Method for manufacturing a molded part of carbon or graphite using 3D printing

Abstract

The present invention relates to a method for the simple manufacture of carbon or graphite molded parts by means of 3D printing, which is achieved by preparing a flowable polymer mixture composed of a polymer or cellulose that is transparent and polymerizable to UV radiation and a resin that is crosslinkable by UV radiation, in which sugar and / or pulp are mixed into the polymer mixture until it has a consistency that allows it to be loaded into a 3D printer and processed by it, and homogenizing the mixture at room temperature or at an elevated temperature of up to about 60° C., loading the mixture into the 3D printer and printing a molded part layer by layer with the 3D printer while simultaneously acting with UV radiation to crosslink the resin that is crosslinkable by UV radiation layer by layer, cleaning the molded part, placing the molded part pre-cured with UV radiation in an oven and stabilizing the molded part pre-cured with UV radiation in air at a predefined stabilization temperature until all the volatile components are degassed from the prefabricated molded part, and then treating the molded part at high temperature in an oven under protective gas for carbonization or graphitization.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a molded part made of carbon or graphite using 3D printing.

Background Art

[0002] Such molded parts made of graphite, which are also suitable for use at high temperatures, can be any three-dimensional member such as a furnace lining, a building member, or any hollow body, such as a packing, a sliding body, or the like.

[0003] These molded parts cannot generally be manufactured by simply molding carbon black or graphite and then sintering it. Therefore, it is generally necessary to manufacture a suitable composition containing carbon and being moldable. For this purpose, it is usual to mix carbon black, coke or graphite in the form of granules with a suitable binder, such as a thermoplastic binder. Pitch based on coal tar or petroleum pitch, or synthetic resins are also considered as binders.

[0004] These mixtures are then press-molded into so-called green blanks by hydrostatic pressing in a suitable mold. Then, it is necessary to remove this blank from the mold, which is a very important step because the blank may be easily damaged here.

[0005] This blank is then carbonized in a furnace at about 3,000 °C, where the binder is decomposed into volatile components. Carbon and binder coke remain in the form of a porous structure as residues of the binder.

[0006] Alternatively, the green molded part can be placed between each electrode in a furnace or the like as a resistance element and heated by an electric current until it is completely carbonized.

[0007] Such a method is relatively complicated to implement. At this time, it is obvious that the process of taking out the blank part from the mold is important, especially because the strength of the blank part at that time is low. These are, in many cases, rotationally symmetric members manufactured in this way. Complex three-dimensional members including perforations or other openings cannot be manufactured using such a method.

[0008] Finally, the finished carbon member can also be mechanically post-processed, for example, smoothed.

[0009] From EP3359318B1 (Patent Document 1), a method for 3D printing a three-dimensional object is known, which includes the following steps: Providing a suspension containing at least one ceramic material and / or solid carbon-containing material (the carbon-containing material can consist of graphite, graphene, carbon nanotubes, and other allotropes of carbon) from 50 to 95% by weight of the total suspension, and at least 5% by weight of one or more fatty acids of the total suspension; 3D printing the object to be printed using the suspension as a raw material, where the 3D printing process can include a robocasting method, a direct ink writing method, an inkjet printing method, a binder jet method, a selective heat sintering method, a selective laser sintering method, a selective laser melting method, a stereolithography method, a filament printing method, a pellet printing method, a powder printing method, a freeform manufacturing method (Freiformherstellung), rapid prototyping, or a deposition technique from a robotic arm, etc.; Immobilizing the printed material by a method selected from the group consisting of sintering, melting, and / or infiltration of the 3D printed material.

[0010] Here, the relatively low stability of the printed blank part is also important, which is related to the ease of handling it in the subsequent stage before immobilization.

[0011] As yet another publication regarding the general state of the art, WO95 / 32824A1 (Patent Document 3) describes a method for use in casting technology. Using this method, a casting mold made of a thermosetting material is manufactured by the selective immobilization of each layer of a layer of molding material under the action of electromagnetic radiation. The molding material consists of a material inert to electromagnetic radiation and a second material curable by electromagnetic radiation, whereby the molding material is immobilized.

[0012] The first material consists of various sands, carbon sand, fused silica, or metal or ceramic powders, and the second material consists of various resins.

