Microwave degreasing method for binder spray-molded green body

Abstract

The invention provides a microwave degreasing method for a binder spray-molded green body, and belongs to the technical field of additive manufacturing post-treatment processes. The microwave degreasing method comprises the following steps: firstly, putting a binder jet-molded blank into microwave heat treatment equipment, and introducing one or more mixed atmospheres of nitrogen, argon and helium; the microwave frequency and the microwave power are adjusted, the green body is controlled to be gradually heated to 600-800 DEG C in a stepped mode, heat preservation is conducted for a period of time, microwave degreasing is conducted, and finally degreasing is completed after the green body is cooled to the room temperature. Compared with a traditional degreasing post-treatment process and an existing microwave vacuum degreasing process, inert atmosphere degreasing and microwave degreasing are combined, cracking and molecule removal of a binding phase of the green body can be accelerated, the degreasing efficiency of the formed green body is remarkably improved, meanwhile, heat treatment energy consumption is greatly reduced, and the heat treatment cost is reduced. And the efficiency and the quality cost are obviously optimized.

Description

Technical Field

[0001] This application relates to the field of additive manufacturing post-processing technology, and in particular to a microwave degreasing method for binder spray-molded preforms. Background Technology

[0002] Additive manufacturing technology, due to its high design freedom and high material utilization, has been applied to the fabrication of various key metal components and high-performance engineering ceramics. Binder spraying is a rapidly developing additive manufacturing technology in recent years, renowned for its rapid prototyping of large-sized structural parts, and widely used in aerospace, automotive, and semiconductor industries. However, binder sprayed preforms often require debinding, de-binding, and sintering densification before final fabrication.

[0003] Conventional debinding techniques primarily employ thermal degradation debinding strategies, where the green body undergoes heat treatment to degrade and remove the internal organic binders. To avoid cracks in the green body during debinding and to reduce the impact of residual carbon impurities on subsequent sintering and densification, traditional debinding and binder removal often requires a low heating rate and a long removal time, resulting in low removal efficiency, incomplete removal, excessively high residual carbon content, and difficulty in avoiding defects such as cracks or low density caused by uneven heating of the green body.

[0004] Improving the efficiency and thoroughness of debinding processes and reducing crack formation are key to significantly improving the quality and performance of binder-sprayed molded parts. Microwave debinding has already been applied in powder metallurgy and additive manufacturing. Compared with traditional debinding technologies, microwave debinding technology rapidly raises the temperature of the organic binder in the preform through microwave heating. Moreover, microwaves can quickly penetrate into the interior of the preform for heating, achieving a rapid and uniform heating effect both inside and outside the preform, which can greatly improve debinding efficiency. However, current microwave debinding usually uses a vacuum atmosphere. The vacuum itself causes a slow removal rate of organic binders, easily producing residual carbon. Furthermore, prolonged high-temperature treatment can easily lead to secondary cracking, producing harmful substances such as hydrocarbons (methane, ethylene), tar, and residual carbon. Subsequent treatment is difficult, causing significant air and environmental pollution, thus limiting the application of microwave debinding technology. Summary of the Invention

[0005] Based on the above problems, the purpose of this invention is to overcome the shortcomings of current microwave degreasing, which relies heavily on vacuum atmosphere, resulting in low degreasing efficiency and incomplete degreasing. This application combines inert atmosphere degreasing with microwave degreasing. By leveraging the high diffusivity and high permeability of small molecule gases in an inert atmosphere, the volatilization and removal of organic binders in the inner and outer parts of the green body are accelerated, effectively reducing the generation of residual carbon during the degreasing process. This fundamentally solves the problems of low degreasing efficiency and incomplete degreasing caused by existing microwave degreasing technology under vacuum conditions, thereby providing a guarantee for subsequent sintering densification.

[0006] To achieve the above objectives, the present invention provides a microwave degreasing method for binder spray-molded preforms, comprising the following steps: The binder-sprayed preform is placed in a microwave heat treatment apparatus, an inert gas is introduced, the microwave frequency and power are adjusted, and the preform is heated at a rate of 1~3℃ / min to 250~600℃ and held for 15~45 minutes. Then, the temperature is increased at a rate of 3~7℃ / min to 600~800℃ and held for 15~45 minutes for microwave degreasing. Finally, it is cooled to room temperature to complete the degreasing process. The inert gas includes at least one of nitrogen, argon and helium. The inert gas is continuously introduced during the microwave degreasing process to carry away the binder and pyrolysis products quickly and inhibit secondary pyrolysis.

