Method for preparing isostatically pressed graphite from waste graphite electrodes

Abstract

This invention discloses a method for preparing isostatically pressed graphite from waste graphite electrodes, comprising the following steps: cleaning the waste graphite negative electrode, purification, grinding, kneading, isostatic pressing, calcination, and graphitization. Using waste graphite negative electrodes as raw materials not only reduces production costs, but also because the waste graphite negative electrodes themselves possess excellent performance. Furthermore, the degree of graphitization of the waste graphite negative electrodes is high, with minimal shrinkage during calcination, minimal porosity generation, and no need for impregnation, effectively reducing production costs and shortening production time. Additionally, the binder used is fluorinated asphalt, which decomposes during calcination to generate fluorine gas for further product purification, thus eliminating the need for a second purification step after graphitization to obtain a high-purity graphitized product.

Description

Technical Field

[0001] This invention relates to the field of graphite technology, and in particular to a method for preparing isostatically pressed graphite from waste graphite electrodes. Background Technology

[0002] Isostatic graphite is produced by mixing crushed aggregates with a binder at high temperature and kneading to uniformly coat the aggregates with the binder, forming a paste. The aggregates can be graphite or graphitizable products, and the binder can be asphalt or resin, etc. The paste is then crushed into small particles of suitable size, filled into an elastic mold and sealed. The elastic mold is then placed in an isostatic pressing container, where isostatic pressure is applied to press the paste powder into a green body. Finally, the green body undergoes a firing-impregnation-firing-graphitization process to completely transform the aggregates and binder into a graphite product, thus obtaining isostatic graphite.

[0003] Isostatic graphite possesses excellent properties such as high density, high purity, high strength, excellent electrical and thermal conductivity, high temperature resistance, corrosion resistance, and thermal shock resistance. Its products have a wide range of applications, including nuclear energy, semiconductors, EDM, and hot-bent glass. However, during the use of isostatic graphite products, some damage or product replacement inevitably occurs, resulting in waste. Although these waste products are visually damaged, they still retain the excellent properties of isostatic graphite. If they can be recycled, not only can costs be saved, but the performance of the products can also be guaranteed. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies of the existing technology, and its main objective is to provide a method for preparing isostatic graphite from waste graphite electrodes. The method uses waste graphite electrodes as raw materials, first purifies the raw materials, then uses fluorinated pitch as a binder, and then further purifies the product in the subsequent calcination and graphitization stages to obtain high-purity isostatic graphite.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing isostatically pressed graphite from waste graphite electrodes includes the following steps:

[0007] (1) Place the waste graphite electrode in purified water and clean it with the aid of an ultrasonic instrument for 10-30 minutes. Then put it in a muffle furnace to dry it and obtain the cleaned waste graphite electrode.

[0008] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 1-4h to obtain the purified waste graphite electrode.

[0009] (3) The purified waste graphite electrode obtained in step (2) is put into a vertical roller mill for grinding to obtain raw material powder;

[0010] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0011] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder;

[0012] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0013] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20-50 min, remove the pressure, and obtain the isostatic graphite green blank.

[0014] (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 280-320℃ at a uniform rate and held for 5-20 hours. Then, the temperature is raised to 600-630℃ at a uniform rate and held for 5-20 hours. Then, the temperature is raised to 1000-1150℃ at a uniform rate and held for 10-25 hours. Finally, the temperature is lowered to room temperature at a uniform rate to obtain the isostatic graphite calcined green body.

[0015] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0016] As a preferred embodiment, in step (1), the drying temperature is 250°C and the drying time is 3-6 hours.

[0017] As a preferred embodiment, the waste graphite electrode in step (1) is an EDM waste graphite electrode.

[0018] As a preferred option, the strong oxidizing gas in step (2) is chlorine.

[0019] As a preferred embodiment, the particle size of the raw material powder in step (3) is 20-30 μm.

[0020] As a preferred embodiment, the particle size of the paste powder in step (5) is 20-35 μm.

