Impregnation method of special graphite

Abstract

The invention relates to an impregnation method of special graphite. The dipping method of the special graphite comprises the following steps: S1, preheating; s2, gas replacement; s3, cleaning; s4, duct dredging; s5, adding a flash evaporation solution until the pressure of the impregnation tank is increased to 10-50 Pa; s6, an impregnant is added, after the impregnation tank is vacuumized for the fourth time, liquid impregnant circulation is established through a circulating pump, variable-pressure impregnation treatment is carried out, the pressure is changed once every hour, and variable-pressure impregnation is carried out for 4-8 h; s7, circulation of the impregnant is stopped, protective gas is introduced to 3.0-3.9 MPa, and heat preservation and pressure maintaining are conducted for 6-12 h; and S8, cooling. According to the impregnation method of the special graphite, the theoretical weight gain rate of the impregnated product is accurate to 16.8% or above from 16% or above, the weight gain rate of the impregnated product is increased by 5-11.8% compared with the weight gain rate of the impregnated product in the prior art, and the impregnation effect is good.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite materials, and in particular relates to a method for impregnating special graphite. Background Art

[0002] Special graphite covers a wide range, mainly referring to high-strength, high-density, and high-purity graphite products (referred to as "three high graphite"). Its material properties are excellent and widely used. The common preparation methods of special graphite include raw material selection, grinding, screening and distribution, kneading and molding, impregnation and roasting, graphitization, and finally mechanical processing into products. Among them, impregnation is to make certain liquid materials (impregnants) penetrate into the pores of the product under a certain temperature and pressure, so as to achieve the purpose of reducing product holes, increasing product density, and improving product quality.

[0003] It is generally believed that graphite products including special graphite include two different forms of pores, one is open pores that are connected to the outside atmosphere, and the other is closed pores that are not connected to the outside atmosphere. At present, polymer materials are commonly used as impregnants, which can penetrate and fill open pores with larger pore sizes, but have little or no effect on closed pores and open pores with smaller pore sizes.

[0004] In recent years, a series of original scientific and technological achievements have been made in the field of graphite product impregnation technology. Representative existing technologies include: using low-viscosity and high-residue carbon asphalt as an impregnating agent. The technical scheme to achieve this is: Step 1, pretreatment: clean and wash the graphite products; Step 2, drying and degassing: heating and drying, vacuum degassing, unblocking the pore channels of graphite products and keeping them in a vacuum state at a constant temperature for standby use; Step 3, impregnating agent treatment: preheat the impregnating agent, stir and homogenize it during the preheating process, and keep it at a constant temperature for standby use; Step 4, impregnation: inject the standby impregnating agent, and impregnate the graphite products under a protective gas atmosphere and different pressures; Step 5, post-treatment: cool, drain, release pressure, etc. to obtain the product.

[0005] However, the existing technical solutions almost all avoid the problem caused by the flash evaporation of the impregnant caused by the negative pressure state when injecting the impregnant. This flash evaporation process includes: 1. The light components contained in the impregnant are volatilized, and the volatilized light components preferentially enter the pores of the graphite product; 2. The gas phase pressure rise in the impregnation tank comes from the flash evaporation of the impregnant and the injection of the impregnant. As the impregnant is continuously injected and the gas phase pressure rises, the flash evaporation gradually weakens until the pressure is balanced and the flash evaporation phenomenon is eliminated; 3. As the impregnant is continuously injected, the flashed impregnant heavy components in the impregnation tank are mixed with the newly injected impregnant to form a mixed solution. The liquid level of the mixed solution continues to rise, gradually flooding from the bottom of the graphite product upwards, and entering the impregnation operation.

[0006] It can be seen from this that: 1. Light components volatilized by flash evaporation remain in the open pores of graphite products; 2. Light components volatilized by flash evaporation remain in the closed pores of graphite products; 3. After flash evaporation occurs, as the impregnant is continuously injected into the graphite product from bottom to top, the gas phase pressure above the impregnant continues to rise, the gas-liquid equilibrium in the impregnation tank continues to change, the number of light components retained in the pores of the graphite product increases from bottom to top, and the flash evaporation process is uncontrolled. Therefore, the existing impregnation process is prone to poor impregnation uniformity and poor controllability. In addition, in actual production, the temperature of the graphite product to be impregnated is 20-40°C higher than the temperature of the impregnant injection, and there are problems of large temperature difference and poor temperature control in the impregnation operation. In addition, in actual production, the liquid level height of the impregnant submerging the top of the graphite product is required to be more than 15cm, and there is a problem of large amount of impregnant used.

[0007] In view of this, the present invention proposes a new impregnation method of special graphite to solve the above problems. Summary of the invention

[0008] The object of the present invention is to provide a method for impregnating special graphite, which solves the problems of poor uniformity, poor controllability and poor temperature controllability of the impregnation operation, saves the amount of impregnating agent, and reduces the impact of flash evaporation on impregnation.

