Electric tubular heating element with connection bolts and manufacturing process for electric tubular heating elements with connection bolts

Abstract

An electric tubular heating element (10, 20) with a tubular metal jacket (11, 21) in the interior of which at least one electric heating element (12, 22, 30, 40, 50, 60, 70, 80), designed as a resistance wire, is arranged at least partially electrically insulated from the tubular metal jacket (11, 21), characterized in that the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) has a base body (12c, 22c, 31, 41, 51, 61, 71) which consists of one or more sections of the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) each with a substantially constant cross-section, and two end sections (12a, 12b, 22a,22b,30a,40a,50a,60a,70a,80a) and that at least one end section (12a,12b,22a,22b,30a,40a,50a,60a, 70a,80a) has at least one of the electrical heating elements (12,22,30,40,50,60,70,80) is shaped so that the cross-section of the end section (12a,12b,22a,22b, 30a,40a,50a, 60a,70a,80a) is at least in partial areas of the end section (12a,12b,22a,22b,30a,40a,50a,60a,70a,80a) is reduced compared to the cross-section in each section of the base body (12c,22c,31,41,51,61,71).

Description

[0001] The invention relates to an electric tubular heating element with connecting bolts having the features of the preamble of claim 1 and a method for manufacturing such electric tubular heating elements.

[0002] Electric tubular heaters are a tried and tested method of providing electric heat. In this category of electric heating devices, the electric heating element, which in many cases is a resistance wire or incorporates a resistance wire, is located inside a tubular metal casing and electrically insulated from it by a highly thermally conductive electrical material such as magnesium oxide or ceramic. The term "electric tubular heater" is used here for all such electrical heating devices without further internal differentiation and thus also includes heating cartridges that have connections on only one end.

[0003] It is known to establish electrical contact between the electric heating element and the conductors of the supply line via connecting bolts in order to limit heat generation as much as possible to the areas of the electric tubular heater where it is desired and to optimize the current supply to the electric heating element. Naturally, it is then important to establish a reliable electrical contact between the electric heating element and the connecting bolts. The effects of contact resistance and local contact problems are particularly problematic here, especially with small available contact areas.

[0004] Problems in ensuring a reliable electrical contact can arise, particularly when the electric tubular heating element—especially with regard to its cross-sectional area—must be designed to be very small. In such cases, particularly when the electric heating element is designed as a straight heating conductor, a butt-welded connection bolt made of pure nickel can be used as a workaround; however, this often results in localized increases in power, which can lead to problems.

[0005] Tubular electric heating elements are known, for example, from US 10 299 317 B2, JP 2002 - 334 768 A, US 3 662 222 A, CN 1 02 934 515 A and CN 1 06 796 030 A.

[0006] The object of the invention is therefore to provide an electric tubular heating element with connecting bolts, featuring improved process reliability in establishing the electrical contact between the electric heating element and the connecting bolt, as well as a method for manufacturing such an electric tubular heating element. This object is achieved by an electric tubular heating element with the features of claim 1 and a method for manufacturing an electric tubular heating element with the features of claim 13. Advantageous embodiments of the invention are the subject of the respective dependent claims.

[0007] The electric tubular heating element according to the invention has a tubular metal jacket in the interior of which at least one electric heating element, designed as a resistance wire, is arranged in an electrically insulated manner from the tubular metal jacket, at least in sections, which can be achieved by embedding the electric heating element in electrically insulating material such as magnesium oxide or a ceramic.

[0008] The phrase "at least partially" is used in particular because, in some embodiments, the tubular metal sheath can be used as a return conductor, and for this purpose, a conductive connection must be established between one end of the electric heating element and the tubular metal sheath. Specifically, if all connections of the electric heating element are led out of the tubular metal sheath at its end face, the electric heating element is completely electrically insulated from the tubular metal sheath.

