GB2139806A - Electric cable - Google Patents

Abstract

Flexible electric cable for signal transfer between a ground control station and a rapidly moving body, comprising at least one and preferably two substantially parallel, varnish-insulated 15, electrical conductors 14, which are approximately centrally embedded over the entire length of a pulling member formed from individual carrier fibre groups formed from a plurality of thin individual filaments 16. The varnish-insulated electrical conductors are bonded together and are held by a first extrusion layer 18 within the carrier fibres passed around the conductors with three to six lays. Onto the first extrusion layer is applied a second extrusion layer 19, which gives the cable an approximately circular cross-section and forms a uniform surface. The fibres are of polyamide or polyester and the extrusion layers of polycarbonate. Apparatus for making the cable comprises a stranding machine (45, Fig. 4) and tandem extrusion heads (56, 57). <IMAGE>

Description

SPECIFICATION Flexible electric cable The invention relates to a flexible electric cable for signal transfer to moving bodies, a process for the production thereof and an apparatus for performing the process according to the preambles of claims 1,3 and 6.

Flexible electric cables or stranded wires for signal transfer between a ground control station and a rapidly moving body, particularly a missile, are for example known from German Patent 1,765,133. In the latter, two parallel, varnish-insulated copper wires are bonded together and are centrally guided in the pulling member held by natural silk covering with carrier threads combined into at least three individual carrier thread groups. Such conductors permit signal transfer to moving missiles up to speeds of approximately 260 m/sec and up to ranges of approximately 5000m.

For movement-kinematic reasons, the conductor supply for signal transfer must be carried in the form of one of more reels in the moving body. Particularly in the case of flying bodies during flight, the static and dynamic loads of the conductor during reeling off are high at the desired flight speeds and ranges and, apart from the widely varying stresses during the launch and cruising phases, must be reproducibly constant during the flight time.

For this purpose, the individual windings of the reels having a plurality of winding layers must be bonded together during the production thereof, i.e.

during winding, in such a way that in addition to a uniform bonding for each winding, there are identical bonding forces, apart from the aforementioned differences in connection with the launch and cruising phases of the missile. Errors in the manufacture of the reels, have a direct influence on the reeling off characteristics thereof when they are used in missiles. For example, non-uniform and lack of bonding lead to the removal of several layers simultaneously which, in the case of reeling off during flight, leads to kinking on the electrical conductors. However, experience has shown that such kinks break during the next load surge, so that communications are interrupted. Furthermore, such removed layer groups are particularly exposed to mechanical and thermal stresses, both during the launch and the cruising phase of such missiles, which are generally driven by a hot gas jet.As is known, during the launch phase, such missiles have to be accelerated from zero speed to cruising speed so that the cable is highly dynamically stressed by the rapid increase in the reeling off speed and is also thermally stressed by the direct proximity of the gas jet. During the cruising phase, the cable is exposed in an uncontrollable manner to the action of hot particles, which are detached from the always present tracer or flare composition on the missile. The action of these particles is particularly devasting when they strike the removed layer groups, quite apart from the fact that as a result of the larger surface area of the latter, they can be struck more easily than a drawn-off single cable winding extending in pear-shaped manner.

Whereas during the manufacture of the conductors, the individual production stages are monitored by suitable measuring processes and means and consequently reproducible values can be respected, this has not been possible or has only been possible in an inadequate manner hitherto during the winding of the reels, because for examining the actual bbnding force between the individual windings, the latter must be removed from the reel, so that the latter is destroyed. Thus, the manufacture of such reels can only be monitored by random sampling, which merely serves to detect error or fault trends. In order to produce a reel, having optimum uniform reeling off characteristics, high workmanship is required of the personnel working on the winding machine. Such a state is not only contrary to modern maufacturing methods, but also involves unacceptably high costs.

A further uncertainty factor is the characteristics of the natural silk fibres, whose specific characteristics fluctuate widely and can therefore vary between individual charges with respect to the impregnation capacity and consequently the bonding force.

It is also becoming increasingly difficult to obtain natural silk. Thus, for a long time, efforts have been made to replace the natural silk by other materials, which can always be produced with the same characteristics and are always available in random quantities. This leads to the problem of the selection and adaption of such materials and production processes for cables of the aforementioned type.