[0009] In order to achieve the above purpose, the technical solution adopted is:

[0010] A method for impregnating special graphite comprises the following steps:

[0011] S1 preheating: Place the special graphite in an impregnation tank for preheating;

[0012] S2 Gas replacement: After preheating to 140-180°C, the impregnation tank is vacuumed for the first time to 50-300Pa, and then the protective gas is filled to replace the gas in the impregnation tank to 50-300Pa. The impregnation tank is vacuumed for the second time to 50-300Pa, and the pressure is maintained at 180-300°C for 0.5-1h;

[0013] S3 cleaning and drying: inject deionized water at 60-80°C into the impregnation tank until the special graphite is submerged, fill with protective gas to 1.8-2.4MPa, soak for 4-6h, then drain the deionized water and reduce the pressure to 300-500Pa;

[0014] S4 channel dredging: after heating to 140-180°C, the impregnation tank is evacuated for the third time to 50-300Pa, and then maintained at a constant temperature and pressure of 160-300°C for 6-10h;

[0015] S5: adding a flash solution at 155-295° C. into the impregnation tank until the pressure of the impregnation tank returns to 10-50 Pa;

[0016] S6: Add an impregnating agent at 155-295° C. to the impregnation tank until the special graphite is submerged, evacuate the tank for the fourth time to 98.6-99.8 KPa, and use a circulating pump to establish a circulation of the liquid impregnating agent to perform variable pressure impregnation treatment, changing the pressure once every hour for 4-8 hours;

[0017] S7: After the variable pressure impregnation treatment is completed, the circulation of the liquid impregnating agent is stopped, and the impregnation tank is filled with protective gas to 3.0-3.9 MPa, and the temperature and pressure are maintained for 6-12 hours;

[0018] S8 Cooling: When the temperature in the impregnation tank is cooled to be 20-40°C higher than the softening point of the impregnating agent, the protective gas is filled into the impregnation tank to 4.0-5.0MPa, and after the impregnating agent is discharged and recovered, the pressure is released when the temperature in the impregnation tank is 25-50°C lower than the softening point of the impregnating agent.

[0019] Furthermore, the protective gas is nitrogen or argon.

[0020] Furthermore, the protective gas is nitrogen.

[0021] Furthermore, in step S1, the heating rate is 30-60°C / h;

[0022] In the step S3, the injection height of the deionized water is at least 3 cm above the top of the special graphite;

[0023] In the step S6, the impregnating agent is injected at a height of 5-10 cm above the top of the special graphite.

[0024] Furthermore, in the step S6, while the impregnating agent is injected, the gas in the impregnation tank is discharged to maintain the pressure at 10-50Pa;

[0025] The pressure-changing impregnation treatment is carried out by filling in protective gas or exhausting gas, and the pressure is 100Pa-2.4MPa.

[0026] Furthermore, the temperature difference between the temperature of the impregnation solution and the flash solution when they are added and the standby impregnation temperature does not exceed 5°C.

[0027] Further, the flash solution is one of toluene, xylene, a fraction obtained by direct distillation of the impregnating agent at room temperature -280°C, and methylnaphthalene;

[0028] The impregnating agent is coal tar pitch with a softening point of 60-160°C.

[0029] Further, the flash solution is methylnaphthalene;

[0030] The impregnating agent is coal tar pitch with a softening point of 80-90°C.

[0031] Furthermore, the preparation temperature is 205-245°C;

[0032] The addition temperature of the flash solution is 200-240°C;

[0033] The impregnating agent is added at a temperature of 200-240°C.

[0034] Another object of the present invention is to provide a special graphite obtained by impregnation using the above impregnation method.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. In the technical solution of the present invention, for graphite products including special graphite, the flash solution is first injected during impregnation, and then the impregnating agent is injected for impregnation. In this process, an appropriate amount of light components are discharged while injecting the impregnating agent, which solves the problem of homogenizing the components in the pores at different positions of the graphite product. At the same time, some light components in the impregnation tank are discharged by pressure changes, and the impregnating agent is homogenized by pressure changes and circulating impregnating agent, which solves the problems of poor uniformity, poor controllability and poor temperature controllability of the impregnation operation, and reduces the impact of flash evaporation on impregnation.

[0037] 2. In the technical solution of the present invention, the temperature difference between the graphite product preparation temperature and the impregnating agent injection temperature is reduced from 20-40°C to 5°C, and the temperature change during the impregnation process is small and well controlled.

[0038] 3. In the technical solution of the present invention, by injecting the flash solution, the liquid level of the impregnant submerging the top of the graphite product is reduced from more than 15 cm to 5-10 cm, solving the problem of large amount of impregnant.

