High-temperature component and method for the production thereof

Abstract

The invention relates to a high-temperature component (10) and to a method for producing a high-temperature component, in particular a resistance heating element (11) or the like, wherein a dimensionally stable green body of the high-temperature component is formed from a composite material by means of an additive manufacturing method, wherein the dimensionally stable green body is formed by means of pyrolysis of the composite material to form the high-temperature component, wherein the composite material is formed from a material mixture of a carbon material, a polymer cross-linkable binder material and a cross-linking agent, wherein the binder material is cross-linked during or after the green body has been formed by means of the additive manufacturing method.

Description

[0001] High-temperature component and manufacturing process

[0002] The invention relates to a method for manufacturing a high-temperature component and a high-temperature component, in particular a resistance heating element or the like, wherein a dimensionally stable green body of the high-temperature component is formed from a composite material by means of an additive manufacturing process, wherein the dimensionally stable green body is formed into the high-temperature component by means of a pyrolysis of the composite material.

[0003] High-temperature components, and especially resistance heating elements, are regularly used in applications where the component is subjected to very high temperatures, for example, up to 900°C or more. It is essential that the high-temperature component is as homogeneous as possible, sufficiently stable, resistant to frequent temperature changes, and does not release any substances into its environment. Particularly when used as a resistance heating element, this allows for a homogeneous glow pattern and prevents the diffusion of substances from the heating element. Since high-temperature components, or resistance heating elements, can have comparatively complex geometries, it has proven advantageous to manufacture such components using additive manufacturing processes.

[0004] While it is also known to manufacture high-temperature components by machining, for example, graphite blocks, the mechanical processing of complex geometries is comparatively expensive, and depending on the shape of the high-temperature component, residual material from the graphite blocks may be generated. Due to its material value, this is regularly stored for further use and the production of other components. A high-temperature component made of graphite can thus be produced with high density and strength; however, this is also associated with high manufacturing costs, and the shape of the high-temperature component must always be adapted to the available machining processes.

[0005] Additive manufacturing processes, on the other hand, have the advantage that virtually any geometry can be produced with hardly any material residue. Since machining is not necessarily required, high-temperature components can be manufactured cost-effectively using additive manufacturing. One such high-temperature component is known, for example, from DE 10 2017 217 122 Al. Here, the high-temperature component, or resistance heating element, is manufactured by so-called 3D printing of a thermoplastic filled with a carbon material. In 3D printing, a green body is created by building up the thermoplastic layer by layer during the printing process. Specifically, the material mixture of carbon material and thermoplastic is melted and deposited in layers through a nozzle, such that these layers at least partially fuse together.This essentially dimensionally stable green body is carbonized by pyrolysis in an oven, whereby the thermoplastic is then at least partially converted into carbon.

[0006] However, as has been shown, a disadvantage of this process is that subsequent heating of the green body during pyrolysis can lead to softening of the thermoplastic, which means that the dimensional stability of the green body is not always guaranteed. Depending on the shape of the green body, undesirable deformation of the green body can occur during corresponding temperature treatment.

[0007] EP 3 380 324 B l also discloses a method for 3D printing a high-temperature component, in which a green body is produced by applying liquid binder material to a powder bed of carbon material. After the binder material has dried or hardened, the green body is complete and can be carbonized. However, high-temperature components produced in this way are comparatively porous, as the binder material dries out or is expelled during carbonization. In particular, the carbonized green body is also intended to be infiltrated with silicon. Furthermore, the green body printed in the powder bed is relatively fragile and has low strength, which complicates handling during the manufacturing process.If a sufficiently stable and dimensionally accurate high-temperature component with high density is to be manufactured, the known manufacturing process of machining a block of material must be used.

[0008] The present invention therefore aims to propose a method for manufacturing a high-temperature component and a high-temperature component that enables efficient manufacturing with high quality. This objective is achieved by a method with the features of claim 1 and a high-temperature component with the features of claim 17.

[0009] In the inventive method for producing a high-temperature component, in particular a resistance heating element or the like, a dimensionally stable green body of the high-temperature component is formed from a composite material by means of an additive manufacturing process, wherein the dimensionally stable green body is formed into the high-temperature component by means of a pyrolysis of the composite material, wherein the composite material is formed from a material mixture of a carbon material, a polymer-linkable binder material and a crosslinking agent, wherein the binder material is crosslinked during or after the formation of the green body by means of the additive manufacturing process.

