Tubular electric heating device

Abstract

A tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) is provided for heating an object (100) to be heated which is inserted into the interior of the tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90), wherein the tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) has a thermally conductive tubular core (11, 21, 31, 41, 61, 71, 81, 91) which carries an electric heating element (13, 23, 33, 43, 83, 93), wherein the tubular core (11, 21, 31, 41, 61, 71, 81, 91) of the electric heating device (10,20,30,40,60,70,80,90) has at least one linear weakening (12,22,32,42,44,62,72,82,92) having at least one section (22a,22b,22c,32a, 32b,32c, 32d,32e,42a,42b,44a, 44b,82a,82b,82c,82d,82e,92a, 92b,92c,92d,92e) in which the linear weakening (12,22,32,42,44,62,72,82,92) only incompletely penetrates the tubular core (11,21,31,41, 61,71,81,91) in a radial direction to the tube's central axis (M).

Description

[0001] Tubular electric heating devices for heating objects inserted into the interior of the tube are widely used, for example as nozzle heaters in injection molding nozzles. They have a tubular, heat-conducting core, which can be made of brass, for example, and which carries the electric heating element, typically designed as a coiled cartridge. The path of the electric heating element, and thus the distribution of the heating power along the tubular, heat-conducting core, is determined by a groove cut into it. The electric heating element is inserted into this groove so that it is in close contact with the groove walls to ensure reliable heat transfer.

[0002] If a closed, cylindrical tube with low fit tolerance is chosen as the tubular, heat-conducting core, the problem arises that such a tubular heating device can tend to get stuck on the object to be heated, making its disassembly very difficult.

[0003] Therefore, as demonstrated, for example, by DE 20 2009 011 904 U1 or DE 10 2013 013 127 B4, embodiments have been developed in which the tubular, heat-conducting core is formed by a slotted cylindrical tube. These slots extend through the tube shell from one end face along its entire length to the other end face, or they are closed on one side, i.e., they end before the other end face and transition into a web. To facilitate removal from the object to be heated in such embodiments, a tool is inserted into the slot to spread it open and thereby release the fixed surface sections from one another by applying mechanical force.At the same time, such slots can also be used to narrow them with a clamping device and thus clamp the electric heating cartridge onto the object to be heated, after it has been able to be slid onto it with more play and therefore more easily, as is described, for example, in DE 10 2021 109 062 A1.

[0004] Unfortunately, practical experience shows that using slotted tubes as the tubular core of a tubular electric heating device results in compromises in achievable precision because dimensional stability is lost after turning and milling. Slots in brass cores, for example, often cause internal stresses that reduce the inner diameter. If the cores are subsequently nickel-plated, they can swell during this process. These effects make further processing and winding of slotted tubular cores into tubular electric heating devices difficult. Furthermore, they increase the effort required for machining automation and make fully automated, unmanned production challenging.

[0005] The object of the invention is therefore to provide a tubular electric heating device that can be manufactured with improved precision, but still offers possibilities for the use of mechanical assistance during disassembly. This object is achieved by a tubular electric heating device with the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0006] The tubular electric heating device according to the invention, for heating an object inserted into the interior of the tubular electric heating device, has a thermally conductive tubular core that carries an electric heating element. A key feature of the invention is that the tubular core of the electric heating device has at least one linear weakening, wherein at least one section is present in which the linear weakening penetrates the tubular core, at least incompletely, in a radial direction to the central axis of the tube. For example, such a section of the linear weakening can be formed by a groove with a groove base.

[0007] The linear weakening is always designed such that it allows the tubular core to be widened by applying circumferential force, which can be achieved, for example, by prying with a tool, in the area of ​​the linear weakening. The points where the tubular core is only partially penetrated in the radial direction can be torn open. This design results in the points where the tubular core is only partially penetrated in the radial direction having a dimension of less than 5 mm, preferably less than 3 mm, and ideally less than 1 mm in at least one dimension.

[0008] Therefore, if a section in which the linear weakening only incompletely penetrates the tubular core in the radial direction to the central axis of the tube is formed by a groove, at least the thickness of the groove base should not exceed this value; if this section is formed by an area in which there is no material removal in the radial direction, its extent in the axial direction of the tubular metal shell should not exceed this value.

