Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/29—Protection against damage caused by extremes of temperature or by flame
  • H01B7/295—Protection against damage caused by extremes of temperature or by flame using material resistant to flame
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B7/00—Insulated conductors or cables characterised by their form
  • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
  • H01B7/18—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring
  • H01B7/182—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring comprising synthetic filaments
  • H01B7/183—Protection against damage caused by wear, mechanical force or pressure; Sheaths; Armouring comprising synthetic filaments forming part of an outer sheath

Definitions

• the present invention relates to a fire-resistant sheath intended mainly for thermal fire and mechanical protection of cables, in particular in the aeronautical, space and industrial fields. It also relates to a method for producing this sheath.
• cables or cable harnesses ensuring electrical connections within mechanical or electronic assemblies are liable to be subjected, over shorter or longer periods, to high temperatures higher than those specified by the manufacturers of the products concerned. In most cases, this results in an interruption of these links which can directly or indirectly lead to destruction of the equipment used.
• the loss of an essential function can lead to the failure of the mission with the resulting financial consequences and in the aeronautics field, the decommissioning of essential equipment such as emergency lighting for example is the direct cause of loss of life when aircraft crash on the ground.
• this temperature resistance is achieved during the final assembly of the materials by covering the cables and cable harnesses with a flexible spiral protection based on a "Jehier” type material or even more protection rigid based on glass fibers or silica such as "Reprobat".
• these solutions apart from the fact that they involve a long exposure time are particularly expensive and penalizing in weight.
• the first of these protections is real only to about 200 ° C and the second suffers from an oven effect caused by the absorption capacity of the heat of the fibers.
• these protections based on glass fibers or silica require special processing precautions, given their toxicity;
• the aim of the present invention is therefore to alleviate all of the aforementioned drawbacks and to provide protection at very high temperature (up to approximately 850 ° C.) from all kinds of cabling, cables and cable harnesses, which is universal, that is to say that can be implemented in any type of industry, in particular to replace current space coatings and certain aeronautical cold protections.
• Another object of the invention is to produce a sheath that does not require complex installation on the integration site.
• Yet another object of the invention is to provide this thermal and mechanical protection in a very small footprint.
• a thermal and mechanical protective sheath for cables and cable bundles obtained directly by braiding around the element to be protected comprising a braided layer of braiding son constituted by several elementary strands formed by interlacing of synthetic fibers obtained after cracking and spinning an aramid fiber and a carbonizable oxidized organic fiber.
• the sheath according to the invention may comprise one or more other braided layers superimposed on the initial layer, the braiding configurations of the various layers may be different. When there are severe pollution constraints, this sheath will preferably include an additional layer intended to remove the fibrous residues resulting from the cracking operation.
• this sheath will preferably include an additional layer intended to remove the fibrous residues resulting from the cracking operation.
• aramid fibers such as Nomex
• FIG. 1 is a schematic representation of a braiding loom intended for producing a thermal protection sheath according to the invention
• FIGS. 2a to 2c and 3a to 3c show two examples of implementation of the method for manufacturing sheaths according to the invention.
• FIG. 1 is a schematic representation of a braiding loom for the realization of the thermal protection sheath according to the invention.
• a loom 1 conventionally comprises, mounted on a support 10, wire supply coils 12 and a supply well 14 from which the element to be braided comes out 2.
• the braiding wire 3 present on the various supply coils is braided directly around the element to be protected 4 leaving the well of the braiding loom.
• This element can consist of a single cable of any diameter, the current trades allowing the production of sheaths from 2 to more than 40 mm in diameter, or even a bundle of cables like those illustrated in FIGS. 2 and 3.
• the braiding yarn consists of several elementary strands formed by interlacing of synthetic fibers obtained after cracking and spinning of an aramid fiber and an oxidizable carbonizable organic fiber.
• Aramid fiber has very good mechanical characteristics and excellent heat resistance (these can be products known under the names of "Kevlar”, “Twaron” or “Technora”).
