A method for recycling 3D printed silicon carbide waste

Abstract

The application discloses a 3D printing silicon carbide waste recycling method, comprising the following steps: S1, mechanically crushing the silicon carbide waste containing resin binder to obtain blocky material with a maximum size of less than 10 cm; S2, placing the blocky material in a vacuum defatting device, heating to 500-800 DEG C for vacuum defatting pretreatment to remove the resin binder; S3, placing the blocky material after vacuum defatting in an oxidation treatment device, heating to 900-1000 DEG C for oxidation treatment to completely oxidize the residual carbon; S4, crushing and screening the blocky material after oxidation treatment to obtain green or gray-green silicon carbide recycled powder. The application fundamentally solves the pain points of 3D printing silicon carbide waste recycling by adopting the innovative process of coarse crushing, vacuum defatting, high-temperature oxidation and powderization treatment, and the overall process has low pretreatment cost and small energy consumption; the recycled powder can be directly used for 3D printing slurry preparation again, and low-cost recycling is realized.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide additive manufacturing technology, and in particular to a method for recycling 3D printed silicon carbide waste. Background Technology

[0002] Silicon carbide (SiC) ceramics possess excellent properties such as high hardness, high temperature resistance, corrosion resistance, and good thermal conductivity, making them widely used in aerospace, semiconductor equipment, and the nuclear industry. With the rapid development of additive manufacturing technology, 3D printing processes, such as photopolymerization, direct ink writing, binder jetting, and selective laser sintering, have become effective means of fabricating complex-shaped silicon carbide ceramic components. These processes typically require the introduction of large amounts of organic resin as binders or photosensitive components to shape the silicon carbide powder into a printed preform with a certain strength.

[0003] However, the aforementioned 3D printing process inevitably generates a large amount of resin-containing silicon carbide waste, mainly including: failed printing blanks, removed support structures, and residual materials from cleaning the printing platform. This waste contains 15%–30% by mass of organic resin and additives. Direct disposal not only results in a huge waste of silicon carbide raw materials and increases production costs, but also poses an environmental pollution risk due to the difficulty in degrading the resin components in the natural environment. Therefore, developing efficient silicon carbide 3D printing waste recycling technology to achieve closed-loop recycling of silicon carbide powder has significant economic and environmental value.

[0004] Currently, the existing technologies for recycling resin-containing silicon carbide waste mainly involve the following approaches: (1) Chemical solvent dissolution method: The waste material is soaked in organic solvents to dissolve the resin and remove it from the surface of silicon carbide particles. This method has problems such as large solvent consumption, high recycling cost, difficulty in solvent recovery, and easy secondary pollution. Moreover, it has limited dissolution effect on cross-linked and cured thermosetting resins, making it difficult to completely remove the resin.

[0005] (2) Direct high-temperature oxidation method: The waste material is crushed and then calcined at high temperature in an air atmosphere to oxidize and decompose the resin and remove it by combustion. Although this method is relatively simple to operate, direct oxidation treatment has obvious shortcomings. First, the resin in the waste material decomposes rapidly at high temperature, producing a large amount of volatile matter and flue gas. If it escapes without sufficient oxidation, it will cause air pollution. Second, the carbon black residue from the pyrolysis of the resin will adhere tightly to the surface and pores of the silicon carbide particles, and it is difficult to be completely oxidized even in an air atmosphere. In practice, it has been found that the recycled material treated by direct air oxidation often appears black or dark gray due to residual carbon (i.e., residual free carbon). When this carbon-containing recycled powder is used to re-formulate the printing paste, it will seriously affect the rheological properties and photocuring characteristics of the paste, which will lead to defects in the printed blank and a significant decrease in the density and mechanical properties of the sintered ceramic parts.