[0009] The incomplete penetration, present at least in certain sections, sufficiently increases dimensional stability to overcome problems in unmanned manufacturing, thus enabling more cost-effective production. Furthermore, it effectively counteracts expansion during nickel plating.

[0010] In a particularly preferred embodiment of the invention, at least one section, in which the linear weakening only incompletely penetrates the tubular core in the radial direction to the central axis of the tube, extends from one of the end faces of the tubular core at least half the length of the tubular core in the axial direction.

[0011] Since at least one section of the obligatory linear weakening must have the property that the linear weakening only incompletely penetrates the tubular core in the radial direction to the tube's central axis, several sections of the linear weakening can have this property, while embodiments in which the entire linear weakening fulfills this condition also fall under this feature.

[0012] A weakening of a tubular core occurs at a point where its thickness is reduced in the radial direction to the tube's central axis, without this reduction being compensated for—for example, by the insertion of an electrical heating element. A section where the linear weakening only partially penetrates the tubular core in the radial direction to the tube's central axis could, for instance, be a groove; however, it could also be obtained, for example, by removing a circular cylinder segment, whose segment height is less than the wall thickness of a cylindrical core, from that cylindrical core.

[0013] The term “linear” is used in this context to describe that the extent of the claimed weakening in the radial direction to the pipe center axis, as well as in the direction of the distance between the side walls of the linear weakening at a given point, is small compared to the length of the extent over its course.

[0014] Linear weakening therefore refers in particular to cracks or slots that completely penetrate the tubular core in a radial direction, but also to areas where this only partially occurs and a residue of material remains, as is the case in particular with grooves where the material has been worn away except for a residue that forms the groove base.

[0015] A linear weakening can also be composed of sections that are partly slots or slits and sections that are grooves or formed by narrow, band-like connections between the edges of the slots or slits, so that the degree or extent of the weakening need not be constant but can vary; however, it cannot have a larger section of the tubular core without weakening that extends more than 5 mm in the axial direction of the tubular core, because at such a point it loses its function of allowing the gap to widen. Preferably, such a section does not extend more than 3 mm in this direction, and particularly preferably, it extends 1 mm or less in this direction.

[0016] The gaps, slots or grooves can have straight and / or curved sections.

[0017] Such a linear weakening is considered "continuous" if the weakening extends – possibly to varying degrees – over the entire extent of the tubular core in the axial direction of the tube's central axis, and this can be in the form of a straight line, but also as a curved line, for example sinusoidal, meandering or spiral.

[0018] As already mentioned, the invention provides that at least one section of the linear weakening is present, in which the linear weakening penetrates the tubular core only incompletely in the radial direction to the tube's central axis, which is realized, for example, in a groove with a groove base.

[0019] Another way to realize such a section is to provide, next to or between one (in the case of an end-face arrangement of the section) or two sections in which the tubular core is completely penetrated, a narrow, band-shaped, unweakened section of the tubular core, which has an extent of less than 1 mm in the direction parallel to the central axis of the tubular core, and thus to design the linear weakening quasi in the manner of a perforation (as is used analogously to enable the defined tearing out of sheets from a block).

[0020] Sections in which the linear weakening only incompletely penetrates the tubular core in a radial direction to the tube's central axis have a shape-stabilizing effect, among other things, during upstream steps in the manufacturing process such as milling or nickel plating of the tubular core, thus avoiding problems that occur with continuous gaps or slots with regard to insufficient shape stability.

[0021] Typically, the object to be heated, or the section of the object to be heated that is inserted into the interior of the tube, is cylindrical; accordingly, the interior of the tubular core also typically has an essentially cylindrical shape.

[0022] Particularly effective shape stabilization during manufacturing is achieved when at least one section of the linear weakening, originating from one of the end faces of the tubular core, only partially penetrates the tubular core in the radial direction to the tube's central axis. This is the case, for example, when it is formed by a groove with a groove base. Another example of such a design is a tubular core with a gap that is bounded at both ends by a narrow, band-shaped, unweakened section of the tubular core, which has an extent of less than 5 mm, preferably less than 3 mm, and most preferably less than 1 mm, in the direction parallel to the central axis of the tubular core.

