Method for manufacturing a device with an inner conductor arranged inside the interior of a tubular metal sheath and electrically insulated from it by an electrically insulating material.

Abstract

Method for manufacturing a device (10, 20, 30) with an inner conductor (11, 21, 31) arranged inside the interior of a tubular metal sheath (12, 22a, 22b, 22c, 32) and electrically insulated from it with an electrically insulating material (13, 23, 33) comprising the steps - Arranging the inner conductor (11,21,31) inside the tubular metal sheath (12,22a,22b,22c,32), - Introducing the electrically insulating material (13,23,33) into the interior of the tubular metal sheath (12,22a,22b,22c,32), and - Compacting the electrically insulating material (13, 23, 33), wherein the electrically insulating material (13, 23, 33) is a magnesium oxide granulate consisting of magnesium oxide grains (14, 24, 34) of different sizes with edges and projections (24a, 34a), which is compacted in the radial direction at least to such an extent that sections, in particular edges and projections (24a, 34a) of magnesium oxide grains (14, 24, 34) are pressed into the inner conductor (11, 21, 31) or into the tubular metal sheath (12, 22a, 22b, 22c, 32) with local deformation of the inner conductor (11, 21, 31) and / or the tubular metal sheath (12, 22a, 22b, 22c, 32), characterized in that in an end section of the device (10, 20, 30) the inner conductor (11,21,31) is exposed and reworked to give shape.

Description

[0001] There are a number of devices with an inner conductor that is arranged inside the interior of a tubular metal sheath and electrically insulated from it by an insulating material. These include, in particular, mineral-insulated sheathed cables, which are widely used for various applications, such as electrical feedthroughs through metal walls.

[0002] Such devices are known, for example, from DE 10 2017 112 328 A1 and DE 10 2013 212 205 A1.

[0003] In practical applications, it has become apparent that the mechanical stability of such devices often does not yet meet the high demands of many technical environments. This is particularly true when the device is subjected to significant torsional forces, pull-out forces, shock, pressure, and / or vibrations, and / or when the inner conductor serves as a suspension for a structure, such as a honeycomb structure used in an exhaust gas purification system.

[0004] The object of the invention is to provide an improved method for manufacturing devices with an inner conductor arranged inside the interior of a tubular metal sheath and electrically insulated from it with an electrically insulating material, which have improved resistance to the aforementioned mechanical stresses.

[0005] This problem is solved by a method having the features of claim 1. Advantageous further developments of the method are the subject of the dependent claims.

[0006] The device producible by the method according to the invention, comprising an inner conductor arranged within the interior of a tubular metal sheath and electrically insulated from it by a compacted, electrically insulating material, is characterized in that the compacted electrically insulating material is a compacted magnesium oxide granulate consisting of magnesium oxide grains of different sizes with edges and projections, and that sections, in particular edges and projections of magnesium oxide grains, are pressed into the inner conductor and / or the tubular metal sheath under local deformation of the inner conductor and / or the tubular metal sheath.

[0007] This approach represents a paradigm shift in a certain sense. Until now, the choice of magnesium oxide and the pressure applied during compaction were primarily driven by the desire to maximize tracking resistance and moisture resistance. Therefore, the focus was on using magnesium oxide powders with very fine and regularly shaped particles, some of which were even pre-processed as a molded part, such as a pipe, to achieve the most homogeneous insulating layer possible during compaction.

[0008] The use of magnesium oxide granules according to the invention differs fundamentally from this. Unlike a powder, a granule as defined in this disclosure has coarse, irregular magnesium oxide grains with edges and protrusions, and thus low roundness. These magnesium oxide grains can also exhibit a relatively broad particle size distribution with a full width half maximum (FWHM) value for the width of the distribution, which lies between a few tens of micrometers and over one hundred micrometers. The maximum of the magnesium oxide grain size distribution of the magnesium oxide granules used can preferably lie in the range between approximately 30 micrometers and approximately 300 micrometers, which shows that the particle size alone is not the decisive parameter.

[0009] An indirect, macroscopically measurable measure of these properties of the magnesium oxide granules is the tapped density. Magnesium oxide granules according to this invention have a tapped density of less than 2.45 g / cm³ before compaction. 3 , while the density of magnesium oxide is 3.58 g / cm³ 3 This is specified. Therefore, when the tubular metal casing is filled, an electrical insulation layer is initially created, which has a significant proportion of empty volume.

[0010] While one might 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 found that, surprisingly, when applying such high pressure that sections of particles located adjacent to the inner conductor and / or tubular metal sheath, in particular edges and protrusions of magnesium oxide grains, are pressed into the inner conductor and / or tubular metal sheath under local deformation, an electrical insulation layer with high tracking resistance and moisture resistance can still be achieved, which also proves to be mechanically significantly more stable than known electrical insulation layers in such devices.

