EP1158542B1 - Flexible coaxial cable and its manufacturing method - Google Patents

Abstract

A flexible coaxial cable includes a shield formed by at least one metal tape provided with a metal coating and wound helically around the insulated core of the cable. The shield is sealed to itself in leakproof manner by the coating which is melted so as to bond directly together the overlapping turns of a single tape or the overlapping turns of two superposed tapes by subjecting the cable provided with the shield to peripheral induction heating.

Description

The present invention relates to flexible coaxial cables and more particularly those of small section, which are usable in particular in medical imaging, or on portable transmission equipment such as computers, or for microwave transmissions.

One of the requirements to be satisfied is that the outside driver or screen of such a cable either and remains perfectly efficient while the cable and so this screen is flexible.

GB-A-2 130 430 discloses a flexible coaxial cable, which has a flexible conductive core, flexible insulation around said soul, a flexible conductor screen around said insulation and a possible flexible outer protective sheath. The screen of this cable is consisting of an internal metal ribbon, which is folded longitudinally around the insulation, an external metal ribbon, which is wound helically around the inner ribbon, and a possible metallic braid, which is then mounted around the outer ribbon and intended to allow make a connection to the screen at the ends of the cable. Ribbon edges internal overlap or are welded along the cable and those of the ribbon external overlap widely from one winding to the next. Each of the ribbons can be in a single metal or be made of composite material by example tinned copper or plastic / metal laminate.

In this cable thus known, the outer ribbon serves to cover cracks or fissures, which are likely to appear in the ribbon internal under the effect of folds / unfolding of the cable. Its windings have however, they themselves tend to move during these folds / unfoldings of the cable, which modifies the contact resistance and the geometry assembly of the windings between them and on the inner ribbon, leading to a helical current path in this outer ribbon and limiting the performance of the screen.

EP-A-0 236 096 also discloses a coaxial cable flexible, which avoids the disadvantages of the cable known from the aforementioned document and has for this purpose a screen with a laid copper ribbon longitudinally or helically wrapped around the insulation by having overlapping edges, a copper braid around this ribbon and a layer of metal closing the opening along the overlapping edges said ribbon and the interstices of the braid and coming to secure the braid and said tape, so that the screen is flexible and without openings.

For the manufacture of such a cable, after the installation of the screen and of the braid, the cable is passed through a bath of molten metal, the occurrence of tin. During the application of this molten metal, the ribbon plays the role of heat shield to thermally insulate the insulation of the molten metal, while in the absence of the ribbon the molten metal would come directly into contact with the insulation and could degrade it.

The coaxial cable thus obtained is flexible while having a screen performance. However, the layer of metal between the braid and the ribbon no uniform thickness all around the cable, due to its fluidity in the state molten. Moreover, the method of manufacturing such a screen is long and dresser. As indicated in this document, it can not be realized in online, because of the very different speeds of setting up its different parts. The setting up of the braid being much slower than that of the other parties. By the way, while using a braid tight is advantageous for a good shutter possible of its interstices by melted metal, it makes it more difficult and uncertain a good flow of the molten metal through it for its bond to the ribbon and the closing the opening line of the edges of the ribbon. In addition, the use a molten tin bath requires safety devices to prevent risk of burns and inhalation of vapors.

The present invention aims to provide a flexible coaxial cable having a reliable screen structure leading to excellent performance and stable over time and allowing a manufacturing process particularly simple and fast.

According to the invention, a flexible coaxial cable comprising a core flexible conductor, flexible insulation around said core and a screen flexible metal around said insulation, said screen having a first metal ribbon with metal coating on at least a face thereof and wound helically around said insulation in having successive windings overlapping in a zone of continuous helical overlap along said cable, is characterized in that that said first ribbon is closed tightly on itself in any said area of overlap of said windings by said coating welding said windings to each other.

Similarly according to the present invention, a flexible coaxial cable, having a flexible conductive core, flexible insulation around said core and a flexible metal screen around said insulation, said screen having a first metal ribbon and a second ribbon outer metal wound helically around said insulation and provided at least for one of them with a metallic coating on the least one face thereof is characterized in that each of said ribbons has windings with a continuous helical gap along said cable, what the windings of said second ribbon totally cover the dejoining the first ribbon and partially the windings of said first ribbon, and in that the overlapping areas of the windings of said ribbons are sealingly welded by said coating provided on to least one of the two faces opposite said ribbons.

