Inductive welding of plastic objects with electrically interrupted heating means

Abstract

Described is a heating means for thermally connecting two objects each having a plastic material, wherein, during the connecting, a first inner object is surrounded at least partially by a second outer object, and the heating means surrounds the first inner object at least partially along a complete circumferential course around the first inner object, and is located between the first inner object and the second outer object. The heating means has a ribbon-type structure. The ribbon-type structure has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along the circumferential course such that an electrical conductivity is interrupted at at least one position along the complete circumferential course around the first inner object. Further described are an arrangement and a system each having such a heating means as well as a method for thermally connecting two plastic objects.

Claims

1. A heating means for thermally connecting two objects each having a plastic material, wherein, during the connecting, (i) a first inner object is surrounded at least partially by a second outer object, and (ii) the heating means surrounds the first inner object at least partially along a complete circumferential course around the first inner object, and is located between the first inner object and the second outer object, the heating means comprising: a ribbon-type structure materially interrupted along the circumferential course, wherein the ribbon-type structure has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along the circumferential course such that an electrical conductivity is interrupted at at least one position along the complete circumferential course around the first inner object, wherein the heating means has a ribbon-type carrier, at which the ribbon-type structure is attached, wherein the ribbon-type carrier has a greater dimension than the ribbon-type structure along a longitudinal direction of the ribbon-type structure and wherein the ribbon-type carrier consists of an electrically non-conductive carrier material.

2. The heating means according to claim 1, wherein the auxiliary heating material is a magnetic material.

3. The heating means according to claim 2, wherein the magnetic material is a ferromagnetic or ferrimagnetic material, which has a Curie temperature that is lower than 460° C.

4. The heating means according to claim 1, wherein the auxiliary heating material is an electrically conductive material.

5. The heating means according to claim 1, wherein the ribbon-type structure has an electrically non-conductive matrix material and a plurality of magnetic and/or electrically conductive particles, which are embedded in the matrix material and which are electrically isolated from each other, wherein the particles have ferrites, and/or wherein the matrix material has a specific electric resistance of at least 1 Ohm/mm.sup.2, and/or wherein the matrix material has at least one of the following materials: (a) thermoplastic polymers; (b) polystyrols and their co-polymers; (c) elastomers; (d) polyesters; (e) halogen polymers; (f) polyamides, as well as, respectively, co-polymers and/or mixtures thereof.

6. The heating means according to claim 1, wherein the ribbon-type structure further has two plane carrier elements, wherein the auxiliary heating material is embedded between the two carrier elements.

7. The heating means according to claim 1, wherein a plurality of openings is formed in the ribbon-type structure, wherein the openings are dimensioned such that molten-on plastic material of the first inner object and/or of the second outer object intrude and connect to the molten-on plastic material of the respective other object, and/or wherein the openings are filled with a plastic material, which connects to the molten-on plastic material of the first inner object and/or of the second outer object.

8. The heating means according to claim 1, wherein any one of the following a) through f) is implemented: a) at least one end of the ribbon-type structure has a corrugated, serrated and/or meandering contour, b) the ribbon-type structure has a structure in layers of different materials, which have a different hardness, a different elasticity and/or a different ductility, c) the heating means further has an adhesive force changing layer, which is attached or formed on at least one surface of the ribbon-type structure, the ribbon-type structure comprises a plurality of openings with respective sidewalls, wherein the adhesive force changing layer has an adhesive force strengthening layer at the surface of the ribbon-type structure and/or an adhesive force reducing layer at the respective sidewalls of the openings, d) the ribbon-type structure comprises a plurality of openings where the openings have an average distance s from each other, which distance satisfies at least one of the following equations in relation to a thickness d of the ribbon-type structure: 0.5<s/d<2; 0.7<s/d<1.5; 0.8<s/d<1.3; 0.9<s/d<1.1, e) the ribbon-type structure comprises a plurality of openings and a transition between a plane surface of the ribbon-type structure and at least some of the openings is rounded-off, f) the ribbon-type structure comprises a plurality of openings and at least some of the openings each have a longitudinal axis, which form an angle that is different from zero with a surface normal of the surface of the ribbon-type structure.

