EP0953990A1 - Electrical wire and method for making the same - Google Patents

Abstract

The invention relates to a wire or cable comprising at least one insulator resistant to the propagation of the electric arc around at least one conductor. The insulation is waterproof and comprises a matrix (12) of PTFE and fibers (141, 142, 143, ...) of mechanical reinforcement, continuous and of great length. The insulation is either in the form of a strip, or in the form of extrudate, of great length. Application to wires or cables for aeronautical and / or space use. <IMAGE>

Description

The invention relates to an insulated conducting wire, especially for aeronautical and / or space applications. She also relates to an insulator for such a wire and to its method Manufacturing.

Electrical wires and cables must meet a number of conditions which depend on their use.

Aeronautical and / or space applications impose severe conditions. In particular, the insulation must have determined mechanical resistance properties. These properties are cut resistance, resistance to abrasion by scraping and abrasion resistance wire by wire.

Cut resistance is measured by force minimum that it is necessary to exercise, at a temperature determined, on an insulator, using a cutting tool standardized, to reach the driver.

The resistance to abrasion by scraping is measured at using a needle with a diameter of approximately 0.5 mm which is applied on the insulation perpendicular to the wire axis with, according to standards, a force of 500g to 1Kg and that we move in one direction and in the other part of the wire. The result is expressed by the minimum number of cycles, i.e. back and forth from the needle, at the end of which the conductor is exposed.

Wire-to-wire abrasion resistance is measured at using a test which consists in rubbing a first wire stretched against a second stretched wire, the first wire moving transversely to the second. Again, the result is expressed by the minimum number of cycles (back and forth) after which the two conductors are laid bare.

Another condition that a thread must meet or electric cable for aeronautical or space application is the insulator has a minimum sensitivity to the propagation of the electric arc.

We know that an electric arc occurs between two neighboring wires when the corresponding conductors are put in short circuit, either by an electrolyte or by an element metallic. When the wire insulation is mainly made of polyimide resin, the electric arc causes a local pyrolysis of the resin and thereby creates a path carbon between the conductors, which facilitates the passage of the electric arc. The phenomenon thus amplifies itself and can lead to the destruction of the beam in which find the two sons concerned.

Despite this drawback, we still use polyimide resin to insulate electrical wires and cables for aeronautical applications because the polyimide insulation has the better mechanical resistance characteristics. However, to improve resistance to arc propagation electric while retaining the advantages of resistance polyimide mechanics it is known to use a combination polyimide tape and polytetrafluoroethylene tape (PTFE), the resistance to propagation of the electric arc being the more important the greater the amount of PTFE, because the fault of propagation of the electric arc does not occur not with PTFE. But this gain in resistance to the propagation of the arc causes a corresponding decrease in the properties of mechanical resistance.

Furthermore, polyimide is a very expensive material, at least around four times more than PTFE. The polyimide price is even higher if it has properties hydrolysis resistance.

The invention makes it possible to produce an electric wire or cable for aeronautical and / or space use with insulation with comparable mechanical strength qualities to those of known insulators but of a price significantly less high and with good resistance properties propagation of the electric arc.

The wire or cable according to the invention comprises an insulator resistant to the propagation of the electric arc around a conductor, characterized in that the insulation is waterproof and includes a matrix, or base, of PTFE polymer and fibers mechanical reinforcement, continuous and of great length.

The fibers will be chosen to ensure the mechanical resistance required for the conductor insulation, i.e. cut resistance and resistance to abrasion (by scraping and thread by thread). They are continuous (no cut).

These fibers can be chosen from the group comprising: meta aramid or para-aramid fibers, polyamide-imide fibers, carbon fibers, fibers polyimides, PTFE fibers. Glass fibers can also be used if low resistance of the insulation to abrasion by scraping is sufficient. We can use either one fiber type, a combination of several types of fibers.

Unless the fiber is polyimide, the risk of propagation electric arc is practically eliminated. In the case where the fibers are polyimide, this risk is, anyway, considerably reduced due to the decrease in the quantity polyimide.

