FI67148B - FOERFARANDE FOER FRAMSTAELLNING AV EN OPTISK KABEL - Google Patents

Description

1 67148

A method of making an optical cable

The invention relates to a method of manufacturing an optical cable comprising a core part, a support and an outer sheath, in which method - a hollow tube comprising a plurality of cavities is extruded onto a central support, - a repetition of cavities is formed placing the fibers in the cavities either in connection with extrusion or by cutting the cavities open along the length of the pipe and guiding the fibers from the incisions into the cavities; and 15 - providing the cable with an external shield.

In practice, optical fibers must always be wired, ie surrounded by a protective structure. This is due to the sensitivity of the fibers to mechanical stresses. Various stresses, such as tension, torsion and bending, can weaken the fibers mechanically and cause very detrimental changes to the optical transmission properties of the fibers, especially the attenuation. Also, to enable installation, the fibers must be surrounded by a sheath structure, as the total diameters of the fibers are in the order of hundreds or less.

25 The cabling aims, for example, at: - strengthening the fibers against mechanical stress, - protecting the surface of the fibers, preventing abrasion and cracking, 30 - equalizing the stresses in the manufacture of the fibers (long-term stability of the structure), - stabilizing the thermal properties, and moisture, 35 - enabling installation and identification, and - preventing external and inter - fiber radiation.

2 67148

In conventional optical cables, fibers shipped either bare or shielded by a very thin primary shielding film (5-10) (polymer film) formed during manufacture must each be individually shielded. As such a protective sheath, a filled plastic layer, a foam layer or a plastic tube is used. The formation of these protective structures around the fiber is often very difficult due to the sensitivity of the fiber to both mechanical and thermal stresses.

The fibers can also be wired directly into various optical cable structures, e.g., as described in U.S. Patent 4,038,489, where the fibers are arranged in the cavities of a plastic tube extruded around a central support. These cavities are then formed with a continuous thread around the cable 15 to improve the mechanical bending strength of the cable. In this case, the cable can also be subjected to tensile stress without being applied to the optical fibers.

However, an extruder with a rotating extrusion head is required to make the cable 20 of said U.S. Patent 4,038,489. Thus, the fibers you learn must be fed into the cavities in precise synchronization with the rotation of the extrusion head. However, such equipment imposes limitations on manufacturing speed and requires high capital costs.

In addition, as already mentioned, the fibers must be protected from moisture, which when placing the fibers in the cavities of the cavity tube requires the placement of an anti-moisture agent in the cavities, as condensation is difficult to prevent in the cavities if the cable is used in varying conditions.

It is therefore an object of the present invention to provide a method of manufacturing an optical cable in which the optical fibers are protected in a very effective manner from external stresses and moisture arising both during the manufacture and installation of the cable 35.

Il 3 67148 This object is achieved by the method according to the invention, which is characterized in that - the central support of the cable is heated before it is fed to the extruder, whereby the support cools longitudinally as it cools, creating an excess length in the cable. This excess length is sufficient to compensate for the elongation during use of the cable.

The method according to the invention will be described in more detail in connection with the accompanying drawings, in which Figure 1 shows a cross-section of a cable according to the invention, Figure 2 shows schematically a process for making a cable according to the invention and Figure 3 shows another process for making a cable according to the invention.

Figure 1 shows a cable produced by the method according to the invention, which in a separate step is covered with a shield 25. The cable has a plastic core 1 extruded around the central support 2 with 20 cavities 13. Each cavity has an optical fiber 3 and a moisture barrier (not shown). .

Figure 2 schematically shows a process for manufacturing a cable according to the invention. The steel wire 2 forming the cable support is fed from the drum 9, which is first heated by means 21, e.g. by a resistance or eddy current method, e.g. to a temperature of 100-200 ° C. In this case, the support shrinks by about 0.1-0.2% as it cools. Next, the support 2, together with the optical fibers 3 fed by the coils 11, is fed to a device 20, 30 connected to the extruder 15, by means of which an anti-moisture agent is fed into the tubes surrounding the fiber feed-through tubes. These tubes, together with the inner part of the extrusion head, are reciprocated by means of a motor 23, whereby the cavities of the hollow tube formed in the extrusion head provide, for example, a reversing rotation in a direction of about 360 ° intervals. In the next step, the cable is cooled, whereupon it shrinks longitudinally * depending on the initial temperature of the support, so that the plastic surrounding it does not prevent this shrinkage, as it shrinks by up to 4% if allowed. A substantial excess of the fibers over the length of the cable is obtained for the cable.

In the process of FIG. The process then continues to a cutting tool 14 where each core cavity is incised open and optical fibers 3 are passed from drums 11. The next step is the cable strip 16 described in Figure 6, where a plastic tape is wrapped around the cable to seal the core cuts. The formation of the actual outer sheath is not shown in Figures 5 or 6, but can be performed in a conventional manner known in the art of cable technology.

Claims (1)

67148 Claim: »A method of manufacturing an optical cable comprising a core portion (1), a bracket (2) and an outer shield 5, the method comprising - extruding a hollow tube (1) comprising a plurality of cavities (13) onto a central support (2); repetition by twisting the Purso tin head, 10. filling the cavities with a moisture barrier, - placing the fibers (3) in the cavities (13) either by extrusion or slitting the cavities open along the length of the pipe and guiding the fibers from the slits into the cavities 15, and characterized in that - the central support (2) of the cable is heated before it is fed to the extruder, whereby the support 20 shrinks in the longitudinal direction as it cools, creating an excess of length in the cables (3).