[0039] 4. After treatment by the technical solution of the present invention, the theoretical weight gain rate of the impregnated product including special graphite is increased from more than 16% to more than 16.8%, which is 5% higher than the accuracy of the theoretical weight gain rate of the impregnated product of more than 16%, and 5-11.8% higher than the weight gain rate of the impregnated product in the prior art.

[0040] 5. The technical solution of the present invention can be extended and applied to the second immersion of three-roasting and two-immersion, and can also be extended and applied to the second immersion or the third immersion of four-roasting and three-immersion, and has a wide range of applications. DETAILED DESCRIPTION

[0041] In order to further illustrate the impregnation method of a special graphite of the present invention and achieve the intended purpose of the invention, the following is a detailed description of the impregnation method of a special graphite proposed according to the present invention, its specific implementation, structure, characteristics and efficacy in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0042] The following is a detailed description of a special graphite impregnation method of the present invention in conjunction with specific embodiments:

[0043] The invention discloses a special graphite impregnation method, which is beneficial to improving the weight gain rate of the impregnated product by cleaning and secondary dredging the pores of the special graphite product; the flash solution is preferentially injected during impregnation, and then the impregnating agent is injected for impregnation, and measures such as low submergence level impregnation, relatively low temperature difference impregnation and variable pressure impregnation are adopted to solve the problems of poor uniformity, poor controllability and poor temperature controllability of the impregnation operation, save the amount of impregnating agent, and reduce the influence of flash evaporation on the impregnation. The technical scheme of the invention is:

[0044] A method for impregnating special graphite comprises the following steps:

[0045] S1 preheating: Place the special graphite in an impregnation tank for preheating;

[0046] S2 Gas replacement: After preheating to 140-180°C, the impregnation tank is vacuumed for the first time to 50-300Pa, and then the protective gas is filled to replace the gas in the impregnation tank to 50-300Pa. The impregnation tank is vacuumed for the second time to 50-300Pa, and the pressure is maintained at 180-300°C for 0.5-1h;

[0047] S3 cleaning and drying: inject deionized water at 60-80°C into the impregnation tank until the special graphite is submerged, fill with protective gas to 1.8-2.4MPa, soak for 4-6h, then drain the deionized water and reduce the pressure to 300-500Pa;

[0048] S4 channel dredging: after heating to 140-180°C, the impregnation tank is evacuated for the third time to 50-300Pa, and then maintained at a constant temperature and pressure of 160-300°C for 6-10h;

[0049] S5: adding a flash solution at 155-295° C. into the impregnation tank until the pressure of the impregnation tank returns to 10-50 Pa;

[0050] S6: Add an impregnating agent at 155-295° C. to the impregnation tank until the special graphite is submerged, evacuate the tank for the fourth time to 98.6-99.8 KPa, and use a circulating pump to establish a circulation of the liquid impregnating agent to perform variable pressure impregnation treatment, changing the pressure once every hour for 4-8 hours;

[0051] S7: After the variable pressure impregnation treatment is completed, the circulation of the liquid impregnating agent is stopped, and the impregnation tank is filled with protective gas to 3.0-3.9 MPa, and the temperature and pressure are maintained for 6-12 hours;

[0052] S8 Cooling: When the temperature in the impregnation tank is cooled to be 20-40°C higher than the softening point of the impregnating agent, the protective gas is filled into the impregnation tank to 4.0-5.0MPa, and after the impregnating agent is discharged and recovered, the pressure is released when the temperature in the impregnation tank is 25-50°C lower than the softening point of the impregnating agent.

[0053] Preferably, the protective gas is nitrogen or argon.

[0054] Further preferably, the protective gas is nitrogen.

[0055] Preferably, in step S1, the heating rate is 30-60°C / h;

[0056] In the step S3, the injection height of the deionized water is at least 3 cm above the top of the special graphite;

[0057] In the step S6, the impregnating agent is injected at a height of 5-10 cm above the top of the special graphite.

[0058] In the above technical solution, by first adding the flash solution and then injecting the impregnating agent for impregnation, low submergence level impregnation can be achieved, thereby improving the uniformity and controllability of the impregnation process while saving the amount of impregnating agent.

[0059] Preferably, in the step S6, while the impregnating agent is injected, the gas in the impregnation tank is discharged to maintain the pressure at 10-50Pa;

[0060] The pressure-changing impregnation treatment is carried out by filling in protective gas or exhausting gas, and the pressure is 100Pa-2.4MPa.

[0061] Preferably, the temperature difference between the impregnation solution and the flash solution when they are added and the standby impregnation temperature does not exceed 5°C.

[0062] In the above technical solution, the temperature difference between the preparation temperature and the temperature of adding the impregnation solution and the flash solution is reduced from 20-40°C to within 5°C, and the temperature change during the impregnation process is small and well controlled.