[0013] Furthermore, US2016 / 0114529A1 (Patent Document 4) describes an apparatus for the manufacture of three-dimensional objects, which is performed by laminating layers using a resin crosslinkable by UV radiation and then heat-treating.

[0014] Finally, US2019 / 0047173A1 (Patent Document 5) describes a method and material for the additive manufacturing of a ceramic-containing material. For this purpose, the ceramic-containing material is mixed with a resin curable in a predetermined ratio and applied layer by layer using a 3D printer.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0015] The present invention is based on the problem of providing a method for manufacturing a molded part made of carbon or graphite, which can now be realized particularly easily and enables the manufacture of complex molded parts without mechanical post-processing using 3D printing.

MEANS FOR SOLVING THE PROBLEMS

[0016] The above problems are Prepare a fluid polymer mixture composed of a polymer or cellulose that can transmit UV radiation and is polymerizable, and a resin that can be crosslinked by UV radiation. Here, sugar and / or pulp are mixed into the polymer mixture until the mixture has a viscosity that allows it to be filled into a 3D printer and thereby processed. Homogenize the mixture at room temperature or at an elevated temperature up to about 60 °C. Fill the mixture into a 3D printer. While simultaneously applying UV radiation to crosslink the resin that can be crosslinked by UV radiation layer by layer, print the molded part layer by layer using a 3D printer. Wash the molded part to remove, in particular, liquid residues and foreign particles. Place the molded part in a furnace and stabilize the UV pre-cured molded part in air at a predetermined stabilization temperature until all volatile components are degassed from the prefabricated molded part, and Then, by subjecting the molded part to high-temperature treatment in a furnace under a protective gas for carbonization or graphitization, A method for manufacturing a molded part made of carbon or graphite is achieved.

[0017] The fluid polymer mixture composed of a polymer or cellulose that can transmit UV radiation and is polymerizable may also be mixed with a solvent.

[0018] As the stabilizable polymer, polyacrylonitrile (PAN) that can be dissolved in a solvent is used.

[0019] As the solvent, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or N-methyl-2-pyrrolidone (NMP) is considered, and in this case, (DMSO) is preferred because the health risk is low.

[0020] In the continuation of the present invention, the stabilization of the pre-cured molded part is performed by uniformly heating it to the stabilization temperature in a furnace and then annealing it at a constant temperature for a short time.

[0021] Preferably, the stabilization of the prefabricated shaped part is carried out at a temperature from 200 °C to a maximum of 450 °C and preferably at a temperature of 250 °C over a period of several hours, depending on the size of the shaped part.

[0022] In one form of the invention, the carbonization of the shaped part is carried out in a furnace under a protective gas or in a vacuum at a temperature of about 1,000 °C.

[0023] In yet another form of the invention, graphitization is carried out in a furnace under a protective gas or in a vacuum at a temperature of 2,000 °C or higher, where complete graphitization is carried out at a temperature > 2,500 °C.

[0024] Preferably, the graphitization of the shaped part is carried out under argon as a protective gas at a pressure of 700 mbar or in a vacuum at a heating rate of 1 °C / min.

[0025] The polymer mixture can also be mixed with metal oxides or silicon oxides, so that after prefabrication of the shaped part using a 3D printer and subsequent stabilization thereof, a high-temperature treatment at > 1,000 °C can be carried out to form metal carbides or silicon carbides, provided that care is taken that the mixture does not become opaque to UV radiation, as is the case, for example, when mixing pitch. Metal or silicon oxides are usually UV-transparent, and as a result, UV radiation is transmitted well.

[0026] Alternatively, it is also possible in principle to mix pure silicon or pure metal into the polymer mixture, but in this case, only thin layers can be printed because the penetration depth of UV radiation is very shallow.

Examples

[0027] Hereinafter, the present invention will be described in more detail based on examples.

[0028] In order to manufacture graphite formed parts using a 3D printer, it is first necessary to prepare a polymer mixture composed of a stabilizable polymer and a resin crosslinkable by UV radiation. At this time, sugar and / or pulp are mixed into the polymer mixture until it has a viscosity that enables processing with a 3D printer.

[0029] The fluid polymer mixture made of a polymer or cellulose that can transmit UV radiation and is polymerizable can also be mixed with a solvent such as DMSO.

[0030] As the stabilizable polymer, polyacrylonitrile (PAN) soluble in a solvent is used.

