Electric heating device and system consisting of an electric heating device and an object to be heated

Abstract

An electric heating device (100, 200, 300, 400, 500) with a substantially cylindrical interior (101, 201, 301, 401, 501) for receiving an object to be heated, wherein the substantially cylindrical interior (101, 201, 301, 401, 501) for receiving the object to be heated is bounded externally by a one- or multi-part heat conductor (110, 210, 310, 410, 510), which can be heated by at least one electric heating element (120, 220, 320, 420, 520) arranged in a groove (111, 211, 311, 411, 511) provided in the one- or multi-part heat conductor (110, 210, 310, 410, 510), characterized in that the electric heating device (100,200,300,400,500) has a higher heating output in at least one more heated section (110a,210a,310a,410a,510a) of the single or multi-part heat conductor (110,210,310,410,510) than in a less heated section (110b,210b) adjacent to this more heated section (110a,210a,310a,410a,510a).310b, 410b, 510b) wherein in the part of the less heated section (110b, 210b, 310b, 410b, 510b) adjacent to the more strongly heated section (110a, 210a, 310a, 410a, 510a) within the heat conductor (110, 210, 310, 410, 510) at least one local area (113, 213, 313, 413, 513) with increased thermal resistance is realized.

Description

The invention relates to a further development of an electric heating device with a substantially cylindrical interior for receiving an object to be heated, wherein the substantially cylindrical interior for receiving the object to be heated is bounded externally by a one- or multi-part heat conductor, which can be heated by at least one electric heating element, in particular a tubular heating element, arranged in a groove provided in the one- or multi-part heat conductor, and a system comprising such an electric heating device and an object to be heated. A method for manufacturing such an electric heating device is also disclosed. Types of electric heating devices are known, for example, from DE 299 23 291 U1, EP 1 590 154 B1 or EP 2 848 381 A1. They are used, for example, as nozzle heaters for injection molding machines. Particularly for this application, but also for other uses, it is necessary to provide different heating power at different points within the electric heating device. This can be controlled by the length of the section of the electric heating element located within a given area of ​​the heat conductor, for example, by arranging several turns of the electric heating element at close intervals within this area, measured in the axial direction of the cylinder axis of the essentially cylindrical interior. For example, in a nozzle heater, one often wants to be able to arrange as much length of the electrical heating element as possible in a small area in the section that heats the nozzle tip, while at the same time the heating power should be rather low in the subsequent area of ​​the nozzle. However, practice shows that when it is possible to concentrate a very high heating power in the area of ​​the nozzle tip - for example by applying the teaching of DE 20 2024 106 645 U1 - the temperature in the subsequent areas, which require less heating, is often too high. The object of the invention is therefore to provide an electric heating device with a substantially cylindrical interior for accommodating an object to be heated, with sections having a higher power concentration than in adjoining, adjacent sections, and a system comprising such an electric heating device and an object to be heated, in which more precise control over the temperature distribution on the surface of the heat-conducting body is ensured. A method for manufacturing such an electric heating device is also described. This problem is solved by an electric heating device with the features of claim 1 and a system with the features of claim 17. Advantageous further developments of the invention are the subject of the dependent patent claims. The electric heating device according to the invention has a substantially cylindrical interior space for receiving an object to be heated. This substantially cylindrical interior space for receiving the object to be heated is bounded externally by a one- or multi-part heat conductor, which can be heated by at least one electric heating element arranged in a groove in the one- or multi-part heat conductor. Such a heat conductor can be tubular, for example, but it can also be formed by winding a metal strip into a spiral or by coiling a rectangular piece of metal around an axis parallel to one of the sides of the rectangle, or it can be composed of several segments connected by fasteners and / or clamping devices, for example, two half-shells. Coiled, rolled, and composite heat conductors, in particular, accordingly exhibit slots and / or gaps that extend essentially along the entire length of the cylindrical axis of the electric heating device and thus represent