In addition, the yarn according to the invention is less expensive than a conventional thread. Indeed, the reinforcing fibers have often a much lower cost than polyimide or PTFE. For example the price per kilogram of a polyamide-imide fiber is about four times less than the price at kilogram of PTFE.

The insulation is preferably produced in the form of very long tape (typically several thousand meters) wrapped around the conductor.

As a variant, the insulation is extruded in great length (typically several thousand meters) around the conductor wire, and therefore it is in the form of a large extrudate length.

In the case where the insulation is a tape, the fibers are advantageously in the longitudinal direction of the ribbon.

The recovery rate between turns of the ribbon is example between 10 and 70%, preferably between 10 and 50%.

Reinforced tape has characteristics sufficient sealing, insulation and mechanical strength to be used alone on the conductor. Sealing is measured for example under atmospheric pressure by the possibility that the cable formed from the insulation around a core not to leave penetrate a fluid such as water radially, the ends said cable being emerged and the rest of the cable being submerged, at least for a few hours, for example some twelve hours. Thus tightness is measured for example by the test of tensile strength according to standard NF C 93523 or any standard equivalent (which corresponds to a 12-hour immersion), or well by the tensile test according to the ASTM standard D 3032 or even ASTM D 149.

However, it may be necessary to have a other PTFE tape around the matrix or PTFE base tape reinforced with fibers to standardize the surface outside of the wire. Indeed, fibers are likely to create irregularities on the outer surface of the wire unacceptable appearance. The external PTFE tape has for example a thickness between 50 and 100 µm and a recovery rate between turns between 20 and 70%.

In one embodiment, the conductor is 20 gauge, that is to say has a cross section of 0.6 mm ² , and the ribbon, with a matrix or base of PTFE reinforced with fibers, has a thickness of 50 µm. Known conductive wires of gauge 20 usually comprise four layers of polyimide insulating tape with a thickness of approximately 30 μm. Thus, if no special precaution is taken, the wire according to the invention will be significantly heavier than the conventional wire, especially since the density of the sintered PTFE (which is 2.2) is greater than the density ( 1.5 to 1.8) of the polyimide. Under these conditions, to limit the weight of the conductive wire fitted with insulating tape according to the invention, it would be advantageous to provide a recovery rate between turns of the tape which is relatively low, for example of the order of 10 to 20%.

Fibers can be used unbound with others, or can be used in an organized form such as nonwoven tape.

In one embodiment, the fibers are embedded in the PTFE matrix.

In another embodiment, the fibers are encrusted on the surface of the matrix, or base, of PTFE.

The conductor is for example made of copper or an alloy of copper or aluminum alloy and is advantageously covered of tin, silver or nickel.

la figure 1 est un schéma d'un ruban selon l'invention,

la figure 2 est un schéma analogue à celui de la figure 1, mais pour une variante,

la figure 3 est un schéma en coupe d'un fil ou câble selon l'invention,

les figures 4 et 4a sont des schémas illustrant un procédé de fabrication d'un ruban du type de celui de la figure 1 ou de la figure 2,

la figure 5 est un schéma illustrant un autre mode de réalisation de ruban selon l'invention et son procédé de fabrication, et

La figure 6 est un schéma montrant un ruban enroulé conformément à l'invention.

Dans les modes de réalisation de l'invention que l'on va décrire en relation avec les figures, l'isolant d'un conducteur pour fil d'usage aéronautique et/ou spatial est sous forme d'un ruban comprenant, d'une part, une matrice, ou base, de PTFE et, d'autre part, des fibres de renforcement mécanique. L'invention représentée concerne alors un tel ruban ainsi qu'un fil conducteur ou câble, notamment pour application aéronautique ou spatiale, équipé d'un tel ruban. Elle concerne aussi un procédé de fabrication d'un tel ruban et d'un fil équipé de ce ruban.Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:

FIG. 1 is a diagram of a ribbon according to the invention,

FIG. 2 is a diagram similar to that of FIG. 1, but for a variant,

FIG. 3 is a diagram in section of a wire or cable according to the invention,

FIGS. 4 and 4a are diagrams illustrating a method of manufacturing a ribbon of the type of that of FIG. 1 or of FIG. 2,

FIG. 5 is a diagram illustrating another embodiment of the ribbon according to the invention and its manufacturing process, and

Figure 6 is a diagram showing a ribbon wound in accordance with the invention.