[0031] In principle, it is also possible to use other polymerizable and thus stabilizable polymers or pulp instead of polyacrylonitrile (PAN). The prerequisite is that the polymer or cellulose used transmits UV radiation.

[0032] In principle, it is also possible to dissolve polyacrylonitrile (PAN) in a solvent or completely replace it with pulp.

[0033] As the solvent, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or N-methyl-2-pyrrolidone (NMP) is considered. In this case, DMSO is preferred because of the low health risk.

[0034] The resin crosslinkable by UV radiation can be a DLP photopolymer resin (resin) or an SLA resin (resin), or other suitable resin transparent to UV radiation.

[0035] Additionally, metal oxides such as silicon oxide can also be mixed into the polymer mixture. In this case, care must be taken to ensure that the mixture does not become opaque to UV radiation, for example, as in the case of mixing pitch.

[0036] Next, while simultaneously applying UV radiation to crosslink the UV-sensitive resin layer by layer, the polymer mixture is printed layer by layer using a 3D printer to produce a molded part.

[0037] For crosslinking the UV-sensitive resin layer by layer, the radiation of a data projector is sufficient if the UV filter is removed.

[0038] The pre-cured molded part thus produced is then directly stabilized in air in a furnace at a temperature from 200 °C to a maximum of 450 °C, preferably at a temperature of 250 °C. During this process, volatile components are degassed from the pre-cured molded part.

[0039] Generally, it is only by using a UV-sensitive resin that crosslinks / cures under the action of UV radiation that it becomes possible to print a molded part so that sufficient stability for handling in subsequent manufacturing steps is achieved during the printing process.

[0040] The stabilization of the UV-cured molded part is carried out by uniformly heating the molded part in a furnace to the stabilization temperature until all the volatile components of the mixture are degassed and then annealing at a constant temperature for a short time.

[0041] Preferably, the stabilization is carried out over a period of several hours depending on the size of the molded part.

[0042] For subsequent graphitization, the furnace is further heated to the temperature required for complete graphitization. After the stabilization of the pre-fabricated molded part, it is carbonized in a furnace under a protective gas or in a vacuum at a temperature of about 1,000 °C.

[0043] Alternatively, the pre-fabricated molded part can be graphitized in a furnace under a protective gas or in a vacuum at a temperature of 2,000 °C or higher, in which case complete graphitization can be achieved at a temperature of > 2,500 °C.

[0044] Preferably, the graphitization of the molded part is carried out at a pressure of 700 mbar under argon as a protective gas or in a vacuum at a heating rate of 1 °C / min. In principle, other noble gases such as neon, krypton, and xenon can also be used. This application relates to the invention described in the claims, but the disclosure of this application also includes the following: 1. A method for manufacturing a shaped part of carbon or graphite using 3D printing, comprising: preparing a fluid polymer mixture composed of a polymer or cellulose that can transmit UV radiation and is polymerizable, and a resin that can be crosslinked by UV radiation, wherein sugar and / or pulp are mixed into the polymer mixture until the mixture has a viscosity such that it can be filled into a 3D printer and thereby processed, and homogenizing the mixture at room temperature or at an elevated temperature up to about 60°C, filling the mixture into a 3D printer, and printing the shaped part layer by layer using a 3D printer while simultaneously applying UV radiation to crosslink the resin that can be crosslinked by UV radiation layer by layer, washing the shaped part to remove, in particular, liquid residues and foreign particles, placing the shaped part pre-cured by UV radiation into a furnace and stabilizing the shaped part pre-cured by UV radiation in air at a predetermined stabilization temperature until all volatile components are degassed from the pre-fabricated shaped part, and then subjecting the shaped part to high-temperature treatment in a furnace under a protective gas for carbonization or graphitization, wherein the method is characterized by the above. 2. The method according to 1 above, characterized in that a solvent is mixed into the fluid polymer mixture of a polymer or cellulose that can transmit UV radiation and is polymerizable. 3. The method according to 1 above, characterized in that polyacrylonitrile (PAN) is used as the stabilizable polymer. 4. The method according to 3 above, characterized in that the polyacrylonitrile is dissolved in a solvent. 5. The method according to 4 above, characterized in that dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or N-methyl-2-pyrrolidone (NMP) is used as the solvent, and preferably dimethyl sulfoxide (DMSO) is used. 6. The method according to any one of 1 to 5 above, characterized in that the stabilization of the shaped part pre-cured by UV radiation is carried out by uniformly heating the pre-cured shaped part in a furnace up to a predetermined stabilization temperature and then annealing it at a constant temperature for a short time. 7. The method according to 6., characterized in that the stabilization of the prefabricated shaped part is carried out at a temperature from 200 °C to a maximum of 450 °C, preferably at a temperature of 250 °C, over a period of several hours. 8. The method according to any one of 1. to 7., characterized in that after stabilization, the shaped part is carbonized in a furnace, under a protective gas or in a vacuum, at a temperature of about 1,000 °C. 9. The method according to any one of 1. to 7., characterized in that the prefabricated shaped part is graphitized in a furnace, under a protective gas or in a vacuum, at a temperature of 2,000 °C or higher. 10. The method according to any one of 1. to 7., characterized in that the complete graphitization of the prefabricated shaped part is carried out at a temperature > 2,500 °C, under a protective gas or in a vacuum. 11. The method according to any one of 7. to 9., characterized in that the carbonization or graphitization of the prefabricated shaped part is carried out at a pressure of 700 mbar, under argon as the protective gas, with a heating rate of 1 °C / min. 12. The method according to any one of 1. to 10., characterized in that a metal oxide or a silicon oxide is mixed into the polymer mixture, and thus, after the prefabrication of the shaped part using a 3D printer and the subsequent stabilization thereof, a high-temperature treatment can be carried out at > 1,000 °C to form a metal carbide or a silicon carbide.