[0006] (3) Mechanical crushing-low temperature degreasing-deep grinding method: After crushing and grinding the waste material into powder of tens of micrometers, it is then degreased and oxidized. Fine particle size is beneficial for resin removal and carbon oxidation, but grinding hard, high-hardness silicon carbide ceramic waste from centimeter-sized blocks to micrometer-sized powder requires a lot of energy, and the grinding media and equipment are severely worn, which significantly increases the recycling cost. Moreover, excessive grinding may introduce impurities, change the original morphology and particle size distribution of silicon carbide particles, and affect the reuse performance of the recycled powder.

[0007] In summary, the core contradiction facing existing silicon carbide 3D printing waste recycling technology lies in the following: if the waste is thoroughly crushed before degreasing and oxidation, although this is beneficial for the removal of organic matter and the oxidation of carbon black, the energy consumption and cost are too high; if the degree of crushing is reduced in order to reduce costs, the resin and carbon black inside the large blocks are difficult to be effectively removed, resulting in the recycled material being black due to carbon residue, which cannot meet the requirements for high-quality reuse. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is: how to completely remove the resin and residual carbon black inside large-sized bulk silicon carbide waste so that the recycled powder can meet the purity requirements for direct use in 3D printing.

[0009] To address the aforementioned technical problems, this invention provides a method for recycling silicon carbide waste from 3D printing, comprising the following steps: S1. Mechanically crush silicon carbide waste containing resin binder to obtain block material with a maximum size of less than 10cm; S2. Place the block material in a vacuum dewaxing device and heat it to 500-800℃ for vacuum dewaxing pretreatment to remove the resin binder; S3. Place the block material after vacuum dewaxing in an oxidation treatment device and heat it to 900~1000℃ for oxidation treatment to completely oxidize the residual carbon. S4. Crush and screen the oxidized material to obtain green or gray-green silicon carbide recycled powder.

[0010] This invention fundamentally solves the pain points of 3D printing silicon carbide waste recycling by adopting an innovative process of coarse crushing, vacuum dewaxing, high-temperature oxidation, and powdering. It can completely remove resin and residual carbon black without fine crushing, and solves the technical problem of difficult removal of organic matter inside large blocks. Vacuum dewaxing greatly reduces the emission of flue gas in the subsequent oxidation stage, and air oxidation completely transforms the waste from black to green or gray-green pure silicon carbide. The overall process has low pretreatment cost and low energy consumption, and the recovered powder can be directly reused in the preparation of 3D printing slurry, realizing low-cost recycling.

[0011] In some preferred or optional embodiments, step S3, after the oxidation treatment is completed, further includes a sub-step: after the material block cools to room temperature in the furnace, its color is observed. If the material block shows a uniform green or grayish-green color, the oxidation treatment is determined to be complete; if the material block is still black or grayish-black, step S3 is repeated for supplementary oxidation treatment. By observing the color of the material block after cooling, a direct and objective endpoint determination basis is provided for the recycling process, avoiding the problems of insufficient processing or over-oxidation caused by equipment differences or fluctuations in operating conditions, ensuring the consistency and high purity of the recovered powder between batches, and eliminating the blindness of processing at fixed times in traditional processes.

[0012] In some preferred or optional embodiments, the oxidation process in step S3 involves heating from room temperature to 900-1000°C at a rate of 1-3°C / min and holding at that temperature for 2-3 hours. The slower heating rate and sufficient holding time ensure that the residual carbon black inside the block material comes into full contact with air and is completely oxidized. This avoids excessively rapid heating that could lead to severe oxidation of the block surface without removing the internal carbon black, and also prevents excessive formation of a silica layer on the surface of the silicon carbide particles. Thus, while thoroughly removing carbon, the original morphology and activity of the silicon carbide particles are maintained, which is beneficial for recovering the powder and re-formulating the slurry.

[0013] In some preferred or optional embodiments, the vacuum dewaxing temperature in step S2 and the oxidation treatment temperature in step S3 satisfy the following relationship: T1 + 250℃ ≤ T2 ≤ T1 + 350℃, where T1 is the vacuum dewaxing temperature and T2 is the oxidation treatment temperature. This achieves optimal energy matching between the pyrolysis and oxidation processes. If the temperature difference is too small, dewaxing will be incomplete, and the residual resin will generate a large amount of smoke and carbon deposits during the oxidation stage; if the temperature difference is too large, it will cause energy waste and may lead to excessive oxidation of the silicon carbide surface. This specific temperature window ensures that the resin is fully vaporized during the dewaxing stage, while only a trace amount of residual carbon needs to be removed during the oxidation stage, achieving the low-energy consumption requirements of industrial production.

