Preparation process of isostatic pressing graphite

Abstract

The invention discloses a preparation technology of isostatic pressing graphite. The preparation technology comprises the following steps of S1, raw material and ingredient pretreatment, S2, grinding, S3, mixing and kneading, S4, forming, S5, roasting, S6, dipping, S7, graphitization, S8, processing and detection and S9, finished product packaging. A graphite grinding machine used for primary grinding in the step S2 is a vertical roller mill; and a graphite mill used for secondary milling is an airflow mill. The kneading machine in the step S3 is a heating type kneading machine. And in the step S4, the vacuumizing time is 0.5 h, and the vacuum degree is 0 to-0.06 MPa. The roasting furnace in the step S5 is a rotary graphite roasting furnace.

Description

Technical Field

[0001] The invention relates to the technical field of graphite preparation, in particular to a preparation process of isostatically pressed graphite. Background Art

[0002] Isostatic graphite, with its excellent properties of high strength, high purity, high electrical and thermal conductivity, is widely used in a wide range of fields, including metallurgy, electronics, and aerospace. However, the traditional isostatic graphite preparation process suffers from issues such as uneven raw material mixing, uneven pressure distribution during molding, high energy consumption during the calcination and graphitization processes, and unstable product quality. These issues lead to low production efficiency, high costs, and difficulty meeting the stringent performance requirements of the high-end market for isostatic graphite. Summary of the Invention

[0003] The object of the present invention is to provide a process for preparing isostatically pressed graphite to solve the problems mentioned in the background technology.

[0004] In order to solve the above technical problems, the solution of the present invention is:

[0005] A process for preparing isostatically pressed graphite comprises the following steps:

[0006] S1. Raw materials and ingredients pretreatment

[0007] Pitch coke is selected as the main aggregate, with the requirements of ash content ≤ 0.7%, graphitization degree ≥ 80%, and particle size of 5μm-10μm;

[0008] Prepare the binder: Use high-quality coal tar as the binder, with the requirements that its ash content is ≤0.1%, softening point ≥120℃, and quinoline insoluble matter ≤1%;

[0009] S2, grinding

[0010] Primary grinding: Using a graphite grinder, the aggregate coke is ground into a powder with an average particle size of 10-15 μm;

[0011] Secondary grinding: After the kneaded paste is crushed, it is further ground using a graphite grinder to reduce the average particle size to less than 5μm to obtain pressed powder;

[0012] S3, Mixing

[0013] The ground pressed powder and coal tar binder are put into a kneader at a mass ratio of 4:1 for kneading. After kneading, the paste is taken out and allowed to cool;

[0014] S4, Molding

[0015] The mold is formed using cold isostatic pressing technology; the pressed powder is filled into the rubber mold, and the pressed powder is initially compacted by high-frequency electromagnetic vibration. The mold is then sealed and vacuumed, and then placed in a high-pressure container filled with oil liquid medium, pressurized to 100MPa, and pressed into a green body.

[0016] S5. Calcination

[0017] The green body is placed in a roasting furnace and preheated at low temperature to make the green body expand evenly. After preheating at low temperature, the temperature is further raised to 1300℃ and maintained for 800h to allow a chemical reaction to occur between the aggregate and the binder. The binder decomposes and releases a large amount of volatile matter, and a condensation reaction occurs at the same time.

[0018] S6. Impregnation

[0019] The calcined product is preheated for 4-6 hours to reach the appropriate impregnation temperature; the preheated product is then placed in an impregnation tank, the temperature of which reaches 100-120°C, and the air and residual volatiles inside the product are removed by vacuum; the impregnation temperature is 180-200°C, and the pressure is applied for 2 hours. Then, melted coal tar is added to the impregnation tank, and the impregnating agent asphalt is allowed to enter the interior of the product at a temperature of 200°C and a pressure of 4MPa; after 3-4 impregnation and calcination cycles,

[0020] S7, graphitization

[0021] The product after 3-4 impregnation and calcination cycles is placed in a graphitization furnace and heated to 2900℃-3000℃. At the high temperature of 2900℃-3000℃, the carbon atom lattice is arranged in an orderly manner, completing the transformation from carbon to graphite.

[0022] S8. Processing and testing

[0023] The graphitized isostatic graphite is mechanically processed and the finished product is fully quality tested.