Claims

1. A method for manufacturing a carbon or graphite shaped part using 3D printing, comprising: preparing a fluid polymer mixture composed of a polyacrylonitrile that is permeable to UV radiation and polymerizable, or cellulose, dissolved in a solvent from dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or N-methyl-2-pyrrolidone (NMP), and a resin crosslinkable by UV radiation, wherein sugar and / or pulp are mixed into the polymer mixture until the mixture can be filled into a 3D printer and thereby processed, and homogenizing the mixture at a temperature up to 60°C, filling the mixture into a 3D printer, and printing the shaped part layer by layer using a 3D printer while simultaneously applying UV radiation to crosslink the resin crosslinkable by UV radiation layer by layer, washing the shaped part to remove, in particular, liquid residues and foreign particles, placing the shaped part pre-cured by UV radiation into a furnace and stabilizing the shaped part pre-cured by UV radiation in air at a predetermined stabilization temperature from 200°C to 450°C until all volatile components are degassed from the prefabricated shaped part, and then heat-treating the shaped part in a furnace under a protective gas or in a vacuum at a high temperature for carbonization or graphitization, The method as claimed in the preceding paragraph, characterized in that.

2. The method according to claim 1, characterized in that the stabilization of the shaped part pre-cured by UV radiation is carried out by uniformly heating the pre-cured shaped part to a predetermined stabilization temperature in a furnace and then annealing it at a constant temperature for a short time.

3. The method according to claim 2, characterized in that the stabilization of the prefabricated shaped part is carried out at a temperature of 250°C over a period of several hours.

4. The method according to any one of claims 1 to 3, characterized in that the shaped part is carbonized in a furnace under a protective gas or in a vacuum at a temperature of 1,000°C after stabilization.

5. The method according to any one of claims 1 to 3, characterized in that the prefabricated shaped part is graphitized in a furnace under a protective gas or in a vacuum at a temperature of 2,000°C or higher, or the complete graphitization of the prefabricated shaped part is carried out under a protective gas or in a vacuum at a temperature > 2,500°C.

6. The method according to claim 4, characterized in that carbonization or graphitization of the prefabricated shaped part is carried out at a heating rate of 1 °C / min under argon as protective gas at a pressure of 700 mbar.

7. The method according to claim 5, characterized in that carbonization or graphitization of the prefabricated shaped part is carried out at a heating rate of 1 °C / min under argon as protective gas at a pressure of 700 mbar.

8. The method according to any one of claims 1 to 3, characterized in that a metal oxide or a silicon oxide is mixed into the polymer mixture, and thus, after prefabrication of the shaped part using a 3D printer and subsequent stabilization thereof, a high-temperature treatment at >1,000 °C can be carried out to form a metal carbide or a silicon carbide.

9. The method according to claim 1, characterized in that the resin crosslinkable by the UV radiation is a DLP photopolymer resin or an SLA resin.