[0063] Preferably, the flash solution is one of toluene, xylene, a fraction obtained by direct distillation of the impregnating agent at room temperature -280°C, and methylnaphthalene;

[0064] The impregnating agent is coal tar pitch with a softening point of 60-160°C.

[0065] In the above technical solution, the coal tar pitch adopts medium-temperature coal tar pitch, high-temperature coal tar pitch and modified coal tar pitch, and its softening point is 60-160°C.

[0066] The selection principles of flash solution are: (1) flash evaporation can be achieved during the impregnation process. (2) the viscosity of the impregnating agent can be reduced, and the softening point of the impregnating agent can be reduced, which is beneficial to impregnation. (3) the residual carbon value of the impregnating agent has little effect. Therefore, in addition to toluene, xylene, the fraction cut from the direct distillation impregnating agent at room temperature -280℃, and methylnaphthalene, solvent oil and washing oil cut from distilled tar that meet the selection principles of flash solution can also be selected.

[0067] Further preferably, the flash solution is methylnaphthalene;

[0068] The impregnating agent is coal tar pitch with a softening point of 80-90°C.

[0069] In the above technical scheme, the flash solution is preferably methylnaphthalene, which has a boiling point of 250°C. Compared with other flash solutions, it has the advantages of reducing the viscosity and softening point of the impregnant while having little effect on the residual carbon value of the impregnant; coal tar pitch with a softening point of 80-90°C is preferred. For three-high graphite products, the weight gain rate after one impregnation can reach the requirement of more than 16% of the theoretical weight gain rate. It should also be noted that this coal tar pitch usually contains methylnaphthalene.

[0070] Further preferably, the pre-immersion temperature is 205-245°C;

[0071] The addition temperature of the flash solution is 200-240°C;

[0072] The impregnating agent is added at a temperature of 200-240°C.

[0073] Example 1.

[0074] The specific steps are as follows:

[0075] S1 Preheating: Load the special graphite product on the bracket and place it in the impregnation tank for preheating, and preheat it to 140°C at a heating rate of 30°C / h.

[0076] S2 Gas replacement: When the temperature in the impregnation tank is preheated to 140℃, the impregnation tank is evacuated for the first time to a vacuum degree of 300Pa, and nitrogen is filled in to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slightly positive pressure of 300Pa, the nitrogen replacement is stopped, and the impregnation tank is evacuated for the second time to a vacuum degree of 50Pa. When the temperature in the impregnation tank rises to 180℃, the constant temperature and pressure are maintained for 1h.

[0077] The purpose of this step is to remove the gas in the special graphite products, mainly to deoxidize, so as to avoid adverse effects on the subsequent impregnation process.

[0078] S3 cleaning and drying: inject 60℃ deionized water into the impregnation tank. When the deionized water submerges the graphite products and the liquid level is 3cm above the top, stop injecting deionized water. Fill the impregnation tank with nitrogen and pressurize it to 1.8MPa. The soaking time is 4h. Then, drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 300Pa and maintain constant pressure operation.

[0079] The purpose of this step is mainly to clean the pores of the special graphite products, so as to facilitate the weight gain of the impregnated products. No heating is required in this step.

[0080] S4 channel unblocking: heat the temperature in the impregnation tank to 140℃ at a heating rate of 30℃ / h, evacuate the tank for the third time to a vacuum degree of 300Pa, maintain the pressure in the impregnation tank unchanged, and wait until the temperature in the impregnation tank rises to the standby temperature of 245℃, and perform constant temperature and pressure drying for 6h.

[0081] The purpose of this step is mainly to remove the water brought by the cleaning step S3, and at the same time to use the generated steam to dredge the channels. The temperature in the impregnation tank is higher than the boiling point of water, the pressure is vacuum, and the water in the special graphite evaporates into gaseous state, and is discharged from the channels and the tank as the vacuum is drawn, achieving the effect of drying and unblocking the channels.

[0082] S5 impregnation-flash evaporation: inject the methylnaphthalene solution heated to 240°C into the impregnation tank. When the pressure in the impregnation tank returns to a slight positive pressure of 50Pa, stop injecting the flash evaporation solution.

[0083] S6 impregnation - variable pressure impregnation: coal tar with a softening point of 90°C is heated to 240°C and injected into the impregnation tank. The gas in the impregnation tank is discharged to maintain a slight positive pressure of 50Pa. When the liquid coal tar submerges the top of the graphite product by 5cm, the injection of liquid coal tar is stopped. The impregnation tank is evacuated for the fourth time to a vacuum degree of 99.8KPa. The vacuum is stopped and a circulation pump is used to establish a liquid coal tar circulation in the impregnation tank. The variable pressure impregnation stage is entered. The pressure in the impregnation tank is changed between a slight positive pressure of 100Pa-2.4MPa by filling nitrogen or discharging gas. The pressure is changed once every hour and the variable pressure impregnation time is 4h. During this period, the gas in the impregnation tank is cooled when it is discharged, and the flash solution is recovered for reuse.

