Electrically insulated electric conductor strip, in particular for electric motors and transformers

An electrically insulated electrical conductive strip (1), especially for electric motors and transformers, having an electrical conductor (2) in strip form that has an upper face (2a) and a lower face (2b), two lateral edge faces (2c) and one end edge face at each end, and having an electrical insulation (3) disposed on at least one face of the strip (2a, 2b). The insulation (3) has an enamel layer (3a) and an adhesive strip (3b) bonded to the lower face (2b) and/or the upper face (2a) of the electrical conductor (2) in strip form, in each case at least in a region (4) that directly adjoins a lateral edge face (2c).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national phase of PCT International Application No. PCT/EP2018/056831, filed Mar. 19, 2018, which claims the benefit of priority under 35 U.S.C. § 119 to German Patent Application No. 10 2017 107 328.0, filed Apr. 5, 2017, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to an electrically insulated electrical conductive strip, especially for electric motors and transformers, having an electrical conductor in strip form that has an upper face and a lower face, two lateral edge faces and one end edge face at each end, and having an electrical insulation disposed on at least one face of the strip.

BACKGROUND

Such electrical conductive strips are referred to, for example, as electrical sheet or electrical strip and are used to establish magnetic circuits for electrical machines, i.e. of cores for dynamos, electric motors, transformers, relays, circuit breakers, inductor coils, ignition coils, electricity meters and controllable deflecting magnets. Customary materials here are especially cold-rolled strips and sheets of iron-silicon alloys. Since eddy currents arise under the influence of variable magnetic fields in a coil core made of solid material, which can cause the core to become hot, the cores are executed exclusively as laminar and insulated sheets in stacks or in the form of wound cut-ribbon cores.

In order to achieve insulation between two mutually superposed conductive strip plies, plastic plies are nowadays used, for example, as insulation in metal strip coils. Polyimide films are often used for this purpose, which are sold, for example, by DuPont under the Kapton® name.

In order to reduce the cost and inconvenience involved in the production of a metal strip coil, an alternative to the laying of films between the strips would be to coat the strip with an electrical insulation enamel on one or both sides, as is known to be implemented with conductors having a round cross section. For this purpose, there are known wire enamels that are synthetic resin-based insulating enamels, which can be applied as very thin, homogeneous, electrically insulating films to copper or aluminium wires. A distinction is made here between different groups of wire enamels, such as THEIC-modified polyesterimides, polyamides and epoxides, solderable wire enamels composed of polyurethane, and adhesive enamels, for example composed of PVB (polyvinylbutyral) and polyimide.

In the enamel coating of an electrical conductive strip of rectangular cross section that can be described as cuboidal in geometric terms and hence has an upper and lower face, two lateral edge faces and one end edge face at each end, however, especially the two lateral edge faces in that case regularly remain insufficiently coated or even completely uncoated. This is because, before the actual polymerization, effected, for example, by what is called a baking operation of the wire enamel, owing to the surface tensions, a meniscus forms, as a result of which the enamel layer then narrows to a minimum or even forms defects during the enamel hardening at the respective upper and lower edge of the lateral edge faces where these each adjoin the faces. The electrical insulating effect is then inadequate here. There can be flashovers between the plies and/or at least formation of stray currents.

It is an object of the present invention to provide an electrically insulated electrical conductive strip of the type specified at the outset, which is producible at reduced cost and inconvenience, especially using a varnish for the insulation, but has a high electrical insulation effect.

SUMMARY

The above object is achieved in accordance with the invention in that the insulation comprises an enamel layer and a film adhesive strip bonded to the lower face and/or the upper face of the electrical conductor in strip form at least, in each case in a region that directly adjoins a lateral edge face.

The strip edge, especially before (or alternatively after) the enamel coating, is laminated with a thermally stable adhesive strip (for example of polyimide). Thus, by comparison with the prior art, it is possible to replace a large area of the costly plastic ply with enamel without impairing the electrical insulation effect at the strip edge.