In the embodiments of the invention which will be described in relation to the figures, the insulation of a conductor for wire for aeronautical and / or space use is in the form of a tape comprising, on the one hand, a matrix, or base, of PTFE and, on the other hand, mechanical reinforcement fibers. The invention shown then relates to such a ribbon as well as a conductive wire or cable, in particular for aeronautical or space application, equipped with such a ribbon. It also relates to a process for manufacturing such a ribbon and a wire equipped with this ribbon.

In the examples shown in Figures 1 and 2, continuous and very long fibers (typically several thousand meters) are drowned in a matrix of PTFE and in the variant shown in Figure 5, said fibers are encrusted on the surface of a PTFE base.

Whatever the embodiment, it is preferable to choose fibers which extend in the longitudinal direction of the ribbon and which have mechanical resistance properties such that the ribbon thus formed has a cut resistance and a resistance to scraping abrasion as high as possible and preferably comparable to the similar properties of known polyimide tapes. Thus, for a measurement made on a conductor comprising a conductive core wire of section 0.6 mm ² and an insulator on this core in a radial thickness of 120 μm, the abrasion wire to wire is typically of the order of 6 million cycles, scraping abrasion is typically of the order of 100 cycles for a force of 0.8 kg, and resistance to cutting, at room temperature, i.e. 20 ° C ± 5 ° C, with a needle 0.5 mm in diameter, is around 10 kgs.

To obtain these mechanical strength properties of the insulator of the conductor, we will preferably choose fibers having a high modulus of elasticity in traction, generally of 2 at 80 N / Tex (where Tex is the weight of the fiber in g / km).

In one example, fibers of polyamide-imide such as Kermel fibers from the company Rhodia. A fiber of this type is usually made up of a set of 200 to 300 fibers each having a diameter of around 5 or 10 µm.

In another example, we use meta fibers aramids such as those known under the brand Nomex or para-aramid fibers known under the brands Kevlar and Twaron of the Dupont de Nemours and Akzo companies. We recall here that a aramid is an aromatic polyamide.

We can also use carbon fibers, polyimide fibers, and possibly PTFE fibers.

In the embodiment shown in FIG. 1, the tape 10 comprises a matrix 12 of PTFE in which polyamide-imide fibers 14 ₁ , 14 ₂ , 14 ₃ , etc. are embedded. These fibers are unrelated to each other. However, they extend over a very long length in the longitudinal direction - represented by the arrow F - of the ribbon 10. In this example, the thickness of the ribbon is approximately 50 μm and its width on the order of 350 mm during its manufacture. After manufacture, the ribbon is cut longitudinally into ribbons of widths of approximately 4 to 15 mm each.

The embodiment shown in FIG. 2 differs from that described in relation to FIG. 1 by the fact that polyamide-imide fibers 14 ₁ , 14 ₂ , 14 ₃ , etc. are used. in the form of a nonwoven ribbon, that is to say that said fibers are organized according to parallel weft threads 14 ₁ , 14 ₂ , 14 ₃ and are assembled by transverse warp threads 16 ₁ (a single warp thread has been shown in Figure 2). In known manner, the distance between two neighboring warp son is significantly greater than the distance between two neighboring weft son 14 ₁ , 14 ₂ .

There is shown in Figure 3 a section of a wire 20 having a central conductor 22 composed of a plurality of strands 21 ₁ , 21 ₂ etc., on which is applied a tape 10 with a recovery rate of the order 20% from one turn to another.

The recovery rate is the ratio between, of a share, the width 1 of overlap of two turns 26 and 28 (Figure 6) of the ribbon wound on the conductor and, on the other hand, the total width L of the ribbon. In this way, along the wire we will have either a single thickness of the ribbon or a double thickness, the double thickness appearing only on approximately 20% of the length. In general, the recovery rate will be between 10 and 50%. However, it is in our interest to minimize this recovery rate so as to limit the weight of the wire and its outside diameter.