[0007] Preferably, the controlled preform is heated to 250-600 °C at a rate of 1-3 °C / min and held for 15-45 minutes for volatilization of the low-boiling-point binder component; or / and the subsequent microwave degreasing is performed by heating to 600-800 °C at a rate of 3-7 °C / min and holding for 15-45 minutes for pyrolysis of the high-boiling-point binder component.

[0008] Preferably, the microwave frequency is 0.9~2.4 GHz and the microwave power is 1~10 kW. As the actual size of the formed blank increases, the microwave frequency and microwave power can be increased. When the three-dimensional dimensions of the blank are greater than 100mm×100mm×50mm, the microwave frequency is 2.0~2.4 GHz and the power is 8~10 kW.

[0009] Preferably, when the inert gas is a nitrogen-argon mixture, the nitrogen volume content is 30-70 vol.%; or, when the inert gas is a nitrogen-helium mixture, the nitrogen volume content is 10-30 vol.%; or, when the inert gas is an argon-helium mixture, the helium volume content is 50-85 vol.%.

[0010] More preferably, when the inert gas is a nitrogen-argon mixture, the nitrogen volume content is 35-50 vol.%; or, when the inert gas is a nitrogen-helium mixture, the nitrogen volume content is 10-12 vol.%; or, when the inert gas is an argon-helium mixture, the helium volume content is 70-75 vol.%.

[0011] Preferably, the flow rate of the inert gas is 1~4 L / min.

[0012] Preferably, the cooling rate to room temperature is 2~10 °C / min.

[0013] Preferably, the material of the molded blank includes metal, ceramic, or metal-ceramic composite material.

[0014] Preferably, the metallic material includes at least one of Ni-based, Mg-based, Cu-based, Fe-based, Al-based, Ti-based metals and their alloy powders.

[0015] Preferably, the metallic material includes a high-temperature alloy or a hard alloy.

[0016] Preferably, the ceramic material includes at least one of oxide ceramics, nitride ceramics, carbide ceramics, boride ceramics, and silicate ceramics.

[0017] More preferably, the oxide ceramic includes at least one of alumina, zirconium oxide, and silicon oxide; the nitride ceramic includes at least one of aluminum nitride and silicon nitride.

[0018] The beneficial effects of this invention are: (1) Microwave degreasing combined with an inert atmosphere can effectively accelerate the decomposition and discharge of organic binders during microwave heat treatment, reduce the amount of carbon residue after degreasing, and provide a guarantee for subsequent sintering densification. (2) Compared with microwave degreasing under vacuum conditions, this application adopts microwave degreasing under an inert atmosphere. The high diffusivity and high permeability of small molecule gas can significantly accelerate the degreasing time of the blank, greatly improve the efficiency of the degreasing process, reduce the overall heat treatment energy consumption, save production costs, and improve the overall economic benefits.

[0019] (3) This application uses an inert atmosphere. The inert atmosphere isolates oxygen and inhibits oxidation side reactions, reducing the generation of substances such as aldehydes and CO. At the same time, the flowing atmosphere can carry the decomposition products away from the reaction zone as soon as possible, preventing secondary cracking from generating more pollutants (such as benzene series compounds, olefins and polycyclic aromatic hydrocarbons and other toxic by-products), and the efficiency is better. Detailed Implementation

[0020] To further clarify the objectives, technical solutions, and advantages of this invention, the following detailed description, in conjunction with specific embodiments, provides a more comprehensive understanding of the invention. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of protection of this invention.

[0021] Example 1 1. An alumina rectangular blank with an organic binder content of 15 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0022] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce a helium atmosphere at a flow rate of 1L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 1 kW respectively, control the billet to heat up to 400 ℃ at 2 ℃ / min and hold for 20 minutes, and then continue to heat up to 700 ℃ at 3 ℃ / min and hold for 10 minutes for microwave degreasing; 4. Finally, cool to room temperature at 2℃ / min to complete degreasing and obtain the degreased alumina ceramic part formed by binder spraying.

[0023] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0024] Example 2 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 100 mm × 100 mm × 45 mm (length × width × height) was prepared by binder spray molding technology.

[0025] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce a nitrogen-argon mixed atmosphere with a nitrogen content of 50 vol.% at a flow rate of 3 L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 9 kW respectively, and control the billet to heat up to 500 ℃ and 800 ℃ at 3 ℃ / min respectively, and hold for 25 minutes each time for microwave degreasing; 4. Finally, cool to room temperature at 2℃ / min to complete degreasing and obtain the degreased 316L stainless steel metal part formed by adhesive spraying.

