ELECTRIC HEATING DEVICE AND METHOD FOR MANUFACTURING AN ELECTRIC HEATING DEVICE

Description

[0001] There are a variety of electric heating devices comprising an electric heating element arranged within the interior of a tubular metal casing and electrically insulated therefrom with an electrically insulating material. Examples are shown in JP S55 153 795 U, US 3,355,802 A, and CN 103 237 374 A, which disclose the features of the preamble of claim 1.

[0002] In practical application, in some cases it is a challenge to dissipate the heat generated by the electrical heating element as effectively as possible, particularly to the tubular metal casing.

[0003] The object of the invention is therefore to provide an electric heating device with an electric heating element arranged within the tube interior of a tubular metal casing and electrically insulated therefrom by an electrically insulating material, in which heat dissipation from the electric heating element is improved, and to specify a manufacturing method for such an electric heating device. This object is achieved by a device having the features of patent claim 1 and a method having the features of patent claim 8. Advantageous further developments are the subject of the dependent patent claims.

[0004] The electric heating device according to the invention has an electric heating element that is arranged without a support within the tube interior of at least one tubular metal casing and is electrically insulated from the casing by a compacted, electrically insulating material. "Support-free" means, in particular, that the electric heating element is not wound onto a coil. Typically, it will be a self-supporting structure that is formed into a predetermined shape and maintains this shape without the influence of external stabilizing measures.

[0005] Firstly, what is essential to the invention is that the electrical heating element has, at least in sections, coils with a flat band geometry, wherein the coils with flat band geometry have an inner diameter, an outer diameter and a distance between adjacent coils and are shaped such that the flat side of the coils with flat band geometry runs parallel to the coil axis. In the simplest case, this can therefore simply be a self-supporting coiled resistance wire with flat band geometry; however, electrical heating elements with a corresponding geometry can also be machined from blanks, e.g., by laser cutting or waterjet cutting. It may also be advisable to first make the cuts on a plate-shaped blank and then deform this, in particular to roll it up or coil it.

[0006] Although the term doesn't really require any explanation, it should be mentioned here that flat band geometry refers to a property of the coil's cross-section, which is perpendicular to the direction of the resistor material from which it is formed. This cross-section is essentially rectangular, with a long extension direction that defines the width and a short extension direction that defines the height. However, the corners can be rounded, and the shape of the sides, especially in the height direction, but also in the width direction, does not have to be exactly linear.

[0007] In fact, when winding a resistance wire with a flat band geometry to form a corresponding electrical heating element, the ideally essentially rectangular cross-sectional geometry may be slightly influenced, but this still justifies the use of the term flat band geometry.

[0008] The flat side of the resistance wire is the side that runs essentially parallel to the long direction of its cross-section.

[0009] The use of the coil with a flat band geometry in an orientation in which the flat side runs parallel to the coil axis means that, even if the electrical heating device in which the electrical heating element is used may only have a small diameter, the electrical heating element can have a large cross-section, which is important for high current loads. In contrast to the relatively large cross-sections of straight resistance wires that have been frequently used to date, the coiled structure enables a more elastic response of the electrical heating element to alternating thermal stress, resulting in significantly slower embrittlement and material fatigue and a lower risk of breakage.

[0010] However, there is a second very important aspect, namely the fact that a coiled resistance wire with flat band geometry in the claimed configuration automatically has larger surfaces than contact surfaces, which enable heat dissipation, particularly in the direction of the tubular metal sheath.

[0011] Tests conducted by the applicant have shown that it is advantageous if the width of the helix with flat band geometry corresponds to at least 30% of the helix's inner diameter. It has proven particularly preferable if the width of the helix with flat band geometry corresponds to the helix's outer diameter.

[0012] Tests have further shown that the width of the coil with flat band geometry is preferably at least twice its width; for some applications, it can even be ten times its height. Preferably, the height should be sufficiently large to allow the coil of the electric heating element to support its own weight, so that the electric heating element maintains its shape even when supported at only one end and does not change under the influence of gravity in unsupported areas.

