Electric heating device

Abstract

An electric heating device (100) with a substantially cylindrical interior space (103) for receiving an object to be heated, wherein the substantially cylindrical interior space (103) for receiving the object to be heated is bounded externally by a one- or multi-part heat-conducting body (110), which can be heated by at least one electric heating element (120) arranged in a groove (111) provided in the one- or multi-part heat-conducting body (110), characterized in that the groove (111) in at least one section of the one- or multi-part heat-conducting body (110) is shaped such that the groove (111) has at least one first arc (121, 122) of about 180°, which lies within a further arc of about 180° in total, wherein the further arc has a larger radius of curvature than the first arc (121, 122).

Description

[0001] 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 delimited to the outside by a single-part or multi-part heat conducting body which can be heated by at least one electric heating element, in particular a tubular heating element, arranged in a groove introduced in the single-part or multi-part heat conducting body.

[0002] Such electrical 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.

[0003] For this application in particular, but also for other uses, it is necessary to provide different heating outputs at different locations of the electric heating device. This can be controlled by the length of the section of the electric heating element arranged in a given area of ​​the heat-conducting body, for example, by arranging several turns of the electric heating element in this area at a short distance from each other, measured in the axial direction of the cylinder axis of the essentially cylindrical interior. Therefore, it is desirable to be able to arrange as much length of the electric heating element as possible in a small area.

[0004] However, in many cases, it is desirable for the electric heating device to be clamped onto the object to be heated, which is why the heat-conducting element usually has gaps or slits whose width can be adjusted during clamping to generate the desired clamping forces. For example, in such cases, it proves disadvantageous to wrap the gap or slit with the electric heating element, especially if there are multiple windings involved.

[0005] To circumvent this problem, it is known from the state of the art to provide a meandering course for the grooves and thus also for the electric heating element in such sections. In practice, however, it has been shown that the higher the required heating output, the greater the problems arise, as the turns of the electric heating element then inevitably become narrower. However, if a tubular heater with a tight bending radius is bent 180°, the casing of the tubular heater is subjected to considerable stress, and the electrically insulating material inside the tubular heater, usually compacted magnesium oxide, has a tendency to crack. This can lead to problems and, in particular, reduces the service life of the tubular heater and increases the number of rejects.

[0006] At least equally problematic is the fact that tight bends in an electric heating element, especially an electric tubular heater, have a fatal tendency to be pushed out of the groove guide during heating. During rapid heating, the temperature rises much faster there than at the heat-conducting element, which is often made of brass or nickel silver. Accordingly, the electric heating element undergoes rapid thermal expansion, which the groove cannot follow, leading to the electric heating element being pushed out of the groove.

[0007] The object of the invention is therefore to provide an improved electric heating device with a substantially cylindrical interior for accommodating an object to be heated, with sections with high power concentration. This object is achieved by an electric heating device with the features of claim 1. Advantageous developments of the invention are the subject of the dependent claims.

[0008] The electric heating device according to the invention has a substantially cylindrical interior space for receiving an object to be heated, which preferably passes through the entire electric heating device in a direction parallel to the cylinder axis, so that the electric heating device is substantially tubular.

[0009] The essentially cylindrical interior is delimited to the outside, i.e. in the radial direction relative to the cylinder axis, by a single- or multi-part heat-conducting body, which can be heated by at least one electric heating element arranged in a groove in the single- or multi-part heat-conducting body. This electric heating element can be, in particular, a tubular heater or a tubular cartridge, for example a high-performance tubular cartridge of the RPZ type from the applicant. The heat-conducting body can have slots or gaps, which can run, for example, parallel to the cylinder axis or helically around it, so that it defines the essentially cylindrical interior but does not form a physical boundary at all points, which can improve the clampability of the electric heating device.

[0010] Essential to the invention is that the groove in at least one section of the single- or multi-part heat-conducting body has at least one first arc of approximately 180° (such as a bend or hairpin bend), which lies within a further arc of approximately 180° in total, which has a larger radius of curvature. As is made clear by the use of the word "total," this further arc can also be composed of several partial arcs, for example, two 90° arcs in the same direction that are connected to each other, for example, by a short straight section.