[0011] This improved mechanical stability has a particularly positive effect on the mechanical breakout behavior at the end faces of the insulation layer. It is also especially beneficial in systems where the inner conductor also serves as a load-bearing element for the structure it supplies, as is the case, for example, with the inner conductor of a bushing that supports a honeycomb structure located in an exhaust duct.

[0012] Another advantage of using magnesium oxide granules according to the invention is that it results in improved tolerance compensation.

[0013] Furthermore, an improvement in the thermal conductivity of the electrical insulation layer is also observed. On the one hand, this can be attributed to a lower proportion of grain boundaries resulting from a higher proportion of larger magnesium oxide grains. On the other hand, pressing the magnesium oxide grains into the inner conductor also promotes heat dissipation, as the effective transfer surface area is increased.

[0014] In this way, the magnesium oxide granules impart an (additional) roughness to the inner conductor and / or the tubular metal sheath during compaction. Experiments show that, for example, arithmetic mean roughness values ​​R for typical inner conductor materials a of a few µm and medium smoothing depths R p of around 10 µm can be achieved.

[0015] The pressure required for compaction can be provided, for example, by press compaction, roller compaction, or hammer compaction. Pressures high enough to plastically deform the inner conductor are particularly preferred, especially reducing its diameter by a few percent, preferably about 5%.

[0016] The advantages of using magnesium oxide granules can be particularly pronounced when the cross-section of the inner conductor deviates from a circular shape, even neglecting the local deformation caused by pressing in the magnesium oxide granules. This increases the surface area available for interaction with the magnesium oxide granules.

[0017] However, it turns out that the ratio of the inner conductor's cross-sectional diameter to the thickness of the electrical insulation layer can influence the homogeneity of the pressure introduction. For example, it may be desirable for this ratio to be approximately 4:1.

[0018] If necessary, the moisture resistance can be further increased by impregnating at least some sections of the compacted magnesium oxide granules.

[0019] Furthermore, by adding an impregnating agent, at least in sections of the device, in particular, for example, by adding 0.5 vol% silicone resin, and subsequently tempering, the magnesium oxide granules can be bonded together, making the resulting structure more resistant and counteracting breakage at the edges of the structure by bonding the magnesium oxide granules together and / or to the inner conductor and / or to the tubular metal sheath.

[0020] The inventive method for manufacturing a device with an inner conductor arranged inside the interior of a tubular metal sheath and electrically insulated from it with an electrically insulating material comprises the steps - Arranging the inner conductor inside the tubular metal sheath, - Introducing the electrically insulating material into empty volumes of the interior of the tubular metal sheath, and - Compacting the electrically insulating material.

[0021] The essential feature of the invention is that the electrically insulating material is a magnesium oxide granulate made up of magnesium oxide grains of different sizes with edges and projections, which is compacted in the radial direction at least to such an extent that sections, in particular edges and projections of magnesium oxide grains, are pressed into the inner conductor or into the tubular metal sheath under local deformation of the inner conductor and / or the tubular metal sheath.

[0022] It is particularly advantageous that the electrically insulating material is introduced into the empty volumes of the interior of the tubular metal jacket by allowing the magnesium oxide granules to trickle into the tubular metal jacket from one end while vibrating. This not only promotes material transport within the free interior volume of the tubular metal jacket, but the resulting pre-configuration of the magnesium oxide grains also proves helpful in reducing and / or eliminating any empty volumes.

[0023] Preferably, a magnesium oxide granulate is used as the electrically insulating material, which is such that the electrically insulating material has a vibration density of less than 2.45g / cm³ before compaction. 3 has.

[0024] To make the electrically insulating material even more stable and, in particular, to counteract its breakout in edge areas, it is advantageous if, at least in sections, magnesium oxide granules mixed with an impregnating agent, especially a silicone resin, are introduced as electrically insulating material into the interior of the tubular metal sheath, and then, but not necessarily immediately afterwards, a tempering step is carried out so that magnesium oxide grains are bonded to each other and / or to the inner conductor and / or to the tubular metal sheath.

[0025] In the method according to the invention, the inner conductor is also exposed and shaped in an end section of the device. This can be done, for example, by machining the end section and the inner conductor.

[0026] It is particularly preferred if, during radial compaction, a pressure high enough is applied to cause plastic deformation of the inner conductor, specifically a reduction in its cross-sectional area of ​​a few percent, i.e., particularly between 2 and 10 percent. However, the ideal pressure depends on the material and geometry of the respective inner conductor and the tubular metal sheath, which can vary. Compaction can be achieved, in particular, by press compaction, roller compaction, or hammer compaction.