[0009] A key aspect of the invention is that the electric heating element has a base body consisting of one or more sections of the electric heating element, each with a substantially constant cross-section, and two end sections, and that at least one end section is machined by forming at least one of the electric heating elements, such that the cross-section of the end section is reduced, at least in partial areas of the end section, particularly at the end face of the end section, compared to the cross-section in each section of the base body. This measure makes it possible to establish contact with a connecting wire or connecting bolt, which can be made not only via end faces but also via side faces, without increasing the cross-section of the overall assembly.

[0010] Optional, but in many cases advantageous, is the fully or partially compressed electric tubular heating element.

[0011] The base body is formed by the wire core in the area between the end sections of the resistance wire. Multiple sections of the base body with essentially constant cross-sections occur particularly when different sections of the electric tubular heater are compressed to varying degrees, resulting in different deformations of the resistance wire in these sections. The meaning of the term "cross-section" becomes clear and immediate when one considers that a resistance wire in its extended state is viewed as an essentially cylindrical system with a cylinder axis parallel to the direction of the resistance wire, to which cross-sectional areas are perpendicular. These considerations are obviously directly transferable to connecting wires or connecting bolts.

[0012] The invention is particularly advantageous for use with linear, especially straight or extended, electrical heating elements.

[0013] Possibilities for shape-changing processing of the end sections of the electrical heating element designed as resistance wire, with which such cross-sectional reductions are possible, include in particular machining processes, but also hammering and pressing processes.

[0014] This involves modifying the heating element, i.e., the resistance wire itself, specifically in one of its end sections, resulting in a reduction of its cross-sectional area. It's important to note that this approach initially contradicts the conventional idea of ​​reducing heating power in an unheated area by increasing the cross-sectional area.

[0015] However, such a reduction in cross-section means that, while the installation space requirements for the electric tubular heating element remain constant, additional interaction surfaces are provided for establishing an electrical contact with the connecting wire or connecting bolt, which has a direct positive effect on process reliability, even if an end-face interaction surface may even be reduced.

[0016] The invention is particularly advantageous in cases where at least one connecting wire or bolt is present, which is in electrically conductive contact with a machined end section of the electric heating element, specifically within the tubular metal casing. In these cases, the connection of the electric heating element to the electrical supply line is therefore not direct, but rather via the connecting wire or bolt, which in particular allows for an unheated end section of the electric tubular heating element.

[0017] A particularly advantageous development of such a configuration is one in which the electrically conductive connection to the machined end section of the electric heating element is made via an end section of the connecting wire or connecting bolt that is machined to have a shape complementary to the shape of the end section of the electric heating element to which it is connected. In this way, the contact area for forming the electrical contact can be maximized, and consequently, the impact of any local problem areas can be minimized. Furthermore, this also improves the mechanical stability of the connection, for example, against vibrations.

[0018] Such increased stability is also advantageous, for example, in cases where the electric tubular heating element is exposed to a large number of temperature cycles, which can put particular stress on the contact point due to the different coefficients of thermal expansion of different materials.

[0019] In principle, magnesium oxide in powder form, or preferably in granular form, can be used for the electrical insulation of the assembly, which consists of an electric heating element on one side and connecting bolts on the other. However, according to a further development of the invention, which is advantageous for certain geometries, the electrical insulation of the assembly, which consists of an electric heating element on one side and connecting wire or connecting bolts on the other, can also be provided by ceramic tubes slid onto the tubular metal casing. From a manufacturing perspective, this is a significant advantage, particularly for small-diameter electric tubular heating elements, because filling them with a material in powder or granular form, e.g., magnesium oxide, is often difficult in these cases.

[0020] It is particularly preferred if this electrical insulation is formed by a single ceramic tube pushed on, which, however, requires that there are no excessively large variations in distance between the outer contour of the assembly and the tubular metal sheath over the volume that must be filled by the electrical insulation, which is promoted by the inventive design of the end sections of the electrical heating element.

[0021] It should be noted, however, that when the electric tubular heating element is compressed, the ceramic tubes are regularly crushed into powder and are therefore often no longer recognizable as tubes in the compressed end products.