[0084] The pressure change process is as follows: the first time (first hour) the pressure change is from 99.8KPa in the immersion tank to 2.4MPa, in the second hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa, in the third hour it is increased from a slightly positive pressure of 100Pa to 2.4MPa, and in the fourth hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa.

[0085] This step is more conducive to the homogenization of the impregnating agent inside and outside the pores through the variable pressure impregnation treatment, and further reduces the impact of adding the flash solution. The pressure is changed once every hour, and the pressure range is 100Pa-2.4MPa.

[0086] S7 impregnation - static impregnation: After the variable pressure impregnation is completed, the circulation of liquid coal tar is stopped, nitrogen is filled into the impregnation tank and pressurized to 3.9MPa, and the constant temperature and pressure are maintained for 12 hours (the constant temperature here means: heating to keep the temperature basically consistent with the temperature after the variable pressure impregnation is completed, and the temperature difference does not exceed 5°C, so as to offset the influence of natural heat dissipation of relevant equipment during the pressure maintenance period).

[0087] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 130°C, fill the impregnation tank with nitrogen and pressurize it to 5.0MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 40°C, release the pressure to obtain the impregnated product.

[0088] Example 2.

[0089] The specific steps are as follows:

[0090] S1 Preheating: The special graphite product identical to that in Example 1 is loaded onto a bracket and placed in an impregnation tank for preheating at a heating rate of 60°C / h to 180°C.

[0091] S2 gas replacement: maintain a heating rate of 60℃ / h. When the temperature in the impregnation tank is preheated to 180℃, evacuate the tank for the first time to a vacuum degree of 50Pa, and fill in nitrogen to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slightly positive pressure of 300Pa, stop nitrogen replacement, evacuate the tank for the second time to a vacuum degree of 300Pa, and wait until the temperature in the impregnation tank rises to 300℃, and maintain the constant temperature and pressure for 0.5h.

[0092] S3 cleaning: inject 80℃ deionized water into the immersion tank. When the deionized water submerges the top of the graphite product and the submerged liquid level is 3cm higher than the top of the special graphite product, stop injecting deionized water and fill the immersion tank with nitrogen to pressurize it to 2.4MPa for 6h. Then, drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 300Pa and maintain constant pressure operation.

[0093] S4 channel unblocking: heat the temperature in the immersion tank to 180℃ at a heating rate of 30℃ / h. While continuing to heat up, evacuate the tank for the third time to a vacuum degree of 50Pa. Maintain the pressure in the immersion tank unchanged. When the temperature in the immersion tank rises to the standby immersion temperature of 205℃, perform constant temperature and pressure drying for 10h.

[0094] S5 impregnation-flash evaporation: inject the methylnaphthalene solution heated to 200°C into the impregnation tank. When the pressure in the impregnation tank rises back to a slight positive pressure of 10Pa, stop injecting the flash evaporation solution.

[0095] S6 impregnation - variable pressure impregnation: heat the coal tar with a softening point of 80℃ to 200℃ and inject it into the impregnation tank. By discharging the gas in the impregnation tank, maintain the micro-positive pressure of 10Pa in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 10cm, stop injecting the liquid coal tar. Evacuate the impregnation tank for the fourth time. When the vacuum degree reaches 98.6KPa, stop evacuating the tank. Use a circulation pump to establish the circulation of the liquid coal tar in the impregnation tank and enter the variable pressure impregnation stage. By filling nitrogen or discharging gas, the pressure in the impregnation tank changes between the micro-positive pressure of 100Pa-2.4MPa. The pressure is changed once every hour. The variable pressure impregnation time is 8h. During this period, the gas in the impregnation tank is cooled when it is discharged, and the flash solution is recovered for reuse.

[0096] The pressure change process is as follows: the first pressure change (first hour) is from the vacuum degree of 98.6KPa in the impregnation tank to 2.4MPa, in the second hour it is reduced from 2.4MPa to a slight positive pressure of 100Pa, in the third hour it is increased from a slight positive pressure of 100Pa to 2.4MPa, in the fourth hour it is reduced from 2.4MPa to a slight positive pressure of 100Pa, in the fifth hour it is increased from a slight positive pressure of 100Pa to 2.4MPa, in the sixth hour it is reduced from 2.4MPa to a slight positive pressure of 100Pa, in the seventh hour it is increased from a slight positive pressure of 100Pa to 2.4MPa, and in the eighth hour it is reduced from 2.4MPa to a slight positive pressure of 100Pa.