• ledit premier ruban présente un pas d'enroulement compris entre 0,2 et 10 mm et ledit câble un diamètre sur ladite isolation compris entre 0,2 et 8 mm.
• ledit écran comporte un ruban métallique intérieur posé longitudinalement directement autour de ladite isolation, en ayant des bords se chevauchant.

This cable advantageously has at least one of the following additional features:

• said first ribbon has a winding pitch of between 0.2 and 10 mm and said cable has a diameter on said insulation of between 0.2 and 8 mm.
• said screen comprises an inner metal ribbon laid longitudinally directly around said insulation, having overlapping edges.

The subject of the invention is also a process for manufacturing said cable, characterized in that it consists in subjecting the cable provided with said screen to a peripheral welding heater of the windings of each ribbon component said screen, without external input welding material.

Advantageously, the peripheral heating of welding is ensured by a high-frequency induction coil, mounted on a continuous production line of said screen.

• la figure 1 est une vue en perspective d'un premier mode de réalisation d'un câble coaxial flexible selon l'invention,
• la figure 2 est une vue en perspective d'un autre mode de réalisation d'un câble coaxial flexible selon l'invention,
• la figure 3 est une vue en perspective d'un autre mode de réalisation du câble selon l'invention,
• la figure 4 est une vue schématique illustrant le procédé de réalisation du câble de la figure 1.

The characteristics and advantages of the invention will emerge from the description given below with reference to the accompanying drawings in which:

• FIG. 1 is a perspective view of a first embodiment of a flexible coaxial cable according to the invention,
• FIG. 2 is a perspective view of another embodiment of a flexible coaxial cable according to the invention,
• FIG. 3 is a perspective view of another embodiment of the cable according to the invention,
• FIG. 4 is a schematic view illustrating the method for producing the cable of FIG. 1.

With reference to FIG. 1, the cable comprises a conductive core flexible 1, a flexible insulation 2 covering said core and a flexible screen 3 surrounding said insulation.

This flexible screen 3 is constituted by a metal strip 4, which is provided with a metal coating 5 on at least its outer face, is helically wrapped around the insulation, having its windings overlapping widely, and is closed tightly on itself by said coating welding said coils to each other in any their area of overlap.

The overlap noted 6 of the windings is illustrated by 50%. In it can be less, however, being at least 20 to 25% and preferably of the order of 40%. It defines the area of overlap welded, without the addition of external material, which is helical and along the cable for a perfect seal and conservation of performance of the screen 3 thus formed.

In this cable, the conductive core 1 is a massive core single conductor or stranded stranded core, for example bare copper, tinned, silver or copper alloy or steel covered with copper.

The insulation is a conventional or expanded dielectric, such as PTFE, FEP, PFA, PE or PP. The screen 4 is preferably made by a ribbon tinned copper, whose tin coating is melted for soldering direct from its coils to each other throughout their entire area of overlap. The ribbon 4 can be tinned on both sides.

This cable is advantageously a coaxial cable diameter on the insulation 2 between 0.2 and 8 mm. The ribbon used 4 has a width of 0.2 to 15 mm and has a winding pitch of 0.12 to 10 mm, depending on the diameter of the insulation.

The cable can of course be provided with an outer sheath of protection, which is optional and not shown.

• Un ruban intérieur 14, qui est posé en long directement autour de l'isolation 2 et a ses bords se recouvrant longitudinalement ainsi que représenté en 15.
• Un ruban intermédiaire 16 enroulé hélicoïdalement autour du ruban 14 et
• Un ruban extérieur 18 enroulé hélidoïdalement autour du ruban 16.

With reference to FIGS. 2 and 3, the screen made around the insulation 2 of the conductive core 1 has been designated by 13 or 13 '. This metal screen 13 or 13' comprises:

• An inner ribbon 14, which is laid lengthwise directly around the insulation 2 and has its overlapping edges longitudinally as shown in 15.
• An intermediate ribbon 16 wound helically around the ribbon 14 and
• An outer ribbon 18 wound helically around the ribbon 16.

The ribbon 14 is advantageously constituted by a laminated ribbon plastic / metal whose plastic side is against insulation 2. Ribbons 16 and 18 are advantageously constituted by metal ribbons, for example made of copper, and provided with metal coating layers 17 and 19, by example tin or tin-based or, at least on their inner side.