[0022] If the connecting wire or connecting bolt has a base body whose cross-section corresponds, at least in one section, to the cross-section of a section of the base body of the electric heating element, the tubular heater has a substantially unheated area without this area requiring significant additional installation space.

[0023] It is particularly preferred if the outer circumferential line of the assembly formed from an electrical heating element on the one hand and connecting wires or connecting bolts on the other hand is constant over the entire area of ​​this assembly which is arranged inside the tubular metal sheath.

[0024] In particular, a preferred embodiment for reducing the cross-section of the end section is achieved when the cross-section of the end section tapers stepwise or continuously towards the end of the electric heating element. Such an embodiment also avoids a abrupt transition between the unheated and heated areas of the electric tubular heater.

[0025] Alternatively, the end section can also be formed, for example, by a projection on an end face of the base body. If such a projection also has an undercut or a thread, the formation and maintenance of the electrical connection are mechanically supported, which, especially in conjunction with complementary designs of the end section of the connecting wire or connecting bolt, leads to particularly reliable connections.

[0026] While the previously discussed examples of cross-sectional reduction require a change in the outer contour of the end section relative to the cross-section of the adjacent section of the base body, it can also be achieved if the outer contour of the end section corresponds to the outer contour of a section of the base body, but the end section has a recess or opening extending from the end face of the electrical heating element. Advantageously, this recess or opening can itself have an undercut or a thread, thereby mechanically supporting the electrical connection.

[0027] The inventive method for manufacturing an electric tubular heating element comprises the steps - Providing a tubular metal sheath, a connecting wire or bolt, and an electrical heating element designed as a resistance wire and having a base body consisting of one or more sections of the electrical heating element, each with a substantially constant cross-section, - Connecting the electric heating element to the connecting wire or terminal bolt, - Arranging at least the electric heating element inside an interior of the tubular metal casing, and - electrical insulation of at least sections of the electrical heating element relative to the tubular metal sheath, whereby the last three steps do not necessarily have to be carried out in this order.

[0028] Essential to the method according to the invention is that at least one end section of at least one of the electrical heating elements is machined by shape transformation, such that the cross-section of the end section is reduced, at least in partial areas of the end section, compared to the cross-section in each section of the base body. This measure makes it possible to establish contact with a connecting wire or connecting bolt, which can be made not only via end faces but also via side faces, without increasing the cross-section of the overall arrangement.

[0029] In an advantageous further development of the method, before connecting the electrical heating element to the connecting wire or connecting bolt, at least one end section of at least one connecting wire or connecting bolt is shaped in a manner complementary to the shape-changing processing of the end section of the electrical heating element, thereby enabling a particularly reliable electrical and mechanical contact between the electrical heating element on the one hand and the connecting wire or connecting bolt on the other.

[0030] It is also considered advantageous that the electrical heating element, together with the connecting wire or connecting bolt, is arranged as an assembly inside the tubular metal sheath, which allows for more controlled establishment of the electrical and mechanical contact and thus contributes to process-reliable and low-rejection manufacturing.

[0031] It is particularly preferred if the electrical insulation of at least sections of the electric heating conductor from the tubular metal sheath is achieved by sliding on ceramic tubes, which significantly simplifies the manufacturing process. It is especially preferred if the electric heating conductor, together with sections of the connecting wire or stud, is electrically insulated from the tubular metal sheath by sliding on a single ceramic tube. This, however, requires that the external dimensions of the assembly consisting of the electric heating element and connecting wires or studs do not vary significantly.

[0032] Shape-changing machining can be carried out, for example, by machining, in particular by milling, turning or grinding, but also by pressing or hammering.