[0014] In some preferred or optional embodiments, in step S2, the vacuum degree of the vacuum dewaxing device is ≤10 Pa, the heating rate is 1-5 °C / min, and the holding time is 1-3 hours. High vacuum promotes rapid vaporization and extraction of resin pyrolysis products, reducing secondary tar condensation; a moderate heating rate prevents violent foaming that could cause the material to break apart; and sufficient holding time ensures complete pyrolysis of the resin inside the block material.

[0015] In some preferred or optional embodiments, in step S2, the volatile organic compounds are condensed and recovered from the exhaust port of the vacuum dewaxing device to obtain dewaxed oil byproducts. This transforms potentially polluting or wasteful resin pyrolysis products into valuable byproducts, while avoiding direct emissions of organic compounds that could cause secondary pollution, reducing exhaust gas treatment costs, and making the entire recycling process more environmentally friendly.

[0016] In some preferred or optional embodiments, in step S2, an inert gas with a flow rate of 0.5~2L / min is introduced into the vacuum dewaxing device under negative pressure to carry away the volatiles generated by pyrolysis. The dynamic airflow can forcibly remove the volatiles generated by pyrolysis in the furnace, preventing them from condensing again on the surface of the cooler block material or the furnace wall to form tar deposits, thereby reducing the burden on subsequent oxidation treatment; at the same time, the inert gas protection can avoid unnecessary oxidation of silicon carbide during the high-temperature dewaxing stage, ensuring precise control of subsequent oxidation steps.

[0017] In some preferred or optional embodiments, step S4 specifically includes: ball milling the oxidized green or grayish-green material block using non-metallic grinding media at a speed of 20–50 rpm for 10–30 minutes, followed by sieving through a 100-mesh sieve to obtain green or grayish-green silicon carbide recycled powder. Using non-metallic grinding media for ball milling avoids contamination of the high-purity silicon carbide powder by metallic impurities; the low speed setting avoids excessively fine powder or grain defects caused by over-crushing, ensuring the consistency of the particle size distribution of the recycled powder with that of the virgin material; sieving yields powder with a D50 of 10–150 μm, which directly meets the particle size requirements of 3D printing slurry.

[0018] In some preferred or optional embodiments, the silicon carbide waste containing resin binder originates from at least one of the following processes: photopolymerization 3D printing, inkjet 3D printing, binder jetting 3D printing, and selective laser sintering 3D printing. The recycling method of this invention has broad applicability, covering most current production scenarios for 3D-printed silicon carbide ceramics. Waste generated from different processes can all be recycled in a green and high-purity manner using the same process.

[0019] In summary, compared with the prior art, the present invention has the following beneficial effects: (1) Thorough carbon removal and color transformation: This invention uses a combination of "coarse crushing - vacuum dewaxing - high-temperature oxidation" to completely transform resin-containing silicon carbide waste from black or dark gray to a uniform green or grayish-green pure powder. The vacuum dewaxing stage fully pyrolyzes the resin matrix, and the subsequent air oxidation completely burns away the residual trace carbon black, solving the technical problem of difficult removal of organic matter inside large-sized blocks. The recovered powder has virtually no free carbon residue.

[0020] (2) Significantly reduced pretreatment costs: Only the waste needs to be mechanically crushed into blocks, without the need for fine crushing to micron-sized particles, which greatly reduces crushing energy consumption and equipment wear. This coarse crushing requirement makes the pretreatment process simple and quick, facilitating large-scale continuous production and overcoming the high cost barrier caused by fine grinding in the existing technology.

