Electrolytic decoupling high temperature thermal insulation

Abstract

The invention relates to an insulating element (1) for thermally insulating an inductively heatable high-temperature process zone (2), wherein a wall of the insulating element (1) comprises a flat material (3) having an electrical resistivity p F of 10 ‑5 ‑1 Ωm, which surrounds a hollow space (4) extending through the insulating element (1) and comprises a break (5) having an electrical resistivity p U greater than p F , wherein the break (5) extends from an outer surface (6) of the flat material (3) into the flat material (3) without interrupting the flat material (3) over its entire cross section (8).​

Description

Technical Field

[0001] The present invention relates to an insulating element for thermally insulating a high-temperature processing zone that can be induction heated, a set of insulating element portions for forming an insulating element including an insulating element portion, a method for producing a flat material that can be used to insulate a high-temperature processing zone that is induction heated, and the use of the insulating element for thermally insulating a high-temperature processing zone that is induction heated. Background Technology

[0002] For example, high-temperature processes conducted in an inert atmosphere above 800°C place high thermal and mechanical requirements on the insulating materials used. Carbonized and optionally graphitized felts are commonly used as materials for insulating the heating chamber from the cooling outer walls of the high-temperature furnace.

[0003] EP 1 852 252 B1 discloses a method for producing high-temperature resistant insulators, wherein multiple bent segments are made, in particular, of a material based on expanded graphite, which is compressed to 0.02 to 0.3 g / cm³. 3 The density between the segments is adjusted to form a hollow cylindrical assembly. In this case, the segments are held together by a carbonizable adhesive containing planar anisotropic graphite particles. Furthermore, graphite foil is arranged on the inner surface of the hollow cylindrical insulator.

[0004] WO 2011 / 106580 A2 discloses an insulator for a reactor made of carbon fiber material, the insulator being assembled from multiple individual plate-like components. The individual components can be connected using additional connecting elements via tongue-and-groove insert connectors.

[0005] Utility model document CN202610393U describes a heat preservation device for producing sapphire crystals, wherein a circumferential graphite felt gasket is formed by combining three fan-shaped soft felts.

[0006] CN102748951A describes a thermal insulation material in the form of a unit composed of multiple slats. The slats include tongues and grooves that can be joined to form an arc-shaped thermal insulation cylinder. Constructing the unit with slats is intended to allow for partial replacement and repair of damaged components. The aim is to achieve excellent thermal insulation properties throughout its entire service life. The insulating cylinder allows for convenient storage and transportation. The insulating cylinder is intended to significantly reduce operating costs.

[0007] DE68920856 T2 describes a tubular thermal insulator comprising: (a) a multilayered carbon fiber felt wound in a helical shape, containing carbonized resin, and (b) a carbonized film and / or mesh and resin present between the felt layers, forming a continuously laminated tubular element, wherein the felt layers are integrally bonded to each other by the carbonized resin present between the felt layers. The thermal insulator is intentionally designed to have a high density and provide excellent thermal insulation and surface smoothness. Its density is intentionally varied along the radial direction. The thermal insulator is also intended to be produced at a high level of productivity without the need for complex methods.

[0008] WO 2013 / 174898 A1 describes a thermal insulator composed of a material comprising carbonized fibers and / or graphitized fibers for lining a high-temperature furnace, wherein the thermal insulator comprises at least two separate components, wherein each of the at least two separate components joined together includes at least one connecting element, and the connecting elements of the at least two separate components joined together are interlocked with each other to form an undercut.

[0009] In some high-temperature processing methods, the substrate to be processed, such as a fiber substrate in glass fiber production, is continuously guided through a high-temperature processing zone. For example, the temperature in the high-temperature processing zone can be at least 800°C.

[0010] To maintain the temperature within a specific, narrow range of high temperatures in the high-temperature processing zone, a continuous power supply must be provided. This is accomplished through inductive heating. In this case, an electric coil arranged around the high-temperature processing zone is inductively coupled to at least one heating element. The heating element can be a high-temperature resistant wall surrounding the high-temperature processing zone. The wall can contain graphite.