[0023] The linear weakening leads to particularly good clamping and release properties with good dimensional stability during the manufacturing processes, if the linear weakening is continuous and both sections of the linear weakening, which originate from one of the end faces of the tubular core, only partially penetrate the tubular core in a radial direction to the tube's central axis.

[0024] In this preferred embodiment of the invention, the tubular core therefore has, in particular, a continuous linear weakening, such that the tubular interior space of the tubular electric heating device, defined by the inner radius of the tubular core, can be reduced during heating by decreasing the distance between the side surfaces of the tubular core that bound the linear weakening. It should be explicitly noted here that a groove with an inserted heating element does not constitute such a weakening within the meaning of this application, because the heating element obviously prevents the reduction of the distance between the side surfaces of the tubular core that bound the linear weakening during heating.

[0025] Particularly with regard to the manufacture of relatively long tubular cores, it is advantageous if, for stabilization purposes, at least one further section of the linear weakening lies between the two sections of the linear weakening that originate from one of the end faces of the tubular core and in which the linear weakening only incompletely penetrates the tubular core in a radial direction to the central axis of the tube, in which the linear weakening only incompletely penetrates the tubular core in a radial direction to the central axis of the tube, and to which a section of the linear weakening is connected on both sides, in which it is designed as a gap.As has already been explained several times, grooves with a groove base and / or band-shaped unweakened sections of the tubular core, which have an extent of less than 5mm, preferably less than 3mm, particularly preferably less than 1mm in the direction parallel to the central axis of the tubular core, are particularly suitable for realizing sections with incomplete penetration.

[0026] The behavior of the groove base when clamping the tubular electric heating device can be positively influenced by the fact that the groove base of the sections of the linear weakening formed by a groove with a groove base is curved.

[0027] Preferably, at least one section in which the linear weakening only partially penetrates the tubular core in the radial direction to the tube's central axis is formed by a band-shaped section of the tubular core that has a maximum extent of at most 20% of the thickness of the tubular core's shell in at least one direction of extension. This preferably applies to all sections in which the linear weakening only partially penetrates the tubular core in the radial direction to the tube's central axis, and the direction of extension in which this occurs may vary.

[0028] An example of such a band-shaped section is a section with a groove base, as discussed above. In this case, the direction of expansion, for which the maximum expansion is determined by the preceding condition, is a direction perpendicular to the central axis of the tubular core, or a radial direction, and the groove base forms, in a sense, a flat band running parallel to this central axis, connecting the two edges of the linear weakening where it transitions into the unweakened tubular core.

[0029] The direction of expansion, for which the maximum expansion is determined by the preceding condition, can, for example, also be the direction parallel to the direction of the tubular core's central axis. In this case, a flat band running essentially perpendicular to this central axis, which connects the two edges of the linear weakening where it transitions into the unweakened tubular core, forms the section in which the linear weakening penetrates the tubular core only incompletely (i.e., not at all) in the radial direction to the central axis.

[0030] Of course, the maximum extent can also fulfill the aforementioned condition in more than one direction. This then no longer necessarily leads to flat-band-like connections, but rather to band-shaped connections between the two edges of the linear weakening, where it transitions into the unweakened tubular core, which can, for example, have a square cross-section.

[0031] In a particularly preferred embodiment, the tubular electric heating device has an outer tube. This makes it possible for the electric heating device to automatically extend itself onto the object to be heated when the material of the outer tube is selected such that the tubular core and the object to be heated expand thermally more than the inner diameter of the outer tube.

[0032] Invar is a material particularly suitable for achieving this effect in the outer tube, as its use ensures that the internal volume of the outer tube remains essentially the same.