[0021] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0022] Using waste graphite anodes as raw materials not only reduces production costs, but also because waste graphite anodes themselves have excellent performance. Furthermore, waste graphite anodes have a high degree of graphitization, with virtually no shrinkage during the calcination process. The calcination process does not produce excessive pores and does not require an impregnation process, effectively reducing production costs and shortening production time. In addition, the binder used is fluorinated asphalt, which decomposes during the calcination process to generate fluorine gas for further product purification. Therefore, high-purity graphitized products can be obtained without a second purification process after graphitization.

[0023] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to specific embodiments. Detailed Implementation

[0024] This invention discloses a method for preparing isostatically pressed graphite from waste graphite electrodes, which includes the following steps:

[0025] (1) Place the EDM waste graphite electrode in purified water and clean it with the aid of an ultrasonic instrument for 10-30 minutes. Then put it in a muffle furnace to dry it to obtain the cleaned waste graphite electrode. The drying temperature is 250℃ and the drying time is 3-6 hours.

[0026] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 1-4h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0027] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0028] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0029] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0030] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0031] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20-50 min, remove the pressure, and obtain the isostatic graphite green blank.

[0032] (8) The isostatic graphite green body obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 280-320℃ at a uniform rate and held for 5-20h. Then, the temperature is raised to 600-630℃ at a uniform rate and held for 5-20h. Then, the temperature is raised to 1000-1150℃ at a uniform rate and held for 10-25h. Finally, the temperature is lowered to room temperature at a uniform rate to obtain the isostatic graphite calcined green body.

[0033] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0034] The following detailed description is based on several embodiments.

[0035] Example 1

[0036] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 10 minutes. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 6 hours.

[0037] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 2h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0038] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0039] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0040] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0041] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0042] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 30 min, remove the pressure, and obtain the isostatic graphite green blank.

[0043] (8) The isostatic graphite green body obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 280℃ at a constant speed and held for 20h, then raised to 620℃ at a constant speed and held for 10h, then raised to 1050℃ at a constant speed and held for 15h, and then cooled to room temperature at a constant speed to obtain the isostatic graphite calcined green body.

[0044] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0045] Example 2

[0046] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 30 minutes. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 3 hours.

[0047] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 2h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0048] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0049] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0050] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0051] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0052] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 40 min, remove the pressure, and obtain the isostatic graphite green blank.

[0053] (8) The isostatic graphite green body obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 320°C at a constant rate and held for 5 hours, then the temperature is raised to 610°C at a constant rate and held for 18 hours, then the temperature is raised to 1000°C at a constant rate and held for 175 hours, and then the temperature is lowered to room temperature at a constant rate to obtain the isostatic graphite calcined green body.

[0054] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0055] Example 3

[0056] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 20 minutes. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 6 hours.

[0057] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 1h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0058] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0059] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0060] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0061] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0062] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 50 min, remove the pressure, and obtain the isostatic graphite green blank.

[0063] (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 300℃ at a constant rate and held for 16 hours, then the temperature is raised to 600℃ at a constant rate and held for 20 hours, then the temperature is raised to 1150℃ at a constant rate and held for 17 hours, and then the temperature is lowered to room temperature at a constant rate to obtain the isostatic graphite calcined green body.

[0064] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0065] Example 4

[0066] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 15 minutes. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 4 hours.

[0067] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 4h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0068] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0069] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0070] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0071] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0072] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20 min, remove the pressure, and obtain the isostatic graphite green blank.

[0073] (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 290°C at a constant rate and held for 8 hours, then the temperature is raised to 630°C at a constant rate and held for 5 hours, then the temperature is raised to 1150°C at a constant rate and held for 25 hours, and then the temperature is lowered to room temperature at a constant rate to obtain the isostatic graphite calcined green body.

[0074] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0075] Example 5

[0076] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 255 min. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 4 h.

[0077] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 1h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0078] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0079] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0080] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0081] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0082] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20-50 min, remove the pressure, and obtain the isostatic graphite green blank.

[0083] (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 310℃ at a constant rate and held for 12 hours, then the temperature is raised to 625℃ at a constant rate and held for 11 hours, then the temperature is raised to 1000℃ at a constant rate and held for 20 hours, and then the temperature is lowered to room temperature at a constant rate to obtain the isostatic graphite calcined green body.