9. The heating means according to claim 1, wherein the ribbon-type structure has a surface having elevations and recesses, wherein an average height difference between the elevations and the recesses is in a range between 0.01 mm and 2 mm.

10. The heating means according to claim 1, further comprising: at least one further ribbon-type structure, which is arranged beside the ribbon-type structure, wherein the further ribbon-type structure is oriented at least approximately parallel to the ribbon-type structure.

11. An arrangement, comprising: a first inner object, which has a first plastic material; a second outer object, which surrounds the first inner object at least partially, and which has a second plastic material; and a heating means including a ribbon-type structure materially interrupted along a circumferential course, wherein the ribbon-type structure has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along the circumferential course such that an electrical conductivity is interrupted at at least one position along a complete circumferential course around the first inner object, which heating means surrounds the first inner object at least partially along the complete circumferential course around the first inner object, and is arranged between the first inner object and the second outer object, wherein the heating means has a ribbon-type carrier, at which the ribbon-type structure is attached, wherein the ribbon-type carrier has a greater dimension than the ribbon-type structure along a longitudinal direction of the ribbon-type structure and wherein the ribbon-type carrier consists of an electrically non-conductive carrier material.

12. The arrangement according to claim 11, wherein the heating means is integrated in the first inner object and/or in the second outer object.

13. The arrangement according to claim 11, further comprising: a third inner object, which has a third plastic material, wherein the second outer object also surrounds the third inner object at least partially, and wherein the heating means is located between the third inner object and the second outer object, wherein the first inner object is a plastic pipe, the third inner object is a further plastic pipe, and the second outer object is a plastic bushing, which surrounds two mutually facing ends, one end of the plastic pipe and one further end of the further plastic pipe.

14. A system, comprising: a generator for generating an electromagnetic field, which inductively couples a coil device of the generator to a heating means, wherein the heating means is configured for thermally connecting two objects each having a plastic material, wherein, during the connecting, (i) a first inner object is surrounded at least partially by a second outer object, and (ii) the heating means surrounds the first inner object at least partially along a complete circumferential course around the first inner object, and is located between the first inner object and the second outer object, and wherein the heating means comprises a ribbon-type structure, which is materially interrupted along a circumferential course, wherein the ribbon-type structure has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along the circumferential course such that an electrical conductivity is interrupted at at least one position along the complete circumferential course around the first inner object, wherein the heating means has a ribbon-type carrier, at which the ribbon-type structure is attached, wherein the ribbon-type carrier has a greater dimension than the ribbon-type structure along a longitudinal direction of the ribbon-type structure and wherein the ribbon-type carrier consists of an electrically non-conductive carrier material.

15. The system according to claim 14, wherein the coil device is an open coil device with respect to an arrangement which comprises a first inner object, which has a first plastic material; a second outer object, which surrounds the first inner object at least partially, and which has a second plastic material; and a heating means including a ribbon-type structure, which is materially interrupted along the circumferential course, wherein the ribbon-type structure has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along a circumferential course such that an electrical conductivity is interrupted at at least one position along a complete circumferential course around the first inner object, which heating means surrounds the first inner object at least partially along a complete circumferential course around the first inner object, and is arranged between the first inner object and the second outer object, wherein the heating means has a ribbon-type carrier, at which the ribbon-type structure is attached, wherein the ribbon-type carrier has a greater dimension than the ribbon-type structure along a longitudinal direction of the ribbon-type structure and wherein the ribbon-type carrier consists of an electrically non-conductive carrier material.

16. The system according to claim 14, wherein the coil device has a coil having turns that are intertwined in each other and are non-circular.

