Thermal joining of plastic objects by means of heating means having low curie temperature

Abstract

Described is a heating means for thermally connecting two objects each having a plastic material, wherein, in the connecting, a first inner object is surrounded at least partially by a second outer object, and the heating means is located between the first inner object and the second outer object. The heating means has a ribbon-type structure, in which a plurality of openings is formed. These openings are dimensioned such that molten-on plastic material of the first inner object and/or of the second outer object can intrude and can connect to molten-on plastic material of the respective other object. Alternatively or in combination, the openings are filled with a plastic material, which can connect to molten-on plastic material of the first inner object and/or of the second outer object. The ribbon-type structure has a ferromagnetic material, which is inductively heatable and which has a Curie temperature that is lower than 460° C. and/or that is adapted to the melting temperature of the first inner object and/or of the second outer object. There is further described a welded arrangement as well as a welding system having such a heating means as well as a method for thermally connecting two objects each having a plastic material.

Claims

1. A heating means for thermally connecting two objects each having a plastic material, wherein, in the connecting, a first inner object is surrounded at least partially by a second outer object and the heating means is located between the first inner object, and the second outer object, the heating means comprising: a ribbon-type structure, in which a plurality of openings is formed, and an adhesion changing layer, which is attached to, or formed at, at least one surface of the ribbon-type structure, wherein the adhesion changing layer effects a flow behavior of molten-on plastic material, wherein the openings are dimensioned such that molten-on plastic material of the first inner object and/or of the second outer object can intrude and can connect the molten-on plastic material of the respective other object, and/or wherein the openings are filled with a plastic material, which can connect to the molten-on plastic material of the first inner object and/or of the second outer object; wherein the ribbon-type structure has a ferromagnetic material, which is inductively heatable, and has a Curie temperature that is less than 460° C.

2. The heating means according to claim 1, wherein the ferromagnetic material has a Curie temperature that is less than 400° C.

3. The heating means according to claim 1, wherein the ribbon-type structure has plural ferromagnetic materials, which have different Curie temperatures.

4. The heating means according to claim 1, wherein 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.

5. The heating means according to claim 1, wherein the ribbon-type structure is configured to form a closed ribbon-type structure, which is continuously electrically conductive.

6. The heating means according to claim 1, wherein the adhesion changing layer has an adhesion force strengthening layer at the surface of the ribbon-type structure and/or an adhesion force reducing layer at the sidewalls of the openings, and/or wherein the adhesion changing layer is an oxide layer and/or has carbonates.

7. The heating means according to claim 1, wherein the openings have an average distance s from each other, which, in relation to a thickness d of the ribbon-type structure, satisfies at least one of the following equations:
0.5<s/d<2;0.7<s/d<1.5;0.8<s/d<1.3;0.9<s/d<1.1.

8. The heating means according to claim 1, wherein a transition between a plane surface of the ribbon-type structure and an opening is rounded-off.

9. The heating means according to claim 1, wherein 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.

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. 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 the range between 0.01 mm and 2 mm.

12. An arrangement, comprising: a first inner object, which has a first plastic material having a first melting temperature; a second outer object, which surrounds the first inner object at least partially, and which has a second plastic material having a second melting temperature; a heating means, which is located between the first inner object and the second outer object, wherein the heating means has a ribbon-type structure and an adhesion changing layer, which is attached to, or formed at, at least one surface of the ribbon-type structure, wherein the adhesion changing layer effects a flow behavior of molten-on plastic material, wherein the ribbon-type structure has a ferromagnetic material, which is inductively heatable, and has a predetermined Curie temperature, which is higher than the first melting temperature and/or the second melting temperature, a plurality of openings is formed in the ribbon-type structure, in which openings a solidified plastic material is located, which connects the first inner object to the second outer object, and a first temperature difference between the predetermined Curie temperature and the first melting temperature and/or a second temperature difference between the predetermined Curie temperature and the second melting temperature is in the range between 5 K and 100 K.

