EP0500449B1 - Elongated member insulated by means of an insulating jacket - Google Patents

Description

The present invention relates to an elongated body insulated by means of an envelope made of an insulating material.

An elongated body is any body of great length in front of its diameter. For example, elongated bodies are qualified as electrical conductors or cables of all kinds, hollow profile bars, tubes, pipes, or more generally pipelines.

The present invention relates in particular to the insulation of cables or electrical conductors. We will focus in the following on the case of electrical conductors.

Patent application FR-2 119 939 reports an electrical conductor insulated by means of a taping with a covering rate at least equal to 50% of a tape made of a synthetic material. This tape is then covered with a varnish of a dried and hardened synthetic material. The preferential recovery rates indicated in this document lead in practice to making so-called "overlapping" or "ribbed" tapes. The presence of these overlaps results in an irregularity in the radial thickness of the conductor; therefore, a smooth exterior surface cannot be obtained.

These overlaps also form projecting edges which constitute points of aggression for external mechanical forces. This can cause the insulation to tear off at the overlapping areas, which exposes the conductor to possible high temperatures, the influence of humidity or chemically aggressive media.

The same problems as those mentioned above arise when it comes to isolating any elongated body.

The object of the present invention is therefore to mark out an elongated body with tape insulation having a smooth external appearance.

The present invention proposes for this purpose an elongated body insulated by means of an insulating envelope, said envelope consisting of a tape of synthetic material tape around said body, and covered with a layer of varnish of a synthetic material, characterized in that the tape is such that there is a groove between the free edge of any part of the coil not covered by the following turns and the surface not covered with the previous turn, the width of said groove being substantially between 0 and 5% of the width of said strip, and strictly greater than zero.

Advantageously, the grooves have a width substantially equal to 1% of that of the ribbon. This value allows the varnish to hang well in the grooves before coating the ribbon.

The layer of varnish can be deposited by soaking in a bath containing the varnish, then undergoing a heat treatment, such as sintering, intended to remove the volatile substances contained in the varnish and to cook the latter.

According to an additional characteristic, the varnish contains suitable surfactants allowing it, before heat treatment, to hang on the surface which it covers.

The varnish layer can also be deposited by an electrostatic process or by a fluidized bed process.

The invention can be applied for example to the external insulation of electric cables, electric conductors, tubes, pipes, or conduits.

It can also be applied to the manufacture of hollow profile bars, the elongated body then being a support body which is removed once the heat treatment has ended.

The electric cables, electric conductors, tubes, pipes, conduits or bars of hollow profiles thus obtained have a smooth external surface and a concentricity greater than 90%.

Other characteristics and advantages of the present invention will appear in the following description of an electrical conductor, the insulating envelope of which conforms to the invention, given by way of illustration and in no way limiting.

• la figure 1 représente un conducteur électrique (ou fil de câblage) dont l'enveloppe isolante est conforme à l'invention,
• la figure 2 est un grossissement d'une partie de la figure 1,
• la figure 3 représente schématiquement un four de vernissage pour enduction du fil de câblage selon l'invention.

In the following figures:

• FIG. 1 represents an electrical conductor (or wiring wire) whose insulating envelope conforms to the invention,
• FIG. 2 is a magnification of part of FIG. 1,
• FIG. 3 schematically represents a varnishing oven for coating the wiring wire according to the invention.

In Figures 1 and 2, a conductor 1 (of diameter equal to 1.25 min) is covered with a PTFE tape 2 of thickness equal to 76 μ and of width L equal to approximately 10 mm. More specifically, the ribbon is banded around the conductor 1 according to a helical winding whose pitch is such that each turn 3 of width L is covered over 49% of its width by the next turn, that is to say over a width L ′ = 49%. L = 4.9 mm. We then say that the recovery coefficient is 49%. Such a winding therefore creates gaps or grooves 4 of width Δ = 1%. L = 0.1 mm between the free edge 5 of any part of the coil not covered by the following turns and the surface 6 not covered by the previous coil.

After taping, the conductor 7 thus obtained is coated with varnish in a varnishing oven 8 (see FIG. 3). The varnishing is carried out in three passes P₁, P₂ and P₃. At each pass, the conductor 7 is dipped in a coating tank 9 containing an aqueous dispersion (or varnish) of polytetrafluoroethylene (PTFE) to which surfactants have been added. These surfactants are adapted to the PTFE varnish so that, when the conductor 7 is removed from the tank 9, the still liquid varnish fills the grooves 4 and coats the conductor 7 while hanging on the surface of the conductor and does not "sinks" not as would happen if the width of the joints was not adapted and if the surface tension created by the surfactants was not optimized.

Then, the conductor 7 coated with the PTFE varnish undergoes, in a vertical baking tower 10, a heat treatment (or sintering) intended to remove the solvents and to bake the varnish.

After the first pass (quenching and sintering), two other similar passes P₂ and P₃ are carried out, in order to obtain a protective layer corresponding to specifications of desired radial thickness and operating voltage.

The foregoing description of a possible mode of application of the varnish has of course been given for information only. The application of the varnish can indeed be carried out by any conventional process in this field; one can thus carry out an application by electrostatic process or an application by fluidized bed.

The final wiring wire obtained therefore has a layer upper varnish 11 coating the tape and inserted into the grooves 4. This layer of varnish has a thickness of between 27 and 36 μ. The wiring wire has, thanks to the coating of varnish and the presence of thin gaps, a smooth exterior appearance offering no point of attack for mechanical forces which could give rise to tearing or tearing of the insulating jacket, and a good characteristic concentricity of the bands, that is to say greater than 90%.