[0013] It has also been experimentally determined that the spacing between adjacent coils is preferably smaller than the width of the coils with flat band geometry. A spacing value of approximately 15% of the width is considered realistic, and small spacing values ​​are the goal.

[0014] Secondly, essential to the invention is that, at least in partial areas of the interior of the tubular metal casing adjacent to at least one coil, the compacted electrically insulating material is a compacted granulate composed of grains of different sizes with edges and projections. This then enables at least one surface of at least one coil to have sections in which grains of this granulate are at least partially pressed into the electrical heating element, subjecting it to local deformation, particularly of the electrical heating element. This results in an increased contact area between the electrical heating element and the electrically insulating material, which enables better heat dissipation.

[0015] Furthermore, it has been shown that the same effect can also be achieved if the compacted insulating material is a compacted molded part made of an electrically insulating material, because then components, in particular fragments, of this molded part are at least partially pressed into the electrical heating element with local deformation, in particular of the electrical heating element.

[0016] The use of magnesium oxide granules is particularly advantageous, which is why this material is the focus of the further description.

[0017] This approach represents a paradigm shift in some ways. Until now, the choice of the electrically insulating material used and the pressure applied during compaction have always been largely determined by the consideration of maximizing tracking resistance and resistance to moisture. This is why powders with very fine and regularly shaped powder particles have been used to achieve the most homogeneous insulating layer possible during compaction.

[0018] The inventive use of granules differs fundamentally from this. Unlike a powder, granules within the meaning of this disclosure have coarse, irregular grains with edges and protrusions, thus having a low degree of roundness. These grains can, in particular, also have a relatively broad particle size distribution with a full width half maximum (FWHM) value for the width of the distribution, which, particularly in the case of magnesium oxide granules, lies between a few tens of µm and over one hundred µm. The maximum of the magnesium oxide grain size distribution of the magnesium oxide granules used can preferably be in the range between approximately 30 µm and approximately 300 µm, which shows that the particle size alone is not the decisive parameter.

[0019] An indirect, macroscopically measurable measure of these properties of the granulate is the tap density. For example, magnesium oxide granules within the meaning of this invention have a tap density of less than 2.45 g / cm³ before compaction, while the density of magnesium oxide is stated as 3.58 g / cm³. Thus, an electrical insulation layer is initially formed when the tubular metal casing is filled, which has a significant amount of empty volume.

[0020] While one would intuitively assume that sufficient tracking resistance and moisture resistance cannot be achieved due to remaining empty volumes within the area filled with electrically insulating material, because the empty volumes counteract these properties, the inventor has surprisingly found that when applying such high pressure that sections of particles arranged adjacent to coils of the electrical heating element and / or to the tubular metal casing, in particular edges and projections of grains, are pressed into the electrical heating element and / or the tubular metal casing with local deformation of the electrical heating element and / or the tubular metal casing, an electrical insulation layer with high tracking resistance and moisture resistance can nevertheless be achieved.which also proves to be mechanically much more stable than known electrical insulation layers in such devices.

[0021] A further advantage resulting from the use of a granulate according to the invention is that it achieves improved tolerance compensation.

[0022] The most important aspect for achieving the object of the invention, however, is that, in addition, a significant improvement in the thermal conductivity of the electrical insulation layer is also observed. On the one hand, a lower proportion of grain boundaries due to a higher proportion of larger granules can contribute to this. On the other hand, pressing the granules into the coil of the electrical heating element also promotes heat dissipation, as the transfer surface is effectively larger. These effects are maximized by the flat band geometry of the coil of the heating element, which is coiled at least in sections.

[0023] The effects described above for granules occur in a similar way when the electrically insulating material is a compacted molded part made of an electrically insulating material. The granules are then replaced by the irregular components or fragments of this molded part that arise during the compaction of the molded part.

[0024] In this way, during compaction, the granulate or the components of the compacted part created during compaction impart an (additional) roughness to the electric heating element or its coil, but generally also to the tubular metal casing. Experiments show that, for example, for typical inner conductor materials, arithmetic mean roughness values ​​Ra of a few µm and average smoothing depths Rp of around 10 µm can be achieved.