Thus, apart from the electrical conductors, carrier fibres are also necessary which, together with the fixing means, must be appropriately related to one another with respect to the breaking length, elasticity, elongation at break and expansion coefficients.

There is also a need for higher reeling off speeds and longer ranges, so that fibres with maximum breaking lengths are required. Finally, considerable difficulties are encountered in processing such fibres, in conjunction with the generally varnish-insulated copper conductors with a diameter of approximately 0.07mm and an elongation at break equal to or greater than 25%. In order to obtain uniform electrical characteristics over the entire length of such a so-called guidance signal line, there must always be a maximum identical geometrical association with the carrier fibres and the braiding fixing the position of the individual components. As a result of this association, the reeling off characteristics of the guidance signal line is greatly influenced by the guidance wire reel located in the body to be guided.

There is consequently a considerable need for a stranded wire or cable to satisfy all these demands, which can be manufactured with identical characteristics over long production periods and which can be more easily uniformly bonded than hitherto on transferring into a so-called steering wire reel, whilst still having uniform reeling off characteristics after prolonged storage.

On the basis of the extrusion process for the production of insulated winding wires, known from DAS 2,638,763, the problem of the invention is to provide a new, flexible, electric cable, a process for the production thereof and an apparatus for performing the process, whose design and construction make it possible to produce electric cables for guidance signal transfer without the use of natural silk fibres, which permit extensive ranges and high reeling off speeds. However, despite the considerable cable length, there must be no deterioration to the uniformity of the geometrical association of electrical conductors, carrier threads and external fixing, together with the external diameter of the cable over the entire cable length.In addition, it must be possible to more easily and reproducibly bond the same during the winding of guidance wire reels, whilst obviating any risk of the conductor wires being destroyed as a result of heat action.

For cables of the aforementioned type, this problem is solved by the characterizing features of claim 1, for the process by the characterizing features of claim 1 and forthe apparatus by the characterizing features of claim 6. Further features of the invention can be gathered from the subclaims.

The flexible cable construction according to the invention for the first time makes any braiding unnecessary and ensures an approximately identical geometrical configuration of the cable over its entire length. When using aromatic polyamide fibres (organic aramide fibres) as the carrier fibres, they can be processed much more easily with the metal conductors than hitherto, because with respect to the following application of the external covering by extrusion, it is necessary to respect much less stringent manufacturing tolerances during the directed supply of conductors and carrier fibres.

Thus, as a result of the extrusion process, both the metal conductors and the carrier fibre group centrally securing the same are permanently fixed in position. As the second extrusion nozzle also acts as a sizing die, a constant diameter and high surface quality of the external covering are always obtained.

Difficulties resulting from natural or artificial silk are completely eliminated. The difficulties caused by the expulsion of the solvents necessary when working with varnished are also eliminated. The varnish solutions hitherto used in the production of such stranded wires have a solids content of between approx. 20% and max. 40%, so that the proportion of solvents to be expelled is 60 to 80%. Thus, there is no further influencing, particularly of the carrier fibre groups, by solvent residues. There was hitherto a risk of solvent residues penetrating the carrier fibre groups, causing stiffening thereof and consequently impairing- the reeling off characteristics of the cable during subsequent use.

As tests have shown, such a cable can undergo winding bonding in an excellent, reproducible manner during the following winding process. Thus, in a predeterminable manner and in a predeterminable quantity, bonding or adhesive agents can be applied to the external extrusion layer, so that it is merely necessary to join together with a constant bonding force the extrusion layers of juxtaposed winding layers adhering to the conductor - carrier fibre group. This also permits an automated mass production of such guidance wire reels with constant characteristics, which has a very favourable effect both on the price and on the reliability of missiles equipped therewith.

The extrusion layers firmly enveloping the conductor - carrier fibre groups are elastic enough to follow the elastic expansion stresses, without being damaged or even destroyed. The extrusion layers almost make it possible to manufacture such cables with a smaller diameter and lower weight than hitherto, so that longer breaking lengths can be obtained, which has a favourable effect on the range of the guidance systems and leads to a greater range for the same winding volume. Due to the reduced cable weight, smaller forces are required for compensating the tensile forces on the body to be guided. Finally, such cables can now also be used without difficulty for the guidance systems of sub- marine bodies, because the double extrusion layer prevents any penetration of water.