[0011] For some insulating materials, the furnace appears to directly radiate excessive heat during induction heating, thus its environment is intensely heated, and additional measures must be taken to dissipate the excess heat, such as complex ventilation or cooling of the production workshop in which the furnace operates. Summary of the Invention

[0012] The objective of this invention is to provide a thermal insulation material that can be used, for example, in a high-temperature furnace for the production of glass fiber, and that enables permanent and reliable induction heating of a high-temperature processing zone at high temperatures, while requiring less effort to dissipate waste heat.

[0013] This objective is achieved through an insulating element for thermally insulating a high-temperature processing zone that can be inductively heated, wherein the wall of the insulating element comprises a flat material with a resistivity ρ. F 10 -5 Up to 10 -1 Ωm, surrounding the cavity extending through the insulating element and including resistivity ρU Greater than ρ F The fracture surface extends from the outer surface of the flat material into the flat material, but does not produce a fracture surface across the entire cross-section of the flat material.

[0014] Because the walls surround and extend through the cavity of the insulating element, the shape of the insulating element can be generally a hollow cylinder. The hollow cylinder includes an inner side, an outer side, and two end faces. The walls of the insulating element extend circumferentially within the region defined by the inner and outer side surfaces and extend from one end face of the hollow cylinder to the other. It goes without saying that, in this case, the hollow cylinder is merely used to define the geometry of the invention.

[0015] The insulating element does not necessarily occupy the entire volume of the hollow cylinder that exists between the sides and is defined by the end face. For example, the insulating element can be a laminated composite material of two hollow cylindrical materials of different lengths, such as a longer inner CFC tube, wherein only a portion of the CFC tube is circumferentially coated with a flat material. Although the inner surface of the CFC tube may roughly coincide with the inner side of the hollow cylinder, and the outer surface of the flat material may coincide with the outer rear surface of the hollow cylinder, the insulating element still does not occupy the entire volume of the hollow cylinder because the flat material does not reach the end face.

[0016] Of course, the insulating element can occupy all or almost all of the entire volume of the hollow cylinder, for example, at least 90% or at least 95% by volume, such as when the insulating element consists only of flat material in the shape of a hollow cylinder.

[0017] This invention does not exclude the fact that, in addition to the flat material, the insulating element also includes an additional high-temperature stable material, which may be present together with the flat material in a composite material, such as a laminated composite material. In a typical insulating element according to the invention, the flat material, together with the break extending from the outer surface of the flat material into the flat material, occupies at least 20% of the volume of the insulating element, typically at least 35% of the volume, preferably at least 50% of the volume, particularly preferably at least 65% of the volume, for example at least 80% of the volume.

[0018] According to the invention, the walls of the insulating element comprise a flat material. Any flat material capable of withstanding the high temperatures exerted on the flat material by high-temperature processing and whose resistivity is within the range specified according to the invention is suitable. It is well known that each of the different high-temperature stable flat materials can be used continuously until the material-specific upper temperature limit is reached. Therefore, those skilled in the art will select the flat material based on the high-temperature application, such that it preferably does not reach, and in particular does not exceed, the material-specific upper temperature limit.

[0019] For example, flat materials can include carbon fibers and / or expanded graphite. This means that the material can be used at high temperatures in an inert environment. Expanded graphite is known to be produced by treating graphite with a specific acid, wherein graphite salts form acid anions embedded between graphene layers. The graphite salts are then converted into expanded graphite by exposure to a high temperature, for example, 800°C.

[0020] The flat material is preferably a carbon-containing flat material, such as a carbon fiber-containing flat material. A carbon fiber-containing flat material can be a carbon fiber felt. "Carbon fiber-containing" means that the flat material contains carbon fibers, such as felt.

