fiberizing operation, different samples of fibers were taken in order to determine the value of the eccentricity of the sheath relative to the optical fiber.

For fiber drawing speeds of 20 meters per minute, 40 meters per minute and 50 meters per minute, the measured eccentricity was approximately 5%, 3.5% and 2% respectively.

After having set the speed of the capstan again to a value of 40 meters per minute, and after having voluntarily deported the 5 mm float-die assembly off the fiber-drawing axis, it appeared that one immediately obtained an offset of approximately 60%. After release of the float-die assembly, it returned very quickly to an equilibrium position in which the centering of the sheath was correct.

EXAMPLE 2.

In this example, a double floating die is used as shown in FIG. 2.

As already indicated, the use of a double die makes it possible to reduce the number of bubbles in the coating resin and to improve the homogeneity of the sheath applied around the fiber.

In this example, the double die, made of brass, weighs approximately 70 grams. The upper reservoir has an opening of 1.7 millimeters in diameter and the lower spherical reservoir an opening of 300 micrometers. The double die is positioned on the float so that the center of gravity of the assembly is practically at the level of the waterline. The initiation of the fiberizing is carried out as in Example 1 above. The resin supply means are then started up, as described above.

The whole of the double die and the float self-center a little more difficult than in the first example, the weight to be moved being greater. When the fiber drawing speed reaches a value of 25 to 30 meters, a correct centering of the sheath around the fiber is obtained. For example, for a fiber drawing speed set at 50 meters per minute, the offset is around 2%.

 The invention thus makes it possible, by particularly simple means, to obtain perfect centering of a sheath around a wire.

Although the invention has been described with particular reference to the cladding of optical fibers, it generally applies to the cladding of any type of moving wire.

Also, the method and the device of the invention allow the sheathing of several wires to be carried out simultaneously by means of several channels used in parallel.

Claims (18)

Claims. 1. Method for sheathing a wire, in particular an optical fiber1 in which the wire (10) is displaced - vertically through at least one die (36) supplied with a coating material in the liquid state, characterized in that said die (36) is fixed to. a float (34) of generally annular shape which surrounds the wire (10) and which is placed on the surface of a fluid medium (32). 2. Method according to claim 1, characterized in that one moves the wire (10) through a simple dies. 3. Method according to claim 1, characterized in that one moves the wire (10) through a double die. 4. Method according to one of claims 1 to 3, characterized in that one feeds the die (36) by a vertical cylindrical flow of coating material in the liquid state, this flow being centered approximately around the axis of movement of the wire (10) and flowing from a supply tank (.68) placed above the die (36). 5. Method according to one of claims 1 to 4, characterized in that the coating material in the liquid state is maintained at constant temperature and circulated by a positive displacement pump (114). 6. Method according to one of claims 4 and 5, characterized in that one adjusts the flow rate of the cylindrical flow flowing from the supply tank (68). 7. Method according to one of claims 1 to 6, characterized in that the fluid medium (32) on the surface of which is placed the float (34), is a liquid such as water. 8. Method according to one of claims 1 to 7, characterized in that the coating material is a plastic material obtained from a photocrosslinkable resin. 9. Method according to one of claims 1 to 8, characterized in that the sheathing of several wires (10) is carried out simultaneously by means of several dies used in parallel. 10. Device for implementing the method according to one of claims 1 to 9, for the sheathing of a wire (10), in particular of an optical fiber, and comprising at least one die (36) through which the wire (10) is vertically movable as well as means (68) for supplying the die with a coating material in the liquid state, characterized in that it comprises a float (34) -of generally annular shape suitable for surrounding the wire (10) and to support the die (36), as well as a container (24) suitable for containing a fluid medium (32) on the surface of which the float (34) is placed. 11. Device according to claim 10, characterized in that the container (24) has a generally annular shape and contains a liquid medium (32) such as water. 12. Device according to one of claims 10 and 11, characterized in that the float (34) is a one-piece element produced for example by molding a plastic material such as dense polystyrene, the float comprising an annular body (38 ) on which depends internally a frustoconical wall (40), the upper edge (42) of this wall being attached to the body (38) and its lower edge (44) forming a support for the die (36). 13. Device according to one of claims 10 to 12, characterized in that the die (36) is arranged such that the center of gravity of the float-die assembly, when the die is filled with the material of coating in the liquid state, is practically at the level of the waterline of the float (34). 14. Device according to one of claims 10 to 13, characterized in that the die (36) is a simple die comprising a reservoir delimited by a hemispherical cap (64) whose bottom is pierced with a calibrated orifice (66) constituting the nozzle of the die. 15. Device according to one of claims 10 to 13, characterized in that the die (36) is a double die comprising an upper reservoir (54) delimited by a conical wall (52) whose bottom is pierced with an orifice calibrated (56) forming die nozzle and communicating with a spherical reservoir (58), the bottom of which is pierced with a calibrated orifice (66) forming die nozzle, the two calibrated orifices (56, 66) being aligned vertically. 16. Device according to one of claims 10 to 15, characterized in that the means for supplying coating material in the liquid state comprise a supply tank (68) equipped with a positive displacement pump and means ( 126, 128, 130) to maintain the coating material at a determined temperature, support means (70, 80) being provided to maintain the reservoir in a fixed position above the die. 17. Device according to claim 16, characterized in that the reservoir (68) comprises a conical bottom wall (118) provided with a circular opening (124) and means for internally supporting a distributor tube (134) passing through through said circular opening, providing an annular opening allowing the flow of the coating material along the tube (134) and in the direction of the die (36).  18. Device according to claim 17, characterized in that the distributor tube (134) is housed inside a tube holder (136) which comprises an intermediate part (138) with external thread (140) adapted to cooperate with an internal thread (142) of a well (106) placed inside the tank, the tube holder ending at its lower part by a bevel (144), the adjustment of the axial position of the tube holder by relative to the reservoir for adjusting the flow rate of the coating material along the distributor tube (134).