EP0809258B1 - Electrical cable core, method for its manufacturing and flexible electrical cable - Google Patents

Description

The present invention relates to a cable core comprising a electrical conductor with a rough outer surface and a hose-like insulation, the inner surface of the insulation being substantially continuous with locally outer surface sections of the conductor in the friction or Slip engagement stands and outer surface sections of the inner lying Conductor with the formation of cavities external to the conductor spanned, with the cable core by a continuous extrusion process for extruding the insulation around the conductor using the hose method can be generated around. Such a cable core can, for example, in multi-core, flexible electrical cables are used.

The invention also relates to a method for manufacturing such a wire and a flexible electrical cable, which comprises at least one such wire.

Flexible cables are used, for example, wherever portable, electrical consumers must be supplied with energy. They are often exposed to extreme operating conditions; strong temperature fluctuations, exposure to moisture, oil and chemicals as well strong alternating bending stresses are only mentioned here as examples. Typical flexible cables (lines) have the following structure:

One or more electrical wires, each consisting of one Strand and a wire insulation enveloping them are, if necessary, common with a parallel support element (core run) from an inner jacket surround. Reinforcement is applied to this inner jacket, for example in the form of a textile braid, and the end to the outside of the cable forms a flexible connection to this reinforcement Outer jacket.

From the book "Cable and wire production", VEB VERLAG TECHNIK, Berlin, 1st edition 1976, pages 28 and 240 to 248 is already a cable of the type mentioned above.

From product information from HÜLS Aktiengesellschaft Concerning VESTODUR (05/92) it follows that a molding compound VESTODUR X7292 can be used for electrical wire insulation.

From US 4,471,161 A is a cable core with a hose-like Insulation known to be around a substantially circular conductor is arranged.

The invention was based on the object of an electrical line wire of the type mentioned above, which can be produced in a simple manner is. The cable core (and also the corresponding electrical cable) should have a high degree of flexibility and durability (service life). Wire or cable should preferably be halogen free and have as small a bending radius as possible. The electrical and insulation properties the wire or cable should be for one given use with the properties of conventional electrical Cable cores or cables must be competitive.

According to the invention, this object is achieved by an electrical line wire solved the type mentioned, in which the insulation from a thermoplastic Plastic with an effective melting range ΔT ≥ 15 ° C exists, with the line core through a continuous extrusion process for extruding the insulation around the conductor using the hose method around can be generated without subsequent heat treatment.

The invention is based on the knowledge that it is possible an electrical conductor with a rough outer surface, typically a stranded wire, with the formation of a cable core in the extrusion process so with one to encapsulate thermoplastic that the plastic encapsulation on the one hand frictionally on the outermost conductor surfaces is present, but on the other hand not in the outer free spaces of the conductor intervenes.

External gusset of the stranded wire of a typical inventive Line wires are thus, for example, from the insulating sheath (hereinafter simply called insulation) spanned and not filled out. The strand is therefore within the insulation in the longitudinal direction displaceable (for example in the case of bending stress), but is not so loosely arranged within the insulation so that it can be used without any special effort could be pulled out of it.

This particular arrangement of the strand therefore causes in particular that a controlled relative movement within the insulation in the event of bending stress can perform. The wire is therefore not under the when bending Insulation compressed, which is why the service life of the wire is otherwise regular is limited by the so-called strand break, is enormously high. The The braid's ability to slide within the insulation also enables easy stripping of the wire, for example when attaching electrical Trimmings is advantageous.

In addition to this mechanical effect occurs in line wires according to the invention another extremely advantageous electrical effect. This was at Dielectric measurements "on the wire" noted, for those for the thermoplastic Insulation material regularly significantly lower dielectric values were determined as separate measurements on the pure, unprocessed Plastic. This effect is of course extremely beneficial, because in the case of electrical cables, low effective permittivities are the insulating materials regularly desired, for example, to interactions between the adjacent wires of a multi-core cable. The causes of the reduction in the effective dielectric constant are not yet known exactly, but they may be based on the presence of the air-filled cavities in the outside Gusset the covered strand. The line conductors according to the invention effective dielectric constant reductions lead to that thermoplastics with a disadvantageously high dielectric constant become competitive with plastics that are already at home have a low dielectric constant.

With the wires according to the invention can be based on the described produce mechanical and electrical advantages according to the invention, Depending on the area of application, the cable diameter is reduced by up to 50% and a correspondingly reduced weight compared to conventional ones Have cables with insulating materials based on rubber and PVC. It it is clear that the reduction of the cable diameter also smaller minimum Bending radii allows, which of course in many practical situations is cheap.

In summary, the wires and cables according to the invention therefore have a number of unexpected mechanical and electrical properties that occur in the Result in considerable material savings and significantly increased Other useful lives compared to conventional wires and cables run at the same level.