[0010] Additive manufacturing makes it possible, in principle, to create any desired shape for a high-temperature component. A high-temperature component, as defined here, is one that can be used at temperatures ranging from 20°C to 3,000°C, preferably from 300°C to 3,000°C. Because the composite material for forming the green body is produced using 3D printing from a mixture of carbon material, a polymer-linkable binder as the matrix material, and a crosslinking agent, it is possible to crosslink the binder material during or after the formation of the green body, thereby permanently and irreversibly solidifying it.

[0011] The polymeric binder material is cross-linked by the cross-linking agent added to the material mixture. It is initially irrelevant whether the cross-linking of the binder material occurs during the formation of the green body, i.e., during 3D printing, or after the green body's shape has been formed by 3D printing. Since the binder material or matrix material of the green body is fully cross-linked, the green body produced according to the invention is significantly more stable in a high-temperature process than, for example, a green body formed with only one thermoplastic or several thermoplastics without cross-linking as the matrix material. The cross-linking of the polymeric binder material allows for a particularly strong bond between the layers of the green body produced by 3D printing. During pyrolysis of the composite material, deformation of the green body due to softening of the binder material at higher temperatures no longer occurs.At the same time, no drying or extrusion of the binder material is involved, which could increase the porosity of the green body or the finished high-temperature component. Overall, this allows for the cost-effective and simple production of a high-temperature component with comparatively high density and stability. Furthermore, the high-temperature component can have complex and intricate geometries, while simultaneously significantly reducing the number of potential rejects during its production.

[0012] Suitable binders or binder components include synthetic resin, natural resin, biomass, cellulose, highly cross-linked aromatic compounds, pitch, at least a fraction of pitch, coal tar pitch, tar resin, petroleum-derived binder, petroleum pitch, bitumen, or at least a fraction of bitumen, particularly a fraction containing oligomers. A comparatively high oligomer content in the pitch or bitumen makes it particularly suitable for polymer cross-linking. Other fractions of the pitch or bitumen that do not contribute to polymer cross-linking need not be present. Furthermore, it is especially advantageous that a large portion of the pitch or bitumen is converted into carbon during the pyrolysis of the green body. This makes it possible to significantly increase the carbon content of the high-temperature component and reduce porosity.Sulfur, a hardener, or an oxidizing agent can be used as a crosslinking agent. Using sulfur as a crosslinking agent allows crosslinking to occur under the influence of heat, although the temperature does not need to be high enough to cause deformation of the green body. Alternatively or additionally, oxidative crosslinking can be carried out during a heat treatment of the green body in air. The oxidizing agent can then be used as an oxidizer.

[0013] Suitable carbon materials include graphite, synthetic graphite, natural graphite, mesophase, anthracite, coke, pitch coke, acetylene coke, carbon black, activated carbon, pyrocarbon, carbon fibers, carbon fibers derived from precursors such as natural fibers or hemp fibers, graphene, and / or carbon nanotubes. These carbon materials are available in powder form, simplifying the preparation of the material mixture. Furthermore, the choice of one or more of these carbon materials can influence the material properties of the finished high-temperature component. In particular, the use of carbon materials allows for a particularly high carbon content in the high-temperature component. It is also possible to use carbon materials as the predominant component in the material mixture.Any potential shrinkage of the high-temperature component during pyrolysis can thus be significantly reduced.

[0014] The material mixture can be formulated with at least one additive, preferably talc. In principle, it is also possible to add organic materials to the mixture that can be converted to carbon through pyrolysis. The additive(s) added to the material mixture can be selected to adapt the mixture and its properties to the specific additive manufacturing process used. The material mixture can consist of 20 to 80 wt.%, preferably 41 to 69 wt.%, carbon material; 21 to 70 wt.%, preferably 25 to 40 wt.%, binder material; and > 0 to 20 wt.%, preferably 7 to 13 wt.%, crosslinking agents and / or additives. The high proportion of binder material in the mixture makes the resulting composite material particularly well-suited for additive manufacturing.At the same time, there is no risk that the high proportion of binder material in the composite material will lead to deformation of the green body or an increase in porosity during pyrolysis. It is also particularly advantageous that a high proportion of the binder material can be converted into carbon during pyrolysis, resulting in a high-density, low-porosity high-temperature component.