[0024] Preferably, the graphite mill used for the first grinding in S2 is a vertical roller mill; the graphite mill used for the second grinding is an air flow mill;

[0025] S9. Finished product packaging

[0026] The finished graphite after processing and testing is packaged.

[0027] Preferably, the kneader in S3 is a heating kneader.

[0028] Preferably, the vacuuming time in S4 is 0.5 h, and the vacuum degree is 0 to -0.06 MPa.

[0029] Preferably, the roasting furnace in S5 is a rotary graphite roasting furnace.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Avoid cracking of green body due to rapid expansion;

[0032] 2. Low energy consumption in the roasting and graphitization process;

[0033] 3. Graphite products have good uniformity;

[0034] 4. The bulk density, electrical conductivity, thermal conductivity and corrosion resistance of graphite products have been greatly improved, and the machining performance has also been significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of the preparation process of isostatically pressed graphite. DETAILED DESCRIPTION

[0036] The following is a further description of specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0037] A process for preparing isostatically pressed graphite comprises the following steps:

[0038] S1. Raw materials and ingredients pretreatment

[0039] Pitch coke is selected as the main aggregate, with the requirements of ash content ≤ 0.7%, graphitization degree ≥ 80%, and particle size of 5μm-10μm;

[0040] 0.5wt% nano silicon carbide is added to the aggregate to enhance thermal conductivity.

[0041] Prepare the binder: Use high-quality coal tar as the binder, with the requirements that its ash content is ≤0.1%, softening point ≥120℃, and quinoline insoluble matter ≤1%;

[0042] S2, grinding

[0043] Primary grinding: Using a graphite grinder, the aggregate coke is ground into a powder with an average particle size of 10-15 μm;

[0044] Secondary grinding: After the kneaded paste is crushed, it is further ground using a graphite grinder to reduce the average particle size to less than 5μm to obtain pressed powder;

[0045] S3, Mixing

[0046] The ground pressed powder and coal tar binder are put into a kneader at a mass ratio of 4:1 for kneading. After kneading, the paste is taken out and allowed to cool;

[0047] S4, Molding

[0048] The mold is formed using cold isostatic pressing technology. The pressed powder is filled into a rubber mold and initially compacted by high-frequency electromagnetic vibration. The mold is then sealed and vacuumed to remove the air between the powder particles. The mold is then placed in a high-pressure container filled with oil liquid medium, pressurized to 100 MPa, and pressed into a green body.

[0049] S5. Calcination

[0050] 8. Place the green body in a roasting furnace for low-temperature preheating to ensure uniform expansion. The heating rate must be controlled during this stage to prevent cracking due to excessive expansion. After low-temperature preheating, continue heating to 1300°C and maintain for 800 hours to allow a chemical reaction between the aggregate and the binder, decomposing the binder and releasing a large amount of volatiles, while also undergoing polycondensation. During low-temperature preheating, increase the temperature at a rate of 1°C / min before reaching 300°C. During this period, increase the temperature at a rate of 0.5°C / min between 300°C and 800°C. This step-by-step roasting process reduces impact cracking caused by volatiles.

[0051] S6. Impregnation

[0052] The calcined product is preheated for 4-6 hours to reach the appropriate impregnation temperature. The preheated product is then placed in an impregnation tank, where the temperature inside the tank reaches 100-120°C, and vacuum is applied to remove air and residual volatiles from the product. The impregnation temperature is 180-200°C and pressurized for 2 hours. Then, melted coal tar is added to the impregnation tank and the impregnating agent asphalt is introduced into the product at a temperature of 200°C and a pressure of 4MPa. After 3-4 impregnation and calcination cycles, the density and performance are further improved.

[0053] S7, graphitization

[0054] The product after 3-4 impregnation and roasting cycles is placed in a graphitization furnace and heated to 2900℃-3000℃. At the high temperature of 2900℃-3000℃, the carbon atom lattice is arranged in an orderly manner, completing the transformation from carbon to graphite and obtaining the finished product.

[0055] S8. Processing and testing

[0056] Mechanical processing of graphitized isostatic graphite; comprehensive quality inspection of finished products;

[0057] S9. Finished product packaging

[0058] The finished graphite after processing and testing is packaged.