[0033] The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. These show: Fig. 1a: a first embodiment of an electric tubular heating element, Fig. 1b: a detailed representation of a first detail of the electric tubular heating element made of Fig. 1a, Fig. 1c: a detailed representation of a second detail of the electric tubular heater made of Fig. 1a before and after compaction, Fig. 2 a second embodiment of an electric tubular heating element, Fig. 3a: a schematic representation of a first step in connecting an electrical heating element and a connecting wire according to a first procedure, Fig. 3b: a schematic representation of a second step for connecting the electrical heating element and connecting wire according to the first procedure, Fig. 3c: a schematic representation of a third step for connecting the electrical heating element and connecting wire according to the first procedure, Fig. 4a: a schematic representation of a first step for connecting an electrical heating element and connecting wire according to a second procedure, Fig. 4b: a cross-sectional view of the step from Fig. 4a, Fig. 4c: a cross-sectional view of a second step for connecting the electrical heating element and the connecting wire according to the second procedure, Fig. 4d: a cross-sectional view of a third step for connecting the electrical heating element and connecting wire according to the second procedure, Fig. 5a: a schematic representation of a first step for connecting an electrical heating element and a connecting wire according to a third procedure, Fig. 5b: a cross-sectional view of the step from Fig. 5a, Fig. 5c: a cross-sectional view of a second step for connecting the electrical heating element and the connecting wire according to the third procedure, Fig. 6a: a schematic representation of a first step for connecting an electrical heating element and a connecting wire according to a fourth procedure, Fig. 6b: a cross-sectional view of the step from Fig. 6a, Fig. 6c: a cross-sectional view of a second step for connecting the electrical heating element and the connecting wire according to the fourth procedure, Fig. 7a: a schematic representation of a first step for connecting an electrical heating element and connecting wire according to a fifth procedure, Fig. 7b: a cross-sectional view of the step from Fig. 7a, Fig. 7c: a cross-sectional view of a second step for connecting the electrical heating element and the connecting wire according to the fifth procedure, Fig. 8a: a first schematic representation of a first way to modify the cross-section of the electrical heating element, Fig. 8b: a second schematic representation of the first type, to modify the cross-section of the electrical heating element, Fig. 8c: a third schematic representation of the first kind, to modify the cross-section of the electrical heating element, Fig. 8d: a schematic representation of a second way to modify the cross-section of the electrical heating element, and Fig. 8e: a schematic representation of a third way to modify the cross-section of the electrical heating element.

[0034] Fig. Figure 1a shows an electric tubular heating element 10 with a tubular metal sheath 11 and an electric heating element 12. The electric heating element 12 is designed as a linear, stretched resistance wire that runs concentrically to the tube axis inside the tubular metal sheath 11.

[0035] The electric heating element 12 has two end sections 12a, 12b, which are shown in the detailed drawings of details A and B respectively according to Fig. 1b or Fig. 1c are each shown enlarged, and a basic body 12c with a substantially constant cross-section. In particular, in cases where an electric tubular heater is compressed to varying degrees in different sections, the different compression can lead to different changes in the electric heating element, resulting in a basic body with several sections corresponding to the zones of different compression, each with a substantially constant cross-section.

[0036] How that in Fig. As illustrated in detail A in Figure 1b, the end section 12a is welded to an electrically conductive ring 13, which in turn is welded to the tubular metal sheath 11. Accordingly, there is an electrical connection between the end section 12a of the electric heating element 12 and the tubular metal sheath 11; the tubular metal sheath 11 serves as a return conductor.

[0037] How that in Fig. As illustrated in detail B (1c) before and after the compression of the electric tubular heating element 10, the end section 12b of the electric heating element 12 is shaped in such a way that its cross-section is reduced, namely stepped. The stepped end section 12b of the electric heating element 12 engages in a complementary stepped recess 15 extending from the end face of the connecting wire or connecting bolt 14 facing the heating element 12, which is located in its end section 14a, so that there is electrical and mechanical contact between the electric heating element 12 and the connecting wire of the connecting bolt 14. At the same time, the outer contours of the electric heating element 12 and the connecting wire or connecting bolt 14 are matched so that their outer surfaces abut flush against each other. Furthermore, a section of the connecting bolt 14 or of its base body 14b protrudes from the tubular metal sheath 11.

[0038] The sections of the electrical heating element 12 located inside the tubular metal sheath 11, with the exception of the end section 12a and the connecting bolt 14, are electrically insulated from the tubular metal sheath 11 by a single ceramic tube 16.

