Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
1999-06-11
2001-10-30
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Optical transmission cable
Loose tube type
C385S109000, C385S106000, C385S114000
Reexamination Certificate
active
06311000
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a method for manufacturing an optical cable, which has an extruded outside cladding in which are embedded both tensile elements and supporting elements.
U.S. Pat. No. 4,743,085, which is incorporated herein by reference thereto, discloses an optical cable in whose outside cladding both tensile elements as well as supporting elements are embedded. The tensile elements are preferably employed for absorbing corresponding longitudinal forces, for example, when laying the cable or during the operation of the cable, for example given overhead cables. By contrast thereto, the supporting elements are important particularly in view of shrink forces of the cable cladding, for example given great changes in the temperature. For example, the tensile elements can be composed of rovings or can be manufactured in the form of yarns or strings. They are relatively flexible, whereas the supporting elements can be composed, for example, of epoxy-cast glass fibers, which are known as GFK elements (fiberglass-reinforced plastic), or FRP elements (fiber-reinforced plastics). These supporting elements are correspondingly stiff, less easily bent and can hardly be compressed at all in the longitudinal direction. The tensile and supporting elements are present as prefabricated elements and must both be introduced into the extruder head so that they can be embedded into the cladding material. This can usually be relatively easily accomplished given the relative flexibility of the tensile elements, whereas the stiff, rather rod-like supporting elements can lead to difficulties in their handling. Moreover, prefabricated supporting elements are generally significantly more expensive than, for example, coextruded supporting elements.
SUMMARY OF THE INVENTION
The present invention is based on the object of simplifying the manufacture of an optical cable. In a method for extruding a jacket or cladding on optical fibers, this object is achieved in that the tensile elements are taken from supply reels and are introduced into the extruder head serving for the manufacture of the outside cladding and in that the supporting elements are manufactured in a coextrusion with the outside cladding.
Since only the tensile elements need to be separately supplied to the extruder in the inventive method, the structure in view of the supply reels is significantly simpler, because only those reels that are required for the tensile elements are needed. The production of the supporting elements that are more difficult to handle in terms of process technology, by contrast, occurs by extrusion, so that the supply reels are not required for these. There is no length limitation for the coextruded supporting elements, which is likewise advantageous. The fashioning of the support elements with an extrusion process is simpler and cheaper because these elements are produced on line only when and where they are, in fact, used. The method is also more beneficial than the delivery of stiff elements, in view of the shaping and embedding into the cladding material. Another advantage of coextruded supporting elements is that these elements are united in a molten form with the sheath into which they are introduced and which is likewise present in an unmolten form. A good adhesion between the supporting elements and the sheath material can thus be achieved.
In order to prevent the supporting elements, as directly shrinking elements during the cooling process, from being excessively compressed or, respectively, crushed, for example due to the shrink process of the cladding material, it is expedient to keep the coextruded support elements until they have hardened or, respectively, until the cladding has hardened under tension. Therefore, the cable cladding or the lead sheath is placed under tension in a cooling means to thus prevent an undesired, excess shrinkage in the longitudinal direction during cooling.
The invention is also directed to an apparatus for the implementation of the inventive method. This apparatus is characterized in that the extruder head is provided in whose inside of the head the light waveguides are supplied through an opening and in that the common annular gap is present surrounding the waveguides into which the guides for the tensile elements and the channels for the supporting elements discharge.
The invention is also directed to an optical cable with tensile elements and supporting elements, which is characterized in that the tensile elements are fashioned skein-like and embedded in the outside cladding and in that the supporting elements are embedded in the outside cladding in an extruded form from a plastic material.
Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and claims.
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Palmer Phan T. H.
Siemens Aktiengesellschaft
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