[0033] The invention is explained in more detail below with reference to figures showing exemplary embodiments. These figures show: Fig. 1a: an isometric representation of a first tubular electric heating device; Fig. 1b: a view of the first tubular heating device made of Fig. 1a; Fig. 2a: an isometric representation of a second tubular electric heating device; Fig. 2b: a view of the second tubular heating device made of Fig. 2a; Fig. 3a: an isometric representation of a third tubular electric heating device; Fig. 3b: a view of the third tubular heating device made of Fig. 3a; Fig. 4a: an isometric representation of a fourth tubular electric heating device; Fig. 4b: a view of the fourth tubular heating device made of Fig. 4a; Fig. 5a: a first step in removing the tubular electric heating device Fig. 3a; Fig. 5b: a second step in removing the tubular electric heating device Fig. 3a; Fig. 5c: a detailed enlargement from Fig. 5b; Fig. 6a: an isometric representation of a fifth tubular electric heating device; Fig. 6b: a cross-section through the fifth tubular electric heating device with an object to be heated inserted therein in an unheated state; Fig. 6c: a detailed enlargement from Fig. 6b; Fig. 6d: a cross-section through the fifth tubular electric heating device with an object to be heated inserted therein in a heated state; Fig. 6e: a detailed enlargement from Fig. 6d; Fig. 7: a sequence of process steps for producing a pre-formed groove base; Fig. 8: a sixth tubular electric heating device; Fig. 9: a seventh tubular electric heating device; Fig. 10a: a first variant of a section with incomplete enforcement; Fig. 10b: a second variant of a section with incomplete enforcement; Fig. 10c: a third variant of a section with incomplete enforcement; and Fig. 10d: a fourth variant of a section with incomplete enforcement.

[0034] The in Fig. 1a and Fig. The first tubular heating device 10 shown in Figure 1b has a tubular core 11 with a continuous linear weakening 12 in the form of a groove. This groove is formed as a straight line, parallel to the central axis M of the tubular core 11, extending from one end face 11a of the tubular core 11 to its other end face 11b by removing material from the tubular core 11 along this line, leaving only a remaining groove base. Accordingly, this groove forms a section in which the linear weakening 12 only partially penetrates the tubular core 11 in the radial direction to the central axis M.

[0035] An electric heating element 13, implemented as a coiled cartridge, is arranged in a meandering pattern on the tubular core 11, so that the linear weakening 12 is not crossed. In this embodiment, the dimensional stability of the tubular core 11 is maximized during manufacturing, but it is more difficult to remove from the object to be heated than other embodiments because the groove base must be torn open along its entire length.

[0036] The in Fig. 2a and Fig. The second tubular heating device 20 shown in 2b, with tubular core 21, continuous linear weakening 22 and electric heating element 23, is constructed analogously to the first tubular heating device 10, but differs from it in that the continuous linear weakening here has sections 22a, 22c, each of which is formed by a groove with a groove base starting from an end face 21a, 21b of the tubular core 21, so that these sections 22a, 22c represent sections in which the linear weakening 22 only incompletely penetrates the tubular core 21 in a radial direction to the tube's central axis M.

[0037] In contrast, section 22b, located between sections 22a and 22c, is formed by a slot that radially penetrates the tubular core. This embodiment ensures end-end dimensional stability at both ends and is significantly easier to remove from the object being heated because only short sections of the groove base need to be opened.

[0038] The in Fig. 3a and Fig. The third tubular heating device 30, shown in Figure 3b, with tubular core 31, continuous linear weakening 32, and electric heating element 33, is constructed analogously to the second tubular heating device 20, but differs from it in that the continuous linear weakening here includes, between the sections 32a, 32e extending from each end face 31a, 31b of the tubular core 31 and formed by a groove with a groove base, a central section 32c, also formed by a groove with a groove base, which is separated from sections 32a, 32e by slots 32b, 32d. The central section 32c exerts a stabilizing effect, particularly in long tubular heating devices.

[0039] The in Fig. 4a and Fig. The fourth tubular heating device 40, shown in Figure 4b, with tubular core 41 and electric heating element 43, has two linear weakenings 42, 44, which extend axially parallel to the central axis M of the tubular core 41, each originating from one of the end faces 41a, 41b of the tubular core 41, over approximately 80% of its length, but not to the opposite end face 41b, 41a. The linear weakenings 42, 44, in particular, have sections 42a, 44a, each formed by a groove with a groove base originating from an end face 41a, 41b of the tubular core 41, while the remainder of the linear weakenings in section 42b, 44b is formed by a slot that penetrates the tubular core 41 in a radial direction.Another difference from the embodiments described so far is that the electrical heating element 43 is wound in a thread-like fashion and crosses the linear weakening 42 several times.