[0021] In this context, any fiber with a carbon content of at least 60% by weight, more preferably at least 80% by weight, particularly preferably at least 92% by weight, especially preferably at least 96% by weight, very particularly preferably at least 99% by weight, and most preferably at least 99.5% by weight is characterized as carbon fiber. Therefore, the term carbon fiber herein includes both carbonized and graphitized fibers. Carbon fibers can be made from viscose-based, panoxel-based, or pyroxene-based carbon fibers. Their surface can be finished, for example, with pyrolytic carbon (PyC) or silicon carbide.

[0022] Flat materials, such as felt, may contain additional components besides carbon fibers. Any sufficiently high-temperature stable material that can achieve adequate thermal insulation even at very high temperatures is considered an additional component. In particular, flat materials may contain ceramic fibers as an additional component.

[0023] A particularly preferred flat material is carbon fiber felt, such as flexible carbon fiber felt or rigid carbon fiber felt. In rigid carbon fiber felt, the fibers are joined together. This joining can be achieved through carbonization residues, such as residual carbonized phenolic resin. The joining can also include the aforementioned carbon-related substances, pyrolytic carbon and / or silicon carbide. Thus, the felt becomes rigid because the fibers no longer move relative to each other at their points of connection. In flexible carbon fiber felt, the fibers are not joined in this manner. For example, flexible carbon fiber felt can be reinforced by needle punching.

[0024] The resistivity ρ of flat materials F 10 -5 ~10 -1 Ωm. The resistivity of flat materials containing carbon, and especially carbon fibers, which have been proven to be successfully used in practical applications for a long time as high-temperature thermal insulation materials and have been discussed in more detail above, is in this range.

[0025] If someone skilled in the art has the freedom to choose a high-temperature stable thermal insulation material, he would not choose one with a resistivity of 10. -5 ~10 -1Flat materials in the range of Ωm. This is because it is clearly shown simultaneously with the present invention that materials having a range of 10 Ωm... -5 ~10 -1 Flat materials with resistivity in the Ωm range tend to produce relatively strong, undesirable heating when interacting with heating coils. However, due to the extremely high requirements for temperature stability and thermal insulation, the range of practically available flat materials is very limited. Therefore, the aforementioned carbon-containing, especially carbon fiber-containing, flat materials have proven successful in practice, particularly because they can be produced from relatively inexpensive starting materials with reasonable effort.

[0026] In having 10 -5 ~10 -1 In these flat materials with average resistivity in the range of Ωm, this interaction between the heating coil and the flat material results in a relatively strong current, which in turn flows through a relatively high resistance. Therefore, flat materials with resistivity in this range tend to require particularly strong, undesirable heating. In this case, the following factors tend to reduce the resistivity of the flat material: 1) a high carbon fiber content in the flat material, and 2) a high content of graphitized carbon fibers in the flat material. Graphitized carbon fibers are obtained by pyrolysis at very high temperatures, for example, 1600 to 3000 °C, preferably 1700 to 2400 °C. Graphitized carbon fibers generally conduct current better than ungraphitized carbon fibers. It goes without saying that the term "carbon fiber" here is not intended to be limited to graphitized carbon fibers. The carbon fibers contained in the flat material can be obtained by pyrolysis at relatively low temperatures, for example, 800 to 1600 °C, particularly 800 to 1200 °C.

[0027] According to the present invention, the wall of the insulating element includes a break, wherein the resistivity ρ U Greater than ρ F The fracture surface extends from the outer surface of the flat material into the flat material. However, it does not create a fracture along the entire cross-section of the flat material.

[0028] The fact that a fracture does not occur across the entire cross-section of a flat material means that the flat material is continuous in the region of flat material directly adjacent to the fracture. To separate two regions of flat material adjacent to the fracture, it is necessary to cut through the flat material.

[0029] In conjunction with this invention, extensive simulations have been performed to describe in more detail the effect of the fracture surface on the amount of heat released to the outside. These simulations surprisingly show that the fracture surface extremely effectively counteracts the intense and undesirable induction heating of popular flat materials with minimal effort. Currents that typically flow circumferentially in flat materials encounter a barrier formed by the fracture surface. In this case, the current bypasses the barrier and transfers to the region beneath the flat material, thereby preventing an increase in resistance on the outer surface of the flat material and the generation of significant amounts of heat within the flat material (e.g., a carbon fiber-containing felt).