It is particularly advantageous if the insulation consists of a thermoplastic polyester, preferably a modified polybutylene terephthalate (PBT). The wire then has a special structural strength and / or elasticity. For example, a circular PBT insulation extruded with an outer diameter of 0.8 mm and a wall thickness of only 0.15 mm around a corresponding strand can only be compressed under considerable pressure, which rarely occurs in practice, so that practically none in use external pressure is passed on to the strand and thus no destructive mechanical load on the strand occurs within the insulation. Even when a wire is flexed, no disadvantageous compression effect is generated. The following table shows the core diameters and the associated wall thicknesses for some typical cores. Vein diameter Wall thickness 1 0.80 mm 0.15 mm 2nd 1.29 mm 0.25 mm 3rd 3.21 mm 0.30 mm 4th 6.42 mm 0.40 mm 5 11.36 mm 0.70 mm (Core insulation: VESTODUR X4159, see below)

A flame retardant is expediently used for the wire according to the invention and / or self-extinguishing insulating plastic selected. Such veins are particularly suitable for areas at risk of fire.

In terms of process engineering, it is particularly favorable to use a thermoplastic according to the invention Use plastic that has an effective melting range ΔT ≥ 15 ° C, preferably ≥ 20 ° C. Such plastics offer the advantage that you Melting range includes a larger temperature interval than the temperature fluctuations on the spray nozzle of a conventional extruder with quite imprecise Temperature control. Such extruders can therefore also Extrusion can be used without the risk that the thermoplastic Plastic due to uncontrollable temperature fluctuations liquefied (too far) and then, for example, in the gusset one parallel leads out leads. A practical example of a special one suitable PBT plastic with an effective melting range ΔT ≥ 20 ° C is the plastic Vestodur X 4159 from Hüls AG, a highly viscous semi-crystalline Molding compound. The term "effective melting range" is used in Incidentally, within the scope of this description always understood the temperature interval, that upwards through the condensing temperature and downwards through the transition from the hard elastic to the plastic state of the respective Plastic is limited.

It should be emphasized that the preferred ones thermoplastic materials, e.g. the modified polybutylene terephthalates, not about plastics with "memory" or "elastic shape memory" acts. The veins according to the invention are therefore by means of a continuous extrusion process without subsequent heat treatment can be generated and also have a substantial length constant mechanical and electrical properties.

Fig. 1

einen schematischen Querschnitt durch ein Ausführungsbeispiel einer erfindungsgemäßen Ader.

Fig. 2

eine vergrößerte Querschnitt-Teilansicht der erfindungsgemäßen Ader aus Fig. 1 im Kontaktbereich zwischen elektrischem Leiter und Isolierung.

Fig. 3

einen schematischen Querschnitt durch ein typisches Ausführungsbeispiel eines erfindungsgemäßen, trommelbaren Kabels.

Preferred exemplary embodiments of the invention are explained in more detail below with reference to the figures. They represent:

Fig. 1

a schematic cross section through an embodiment of a wire according to the invention.

Fig. 2

an enlarged cross-sectional view of the core of the invention from FIG. 1 in the contact area between the electrical conductor and insulation.

Fig. 3

a schematic cross section through a typical embodiment of a reelable cable according to the invention.

In Figures 1 and 2 is an embodiment of an inventive Line wire shown, designated 1 in Fig. 1 in total is. The wire 1 comprises a strand 3 as an electrical conductor, and this is made from a large number of thin metallic lead wires 5, which are extend transversely to the cross-sectional plane shown in the longitudinal direction of the wire. The ensemble of lead wires (the strand) is tightly packed and in its Entirely round shape. Since the strand is made of individual Wires is formed, their surface (outer surface) is not smooth, but rough (contoured); in particular, it has between two neighboring ones external lead wires gusset 7.

The strand is of a tubular insulation made of a thermoplastic Polyester molding compound based on modified polybutylene terephthalate (PBT) coated. The product has proven particularly useful as a molding compound Vestodur X4159 from Hüls AG. The inner surface of the insulation is related on the longitudinal direction of the vein - essentially continuously with the locally outer surface sections of the outermost layer of the strand forming lead wires in friction or slip engagement. How best can be seen from Fig. 2, the more inner contour-forming Surface sections of the associated gusset 7 tight from the insulation spanned, forming cavities that essentially the gusset correspond.

On the one hand, there is good adhesion between the strand and the insulation, on the other hand, the gussets 7 are not covered by the insulation molding compound filled out. The line core 1 can therefore be particularly easy stripping, but this is not the only benefit. The structural property the wire also allows strand 3 and insulation 9 move in the longitudinal direction with respect to a bending stress relative to each other. This is particularly important if you have the wire with a small radius of curvature wants to wind up or drum up. It then comes advantageously not to compress the strand under the insulation originally preferably soft annealed lead wires do not harden, and there is therefore no breakage of the outer individual wires subsequent strand break. In practice, therefore, there is an undesirable one Failure of the wire according to the invention occurs only extremely rarely.