[0039] The manufacture of the electric tubular heating element 10 is extremely simple. The end section 12b of the electric heating element 12 is machined, for example by turning, to create the stepped contour. The connecting bolt 14 is drilled into its end section 14a to create the complementary recess 15.

[0040] The ring 13 can then be placed onto the end section 12a, the end section 12b inserted into the complementary recess 15, and the resulting assembly—if necessary after welding or soldering the components together—inserted into the tubular metal casing 11. The ring 13 is then welded to the tubular metal casing 11, and the ceramic tube 16 is slid onto it before the electric tubular heating element 10 is completed by crimping. It should be noted that if welding or soldering is to be avoided, such crimping can already result in a usable press-fit connection.

[0041] The in Fig. The electric tubular heating element 20 shown in Figure 2 has a tubular metal jacket 21 and an electric heating element 22 with end sections 22a, 22b. In this example, both end sections are shaped analogously to the end section 12b of the electric heating element 12 of the electric tubular heating element 10, so that their cross-sections are reduced towards the ends of the electric heating element by means of a step. Two connecting wires or connecting bolts 23, 24 are provided, which have end sections 23a, 24a that are shaped analogously to the connecting bolt 14 and its end section 14a, respectively, and are provided with recesses 25, 27. In this embodiment, the complete electrical insulation of the assembly consisting of the electric heating element 22 and the connecting bolts 23, 24 from the tubular metal jacket 21 is ensured by a single ceramic tube 26.

[0042] During the Fig. The production of the connection between an electrical heating element 30 and a connecting wire or connecting bolt 35, whose base bodies 31, 36 have the same cross-section, as shown in 3a to 3c, is carried out as in the Fig. As can be seen particularly well in section 3a, the end section 30a of the electrical heating element 30 and the end section 35a of the connecting wire or connecting bolt 35 are each chamfered at the same cutting angle in the same cutting direction. Accordingly, the cross-sections of these end sections 30a and 35a are each reduced compared to the respective base body by means of form-changing machining.

[0043] The contact surfaces 32, 37 produced in this way can then, as the Fig. 3b shows, precisely stacked on top of each other and, as in Fig. As shown in 3c, they are welded together. It is immediately apparent that this method significantly increases the contact area compared to a butt-end contact, which considerably reduces the relevance of any local contact problems that may occur.

[0044] During the Fig. The production of the connection between an electrical heating element 40 and a connecting wire or connecting bolt 45, whose base bodies 41, 46 have the same cross-section, as shown in 4a to 4d, is as in the Fig. 4a and Fig. As can be seen particularly well in Figure 4b, the end section 40a of the electrical heating element 40 is formed in a stepped manner by radially removing material from the resistance wire, while the end section 45a of the connecting wire or connecting bolt 45 has a complementary stepped recess 47 extending from the end face of the connecting wire or connecting bolt 45. Accordingly, the cross-sections in the end sections 40a and 45a are also reduced compared to the cross-section of the base body 41 and 46 by means of form-changing machining.

[0045] Accordingly, the end section 40a of the electrical heating element 40 can be inserted into the recess 47 of the connecting wire or connecting bolt 45, as shown in Fig. 4c is shown, and then by pressing, as in Fig. As shown in 4d, the electrical contact is ensured.

[0046] Of course, such an arrangement can also be implemented with the roles reversed, i.e., with a stepped recess extending from the end face of an electrical heating element into it to receive a complementarily stepped end section of the connecting wire or connecting bolt. The choice of one of these alternatives can be motivated, for example, by the specific materials used and their behavior during processing.

[0047] During the Fig. The production of the connection between an electrical heating element 50 and a connecting wire or connecting bolt 55, whose base bodies 51, 56 have the same cross-section, as shown in Figures 5a to 5c, is as described in the Fig. 5a and Fig. As can be seen particularly well in Figure 5b, the end section 50a of the electrical heating element 50 is shaped to be conical by radially removing material from the resistance wire, while the end section 55a of the connecting wire or connecting bolt 55 has a complementary conically tapered recess 57 extending from the end face of the connecting wire or connecting bolt 55. Accordingly, the cross-sections in the end sections 50a and 55a are also reduced compared to the cross-section of the base body 51 and 56 by means of form-changing machining.