[0021] (3) Reliable process and synergistic energy saving: Color discrimination is introduced as the basis for the end point of oxidation treatment, eliminating the risk of insufficient treatment or over-oxidation caused by equipment differences and operating condition fluctuations, and ensuring batch-to-batch consistency. At the same time, the vacuum dewaxing temperature and oxidation temperature are limited to meet a specific temperature difference relationship, so as to achieve energy matching between pyrolysis and oxidation, avoid excessive oxidation load or energy waste, and prevent excessive oxidation of silicon carbide surface.

[0022] (4) Environmental and resource benefits: Volatile organic compounds are condensed and recovered during the vacuum dewaxing process to obtain dewaxed oil byproducts, which can be reused as fuel or chemical raw materials, avoiding secondary pollution. Inert gas dynamic purging is preferred to prevent secondary tar deposition, further reduce flue gas generation and tail gas treatment burden, and achieve clean production.

[0023] (5) The recycled powder can be directly reused and has a wide range of applications: After light ball milling and sieving, the green block material obtained is powder with a suitable particle size distribution, and its morphology and activity are similar to those of the virgin material. It can be directly re-formulated into 3D printing slurry. This method is applicable to waste blanks, support structures and cleaning waste generated by various 3D printing processes such as photopolymerization, direct ink writing, binder jetting and laser sintering. It has good process robustness and industrial promotion value. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating a method for recycling 3D-printed silicon carbide waste in a specific embodiment of the present invention.

[0025] Figure 2 This is a physical image of the silicon carbide waste in Embodiment 1 of the present invention.

[0026] Figure 3 This is a physical image of the silicon carbide recycled powder in Example 1 of the present invention. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0030] The present invention provides a method for recycling silicon carbide waste from 3D printing. Addressing the technical problems in existing technologies, such as incomplete removal of resin and carbon black, the inability to directly reuse the recycled powder due to its black color, and the high cost of pretreatment requiring fine crushing, the method employs a combined process of "coarse crushing—vacuum dewaxing—high-temperature oxidation—light crushing and screening" to completely remove organic matter from large-sized blocky waste materials. This transforms the waste from black to green or grayish-green pure silicon carbide powder, which can then be directly reused in the preparation of 3D printing slurry.

[0031] Combination Figure 1 The process flow diagram shown illustrates that the recycling method of this invention includes the following steps: S1, Mechanical Crushing Silicon carbide waste containing resin binders is mechanically crushed to obtain blocks with a maximum size of less than 10 cm. This step does not require crushing to the micron level; it only disrupts the original billet structure, thus significantly reducing crushing energy consumption and equipment wear.

[0032] In some specific implementations, the waste comes from photopolymerization 3D printing, ink direct writing 3D printing, binder jetting 3D printing, or selective laser sintering 3D printing processes, including scrapped blanks, support structures, overflow, or cleaning waste. The waste shape can be irregular blocks, flat plates, or long strips. It is crushed to a maximum size of less than 10cm by hammering, jaw crushers, or cutting machines, with most block sizes controlled within the range of 3~8cm, which is beneficial for the uniform removal of internal resin during subsequent heat treatment.

[0033] In a specific embodiment, for thick scrap blanks (such as large support structures exceeding 30cm in size), the long strips are first cut with a cutting machine, and then hammered into small pieces less than 10cm in size. This coarse crushing process does not require strict control of particle size distribution, allowing for a certain degree of size variation, which facilitates rapid batch processing.

[0034] S2, Vacuum dewaxing pretreatment The crushed block material is placed in a vacuum dewaxing device and heated to 500~800℃ under vacuum conditions for vacuum dewaxing pretreatment to remove most of the resin binder and low molecular weight organic matter from the waste material.

[0035] In some specific embodiments, the vacuum degree of the vacuum dewaxing device is controlled at ≤10Pa, the heating rate is 1~5℃ / min, and the holding time is 1~3 hours. High vacuum promotes rapid vaporization and extraction of resin pyrolysis products, reducing secondary tar condensation; a moderate heating rate prevents violent foaming that could cause material fragmentation; and sufficient holding time ensures complete resin pyrolysis inside blocks smaller than 10cm. After vacuum dewaxing, the waste changes from black to dark gray-black, with a mass reduction of approximately 5%~15%, forming resin pyrolysis carbon, which facilitates subsequent oxidation and combustion treatment.