[0011] In this way, the risk of tight turns of the electric heating element jumping out of the groove can be effectively reduced because the additional heating of the heat conducting body at the tip of the turn by the section of the electric heating element arranged in the wider arc of approximately 180° causes the heat conducting body to heat up more quickly and thus reduces the tendency of the section of the heat conducting element arranged in the first arc to jump out of the groove.

[0012] Preferably, the respective first arc is the narrowest arc in an area with increased heating output.

[0013] A particularly preferred development of the invention further provides that the groove is shaped such that it receives a section of the electrical heating element with a course that can be produced by rolling up, preferably by a total of at least 270° or more, or by multiple bending in the same direction (and thus, unlike meandering courses, not alternating in opposite directions), likewise preferably at a total angle of at least 270° or, even more preferably, 360° or more, of a substantially U-shaped section of the electrical heating element.It should be noted that the condition that the multiple bending, which takes place at different points of the U-shaped section, should take place in the same direction for a given U-shaped section of the electric heating element (which can be realized, for example, by a protuberance in its otherwise arbitrary course), does not exclude the possibility that there is a point somewhere further away from the bottom of the U at which the electric heating element is bent or rolled in the opposite direction or is bent or rolled several times in the opposite direction.

[0014] This shape automatically means that the groove in at least one section of the single-part or multi-part heat-conducting body has at least a first arc of approximately 180° (such as a bend or hairpin bend), which lies within a further arc of a total of approximately 180°.

[0015] In particular, embodiments are also considered to be essentially U-shaped if they have a bend at the bottom of the U, with a change in direction of slightly more than 180°, for example between approximately 180° and 200° between the sections of the legs of the U leading towards and away from the bend, so that these legs can converge towards each other in sections in the direction away from the bottom of the U before becoming essentially parallel. It should be noted in this context that the change in direction caused by the bottom of the U is not included in the total angles discussed in the previous section; rather, these total angles refer to changes in direction followed by both legs.

[0016] This makes it possible to create very closely spaced sections of the electric heating element with a minimal number of tight bends. Starting from the bend that forms the bottom of the U, the radius of a rolled-up shape continuously increases. In the case of a shape created by multiple bends in the same direction, a bend following the bottom can have a comparably small radius of curvature. Since the bending is repeated in the same direction, the radii of curvature must increase, or the next change of direction of 180° must be divided into several changes of direction at smaller angles, possibly with straight sections in between.

[0017] Since these smaller bends place significantly less mechanical stress on the electric heating element than is the case with a 180° turn, in a particularly preferred development of the invention there is at least one section of the one-part or multi-part heat-conducting body in which the groove is shaped such that it has at least one change of direction by 180° in a section of the electric heating element with a course that can be generated by repeatedly bending a substantially U-shaped section of the electric heating element in the same direction, which change is realized by repeatedly bending in the same direction by an angle that is smaller than 180° in each case.

[0018] If at least one part of the at least one-piece heat-conducting body is formed by a rolled-up plate with two end sections with a substantially rectangular plate surface, which is formed by a central section with a substantially parallelogram-shaped plate surface, these end sections provide a large surface on which a long section of the electric heating element can be arranged, thus providing a particularly high heating output. The central section, in which inclined sides of the parallelogram connect the two sides adjacent to each of the end sections, forms a tubular casing when rolled up, which is penetrated by a spiral-shaped slot that can have a self-clamping effect.

[0019] It has also proven advantageous if the side of the single- or multi-part heat-conducting body into which the groove, in which the electric heating element runs, is inserted faces the essentially cylindrical interior. If the electric heating element is inserted into the groove while the heat-conducting body is still in a plate shape and then rolled up, sections of the electric heating element that run parallel to the cylinder axis of the essentially cylindrical interior are clamped.

[0020] Especially when used as a nozzle heater in injection molding, it is important to precisely control the temperature at the nozzle outlet. Therefore, it is advantageous if the electric heating device has a thermal sensor that is arranged at least partially in a further groove in the single- or multi-part heat-conducting body, and whose measuring point is located on one end face of the electric heating device.

[0021] In a particularly preferred development of the embodiment just discussed, it is further provided that the additional groove is arranged on the surface of the single- or multi-part heat-conducting body that is opposite the surface into which the groove containing the electric heating element is inserted. This significantly increases the flexibility in determining the path of the electric heating element.

