Inductive connecting of plastic objects by a coil arrangement with multiple individual coils

1. A heating system for thermally connecting a pipe, which has a first plastic material, to a bushing, which has a second plastic material, and which surrounds at least a section of the pipe wherein an inductively heatable heating means is located between the pipe and the bushing and/or integrated in the pipe and/or in the bushing, the heating system comprising:

a generator;

a heating device with a coil arrangement, which is excitable by the generator, and

a tensioning device;

wherein the coil arrangement has

a first coil, which has at least one complete winding within a first cross-sectional area, and

a second coil, which is electrically coupled to the first coil, and which has at least one complete winding within a second cross-sectional area, wherein the first cross-sectional area is different from the second cross-sectional area;

wherein the tensioning device is configured to be laid alongside an outward facing surface of the bushing, such that the bushing is subjected to a pressure that is constant along an outer circumference of the bushing.

2. The heating system according to claim 1 , wherein the first cross-sectional area and the second cross-sectional area have an overlap.

3. The heating system according to claim 1 , wherein the two coils are mechanically connected flexibly to each other and/or have themselves at least a certain flexibility.

4. The heating system according to claim 1 , wherein the two coils are electrically coupled to each other such that upon an excitation of the coil arrangement, a first magnetic field generated by the first coil is antiparallel to a second magnetic field generated by the second coil.

5. The heating system according to claim 1 , wherein the first cross-sectional area and/or the second cross-sectional area is smaller than 1 m 2 .

6. The heating system according to claim 1 , wherein the first cross-sectional area and/or the second cross-sectional area have at least one of

an oval shape,

a circular shape,

a triangular shape, and

a quadrangular shape.

7. The heating system according to claim 1 , further comprising:

at least one further coil, which has at least one complete winding within a further cross-sectional area, wherein the further cross-sectional area is different from both the first cross-sectional area and the second cross-sectional area.

8. The heating system according to claim 1 , wherein the coils are electrically interconnected in series and/or in parallel to each other.

9. The heating system according to claim 1 , wherein the coil arrangement further has

at least one outer coil, which is arranged above the first coil and/or above the second coil, wherein a cross-sectional area of the outer coil is, in a plane parallel to the plane of the first cross-sectional area and/or parallel to the plane of the second cross-sectional area, offset with respect to the first cross-sectional area and/or with respect to the second cross-sectional area.

10. The heating system according to claim 1 , further comprising:

a capacitive element, which, together with the coil arrangement, forms an oscillator circuit.

11. A method for thermally connecting a pipe, which has a first plastic material, to a bushing, which has a second plastic material, and which surrounds at least a section of the pipe, wherein an inductively heatable heating means is located between the pipe and the bushing and/or integrated in the pipe and/or the bushing, the method comprising:

laying alongside a heating device to the bushing from an outside, the heating device including a coil arrangement, which is excitable by a generator, and which has a first coil, which has at least one complete winding within a first cross-sectional area, and a second coil, which is electrically coupled to the first coil, and which has at least one complete winding within a second cross-sectional area, wherein the first cross-sectional area is different from the second cross-sectional area;

laying a tensioning device alongside an outward surface of the bushing, such that the bushing is subjected to a pressure that is constant along an outer circumference of the bushing;

exciting the coil arrangement; and

removing the heating device from the bushing.

12. The method according to claim 11 , further comprising, prior to the applying the heating device,

axially bringing together the pipe with a further pipe, such that an end of the pipe and an end of the further pipe face on their face sides;

laying alongside at least partially circumferentially the heating means around the end of the pipe and the end of the further pipe; and

slipping over the bushing around the heating means that is laid alongside.

13. The method according to claim 12 , wherein the two pipes are district heating pipelines, which have an outer pipe made of plastic and an inner pipe made of plastic or steel.

14. The method according to claim 11 , wherein the coil arrangement is embodied electrically such that, and/or the coils of the coil arrangement are excited such that, along the complete circumference course around the bushing, an electric current flow completely around the bushing is prevented.

15. The method according to claim 11 , wherein the heating means has a ribbon-type structure having an auxiliary heating material which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged such that, along the complete circumference course around the pipe, an electrical conductivity is interrupted at at least one position.

16. The method according to claim 11 , wherein the heating means has a ferromagnetic material, which is inductively heatable, and which has a Curie temperature that is less than 460° C.

17. The method according to claim 11 , wherein the first coil and the second coil are excited temporarily offset relative to each other.

18. The method according to claim 11 , wherein the coil arrangement is excited with a frequency between 100 Hz and 10 MHz.