[0097] S7 impregnation - static impregnation: After variable pressure impregnation, stop the circulation of liquid coal tar, fill the impregnation tank with nitrogen and pressurize it to 3MPa, and maintain constant temperature and pressure for 6 hours.

[0098] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 100°C, fill the impregnation tank with nitrogen and pressurize it to 4.0MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 55°C, release the pressure to obtain the impregnated product.

[0099] Example 3.

[0100] The specific steps are as follows:

[0101] S1 Preheating: The special graphite product identical to that in Example 1 is loaded onto a bracket and placed in an impregnation tank for preheating at a heating rate of 45°C / h to 160°C.

[0102] S2 Gas replacement: Maintain a heating rate of 45°C / h. When the temperature in the impregnation tank is preheated to 160°C, evacuate the tank for the first time to a vacuum degree of 100Pa, and fill in nitrogen to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slightly positive pressure of 300Pa, stop nitrogen replacement, evacuate the tank for the second time to a vacuum degree of 300Pa, and wait until the temperature in the impregnation tank rises to 260°C, and maintain the constant temperature and pressure for 0.8h.

[0103] S3 cleaning and drying: inject deionized water at 70℃ into the immersion tank. When the deionized water submerges the top of the graphite product and the submerged liquid level is 3cm higher than the top, stop injecting deionized water, fill the immersion tank with nitrogen and pressurize it to 2.2MPa. The immersion time is 5h, and then drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 300Pa and maintain constant pressure operation.

[0104] S4 channel unblocking: heat the temperature in the immersion tank to 160℃ at a heating rate of 30℃ / h. While continuing to heat up, evacuate the tank for the third time to a vacuum degree of 100Pa. Maintain the pressure in the immersion tank unchanged. When the temperature in the immersion tank rises to the standby immersion temperature of 225℃, perform constant temperature and pressure drying for 8h.

[0105] S5 impregnation-flash evaporation: inject the methylnaphthalene solution heated to 220°C into the impregnation tank. When the pressure in the impregnation tank returns to a slight positive pressure of 30Pa, stop injecting the flash evaporation solution.

[0106] S6 impregnation - variable pressure impregnation: heat the coal tar with a softening point of 85℃ to 220℃ and inject it into the impregnation tank. By discharging the gas in the impregnation tank, maintain the micro-positive pressure of 10Pa in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 8cm, stop injecting the liquid coal tar. Evacuate the impregnation tank for the fourth time. When the vacuum degree reaches 99.0KPa, stop evacuating the tank. Use a circulation pump to establish the circulation of the liquid coal tar in the impregnation tank and enter the variable pressure impregnation stage. By filling nitrogen or discharging gas, the pressure in the impregnation tank changes between micro-positive pressure of 100Pa-2.4MPa. The pressure is changed once every hour. The variable pressure impregnation time is 6h. During this period, the gas in the impregnation tank is cooled when it is discharged, and the flash solution is recovered for reuse.

[0107] The pressure change process is as follows: the first pressure change (first hour) is from the vacuum degree of 99.0KPa in the immersion tank to 2.4MPa, in the second hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa, in the third hour it is increased from a slightly positive pressure of 100Pa to 2.4MPa, in the fourth hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa, in the fifth hour it is increased from a slightly positive pressure of 100Pa to 2.4MPa, and in the sixth hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa.

[0108] S7 impregnation - static impregnation: After variable pressure impregnation, stop the circulation of liquid coal tar, fill the impregnation tank with nitrogen and pressurize it to 3.5MPa, and maintain constant temperature and pressure for 8 hours.

[0109] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 110°C, fill the impregnation tank with nitrogen and pressurize it to 4.5MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 50°C, release the pressure to obtain the impregnated product.

[0110] Example 4.

[0111] The specific steps are as follows:

[0112] S1 Preheating: The special graphite product same as that in Example 1 is loaded on a bracket and placed in an impregnation tank for preheating at a heating rate of 50°C / h to 180°C.

[0113] S2 Gas replacement: Maintain the heating rate of 50℃ / h. When the temperature in the impregnation tank is preheated to 180℃, evacuate the tank for the first time to a vacuum degree of 150Pa, and fill in nitrogen to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slightly positive pressure of 300Pa, stop nitrogen replacement, evacuate the tank for the second time to a vacuum degree of 150Pa, and wait until the temperature in the impregnation tank rises to 275℃, and maintain the constant temperature and pressure for 0.7h.

[0114] S3 cleaning and drying: inject 72℃ deionized water into the impregnation tank. When the deionized water submerges the top of the graphite product and the submerged liquid level is 3cm above the top, stop injecting deionized water and fill the impregnation tank with nitrogen to pressurize it to 2.3MPa for 5h. Then, drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 300Pa and maintain constant pressure operation.