[0027] Preferably, magnesium oxide granules with a particle size distribution whose maximum lies in the range between 30 µm and 300 µm are used. It is particularly preferred if the width of the particle size distribution covers a range between approximately 30 µm and over 100 µm.

[0028] The invention is explained in more detail below with reference to figures illustrating exemplary embodiments. These show: Fig. 1: A partially opened representation of a first embodiment of a device producible according to the invention in the form of a feedthrough in the application case, Fig. 2a: a partially opened representation of a second embodiment of a device producible according to the invention in the form of a feedthrough, Fig. 2b: a detailed enlargement from Fig. 2a, Fig. 3a: a cross-sectional view from a first phase of the manufacturing process according to the invention, Fig. 3b: a detailed enlargement from Fig. 3a, Fig. 4a: a cross-sectional view from a second phase of the manufacturing process according to the invention, Fig. 4b: a detailed enlargement from Fig. 4a, and Fig. 5: a cross-sectional view from a further phase of the manufacturing process according to the invention.

[0029] Fig. Figure 1 shows a device 10 designed as a through-wall 1, which is welded to the metal wall 1 through which it passes by means of welds 2. The device 10 has an inner conductor 11, which is arranged inside the interior of a tubular metal sheath 12 and is electrically insulated from it by a dense, electrically insulating material 13. A connecting section 11a of the inner conductor 11 projects from the tubular metal sheath 12 and is provided at its end with a thread that is inserted into the connecting section 11a of the inner conductor 11, on which an electrical contact 4 is fixed by means of a nut 3. Accordingly, during intended use, the device 10 is temporarily subjected to a considerable torque M, particularly when the nut 3 is tightened with a wrench 5 to secure the contact 4, which must be absorbed by the electrically insulating material 13.

[0030] This is made possible by the fact that the electrically insulating material is a magnesium oxide granulate consisting of magnesium oxide grains 14 of different sizes with edges and projections, and which has been compacted in particular so that sections, especially edges and projections of magnesium oxide grains 14, are pressed into the inner conductor 11 and the tubular metal sheath 12 respectively under local deformation of the inner conductor 11 and the tubular metal sheath 12.

[0031] The in the Fig. 2a and Fig. The embodiment of device 20 shown in Figure 2b is also a feedthrough, but it is not yet in its application state. Device 20 also has an inner conductor 21, which is arranged within the interior of the tube of segments of a tubular metal sheath 22a, 22b, 22c, and thus within at least one tubular metal sheath, and is electrically insulated from these segments by a dense, electrically insulating material 23. A connecting section 21a of the inner conductor 21 also projects from the tubular metal sheath and is provided at its end with a thread inserted into the connecting section 21a of the inner conductor 21. The segments of the tubular metal sheath 22a, 22b, 22c are separated from one another by areas 25 in which the tubular metal sheath and the electrically insulating material are removed down to the inner conductor 21.This increases the tracking resistance of the device 20, but leads to even higher mechanical loads that must be absorbed by the material 23.

[0032] This is made possible, as detailed in the description of the Fig. 2b is particularly evident from the fact that the electrically insulating material 23 is a magnesium oxide granulate consisting of magnesium oxide grains 24 of different sizes with edges and projections 24a, and which has been compacted in particular such that sections, especially edges and projections 24a of magnesium oxide grains 24, are pressed into the inner conductor 21 and into the segment of the tubular metal sheath 22b respectively, with local deformation of the inner conductor 21 and the segment of the tubular metal sheath 22b.

[0033] What is noteworthy about the Fig. 2b is also that despite the edges and protrusions 24a of the magnesium oxide grains 24, after compaction, due to the high pressure between the magnesium oxide grains 24, there is largely a planar contact, so that there are hardly any empty volumes between the magnesium oxide grains 24.

[0034] What makes this even more special is the Fig. 2a clearly shows that such a design can be produced simply by machining a section of a mineral-insulated sheathed cable of the invention.

[0035] The Fig. 3a and Fig. 3b, Fig. Figures 4a and b as well as 5 each illustrate a snapshot of phases of the manufacture of a device 30 which is only shown section by section, which is why identical reference numerals are used in these figures.

[0036] In the Fig. 3a and Fig. In the phase shown in 3b, the inner conductor 31 is already arranged in the interior 35 of the tubular metal sheath 32, and the electrically insulating material 33 in the form of magnesium oxide grains 34 of different sizes with edges and projections 34a is being poured into the remaining interior 35 of the tubular metal sheath 32, which is already partially filled with such magnesium oxide grains 34, while being shaken from an end face of the tubular metal sheath 32.