[0048] Accordingly, the end section 50a of the electrical heating element 50 can be inserted into the recess 57 of the connecting wire or connecting bolt 55, as shown in Fig. 5c is shown, and then, for example, the electrical contact can be ensured by crimping.

[0049] Of course, this arrangement can also be implemented with the roles of the electric heating element on the one hand and the connecting wire or connecting bolt on the other reversed.

[0050] During the Fig. The production of the connection between an electrical heating element 60 and a connecting wire or connecting bolt 65, whose base bodies 61, 66 have the same cross-section, as shown in 6a to 6c, is as in the Fig. 6a and Fig. As can be seen particularly well in Figure 6b, the end section 60a of the electrical heating element 60 is reshaped into a projection 62 by removing material from the resistance wire, which in this example also has an undercut. The end section 65a of the connecting wire or connecting bolt 65 has a complementary groove 67 extending from the end face of the connecting wire or connecting bolt 55.

[0051] Accordingly, the end section 60a of the electrical heating element 60 or its projection 62 can be inserted into the groove 67 of the connecting wire or connecting bolt 65, as shown in Fig. 6c is shown.

[0052] Of course, this arrangement can also be implemented with the roles of the electric heating element on the one hand and the connecting wire or connecting bolt on the other reversed.

[0053] During the Fig. The production of the connection between an electrical heating element 70 and a connecting wire or connecting bolt 75, whose base bodies 71, 76 have the same cross-section, as shown in 7a to 7c, is as in the Fig. 7a and Fig. As can be seen particularly well in Figure 7b, the end section 70a of the electrical heating element 70 is reshaped by removing material from the resistance wire into a cylindrical projection 72, into which a thread is cut. The end section 75a of the connecting wire or connecting bolt 75 has a complementary bore 77 extending from the end face of the connecting wire or connecting bolt 65, into which a matching mating thread is cut.

[0054] Accordingly, the end section 70a of the electrical heating element 70 or its projection 72 can be screwed into the bore 77 of the connecting wire or connecting bolt 75, as shown in Fig. Figure 6c is shown. The roles of the electric heating element 70 and the connecting wire or connecting bolt 75 can also be reversed in this connection.

[0055] The Fig. Figures 8a to 8e illustrate three different procedures for the shape-changing processing of an end section 80a of an electrical heating element 80 formed by a heating conductor, which are of course equally applicable to connecting wires or connecting bolts.

[0056] The Fig. Figures 8a to 8c show the first variant: hammering in a predefined profile. Fig. Figure 8a shows the hammer jaws 81 extended in cross-section before the electric heating element 80 is inserted. Fig. Figure 8b shows the arrangement of hammer jaws 81 and inserted electric heating element 80 from above. Fig. Figure 8c shows the state of this arrangement during hammering.

[0057] Fig. Figure 8d illustrates the machining of the electrical heating element 80 or of its end section 80a by turning with a schematically represented turning tool 82; Fig.8e the machining of the electrical heating element 80 or of its end section 80a by turning with a schematically illustrated milling tool 83. Reference symbol list 10.20 Tubular radiators 11.21 12,22,30,40,50,60,70, metal jacket 80 electric heating element 12a,12b,22a,22b,30a, 40a,50a,60a,70a,80a end section 12c, 22c, 31, 36, 41, 46, 51, 56, 61, 66, 71, 76 Basic body 13 Ring 14, 23, 24, 35, 45, 55, 65, 75, 85 Connecting wire or connecting bolt 14a,23a,24a,35a,45a, 55a,65a,75a end section 15, 25, 27, 47, 57 Exclusion 16.26 ceramic tube 32.37 Contact area 62.72 lead 67 Nut 77 bore 81 hammer jaws 82 Turning tool 83 milling tools