[0025] The pressure required for compaction can be provided, for example, by press compaction, roller compaction, or hammer compaction. Particularly preferred are pressures high enough to cause plastic deformation of the inner conductor, in particular to reduce the diameter of the inner conductor by several percent, preferably approximately 5%.

[0026] If necessary, the moisture resistance can be further increased by impregnating the compacted granulate, in particular magnesium oxide granulate, at least in sections.

[0027] In addition, by adding impregnating agent at least in sections of the device, in particular e.g. adding 0.5 vol% silicone resin, and subsequent tempering, granulate grains can be bonded to one another, which makes the resulting structure more resistant and counteracts breakouts at the edges of the structure by bonding grains of the granulate to one another and / or to the inner conductor and / or to the tubular metal sheath.

[0028] It is particularly advantageous if the helix axis runs parallel to the central axis of the tubular metal casing. This means that the contact surfaces between the electric heating element and the electrically insulating material, into which granules or components of the molded part are pressed, run essentially parallel or at right angles to the inner side of the casing.

[0029] It is particularly preferred if at least one coil has multiple surfaces in which granules or components of the molded part are at least partially pressed into the electric heating element under local deformation, so that the contact area between the electric heating element and the electrically insulating material is increased. In this way, heat dissipation can be improved in all directions, including inward and into the coil spaces.

[0030] In an advantageous development of this embodiment, the relative enlargement of the contact area between the electrical heating element and the electrically insulating material is different for at least two different surfaces into which granules or components of the molded part are at least partially pressed into the electrical heating element under local deformation. This can be achieved in particular by deliberately introducing different electrically insulating materials.

[0031] For example, the surface area increase can be influenced by the particle size distribution of the granules.

[0032] One way to vary the surface area enlargement is to use a porous molded body as an additional electrically insulating material. For example, a rod-shaped molded body made of magnesium oxide can be inserted into the interior of the coil and a relatively coarse magnesium oxide granulate can be trickled into the remaining annular gap between the outer tube and the electric heating element. After compaction, a surface modification is obtained on all surfaces of the coils that is different, particularly more pronounced, than on the inward-facing surface.

[0033] In the interest of heat dissipation, it is advantageous if the relative increase in the contact area between the electrical heating element and the electrically insulating material is greatest for the surface facing the tubular metal casing, into which granules or components of the molded part are at least partially pressed into the electrical heating element under local deformation.

[0034] The method according to the invention for producing an electric heating device with an electric heating element which has at least partially coils with a flat band geometry, wherein the coils with a flat band geometry have an inner diameter, an outer diameter and a distance between adjacent coils and are shaped such that the flat side or surface of the coils with a flat band geometry runs parallel to the coil axis, wherein the electric heating element is arranged within the tube interior of a tubular metal casing and is electrically insulated therefrom with an electrically insulating material, comprises the following steps: Creating the electrical heating element, arranging the electrical heating element in the interior of the tubular metal casing, introducing the electrically insulating material into the interior of the tubular metal casing, and compacting the electrically insulating material. It is essential to the invention that the electrically insulating material is a granulate of grains of different sizes with edges and projections or a shaped body which is compacted in the radial direction at least to such an extent that

[0035] Sections, in particular edges and projections, of granules or of fragments of the shaped body resulting from compaction are pressed into at least one coil surface of at least one coil with flat band geometry under local deformation of the electric heating element.

[0036] Magnesium oxide in particular is well suited as a base material for the electrically insulating material.

[0037] It is particularly preferred that the electrically insulating material is introduced into empty volumes within the interior of the tubular metal casing at least partially by allowing the granules to trickle into the tubular metal casing from one end face while shaking. This not only promotes material transport within the free interior volume of the tubular metal casing, but the resulting preconfiguration of the granules also proves helpful in reducing and / or avoiding any empty volumes.

[0038] Preferably, a magnesium oxide granulate is used as the electrically insulating material, which is such that the electrically insulating material has a tap density of less than 2.45 g / cm3 before compaction.