[0026] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0027] Example 3 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0028] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce a nitrogen-argon mixed atmosphere with a nitrogen content of 50 vol.% at a flow rate of 3 L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 1 kW respectively, and control the billet to heat up to 500 ℃ and 700 ℃ at 3 ℃ / min respectively, and hold for 15 minutes each for microwave degreasing; 4. Finally, cool to room temperature at 2℃ / min to complete degreasing and obtain the degreased 316L stainless steel metal part formed by adhesive spraying.

[0029] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0030] Example 4 1. An alumina rectangular blank with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0031] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce a nitrogen-argon mixed atmosphere with a nitrogen content of 35 vol.% at a flow rate of 1 L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 1.1 GHz and 8 kW respectively, control the billet to heat up to 250℃ at 1℃ / min and hold for 15 minutes, and then continue to heat up to 630℃ at 7℃ / min and hold for 40 minutes each time for microwave degreasing; 4. Finally, the degreasing is completed by cooling to room temperature at 7℃ / min, resulting in a degreased alumina ceramic part formed by adhesive spraying.

[0032] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0033] Example 5 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0034] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce a nitrogen-helium mixed atmosphere with a nitrogen content of 12 vol.% at a flow rate of 1.5 L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2GHz and 6kW respectively, control the billet to heat up to 300℃ at 2℃ / min and hold for 15 minutes, and then continue to heat up to 650℃ at 6℃ / min and hold for 45 minutes each time for microwave degreasing; 4. Finally, the degreasing is completed by cooling to room temperature at 10℃ / min, resulting in a degreased 316L stainless steel metal part formed by adhesive spraying.

[0035] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0036] Example 6 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0037] 2. Place the binder-sprayed preform into the microwave degreasing furnace cavity, and introduce an argon-helium mixed atmosphere with a helium content of 75 vol.% at a flow rate of 3 L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 6 kW respectively, control the billet to heat up to 480℃ at 2.5℃ / min and hold for 18 minutes, then continue to heat up to 800℃ at 3℃ / min and hold for 30 minutes each time for microwave degreasing; 4. Finally, cool to room temperature at 3℃ / min to complete degreasing and obtain the degreased 316L stainless steel metal part formed by adhesive spraying.

[0038] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0039] Example 7 1. An alumina rectangular blank with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0040] 2. Place the binder-sprayed preform into the microwave degreasing oven cavity and introduce a nitrogen atmosphere at a flow rate of 1L / min; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 1.1 GHz and 8 kW respectively, control the billet to heat up to 250℃ at 1℃ / min and hold for 15 minutes, and then continue to heat up to 630℃ at 7℃ / min and hold for 40 minutes each time for microwave degreasing; 4. Finally, the degreasing is completed by cooling to room temperature at 7℃ / min, resulting in a degreased alumina ceramic part formed by adhesive spraying.

[0041] Before introducing inert gas, a certain vacuum can be drawn first, and then inert gas can be introduced; during the degreasing process (which can also be understood as the glue removal process), inert gas can be introduced while glue is being removed to avoid secondary pyrolysis and the generation of more contaminants.

[0042] Comparative Example 1 1. An alumina rectangular blank with an organic binder content of 15 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0043] 2. Place the binder-sprayed preform into the microwave degreasing oven cavity, and evacuate the cavity to a vacuum level of 1×10⁻⁶. -2 MPa; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 1 kW respectively, control the billet to heat up to 400 ℃ at 2 ℃ / min and hold for 20 minutes, and then continue to heat up to 700 ℃ at 3 ℃ / min and hold for 10 minutes for microwave degreasing; 4. Finally, cool to room temperature at 2℃ / min to complete degreasing and obtain the degreased alumina ceramic part formed by binder spraying.

[0044] Comparative Example 2 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0045] 2. Place the binder-sprayed preform into the microwave degreasing oven cavity, and evacuate the cavity to a vacuum level of 1×10⁻⁶. -2 MPa; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 2.4 GHz and 1 kW respectively, control the billet to heat up to 400 ℃ at 2 ℃ / min and hold for 20 minutes, and then continue to heat up to 700 ℃ at 3 ℃ / min and hold for 10 minutes for microwave degreasing; 4. Finally, cool to room temperature at 2℃ / min to complete degreasing and obtain the degreased 316L stainless steel part formed by adhesive spraying.

[0046] Comparative Example 3 1. A rectangular blank of 316L stainless steel with an organic binder content of 25 vol.% and three-dimensional dimensions of 50 mm × 50 mm × 20 mm (length × width × height) was prepared by binder spray molding technology.