As the polyether sulphones used here have excel lebtflameproofcharacteristics, the further advantage is obtained that no special fireproofing means have to be used when producing the cables.

The invention is described in greater detail hereinafter relative to a non-limitative embodiment and the attached drawings, wherein show: Figure 1 the cable in flight operation.

Figure 2 on a much largerscale, a perspective view of the cable construction.

Figure 3 a production diagram of the cable of Figure 2.

Figure 4 the basic arrangement for the production of a cable according to the invention.

In Figure 1, is a jet propelled missile, which is supplied from a fixed or movable control station 11 with guidance signals by means of a flexible electric stranded wire or cable 12 interconnecting the control station and the missile.

Cable 12 comprises two electric conductor wires 14 with a diameter of approximately 0.07mm made from very pure electrolytic copper with a high elongation at break equal to or greater than 25%.

Prior to embedding carrier fibres 16, the bare copper conductors 14 are given an insulation 15 by means of a per se known varnishing process. The varnish is applied in several coatings until a varnish increase of approximately 24 to 30 11 is obtained. Following the hardening of insulation 15, the individual copper conductors 14 are bonded parallel to one another in a further operation using the same varnish from which insulation 15 is made, so that the shape shown in Figure 2 is obtained.

As is shown by Figure 2, the parallel-bonded copper conductors 14 are located centrally in a carrier fibre group 16 comprising n polyamideor polyester fibres having a slight lay.

In order to obtain the central positioning of the parallel-bonded copper conductors within the carrier fibre group 16 over the entire length of the cable, priorto its directed supply, said group is subdivided into at least two and preferably three carrier fibre groups of the same size, whereof each group, which has a diameter of approximately 14 L is formed from e.g. 70 elementary fibres of filaments.

A first extrusion layer 18 is provided for fixing the assembly formed from central copper conductors and carrier fibre groups. A further extrusion layer 19 is applied to extrusion layer 18.

In conjunction with Figure 4, an apparatus for producing the cable shown in Figure 2 will now be described.

The electrical conductors 14 used for signal transfer purposes are drawn from the reel 40 diagrammatically shown in Figure 4 and by means of a guide mechanism 41 with guide pulleys 42,43 and 44 are horizontally supplied to a stranding machine 45 and pass through a horizontal opening 47 of a delivery drum 48, which is rotatable about a horizontal axis.

The delivery drum is driven by adjustable electric motor 49. The conductors 14 are also guided through an only intimated central opening of a distributor plate 50, which is also rotated about a horizontal axis, and which is fixed by means of a clip 51 to the frame 52 of stranding machine 45, in such a way that the central opening is at the same height as the central opening 47 of the delivery drum.

By means of gimbal bearings 49 located in the drum edge region, reels 54 are rotated about axes perpendicular to the drum rotation axis and onto said reels are wound the carrier fibres 16, subdivided into the aforementioned two and preferably three carrier fibre groups. The latter are then removed from the reels 54 and guided by means of the distributor plate 50 and specifically by means of uniformly circumferentially distributed once again only intimated, openings which are inclined with respect to the central passage opening and which lead to the central opening, through which the conductors 14 are passed. Thus, the conductors 14 passing through the central opening are centally enclosed by the carrier fibre groups supplied through the edge openings.

Following distributor plate 50 are provided two extruders El and E2, whose extrusion nozzles 56, 57 used for producing extrusion layers 18 and 19 are at the same height as the aforementioned passage openings of the delivery drum and distributor plate.

Extruder E2 is followed by a cooling means 60, which is once again at the same height. Finally, a winding-on device 70 is provided, which is used for producing the removal forces for conductors 14 and the carrier fibre group 16, as well as serving to wind up the extruded cable.

In per se known manner, the removal forces are determined by not shown brakes, which e.g. act on the bearings of reels 40 and 54. The speed of the delivery drum driven by means of motor 49 is regulated as a function of the winding-on device 70 which is driven by a not shown motor, in such a way that a constant length of lay of the carrier fibre groups of approximately 3 to 6 lays per metre of conductor length is obtained, whilst taking account of the extrusion rate. As a result of the gimbal bearings of reels 54 on the delivery drum 48, it is possible to compensate unavoidable winding irregularities. As has already been stated, distributor plate 50 is used for guiding the rotating carrier fibre groups on conductors 14, whilst centrally embedding the latter, whilst feeding the conductor - carrier fibre group in directionally defined manner to the intake of first extruder El.