[0039] Particularly when varying degrees of surface modification are to be achieved by pressing granules into different coil surfaces, it is helpful to also introduce a portion of the electrically insulating material into the interior of the tubular metal casing as a shaped body. For example, a rod-shaped shaped body can be inserted into the coil interior of the coils of the electric heating element, or a tubular body can be inserted into the annular gap between the electric heating element and the tubular metal casing.

[0040] Differences in the strength of the respective surface modifications can also be brought about by using different granules with different grain size distributions to fill different areas of the interior of the tubular metal shell.

[0041] In order to make the electrically insulating material even more stable and in particular to counteract its breakout in edge regions, it is advantageous if, at least in sections, a magnesium oxide granulate mixed with an impregnating agent, in particular a silicone resin, is introduced as an electrically insulating material into the interior of the tubular metal sheath and then, but not necessarily immediately thereafter, a tempering step is carried out so that granulate grains or components or fragments of the shaped body created by compaction are bonded to one another and / or to the inner conductor and / or to the tubular metal sheath.

[0042] It is particularly preferred if such a high pressure is applied during radial compaction that it results in plastic deformation of the electric heating element, in particular a reduction in its cross-section of several percent, i.e., in particular between 2 and 10 percent. However, the ideal pressure depends on the material and the geometry of the respective electric heating element and the tubular metal casing, which can vary. Compaction can be achieved, in particular, by press compaction, roller compaction, or hammer compaction.

[0043] Preferably, magnesium oxide granules with a grain size distribution whose maximum lies in the range between 30 µm and 300 µm are used. It is particularly preferred if the grain size distribution ranges from approximately 30 µm to over 100 µm.

[0044] The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. It shows: Fig. 1a: a first embodiment of an electric heating device in a partially opened view, Fig. 1b: the electric heating element of the electric heating device from Figure 1a in a first sectional view, Fig. 1c: the electric heating element from Figure 1b with connecting bolts arranged thereon, Fig. 1d: an enlarged detail of an area inside the electric heating device from Figure 1a , Fig. 1e: a schematic diagram of the structure of magnesium oxide grains and sections of the coil of the electric heating element and the tubular metal sheath of the electric heating device made of Figure 1a , Fig. 2a: a second embodiment of an electric heating device in a partially opened view, Fig. 2b: the electric heating element of the electric heating device from Figure 2awith connecting bolts arranged thereon, Fig. 2c: an enlarged detail of an area inside the electric heating device from Figure 1a , Fig. 3a: a first variant of a coil of an electrical heating element with surface structures caused by pressing in grains of the electrically insulating material, in cross section, Fig. 3b: a second variant of a coil of an electrical heating element with surface structures caused by pressing in grains of the electrically insulating material, in cross section, Fig. 3c: a third variant of a coil of an electrical heating element with surface structures caused by pressing in grains of the electrically insulating material, in cross section, and Fig. 3d: a fourth variant of a coil of an electrical heating element with surface structures caused by pressing in grains of the electrically insulating material.

[0045] The Figures 1a to 1edescribe a first embodiment of an electric heating device 1 in a partially opened view, in which, however, in particular in Figure 1a The electrically insulating material 14 has been omitted for clarity. The tubular metal casing 13 with central axis AR can be seen, within the interior of which the electrical heating element 10 is arranged, which can be supplied with power via connecting bolts 11, 12.

[0046] Figure 1b shows a section through the electric heating element 10 from Figure 1a, which here is formed by a coiled resistance wire with flat band geometry, whereby a series of variables with which the flat band geometry and the coiled arrangement can be characterized are additionally shown. The essentially rectangular cross-sectional areas Q can be seen with a long extension direction that defines the width B and a short extension direction that defines the height H. The individual coils W10, which each run around the coil axis AW shown in dashed lines, each have an outer diameter D1 and an inner diameter D2 and adjacent coils W10 are each spaced from each other by a distance S.

[0047] In particular, one can see in the illustrated coiled resistance wire 10 in flat band geometry that the width B of the resistance wire with flat band geometry corresponds approximately to the outer coil diameter D1, that the width B of the resistance wire with flat band geometry is approximately five times its height H, and that the distance S between adjacent coils W10 is smaller than the width B of the resistance wire with flat band geometry, more precisely, it is approximately 25 percent of the width B.