17. The system according to claim 14, wherein the coil device has a plurality of individual coils.

18. A method for thermally connecting two objects each having a plastic material, the method comprising: spatially arranging a first inner object, a second outer object, and a heating means including a ribbon-type structure, wherein the ribbon-type structure is materially interrupted along a circumferential course and has an auxiliary heating material, which is inductively heatable, wherein the auxiliary heating material is spatially distributed or arranged along the circumferential course such that an electrical conductivity is interrupted at at least one position along a complete circumferential course around the first inner object, such that (i) the first inner object is surrounded at least partially by the second outer object, and (ii) the heating means surrounds the first inner object at least partially along a completely circumferential course around the first inner object, and is located between the first inner object and the second outer object; inductively heating the heating means such that molten-on plastic material of the first inner object and/or of the second outer object connects directly or indirectly to molten-on plastic material of the respective other object, and cooling down the heating means, wherein the heating means has a ribbon-type carrier, at which the ribbon-type structure is attached, wherein the ribbon-type carrier has a greater dimension than the ribbon-type structure along a longitudinal direction of the ribbon-type structure and wherein the ribbon-type carrier consists of an electrically non-conductive carrier material.

19. The method according to claim 18, wherein the inductive heating includes exciting a coil device of an induction generator for generating electromagnetic waves, which couple inductively to the heating means, wherein the electromagnetic waves have a frequency, which is greater than 8 kHz.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1a shows, in a top view, a heating means having a plurality of openings, which are formed irregularly in a ribbon-type structure.

(2) FIG. 1b shows, in a top view, a heating means having a plurality of openings, which are arranged in a regular pattern.

(3) FIG. 2 shows, in a top view, a heating means, which has an electrically isolating matrix material and ferromagnetic particles embedded therein.

(4) FIG. 3 shows, in a side view, a heating means having a ribbon-type structure, which has a matrix material having embedded ferromagnetic particles and two flexible carrier elements embodied as carrier films.

(5) FIG. 4 shows, in a magnified cross-sectional view, a heating means having an opening, wherein respectively one adhesion increasing layer is formed on the two plane surfaces of the heating means and an adhesion reducing layer is formed at the walls of the opening.

(6) FIG. 5 shows, in a magnified cross-sectional view, an opening formed in a heating means, which opening has a rounding-off at an upper side.

(7) FIG. 6 shows, in a magnified cross-sectional view, a heating means having an inclined opening.

(8) FIG. 7 shows, in a schematic top view, an arrangement having two inner pipes and one outer bushing, which are all welded to each other by a heating means having in total four ribbon-type structures.

(9) FIG. 8 shows a system having (a) an induction generator, (b) an arrangement to be welded together consisting of an inner plastic pipe and an outer bushing, and (b) a materially closed but electrically interrupted heating means between the inner pipe and the outer bushing.

(10) FIG. 9 shows a system having (a) an induction generator having an open coil device, (b) an arrangement to be welded together consisting of one inner plastic pipe and one outer bushing, and (b) a both materially and electrically interrupted heating means between the inner pipe and the outer bushing.

(11) FIG. 10 shows an open coil device having intertwisted windings.

(12) FIG. 11 shows, in a top view, a heating means having serrated ends.

(13) FIG. 12 shows, in a cross-sectional view, a heating means, which has a ribbon-type structure, which is arranged on a ribbon-type carrier.

(14) FIG. 13 shows, in a side view, a heating means, which has plural ferromagnetic layers, which respectively have a different Curie temperature.

(15) FIG. 14 shows an arrangement to be welded together and having an inner plastic pipe and an outer bushing, in which respectively a materially closed but electrically interrupted heating means is integrated.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

(16) It is pointed out that in the following detailed description, features and/or components of different embodiments, which are equal or at least functionally equal to the corresponding features and/or components of another embodiment, are provided with the same reference numerals or with reference numerals, which are identical in the last two digits to the reference numerals of corresponding equal or at least functionally equal features and/or components. For avoiding unnecessary repetitions, features and/or components, which have been explained already with reference to a previously described embodiment, are not explained any more in detail later.

