FR2692713A1 - Reduced weight stranded conductor esp. for aviation applications - has two layers of bare strands of progressively smaller diameter laid up helically over central strand - Google Patents

Abstract

The stranded conductor includes a central strand (10) around which six wires (11) of the same diameter (D1) are laid up helically, with the central conductor having the same or slightly greater diameter (D0). An outer layer of twelve wires (12) of slightly smaller diameter (D2) is added, with an overall insulating sheath (13). No radial pressure, deforming strands are applied. The ratio of outer to inner strand diameters (D2/D1) lies between 0.93 and 0.97. The common lay-pitch varies according to this ratio between about 8 to 10 times the overall bare conductor diameter at 0.93 to 12 times at 0.97. A further 24-strand layer may optionally be added with a similar diameter decrement. The central wire may also be completely omitted. ADVANTAGE - Mass per unit length is about 3 per cent less than in conventional conductor of same section.

Description

Light conductive strand
The present invention relates to conductive strands having a high electrical conductivity and having a relatively low linear density. It relates to such electrical conductors, in particular for the aeronautical or aerospace industry, which are said to be lightened.

 The conductors of this type are in known manner formed of multiple conductor wires, most often all of copper or, in a variant, all of aluminum assembled in a bare strand which is coated with an insulating sheath. In particular, such a conductor is formed of 19 conductive wires arranged in an internal layer of six contiguous wires wound helically on a central wire and a layer of twelve contiguous wires and wound helically on the internal layer. In general, the 19 wires are all of the same nature, in particular copper for better conductivity, and are all of the same diameter. The two layers of wires have the same winding direction to obtain a relatively flexible strand or have opposite winding directions. The assembly of conductive wires of the same diameter can be carried out without tightening the outer layer of wires on the internal one or with tightening of this external layer on the internal one.

 In the first assembly mode, the winding pitch of the two layers of wires is relatively long, of the order of 12 times or more the diameter of the resulting strand. This first resulting bare strand is of hexagonal cross section. Its final insulating sheath gives it its circular section.

 The second assembly mode is in turn carried out in tight dies with a shorter wiring pitch than previously and special guides of the wires, at least of the wires of the outer layer. It gives rise to a deformation of the wires and to a slight crushing of the wires one after the other in their contact zones, for which the second resulting bare strand is of so-called circular cross section.

 Compared for two insulated strands of the same section, this second strand requires less sheathing insulating material than the first. It has an electrical resistance per unit of length lower than the first but has a higher linear density.

 Various particular embodiments are also known to enable a better compromise to be obtained between the electrical characteristics and the linear mass of such conductors or strands of assembled multiple conductor wires.

 Documents US-A 3633103 and 4471161 in particular describe such known embodiments which have been illustrated in Figures 1 and 2 of the attached drawing.

The bare strand illustrated in FIG. 1 is of the type of the aforementioned first strand, which is made lighter according to the teaching of the first document cited above. It is made up of 19 wires, one of which 1 is central, six others 2 are contiguous and constitute the inner layer and the other twelve 3 also contiguous constitute the outer layer. The winding pitch of the two layers of wires 2 and 3 is long. The wires 1, 2 and 3 are all of the same diameter
D and are neither distorted nor crushed against each other. The cross section of the bare strand is hexagonal.

 For the reduction in linear density of this first lightened strand, compared to the corresponding first strand, the wires of which are all made of copper, some of its wires are substantially made of copper but the others are made of substantially aluminum. This reduction in linear mass is thus obtained to the detriment of the electrical resistance per unit of length made greater than that of the first strand with all copper wires. In addition, given the different nature of its wires, these must initially be coated with the same conductive material, for example silver, nickel or tin, avoiding any corrosion by galvanic effect during the passage of the running through the wires. This coating imposes cabling precautions and opposes any tightening or crushing of the wires, to avoid damage and subsequent damage.

 The conductor illustrated in Figure 2 conforms to the second cited document. It is without tightening of its wires and constitutes another resulting lightened strand. It is also formed by 19 wires designated by the reference 5 for the central one, by the reference 6 for the six wires of the inner layer, and by the reference 7 for the first six wires of the outer layer and the reference 8 for the other six son of this outer layer.

 In this other lightened strand, the wires 5, 6 and 7 have the same diameter D ′.

The wires 8 are interposed between the wires 7 and are of diameter D ″ significantly smaller than the diameter D ′, this diameter
D "being of the order of 0.68 to 0.78 times the diameter D '.

Each of these wires 8 thus leaves a clearance between itself and the two adjacent wires 7.

 These provisions make it possible to obtain a so-called circular cross section, without deformation or crushing of the wires of this other lightened strand. Compared to the second strand of the same section whose wires are deformed and crushed, this other lightened strand has a lower linear density but has an electrical resistance per unit of greater length. In addition, its realization is long and delicate.

 The object of the present invention is to produce a lightened conductive strand, allowing a substantial reduction in its linear mass but this substantially without degradation of its electrical characteristics remaining similar to those of a strand corresponding to deformed and crushed wires.

 It relates to a lightened conductive strand, comprising a central core formed of first conductive wires, a layer of second conductive wires wound helically on said core, characterized in that said second wires are of diameter substantially less than the diameter of said first wires, are wound together without deformation on said core and define a strand resulting from a so-called circular cross section.

