FR2762335A1 - Stranded electric cable - Google Patents

Abstract

To produce a stranded electric cable, the central strand (31) is tin ironed, to be assembled with the peripheral strands (32) to give the stranded cable (300). The cable is heated to melt the tin iron, and fuse the strands together along their contact lines (33).

Description

 The present invention relates to a method of assembling an electric conductor with strand formed from a central strand and at least one layer of peripheral strands wound around the central strand.

 The invention also relates to an electrical conductor obtained by this method.

 In electrical wiring, it is known to use, instead of a single conductor, a strand formed of a set of conductors of smaller diameter but whose total section is equal to that of the single conductor. This technique generally aims to obtain greater flexibility.

 By way of example, FIG. 1 shows an assembly of seven conductors formed by a central strand 11 surrounded by six peripheral strands 12 of the same diameter, the assembly forming a cord or a strand.

 The elementary strands are sometimes protected by a protective metallic coating in order to prevent oxidation and / or to facilitate connections.

 To establish electrical connections, you must access the insulated conductors by removing the insulation or moving it (displacement of the insulation).

 In the case of removal (stripping), the stranded conductor is released and the elementary strands are free and separate from each other. To pass the multi-strand conductor through a hole, the strands must be grouped together by any means, for example, the whole can be tinned, i.e. over-tinned.

 In the case of displacement of the insulator, there is a local modification of the shape of the multi-strand conductor with uncertainty about the pressure between the self-stripping fork and the conductive strands. Sometimes even, in the case of extreme tolerance, one or more strands are thrown outside the fork, which increases the risk of untimely contact with other neighboring elements.

 To avoid these problems associated with cables with stranded conductors (or strands), it is also known to complete the treatment of the strand for a cable with a second overall treatment, that is to say applied to the finished strand.

 In the case of tinned strands, this second treatment is an over-tinning operation, for example by passing through a bath of molten tin. The molten tin covers the outside of the strand.

Over-tinning has in principle very interesting advantages: - the strands of the strand remain joined in the event of stripping, - the strand has very good resistance in the event of connection by die
insulation placement.

But this over-tinning also has a certain number of serious drawbacks - an external tin deposit, - an inevitable increase in weight and external diameter
of the strand for an imposed copper section, - for conductors used in an insulating sheet, the ne
ceased to obtain a precise positioning of the elements im
pose to limit as much as possible the play between the interior shape
of the extrusion device and the strand. Over-tinned strands
always leave a tin deposit outside the hole in the
extrusion device followed by a jam resulting in
breakage of the strand pulled through the installation.

- the thickness of the tin film is difficult to adjust and for
make very small conductors, the tin / copper ratio
becomes bad for conductivity, - the interior of the strand is little or not wet by the tin and the
central strand is poorly connected to others.

The over-tinning process also has the following disadvantages - the slowness of the process considerably increasing the cost of
the implementation, - of the tin badly placed and put in too large quantity.

 The present invention aims to develop a method of assembling an electric stranded conductor for producing flat electric cables, overcoming the drawbacks mentioned above.

To this end, the invention relates to a process characterized in that - the central strand is tin-plated, - the central strand and the peripheral strands are assembled to
form a strand, - the strand is heated to melt the tinning product and
solder the central strand and the peripheral strands along the
contact lines.

 This over-tinning can be done with tin or an alloy such as an alloy of tin and lead.

 It may also be advantageous, according to another characteristic of the invention, to make, after the deposit of tin, a deposit of flux flux on the central strand.

 According to the invention, the over-tinning deposit is made either prior to the assembly of the strand, or at the time of the emission of the central strand which passes into a super-tinning bath then, if necessary, in a station for depositing the flux flux.

 The assembly is done continuously and the welding is also done behind the assembly point of the strand.

The tin, or more generally the over-tinning product, is deposited on the central strand to suffice to weld only the contact lines between the central strand and the peripheral strands without overflowing or protruding from the peripheral strands. The amount of tin or alloy thus added to the central strand represents a negligible weight relative to the weight of the strand and does not modify the section of the strand. This also retains the flexibility of the strand as opposed to over-tinning the complete strand which considerably stiffens the strand. The strand passing through the extrusion device (at the same time as the other strands) during the manufacture of a multiconductor cable (that is to say comprising several or multiple parallel strands) is not likely to leave tin deposits on the strand guide and alignment device.

 Furthermore, as the over-tinning product is on the central strand, and in sufficient but not excessive quantity to fill the interstices between the central strand and the peripheral strands, an excellent bond is produced between the different strands which gives the strand strength. , for example for stripping or for insulation displacement connections.