(17) Furthermore, it is pointed out that the subsequently described embodiments represent only a limited selection of embodiment variants of the invention. In particular, it is possible to combine the features of individual embodiments with each other in a suitable manner, so that a plurality of different embodiments is to be considered as obviously disclosed for the skilled person with the embodiment variants illustrated explicitly herein.

(18) In addition, it is pointed out that space-related terms, such as for example “in front” and “behind”, “at the top” and “at the bottom”, “left” and “right”, etc. are used to describe the relation of an element to another element or to other elements such as it is illustrated in the figures. Accordingly, the space-related terms may apply for orientations, which differ from the orientations that are represented in the figures. It is however understood by itself that all such space-related terms, for the reason of simplicity of the description, relate to the orientations represented in the drawings and are not necessarily limiting, because the respective illustrated device, component, etc., when it is in use, may assume orientations, which may be different from the orientations illustrated in the drawings.

(19) FIG. 1a shows, in a top view, a heating means 100. The heating means 100 may consist substantially of a ribbon-type (or belt-type) structure 102, in which a plurality of openings 110 may be formed, for example by punching. According to the embodiment example represented here, the openings 110 may be spatially arranged irregularly. As has been explained in-depth above, the openings may enable a flowing through of molten-on plastic material through the ribbon-type structure 102 in a welding process.

(20) In preferred embodiment examples, a length L of the ribbon-type structure 102 may be in the range of 40 mm to 3200 mm, and in particular in the range from 60 mm to 800 mm. A typical ratio between the length L and a width B of the ribbon-type structure 102 may be less than 1:10, in particular less than 1:100.

(21) FIG. 1b shows, in a top view, a heating means 200 according to a further embodiment example of the invention. Herein, the openings 110 may be arranged in a regular pattern. In other embodiments, which are not represented, the openings may be offset relative to each other such that a regular pattern may result, too.

(22) Both regularly and also irregularly arranged openings 110 may have an average distance to each other, which may be in the range between 0.1 mm and 5 mm, and in particular in the range between 0.5 mm and 3 mm.

(23) The ribbon-type structure 102 may consist of a perforated metal ribbon (or metal belt). The ferromagnetic material of the ribbon-type structure 102 may for example be steel. In order to achieve an additional, not represented contouring, the perforated metal ribbon may be a metal ribbon that may have been stretched by a sufficient tensile force.

(24) As has been described above, the ribbon-type structure 102 must not compulsory consist of a ferromagnetic material. Beside ferrimagnetic materials, in principle all materials can be used, which can be heated inductively. Such materials are referred to in this document generally as auxiliary heating materials. A suitable material, for which the heating may be primarily based on the electrical conductivity and the eddy currents resulting therefrom, may be e.g. the non-magnetic material aluminium.

(25) In other embodiments, the ribbon-type structure 102 can be a woven or braided roving (or strand, or scrim) of single wires. These may optionally have a functional coating for an improved heat conductivity, a corrosion protection, etc.

(26) FIG. 2 shows, in a top view, a heating means, which has an electrically isolating matrix material and ferromagnetic particles embedded therein. According to the embodiment example illustrated herein, the matrix material may consist of polyethylene (PE) or at least has this. The particles may have an average size having a diameter of less than 1 mm, in particular less than 0.1 mm and further in particular less than 0.01 mm. According to the embodiment example illustrated herein, the particles may be ferrites.

(27) The comparably small ferromagnetic particles may have the advantage that very high frequencies can be used for an inductive heating. Orders of magnitudes for suitable frequencies have been mentioned already above. As has also been mentioned above, at high frequencies, coil devices having different geometries that may be suitable for the respective application case can be used in order to generate the electromagnetic field that may be necessary for an inductive heating.

(28) FIG. 3 shows, in a side view, a heating means 300 having a ribbon-type structure, which may have a matrix material 222 with embedded ferromagnetic particles 220 and two flexible carrier elements 324 formed as carrier films. The matrix material 222 may be located between the two carrier films 324. The carrier elements 324 may be films provided with an adhesive agent, to which the matrix material adheres. Such a structure in layers (or layer-wise composition) of the heating means 300 may enable an easy handling of the heating means.

