Patent Application
20100054690
1. Field of the Invention
The disclosure is directed to flame-retardant fiber optic assemblies. More specifically, the disclosure is directed to fiber optic assemblies having transition locations that are flame-retardant for indoor or indoor/outdoor use.
2. Technical Background
Fiber optic cables developed for indoor or indoor/outdoor use are required to meet stringent flame and/or smoke ratings, which are tested by independent laboratories. Typically, indoor or indoor/outdoor fiber optic cables are preconnectorized at respective ends with conventional fiber optic connectors and these assemblies meet the desired ratings for the space without modification. As optical fiber moves toward the subscriber and private networks become more advanced, there is a need for more robust and ruggedized fiber optic assemblies to interface with the emerging plug and play networks deployed for indoor and indoor/outdoor applications.
Meeting this emerging demand can be very challenging since the fiber optic assemblies must meet the flame and/or smoke ratings along with still meeting the desired mechanical and optical performance characteristics. One skilled in the art realizes that the flame and/or smoke ratings can be difficult to pass since they generally involve an open flame and require all combustion to cease shortly after removal of the flame. Conversion of outdoor products to nonflammable assemblies by material substitution can be difficult due to the mechanical and environmental requirements that the assemblies must pass. Still further even minor variations in material composition may result in unwanted side effects, and complete material substitutions may exacerbate these unwanted effects. Moreover, designing and testing of the fiber optic assemblies is expensive and time consuming. The fiber optic industry requires a simple, reliable, and effective way to make fiber optic assemblies suitable for indoor and indoor/outdoor applications without extensive redesign and testing of the same.
The disclosure is directed to various embodiments and methods for fiber optic assemblies having a covering that is flame-retardant for use at a transition location or the like. The covering has multiple components and provides the necessary characteristics to pass burn testing, thereby allowing indoor and/or indoor/outdoor use. The covering includes a heat dissipative structure and a heat resistant structure disposed about a transition location of the fiber optic assembly. Additionally, the covering may include an optional flame-retardant wrap configured for sealing and/or securing the covering such as a flame-retardant heat-shrink material. By way of example, the heat dissipative structure is a foil, such as an aluminum foil and the heat resistant structure is made of mica, but other materials are possible. The covering can have many suitable constructions for application such as individual components applied sequentially or a composite structure such as a wrap or tube for application together. Thus, the fiber optic assemblies are easy to manufacture and reliable.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate the various example embodiments of the invention and, together with the description, serve to explain the principals and operations of the invention.
Detailed reference will now be made to the drawings in which examples of the present invention are shown. The detailed description uses numerical and letter designations to refer to features of the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention where possible.
The drawings and detailed description provide a full and written description of the examples of the invention, and of the manner and process of making and using these examples, so as to enable one skilled in the pertinent art to make and use them, as well as the best mode of carrying out the invention. The examples set forth in the drawings and detailed description are provided by way of explanation only and are not meant as limitations of the invention. The present invention thus includes any modifications and variations of the following examples as come within the scope of the appended claims and their equivalents.
The figures that are about to be described in detail show exemplary flame resistant coverings or structures for a transition location. These coverings generally include various layers and materials combined to provide flame or burn-through resistance more effectively than, for instance, a stand-alone, flame-resistant heat shrink employed over a spliced area of an enclosure. The components and materials of the composite flame resistant coverings are simple and economical to manufacture and use. Other advantages of the flame resistant coverings will be apparent from the following description and the attached drawings or can be learned through practice of the embodiments and their equivalents.
Covering 10 is advantageous since it provides the transition location TL with the suitable characteristics so that fiber optic assembly 100 passes flame-retardant ratings such as UL 746C or the like, thereby qualifying the assembly for indoor or indoor/outdoor applications. Examples of transition locations TL include demarcation locations such as where optical fibers are spliced together such as attaching one or more preconnectorized assemblies, tap locations where optical fibers are extracted from a distribution cable, where fiber optic cables are opened and/or optical fibers are secured to inhibit the migration of excess fiber length along the assembly, and the like. In this embodiment, covering 10 has a multi-layer construction. Covering 10 generally includes a heat dissipative structure 14 and a heat resistant structure 16. Heat dissipative structure 14 is disposed about a portion of transition location TL and acts as a heat shield, whereas heat resistant structure 16 is disposed about a portion of heat dissipative structure 14. An optional flame-retardant wrap 18 such as a heat shrink tubing or wrap may be placed about a portion of the heat resistant structure 16. As discussed below, covering 10 can be a composite structure or formed from individual components.