 The process according to the invention, which is carried out on parade, at the speed of assembly of the strand, does not present any drawback linked to an additional operation or to a slowness of implementation since the application of the over-tinning product and that possible welding flux are done in hidden time.

 Finally, at no time is there an excessive quantity of tin.

 The invention also relates to a stranded electrical conductor formed by a central strand and at least one layer of coiled peripheral strands, the contact lines formed between the central strand and the peripheral strands are occupied with tinning product welding the central strand to the peripheral strands.

 The present invention will be described below in more detail with the aid of the accompanying drawings in which the strands and the strands are shown on a very enlarged scale.

FIG. 1 is a schematic section of a strand of electric conductor with seven strands,
FIG. 2 shows, in cross section, a strand according to FIG. 1, over-tinned,
FIG. 3 schematically shows the displacement of the strands of a strand of a flat cable when making a connection by displacement of insulation,
- Figure 4 shows schematically a section of a stranded conductor according to the present invention.

 According to FIG. 1, an example of a strand to which the invention applies consists of a central strand 11 surrounded by peripheral strands 12. These peripheral strands 12 form a helix, either on the left or on the right, surrounding the central strand 11. This propeller can also have an alternating twist known as an SZ assembly. In this case the propeller, formed by the outer strands 12, is for example first turned to the left for a certain number of steps then to the right then to the left and so on alternating. Usually, the strand 100 thus produced is fixed by a crossed covering made directly after the assembly of the strands. This is true for optical cables. In the case of an electrically conductive strand, the strand is blocked by welding immediately after stranding.

 In the case of stranding in one direction, the welding is important to have the advantages already mentioned above. In the case of SZ stranding, welding is essential to block stranding.

 FIG. 2 schematically shows the section of an over-tinned strand according to the prior art. This strand, also composed of a central strand 11 and peripheral strands 12, has received by over-tinning a layer of over-tinning product 13 intended to block the strand.

 However, this tinning product 13 is localized only in the intervals in the form of external corners 14 of the external strands 12 and does not penetrate or only very difficultly into the internal corners 15 formed between the internal strand 11 and the external strands 12.

 Figure 3 shows in section the deformation undergone by a strand 100 integrated in a flat cable 200 when a connection is made by displacement of insulation; only the strand 100 and the insulation 201, 202 are represented and not the other parallel strands forming part of the flat cable.

 The connection to flat cables of the cable 200 type is generally made by a cutting fork 15 which plugs into the cable 200 in line with a conductor (strand 100). The two branches 151, 152, with their cutting ends, penetrate the cable and push back the insulation to cover the strand 100. When the strand is not assembled with over-tinning, the strands 11, 12 can move relative to each other. to the others under the effect of the thrust of the fork 15 and take the form shown in FIG. 3. This situation has already been mentioned in the preamble.

 Figure 4 is a cross section of a strand 300 according to the invention. This strand, shown in the case of an example with a central conductor 31 and six peripheral conductors 32, shows that the contact lines 33, between the central strand 31 and the peripheral strands 32, are occupied with tinning product which forms a weld and does not extend beyond the outer strands 32.

 A suitable dimensioning of the thickness of the coating of the central strand 31 makes it possible to guarantee that there will be no excess tin passing outside.

 Any heating mode can be used for this fusion. It is easy to maintain the central strand 31 in its central position with the usual cabling means.

 The invention can be applied to very different constructions such as for example the construction (1 + 6) described above or (3 + 9).

 Tin can also be replaced by an alloy such as a tin / lead alloy.

Claims (3)

CLAIMS 1 ") Method for assembling an electric conductor with strand formed from a central strand and at least one layer of peripheral strands wound around the central strand, characterized in that - a central tin strand is tin-plated (31), - the central strand (31) and the peripheral strands (32) are assembled to form a strand (300), - the strand is heated to melt the tinning product and weld the central strand (31) and the peripheral strands (32) along the contact lines (33). 20) Method according to claim 1, characterized in that the over-tinning is carried out with tin or a tin / lead alloy. 30) Method according to claim 1, characterized in that a flux flux is deposited on the central strand over-tin. 40) electric conductor with strand formed by a central strand and at least one layer of coiled peripheral strands, produced according to the method of any one of claims 1 to 3, characterized in that the contact lines (33) between the central strand (31) and the peripheral strands (32) are occupied with tinning product welding the central strand (31) to the peripheral strands (32).