[0059] Specifically, the graphite mill used for the primary grinding in S2 is a vertical roller mill, and the graphite mill used for the secondary grinding is an air flow mill, so that the aggregate coke is ground finer and the particle size between the powder particles is reduced.

[0060] Furthermore, the kneading machine in S3 is a heated kneading machine, so that a layer of asphalt is evenly attached to the surface of the powdered coke particles. The kneading temperature is higher than that of ordinary graphite production, and the kneading time is also longer.

[0061] Furthermore, the vacuuming time in S4 is 0.5 h, and the vacuum degree is 0 to -0.06 MPa, so as to more efficiently discharge the air between the powder particles.

[0062] Furthermore, the roasting furnace in S5 is a rotary graphite roasting furnace. The graphite material moves continuously in the rotary drum and is roasted in heating zones of different temperatures, so that the graphite material is heated evenly and cracking of the green body due to excessive expansion is avoided.

[0063] Example 1

[0064] Raw materials and ingredient pretreatment: pitch coke with ash content of 0.6%, graphitization degree of 82% and particle size of 6 μm is selected; coal tar with ash content of 0.08%, softening point of 130°C and quinoline insoluble matter of 0.8% is used as the binder.

[0065] Grinding: After the first grinding, the average particle size of the aggregate is 11μm, and the second grinding makes the average particle size of the paste reach 3μm.

[0066] Mixing: Pressed powder and coal tar pitch are mixed in a mass ratio of 4:1 at 180°C for 2.5 hours.

[0067] Molding: During cold isostatic pressing, maintain pressure at 100 MPa for 50 minutes.

[0068] Calcination: Preheat at low temperature at a rate of 0.6°C / h, and maintain at 1300°C for 800h in the high temperature stage.

[0069] Impregnation: The product was preheated for 4.5 h, impregnated at 185 ° C and 4 MPa pressure for 2 h, and four impregnation and roasting cycles were performed.

[0070] Graphitization: heating to 2920°C at 2.2°C / min.

[0071] Finished product performance: density 1.93g / cm 3 , hardness 83HRB, compressive strength 78MPa, resistivity 13μΩ·m.

[0072] Example 2

[0073] Raw materials and ingredient pretreatment: asphalt coke ash content 0.5%, graphitization degree 85%, particle size 8μm; coal pitch ash content 0.06%, softening point 140℃, quinoline insoluble matter 0.7%.

[0074] Grinding: The average particle size of the aggregate in the first grinding is 13μm, and the average particle size of the paste in the second grinding is 4μm.

[0075] Mixing: Mix the pressed powder and coal tar pitch in a mass ratio of 4:1 at 200℃ for 3 hours.

[0076] Molding: 100MPa pressure for 1h.

[0077] Calcination: preheat at low temperature at 0.7℃ / h, keep at 1300℃ for 800h.

[0078] Impregnation: preheating for 5.5h, impregnation at 195℃ and 4MPa for 2h, 3 impregnation and roasting cycles.

[0079] Graphitization: heating at 2.8°C / min to 2980°C.

[0080] Finished product performance: density 1.98g / cm 3 , hardness 88HRB, compressive strength 85MPa, resistivity 10μΩ·m.

[0081] Example 3

[0082] Raw materials and ingredient pretreatment: asphalt coke ash content 0.7%, graphitization degree 80%, particle size 5μm; coal tar ash content 0.1%, softening point 120℃, quinoline insoluble matter 1%.

[0083] Grinding: The average particle size of the aggregate in the first grinding is 10μm, and the average particle size of the paste in the second grinding is 2μm.

[0084] Mixing: Mix the pressed powder and coal tar pitch in a mass ratio of 4:1 at 170℃ for 2h.

[0085] Molding: 100MPa pressure holding for 40min.

[0086] Calcination: Preheat at low temperature, increase temperature by 0.5℃ / h, and maintain at 1300℃ for 800h.

[0087] Impregnation: preheating for 4 hours, impregnation at 180℃ and 4MPa for 2 hours, 4 impregnation and roasting cycles.

[0088] Graphitization: heating to 2900°C at 2°C / min.

[0089] Finished product performance: density 1.90g / cm 3 , hardness 80HRB, compressive strength 75MPa, resistivity 15μΩ·m.