In the present embodiment, extruder nozzle 56 has a diameter of 0.32mm and ensures that the conductor - carrier fibre group is fixed without any intermediate cavities, so that the central position of the conductors is maintained. A polycarbonate is preferably used as the extrusion material.

Extruder nozzle 57 not only applies the second extrusion layer 19, but simultaneously acts as a sizing die, so that a round cross-section of cable 12 and also a high surface quality are obtained. This is assisted by the fact that a polyamide is used as the extrusion material in the second extruder E2.

For reasons of completeness, it is pointed out that the aforementioned, not shown brakes are set in such a way that both the conductors 14 and the carrier fibre bundles are removed from the windingon device with a tensile stress of approximately 1 ON.

Claims (9)

1. Flexible electric cable for signal transfer between a ground control station and a rapidly moving body, comprising at least one and preferably two substantially parallel, varnish-insulated, electric conductors, which are approximately centrally embedded over the entire length of a pulling member formed from individual carrier groups formed from a plurality of thin individual filaments, characterized in that the varnish-insulated, electrical conductors are preferably bonded together and are held within the carrier fibres by a first extrusion layer fixing the spatial position of the carrier fibres and the electrical conductors, and that the first extrusion layer is surrounded buy a second extrusion layer, which gives the cable an approximately circular cross-section and forms a uniform surface.

2. Cable according to claim 1, characterized in that the carrier fibre groups comprise n aromatic polyamide fibres with an elongation at break of 2.4 to 4%, that the parallel, bonded together copper conductors have a diameter of approximately 0.07mm, that the first extrusion layer is polycarbonate and the second extrusion layer of polyamide, and that the cable diameter is equal to or smaller than 0.45mm.

3. Process for the production of a flexible electric cable for signal transfer between a ground control station and a rapidly moving body, comprising at least one and preferably two parallel, bonded together, varnish-insulated electrical conductors, which are substantially centrally embedded in a pulling member formed from individual carrierfibre groups constituted by a plurality of thin individual filaments, characterized in that to the electrical conductor or conductors are supplied at least two and preferably three carrier fibre groups, which approximately centrally enclose the conductors, that a first extrusion layer is applied to said conductor carrier fibre group and fixed the spatial position thereof and that subsequently a second extrusion layer centrally enclosing the conductor, carrier fibres and first extrusion layer, whilst forming a circular cross-section and a uniform surface.

4. Process according to claim 3, characterized in that the electrical conductors are guided approxi mately horizontal with a tensile stress of 10 N, that the carrier fibre groups are placed round the conductors with 3 to 6 lays per metre and a tensile stress of 10 N, that the conductors and the carrier fibres placed round them are fixed in correct position by the first extrusion layer and in an approximately cavity-free manner and subsequently the second extrusion layer determines their cross-sectional shape and their external diameter, after which the thusformed cable is passed through a coiling means and is wound up.

5. Process according to claims 3 and 4, characterized in that the electrical conductors are varnishinsulated, parallel, bonded together copper wires with a diameter of 0.07mm, the carrier fibres are polyamide fibres with an elongation at break of 2.4 to 3%, the first extrusion material is polycarbonate and the second extrusion material is polyamide.

6. Apparatus for performing the process according to claims 3 to 5, using a stranding machine with centrally supplied electrical conductors, characterized in that the stranding machine (45) has a delivery drum (48) rotatable about a horizontal axis and with gimbal-mounted reel carriers (49) for the reels (54) carrying the carrier thread (16) and a distributor plate (50), which can also be rotated about a horizontal axis and whose horizontal passage openings (47) for the conductors (14) are positioned horizontally, that extruders (E1,E2) are successively arranged with extrusion nozzles (56, 57), which are also horizontally oriented and at the same height as the passage openings for the electrical conductors of the stranding machine and the distributor plate, that the final extrusion nozzle (57) is followed by a cooling means (60) at the same height and that a winding-up device (70), which removes both the conductors and the carrier fibres and draws them through the extrusion nozzles.

7. A flexible electric cable substantially as herein described and shown in the accompanying drawings.

8. A process for producing a flexible electric cable substantially as herein described with reference to the accompanying drawings.

9. Apparatus for producing a flexible electric cable substantially as herein described and shown in the accompanying drawings.