[0036] In some specific embodiments, the vacuum dewaxing temperature is preferably 600~700℃, and the holding time is preferably 2 hours. Within this temperature window, the resin pyrolysis is more complete, resulting in less residual carbon black and reducing the burden on subsequent oxidation stages.

[0037] In some specific embodiments, during the vacuum dewaxing process, the volatile organic compounds are condensed and recovered from the exhaust port of the vacuum dewaxing device to obtain dewaxed oil as a byproduct. This dewaxed oil, after simple filtration, can be used as a calorific value fuel or chemical raw material, realizing the resource utilization of organic matter and avoiding secondary pollution caused by direct emissions.

[0038] In some specific embodiments, an inert gas (such as nitrogen or argon) at a flow rate of 0.5~2L / min is introduced into the vacuum dewaxing device under negative pressure to rapidly expel the volatiles generated by pyrolysis, preventing secondary condensation and tar deposition on the surface of the lumpy material or the furnace wall. The dynamic airflow can forcibly remove the volatiles, while the inert gas can prevent unnecessary oxidation of silicon carbide during the high-temperature dewaxing stage.

[0039] S3, High-temperature oxidation treatment The vacuum-dewaxed block material (without any intermediate crushing or grinding) is placed directly into an oxidation treatment device (such as a muffle furnace) and heated to 900~1000℃ in an air atmosphere for oxidation treatment, so that the residual carbon is completely oxidized and burned, and the color of the waste changes from dark gray-black to uniform green or gray-green.

[0040] In some specific embodiments, the oxidation process involves heating from room temperature to 900-1000°C at a rate of 1-3°C / min, and holding at that temperature for 2-3 hours. The slower heating rate and sufficient holding time ensure that the residual carbon black inside the block material comes into full contact with the air and is completely oxidized, while avoiding excessive oxidation of the block surface due to rapid heating without removing the internal carbon black, and preventing excessive formation of a silica layer on the surface of the silicon carbide particles.

[0041] In some preferred embodiments, the vacuum dewaxing temperature T1 in step S2 and the oxidation treatment temperature T2 in step S3 satisfy the following relationship: T1 + 250℃ ≤ T2 ≤ T1 + 350℃. This temperature window ensures that the resin is fully vaporized during the dewaxing stage, and only trace amounts of residual carbon need to be treated during the oxidation stage, achieving energy matching between pyrolysis and oxidation. For example, when T1 = 600℃, T2 should be controlled between 850 and 950℃; when T1 = 700℃, T2 should be controlled between 950 and 1000℃.

[0042] In some preferred embodiments, after step S3, a color determination sub-step is included: after the material block cools naturally to room temperature with the furnace, it is taken out and its color is observed. If the material block is uniformly green or grayish-green, the oxidation treatment is considered complete, and the next step can be carried out; if the material block is still black or grayish-black, it is put back into the oxidation treatment device, and step S3 is repeated for supplementary oxidation treatment (the holding time can be appropriately extended) until the color meets the standard. This color determination provides an intuitive and objective basis for determining the endpoint of the recycling process, avoiding problems of insufficient or excessive oxidation caused by equipment differences or fluctuations in operating conditions.

[0043] S4. Crushing and Screening The green or grayish-green material blocks obtained after oxidation treatment are lightly crushed and screened to obtain green or grayish-green silicon carbide recycled powder.

[0044] In some specific embodiments, non-metallic grinding media (such as alumina balls, silicon carbide balls, or zirconium oxide balls) are used to ball mill the material blocks. The ball milling speed is controlled at 20-50 rpm, and the ball milling time is 10-30 minutes, after which the material is passed through a 100-mesh sieve. Low-speed, short-time ball milling only disperses the loose agglomerates of the blocky material without further grinding the original silicon carbide particles, thereby maintaining its original particle size distribution and morphology, which is beneficial to the rheological properties and sintering activity when reformulating the slurry.