[0040] The Fig. 5a to 5c show, using the example of the tubular electric heating device 30, Fig. 3a and Fig. 3b how by applying and rotating a tool 50 in the area of ​​the linear weakening 32 the groove bases in sections 32a, 32c and 32e are torn apart so that the mechanical removal of a tubular heating device 30 “baked” onto the object to be heated can take place.

[0041] Based on the tubular electric heating device 60, which is located in the Fig. Figures 6a to 6e illustrate the behavior of the groove base in areas where the linear weakening 62 is formed by a groove. The tubular electric heating device 60 is designed as a self-tensioning tubular electric heating device 60 when heated. In addition to a tubular core 61, which carries the electric heating element 63, and a linear weakening 62 designed as a groove with groove base 62a, the electric heating device 60 has an outer tube 64 made of Invar.

[0042] Fig. Figure 6b shows the tubular electric heating device 60 in its unheated state, pushed onto an object 100 to be heated. It is particularly evident that the cross-section of the inner space of the tubular core 61 is slightly larger than the cross-section of the object 100 to be heated, resulting in a gap 101, which is especially clear in the detailed magnification of the Fig. 6c comes to light.

[0043] When the object 100 to be heated is heated, thermal expansion occurs both in the object 100 to be heated and in the tubular core 61 of the tubular electric heating device 60. However, since Invar hardly expands, the volume available in the outer tube 64 remains essentially the same. As a consequence, the Fig. 6d recognizable desired intimate contact between the tubular core 61 and the object 100 to be heated is created, whereby the linear weakening 62 is deformed in such a way that its side walls 62b, 62c are moved towards each other and the groove base 62a is pushed together, as can be seen particularly well in the enlarged section according to Fig. 6e recognizes. Analogous behavior occurs when a movement of the side walls 62b,62c towards each other of a linear weakening 62 is forced by mechanical clamping means.

[0044] In order to better control such deformations of a groove base, it may be useful to provide sections of the linear weakening designed as a groove with a convex groove base. Fig. Figure 7 reveals the necessary steps: First, in step 1, a pre-stage 74 of the tubular core is provided, in which the linear weakening 72 towards the groove base 72a is already incorporated. The pre-stage 74 is then positioned on a mandrel 73 with a projection 73a, the outer contour of which corresponds to the desired curvature of the groove base 72a, with the pre-stage 74 being aligned on the mandrel 73 such that the groove base 72a lies in the area of ​​the projection 73a of the mandrel 73. In this embodiment, as shown in step 2, compaction is carried out on all sides.In the transition to step 3, the mandrel 73 is then removed, and a tubular core 71 with a linear weakening 72 is obtained, the base of which of the groove 72a is curved, which means that the direction in which this base of the groove 72a deforms when the tubular core 71 is clamped with a clamping device or by thermal expansion when heating a workpiece to be heated, so that the side walls 72b,72c of the linear weakening 72 move towards each other.

[0045] The in Fig. The sixth tubular heating device 80 shown in Figure 8, with tubular core 81, continuous linear weakening 82 and electric heating element 83, is constructed analogously to the third tubular heating device 30 and, like the latter, has two slots 82b, 82d, which are bounded by sections 82a, 82c and 82e, in which the linear weakening 82 only incompletely, namely not at all, penetrates the tubular core 81 in a radial direction to the central axis of the tube.The fact that a linear weakening 82 still exists, which presupposes that a widening of the gap is made possible, in particular by a machine operator by applying and levering with a tool and typically accompanied by a tearing apart of the sections in which the linear weakening only incompletely penetrates the tubular core in the radial direction to the tube's central axis, is due to the fact that the sections 82a, 82c and 82e are each designed as (flat) bands and have only a small extent in the axial direction, as is particularly evident from the enlarged section of the . Fig. 8 is recognizable.