[0115] S4 channel unblocking: heat the temperature in the immersion tank to 170℃ at a heating rate of 30℃ / h. While continuing to heat up, evacuate the tank for the third time to a vacuum degree of 180Pa. Maintain the pressure in the immersion tank unchanged. When the temperature in the immersion tank rises to the standby immersion temperature of 220℃, perform constant temperature and pressure drying for 9h.

[0116] S5 impregnation-flash evaporation: inject the methylnaphthalene solution heated to 215°C into the impregnation tank. When the pressure in the impregnation tank rises back to a slight positive pressure of 40Pa, stop injecting the flash evaporation solution.

[0117] S6 impregnation - variable pressure impregnation: heat the coal tar with a softening point of 86℃ to 215℃ and inject it into the impregnation tank. By discharging the gas in the impregnation tank, maintain the micro-positive pressure of 30Pa in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 7cm, stop injecting the liquid coal tar. Evacuate the impregnation tank for the fourth time. When the vacuum degree reaches 99.5KPa, stop evacuating the tank. Use a circulation pump to establish the circulation of the liquid coal tar in the impregnation tank and enter the variable pressure impregnation stage. By filling nitrogen or discharging gas, the pressure in the impregnation tank changes between micro-positive pressure 100Pa-2.4MPa. The pressure is changed once every hour. The variable pressure impregnation time is 6h. During this period, the gas in the impregnation tank is cooled when it is discharged, and the flash solution is recovered for reuse.

[0118] The pressure change process is as follows: the first pressure change (first hour) is from the vacuum degree of 99.5KPa in the impregnation tank to 2.4MPa, in the second hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa, in the third hour it is increased from a slightly positive pressure of 100Pa to 2.4MPa, in the fourth hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa, in the fifth hour it is increased from a slightly positive pressure of 100Pa to 2.4MPa, and in the sixth hour it is reduced from 2.4MPa to a slightly positive pressure of 100Pa.

[0119] S7 impregnation - static impregnation: After variable pressure impregnation, stop the circulation of liquid coal tar, fill the impregnation tank with nitrogen and pressurize it to 3.8MPa, and maintain constant temperature and pressure for 11 hours.

[0120] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 100°C, fill the impregnation tank with nitrogen and pressurize it to 4.0MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 50°C, release the pressure to obtain the impregnated product.

[0121] Comparative Example 1.

[0122] This comparative example 1 is a comparative example of Example 1. Both use the same impregnation equipment. The impregnation-flash evaporation process in step S5 of Example 1 is omitted during the operation. The process of discharging the gas in the impregnation tank, the fourth vacuuming, the liquid coal tar circulation, the pressure-changing impregnation and the flash solution recovery process in step S6 of Example 1 are omitted. The other processes remain unchanged.

[0123] Comparative Example 2.

[0124] This comparative example 2 is a comparative example of Example 2. Both use the same impregnation equipment. The impregnation-flash evaporation process in step S5 of Example 2 is omitted in the operation. The exhausting of the gas in the impregnation tank, the fourth vacuuming, the liquid coal tar circulation, the pressure-changing impregnation and the flash solution recovery process in step S6 of Example 2 are omitted. The rest remains unchanged.

[0125] Comparative Example 3.

[0126] This comparative example 3 is a comparative example of Example 3. Both use the same impregnation equipment. The impregnation-flash evaporation process in step S5 of Example 3 is omitted in the operation. The exhausting of the gas in the impregnation tank, the fourth vacuuming, the liquid coal tar circulation, the pressure-changing impregnation and the flash solution recovery process in step S6 of Example 3 are omitted. The rest remains unchanged.

[0127] Comparative Example 4.

[0128] This comparative example 4 is a comparative example of Example 4, and both use the same impregnation equipment. The impregnation-flash evaporation process in step S5 of Example 4 is omitted in the operation, and the exhausting of the gas in the impregnation tank, the fourth vacuuming, the liquid coal tar circulation, the pressure change impregnation and the flash solution recovery process in step S6 of Example 4 are omitted, and the rest remain unchanged.

[0129] Comparative Example 5.

[0130] The Example 4 of the announcement number CN114573371A and the name of a deep impregnation method for isostatic graphite is used as a control. This control adds the gas replacement step S2, the cleaning step S3, the channel dredging step S4, the impregnation-flash evaporation step S5 of the present invention, and adds the steps of discharging the gas in the impregnation tank, vacuuming, circulating the liquid coal tar, and the pressure-changing impregnation and flash solution recovery in step S6, and adds the step of stopping the circulation of the liquid impregnating agent in step S7. The rest remains unchanged, specifically:

[0131] The special graphite product identical to that in Example 1 of the present invention is placed in an impregnation tank and preheated to 180°C. The impregnation tank is evacuated for the first time to a vacuum degree of 50Pa, and nitrogen is introduced to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slightly positive pressure of 300Pa, the nitrogen replacement is stopped, and the impregnation tank is evacuated for the second time to a vacuum degree of 300Pa. When the temperature in the impregnation tank rises to 300°C, the constant temperature and pressure are maintained for 0.5h.