[0045] In some specific embodiments, the sieved powder is further washed with deionized water until the conductivity of the washing solution is ≤10μS / cm, and then dried at 80~120℃ to obtain dry green silicon carbide recycled powder. The particle size D50 of this powder is 10~150μm, and it can be directly used to re-formulate 3D printing slurry.

[0046] The technical effects of the present invention will be described below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the embodiments of this application are all obtained through commercial means.

[0047] Example 1 Raw material: Failed photopolymerized silicon carbide ceramic preforms from 3D printing, such as... Figure 2 As shown, it is black in appearance and contains approximately 18 wt% resin binder.

[0048] The waste recycling process is as follows: (1) Coarse crushing: The billet is crushed into blocks with a maximum size of less than 10cm by a jaw crusher, with the actual size ranging from 3 to 8cm.

[0049] (2) Vacuum dewaxing: The block material was placed in a vacuum dewaxing furnace, the vacuum was reduced to 8 Pa, and the temperature was increased to 750℃ at 3℃ / min and held for 2 hours. After dewaxing, the block material was dark gray-black and the mass decreased by 10.5%. About 35 mL / kg of yellow dewaxing oil was collected from the exhaust port.

[0050] (3) High-temperature oxidation: After dewaxing, the blocks are placed directly into a muffle furnace in an air atmosphere and heated to 950°C at a rate of 2°C / min. The temperature is maintained for 2.5 hours and then allowed to cool naturally. After removal, all blocks are uniformly grayish-green.

[0051] (4) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0052] Result: Grayish-green silicon carbide recycled powder was obtained, with an appearance similar to... Figure 3 As shown, the yield is approximately 96.2%. XRD analysis of the powder revealed that it is primarily composed of the SiC phase, with no obvious crystalline impurities detected, indicating high phase purity; the D50 is approximately 100 μm. This powder can be reformulated into a photocurable slurry for the preparation of 3D printed silicon carbide ceramics.

[0053] Example 2 Raw material: failed silicon carbide ceramic preform for photopolymerization 3D printing, resin content approximately 22wt%, maximum size of broken pieces approximately 9cm.

[0054] The waste recycling process is as follows: (1) Coarse crushing: The billet is crushed into blocks with a maximum size of less than 10cm by a jaw crusher, and the actual size is distributed between 4 and 9cm.

[0055] (2) Vacuum dewaxing: The block material is placed in a vacuum dewaxing furnace, the vacuum degree is evacuated to 10 Pa, the temperature is increased to 500℃ at 2℃ / min, and the temperature is held for 3 hours. After dewaxing, the block material is blackish-gray and the mass is reduced by 14.8%.

[0056] (3) High-temperature oxidation and color identification: The dewaxed blocks were placed directly into a muffle furnace in an air atmosphere and heated to 900°C at a rate of 2°C / min. The temperature was maintained for 1 hour, and then allowed to cool naturally. After removal, the color was observed. It was found that some blocks were still partially grayish-black and had not achieved a uniform green color. These substandard blocks were picked out and placed back into the muffle furnace. The temperature was increased to 950°C at a rate of 2°C / min, and oxidation was carried out for another hour. After cooling again, all blocks turned into a uniform grayish-green color.

[0057] (4) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0058] Results: A grayish-green recycled silicon carbide powder was obtained, with SiC as the main phase and a yield of approximately 95.5% and a D50 of approximately 100 μm. Without color discrimination and supplementary oxidation, grayish-black particles would be mixed into the powder after the mixed treatment, resulting in an overall light gray color.

[0059] Example 3 Raw materials: binder-jet 3D printing silicon carbide support waste, resin content approximately 20wt%, initial block maximum size 12cm.

[0060] The waste recycling process is as follows: (1) Coarse crushing: Cut the long strip structure with a cutting machine, and then hammer it into blocks with a maximum size of less than 10cm, with the actual distribution ranging from 5 to 8cm.