global structures. According to the invention, the electric heating device has a higher heating power in at least one more intensely heated section of the single- or multi-part heat conductor than in a less intensely heated section adjacent to this section, wherein at least one local area with increased thermal resistance is realized within the heat conductor between these sections in the part of the less intensely heated section adjacent to the more intensely heated section. It is understood that, in the case of multi-part heat conductors, these sections must each be present on the same part of the heat conductor. Different heating intensities in different sections of the heat conductor can be achieved, in particular, by using sections of an electric heating element or multiple electric heating elements of varying lengths within that section. The greater the total length of the electric heating element(s) running through a given section of the heat conductor, the higher the heating power in that section and the more intensely that section is heated. By creating one or more local areas of increased thermal resistance between the more heated section and the less heated section, heat transfer from the more heated section to the less heated section can be effectively reduced. This offers two advantages: First, it is often a complex problem to accommodate sufficient heating power on the limited area of ​​the more heated section, which is typically dictated by the application, to achieve the desired temperature profile. Reducing heat transfer from the more heated section to adjacent areas of the heat sink simplifies this process, as losses are reduced. Second, the unwanted input of heat into the less heated section is avoided.This is particularly important in cases where the length of sections of an electric heating element arranged in the less heated section is already minimized, so that there is no possibility of compensating for such additional heat input through heat transport into this section by heating it less with the electric heating element. Preferably, the smallest distance between a local area with increased thermal resistance and the adjacent, more intensely heated section is at most 5 mm, preferably at most 2 mm. In principle, the smallest possible distance is desirable. It is important to consider that the smallest distance must meet this condition; thus, for example, in a multi-row arrangement of local areas with increased thermal resistance offset axially parallel to the cylinder axis of the essentially cylindrical interior, there can also be local areas with increased thermal resistance at a greater distance from the more intensely heated section. One specific way to create a local area of ​​increased thermal resistance is to incorporate a substantially enclosed opening, such as a circular hole or an elongated slot, into the thermal interface material. This opening then forms such a local area of ​​increased thermal resistance. However, it is possible that this hole or slot is intersected by a groove in the thermal interface material, so that the edge of the enclosed opening is crossed by such a groove, which is why the phrase "substantially enclosed" is used. An opening extending from one end of the thermal interface material, on the other hand, is not substantially enclosed. Another way to create a local area of ​​increased thermal resistance is to introduce a local weakening of the wall thickness of the thermal interface material, i.e., local depressions. Such local weakenings or depressions can be introduced into the thermal interface material from the outside, the inside, or both. However, it should be emphasized here that not every opening or recess in a thermal interface material exhibits all the claimed characteristics of a local area with increased thermal resistance. For example, openings in the form of slots that extend the entire length of the thermal interface material from one end to the other do not define a local, but rather a global area with increased thermal resistance; moreover, they do not fulfill the condition that the area with increased thermal resistance they create must lie between a more heated section and a less heated section adjacent to that section. Spatial areas located between the individual parts of a multi-part thermal interface material are also not local areas with increased thermal resistance as defined in this description. In particular, such a local area must lie within the thermal interface material itself; in the case of a multi-part thermal interface material, this means within one of the parts of the thermal interface material, which is clearly not the case for spatial areas between the parts of a multi-part thermal interface material. It is also known to provide openings and / or recesses to allow the engagement of a tool; however, such openings and / or recesses do not regularly meet the condition that the area created by them with increased thermal