[0030] In some embodiments, the wall of the insulating element includes only one break. Typically, multiple breaks are preferred. Therefore, the number of breaks can be at least 2, at least 3, at least 4, at least 6, at least 8, at least 10, at least 12, at least 16, or at least 20; preferably at least 3, at least 4, or at least 6. This implies an increase in the detour of current flow or an increase in resistance. It goes without saying that the following characteristics related to the break are each intended only to apply to one break, two or more breaks, or all breaks.

[0031] A fracture can be a cut made in a flat material. To date, a cut is the simplest method to create the desired fracture. In this case, the flat material is only cut into, not through. This ensures that the flat material is not destroyed by the cut across its entire cross-section.

[0032] At least a portion (particularly preferably the entire fracture) of the fracture surface preferably does not extend orthogonally to two adjacent surface regions of the flat material. This means that the spectral coefficient of thermal radiation between the hot surface and the cold environment is reduced. The proportion of radiation reaching the environment through the fracture surface is thus minimized. This radiation particularly originates from the hot surface of the base.

[0033] For the insulating element according to the invention, its shape can be approximately a hollow cylinder, and preferably the length, shape, and orientation of the fracture at the outer surface of the flat material are selected such that the following conditions apply:

[0034] L u >a·L t

[0035] in,

[0036] L t The length of the shortest path around the flat material, which extends along the outer surface of the flat material, crosses the fracture, and enters the central cutting plane, which is orthogonal to the longitudinal axis of the hollow cylinder, dividing the flat material into two equal halves of the flat material volume.

[0037] L uThe length of the shortest path around the flat material, which in each case extends from one fracture to another in the central cutting plane, but does not cross the fracture, but rather goes around it, and

[0038] a is 2, preferably 5.

[0039] This is Figure 1C and Figure 1D As shown in the diagram. This means that the induced current cannot flow freely in the circumferential direction, but is redirected around the fracture, thereby increasing the resistance and reducing the induced current in the flat material.

[0040] Typically, it is preferred that the fracture surface has a much higher resistivity than that of a flat material. ρ U Preferably at least 100·ρ F Especially at least 1000·ρ F For example, at least 10000·ρ F The resistivity of air is >10. 14 The order of magnitude is Ωm, where the exact value depends on factors such as the moisture content of the air. If the fracture is a cut, then ρ U Ratio ρ F Several orders of magnitude higher. However, when ρ U Much higher than ρ F In this case, an intentional diversion of the current induced in the flat material is always achieved around the fracture surface. It is not necessary to provide a true insulator or a fracture surface in the form of a cut to achieve the desired effect according to the invention. ρ U At least 100·ρ F The desired relationship can also be achieved without difficulty using other high-temperature stable materials that may potentially serve as the fracture surface (such as boron nitride), because ρ F Approximately 10 in a typical carbon fiber felt -3 Ωm. Resistivity is measured according to DIN 51911. This standard pertains to the measurement of the resistance of graphite.

[0041] The flat material extends from a first edge to a second edge. The first edge of the flat material faces or coincides with the first end face of the hollow cylinder used to define the invention. The second edge of the flat material faces or coincides with the second end face of the hollow cylinder. Preferably, the fracture is spaced apart from at least one of the two edges, particularly from both edges of the flat material. The fracture then does not occur in the flat material, particularly in a region of the flat material extending from one end of the fracture to one edge of the flat material. The fracture then preferably does not occur in the flat material, particularly in two regions of the flat material, wherein one of these two regions extends from one end of the fracture to one edge of the edge, and the other of these two regions extends from a different end of the fracture to another edge. Therefore, the flat material is continuous in the region of the flat material extending from one end of the fracture to one edge of the flat material, or preferably continuous in two regions of the flat material, each extending from a different end of the fracture to a different edge of the flat material. This means that hollow cylindrical insulating elements or their flat materials are more stable on the one hand, and do not need to be constructed from multiple separate components on site on the other.