[0048] Furthermore, in conjunction with Figure 1a that the spiral axis AW of the electric heating element 10 and the central axis AM of the tubular metal casing 13 coincide, so that these two components are arranged concentrically to each other.

[0049] Figure 1c shows the electric heating element 10 from Figure 1bin another sectional view with connecting bolts 11, 12 arranged thereon. It can be seen that these each engage with connecting sections 11a, 12a into the coil interior of the coils of the electrical heating element 10 and can be press-connected there, for example.

[0050] The enlarged detail of an area inside the electric heater from Figure 1a according to Figure 1d and the schematic diagram of the structure of granules 14.1,14.2, here magnesium oxide granules, and sections of the coil W10 of the electric heating element 10 and the tubular metal casing 13 of the electric heating device from Figure 1a , according to Figure 1eillustrate the important aspect of the invention that the electrically insulating material 14 is a granulate of (magnesium oxide) grains 14.1, 14.2 of different sizes with edges and projections 14.3, and that at least one surface of at least one coil W10 has sections in which (magnesium oxide) grains are at least partially pressed into the electric heating element under local deformation, which is illustrated by the irregularly serrated surfaces of the coil W10. As can be seen in Figure 1e detects, a corresponding modification of the inside of the tubular metal jacket 13 is also carried out, which in particular also improves the heat transfer and also contributes to increased mechanical stability.

[0051] The Figures 2a to 2c describe a second embodiment of an electric heating device 2 in a partially opened view, in which, however, in particular in Figure 2aThe electrically insulating material 24 has been omitted for clarity. The tubular metal casing 23 with central axis AR can be seen, in the interior of which the electrical heating element 20 is arranged, which can be supplied with power via connecting bolts 21, 22.

[0052] Figure 2b shows an external view of the electric heating element 20 from Figure 2a , which is created here by winding a slotted plate made of a resistance wire material, whereby the resulting coils W20 are imprinted with a flat band geometry. Furthermore, in conjunction with Figure 2a that the spiral axis AW of the electric heating element 20 and the central axis AM of the tubular metal casing 23 coincide, so that these two components are arranged concentrically to each other.

[0053] The enlarged detail of an area inside the electric heater from Figure 2aaccording to Figure 2d illustrate essentially in the same way as the Figures 1d and 1e that the electrically insulating material 24 comprises a granulate of (magnesium oxide) grains of different sizes with edges and projections, and that at least one surface of at least one coil W10 has sections in which (magnesium oxide) grains are at least partially pressed into the electrical heating element under local deformation, which is illustrated by the irregularly serrated surfaces of the coil W10.

[0054] The Figures 3a to 3dshow four different variants of coils W1, W2, W3, and W4 in cross-section, clearly revealing the flat-band cross-section. The coils W1, W2, W3, and W4 each have four sides or surfaces W1.1, W1.2, W1.3, W1.4; W2.1, W2.2, W2.3, W2.4; W3.1, W3.2, W3.3, W3.4; W4.1, W4.2, W4.3, W4.4, which differ in terms of their surface roughness caused by the indentation of particles of the electrically insulating material, in particular magnesium oxide granules, and thus the effective interface available for heat transfer to the electrically insulating material. The sides or surfaces W1.1,W2.1,W3.1 and W4.1 face the inside of the tubular metal casing, the sides or surfaces W1.2,W2.2,W3.2 and W4.2 face its central axis AR and the remaining sides or surfaces W1.3,W2.3,W3.3,W4.1,W4.1,W4.2, W4.3,W4.4 face adjacent coils.

[0055] In the representation according to Figure 3aThe achieved surface roughness of the helix W1 is approximately the same on all four sides or surfaces W1.1, W1.2, W1.3, and W1.4. This result is achievable with a homogeneous filling of (magnesium oxide) granules; the degree of roughness can be influenced by the choice of grain size distribution.

[0056] In the representation according to Figure 3b On the other hand, the achieved surface roughness of the helix W2 on the side or surface W2.2 facing the central axis AR of the tubular metal casing is lower than on the other sides or surfaces W2.1,W2.3,W2.4.