resistance must lie between a more heated section and a less heated section adjacent to this section. Advantageously, several local areas with increased thermal resistance are provided, arranged in a ring. "Arranged in a ring" here means, in particular, that they are situated on a ring whose center lies on the central axis of the essentially cylindrical interior of the electric heating device. This improves the efficiency of the thermal decoupling between the more heated section of the heat conductor and the less heated section. It is particularly preferred that the geometry of these local areas with increased thermal resistance is identical, which increases their efficiency, and / or that the distance between them is essentially identical, which promotes a uniform heat distribution. Preferably, on such a ring, the proportion of the ring surface formed by local areas with increased thermal resistance is at least 25%; most preferably at least 50%. Maximizing this proportion is desirable, but is limited, on the one hand, by the structural requirements for the strength of the thermal interface material. Therefore, and because of the resulting asymmetry of the heating profile on the thermal interface material, designs with only one opening in the thermal interface material are less advantageous, so that designs with more than one local area with increased thermal resistance are generally preferred. The unwanted heat flow from the more heated to the less heated section can be reduced even further if several local areas with increased thermal resistance are arranged with an axial offset from each other, i.e., offset in the direction parallel to the cylinder axis of the essentially cylindrical interior. It is particularly advantageous if the heat conductor has at least two rings of annularly arranged local areas with increased thermal resistance with an axial offset from each other, especially if these are arranged rotated relative to each other, so that a local area with increased thermal resistance of the other ring is arranged axially offset from the points of one ring where the thermal resistance is not increased, which can improve the homogeneity of the heat distribution in the circumferential direction.Preferred configurations are those in which the annularly arranged local areas with increased thermal resistance adjacent to each other on the ring are arranged at the same distance from one another, which contributes to symmetrization. Furthermore, it can be advantageous to have an outer tube slid onto the heat conductor, at least partially covering local areas with increased thermal resistance. Such a configuration proves particularly useful when the thermal conductivity of the outer tube is lower than that of the heat conductor, because the outer tube can provide mechanical stability, thus allowing for the creation of such large areas of increased thermal resistance within the heat conductor that its mechanical stability is compromised. Stainless steels are a particularly suitable material class for use as outer tubes. Outer tubes with a wall thickness less than that of the heat conductor are preferred in order to contribute to the highest possible thermal resistance of the outer tube. In another embodiment of the electric heating device, at least 40%, preferably at least 50%, and most preferably at least 60% of the total heating power is directed to the more intensely heated section adjacent to the less intensely heated section within the heat-conducting body, in which at least one local area with increased thermal resistance is realized. In this way, excellent heating of the nozzle tip area can be achieved when the electric heating device is used as a nozzle heater. An extremely high concentration of heating power is achieved in particular when the length of the more strongly heated section, to which the part of the less strongly heated section within the thermal conductivity body, in which at least one local area with increased thermal resistance is realized, is adjacent, is less than 30% of the total length of the thermal conductivity body, preferably even less than 20% of the total length of the thermal conductivity body. Another measure that can contribute to high and highly localized heat concentrations is to increase the power density of the electric heating element (or the heating power it delivers per unit length) in the region of the more intensely heated section adjacent to the part of the less intensely heated section within the thermal interface material, in which at least one local area with increased thermal resistance is realized. This increase is preferably at least 30% greater and most preferably at least 50% greater than the power density over the remaining length of the electric heating element. For electric heating elements designed as a coiled cartridge, this can be achieved, for example, by varying the heating wire (e.g., its material or cross-section) or by varying its coil shape or