[0042] Preferably, at least two fracture surfaces are inclined in the same direction relative to the outer surface of the flat material. Fracture surfaces inclined in the same direction can have a greater depth, and the spacing between them is also very small. If two fracture surfaces are inclined in the same direction, one fracture surface will transition to the other, which is generally undesirable. If the fracture surfaces are transitional cuts, the portion of flat material arranged between the cuts may be prone to fracture. Therefore, fracture surfaces inclined in the same direction allow for a smaller spacing between the fracture surfaces, resulting in higher electrical decoupling efficiency of the flat material without significantly affecting its stability. Ultimately, this makes stable insulating elements easy to handle and has a particularly low tendency to undesirably heat the flat material they contain.

[0043] Particularly preferably, the fracture lies entirely between two parallel extending planes, and the distance between the two planes is at most 25%, particularly at most 15%, for example at most 10%, of the maximum depth of the fracture. This means that the fracture extends in a substantially flat manner. A substantially flat cut can be made in a flat material in a particularly simple manner using a rotating blade (similar to a circular saw, but without teeth). The maximum depth of the fracture corresponds to the maximum insertion depth of the blade measured from the surface of the flat material along the cut direction. In this case, the inclination of the planes is not limited. However, preferably, the inclination of the planes is predetermined by the fracture such that at least one of the two planes does not intersect the inner surface of the flat material or the angle of intersection with said surface is no greater than 45°.

[0044] Preferably, the flat material has a low thermal conductivity. The flat material preferably has a thermal conductivity of less than 10 W / m². -1 K -1 The degree of thermal conductivity is advantageous because it further reduces the dissipation of waste heat during induction heating in the high-temperature processing zone. If the flat material has a particularly low thermal conductivity, less heat leaves the high-temperature processing zone. This also reduces the effort required to dissipate waste heat from the hall where the high-temperature processing is carried out.

[0045] The wall thickness of the flat material of the insulating element preferably varies by no more than 10% in at least one cutting plane. A cutting plane is any plane orthogonal to the axis of the hollow cylinder. This is advantageous because unwanted heat loss occurs uniformly in the radial direction, at least in the region of that cutting plane. This results in fewer defective products produced.

[0046] Flat materials can be circumferentially continuous flat materials containing carbon fibers, particularly circumferentially continuous felts containing carbon fibers, such as circumferentially continuous carbon fiber felts. Circumferentially continuous carbon fiber felts can be produced from circumferentially continuous felts made from carbonizable fibers using known circular needle punching methods, and by converting circumferentially continuous felts into circumferentially continuous carbon fiber felts through high-temperature treatment in an oxygen-free atmosphere. This is advantageous because flat materials do not contain any seams or joints, and therefore do not suffer from the weakness of material fatigue or delamination that can occur during continuous use as high-temperature insulation.

[0047] Circumferential continuity means an irregular arrangement of fibers interconnected circumferentially, a characteristic of felt produced when the felt is manufactured as a flat web of felt. When a circumferentially continuous felt containing carbon fibers is cut orthogonally to the longitudinal axis of the insulating element, neither the start nor the end point of the circumferential felt containing carbon fibers can be identified at the intersection. In particular, there are no joints or seams in the cut surface. The fracture according to the invention must then be formed entirely in a downstream production step. This is advantageous because only the fracture specifically counteracts the heating of the flat material, without having to consider the inherent non-uniformity of the flat material, such as joints or seams, when forming the fracture. As a result, heat is introduced into the high-temperature processing zone in a particularly uniform manner. This further reduces the proportion of non-conforming (scrap) products generated during the high-temperature processing.