[0084] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0085] Example 6

[0086] (1) The EDM waste graphite electrode was placed in purified water and cleaned with the aid of an ultrasonic instrument for 8 minutes. Then it was placed in a muffle furnace to dry, and the cleaned waste graphite electrode was obtained. The drying temperature was 250℃ and the drying time was 4.5h.

[0087] (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 2.5h to obtain the purified waste graphite electrode. The strong oxidizing gas is chlorine.

[0088] (3) The purified waste graphite electrode obtained in step (2) is placed into a vertical roller mill for grinding to obtain raw material powder; the particle size of the raw material powder is 20-30μm.

[0089] (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to a temperature of less than 50°C by water cooling to obtain a paste.

[0090] (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; the particle size of the paste powder is 20-35μm.

[0091] (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained.

[0092] (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20 min, remove the pressure, and obtain the isostatic graphite green blank.

[0093] (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 280°C at a constant rate and held for 16 hours. Then, the temperature is raised to 620°C at a constant rate and held for 8 hours. Then, the temperature is raised to 1150°C at a constant rate and held for 16 hours. Finally, the temperature is lowered to room temperature at a constant rate to obtain the isostatic graphite calcined green body.

[0094] (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

[0095] Performance tests were conducted on the above embodiments, and the test results are shown in Table 1.

[0096]

[0097] Table 1

[0098] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing isostatically pressed graphite from waste graphite electrodes, characterized in that: It includes the following steps: (1) Place the waste graphite electrode in purified water and clean it with the aid of an ultrasonic instrument for 10-30 minutes. Then put it in a muffle furnace to dry it and obtain the cleaned waste graphite electrode. (2) The cleaned waste graphite electrode obtained in step (1) is placed in a purification furnace and heated while a strong oxidizing gas is continuously introduced. The heating temperature is 2000℃ and the heating time is 1-4h to obtain the purified waste graphite electrode. (3) The purified waste graphite electrode obtained in step (2) is put into a vertical roller mill for grinding to obtain raw material powder; (4) The raw material powder obtained in step (3) is put into a heating kneader together with fluorinated asphalt and kneaded to make the surface of the raw material powder uniformly coated with a layer of fluorinated asphalt. Then it is placed into the cooling layer and cooled to less than 50°C by water cooling to obtain a paste. (5) The paste obtained in step (4) is fed into a vertical roller mill for grinding to obtain paste powder; (6) The paste powder obtained in step (5) is filled into the rubber mold, compacted by high frequency vibration, sealed and vacuumed to remove residual air inside the product, and a preformed isostatic graphite green blank is obtained. (7) Place the preformed isostatic graphite green blank obtained in step (6) into an isostatic pressing equipment, apply a pressure of 130 MPa and maintain it for 20-50 min, remove the pressure, and obtain the isostatic graphite green blank. (8) The isostatic graphite green obtained in step (7) is placed in a calcining furnace and calcined. First, the temperature is raised to 280-320℃ at a uniform rate and held for 5-20 hours. Then, the temperature is raised to 600-630℃ at a uniform rate and held for 5-20 hours. Then, the temperature is raised to 1000-1150℃ at a uniform rate and held for 10-25 hours. Finally, the temperature is lowered to room temperature at a uniform rate to obtain the isostatic graphite calcined green body. (9) The isostatic graphite calcined preform obtained in step (8) is placed in a graphitization furnace for graphitization treatment to obtain isostatic graphite.

2. The method for preparing isostatic graphite from waste graphite electrodes according to claim 1, characterized in that: In step (1), the drying temperature is 250℃ and the drying time is 3-6h.

3. The method for preparing isostatically pressed graphite from waste graphite electrodes according to claim 1, characterized in that: The waste graphite electrode in step (1) is an EDM waste graphite electrode.

4. The method for preparing isostatically pressed graphite from waste graphite electrodes according to claim 1, characterized in that: The strong oxidizing gas in step (2) is chlorine.

5. The method for preparing isostatically pressed graphite from waste graphite electrodes according to claim 1, characterized in that: The particle size of the raw material powder in step (3) is 20-30 μm.

6. The method for preparing isostatically pressed graphite from waste graphite electrodes according to claim 1, characterized in that: The paste powder in step (5) has a particle size of 20-35 μm.

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