[0046] The in Fig. The seventh tubular electric heating device 90, shown in Figure 9, with tubular core 91, continuous linear weakening 92, and electric heating element 93, is constructed analogously to the sixth tubular heating device 80 and, like the latter, has two slotted sections 92b and 92d, which are bounded by sections 92a, 92c, and 92e. In these sections, the linear weakening 92 only partially, or not at all, penetrates the tubular core 91 in the radial direction to the central axis of the tube. In this embodiment, however, sections 92a, 92c, and 92e are each curved, which is already related to the Fig. 7 discussed advantages and effects.

[0047] The Fig. Sections 10a to 10d show further variants of sections with incomplete enforcement 102a, 102b, 102c and 102d respectively, which are in the Fig. Figures 10a to 10d are shown on an end face of a tubular core with linear weakening, but can also be arranged in the same configuration at another location of the linear weakening, for example in the middle area of ​​the respective tubular core.

[0048] The incomplete enforcement of Section 102a from Fig. 10a is formed by a band-like connection in which the material of the tubular core is weakened both radially and axially from the direction of its interior at least to such an extent that the band-like connection can be torn open by widening the tubular core by exerting a circumferential force, which can be achieved, for example, by levering with a tool.

[0049] The in Fig. The second variant of a section with incomplete enforcement, as shown in 10b, differs from the variant shown in 102b. Fig. 10a by introducing an additional bulge into the otherwise identically formed band-like connection.

[0050] The in Fig. The third variant of a section with incomplete enforcement, shown in 10c, differs from the variant in 102c. Fig. 10a by the fact that the material of the tubular core is weakened not only radially and axially from the direction of its inner tube, but also radially from the direction of the outer tube shell, at least to such an extent that the band-like connection can be torn open by widening the tubular core by exerting a circumferential force, which can be achieved, for example, by prying it open with a tool.

[0051] The in Fig. The fourth variant of a section with incomplete enforcement, shown in 10d, differs from the variant shown in 102d. Fig.10c by introducing an additional bulge into the otherwise identically formed band-like connection. Reference symbol list 10, 20, 30, 40, 60, 70, 80, 90 11, 21, 31, 41, 61, 71, 81, 91 electric heating device tubular core 11a,11b,21a,21b,31a,31b, 41a,41b,81a,81b,91a,91b Front 12, 22, 32, 42, 44, 62, 72, 82, 92 linear weakening 13, 23, 33, 43, 83, 93 electric heating element Sections 22a, 22b, 22c Section 32a, 32b, 32c, 32d, 32e Sections 42a, 42b, 44a, 44b 50 tools 62a,72a Nutgrund 62b, 62c, 72b, 72c side walls 64 Outer pipe 73 Dorn 73a advantage 74 Pre-stage Sections 82a, 82b, 82c, 82d, 82e Sections 92a, 92b, 92c, 92d, 92e 100 Item to be heated 101 gap Sections 102a, 102b, 102c, 102d M pipe center axis QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 20 2009 011 904 U1

[0003] DE 10 2013 013 127 B4

[0003] DE 10 2021 109 062 A1

[0003]