In comparison to conventional insulation, that in FIGS. 1 and 2 Insulation of the illustrated wire 1 according to the invention shown thin-walled. This enables material savings of up to 50 X without the wire quality would be reduced compared to conventional wires, conventional PVC or rubber insulation around an identical strand wear.

The wires according to the invention are produced through a pore-free extrusion in the tube process. The core insulation receives a high structural strength, but remains elastic and resistant to impact and bending fatigue. The high tensile strength of the preferred polybutylene terephthalate molding compositions (in addition to Vestodur X4159 has also proven itself outstandingly Vestodur X7292) additionally guarantees that a tensile load of the wire insulation and not the stranded wire. The high pressure resistance of the preferred materials causes the core insulation remains round and prevented even at comparatively high pressures so that an additional friction or compression effect when flexing a wire the strand occurs. The conventional insulation materials like rubber, In comparison, PVC or PE have significantly poorer tensile strengths and pressure resistance.

Moreover, unusually low effective dielectric constants ε _R have been able to be measured in measurements on wires according to the invention of the type shown in FIGS. 1 and 2. These low dielectric constants are not a purely material property of the insulating molding compound - hence the addition "effective" - but they only result from the type of strand sheathing according to the invention. It is probably the (spanned) air-filled gusset cavities that, for example for Vestodur X4159, whose dielectric constant is given by the manufacturer as 4, lead to a reduction in the effective dielectric constant at the core to approx. 2.6-2.8. This means that this effective dielectric constant is comparable to that of unprocessed polyethylene (PE).

The cross section shown in Fig. 3 of a drumable according to the invention Cable 20 has a centrally arranged support member, the total seven line wires 21 according to the invention is surrounded. To the arrangement a four-layer jacket runs from the supporting element and veins. The inner layer of the jacket consists of a polyester sliding film 24, which allows the wires 21 to slide within the jacket. Outward this sliding film is followed by an inner jacket 26 made of polyurethane, which is particularly useful at higher nominal voltages. With the outside the next layer is a textile braid 28, which for a high transverse stability (resistance to twisting) of the cable 20 ensures. Extreme there is finally an outer jacket 30 made of polyurethane. This in Fig. 3 cable is therefore halogen-free.

The wires 21 are in the longitudinal direction of the cable 20 with a short lay length stranded around the preferably textile support member 22. In the large volume Gussets between the wires can become polyester filler threads if necessary located (not shown). The braid preferably consists of Artificial silk.

In practice, the strands within the wires 21 can be, for example, very fine-stranded with cross-sectional areas of 1.5 mm ² - 35 mm ² or finely stranded with cross-sectional areas of 50 mm ² - 120 mm ² . Compared to the reelable cables previously used, the cable diameter can be reduced by up to 50% with comparable electrical properties, which of course also results in smaller bending radii. A weight reduction of up to 50% is possible.

The cable shown in Fig. 3 can of course be vary in many ways. However, essential for its properties is in in any case the use of one or more wires according to the invention.

It has already been mentioned that veins according to the invention in Hose processes are manufactured. This will be useful strands preheated at least approximately to the molding compound temperature (cf. 3, Fig. 1) or other conductors (ropes etc.) through a central hole in fed to the quill of the extruder. For the extruded, already quite tough Insulation molding compound, a short cone is set and it settles with this setting as described above, close to the strand.

Claims (8)

1. Cable core, comprising

   an electrical conductor (3) having a rough outer surface, and

   a flexible-pipe-like insulation (9) of a thermoplastic plastics material having an effective melting range ΔT ≥ 15° C,

   with the inner surface (11) of the insulation (9) being in frictional or sliding engagement substantially continuously with locally outwardly disposed surface portions of the conductor (3), and stretching over more inwardly disposed outer-surface portions of the conductor (3), while forming hollow spaces which, with respect to the conductor (3), are disposed on the outer side, and

   wherein the cable core is designed to be produced in a continuous extrusion process for extruding the insulation (9), in a profile extrusion process, about the conductor (3) without any subsequent thermal treatment.
2. Core according to claim 1, characterized in that the electrical conductor comprises a stranded conductor of thin metal conducting wires (5) and the insulation (9) does not substantially engage in the V-formations (7) in the stranded conductor.
3. Core according to one of the preceding claims, characterized in that the insulation (9) consists of a thermoplastic polyester.
4. Core according to claim 3, characterized in that the polyester comprises a modified polybutylene terephthalate.
5. Core according to one of the preceding claims, characterized in that the plastics material is flame resistant and/or self-extinguishing.
6. Core according to one of the preceding claims, characterized in that the plastics material has an effective melting range ΔT ≥ 20° C.
7. Process in which a core according to one of claims 1-6 is produced, characterized in that a thermoplastic plastics material, having an effective melting range of ΔT ≥ 15° C, is extruded about the conductor (3) in a profile extrusion process and, at a temperature below its melting temperature, is subsequently brought into abutting contact with said conductor.
8. Electrical cable, comprising at least one core according to one of claims 1-6 and a cable inner sleeve of polyurethane and/or a cable outer sleeve of polyurethane.

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