(29) According to the embodiment example illustrated here, the heating means 300 constructed in layers may have a thickness D of 0.5 μm. However, also other thicknesses from 0.1 mm to 3 mm, in particular from 0.2 mm to 2 mm, and further in particular from 0.3 mm to 1 mm, can be used.

(30) FIG. 4 shows, in a magnified cross-sectional view, a heating means 400 having an opening 110 out of a plurality of openings. An adhesion strengthening layer 422 may be formed on the two plane surfaces, i.e. the lower side and the upper side, of the heating means 400, respectively. An adhesion reducing layer 424 may be formed at the sidewalls of the opening 110. Thereby, the flow behaviour of molten-on plastic through the openings 110 may thereby be improved in an advantageous manner, such that a particularly stable plastic connection may be formed through the opening 110.

(31) Furthermore, also a mechanically more or less strong connection between the heating means 400 and the respective plastic object may be produced at the two plane surfaces of the ribbon-type structure 102 by an adhesive force strengthening. This may contribute to a further improvement of the overall welded connection.

(32) FIG. 5 shows, in a magnified cross-sectional view, a heating means 500, in which a plurality of openings 110 is formed. As can be seen from the exemplary illustrated opening 110, a transition from a plane upper side of the ribbon-type structure to the opening 110 occurs with a rounding-off (or chamfering) 530. This may contribute to that an initially horizontally flowing molten-on plastic material must not flow around a corner when intruding into the opening 110. Thereby, the flow behaviour of the molten-on plastic material into the opening 110 may be improved.

(33) In preferred embodiment examples, a radius R of the rounding-off may be in a range from 1 μm to 100 μm. It is however pointed out that instead of a rounding-off, which may be circular in cross-section, also other types of chamfered edges, for example a countersink, may contribute to an improved flow behaviour of molten-on plastic material into the opening 110.

(34) FIG. 6 shows, in a magnified cross-sectional view, a heating means 600, in which an inclined (or slanting) opening 610 may be formed. Herein, the “inclination” of the openings refers to an angle, which may be formed between a longitudinal axis 610a of the opening 610 and a surface normal 600a of the plane surface of the heating means 600. In preferred embodiment examples, this angle may be in a range between 10° and 60°, in particular in a range between 20° and 50°, and further in particular in a range between 30° and 40°.

(35) It is pointed out that also in this embodiment example, the heating means 600 may have a plurality of openings, of which at least some may be inclined openings. For reasons of clarity, only one inclined opening 610 is illustrated in FIG. 6.

(36) FIG. 7 shows, in a schematic top view, an arrangement 785 having two inner plastic objects 760 and 780 each formed as a pipe, and an outer plastic object 770 formed as a bushing, which have all been welded to each other by a heating means 700. According to the embodiment example illustrated here, the heating means 700 may have in total four ribbon-type structures, a first ribbon-type structure 102 as well as three further ribbon-type structures 750, 752 and 754, which may have been wound around the plastic pipe 760 and/or around the further plastic pipe 780 parallel to each other, respectively, with a small distance. As can be seen from FIG. 7, the heating means 700 having four ribbon-type structures may be located between the bushing 700 and the plastic pipe 760 and/or between the bushing 770 and the further plastic pipe 780.

(37) The ribbon-type structures 102, 750, 752 and 754 may be structures, which may be materially closed around the inner plastic objects 760 and 780 (and are only interrupted electrically), and which may have a matrix material and embedded therein ferromagnetic particles, which may be electrically isolated from each other. Alternatively, the ribbon-type structures 102, 750, 752 and 754 may also be both materially and electrically interrupted structures, which are described in more detail in the following. Also, a combination of materially closed structures and materially interrupted structures may be used for the heating means 700.

(38) In this relation, it is pointed out that the FIG. 7 shows the arrangement 785 basically in a top view. For reasons of a better clarity, only the bushing 770 is illustrated in a cross-sectional view.