13. The arrangement according to claim 12, wherein the first temperature difference and/or the second temperature difference is in the range between 10 K and 80 K.

14. The arrangement according to claim 12, wherein the two plastic materials are the same.

15. The arrangement according to claim 12, further comprising: a third inner object, which has a third plastic material having a third melting temperature, wherein the second outer object surrounds at least partially also the third inner object, and wherein the heating means is located also 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, an end of the plastic pipe and a further end of the further plastic pipe.

16. A system, comprising: a first inner object which has a first plastic material with a first melting temperature; a second outer object, which surrounds the first inner object at least partially, and which has a second plastic material with a second melting temperature; a heating means located between the first inner object and the second outer object, wherein the heating means has a ribbon-type structure and an adhesion changing layer, which is attached to, or formed at, at least one surface of the ribbon-type structure, wherein the adhesion changing layer effects a flow behavior of molten-on plastic material, wherein the ribbon-type structure has a ferromagnetic material, which is inductively heatable, and has a predetermined Curie temperature, which is higher than the first melting temperature and/or the second melting temperature, a plurality of openings formed in the ribbon-type structure, in which openings a solidified plastic material is located, which connects the first inner object to the second outer object, and a first temperature difference between the predetermined Curie temperature and the first melting temperature and/or a second temperature difference between the predetermined Curie temperature and the second melting temperature is in the range between 5 K and 100 K; and a generator for generating an electromagnetic field, which inductively couples a primary coil of the generator to the heating means.

17. A method for thermally connecting two objects each having a plastic material, the method comprising: laying a heating means alongside to a first inner object or to a second outer object, wherein the heating means has a ribbon-type structure having a plurality of openings and a ferromagnetic material and an adhesion changing layer, which is attached to, or formed at, at least one surface of the ribbon-type structure, wherein the adhesion changing layer effects a flow behavior of molten-on plastic material; arranging the second outer object relative to the first inner object, such that the first inner object is surrounded at least partially by the second outer object and the heating means is located between the first inner object and the second outer object; inductively heating the heating means such that plastic material of the first inner object and/or plastic material of the second outer object melts on; intruding molten-on plastic material of the first inner object and/or of molten-on plastic material of the second outer object into the openings, such that the two plastic materials come in contact with each other, and/or melting-on of plastic material, which is already located in the openings; reducing a power, which is inductively transmitted to the heating means as a consequence of an approaching of the temperature of the ferromagnetic material to a Curie temperature of the ferromagnetic material; and cooling down the molten-on plastic material of the first inner object and/or of the molten-on plastic material of the second outer object and/or of the plastic material located in the openings, such that the two objects are mechanically connected to each other.

18. The method according to claim 17, wherein the heating means is laid alongside to the first inner object or to the second outer object, such that the two ends of the ribbon-type structure overlap.

19. The method according to claim 17, wherein the heating means is laid alongside to the first inner object or to the second outer object, such that the two ends of the ribbon-type structure are separated from each other.

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.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

(11) 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.

(12) 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 are to be considered as obviously disclosed for the skilled person with the embodiment variants illustrated explicitly herein.

(13) 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.

(14) FIG. 1a shows, in a top view, a heating means 100. The heating means 100 may consist substantially of a ribbon-type structure 102, in which a plurality of openings 110 may be formed, for example by punching. According to the embodiment example represented herein, the openings 110 may be spatially arranged irregularly. As has been discussed above, in a welding process, the openings may enable a flowing through of molten-on plastic material through the ribbon-type structure 102. Alternatively or in combination, also a suitable plastic material may be located in the openings already before the very welding process, which plastic material then, during the welding, may connect to the plastic materials of the two objects to be welded together.

(15) 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.

(16) 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.

(17) 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.

(18) 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 has been stretched by a sufficient tensile force.

(19) In other embodiments, the ribbon-type structure 102 may 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.