 The strand according to the invention also has at least one of the following additional characteristics: the diameter of said second wires is at least equal to 0.90 times the diameter of the first, the difference between these diameters preferably being 3 at 7%; - Said second wires are wound on said core with a pitch adapted to the value of said difference, said pitch being long for the smallest values of said difference and being substantially reduced for the highest values of said difference; - Said first son are themselves wound together and substantially the same as said second son on a selected central wire of diameter substantially greater than that of said first son; ; the strand comprises an additional layer of wires on the layer of second wires, the wires of this additional layer being of diameter substantially smaller than that of said second wires and wound together, without deformation, on the layer of second wires and defining a final strand of so-called circular section.

 The characteristics and advantages of the present invention will emerge from the description given below of a preferred embodiment illustrated in the attached drawings. In these drawings: - Figure 1 is a sectional view of a bare strand according to a first known embodiment, - Figure 2 is a sectional view of a bare strand according to a second known embodiment, - FIG. 3 is a sectional view of a strand according to the invention, with the same basic construction as the strands according to the known embodiments of FIGS. 1 and 2.

 The lightened conductive strand according to the invention, illustrated in FIG. 3 is shown to be formed of 19 wires and of the same basic type of construction as the known strands illustrated in FIGS. 1 and 2. It comprises a central wire 10 of diameter Do, six wires 11 of diameter D1 which are joined and helically wound on the central wire, and twelve wires 12 of diameter D2, which are also contiguous and helically wound on the internal layer with the same wiring pitch as the wires 11 of this internal layer . This bare strand is coated with an insulating sheath 13.

 The two layers of wires 11 and 12 are blocked one on the other without deformation or crushing of their wires.

The cross section of this strand resulting from this assembly without shrinking its wires is said to be circular and directly obtained in this way. This results from the wires 12 of the outer layer which are of diameter D2 slightly less than the diameter D1 of the wires 11, with the value of this diameter D2 chosen at least equal to 0.90 times the diameter
D1.

 The difference between these two diameters is preferably between 3 and 7%.

 The storage and locking of the wires 12 without deformation and crushing are carried out with the same substantially wiring pitch of the wires 11 and 12. This pitch is simply adapted to the difference between the diameters of the wires 12 and 11. It is long and 12 times and more the diameter of the bare strand when the difference in diameters D1 and D2 is small and does not exceed 3%. I1 is reduced, and of the order of 8 to 10 times the diameter of the strand, when the difference between the diameters D1 and D2 is relatively large, ie from 6 to 7%. It is around 10 to 12 times the diameter of the bare strand for an intermediate gap.

 The absence of deformation of the wires of this bare strand of so-called circular section and the suitable winding pitch of its two layers of contiguous wires lead to a substantial reduction in its linear mass, without however leading to a significant deterioration in its characteristics. electric, compared to a strand having the same section, with low tolerances allowable close, and whose wires are deformed and crushed.

 This reduction in linear mass is of the order of 3% for wires 11 and the central wire 10 having the same diameter, ie Do = D1. It can be slightly accentuated for a central wire 10 of diameter Do itself slightly greater than the diameter D1 of the wires 11 of the internal layer.

This strand of FIG. 3 of so-called circular section can receive an additional outer layer of wires, under the same conditions as the layer of wires 12, namely consisting of 24 contiguous but non-deformed wires whose diameter is itself slightly less than the diameter
D2, to obtain a resulting strand also having a so-called circular cross section.

 As a variant, this strand may be of another type of construction, for example with an inner core formed of 3 or 4 wires stranded together, without central wire, and with a layer of contiguous wires of diameter slightly smaller than the wires of the core and wound helically without shrinking on this core, leading to a strand resulting from a so-called circular section.

 In addition, advantageously, all the wires of the strand or the only wires of its outermost layer receive an initial treatment, in particular of nickel plating, for a better subsequent electrical connection of terminal connectors to the final conductor.

Claims (6)

1 / Lightened conducting strand, comprising a central core formed of first conducting wires, a layer of second conducting wires wound helically on said core, characterized in that said second wires (12) are of diameter (D2) substantially less than the diameter (D1 ) of said first wires (11), are wound helically and contiguously without deformation on said core and define a strand resulting from a so-called circular cross section. 2 / light conductive strand according to claim 1, characterized in that the diameter (D2) of the second son (12) is at least equal to 0.90 times the diameter (D1) of said first son (11). 3 / light conductive strand according to claim 3, characterized in that the difference between the diameters (D2 and D1) of said second and first wires is 3 to 7%. 4 / light conductive strand according to one of claims 1 to 3, characterized in that the winding pitch of said second wires is adapted to the value of said difference between the diameters of said first and second wires, said pitch being long for the most small values of said deviation and being substantially reduced for the highest values of said deviation 5 / lightened conductive strand according to one of claims 1 to 4, in which said first wires are themselves wound helically on a central wire, characterized in that said central wire (10) is itself of diameter (Do) substantially greater than the diameter (D1) of said first wires (11), and that said first and second wires have substantially the same winding pitch. 6 / light conductive strand according to one of claims 1 to 5, characterized in that it comprises an additional layer of wires, themselves chosen with a diameter substantially less than the diameter (D2) of said second wires and wound together without deformation on said second wires, by defining a final strand resulting from a so-called circular section. 7 / light conductive strand according to claim 6, characterized in that the son of said additional layer have substantially the same winding pitch as the first and second son.