[0057] In particular, by layer-wise filling of (magnesium oxide) granules with different grain size distributions, it is possible to vary the roughness of sides or surfaces W3.1,W3.2,W4.1, W4.2, which are oriented in or against the radial direction compared to sides or surfaces W3.3,W3.4,W4.3,W4.4, which are oriented in or against the extension direction of the electric heating device, as shown in the Figures 3c and 3d can be seen. List of reference symbols

[0058] 1,2 electric heating device 10,20 electric heating element 11,12,21,22 connecting bolt 11a,12a connecting section 13,23 tubular metal casing 14,24 electrically insulating material 14.1,14.2 granules 14.3 projection AR central axis AW helix axis BWidth D1 outer diameter D2 inner diameter HHeight Q cross-sectional area SA distance W1,W2,W3,W4,W10,W20 helix W1.1,W1.2,W1.3,W1.4, W2.1,W2.2,W2.3,W2.4, W3.1,W3.2,W3.3,W3.4, W4.1,W4.2,W4.3,W4.4, surface

Claims

1. Electric heating device (1, 2), having an electric heating element (10, 20), which is arranged unsupported inside the tubular interior of at least one tubular metal casing (13, 23), and which is electrically insulated from the latter by means of a compressed, electrically insulating material (14, 24), wherein the electric heating element (10, 20) comprises, at least partially, helices (W1, W2, W3, W4, W10, W20) which have a flat strip geometry, wherein the helices (W1, W2, W3, W4, W10, W20) with flat strip geometry comprise an inner diameter (D2), an outer diameter (D1), and a distance (S) between adjacent helices (W1, W2, W3, W4, W10, W20) and are formed such that the flat side of the helices (W1, W2, W3, W4, W10, W20) with flat strip geometry extends parallel to the axis of the helix (AW), characterized in that, at least in some regions of the interior of the tubular metal casing (13, 23) which are adjacent to at least one helix (W1, W2, W3, W4, W10, W20), the compressed electrically insulating material (14, 24) is either a compressed granulate material consisting of granules (14.1, 14.2) of different sizes and having edges and protrusions (14.3), or the compressed insulating material is a compressed molded part consisting of an electrically insulating material, and in that at least one surface (W1.1, W1.2, W1.3, W1.4, W2.1, W2.2, W2.3, W2.4, W3.1, W3.2, W3.3, W3.4, W4.1, W4.2, W4.3, W4.4) of at least one helix (W1, W2, W3, W4, W10, W20) comprises sections in which either granules (14.1, 14.2) or components of the molded part created during the compression of the molded part, are pressed, under local deformation of the electric heating element (10, 20), at least partially into the electric heating element (10, 20).

2. Electric heating device (1, 2) in accordance with claim 1, characterized in that the compressed granulate material is at least partially impregnated.

3. Electric heading device (1, 2) in accordance with claim 2, characterized in that granules (14.1, 14.2) of the compressed granulate material are bonded to each other and / or to the electric heating element (10, 20) and / or to the tubular metal casing (13, 23) by means of adding the impregnating agent and subsequent annealing.

4. Electric heating device (1, 2) in accordance with any of the preceding claims, characterized in that the axis of the helix (AW) extends parallel to the tubular middle axis (AR) of the tubular metal casing (13, 23).

5. Electric heating device (1, 2) in accordance with any of the preceding claims, characterized in that at least one helix (W1, W2, W3, W4, W10, W20) comprises numerous surfaces (W1.1, W1.2, W1.3, W1.4, W2.1, W2.2, W2.3, W2.4, W3.1, W3.2, W3.3, W3.4, W4.1, W4.2, W4.3, W4.4) in which granules (14.1, 14.2), or components of the molded part created during the compression of the molded part, are at least partially pressed, under local deformation of the electric heating element (10, 20), into the electric heating element (10, 20).