density. Another highly effective method is to locally increase the heating power by short-circuiting the coils, e.g., by...to lower them with a wire bridging them, or by inserting a wire between two coils or coiled sections. If, in the area of ​​the more intensely heated section adjacent to the less intensely heated section within the heat sink (where at least one local area with increased thermal resistance is present), the essentially cylindrical interior has a reduced inner diameter, at least in some sections, this measure can contribute to better heat transfer in this area through a tighter fit. This reduction in the interior diameter can be achieved, for example, by a tapered section, but also by local structures, particularly thickenings of the heat sink. Preferably, the electric heating element crosses at least one local area with increased thermal resistance. However, it is also possible for the electric heating element to be guided over a web of the thermal conductor that is bounded on both sides, i.e., at both edges of the web, by a local area with increased thermal resistance, wherein the web extends in the circumferential direction of the thermal conductor over an angular range of at most 90°, preferably at most 45°, particularly preferably at most 30°, and most preferably at most 15°. Optionally, the web can be bounded on both sides by the same local area with increased thermal resistance. The system according to the invention consists of an object to be heated, preferably an injection molding nozzle, with an electrical heating device according to the invention arranged thereon. The novel method serves to manufacture an electric heating device with a substantially cylindrical interior for accommodating an object to be heated, wherein the substantially cylindrical interior for accommodating the object to be heated is bounded externally by a one- or multi-part thermal conductor, which can be heated by at least one electric heating element arranged in a groove provided in the one- or multi-part thermal conductor. It is characterized by the step of incorporating local areas of increased thermal resistance into the one- or multi-part thermal conductor, which are realized in the part of the less heated section within the thermal conductor adjacent to the more strongly heated section.This can be achieved, for example, by introducing openings, in particular slots, elongated holes, holes or bores, or by introducing depressions, such as troughs, grooves or trenches into the heat conductor. The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. Figure 1a shows a top view of a first embodiment of an electric heating device; Figure 1b shows a longitudinal section through the electric heating device from Figure 1a; Figure 1c shows an isometric view of an end section of the electric heating device from Figure 1a with a more intensely heated end area and an adjoining less intensely heated area; Figure 2a shows a top view of a first variant of the embodiment of an electric heating device from Figure 1a; Figure 2b shows a longitudinal section through the end section of the electric heating device from Figure 2a; Figure 2c shows an isometric view of an end section of the electric heating device from Figure 2a with a more intensely heated end area and an adjoining less intensely heated area; Figure 2c shows a longitudinal section through the end section of the electric heating device from Figure 2a with a more intensely heated end area and an adjoining less intensely heated area.Fig. 3a: an isometric view of an end section of a second variant of the electric heating device from Fig. 1a; Fig. 3b: a longitudinal section through the end section of the electric heating device from Fig. 3a; Fig. 4a: an isometric view of an end section of a third variant of the electric heating device from Fig. 1a; Fig. 4b: a longitudinal section through the end section of the electric heating device from Fig. 4a; Fig. 5a: an isometric view of an end section of a modification of the second variant of the electric heating device from Fig. 3a; and Fig. 5b: a longitudinal section through the end section of the electric heating device from Fig. 5a. The electric heating device 100 shown in Figs. 1a to 1c, designed as a nozzle heater, has a substantially cylindrical interior 101 for receiving an object to be heated, wherein the substantially cylindrical interior 101 for receiving the object to be heated is bounded to the outside by a heat conductor 110 which in this embodiment is a single piece. A first groove 111 is formed in the heat conductor 110, into which an electric heating element 120, for example a coiled cartridge, is inserted. A thermocouple 130 is arranged in a second groove 112. The shape of the first groove 111 illustrates that the heat conductor 110 is divided into three sections 110a, 110b, and 110c with different heating intensities. In the section facing downwards, shown in Figs. 1a and 1b and also depicted in Fig. 1c, which