[0022] The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. It shows: Fig. 1: An intermediate step in the manufacture of an embodiment of an electric heating device; Fig. 2: an electric heating device, which can be produced by rolling up the heat conducting body Fig. 1 and adding a thermal sensor; Fig. 3: a schematic illustration of the clamping of sections of an electric heating element in a groove when rolling up the heat conducting body; and Fig. 4: an example of a section of an electric heating element with a profile that can be produced by repeatedly bending a substantially U-shaped section of the electric heating element in the same direction.

[0023] Fig. Figure 1 shows an intermediate step in the manufacture of an embodiment of an electric heating device 100. It shows a plate, from which the heat-conducting body 110 is later formed, made of heat-conducting material, for example brass or nickel silver, and an electric heating element 120, the course of which is defined by a groove 111 formed in the plate. This groove is shown in the illustration of Fig. 3 easier to recognize because in the Fig. 1 Sections of the electric heating element 120 that are inserted into the groove 111 cover the groove 111. The electric heating element 120 can be flush with the upper edge of the groove 111, but it can also protrude slightly beyond the upper edge of the groove 111 or not completely fill the groove 111.

[0024] It should be emphasized that the heat-conducting body 110 does not necessarily have to be manufactured by rolling a plate. For example, it is also possible to machine a heat-conducting body from a solid material with a geometry that, when rolled out, corresponds to the geometry of the plate.

[0025] The plate has two end sections 112,113 with a substantially rectangular plate surface, which are connected to each other by a central section 114 with a substantially parallelogram-shaped plate surface.

[0026] In both the end section 112 and the end section 113, the groove 111 and thus also the section of the electric heating element 120 inserted into the corresponding part of the groove 111 are each shaped such that the groove 111 receives a section of the electric heating element 120 with a profile that can be produced by rolling up or repeatedly bending in the same direction a substantially U-shaped section of the electric heating element 120 with base 121 or 122. In this case, one can see in the Fig. 1, when considering the course of the legs of the respective section starting from the respective base 121,122 of the U, that in the sense of this disclosure the legs do not necessarily have to run parallel to each other, but can also run slightly towards each other, which is why the section in question is described as essentially U-shaped.

[0027] For the groove course in the end section 112 and 113, this can be done conceptually using the Fig. 1 by performing the reverse process in your mind: The groove profile in the end section 112 or the section of the electric heating element 120 inserted into it can be converted into a substantially U-shaped section by attaching it to the Fig. 1 is bent 90° clockwise at the point marked A1 and then 180° clockwise at the point marked A2, i.e., by repeated bending in the same direction by a total of at least 270°. It should be noted that bending a U-shaped section always means that two adjacent sections of the electric heating element 120 are bent.

[0028] The reverse process, which creates the essentially U-shaped section by bending it twice in the same direction by 180° and 270°, here in each case counterclockwise, is shown in the Fig. 4a to 4c illustrates.

[0029] The groove profile in the end section 113, or the section of the electric heating element 120 inserted into it, can be converted into a substantially U-shaped section by successively bending it 90° counterclockwise at the points marked B1, B2, and B3, and then bending it 180° counterclockwise at the points marked B4 and B5. This section of the electric heating element 120 can thus also be produced from a substantially U-shaped section of the electric heating element 120 by repeatedly bending it clockwise in the same direction, namely by 180°, 180°, 90°, 90°, and 90°. This profile therefore includes 180° turns, which are divided into two 90° bends with a straight heating element section running between them.

[0030] It should be emphasized that in the actual manufacturing process, it is not necessary to first completely reshape the electric heating element 120 and then insert it into the groove, but rather, it can be formed into the desired shape piece by piece by inserting it into the groove 111. As already mentioned, the electric heating element 120 does not have to be inserted into a groove running in a flat plate and then rolled up, but can also be inserted into a groove in a heat-conducting body machined from solid material.

[0031] The groove profile in the end section 113 or the profile of the electric heating element 120 inserted into the groove 111 shows particularly well how the inventive shape of the groove makes it possible to achieve a high number of parallel sections of the electric heating element 120 at a short distance from one another, while at the same time the formation of tight bends which place a great deal of stress on the electric heating element is almost completely avoided.