The ribbon 10 is covered by another ribbon 30 in PTFE of conventional type with a thickness between 30 and 100 µm. This ribbon 30 is wound in the opposite direction of the ribbon 10, and with a recovery rate between 20 and 70%.

We will describe below in relation to Figures 4 and 4a, a method of manufacturing the ribbon of FIGS. 1 and 2.

Prior to the corresponding manufacturing stages in FIGS. 4 and 4a, a surface treatment of the fibers so as to improve the bond, or adhesion, between these and the PTFE matrix. For this purpose, the fibers of an aqueous dispersion of PTFE. PTFE in solution aqueous is in the form of fine particles each of which has dimensions of the order of 0.1 µm.

In place of, or in addition to, this coating of fibers, it is also possible to provide a treatment using the Corona effect. In a way in itself known, the treatment by Corona effect consists in making circulate a fiber between two electrodes between which creates an electric arc. The plasma of the electric arc performs a surface treatment of the fiber which helps its adhesion subsequent to the PTFE in which it will be embedded or on which it will be encrusted.

After this fiber coating and / or treatment by Corona effect, the fibers and PTFE are introduced into a PTFE extruder operating according to a process known as "pultrusion". Unsintered PTFE powder is mixed with a lubricant such as a hydrocarbon, this mixture forming a whole pasty called "preform".

The pultrusion device comprises, first of all, a guide device 32 into which the fibers are introduced longitudinally at the same time as the pasty mixture.

Then the fibers are pulled and the mixture pasty is pushed under high pressure and at a temperature of the order of 40 ° C, in a flat die 34 which reduces the cross section of the assembly to reach a ribbon thickness of the order of 60 µm. After passing through the die 34, the ribbon undergoes at the station cooking 36 cooking at a lower or equal temperature at 250 ° C intended to evaporate the lubricant. The effort of traction at the exit of station 32 or 34 allows the installation of fibers in longitudinal direction. After station 36, the ribbon is introduced into a calendering station 38 which is shown schematically in Figure 4a. Calendering consists of reduce the thickness of the tape previously formed so as to reduce its thickness from 60 to 50 µm for example. This operation is generally carried out hot. It consists, in a way conventional, to provide two rollers 40 and 42 between which passes the ribbon 44 whose thickness is to be reduced.

Finally, the ribbon 10 thus produced is wound on a drum 46, then cut longitudinally as mentioned above.

To make the wire 20 (Figure 3), the non-sintered PTFE tape thus manufactured around the conductor 22 with, as mentioned above, a rate of recovery preferably around 20%, then the non-sintered PTFE tape 30 around this tape 10 in the opposite direction opposite. The assembly thus formed, which comprises non-PTFE sintered, is then subjected to a sintering operation which consists of heating to a temperature of at least 342 ° C for about 1 minute. This PTFE sintering operation increases the density of the latter, secures them different layers of ribbons, and changes the structure crystal of the PTFE polymer. Finally, sintering expels air residual trapped by unsintered PTFE tapes.

In the variant shown in Figure 5, the ribbon 50 is formed by the incrustation, by pressure, of fibers 52 at the surface of a ribbon 54 of unsintered PTFE whose thickness is between 25 and 40 µm. For this purpose, we start with a ribbon of fibers 52 arranged in a very long nonwoven ribbon and previously coated with an aqueous dispersion of PTFE and / or subjected to a Corona treatment as described above. This pre-treatment is particularly useful in this realization, because the pressures exerted between the ribbon 54 of PTFE and the fiber ribbon 52 are significantly less important than in the process described in relation to Figures 4 and 4a.

After processing the fibers, the ribbon 52 of fibers non woven is applied to the PTFE 54 tape and the assembly is hot calendered as described with figure 4a. Pressure exerted between the calendering rollers 56 and 58 encrusts the fibers in the surface of the ribbon 54, thereby forming the ribbon 50.

Alternatively (not shown), the nonwoven ribbon 52 is placed between 2 PTFE tapes.

Whatever the embodiment, the ribbon based of non-sintered PTFE which is thus formed is wound around the wire conductor as described with other modes of production.