[0037] How the detailed presentation of the Fig. Figure 3b shows that a loose structure of magnesium oxide grains 34 is initially formed in the already filled area, but this has considerable empty volumes 36 and thus does not initially appear to form a promising starting structure for a creepage current-resistant electrical insulation that reliably prevents the ingress of moisture.

[0038] In the Fig. 4a and Fig. The phase shown in 4b is this arrangement, as shown in Fig. As illustrated by the arrows shown in Figure 4a, the material has been compacted in the radial direction at least to such an extent that sections 34a, in particular edges and projections of magnesium oxide grains 34, are pressed into the inner conductor 31 and the tubular metal sheath 32, respectively, under local deformation of the inner conductor 31 and the tubular metal sheath 32, respectively. This clearly shows the change in the outer surface of the inner conductor 31 and the inner surface of the tubular metal sheath 32. Presumably, this deformation also enables a rearrangement of the magnesium oxide grains 34, which is shown in Figure 4a. Fig. 3b remaining empty volumes 36 largely eliminated.

[0039] Fig.Figure 5 illustrates that relatively complex geometries of feedthroughs, including a connection section 31a for the inner conductor 31, can be easily realized from a mineral-insulated sheathed cable produced in this way using a machining tool 50. Reference symbol list 1 metal wall 2 weld seam 3 mother 4 electrical contacts 5 wrenches 10, 20, 30 Device 11, 21, 31 Inner conductor 12,22a,22b,22c,32 tubular metal jacket 13, 23, 33 electrically insulating material 14,24,34 Magnesium oxide grain 24a,34a Edges and projections 25 area 35 Interior 36 empty volumes 50 machining tools M torque

Claims

[1] Method for manufacturing a device (10, 20, 30) with an inner conductor (11, 21, 31) arranged inside the interior of a tubular metal sheath (12, 22a, 22b, 22c, 32) and electrically insulated from it by an electrically insulating material (13, 23, 33) comprising the steps - Arranging the inner conductor (11,21,31) inside the tubular metal sheath (12,22a,22b,22c,32), - Introducing the electrically insulating material (13,23,33) into the interior of the tubular metal sheath (12,22a,22b,22c,32), and - Compacting the electrically insulating material (13, 23, 33), wherein the electrically insulating material (13, 23, 33) is a magnesium oxide granulate consisting of magnesium oxide grains (14, 24, 34) of different sizes with edges and projections (24a, 34a), which is compacted in the radial direction at least to such an extent that sections, in particular edges and projections (24a, 34a) of magnesium oxide grains (14, 24, 34) are pressed into the inner conductor (11, 21, 31) or into the tubular metal sheath (12, 22a, 22b, 22c, 32) with local deformation of the inner conductor (11, 21, 31) and / or the tubular metal sheath (12, 22a, 22b, 22c, 32), characterized by , that in an end section of the device (10,20,30) the inner conductor (11,21,31) is exposed and reshaped. [2] Method according to claim 1, characterized by, that the introduction of the electrically insulating material (13,23,33) into the interior of the tubular metal jacket (12,22a, 22b,32) is carried out by letting the magnesium oxide grains (14,24,34) of the magnesium oxide granules trickle into the tubular metal jacket (12,22a,22b,22c,32) from one end face while vibrating. [3] Method according to claim 1 or 2, characterized by , that the electrically insulating material (13,23,33) has a vibration density of less than 2.45 g / cm³ before compaction 3 has. [4] Method according to any one of claims 1 to 3, characterized by, that at least in sections a magnesium oxide granulate impregnated with an impregnating agent, in particular a silicone resin, is introduced as an electrically insulating material (13,23,33) into the interior of the tubular metal sheath (12,22a, 22b,32) and that a tempering step is carried out so that magnesium oxide grains (14,24,34) are bonded to each other and / or to the inner conductor (11,21,31) and / or to the tubular metal sheath (12,22a,22b,22c,32). [5] Method according to any one of claims 1 to 4, characterized by , that during compaction such high pressure is applied that plastic deformation of the inner conductor (11,21,31) occurs, in particular a reduction in the cross-sectional area of ​​the inner conductor (11,21,31) of a few percent. [6] Method according to any one of claims 1 to 5, characterized by , that a magnesium oxide granulate with a particle size distribution whose maximum lies in the range between 30µm and 300 µm is used. [7] Method according to claim 6, characterized by , that the FWHM width of the particle size distribution of the magnesium oxide granules covers a range between approximately 30µm and over 100µm.

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