[0061] (2) Vacuum dewaxing: The block material is placed in a vacuum dewaxing furnace, the vacuum degree is reduced to 5 Pa, the temperature is increased to 700℃ at 4℃ / min, and the temperature is maintained for 1.5 hours. After dewaxing, the block material is dark gray-black and the mass is reduced by 7%.

[0062] (3) High temperature oxidation: After dewaxing, the block material is directly put into the muffle furnace, and the air atmosphere is used to raise the temperature at 2℃ / min. When the temperature inside the furnace reaches 720℃, water vapor with a volume concentration of 10% is introduced into the furnace and continued to be introduced for 45 minutes (the temperature continues to rise). After reaching 980℃, the water vapor is stopped, and the temperature is kept for 2 hours and then cooled naturally.

[0063] (4) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0064] Results: Green silicon carbide recycled powder was obtained with a yield of approximately 96.0%, the main phase being SiC, and the D50 being approximately 95 μm.

[0065] Example 4 Raw material: Selective laser sintering 3D printing silicon carbide waste, flat (15cm×10cm×2cm), resin content approximately 15wt%.

[0066] The waste recycling process is as follows: (1) Coarse crushing: The plate is cut into blocks with a maximum size of less than 10cm using a cutting machine, with the actual size being 3~5cm.

[0067] (2) Vacuum dewaxing: Place the block material in a vacuum dewaxing furnace and evacuate to 6 Pa. Increase the temperature to 600°C at 3°C / min and hold for 2 hours. During the heating process, introduce nitrogen gas from the bottom of the furnace at a flow rate of 1.2 L / min, while maintaining the absolute pressure inside the furnace at ≤100 Pa. After dewaxing, there is no tar deposit on the furnace wall and the surface of the block material.

[0068] (3) High-temperature oxidation: After dewaxing, the block material is directly placed into a muffle furnace, in an air atmosphere, and heated to 950°C at 2°C / min, held for 2.5 hours, and then cooled naturally.

[0069] (4) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0070] Results: Gray-green recycled silicon carbide powder was obtained with a yield of approximately 96.8%, the main phase being SiC, and the D50 being approximately 90 μm.

[0071] Example 5 Raw materials: Waste material from large silicon carbide ceramic support structures for photopolymerization 3D printing, with original dimensions of approximately 35cm × 20cm × 15cm and resin content of approximately 20wt%.

[0072] The waste recycling process is as follows: (1) Coarse crushing: Use a cutting machine to cut large pieces of waste into several blocks, with the maximum size controlled at 9~10cm. The cross-section of the block shows that the inside is black.

[0073] (2) Vacuum dewaxing: The block material is loaded into a vacuum dewaxing furnace, the vacuum degree is evacuated to 10 Pa, the temperature is increased to 800℃ at 5℃ / min, and the temperature is held for 1 hour. After dewaxing, the block material is dark gray-black and the mass is reduced by 8.5%.

[0074] (3) High temperature oxidation: After dewaxing, the block material is directly put into the muffle furnace, in air atmosphere, and heated to 1000℃ at 2℃ / min, held for 3 hours, and then cooled naturally.

[0075] (4) Crushing and screening: Silicon carbide ceramic grinding media are used, the ball mill speed is 20 rpm, the ball milling time is 30 minutes, the material is passed through a 100-mesh sieve, washed with deionized water, and dried at 100℃.

[0076] Results: Gray-green recycled silicon carbide powder was obtained with a yield of 95.8%, the main phase being SiC, and the D50 being approximately 80 μm.

[0077] Comparative Example 1 Raw materials: Waste silicon carbide ceramic blanks from the same batch as in Example 1.

[0078] The waste recycling process is as follows: (1) Coarse crushing: The billet is crushed into blocks with a maximum size of less than 10cm by a jaw crusher, with the actual size ranging from 3 to 8cm.

[0079] (2) High-temperature oxidation: The block material is directly put into the muffle furnace, in air atmosphere, heated to 950℃ at 2℃ / min, held for 2.5 hours, and then cooled naturally.