Although it is most often beneficial to minimize the tape recovery rate in order to limit the weight of the trained conductor, it can happen that, on the contrary, interest in increasing it so as to improve resistance of the insulation thus formed. Also to optimize mechanical performance, two ribbons can be combined according to the invention each having a recovery rate of around 20 to 30%; in other words, in the embodiment shown in Figure 3, you can replace the PTFE tape 30 with a another ribbon according to the invention.

Claims (24)

Wire or cable comprising at least one insulator resistant to the propagation of the electric arc around at least one conductor, characterized in that the insulator is waterproof and comprises a matrix (12), or base (54), made of polymer polytetra-fluorethylene PTFE and mechanical reinforcement fibers (14 ₁ , 14 ₂ , ... 52) continuous and of great length. Wire or cable according to claim 1, characterized in that the fibers (14 ₁ , 14 ₂ , ...) are embedded in a matrix (12) of PTFE. Wire or cable according to claim 1, characterized in that the fibers (52) are embedded on the surface of the base (54) of PTFE. Wire or cable according to any one of the claims above, characterized in that the insulation has the form of a very long ribbon. Wire or cable according to claim 4, characterized in that the recovery rate of the turns of the ribbon is between 10 and 70%, preferably between 10 and 50%. Wire or cable according to claim 5, characterized in that the recovery rate of the turns of the ribbon is around 20%. Wire or cable according to claim 4, 5 or 6, characterized in that the ribbon has a thickness of the order of 50 µm. Wire or cable according to any one of the claims 1 to 3, characterized in that the insulation is in the form of a very long extrudate. Wire or cable according to any one of the preceding claims, characterized in that the mechanical reinforcement fibers (14 ₁ , 14 ₂ ... 52) form a non-woven tape. Wire or cable according to any one of Claims 1 to 8, characterized in that the mechanical reinforcement fibers (14 ₁ , 14 ₂ ... 52) are arranged in the matrix or on the base without any connection with each other . Wire or cable according to any one of the preceding claims, characterized in that the mechanical reinforcement fibers (14 ₁ , 14 ₂ ... 52) have a high modulus of elasticity. Wire or cable according to any one of previous claims, characterized in that the PTFE is Unsintered PTFE. Wire or cable according to any one of the claims previous, characterized in that the reinforcing fibers are chosen from the group comprising: meta-aramid fibers, para-aramid fibers, polyamide-imide fibers, carbon fibers, polyimide fibers and PTFE fibers. Wire or cable according to any one of the claims previous, characterized in that the conductor is in copper or copper alloy or aluminum alloy and is, of preferably coated with tin, silver, or nickel. Wire or cable according to any one of the claims previous, characterized in that the insulation is covered with PTFE insulator (30), for example in the form of a tape thickness of the order of 50 to 100 µm wrapped with a recovery coefficient between turns between 20 and 70%. Wire or cable according to any one of the claims previous, characterized in that the insulator is arranged directly against the conductor (22). Wire or cable according to any one of the claims previous, characterized in that the insulation is devoid polyimide. Wire or cable according to any one of the claims 4 to 7, characterized in that it has two ribbons overlapping. Application of a wire or cable according to one any of the preceding claims for use in aeronautics and / or space. PTFE-based insulating tape according to one of the claims 4 to 7 comprising a matrix, or base, in unsintered PTFE polymer and reinforcing fibers mechanical, continuous and very long, oriented substantially in the longitudinal direction of said ribbon. Method of manufacturing a ribbon according to claim 20, characterized in that the fibers being embedded in the PTFE matrix, we use a pultrusion process which consists of a pasty extrusion of PTFE and a traction simultaneous on fibers. Method of manufacturing a ribbon according to claim 20, characterized in that the fibers being encrusted in the PTFE base, apply by hot calendering and under pressing the fibers against a surface of PTFE tape. Method according to claim 22, characterized in what we choose a thick sintered PTFE tape between 25 and 40 µm. Method of manufacturing a ribbon according to claims 21 to 23, characterized in that before the assembly of the matrix, or base, to the fibers, one undergoes a treatment with fibers to improve the adhesion of the latter to PTFE, which treatment consisting in coating an aqueous solution of PTFE and / or a Corona treatment.

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