is intended for heating the nozzle tip, many turns of the groove 111 run close together, so that the high heating power thus introduced by the electric heating element 120 results in a more intensely heated section 110a. This more intensely heated section 110a, which in this example comprises less than 20% of the total length of the heat conductor 110, is adjoined by a less intensely heated section 110b.In particular, it can be seen that in this less heated section 110b, there is at most one helix of the section of the electric heating element 120 leading towards the more heated section 110a and one helix of the section of the electric heating element 120 leading away from the more heated section 110a, so that its heating is minimized. In the part of the less heated section 110b adjacent to the more heated section 110a, circular, fully encircled openings, designed as bores, are arranged within the heat conductor 110. These openings create local areas 113 with increased thermal resistance by impeding and reducing the axial heat flow from the more heated section 110a to the less heated section 110b. These local areas 113 with increased thermal resistance are also arranged on two imaginary rings adjacent to each other with an axial offset. The center of each ring lies on the cylinder axis A of the cylindrical interior 101, and the rings are oriented perpendicular to the cylinder axis A.Furthermore, it can be seen that these two imaginary rings are arranged rotated relative to each other, so that a local area 113 with increased thermal resistance of the other ring is arranged axially offset from the points of one ring where the thermal resistance is not increased, and vice versa. In this way, the heat input from the more heated section 110a to the less heated section 110b can be effectively reduced. As can be seen particularly well in Fig. 1a, in this embodiment the electrical heating element is also guided over a bridge (here formed by a sequence of two bridges arranged one after the other), which is bounded on both sides by a local area 113 with increased thermal resistance and in the illustrated example covers an angular range of about 15° in the circumferential direction. The embodiment of an electric heating device 200 designed as a nozzle heater, shown in Figs. 2a to 2c, with a substantially cylindrical interior 201 for receiving an object to be heated, which is bounded externally by a heat conductor 210 which in this embodiment is a single piece, with an electric heating element 220 inserted in a first groove 211, and with a thermocouple 230 arranged in a second groove 212, is essentially identical in construction to the electric heating device 100 with regard to the aforementioned components and is thus also divided into three sections heated to different degrees, namely the section 210a which is heated to a greater degree, the section 210b which is heated to a lesser degree and a further section 210c which is heated to a somewhat greater degree. The essential difference between the electric heating device 100 and the electric heating device 200 is that the latter, in the part of the less heated section 210b adjacent to the more heated section 210a, has slot- or elongated openings within the heat conductor 210 that are essentially—more precisely, except for a portion of the edge where the grooves 211 and 212 intersect it—completely enclosed. These openings create local areas 213 with increased thermal resistance by impeding and reducing the axial heat flow from the more heated section 210a to the less heated section 210b. These local areas 213 with increased thermal resistance are also arranged on two imaginary rings adjacent to each other with an axial offset. The center of each ring lies on the cylinder axis A of the cylindrical interior 201, and the rings are oriented perpendicular to the cylinder axis A.Furthermore, it can be seen that these two imaginary rings are arranged rotated relative to each other, so that a local area 213 with increased thermal resistance of the other ring is arranged axially offset from the points of one ring where the thermal resistance is not increased, and vice versa. In this way, the heat input from the more heated section 210a to the less heated section 210b can be reduced even more than with the electric heating device 100; however, as a consequence, the resulting thermal conductor 210 of the electric heating device 200 is somewhat less stable than that of the electric heating device 100. As can be seen particularly well in Fig. 2a, in this embodiment the electric heating element 220 crosses two local areas 213 with increased thermal resistance. It should also be noted that this embodiment has an opening in the heat-conducting body 210, which serves as a tool holder 215. The tool holder 215 also generally results in an increased thermal resistance in its area; however, it is no longer located in the part of the less heated section 210b adjacent to the more heated