Claims

[1] Electric tubular heating element (10,20) with a tubular metal jacket (11,21) in the interior of which at least one electric heating element (12,22,30,40,50,60,70,80), designed as a resistance wire, is arranged in an electrically insulated manner from the tubular metal jacket (11,21) at least in sections, characterized by, that the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) has a base body (12c, 22c, 31, 41, 51, 61, 71) consisting of one or more sections of the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) each with a substantially constant cross-section, and has two end sections (12a, 12b, 22a, 22b, 30a, 40a, 50a, 60a, 70a, 80a) and that at least one end section (12a, 12b, 22a, 22b, 30a, 40a, 50a, 60a, 70a, 80a) is shaped by at least one of the electric heating elements (12, 22, 30, 40, 50, 60, 70, 80) such that the cross-section of the The cross-section of the end section (12a,12b,22a,22b, 30a,40a,50a, 60a,70a,80a) is reduced at least in parts of the end section (12a,12b,22a,22b,30a,40a,50a,60a,70a,80a) compared to the cross-section in each section of the base body (12c,22c,31,41,51,61,71). [2] Electric tubular heating element (10, 20) according to claim 1, characterized by, that at least one connecting wire or connecting bolt (14,23,24,35, 45,55,65,75,85) is present which is in electrically conductive contact with a machined end section (12a,12b,22a,22b,30a,40a,50a, 60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) within the tubular metal sheath (11,21). [3] Electric tubular heating element (10, 20) according to claim 2, characterized by , that the electrically conductive connection to the machined end section (12a,12b,22a,22b,30a,40a,50a, 60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) is made via an end section of the connecting wire or connecting bolt (14,23,24,35,45,55,65,75,85) which is machined in such a way that it has a shape complementary to the shape of the end section (12a,12b,22a,22b,30a,40a,50a,60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) to which it is connected. [4] Electric tubular heating element (10, 20) according to claim 2 or 3, characterized by , that the electrical insulation of the assembly, which is formed from an electrical heating element (12,22,30,40,50,60,70,80) on the one hand and connecting wire or connecting bolt (14,23,24,35,45,55,65,75,85) on the other hand, is formed from the tubular metal sheath (11,21) by magnesium oxide powder, magnesium oxide granules or by ceramic tubes (16,26) pushed on. [5] Electric tubular heating element (10, 20) according to claim 4 characterized by , that the electrical insulation of the assembly, which is formed from an electrical heating element (12,22,30,40,50,60,70,80) on the one hand and connecting wire or connecting bolt (14,23,24,35,45,55,65,75,85) on the other hand, is formed over the entire area of ​​the tubular metal sheath (11,21) by a single ceramic tube (16,26) pushed on. [6] Electric tubular heating element (10, 20) according to one of claims 2 to 5, characterized by, that the connecting wire or connecting bolt (14,23,24,35,45,55,65,75,85) has a base body (36,46,56,66,76) whose cross-section corresponds at least in one section to the cross-section of a section of the base body (12c,22c,31,41,51,61,71) of the electrical heating element (12,22,30,40,50,60,70,80). [7] Electric tubular heating element (10,20) according to claim 6, characterized by , that the outer circumferential line of the cross-sections of the assembly formed from an electrical heating element (12,22,30,40,50,60,70,80) on the one hand and connecting wires or connecting bolts (14,23,24,35,45,55,65,75,85) on the other hand is constant over the entire area of ​​this assembly which is arranged inside the tubular metal sheath (11,21). [8] Electric tubular heating element (10, 20) according to any one of the preceding claims, characterized by, that the cross-section of the end section (12a,12b,22a,22b,30a,40a, 50a,60a,70a,80a) of the electric heating element (12,22,30, 40,50,60,70,80) tapers stepwise or continuously towards the end of the electric heating element (12,22,30,40,50,60,70,80). [9] Electric tubular heating element (10, 20) according to one of the preceding claims, characterized by , that the end section (12a,12b,22a,22b,30a,40a,50a, 