[0048] The flat material can also be formed from a set of flat material elements, and at least one joint region can be provided between the flat material elements to create a fracture over the entire cross-section of the flat material. Then, at least one of the flat material elements includes at least one fracture. Preferably, at least two flat material elements include fractures. The hollow cylinder of the flat material element is then formed, for example, by joining a felt pad containing carbon fibers in one or more joint regions.

[0049] The present invention also relates to a set of insulating element portions for forming an insulating element, particularly for forming the aforementioned insulating element, the insulating element comprising the insulating element portions, wherein at least one of the insulating element portions comprises a flat material having a resistivity of 10. -5 ~10 -1 Ωm, and includes resistivity ρ U Greater than ρ F The fracture surface extends from the outer surface of the flat material into the flat material, but does not produce a fracture surface across the entire cross-section of the flat material.

[0050] The insulating element according to the invention can be fabricated on-site from a set of insulating element parts in a particularly simple manner. This is advantageous when there is insufficient space to transport or install the integrally formed insulating element at its place of use. When multiple individual insulating element parts are braided, an insulating element is formed, thereby creating a joint area through the braiding process. The joint area creates a break in the entire planar material cross-section of the flat material of the individual insulating element parts. However, this is not a break like the flat material itself, but a break in the joint area, thus the resistance in the joint area is substantially not increased. This is especially true if no spacing is provided during bonding.

[0051] Additionally, the present invention relates to a method for producing a flat material that can be used to insulate a high-temperature processed area subjected to induction heating, wherein the resistivity ρ F In 10 -5 ~10 -1 Flat materials within the range of Ωm are cut into the flat material from its main surface without cutting through the entire flat material.

[0052] Furthermore, the present invention relates to the use of an insulating element according to the invention, or to the use of an insulating element formed from a set of insulating element portions according to the invention, the insulating element being used for thermal insulation of a high-temperature processing zone that is induction heated, for example for thermal insulation of a high-temperature processing zone in which glass fibers or single crystals that are melted at temperatures above 1000°C are produced. Attached Figure Description

[0053] The present invention will be illustrated by the following figures, but is not limited thereto.

[0054] Figure 1 This is a perspective view of the first insulating element according to the invention, showing the coil and the base.

[0055] Figure 1A A first insulating element according to the present invention is shown.

[0056] Figure 1BIt is the cross-section passing through the first insulating element according to the invention.

[0057] Figure 1C and Figure 1D The length of the path of the flat material around the first insulating element according to the invention is shown.

[0058] Figure 2A A second insulating element according to the invention is shown.

[0059] Figure 2B It is the cross-section passing through the second insulating element according to the invention.

[0060] Figure 3A A third insulating element according to the invention is shown.

[0061] Figure 3B It is the cross section passing through the third insulating element according to the invention.

[0062] Figure 4A It is the cross-section passing through the fourth insulating element according to the invention, and

[0063] Figure 4B From Figure 4A A portion of the cut-off image. Detailed Implementation

[0064] The four different embodiments of the invention shown in the accompanying drawings are all insulating elements 1 used for thermal insulation of the inductively heated high-temperature processing zone 2. The perspective views of the indicating coil and outer surface 6, as well as the base and inner surface, only show the first embodiment. Figure 1 The other three embodiments can be used in exactly the same manner as indicated herein with respect to the first embodiment.

[0065] Especially Figure 1B , Figure 2B , Figure 3B and Figure 4A As can be clearly seen, the wall of insulating element 2 comprises flat material 3 in all four embodiments. In each case, the wall is made of flat material (with a thermal conductivity significantly lower than 10 W / m²). -1 K -1 It is made of soft carbon fiber felt. The resistivity ρ of the flat material F 10 -5 Up to 10 -1 Ωm. Soft carbon fiber felt surrounds cavity 4, which extends through insulating element 1. The figures also clearly show that the number of breaks 5 in each embodiment shown herein is equal to 12. In any embodiment, none of the breaks extend orthogonally to the two surfaces 6 and 7 of the flat material 3, and all are inclined in the same direction. Each of these breaks is a cut. Therefore, these breaks are electrically insulating.