(39) FIG. 8 shows a system 890 having (a) the arrangement 785, which is represented in a cross-sectional view, and (b) an induction generator 895, which is provided to inductively heat the heating means 100 (and as the case may be also the non-illustrated further heating means), and thus to weld together the bushing 770 with the plastic pipe 760. The induction generator 895 may have an excitation device 896 as well as a coil device 897 having a plurality of excitation coils 897a. The coil device 897 may be arranged around the bushing 770. According to the embodiment example represented here, each one of the individual excitation coils 897a may be fed individually with current by the excitation device 896.

(40) As can be seen from FIG. 8, according to the embodiment example illustrated here, the heating means 100 may be wound completely around the plastic pipe 760, such that a non-illustrated overlap may occur between the two ends of the heating means 760. The heating means may however not be considered as a (closed) secondary coil, because the ferromagnetic particles that may be embedded in the above-described matrix material may be electrically isolated from each other, and thus a so-called short-circuit current around the whole inner plastic pipe 760 may not be possible.

(41) It is pointed out that the coil device may alternatively also have only one primary coil, which may extend around the bushing 770. Such a single primary coil that may be laid around the bushing 770 may be realized for example with suitable electrical plug connections, which may be opened after a hopefully successful welding process, so that the single primary coil of the arrangement 780 can be removed.

(42) In preferred embodiment examples, the bushing 770 may consist of a material, which would perform a shrinkage along its circumference without a counterpressure by the plastic pipe 760 in a virtual welding process, which shrinkage amounts to at least 10%, preferably at least 20%, and further preferably at least 30%. Thereby, in practice, thus with a counterpressure by the plastic pipe 760, a mechanical tension may be generated, which may result in an improvement of the welding result.

(43) FIG. 9 shows a system 990 having (a) an induction generator 995 having an open coil device 997, (b) an arrangement to be welded together and consisting of an inner plastic pipe 760 and an outer bushing 770, and (b) a heating means 900 between the inner pipe 760 and the outer bushing 770, which heating means may be interrupted both materially and electrically.

(44) The heating means 900 according to embodiment example illustrated here may have an electrically conductive and in particular ferromagnetic material. Thus, basically, not only microscopic (eddy) currents but also macroscopic currents may form in the heating means 900.

(45) It can be seen from FIG. 9, that the heating means 900 may surround the plastic pipe 760 only partially, and thus may form a both materially open and electrically interrupted structure along the circumference of the plastic pipe 760. The open region is indicated in FIG. 9 by the reference numeral 900a. The interruption of the open coil device 997 is provided with the reference numeral 997a. As has been described already above, for the open loop given by the heating means 900, an inductive energy transfer can only be ensured by the generation of eddy currents, which may require a microscopic conductivity of the ribbon-type structure of the heating means 900. A short-circuit current around the whole inner plastic pipe 760 cannot form as a result of the open region 900a.

(46) FIG. 10 shows an open coil device 1097 having intertwined windings. The coil device 1097 may be laid around the arrangement consisting of at least two objects to be welded together without a slipping over (or sheathing) in an easily handable manner. Stated demonstratively, the coil device 1097 may be laid around an outer bushing and/or an outer plastic object like a flexible and elongated inductive cooker plate.

(47) FIG. 11 shows, in a top view, a heating means 1100 having serrated ends 1115. The heating means 1100 may have a ribbon-type structure 1102 consisting of a ferromagnetic material 1140. Also, the heating means 1100 may have a plurality of openings 110.

(48) The heating means 1100 according to the embodiment example illustrated here may be used as a materially open and/or interrupted heating means. During an application, the material interruption may be located between the two ends 1115.

(49) FIG. 12 shows, in a cross-sectional view, a heating means 1200, which may have a ribbon-type structure 1102 that is located on a ribbon-type carrier 1248. The ribbon-type structure 1102 may have a continuous ferromagnetic material 1140. The ribbon-type carrier 1248 may consist of an electrically non-conductive carrier material.