[0015] The material mixture can be formed by mixing the carbon material, the binder material, and the crosslinking agent. This mixture can then be processed into a filament or granules by extrusion, or into a powder by grinding and / or sieving, resulting in a composite material that is at least partially meltable. The mixing of the carbon material, the binder material, and the crosslinking agent can be carried out in a mixer or by a suitable mixing process. The materials can be present entirely or partially in powder form. During the mixing process, the materials can be kneaded. The mixture can be produced under the influence of heat, so that the resulting composite material can be a solid. The material mixture can then be processed into a filament or granules using an extruder or other suitable equipment.The filament or granules can then be easily processed further in a 3D printer. Crucially, the composite material must still be malleable or meltable at this stage of the manufacturing process, and the binder material must not yet have undergone significant cross-linking. In particular, it may be possible to at least partially cross-link the material mixture to obtain a sufficiently dimensionally stable material. Furthermore, the material mixture may be ground back into a powder. Additionally, the powder can be sieved or homogenized to obtain a particularly fine-grained powder and / or a powder with a homogeneous, defined particle size or particle size distribution. This powder can then be used in powder bed 3D printing. The composite material obtained from the powder mixture through extrusion or grinding may be partially meltable.This makes it possible to use the composite material in an additive manufacturing process and to build up the green body layer by layer. During the build-up of the layers in the additive manufacturing process, they can then adhere to one another.

[0016] Additive manufacturing can be achieved by depositing binder material into a powder bed, for example, by injection molding, particularly using free-jet binder deposition. In this process, which can also be called binder jetting, the binder material is applied in molten form to a powder bed. The powder bed is then formed from the powdered composite material. The powder in the powder bed can therefore already contain portions of binder material, especially if the powder itself consists of the composite material. Furthermore, it is conceivable to mix carbon black or similar substances into the binder material to be injected / printed, thereby increasing the carbon content. The binder material can be added to the material mixture completely or partially by injection molding into the powder bed.Forming the green body within the powder bed makes it possible to produce multiple green bodies simultaneously in a single powder bed, thus significantly simplifying the mass production of high-temperature components. Furthermore, the free-jet binder application allows for the production of particularly delicate green bodies and, consequently, high-temperature components.

[0017] Alternatively, additive manufacturing can be carried out using powder-based melting, in particular melting the binder material in the powder bed, preferably using a laser. The powder bed can then be formed from a powder consisting of the composite material. Using a laser or another radiation source, the powder in the powder bed can be selectively partially melted, and the green body can thus be built up layer by layer.

[0018] Alternatively, additive manufacturing can be achieved by extruding the material mixture, specifically by printing the composite material through a nozzle. Partial melting of the composite material or the binder in the mixture can then occur in an extruder, allowing the softened or pasty composite material to be deposited in layers through the nozzle under pressure. The composite material can be fed to the extruder in the form of filament, granules, or pellets. This additive manufacturing process is particularly suitable for producing large-volume, high-temperature components as well as individual pieces or small batches of high-temperature components.

[0019] The formation of the dimensionally stable, infusible green body can be achieved by crosslinking the binder material through the application of heat and / or oxidizers to the binder and crosslinking agent. Oxidative crosslinking can also be carried out during heat treatment. It is essential that after crosslinking, the green body is infusible, meaning the binder material does not melt and the green body does not soften. Following this treatment, the composite material can then undergo pyrolysis to produce the high-temperature component. Crosslinking of the binder material can be achieved by treating the green body in an oven. It has been found that oven treatment can be advantageous for adjusting the moisture content of the green body and / or driving off substances from it.In the oven, crosslinking can occur partially or completely through the application of temperature. Furthermore, it is possible to perform crosslinking in the oven as a supplement to, or exclusively as the sole treatment. This is advantageous because the atmosphere surrounding the green body can also be influenced by adding or removing gases. It is also possible to set a temperature in the oven that facilitates crosslinking of the binder material.