[0066] exist Figure 1A , Figure 2A and Figure 3A In the diagram, the area of ​​fracture 5 covered by the flat material 3 is shown by dashed lines. The inner surface of the flat material covered by the dashed lines is also shown. Due to the air within and the cut carbon fibers, the resistivity ρ of fracture 5 is... U The resistivity ρ of soft carbon fiber felt F Several times larger. In all four embodiments, the fracture 5 extends from the outer surface 6 of the flat material 3 into the flat material 3.

[0067] from Figure 1A It can be clearly seen that in the first embodiment, the fracture 5 does not create a fracture along the entire cross-section of the flat material 3. The cut is not made as far as... Figure 1 The two edges 9 and 10 are shown. Therefore, the fracture 5 here is spaced apart from the two edges 9 and 10 of the flat material 3. From Figure 1B It can be clearly seen that in the first embodiment, the cut is not made as far as the inner surface 7. Therefore, the break 5 here is also spaced apart from the inner surface 7.

[0068] Figure 2A The second embodiment shows the cut intersecting with both edges. However, according to the invention, the cut still does not create a break across the entire cross-section of the flat material 3. Figure 2B As can be clearly seen in the first embodiment, the cut is not made as far as the inner surface 7. Here, the break 5 is also spaced apart from the inner surface 7.

[0069] In the third embodiment, the cut was not made as far as both edges ( Figure 3A Therefore, the cut will not create a break across the entire cross-section of the flat material 3. In contrast to the first and second embodiments, the cut in the third embodiment cuts the inner surface 7 (…). Figure 3B ).

[0070] In the first, second and third embodiments, the flat material 3 is therefore a circumferentially continuous flat material 3 containing carbon fibers.

[0071] For the first embodiment, Figure 1C and Figure 1D The length, shape, and orientation of the fracture 5 at the outer surface of the flat material 3 are shown to be selected such that when a equals 2, L U >a·L t Applicable. Figure 1C L is shown U L UL is the length of the shortest path around the flat material 3, which in each case extends from one fracture 5 to the other in the central cutting plane without passing through the fracture 5 but rather around it. The central cutting plane is orthogonal to the longitudinal axis of the hollow cylinder, dividing the flat material 3 into two equal halves of the flat material volume. t The length of the shortest path around the flat material 3, which extends along the outer surface of the flat material 3 across the fracture 5 in a central cutting plane orthogonal to the longitudinal axis of the hollow cylinder, divides the flat material 3 into two equal halves of flat material volume. Clearly, in the embodiment shown here, L... U For L t About three times the size.

[0072] In the fourth embodiment ( Figure 4A and Figure 4B In this embodiment, the flat material 3 is formed from a set of two flat material elements 11. In the embodiment shown here, two joint regions 12 are also provided between these flat material elements 11. Each joint region creates a break in the entire cross-section of the flat material 3. Therefore, the joint region is formed from one edge to the other along the entire length of the insulating element and cuts through the insulating element along the entire length from the outer surface 6 to the inner surface 7. In contrast to the first, second, and third embodiments, the flat material 3 in the fourth embodiment is therefore not a circumferentially continuous flat material 3 containing carbon fibers.

[0073] List of reference numerals

[0074] 1. Insulating element

[0075] 2 High-temperature processing area

[0076] 3. Flat materials

[0077] 4. Cavity

[0078] 5. Fracture

[0079] 6. Outer surface

[0080] 7. Inner surface

[0081] 8. Cross-section of flat material

[0082] 9, 10 Edges

[0083] 11 Flat material components

[0084] 12. Connector area.

Claims

1. An insulating element (1) for thermally insulating a high-temperature processing zone (2) that can be induction heated, wherein, The wall of the insulating element (1) comprises a flat material (3), the resistivity of which is... ρ F 10 -5 Up to 10 -1 Ωm, the flat material surrounds the cavity (4) extending through the insulating element (1) and includes a break (5) in which the resistivity is Ωm. ρ U Greater than ρ F ,in, ρ U For at least 100 ρ F The fracture (5) extends from the outer surface (6) of the flat material (3) into the flat material (3) but does not create a fracture in the flat material (3) across the entire cross-section of the flat material.