6. Electric heating device (1, 2) in accordance with claim 5, characterized in that the relative enlargement of the contact surface between the electric heating element (10, 20) and the electrically insulating material (14, 24) differs for at least two different surfaces (W1.1, W1.2, W1.3, W1.4, W2.1, W2.2, W2.3, W2.4, W3.1, W3.2, W3.3, W3.4, W4.1, W4.2, W4.3, W4.4) in which granules (14.1, 14.2) are at least partially pressed, under local deformation of the electric heating element (10, 20), into the electric heating element (10, 20).

7. Electric heating device (1, 2) in accordance with claim 6, characterized in that the relative enlargement of the contact surface between the electric heating element (10, 20) and the electrically insulating material (14, 24) is the largest for the surface facing the tubular metal casing (13, 23) in which the granules (14.1, 14.2), or the components of the molded part created during the compression of the molded part, are at least partially pressed, under local deformation of the electric heating element (10, 20), into the electric heating element (10, 20).

8. Method for manufacturing an electric heating device (1, 2) having an electric heating element (10, 20) which comprises, at least partially, helices (W1, W2, W3, W4, W10, W20) which have a flat strip geometry, wherein the helices (W1, W2, W3, W4, W10, W20) with flat strip geometry comprise an inner diameter (D2), an outer diameter (D1, and a distance (S) between adjacent helices (W1, W2, W3, W4, W10, W20) and are formed such that the flat side of the helices (W1, W2, W3, W4, W10, W20) with flat strip geometry extends parallel to the axis of the helix (AW), wherein the electric heating element (10, 20) is arranged inside the tubular interior of a tubular metal casing (13, 23) and is electrically insulated from the latter by means of an electrically insulating material (14, 24), and comprising the steps: - producing the electric heating element (10, 20), - arranging the electric heating element (10, 20) in the interior of the tubular metal casing (13, 23), - introducing the electrically insulating material (14, 24) into the interior of the tubular metal casing (13, 23), and - compressing the electrically insulating material (14, 24), characterized in that the electrically insulating material (14, 24) is a granulate material consisting of granules (14.1, 14.2) of differing sizes and having edges and protrusions (14.3), or a molded part, wherein the granulate material or the molded part is compressed in the radial direction at least strongly enough in order to press parts, in particular the edges and protrusions (14.3), of granules (14.1, 14.2) or components of the molded part created during the compression of the molded part, are pressed, under local deformation of the electric heating element (10, 20), into at least one surface (W1.1, W1.2, W1.3, W1.4, W2.1, W2.2, W2.3, W2.4, W3.1, W3.2, W3.3, W3.4, W4.1, W4.2, W4.3, W4.4) of at least one helix (W1, W2, W3, W4, W10, W20) with flat strip geometry.

9. Method in accordance with claim 8, characterized in that the introduction of the electrically insulating material (14, 24) into the interior of the tubular metal casing (13, 23) is at least partially carried out by causing the granules (14.1, 14.2) of the granulate material to trickle into the tubular metal casing (13, 23) from and end face by means of shaking.

10. Method in accordance with claim 8 or 9, characterized in that the electrically insulating material (14, 24) has a tap density of less than 2.45 g / cm3 before the compression.

11. Method in accordance with claim 9 or 10, characterized in that a portion of the electrically insulating material (14, 24) is introduced into the interior of the tubular metal casing (13, 23) as molding particles.

12. Method in accordance with any of claims 8 to 11, characterized in that, at least partially, a granulate material to which an impregnating agent, in particular a silicone resin, has been added is introduced into the interior of the tubular metal casing (13, 23) as electrically insulating material (14, 24), and in that an annealing step is carried out in order that the granules become bonded to each other and / or to the electric heating element (10, 20) and / or to the tubular metal casing (13, 23).

13. Method in accordance with any of claims 8 to 12, characterized in that, during compression, a pressure is used that is high enough so as to bring about a plastic deformation of the electric heating element (10, 20), in particular a reduction of a few percent of the cross section of the electric heating element (10, 20).

14. Method in accordance with any of claims 8 to 13, characterized in that a magnesium oxide granulate material with a particle size distribution in the maximum range of 30µm and 300µm is used.

15. Method in accordance with claim 14, characterized in that the FWHM width of the particle size distribution of the magnesium oxide granulate material covers a range of between approximately 30µm and over 100µm.