section 210a. The embodiments of electric heating devices 300, 400, 500 designed as nozzle heaters, shown in Figures 3a and 3b, 4a and 4b, and 5a and 5b, also have a substantially cylindrical interior 301, 401, 501 for receiving an object to be heated. This interior is bounded externally by a heat-conducting element 310, 410, 510, which in these embodiments is a single piece. An electric heating element 320, 420, 520 is inserted into a first groove 311, 411, 511, and a thermocouple 330, 430, 530 is inserted into a second groove 312, 412, 512. With regard to these components, the electric heating devices 300, 400, 500 are essentially identical in construction to the electric heating device 100.The heat conductor 310,410,510 is thus also divided into three differently heated sections, namely the more strongly heated section 310a,410a,510a, the less strongly heated section 310b,410b, 510b and a further section, not shown in Fig. 3a and Fig. 3b or 4a and Fig. 4b, which is again somewhat more strongly heated. The essential difference between the electric heating devices 100 or 200 on the one hand and the electric heating devices 300, 400 or 500 on the other hand is that in the electric heating devices 300, 400, 500 a local area 313, 413, 513 with increased thermal resistance is formed by a local weakening of the wall thickness of the heat conductor 310, 410, 510. In the embodiments shown in Figs. 3a and 3b as well as 5a and 5b, the local area 313, 513 with increased thermal resistance is realized by a ring-shaped local weakening of the wall thickness of the heat conductor 310, 510 from the outside; in the embodiment shown in Figs. 4a and 4b, the local area 413 with increased thermal resistance is realized by a ring-shaped local weakening of the wall thickness of the heat conductor 410 from the inside. The embodiment shown in Figures 5a and 5b is further characterized by the fact that an outer tube 514, preferably made of thin stainless steel, is slid onto it. This is also the reason why dashed lines are used in Figure 5a; the structures shown there are actually concealed by the outer tube 514 and therefore not visible. The outer tube 514 gives the electric heating device 500 additional stability and thus makes it possible to achieve a particularly pronounced increase in thermal resistance in the local area 513 by making the recess in the heat conductor 510 so deep that the mechanical stability of the heat conductor 510 alone would no longer be sufficient in this area. Reference symbol list 100, 200, 300, 400, 500 electric heating device 101, 201, 301, 401, 501 interior 110, 210, 310, 410, 510 heat conductor 110a, 210a, 310a, 410a, 510a more heated section 110b, 210b, 310b, 410b, 510b less heated section 110c, 210c more heated section 111, 112, 211, 212, 311, 312, 411, 412, 512 groove 120, 220, 320, 420, 520 electric heating element 130, 230, 330, 430, 530 thermocouple 113, 213, 313, 413, 513 local area 215 Tool holder 514 Outer tube A Cylinder axis QUOTES INCLUDED IN THE DESCRIPTION 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 DE 299 23 291 U1

[0002] EP 1 590 154 B1

[0002] EP 2 848 381 A1

[0002] DE 20 2024 106 645 U1

[0005]

Claims

An electric heating device (100, 200, 300, 400, 500) with a substantially cylindrical interior (101, 201, 301, 401, 501) for receiving an object to be heated, wherein the substantially cylindrical interior (101, 201, 301, 401, 501) for receiving the object to be heated is bounded externally by a one- or multi-part heat conductor (110, 210, 310, 410, 510), which can be heated by at least one electric heating element (120, 220, 320, 420, 520) arranged in a groove (111, 211, 311, 411, 511) provided in the one- or multi-part heat conductor (110, 210, 310, 410, 510), characterized in that the electric heating device (100,200,300,400,500) has a higher heating output in at least one more heated section (110a,210a,310a,410a,510a) of the single or multi-part heat conductor (110,210,310,410,510) than in a less heated section (110b,210b) adjacent to this more heated section (110a,210a,310a,410a,510a).310b, 410b, 510b) wherein in the part of the less heated section (110b, 210b, 310b, 410b, 510b) adjacent to the more strongly heated section (110a, 210a, 310a, 410a, 510a) within the heat conductor (110, 210, 310, 410, 510) at least one local area (113, 213, 313, 413, 513) with increased thermal resistance is realized. Electric heating device (100, 200, 300, 400, 500) according to claim 1, characterized in that the smallest distance between a local area (113, 213, 313, 413, 513) with increased thermal resistance and the adjacent more heated section (110a, 210a, 310a, 410a, 510a) is at most 5mm, preferably at most 2mm. Electric heating device (100, 200) according to claim 1 or 2, characterized in that at least one local area (113, 213) with increased thermal resistance is formed by a substantially circumscribed opening in the heat conductor (110, 210). Electric heating device (300, 400, 