The ribbons 16 and 18 are wound in the same direction and at the same not, being shifted relative to each other on the order of ¼ to ¾ of the value of the winding pitch. They are welded to each other and to the ribbon 14 by the covers 17 and 19.

In FIG. 2, each of the two helical ribbons 16 and 18 has its windings overlapping widely. The inner longitudinal ribbon 14 is optional.

In FIG. 3, each of the helical ribbons 16 and 18 presents a 16 'and 18' between its windings, this gap being continuous along the cable. The coils of the outermost helical ribbon 18 overlap totally the splice 16 'of the ribbon 16 and partially the windings of this one. The longitudinal tape 14 is optional in the cable screen.

The cable of FIG. 2 or 3 may also comprise a sheath external protection, not shown. Its dimensions and not winding of its helical ribbons are as defined for the cable of Figure 1.

With reference to FIG. 1, it can be seen that the cable may comprise a longitudinal ribbon (such as ribbon 14 in Figure 2 or 3) under the ribbon helical 4, the latter then being provided with an inner metal coating and optionally the outer metal coating 5.

The process of continuous online production of the screen 3 on the soul conductor 1 provided with its insulation 2 is illustrated in FIG. insulated conductor denoted by references 1 and 2 is taken from a coil 20 and passes through a tape station 22, which receives the tape 4 5. This tape is taken from a roll 21 and is helically wrapped around the isolated core, as described next to Figure 1. The cable provided with this ribbon then passes to a station 23 of welding of the ribbon windings to each other, in which the welding is carried out, without external contribution of welding material, directly by the coating 5. This welding station comprises at this effect an induction coil 24 fed at high frequency, which ensures the melting of the coating 5 and the resultant welding of the coils each to others. The cable provided with its screen 3 thus sealed is stored on a receiving coil 25.

Of course, the continuous production of the screen 13 or 13 ' cable of Figure 2 or 3 is obtained in a similar way, by putting the if necessary in place the optional internal ribbon laid lengthwise around the soul isolated then the first helical ribbon and finally the outer helical ribbon by then scrolling the cable in the aforementioned soldering station. The cable is then stored on the receiving coil.

Claims (9)

1. A flexible coaxial cable including a flexible conducting core (1), a flexible insulation (2) around said core and a flexible metal shield (3, 13, 13') around said insulation, said shield including a first metal tape (4, 16), provided with a metal coating (5, 17), on at least one face of the latter and helically wound around said insulation while having overlapping successive windings according to a continuous helical overlapping area along said cable, characterized in that said first tape (4) is sealed over itself in the whole of said overlapping area of said windings by said coating (5) soldering said windings with each other.
2. The cable according to claim 1, characterized in that it includes a second metal tape (18) helically wound onto said first tape (16) by having windings overlapping each other, provided with a metal coating (19) on at least one of its faces located facing said first tape and with its windings soldered to each other and to those of said first tape.
3. A flexible coaxial cable, including a flexible conducting core (1), a flexible insulation (2) around said core and a flexible metal shield (13') around said insulation, said shield including a first metal tape (16) and a second external metal tape (18) helically wound around said insulation and provided, at least for one of them, with a metal coating (17, 19) on at least one face of the latter, characterized in that each of said tapes (16, 18) has windings with a continuous helical butt-gap (16', 18') along said cable, in that the windings of said second tape (18) cover the butt-gap of the first tape (16) totally and the windings of said first tape partly, and in that the overlapping areas of the windings of said tapes are sealably soldered (17, 19), provided on at least one of the two faces facing said tapes.
4. The cable according to any of claims 1 to 3, characterized in that said shield further includes an interior metal tape (14), longitudinally set down directly around said insulation, while having overlapping edges (15).
5. The cable according to claim 4, characterized in that said interior tape is in plastic/metal laminate.
6. The cable according to any of claims 1 and 3, characterized in that said first tape (4, 16) has a coil pitch between 0.2 and 10 mm and said cable has a diameter on said insulation between 0.2 and 8 mm.
7. The cable according to any of claims 1 to 6, characterized in that each tape provided with a metal coating is in tinned copper.
8. A method for manufacturing a cable according to any of claims 1 to 7, characterized in that it consists of subjecting the cable provided with said shield to peripheral heating for soldering the windings of each tape making up said shield, without any external supply of solder material.
9. The method according to claim 8, characterized in that it consists of providing said peripheral heating for soldering by means of high frequency induction coiling (24), which is provided on a continuous line for manufacturing said shield on the cable and is crossed by said cable.

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