[0020] Pyrolysis can convert up to 35 wt.%, preferably up to 40 wt.%, and particularly preferably up to 50 wt.% or more, of the binder material into carbon. Pyrolysis can be carried out in a temperature range of 280 °C to 900 °C. The carbon can then be graphite or graphite-like. By converting such a large proportion of binder material to carbon during pyrolysis or carbonization, a high-temperature component with high density or a high carbon content and low porosity can be produced.

[0021] Following pyrolysis, the high-temperature component can undergo high-temperature treatment. This treatment can be carried out in a temperature range of 900 °C to 3,000 °C. The high-temperature treatment can serve, among other things, to remove oxygen, nitrogen, and non-carbon atoms from the component and / or to reorganize the carbon within the component. It can be performed under vacuum or in a protective gas atmosphere. Alternatively, the high-temperature treatment can be carried out in a gas atmosphere, using a gas from which a coating material is deposited. For example, it may also be possible to infiltrate the component and then subject it to the high-temperature treatment or further high-temperature treatments. Infiltration can be achieved, for example, using silicon, tantalum, or similar materials.During high-temperature treatment, the carbon of the high-temperature component can be converted, at least partially, into a carbide.

[0022] The high-temperature component can be coated with silicon carbide or carbon pyrocarbon. The coating can be applied to the surface of the component. This can be done in a furnace or reaction chamber. For example, a CVD coating (chemical vapor deposition) can be used. In CVD coating, a silicon carbide or carbon pyrocarbon layer is applied to the high-temperature component at temperatures of, for example, 700 °C to 1,500 °C. The layer essentially completely surrounds the component. This coating prevents the release of substances from the component during operation.

[0023] The high-temperature component can be manufactured in one piece. This one-piece design eliminates the need to assemble multiple components into the high-temperature part, making it easier to manufacture overall. With a one-piece design of the high-temperature component, the green body can also be manufactured in one piece.

[0024] The high-temperature component according to the invention, in particular a resistance heating element or the like, is formed by means of pyrolysis of a dimensionally stable green body formed by means of an additive manufacturing process from a composite material, wherein the composite material is formed from a material mixture of a carbon material, a polymer-crosslinkable binder material and a crosslinking agent, wherein the binder material is crosslinked during or after the formation of the green body by means of the additive manufacturing process, wherein the high-temperature component has a density > 1.2 g per cm³ 3 , preferably of > 1.6 g per cm 3 , exhibits. For the advantages of the high-temperature component according to the invention, reference is made to the description of advantages of the method according to the invention.

[0025] If the high-temperature component has a density of > 1.2 g per cm³ 3 , preferably of > 1.6 g per cm 3Given its properties, this high-temperature component can be used for tasks or applications for which previously only components made of machined graphite could be used. In particular, the high-temperature component then consists essentially of carbon or graphite, or a graphite-like carbon material with the specified density.

[0026] The high-temperature component can have a specific electrical resistance of 7 to 50 pΩ, preferably 12 to 22 pΩ. The high-temperature component is then advantageously usable as a resistance heating element. Therefore, the high-temperature component can also be a resistance heating element.

[0027] Further advantageous embodiments of a high-temperature component result from the feature descriptions of the dependent claims relating to method claim 1.

[0028] The invention will now be explained in more detail with reference to the accompanying drawing.

[0029] The figure shows a high-temperature component 10, which in the embodiment shown here forms a resistance heating element 11. The high-temperature component 10 is formed in one piece and has a heating conductor 12. At the ends 13 of the resistance heating element 11, two connection surfaces 14 are formed for connecting the resistance heating element 11 to connection contacts of a connection device (not shown here). The high-temperature component 10 is essentially flat and is formed by an additive manufacturing process. To produce the high-temperature component 10, a composite material was formed from a mixture of a carbon material, a polymer-crosslinkable binder material, and a crosslinking agent by mixing these materials.Subsequently, a green body of the high-temperature component was formed from the composite material using an additive manufacturing process, whereby the binder material was crosslinked during or after the formation of the green body by the additive manufacturing process. In the example shown here, pitch or bitumen was used as the binder material and sulfur as the crosslinking agent. During pyrolysis of the dimensionally stable green body, a significant proportion of the binder material was converted into carbon, whereby the green body was not deformed during pyrolysis due to the crosslinking of the binder material. The high-temperature component 10 therefore has a comparatively high density of > 1.6 g per cm³. 3 , exhibiting low porosity and high strength.