Further advantageous executions of the invention are described in the detailed description that follows.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

With regard to the description that follows, it is explicitly emphasized that the invention is not limited to the example, nor is it limited to all or multiple features of combinations of features described. Instead, any individual component feature of the example may be of inventive significance on its own, and also in combination with other component features, even in isolation from all other component features described in connection therewith.FIGS. 2 to 7identify identical parts of the conductive strip by the same reference numerals.

The inventive conductive strip1shown inFIG. 1comprises an electrical conductor2in strip form that has an upper face2aand a lower face2b, two lateral edge faces2cand an end edge face at each end (not shown). In addition, the inventive conductive strip1comprises an electrical insulation3applied on at least one side of the strip1; in the embodiment shown, both to the lower face2band to the upper face2a.

The insulation comprises an enamel layer3aand an adhesive strip3b, especially a film adhesive strip, consisting of plastic and bonded to the lower face2band/or the upper face2aof the electrical conductor2in strip form, in each case at least in a region4directly adjoining a lateral edge face2c.

The adhesive strip3bhas an excess 5 with respect to the lateral edge face2cof the electrical conductor1in strip form, which can prevent stray currents. The excess 5 may preferably have a length L in the range of 0 cm<L≤5 cm.

The electrical conductor2in strip form may especially consist of aluminium or of an aluminium alloy and preferably have a thickness D in the range from 0.1 mm to 1.5 mm.

The enamel of the enamel layer3a, which can be applied by dipping, as by electrocoating, or by brush application, roll application, spin-coating, spraying, especially in a continuous belt method, and then cured, has the effect that at least the lower face2band/or the upper face2ahas adequate electrical insulation.

The enamel layer3amay be formed here from an enamel based on organic polymers, as of an acrylic enamel, epoxy enamel, polyester enamel, polyamide enamel or fluoropolymer enamel, or be based on sol-gel compositions, especially of a wire enamel such as a THEIC-modified polyesterimide. It may preferably have a thickness DL in the range from 5 μm to 50 μm. As stated, in the region of the adhesive strip3b, this thickness DL may also be smaller, especially in order to give rise to a flat surface O of the insulation3.

The adhesive strip3bmay preferably have a thickness DK in the range from 3 μm to 20 μm, where this thickness DK may preferably be at least half the thickness DL of the enamel layer3ain the region where there is no adhesive strip3b.

The region4directly adjoining the lateral edge face2cof the electrical conductor2in strip form may have a width B in the range from 0.2 cm to 4.5 cm, preferably in the range from 0.5 to 1.5 cm.

InFIG. 2, the two excesses5of the adhesive strips3a,3bapplied at either end are bonded to one another by a glue.

InFIG. 3, the adhesive strip3bhas been applied with the excess5only at one end, and the enamel layer3atapers like a meniscus on the adhesive strip3band ends before the excess5. In this case, the lower face2band the respectively adjoining lateral edge face2chas been provided with the enamel layer3a, where the enamel layer3aat the transition to the lateral edge face2cand thereon may have such a thickness DL that, in itself, is insufficient for the required electrical insulation.

FIG. 4shows an alternative toFIG. 3, in which the face2band lateral edge face2ceach have no electrical insulation and especially no enamel layer3a.

FIG. 5shows a variant in which the adhesive strip3bis bonded in a C shape around the lateral edge face2cproceeding from the two faces2a,2bby a cover section3c. In this execution too, the enamel layer3aends like a meniscus on the adhesive strip3abefore commencement of the cover section3c.

FIG. 6shows an alternative toFIG. 3. In this case, the enamel layer3ahas been applied only on one side of the upper face2aand on the adhesive strip3bup to the start of the cover section3c.

FIG. 7shows a variant ofFIG. 5. Here, the electrical conductor2, in the region of its lateral edge face2c, has a reduced strip thickness Di compared to the strip thickness D in the rest of the strip region. In this case, in particular, the reduction in strip thickness in the region of the faces2a,2bis the same and is less than/equal to the thickness DK of the adhesive strip3b. The enamel layer3aruns here continuously up to the cover section3c.

The person skilled in the art is also able to add further technical features without leaving the scope of the invention. For instance, the working example shows just one option for the lamination with the adhesive strip3b. Alternatively, it is also possible to lay an adhesive strip3baround the edge area2c, or the enamel layer3acould be beneath the adhesive strip3b.