(50) The ribbon-type carrier 1248 may be significantly longer in comparison to the ribbon-type structure 1102. This may have the advantage, that the heating means 1200 can materially be so long that it can be wound completely around a first inner object for an inductive welding process, wherein by an according short embodiment of the electrically conductive ribbon-type structure 1102 it may be ensured that the heating means 1200 does not represent a closed secondary coil having the above-described disadvantages of the development of short-circuit currents.

(51) FIG. 13 shows, in a side view, a heating means 1300, which may have a ribbon-type structure 1302, which may be composed of plural (here three) layers each made of a different ferromagnetic material. A first layer may have a first ferromagnetic material 1140 having a first Curie temperature. A second layer may have a second ferromagnetic material 1342 having a second Curie temperature. A third layer may have a third ferromagnetic material 1344 having a third Curie temperature. According to the embodiment example illustrated here, the three Curie temperatures may be different. Thus, an average Curie temperature of the heating means 1300 may result, which may be adjusted to the respective specific welding application by a suitable selection of the three ferromagnetic materials.

(52) In another embodiment, no common average Curie temperature may arise (or materialize), such that, after a reaching of the lower Curie temperature, an inductive energy input to the heating means 1300 may be reduced, but not prevented completely. As a consequence, a slower temperature increase may result for a same inductive excitation, wherein with the reaching of the respective next higher Curie temperature an inductive coupling between an excitation coil and the heating means 1300 may be reduced.

(53) In a preferred embodiment, a thickness D of the heating means 1300 may be in a range between 0.1 mm and 5 mm, and in particular in a range between 0.5 mm and 3 mm. These dimensions (or sizes) may hold also for a ribbon-type structure, which may consist of only one layer of a ferromagnetic material.

(54) It is pointed out that layered heating means may also have 2, 4 or more layers.

(55) It is further pointed out that the heating means 1300 may have a surface roughness at its plane (or two-dimensional) sides, i.e. in FIG. 13 at the upper surface and/or at the lower surface. Such a surface roughness may be based on elevations and recesses, which may have an average height difference relative to each other. In preferred embodiments, this average height difference may be greater than 10 μm. A surface roughness may lead to improved welding results also for the other heating means described in this document.

(56) FIG. 14 shows an arrangement 1485 to be welded together and having an inner plastic pipe 1460 and an outer bushing 1470, in each of which a materially closed but electrically interrupted heating means 1400 may be integrated. Thereby, the handling and/or the performing of an inductive welding process may be simplified, because only the objects to be welded together, and not in addition a still further (external) heating means must be handled by an operator.

(57) It should be noted that the expression “having” (or “comprising”) does not exclude other elements, and that the article “a” (or “an”) does not exclude a plurality. Also, elements which are described in connection with different embodiment examples, may be combined.

REFERENCE NUMERALS

(58) 100 heating means 102 ribbon-type structure 110 openings L length B width 200 heating means 220 particles/ferrites 222 matrix material 300 heating means 324 carrier elements/carrier films D thickness 400 heating means 422 adhesive force changing layer/adhesive force strengthening layer 424 adhesive force changing layer/adhesive force reducing layer 500 heating means 530 rounding-off R rounding-off radius 600 heating means 600a surface normal 610 inclined opening 610a longitudinal axis 700 heating means 750 further ribbon-type structure 752 further ribbon-type structure 754 further ribbon-type structure 760 first inner object/plastic pipe 770 second outer object/bushing 780 third inner object/further plastic pipe 785 arrangement 800 system 895 generator/induction generator 896 excitation device 897 coil device 897a excitation coil 900 heating means 900a interruption of heating means/open region 990 system 995 generator/induction generator 997 coil device 997a interruption 1097 coil device having intertwined windings 1100 heating means 1102 ribbon-type structure 1115 serrated ends 1140 ferromagnetic material 1200 heating means 1248 ribbon-type carrier 1300 heating means 1302 ribbon-type structure 1342 ferromagnetic material 1344 ferromagnetic material 1400 heating means (integrated) 1460 first inner object/plastic pipe 1470 second outer object/bushing 1485 arrangement