[0047] 2. Place the binder-sprayed preform into the microwave degreasing oven cavity, and evacuate the cavity to a vacuum level of 1×10⁻⁶. -2 MPa; 3. Adjust the microwave frequency and microwave power of the microwave degreasing oven to 1.1 GHz and 8 kW respectively, control the billet to heat up to 300℃ at 2℃ / min and hold for 40 minutes, and then continue to heat up to 650℃ at 6℃ / min and hold for 45 minutes for microwave degreasing; 4. Finally, the degreasing is completed by cooling to room temperature at 7℃ / min, resulting in a degreased 316L stainless steel part formed by adhesive spraying.

[0048] Weight change tests were conducted on the corresponding blanks and degreased parts in Examples 1-6 and Comparative Examples 1-3 of the present invention. The degreasing rate was calculated according to the following formula (1) and compared. The specific test performance results are shown in Table 1.

[0049] (1)

[0050] Among them, W 脱脂件 and W 坯体件 These refer to the thermal weight loss of the blank and the corresponding degreased part within the same temperature range, respectively.

[0051] Table 1. Experimental data and comparative data of Examples 1-7 and Comparative Examples 1-3 of this application.

[0052] As shown in Table 1, the inert atmosphere-assisted microwave degreasing process of this invention can significantly improve the degreasing rate and greatly reduce the residual carbon content. Compared with a single atmosphere, the degreasing rate of a mixed atmosphere is more significant. Different inert gases have different properties. Helium has a high thermal conductivity, which can accelerate the heat diffusion inside the billet and improve the heating efficiency. In addition, helium molecules have a small diameter and a high diffusion coefficient, which can quickly penetrate into the pores inside the billet and accelerate the discharge of binder cracking products (such as small molecule hydrocarbons). Argon has a high density and can form a stable gas layer on the surface of the billet, covering the billet and promoting the discharge of organic matter in deep pores, while preventing external oxygen intrusion and inhibiting oxidation side reactions.

[0053] This application primarily seeks protection for an inert atmosphere-assisted microwave degreasing process for binder spray-molded preforms, with no special restrictions on the preform material.

Claims

1. A microwave degreasing method for binder spray-molded preforms, characterized in that: Includes the following steps: The binder-sprayed preform is placed in a microwave heat treatment apparatus, an inert gas is introduced, and the microwave frequency and power are adjusted. The preform is heated at a rate of 1-3℃ / min to 250-600℃ and held for 15-45 minutes. Then, it is heated at a rate of 3-7℃ / min to 600-800℃ and held for 15-45 minutes for microwave degreasing. Finally, it is cooled to room temperature to complete the degreasing process. The inert gas includes at least one of nitrogen, argon, and helium. The inert gas is continuously introduced during the microwave degreasing process to carry away the binder and pyrolysis products rapidly and inhibit secondary pyrolysis.

2. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: The controlled preform is heated to 250-600 °C at a rate of 1-3 °C / min and held for 15-45 minutes for volatilization of the low-boiling-point binder component; or / and the subsequent heating to 600-800 °C at a rate of 3-7 °C / min and held for 15-45 minutes for microwave degreasing for pyrolysis of the high-boiling-point binder component.

3. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: The microwave frequency is 0.9~2.4 GHz, and the microwave power is 1~10 kW.

4. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: When the three-dimensional dimensions of the blank are greater than 100mm×100mm×50mm, the microwave frequency is 2.0~2.4 GHz and the power is 8~10 kW.

5. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: When the inert gas is a nitrogen-argon mixture, the nitrogen volume content is 30-70 vol.%; or, when the inert gas is a nitrogen-helium mixture, the nitrogen volume content is 10-30 vol.%; or, when the inert gas is an argon-helium mixture, the helium volume content is 50-85 vol.%.

6. The microwave degreasing method for adhesive spray-molded preforms according to claim 5, characterized in that: When the inert gas is a nitrogen-argon mixture, the nitrogen volume content is 35-50 vol.%; or, when the inert gas is a nitrogen-helium mixture, the nitrogen volume content is 10-12 vol.%; or, when the inert gas is an argon-helium mixture, the helium volume content is 70-75 vol.%.

7. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: The inert gas flow rate is 1~4 L / min, or / and, and the cooling rate to room temperature is 2~10 ℃ / min.

8. The microwave degreasing method for adhesive spray-molded preforms according to claim 1, characterized in that: The material of the molded blank includes metal, ceramic or metal-ceramic composite material.

9. The microwave degreasing method for adhesive spray-molded preforms according to claim 8, characterized in that: The metallic material includes at least one of Ni-based, Mg-based, Cu-based, Fe-based, Al-based, Ti-based metals and their alloy powders.

10. The microwave degreasing method for binder-sprayed preforms according to claim 8, characterized in that: The ceramic material includes at least one of oxide ceramics, nitride ceramics, carbide ceramics, boride ceramics, and silicate ceramics.

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