2. The insulating element (1) according to claim 1, wherein, The fracture (5) is a cut (51) made in the flat material (3).

3. The insulating element (1) according to claim 1, wherein, At least a portion of the fracture (5) does not extend orthogonally to the outer surface (6) and inner surface (7) of the flat material (3).

4. The insulating element (1) according to claim 1, wherein, The flat material (3) has a content of less than 10 Wm -1 K -1 The degree of thermal conductivity.

5. The insulating element (1) according to claim 4, wherein, The flat material (3) comprises carbon fiber and / or expanded graphite.

6. The insulating element (1) according to claim 1, wherein, The number of the fractures (5) is greater than or equal to 2.

7. The insulating element (1) according to claim 6, wherein, The number of the fractures (5) is greater than or equal to 3.

8. The insulating element (1) according to claim 7, wherein, The number of the fractures (5) is greater than or equal to 4.

9. The insulating element (1) according to claim 8, wherein, The number of fractures (5) is greater than or equal to 6.

10. The insulating element (1) according to claim 1, wherein, The insulating element can be approximately a hollow cylinder, wherein the length, shape, and orientation of the fracture (5) at the outer surface of the flat material (3) are selected such that the following conditions apply: L u > a L t in, L t The length of the shortest path around the flat material (3) is defined as follows: the shortest path extends along the outer surface of the flat material (3), crosses the fracture (5), and enters the central cutting plane, which is orthogonal to the longitudinal axis of the hollow cylinder, dividing the flat material (3) into two equal flat material volumes. L u The length of the shortest path around the flat material (3) is as follows: in each case, the shortest path extends from one fracture (5) to another fracture (5) in the central cutting plane, but does not cross the fracture (5), but instead bypasses the fracture, and a is 2.

11. The insulating element (1) according to claim 10, wherein, a is 5.

12. The insulating element (1) according to claim 1, wherein, The break (5) is spaced apart from the two edges (9, 10) of the flat material (3).

13. The insulating element (1) according to claim 6, wherein, At least two breaks (5) are inclined in the same direction relative to the outer surface of the flat material (3).

14. The insulating element (1) according to claim 1, wherein, The flat material (3) is a circumferentially continuous flat material (3) containing carbon fibers.

15. The insulating element (1) according to claim 1, wherein, The flat material (3) is formed by a set of flat material elements (11), and at least one joint area (12) is provided between the flat material elements (11) to break the flat material (3) across the entire cross-section of the flat material.

16. A set of insulating element portions for forming an insulating element (1), wherein, The insulating element (1) includes the insulating element portions, wherein at least one of the insulating element portions includes a flat material (3) with a resistivity of ρ F 10 -5 ~10 -1 Ωm and includes a fracture (5), in which the resistivity is ρ U Greater than ρ F ,in, ρ U For at least 100 ρ F The fracture (5) extends from the outer surface (6) of the flat material (3) into the flat material (3) but does not create a fracture in the flat material (3) across the entire cross-section (8) of the flat material.

17. A method for producing a flat material (3), said flat material (3) being usable for insulating a high-temperature processing zone (2) subjected to induction heating, wherein, The resistivity of the flat material (3) ρ F In 10 -5 ~10 -1 Within the range of Ωm, the flat material (3) is cut from the main surface of the flat material (3) into the flat material (3) but not through the entire flat material (3) to form a fracture (5), wherein the resistivity in the fracture (5) is... ρ U Greater than ρ F ,in, ρ U For at least 100 ρ F .

18. The use of an insulating element according to any one of claims 1 to 15 or an insulating element formed from a portion of a set of insulating elements according to claim 16 for thermal insulation of a high-temperature processing zone (2) subjected to induction heating.

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