[0080] (3) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0081] Results: The oxidation process produced a large amount of dense smoke. After removal, the surface of the material block was grayish-black, while the interior remained black. The powder after crushing was dark gray, indicating that the waste material, which had not undergone vacuum dewaxing pretreatment, had insufficient resin pyrolysis, and the carbon black was difficult to completely remove through air oxidation.

[0082] Comparative Example 2 Raw materials: Waste silicon carbide ceramic blanks from the same batch as in Example 1.

[0083] The waste recycling process is as follows: (1) Coarse crushing: The billet is crushed into blocks with a maximum size of less than 10cm by a jaw crusher, with the actual size ranging from 3 to 8cm.

[0084] (2) Low-temperature air calcination: Place the block material into a muffle furnace, in an air atmosphere, heat to 600℃ at 2℃ / min, hold for 4 hours, and then cool naturally.

[0085] (3) Crushing and screening: Alumina ceramic grinding media are used, the ball mill speed is 40 rpm, the ball milling time is 20 minutes, the material is passed through a 200-mesh sieve, washed with deionized water, and dried at 100℃.

[0086] Result: The powder was black, and the resin was carbonized but not oxidized and removed.

[0087] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A method for recycling silicon carbide waste from 3D printing, characterized in that, Includes the following steps: S1. Mechanically crush silicon carbide waste containing resin binder to obtain block material with a maximum size of less than 10cm; S2. Place the block material in a vacuum dewaxing device and heat it to 500-800℃ for vacuum dewaxing pretreatment to remove the resin binder; S3. Place the block material after vacuum dewaxing in an oxidation treatment device and heat it to 900~1000℃ for oxidation treatment to completely oxidize the residual carbon. S4. Crush and screen the oxidized material to obtain green or gray-green silicon carbide recycled powder.

2. The recycling method according to claim 1, characterized in that, In step S3, after the oxidation treatment is completed, a sub-step is also included: after the material block cools to room temperature with the furnace, observe its color. If the material block shows a uniform green or grayish-green color, the oxidation treatment is determined to be completed; if the material block is still black or grayish-black, step S3 is repeated for supplementary oxidation treatment.

3. The recycling method according to claim 1, characterized in that, In step S3, the oxidation process is as follows: the temperature is increased from room temperature to 900-1000℃ at a rate of 1-3℃ / min, and held at that temperature for 2-3 hours.

4. The recycling method according to claim 1, characterized in that, The vacuum dewaxing temperature in step S2 and the oxidation treatment temperature in step S3 satisfy the following relationship: T1+250℃≤T2≤T1+350℃, where T1 is the vacuum dewaxing temperature and T2 is the oxidation treatment temperature.

5. The recycling method according to claim 1, characterized in that, In step S2, the vacuum degree of the vacuum dewaxing device is ≤10Pa, the heating rate is 1~5℃ / min, and the holding time is 1~3 hours.

6. The recycling method according to claim 1, characterized in that, In step S2, the volatile organic compounds are condensed and recovered from the exhaust port of the vacuum dewaxing device to obtain dewaxed oil byproduct.

7. The recycling method according to claim 6, characterized in that, In step S2, an inert gas with a flow rate of 0.5~2L / min is introduced into the vacuum dewaxing device under negative pressure to carry away the volatiles generated by pyrolysis.

8. The recycling method according to claim 1, characterized in that, Step S4 specifically includes: using non-metallic grinding media to ball mill the green or grayish-green material blocks after oxidation treatment, with a ball milling speed of 20-50 rpm and a ball milling time of 10-30 minutes, and then passing it through a 100-mesh sieve to obtain green or grayish-green silicon carbide recycled powder.

9. The recycling method according to any one of claims 1-8, characterized in that, The silicon carbide waste containing resin binder originates from at least one of the following processes: photopolymerization 3D printing, ink direct writing 3D printing, binder jetting 3D printing, and selective laser sintering 3D printing.

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