Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Optical fiber – waveguide – or preform
Patent
1993-10-14
1995-07-25
Vargot, Mathieu D.
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Optical fiber, waveguide, or preform
264 129, 264 16, 264 17, 264174, 425113, 425467, B29D 1100, B29C 4702
Patent
active
054359449
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a process and applications for manufacturing cables, particularly optical fibre cables, by plastics extrusion.
RELATED ART
Fibre optic cables in which fibre elements are loosely contained within a channel or tube are currently manufactured by a multistage process. A channel/strength member is first made e.g. by profile extrusion. Next the fibre element is fed into the channel which is closed by a close-fitting sealing strip. The assembly is then fed into an extruder to apply a protective plastics sheath.
In an attempt to reduce manufacturing costs it has been proposed to manufacture such a cable by a single extrusion. However this results in a structure in which access to the fibre elements is rendered extremely difficult. It will be appreciated that it is necessary to access the fibres at various points along a cable to provide junctions and terminations.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to minimise or to overcome this disadvantage.
According to one aspect of the invention there is provided a method of manufacturing a fibre optic cable by extrusion of a plastics material through a die around a fibre optic element so as to contain the element loosely, wherein during extrusion the plastics flow is partitioned into two or more separate flows by a tubular member through which the fibre optic element is fed over a distance such that, when the flows recombine, a weak bond is formed at the interface therebetween whereby to facilitate selective splitting of the plastics of the cable to access the fibre optic elements.
According to another aspect of the invention there is provided an apparatus for manufacturing a fibre optic cable, the apparatus including a plastics extruder for providing a plastics protection around a fibre optic element by extrusion through a die, the extruder having a tubular member through which the optical element is fed and arranged to partition extruded plastics material into two or more separate flows over a distance such that, when the flows are recombined, a weak bond us formed therebetween whereby to facilitate selective splitting of the plastics of the cable to access the fibre optic element.
The technique is of particular application to the manufacture of self-supporting or aerial cables in which optical fibre elements are contained in a channel formed in a longitudinal dielectric strength member.
Reference is here directed to our copending United Kingdom Application No. 91 10264.0 of even date which relates to cable construction formed e.g. by the process described in the present application.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described with reference to the accompanying drawings in which: applications; extruder of FIG. 1; and
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIGS. 1 and 2, the extruded includes a die 11 defining the outer form of an extruder cable and into the throat 110 of which a point assembly 12 projects. The point assembly has one or more passageways 120 for receiving optical fibre elements to be sheathed and may also have a further passageway 121 for receiving a cable strength member, e.g. a dielectric strength member. Advantageously a bearing 123 is provided whereby the point assembly 12 may be rotated relative to the die e.g. to impart an S-Z twist into the extruded cable.
The construction of the point assembly is shown in more detail in FIG. 2. As can be seen from FIG. 2 the assembly includes a hollow generally cylindrical shield member 21 supported via a rod 210 and a circumferential clamp 211 whereby the position of the point assembly within the extruder may be adjusted. In use the plastics material flows both through and outside the shield member. Within the shield member 21 a generally rectangular tube 22 is disposed. This tube receives the fibre ribbon element and defines the channel in the cable within which that element is accommodated. The tube 22 communicates with the passageway 120 in the
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Northern Telecom Limited
Vargot Mathieu D.
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