Claims

[1] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) for heating an object (100) to be heated which is inserted into the interior of the tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90), wherein the tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) has a thermally conductive tubular core (11, 21, 31, 41, 61, 71, 81, 91) which carries an electric heating element (13, 23, 33, 43, 83, 93), characterized by , that the tubular core (11, 21, 31, 41, 61, 71, 81, 91) of the electric heating device (10, 20, 30, 40, 60, 70, 80, 90) has at least one linear weakening (12, 22, 32, 42, 44, 62, 72, 82, 92) wherein at least one section (22a, 22b, 22c, 32a, 32b, 32c, 32d, 32e, 42a, 42b, 44a, 44b, 82a, 82b, 82c, 82d, 82e, 92a, 92b, 92c, 92d, 92e) is present in which the linear weakening (12, 22, 32, 42, 44, 62, 72, 82, 92) extends the tubular core (11,21,31,41,61,71,81,91) in the radial direction to the pipe center axis (M) only partially penetrated. [2] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to claim 1, characterized by , that the linear weakening extends from one of the end faces (11a,11b,21a,21b,31a,31b,41a,41b,81a,81b,91a,91b) of the tubular core (11,21,31,41,61,71,81,91) at least half the length of the tubular core (11,21,31,41,61,71,81,91) in an axial direction from its central tube axis (M). [3] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to claim 2, characterized by , that in at least one section (22a, 22c, 32a, 32e, 42a, 44a, 82a, 82e, 92a, 92e) of the linear weakening (12, 22, 32, 42, 44, 62, 72, 82, 92) originating from one of the end faces (11a, 11b, 21a, 21b, 31a, 31b, 41a, 41b, 81a, 81b, 91a, 91b) of the tubular core (11, 21, 31, 41, 61, 71, 82, 92), the linear weakening (12, 22, 32, 42, 44, 62, 72, 82, 92) extends the tubular core (11, 21, 31, 41, 61, 71, 81, 91) in a radial direction towards Pipe center axis (M) only partially penetrated. [4] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to one of claims 2 or 3, characterized by , that the linear weakening (12,22,32,42,44,62,72,82,92) is continuous and that in both sections (22a,22c, 32a,32e,82a,82e,92a,92e) of the linear weakening (12,22,32,42,44,62,72,82,92) originating from one of the end faces (11a,11b,21a,21b,31a,31b,41a,41b,81a,81b,91a,91b) of the tubular core (11,21,31,41,61,71,81,91), the linear weakening (12,22,32,42,44,62,72,82,98) of the tubular core (11,21,31,41,61,71,81,91) in the radial direction to the pipe center axis (M) only partially penetrated. [5] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to claim 4, characterized by, that between the two sections (22a,22c,32a,32e,82a,82e,92a,92e) of the linear weakening (12,22,32,42,44,62,72,82, 92) originating from one of the end faces (11a,11b,21a,21b,31a,31b,41a,41b,81a,81b,91a,91b) of the tubular core (11,21,31,41,61,71,81,91) and in which the linear weakening (12,22,32,42,44,62,72,82,92) only incompletely weakens the tubular core (11,21,31,41,61,71,81,91) in a radial direction to the tube's central axis (M) at least one further section (32c,82c,92c) of the linear weakening (12,22,32,42,44,62,72,82,92) is located, in which the linear weakening (12,22,32,42, 44,62,72,82,92) only incompletely penetrates the tubular core (11,21,31,41,61,71, 81,91) in a radial direction to the tube's central axis (M) (62a,72a) and to which a section (32b,32d,82b,82d,92b,92d) of the linear weakening (12,22,32,42,44,62,72,82,92) is attached on both sides, in which it is designed as a gap. [6] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to any one of claims 1 to 5, characterized by , that at least one section in which the linear weakening (12,22,32,42,44,62,72,82,92) only incompletely penetrates the tubular core (11,21, 31,41,61,71,81,91) in a radial direction to the tube's central axis (M) is formed by a groove with a groove base (62a,72a). [7] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to claim 6, characterized by , that the groove base (62a,72a) of the sections (22a,22c,32a,32c,32e,42a, 44a,82a,82e,92a,92e) of the linear weakening (12,22, 32,42,62,72,82,92) formed by a groove with groove base (62a,72a) is convex. [8] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90 (according to any one of claims 1 to 7, characterized by, that at least one section in which the linear weakening (12,22,32,42,44,62,72,82,92) of the tubular core (11,21, 31,41,61,71,81,91) is only incompletely penetrated in the radial direction to the tube's central axis (M) by a band-shaped section (82a,28c,82e,92a,92c,92e,102a,102b, 102c,102d) of the tubular core (11,21,31,41,61,71,81, 91) which has a maximum extent of at most 20% of the thickness of the tubular shell of the tubular core (11,21,31, 41,61,71,81,91) in at least one direction of extension. [9] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to any one of claims 1 to 8, characterized by , that the tubular electric heating device (10,20,30,40,60,70,80,90) has an outer tube (64). [10] Tubular electric heating device (10, 20, 30, 40, 60, 70, 80, 90) according to claim 9, characterized by that the outer tube is made of Invar.

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