500) according to claim 1 or 2, characterized in that at least one local area (313, 413, 513) with increased thermal resistance is formed by a local weakening of the wall thickness of the heat conductor (310, 410, 510). Electric heating device (300, 500) according to claim 4, characterized in that at least one local weakening of the wall thickness of the heat conductor (310, 510) is present from the outside. Electric heating device (400) according to claim 4 or 5, characterized in that at least one local weakening of the wall thickness of the heat conductor (410) is present from the inside. Electric heating device (100, 200) according to one of the preceding claims, characterized in that several local areas (113, 213) with increased thermal resistance are present, which are arranged in a ring shape. Electric heating device (100, 200) according to claim 7, characterized in that the ring-shaped local areas (113, 213) with increased thermal resistance are each arranged at the same distance from each other. Electric heating device (100, 200) according to one of the preceding claims, characterized in that several local areas (113, 213) with increased thermal resistance are arranged with axial offset to each other. Electric heating device (500) according to one of the preceding claims, characterized in that an outer tube (514) is pushed onto the heat conductor (510), which at least partially covers local areas (513) with increased thermal resistance. Electric heating device (100, 200, 300, 400, 500) according to one of the preceding claims, characterized in that at least 40%, preferably at least 50% and most preferably at least 60% of the total power is arranged in the more strongly heated section (110a, 210a, 310a, 410a, 510a), to which the part of the less strongly heated section (110b, 210b, 310b, 410b, 510b) within the heat conducting body (110, 210, 310, 410, 510) adjoins, in which at least one local area (113, 213, 313, 413, 513) with increased thermal resistance is realized. Electric heating device (100, 200, 300, 400, 500) according to one of the preceding claims, characterized in that the length of the more strongly heated section (110a, 210a, 310a, 410a, 510a), to which the part of the less strongly heated section (110b, 210b, 310b, 410b, 510b) within the heat conductor (110, 210, 310, 410, 510) in which at least one local area (113, 213, 313, 413, 513) with increased thermal resistance is adjacent, is less than 30% of the total length of the heat conductor (110, 210, 310, 410, 510), preferably less than 20% of the total length of the heat conductor (110, 210, 310, 410, 510). An electric heating device (100, 200, 300, 400, 500) according to one of the preceding claims, characterized in that the power density of the electric heating element (120, 220, 320, 420, 520) in the region of the more intensely heated section (110a, 210a, 310a, 410a, 510a), to which the part of the less intensely heated section (110b, 210b, 310b, 410b, 510b) within the heat conductor (110, 210, 310, 410, 510) in which at least one local region (113, 213, 313, 413, 513) with increased thermal resistance is adjacent, is greater, preferably at least 30% greater, and most preferably at least 50% greater than the power density over the remaining length of the electric heating element. (120,220,320,420,520). Electric heating device (100, 200, 300, 400, 500) according to one of the preceding claims, characterized in that in the area of ​​the more strongly heated section (110a, 210a, 310a, 410a, 510a), to which the part of the less strongly heated section (110b, 210b, 310b, 410b, 510b) within the heat conductor (110, 210, 310, 410, 510) in which at least one local area (113, 213, 313, 413, 513) with increased thermal resistance is realized, the substantially cylindrical interior space (101, 201, 301, 401, 501) adjoins, at least section by section, a reduced inner diameter in order to contribute to better heat transfer in this area by a higher fit. Electric heating device (100, 200, 300, 400, 500) according to one of the preceding claims, characterized in that the electric heating element (120, 220, 320, 420, 520) crosses at least one local area (113, 213, 313, 413, 513) with increased thermal resistance. Electric heating device (100, 200, 300, 400, 500) according to one of claims 1 to 15, characterized in that the electric heating element (120, 220, 320, 420, 520) is guided over a web of the heat conductor (110, 210, 310, 413, 513) bounded on both sides by a local area (113, 213, 313, 413, 513) with increased thermal resistance, wherein the web extends in the circumferential direction of the heat conductor (110, 210, 310, 410, 510) over an angular range of a maximum of 90°, preferably a maximum of 45°, particularly preferably a maximum of 30° and most preferably a maximum of 15°. System comprising an electric heating device according to one of claims 1 to 16 and an object to be heated.

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