(20) FIG. 2 shows, in a side view, a heating means 200, which has two layers of ferromagnetic materials. A first layer 201 may have a ferromagnetic material having a first Curie temperature. The second layer 207 may have a second ferromagnetic material having a second Curie temperature. According to the embodiment example represented herein, the two Curie temperatures may be different. Thus, an average Curie temperature of the heating means 200 may result, which may be adapted to the respective specific welding application by a suitable selection of the two ferromagnetic materials.

(21) In other embodiments, no common average Curie temperature may arise, such that an inductive energy input to the heating means 200 may be, upon a reaching of the lower Curie temperature, reduced, but not prevented completely. As a consequence, for a same inductive excitation, a slower temperature increase may result, wherein an inductive coupling between the excitation coil and the heating means may be switched off upon reaching the higher Curie temperature.

(22) In preferred embodiments, a thickness D of the heating means 200 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.

(23) It is pointed out that the heating means 200 may have a surface roughness at its plane (or two-dimensional) sides, i.e. in FIG. 2 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 result in improved welding results also for a single-layered ribbon-type structure.

(24) FIG. 3 shows, in a side view, a heating means 300 having an adhesion changing layer 320, which may be formed on a ribbon-type structure 102, which may have a ferromagnetic material 305. According to the embodiment example represented herein, the adhesion reducing means may be a simple oxide layer.

(25) The adhesion changing layer 320 may contribute to improving the flow behaviour of molten-on plastic material, which may come in contact with the heating means 300 in view of a particularly stable welded connection after the cooling down.

(26) 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. 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.

(27) FIG. 5 shows, in a magnified cross-sectional view, a heating means 500, wherein, also in a ribbon-type structure 102 made of a ferromagnetic material 305, 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 may occur with a rounding-off (or chamfering) 530. This may contribute to that an initially horizontally flowing molten-on plastic material may not have to 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.

(28) 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.

(29) 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°.

(30) 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 may 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.

(31) 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.

(32) 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 may be provided to inductively heat the heating means 100, 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 primary coil arrangement having a plurality of primary coils 897, which primary coil arrangement may be arranged around the bushing 770, and which may be fed with current being an electrically alternating current by the excitation device 896.

(33) As can be seen from FIG. 8, according to the embodiment example represented herein, the heating means 100 may be wound completely around the plastic pipe 760, such that a non-represented overlap may result between the two ends of the heating means 760. The heating means may thus be considered as a (closed) secondary coil, which may be electromagnetically coupled to the plurality of the primary coils 897, and thus also inductively coupled.

(34) It is pointed out that the arrangement of the primary coil may alternatively also have only one single primary coil, which may run 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, such that the single primary coil can be removed from the arrangement 785. The inductive coupling between the induction generator 895 and/or the primary coil arrangement thereof and the heating means 100, which may represent a closed coil winding, may correspond to the magnetic and/or inductive coupling in a conventional transformer, wherein the primary coil arrangement may correspond to the primary coil of the transformer, and the heating means 100 may correspond to the secondary coil of the transformer.

(35) 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 may amount 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.

(36) FIG. 9 shows, in a cross-sectional view, a heating means 900, which may surround the plastic pipe 760 only partially, and thus may form an open structure. In FIG. 9, the open region is indicated with the reference numeral 900a. As has been described already above, for the open loop that may be given by the heating means 900, an inductive energy transfer may be ensured only by the generation of eddy currents, which may require a microscopic conductivity of the ribbon-type structure of the heating means 900.

(37) 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

(38) TABLE-US-00001 100 heating means 102 ribbon-type structure 110 openings L length B width 200 heating means 201 first layer/first ferromagnetic material having first Curie temperature 207 second layer/first ferromagnetic material having second Curie temperature 300 heating means 305 ferromagnetic material 320 adhesive force changing layer D thickness 400 heating means 422 adhesive force strengthening layer 424 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 890 system 895 generator/induction generator 896 excitation device 897 primary coil 900 heating means 900a open region