• the carbonizable oxidized organic fiber, in particular based on polyacrylonitrile, is a thread known for example under the name of "Sigrafil". After cracking, these two threads are preferably used respectively for 30 and 70% in the manufacture of an elementary strand at the base of the braiding thread. This preferential report does not exclude a different ratio to the extent that a preponderance is left to the oxidized organic fiber.
• this elementary strand it may be necessary to combine with the synthetic fiber obtained previously another fiber having specific characteristics adapted to this application. For example, if it is desired to improve the thermal properties by conduction of the sheath, the use of a material having, for example, good thermal resistivity, in addition to the aforementioned synthetic fiber, proves to be particularly judicious. It should be noted that this addition of an additional wire material can be carried out during braiding by loading one or more supply coils with this specific material, the other coils receiving the synthetic fiber obtained from the initial treatment.
• a first layer of thermal protection is then obtained simply by braiding with a determined braiding angle and from a number of predefined coils, the braiding wire produced previously. If necessary, one or more additional layers can be braided on this first layer, adopting an identical or different braiding angle.
• thermal protection layer In applications where the pollution constraints are high, for example in the space field, it may be necessary to cover the thermal protection layer (s) with an additional layer making it possible to remove the barbs present at the level of the synthetic fiber. and from the cracking process.
• An additional braiding based on aramid yarn such as Nomex may be perfectly suitable for such pollution protection.
• a specific impregnation of the sheath is also possible.
• Another solution, not requiring the use of an additional layer consists in purifying the elementary strands, before any braiding (by combing for example).
• the various stages making it possible to produce a thermal protection sheath for cables and cable bundles are the following: a) formation of elementary strands from a predetermined number of synthetic fibers obtained after cracking and spinning in given proportions of an aramid yarn and a preoxidized yarn, b) mounting these strands on a predetermined number of spools or spindles for supplying wire to a braiding loom, and c) from these supply coils, realization of the protective sheath by braiding these wires at a predetermined angle directly around the cable or bundle of cables to be protected.
• the braiding step c) is repeated at least a second time, possibly with a braiding configuration distinct from the previous one.
• this process comprises an additional step: d) consisting either of covering the sheath thus braided with an additional layer of another cleanroom compatible wire of the "Nomex" type, or to make a specific impregnation on the sheath thus braided, this impregnation ensuring a tightness against the runoff of liquids which can come into contact with this sheath.
• Figures 2a to 2c and 3a to 3c show two embodiments of a braiding of a sheath surrounding a bundle of cables 20 comprising a main strand 21 on which are grafted several auxiliary branches 22, 23, 24 forming like a fork with the main strand (see Figures 2a and 3a).
• the braiding of the auxiliary branches which are covered with a sheath 4 is carried out first, this braiding being carried out so as to include retaining accessories 30 (ribbons, frets , etc) arranged at the junctions of the main strand.
• the main strand can be braided in one go, the sheath 40 then covering the part of the previous braiding covering the retaining tapes.
• Item referenced 41 corresponds to what is commonly called the braiding tail, which can become a means of fixing the sheath on its receiving structure.
• the first braiding of the free ends of the cable bundle is carried out, that is to say of the auxiliary branches 22 to 24 and of the end of the main strand 25
• the main strand 21 is braided, which will cover the unprotected parts of the cable bundle, a round trip 45 being made at the junctions with the auxiliary branches to ensure maximum optical coverage without interrupting the braiding.
• these two preferred embodiments are in no way limiting and other more conventional modes can similarly be implemented without departing from the scope of the invention.

Landscapes

• Braiding, Manufacturing Of Bobbin-Net Or Lace, And Manufacturing Of Nets By Knotting (AREA)
• Ropes Or Cables (AREA)

Applications Claiming Priority (3)

Publications (2)

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Country Status (6)

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Family Cites Families (9)

• 1993
  • 1993-07-30 FR FR9309406A patent/FR2708781B1/fr not_active Expired - Lifetime
• 1994
  • 1994-07-27 US US08/406,949 patent/US5604331A/en not_active Expired - Lifetime
  • 1994-07-27 EP EP94923744A patent/EP0663100B1/de not_active Expired - Lifetime
  • 1994-07-27 CA CA002145504A patent/CA2145504C/en not_active Expired - Lifetime
  • 1994-07-27 WO PCT/FR1994/000941 patent/WO1995004358A1/fr active IP Right Grant
  • 1994-07-27 DE DE69402522T patent/DE69402522T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

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