Claims

Patent claims 1. Method for producing a high-temperature component (10), in particular a resistance heating element (11) or the like, wherein a dimensionally stable green body of the high-temperature component is formed from a composite material by means of an additive manufacturing process, wherein the dimensionally stable green body is formed into the high-temperature component by means of a pyrolysis of the composite material, characterized in that the composite material is formed from a material mixture of a carbon material, a polymer-linkable binder material and a crosslinking agent, wherein the binder material is crosslinked during or after the formation of the green body by means of the additive manufacturing process.

2. Method according to claim 1, characterized in that the binder material is synthetic resin, natural resin, biomass, cellulose, highly cross-linked aromatic compounds, pitch, at least one fraction of pitch, coal tar pitch, tar resin, petroleum-derived bin- The product used is petroleum pitch, bitumen or at least a fraction of bitumen.

3. Method according to claim 1 or 2, characterized in that sulfur, hardener or an oxidizing agent is used as a crosslinking agent.

4. Method according to one of the preceding claims, characterized in that graphite, synthetic graphite, natural graphite, mesophase, anthracite, coke, pitch coke, acetylene coke, soot, activated carbon, pyrocarbon, carbon fibers, graphene and / or carbon nanotubes are used as the carbon material.

5. Method according to one of the preceding claims, characterized in that the material mixture is formed with at least one additive, wherein talc is preferably used as the additive.

6. Method according to one of the preceding claims, characterized in that the material mixture is formed from 20 to 80 wt.%, preferably 41 to 69 wt.%, carbon material, 21 to 70 wt.%, preferably 25 to 40 wt.%, binder material and > 0 to 20 wt.%, preferably 7 to 13 wt.%, crosslinking agent and / or additives.

7. Method according to one of the preceding claims, characterized in that the material mixture is formed by mixing the carbon material, the binder material and the crosslinking agent. is processed into the at least partially meltable composite material by extrusion into a filament or granules, or by grinding and / or sieving into a powder.

8. Method according to one of the preceding claims, characterized in that the additive manufacturing is carried out by means of applying the binder material in the powder bed, in particular free jet binder application.

9. Method according to one of claims 1 to 7, characterized in that the additive manufacturing is carried out by means of powder bed-based melting, in particular melting of the binder material in the powder bed, preferably by means of a laser.

10. Method according to one of claims 1 to 7, characterized in that the additive manufacturing is carried out by extrusion of the material mixture, in particular by printing the composite material through a nozzle.

11. Method according to one of the preceding claims, characterized in that the formation of the dimensionally stable, infusible green body is effected by crosslinking the binder material by means of temperature action and / or action of oxidizers on the binder material and the crosslinking agent.

12. Method according to one of the preceding claims, characterized in that , that the cross-linking of the binder material takes place by treating the green body in an oven.

13. Method according to one of the preceding claims, characterized in that a proportion of up to [amount] of the binder material is removed by means of pyrolysis. 35 wt.%, preferably up to 40 wt.%, particularly preferably up to 50 wt.% or more, is converted into carbon.

14. Method according to one of the preceding claims, characterized in that a high-temperature treatment of the high-temperature component (10) is carried out after the pyrolysis.

15. Method according to one of the preceding claims, characterized in that the high-temperature component (10) is coated with silicon carbide or pyrocarbon.

16. Method according to one of the preceding claims, characterized in that the high-temperature component (10) is formed in one piece.

17. High-temperature component (10), in particular resistance heating element (11) or the like, wherein the high-temperature component is formed by pyrolysis of a dimensionally stable green body produced by an additive manufacturing process from a composite material, characterized in that the composite material consists of a material mixture of a carbon material, a polymer-linkable binder material and is formed with a crosslinking agent, wherein the binder material is crosslinked during or after the formation of the green body by means of the additive manufacturing process, wherein the high-temperature component has a density of > 1.2 g per cm³ 3 , preferably of > 1.6 g / cm³ 3 , exhibits.

18. High-temperature component according to claim 17, characterized in that the high-temperature component (10) has a specific electrical resistance of 7 to 50 pQm, preferably 12 to 22 pQm.

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