60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) is formed by a projection on an end face of the base body of the electric heating element (12,22,30,40,50,60,70,80). [10] Electric tubular heating element (10, 20) according to claim 9, characterized by that the projection has an undercut or a thread. [11] Electric tubular heating element (10, 20) according to one of the preceding claims, characterized by, that the outer contour of the end section (12a,12b,22a,22b,30a,40a,50a, 60a,70a,80a) of the electric heating element (12,22,30,40, 50,60,70,80) corresponds to the outer contour of a section of the base body (12c,22c,31,41,51,61,71) of the electric heating element (12,22,30,40,50,60,70,80), but the end section (12a,12b,22a,22b,30a,40a,50a,60a,70a,80a) has a recess or opening extending from the end face of the electric heating element (12,22,30,40,50,60,70,80). [12] Electric tubular heating element (10, 20) according to claim 11, characterized by that the recess or opening has an undercut or a thread. [13] Method for manufacturing an electric tubular heating element (10,20) comprising the steps - Providing a tubular metal sheath (11, 21), a connecting wire or connecting bolt (14, 23, 24, 35, 45, 55, 65, 75, 85) and an electric heating element (12, 22, 30, 40, 50, 60, 70, 80) designed as a resistance wire and having a base body (12c, 22c, 31, 41, 51, 61, 71) consisting of one or more sections of the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) each having a substantially constant cross-section, - Connecting the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) to the connecting wire or connecting bolt (14, 23, 24, 35, 45, 55, 65, 75, 85), - Arranging at least the electric heating element (12, 22, 30, 40, 50, 60, 70, 80) in an interior of the tubular metal sheath (11, 21), and - electrical insulation of at least sections of the electrical heating element (12, 22, 30, 40, 50, 60, 70, 80) relative to the tubular metal sheath (11, 21), characterized by, that at least one end section (12a,12b,22a,22b,30a,40a,50a,60a, 70a,80a) of at least one electric heating element (12,22,30,40,50,60,70,80) is shaped so that the cross-section of the end section (12a,12b,22a,22b, 30a,40a,50a, 60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) is shaped at least in partial areas of the end section (12a,12b,22a,22b,30a,40a,50a,60a,70a,80a) of the electric heating element (12,22,30,40,50,60,70,80) is reduced compared to the cross-section in each section of the base body (12c,22c,31,41,51,61,71) of the electric heating element (12,22,30,40,50,60,70,80). [14] Method according to claim 13, characterized by, that before connecting the electrical heating element (12,22,30,40,50, 60,70,80) with the connecting wire or connecting bolt (14, 23,24,35,45,55,65,75,85) at least one end section of at least one connecting wire or connecting bolt (14, 23,24,35,45,55,65,75,85) is shaped in a manner complementary to the shape-changing processing of the end section (12a,12b,22a,22b,30a,40a, 50a,60a,70a,80a) of the electrical heating element (12,22, 30,40,50,60,70,80). [15] Method according to claim 13 or 14, characterized by , that the electric heating element (12,22,30,40,50,60,70,80) is arranged together with the connecting wire or connecting bolt (14,23,24, 35,45,55,65,75,85) inside the tubular metal sheath (11,21). [16] Method according to any one of claims 13 to 15, characterized by, that the electrical insulation of at least sections of the electrical heating element (12,22,30,40,50,60,70,80) from the tubular metal sheath (11,21) is carried out by filling with magnesium oxide as powder or granules or by sliding on ceramic tubes (16,26). [17] Method according to claim 16, characterized by , that the electric heating element (12,22,30,40,50,60,70,80) together with sections of the connecting wire or connecting bolt (14,23,24,35,45,55,65,75,85) is electrically insulated from the tubular metal sheath (11,21) by sliding on a single ceramic tube (16,26). [18] Method according to any one of claims 13 to 17, characterized by that the shape-changing machining is carried out by machining, pressing or hammering. [19] Method according to any one of claims 13 to 18, characterized by , that the electric tubular heating element (10,20) is completely or partially compressed.

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