The combination of a high temperature capable substrate, such as mica, along with an underlying heat dissipative structure, such as metal foil, provides the needed burn-through resistance that a single layer of either material is incapable of providing. Moreover, although flame-retardant wrap 18 is optionally used as part of covering 10 for sealing and/or mechanical protection and for some flame protection, heat shrink alone generally is also insufficient to provide the desired characteristics. Thus, covering 10 provides superior flame-resistance/performance. Additionally, covering 10 is suitable for use over structure that is inherently flammable, thereby providing the desired characteristics for the portion having the underlying flammable structure. By way of example, transition location TL may include an overmold portion that is inherently flammable, but after covering 10 is applied the transition location TL has the desired characteristics.
Heat dissipative structure 14 can be any suitable material, but preferably has a metallic content for effective transfer of the thermal energy. By way of example, heat dissipative structure 14 is formed from a metal foil such as aluminum. The thickness of heat dissipative structure 14 may depend on the material used, but one embodiment has a heat dissipative structure 14 with a thickness between about 0.02 millimeters and about 0.2 millimeters, but other thicknesses are possible. A material such as aluminum acts as a heat shield because of its thermal conduction properties that reduce localized heating. A typical aluminum foil has a thickness greater than about 0.02 millimeters such as between about 0.025 millimeters and 0.075 millimeters. The skilled artisan will recognize that materials other than aluminum may be utilized for heat dissipative structure 14 depending on specific requirements and/or regulations. For instance, relatively thin steel, copper, stainless steel or other metallic tapes wrapped longitudinally or tangentially may be used.
Heat resistant structure 16 is disposed about a portion of heat dissipative structure 14. Heat resistant structure 16 can withstand temperatures of up to about 1000 degrees C. By way of example, heat resistant structure 16 may be mica material such as a mica tape. A suitable heat resistant mica tape is available from Coebgi, Inc. of Dover N.H. Of course, other suitable heat resistant structures are possible. For instance, heat resistant structure 16 may includes a polyurethane/polyphosphazene blends or aramid yarns and is not limited to mica.
The multiple components of covering 10 may have any suitable construction and/or method for applying the same about the transition location TL. For instance, covering 10 may be provided in separate layers such as a metal foil that is formable about a portion of transition location TL and a mica tape. Generally speaking, aluminum foil readily takes the desired set and seals about the transition location without much difficulty. However, the mica tape does not form like the aluminum foil so it may optionally include an adhesive layer or have other means such as applying an adhesive to the structure for forming and/or retaining about transition location TL if necessary. Adhesive layer can be applied to one of the components with any suitable method such as spray, brush, etc. However, it is noted that the adhesive, glue, or the like may be flammable and it should be used sparingly. In other embodiments, covering 10 is a composite structure so that the layers may be applied about the transition location TL together. Moreover, covering 10 may include a further outer layer for sealing and/or mechanical protection
As shown, flame-retardant wrap 18 generally surrounds the transition location TL. Flame-retardant wrap 18 may be manufactured from any suitable material such as flame retardant polyolefin, fluoropolymer (such as fluorinated ethylene propylene (FEP) or PTFE), PVC, neoprene, or silicone elastomer. Flame-retardant wrap 18 may also be a heat shrink material that includes polyolefin heat shrink or ATUM flame retardant heat shrink tubing such as available from Raychem of Menlo Park, Calif., or FEP heat shrinks or Teflon® heat shrink tubing from Zeus Industrial Products, Inc. of Orangeburg, S.C. Of course, suitable heat shrink materials are not limited to the foregoing sources and examples.
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In any of its alternative forms, covering 110 provides necessary burn-through protection by using flame retardant particles or pieces 130 that may trapped between, for instance, the flame-retardant wrap 118 and the underlying structure of the fiber optic assembly. In this example, the pieces 130 are combinations of mica and aluminum schematically represented as square shapes but may present a honeycomb pattern or have a variety of other geometric forms, the size and distribution of which are such that upon heating, the particles 130 converge or are brought in close proximity to each other to produce a generally solid layer 132 as covering shrinks about the structure. In other embodiments, strips of metal foil having mica particles can be attached to an inner surface of a flame-retardant wrap or heat shrink tubing. Again, mica is suitable as a heat shield and the aluminum (or other suitable material) adds shielding and conduction to minimize localized heating, but, as noted above, other flame resistant and conductive materials may used in the alternative, or in addition to mica and aluminum.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention, provided they come within the scope of the appended claims and their equivalents.