[0090] After testing various indicators of the present invention, the following table is obtained:

[0091]

[0092] From the table above, we can see that its volume density is higher than that of traditional process, and its volume density is 1.9g / cm 3 Higher than the 1.82g / cm3 of traditional process 3 Its flexural strength is 78MPa, which is higher than the 65MPa of the traditional process. Its resistivity is 9μΩ·m, which is lower than the 12μΩ·m of the traditional process. Its thermal expansion coefficient is 4.2X10 -6 / K, lower than the 5.8Ⅹ10 of traditional process -6 / K, its ash content is 3PPm, which is much smaller than the 250PPm of the traditional process.

[0093] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations to these embodiments may be made without departing from the principles and spirit of the present invention, and these changes and modifications still fall within the scope of protection of the present invention.

Claims

1. A process for preparing isostatically pressed graphite, characterized in that: The following steps are involved: S1. Raw materials and ingredients pretreatment Asphalt coke is selected as the main aggregate, with an ash content of ≤0.7%, a graphitization degree of ≥80%, and a particle size of 5μm-10μm; Prepare the binder: Use coal tar as the binder, with an ash content of ≤0.1%, a softening point of ≥120°C, and quinoline insoluble matter of ≤1%; S2, grinding Primary grinding: Using a graphite grinder, the aggregate coke is ground into a powder with an average particle size of 10-15 μm; Secondary grinding: After the kneaded paste is crushed, it is further ground using a graphite grinder to reduce the average particle size to less than 5μm to obtain pressed powder; S3, Mixing The ground pressed powder and coal tar binder are put into a kneader at a mass ratio of 4:1 for kneading. After kneading, the paste is taken out and allowed to cool; S4, Molding The mold is formed using cold isostatic pressing technology. The pressed powder is filled into a rubber mold and initially compacted by high-frequency electromagnetic vibration. The mold is then sealed and vacuumed. The mold is then placed in a high-pressure container filled with oil liquid medium, pressurized to 100 MPa, and pressed into a green body. S5. Calcination The green body is placed in a roasting furnace and preheated at low temperature to allow the green body to expand evenly. After preheating at low temperature, the temperature is raised to 1300℃ and maintained for 800 hours to allow a chemical reaction to occur between the aggregate and the binder. The binder decomposes and releases a large amount of volatile matter, while the polycondensation reaction occurs. S6. Impregnation The calcined product is preheated for 4-6 hours to reach the impregnation temperature; the preheated product is then placed in an impregnation tank, the temperature of which reaches 100-120°C, and the air and residual volatiles inside the product are removed by vacuum; the impregnation temperature is 180-200°C, and the pressure is applied for 2 hours. Then, melted coal tar is added to the impregnation tank, and the impregnating agent asphalt is allowed to enter the interior of the product at a temperature of 200°C and a pressure of 4MPa; after 3-4 impregnation and calcination cycles, S7, graphitization The product after 3-4 impregnation and calcination cycles is placed in a graphitization furnace and heated to 2900℃-3000℃. At the high temperature of 2900℃-3000℃, the carbon atom lattice is arranged in an orderly manner, completing the transformation from carbon to graphite. S8. Processing and testing Mechanical processing of graphitized isostatic graphite; comprehensive quality inspection of finished products; S9. Finished product packaging The finished graphite after processing and testing is packaged.

2. The process for preparing isostatically pressed graphite according to claim 1, wherein: The graphite mill used for the primary grinding in S2 is a vertical roller mill; the graphite mill used for the secondary grinding is an air flow mill.

3. The process for preparing isostatically pressed graphite according to claim 1, wherein: 0.5wt% of nano silicon carbide is added into the aggregate.

4. The process for preparing isostatically pressed graphite according to claim 1, wherein: During low-temperature preheating, the heating rate is 1°C / min before the temperature reaches 300°C. When heating, when the temperature is between 300 and 800°C, the heating rate is 0.5°C / min.

5. The process for preparing isostatically pressed graphite according to claim 1, wherein: The kneader in S3 is a heating kneader.

6. The process for preparing isostatically pressed graphite according to claim 1, wherein: The vacuuming time in S4 is 0.5h, and the vacuum degree is 0~-0.06MPa.

7. The process for preparing isostatically pressed graphite according to claim 1, wherein: The roasting furnace in S5 is a rotary graphite roasting furnace.

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