[0032] The groove course in Fig. 1 further comprises at least one first arc of approximately 180°, which lies within a further arc of approximately 180° in total, wherein the further arc has a larger radius of curvature than the first arc. This condition is met in particular for the bases 121, 122, but also, for example, for the respective inner arc of the pair of arcs A2 or B5.

[0033] Fig. 2 shows an electric heating device 100, which can be produced by rolling up the plate-shaped heat conducting body made of Fig. 1 and adding an optional thermal sensor 130. The thermal sensor 130 is accommodated in an additional groove 115, which is machined on the side of the heat-conducting body 110 opposite the side in which the groove 111 is machined. Its measuring point 131 is located on an end face 101 of the electric heating device 100. Of course, it is also possible to arrange the thermal sensor 130 on the same side as the electric heating element 120.

[0034] If it is desired that the electric heating element 120 is located on the outside of the electric heating device 100, this can be achieved by differently rolling up the plate-shaped heat conducting body made of Fig. 1 be made possible.

[0035] The electric heating device 100 is also tensionable. For this purpose, it is provided with a gap 102, the central section of which extends helically and which has end sections on both sides, in which it runs essentially parallel to the cylinder axis Z of its essentially cylindrical interior space 103.

[0036] In the schematic representation of the Fig. 3, which shows a cross-section through a section of the Fig. 1 in the end region 113 in the flat and rolled state, it can be clearly seen that when the heat conducting body 110 is rolled up, the electrical heating element 120 inserted into the groove 111 becomes clamped. List of reference symbols 100 electric heaters 101 Front side 102 gap 103 Interior 110 heat sinks 111 groove 112,113 final section 114 Middle section 115 additional groove 120 electric heating element 121,122 Floor of the U 130 thermal sensors 131 measuring point A1,A2 position B1,B2,B3,B4,B5 position Z cylinder axis QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] DE 299 23 291 U1

[0002] EP 1 590 154 B1

[0002] EP 2 848 381 A1

[0002]

Claims

[1] Electric heating device (100) with a substantially cylindrical interior (103) for receiving an object to be heated, wherein the substantially cylindrical interior (103) for receiving the object to be heated is delimited to the outside by a single-part or multi-part heat-conducting body (110) which can be heated by at least one electric heating element (120) arranged in a groove (111) provided in the single-part or multi-part heat-conducting body (110), characterized by that the groove (111) is shaped in at least one section of the single-part or multi-part heat-conducting body (110) such that the groove (111) has at least a first arc (121, 122) of approximately 180°, which lies within a further arc of a total of approximately 180°, wherein the further arc has a larger radius of curvature than the first arc (121, 122). [2] Electric heating device (100) according to claim 1, characterized bythat the groove (111) in at least one section of the single-part or multi-part heat-conducting body (110) is shaped such that it receives a section of the electrical heating element (120) with a course that can be produced by rolling up or repeatedly bending in the same direction a substantially U-shaped section of the electrical heating element (120). [3] Electric heating device (100) according to claim 2, characterized by that the groove (111) in at least one section of the single-part or multi-part heat-conducting body (110), in which it is shaped such that it receives a section of the electrical heating element (120) with a course that can be produced by repeatedly bending a substantially U-shaped section of the electrical heating element (110) in the same direction, has at least one change of direction by 180°, which is realized by repeatedly bending in the same direction by an angle that is in each case smaller than 180°. [4] Electric heating device (100) according to one of claims 1 to 3, characterized by that at least a part of the at least one-piece heat-conducting body (110) is formed by a rolled-up plate with two end sections (112, 113) with a substantially rectangular plate surface, which are connected to one another by a central section (114) with a substantially parallelogram-shaped plate surface. [5] Electric heating device (100) according to one of the preceding claims, characterized by that the side of the single-part or multi-part heat-conducting body (110) into which the groove (111) is introduced faces the substantially cylindrical interior space (103). [6] Electric heating device (100) according to one of the preceding claims, characterized bythat the electric heating device (100) has a thermal sensor (130) which is arranged at least in sections in an additional groove (115) in the one-part or multi-part heat-conducting body (110) and whose measuring point is arranged on an end face (101) of the electric heating device (100). [7] Electric heating device (100) according to one of the preceding claims, characterized by that the additional groove (115) is arranged on the surface of the one-part or multi-part heat-conducting body (110) which is opposite the surface into which the groove (111) in which the electric heating element (120) is arranged is introduced.

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