Unlike the wiring wires of the prior art, the wiring wires according to the invention also have gaps of reduced width allowing the varnish not to slip on the tape and to fill the grooves formed before coating. the ribbon to form a smooth envelope.

In addition, the manufacture of the wiring wires according to the invention does not involve any complex modification of conventional technologies. In fact, a conventional tape tray is used by simply adapting the tape pitch to the desired covering coefficient, and the varnishing is also carried out according to a conventional technique. The product obtained is of better quality, and has electrical, chemical and operating voltage characteristics identical to those of the cabling wires with tape or extruded insulation of the prior art. In particular, the external insulation obtained is capable of withstanding electrical and mechanical stresses.

Of course, the present invention is not limited to the mode of implementation which has been described.

First, the width of the gap is not necessarily equal to 1% of the width of the ribbon, and it can preferably take any value between 0 and 5% and always strictly greater than 0. For a width greater than 5 % of the width of the tape, the varnish may slip on the tape without filling the gaps, even in the presence of tension-active agents. It would then be more difficult to obtain a smooth insulating envelope.

Furthermore, a wiring wire has been described in which the ribbon and the varnish are made from the same material, but it is possible to choose the ribbon and the varnish in different materials, from the moment that they are compatible with each other and that the varnish can adhere to the tape.

For example, you can take a PTFE tape with a varnish in aqueous solution of ethylene fluorinated propylene copolymer (FEP) or a polyimide tape (like the "KAPTON" registered trademark) with a polyurethane varnish or polyimide, or finally a polyester tape with a nylon or polyester varnish.

In addition, the invention can be applied to a structure other than that of the wiring wire, such as for example a coaxial cable, the outer insulating envelope of which consists of a composite tape of polyimide and PTFE and a varnish. PTFE or FEP. Obviously all the pairs of materials mentioned above can also be used to produce the outer envelope of a coaxial cable.

For cables of non-circular section (rectangular or polygonal for example), where it is impossible to obtain by extrusion a centered external insulation, the invention makes it possible to produce an insulating envelope having all the necessary qualities.

Advantageously, it is possible to coat the cable or the conductor with more than three layers of varnish. This makes it possible to fill all the grooves well, to meet the desired performance in operating voltage for the cable and to constitute a radial thickness of insulation in accordance with the requested specifications.

In general, the invention can be applied to the insulation of any elongated body and in particular to that of cables of all types, including fiber optic cables, electrical conductors of all kinds and possibly pipes, tubes. or pipes whose operating environment implies an insulating protection having the qualities of that produced according to the invention.

The invention can also be applied to the manufacture of hollow profile bars. For this, it suffices to provide the insulation on a support or support body which is removed after manufacture of the formed profile bar.

It is quite obvious that the numerical values given constitute only one example of realization which can in no case be considered limiting. For example, the thickness of the ribbon can be between 50 and 200 μ and its width between 7 and 12 mm.

Claims (14)

1. An elongate body insulated by means of an insulating covering, said covering being constituted by a tape (2) made of synthetic material taped around said body (1) and covered in a layer of varnish (11) made of synthetic material, the body being characterized in that the taping is such that there exists a groove (4) between the free edge (5) of any portion of a turn (3) that is not covered by the following turns and the uncovered surface (6) of the preceding turn, the width of said groove (4) lying substantially in the range 0% to 5% of the width of said tape (2) and being strictly greater than zero.
2. A body according to claim 1, characterized in that the width of said groove (4) is substantially equal to 1% of the width of said tape (2).
3. A body according to claim 1 or 2, characterized in that said tape (2) is made of PTFE, and in that said varnish is based on PTFE.
4. A body according to claim 1 or 2, characterized in that said tape (2) is made of PTFE, and in that said varnish is an aqueous solution of FEP.
5. A body according to claim 1 or 2, characterized in that said tape (2) is made of polyamide, and in that said varnish is selected from a varnish based on polyurethane and a varnish based on polyamide.
6. A body according to claim 1 or 2, characterized in that said tape (2) is made of polyester, and in that said varnish is selected from a nylon varnish and a polyester varnish.
7. A body according to any one of claims 1 to 6, characterized in that said layer of varnish (11) is deposited by immersion in a bath containing said varnish, followed by heat treatment for eliminating the volatile substances contained in said varnish and for curing said varnish.
8. A body according to claim 7, characterized in that said varnish contains appropriate wetting agents enabling it to adhere to the surface it covers prior to said heat treatment.
9. A body according to claim 7 or 8, characterized in that said heat treatment is sintering.
10. A body according to any one of claims 1 to 6, characterized in that said layer of varnish (11) is applied by an electrostatic method.
11. A body according to any one of claims 1 to 6, characterized in that said layer of varnish (11) is applied by a fluidized bed method.
12. A body according to any one of claims 1 to 11, characterized in that it is constituted by an electrical conductor insulated by means of said covering, and in that its outside surface is smooth having concentricity greater than 90%.
13. A body according to any one of claims 1 to 11, characterized in that it comprises, coaxially from the inside towards the outside:
       a central conductor;
       an intermediate sheath of dielectric material; and
       an outer conductor;
       in that it is insulated by means of said covering, and in that it has a smooth outside surface with concentricity greater than 90%.
14. A body according to any one of claims 1 to 11, characterized in that it is constituted by a tube, a pipe, or a duct isolated by means of said covering and having a smooth outside surface with concentricity greater than 90%.

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