[0132] Inject 80°C deionized water into the impregnation tank. When the deionized water submerges the top of the graphite product and the submerged liquid level is 3 cm higher than the top of the special graphite product, stop injecting deionized water and fill the impregnation tank with nitrogen to pressurize it to 2.4 MPa. The immersion time is 6 hours.

[0133] Then, the deionized water was discharged. When draining, the pressure was reduced to a slight positive pressure of 300Pa. The temperature was raised to 250℃ at a heating rate of 40℃ / h. The impregnation tank was vacuumed for the first time to reduce its pressure to 600Pa and maintained at this pressure for 2h. Subsequently, nitrogen was injected into the impregnation tank to increase its pressure to 1.0MPa and maintained at this pressure for 5h. Then, the fourth vacuuming was performed to reduce its pressure to 150Pa and maintained at this pressure for 3h.

[0134] Inject the methylnaphthalene solution heated to 230°C into the impregnation tank. When the pressure in the impregnation tank rises back to a slight positive pressure of 30Pa, stop injecting the flash solution. Inject coal tar with a toluene content of 1.5%, a softening point of 80°C and a temperature of 230°C into the impregnation tank. Maintain a slight positive pressure of 30Pa in the impregnation tank by discharging the gas in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 10cm, stop injecting the liquid coal tar. Evacuate the impregnation tank for the fifth time to 99.5KPa, stop evacuating, establish a circulation of the liquid coal tar in the impregnation tank with a circulating pump, and enter the variable pressure impregnation stage. The gas is discharged or exhausted to make the pressure in the impregnation tank change between the micro-positive pressure of 100Pa-2.4MPa, and the pressure is increased or decreased once every hour. The variable pressure impregnation time is 4h (the pressure change process is: the pressure is increased from the vacuum degree of the impregnation tank of 99.5KPa to 2.4MPa in the first time (first hour), and decreased from 2.4MPa to the micro-positive pressure of 100Pa in the second hour, and increased from the micro-positive pressure of 100Pa to 2.4MPa in the third hour, and decreased from 2.4MPa to the micro-positive pressure of 100Pa in the fourth hour. During this period, the gas in the impregnation tank is cooled when the gas is discharged, and the flash solution is recovered for reuse.

[0135] After the variable pressure impregnation, the circulation of liquid coal tar was stopped, and nitrogen was filled into the impregnation tank until the pressure reached 2.0MPa, and the pressure was maintained for 4 hours. Then nitrogen was continued to be filled until the pressure in the tank reached 3.6MPa, and the pressure was maintained for 8 hours. The temperature in the tank was maintained at 230℃ during the impregnation process.

[0136] After the impregnation is completed, turn off the heating, continue to fill with nitrogen, and discharge the coal tar so that the pressure in the tank is maintained at 4.6MPa until the temperature drops to 70℃. Then stop passing nitrogen, release the tank pressure, and cool the impregnated product naturally.

[0137] Example 5.

[0138] The impregnated products obtained by Examples 1-4 and Comparative Examples 1-5 are compared, specifically:

[0139] (1) Weight gain rate of impregnated products

[0140] For graphite products with three highs (special graphite), the performance after one impregnation is far from reaching the quality target and performance index. Three-baking and two-impregnation process, or even five-baking and four-impregnation process, is often used to ensure that the quality and performance of graphite products meet the standards. Usually, the theoretical weight gain rate of a single impregnation product is above 16%. The so-called theoretical weight gain rate is the maximum weight gain rate calculated when the coal tar impregnant enters all the pores or gaps inside the graphite product.

[0141] The impregnated products obtained in Examples 1-4 and Comparative Examples 1-5 were weighed to determine the weight gain rate of the impregnated products. The results are shown in Table 1.

[0142] Table 1 Weight gain rate of impregnated products of examples and comparative examples

[0143]

[0144] Table 1 is a table of weight gain rates of the impregnated products of the embodiments and comparative examples. It can be seen from Table 1 that, when the method of the present invention is used for impregnation: (1) the weight gain rate of the impregnated product is stable at more than 16.8%, and the weight gain rate of the impregnated product is increased by 5-11.8% compared with the traditional method. (2) After being treated by the technical solution of the present invention, the theoretical weight gain rate of the impregnated product is increased from more than 16% and accurately to more than 16.8%.

[0145] (2) Weight gain of samples in the examples and comparative examples

[0146] The existing impregnation process is prone to poor impregnation uniformity. In order to illustrate the unevenness caused by impregnation, an experiment is set up, the method is as follows: in Examples 1-4 and Comparative Examples 1-5, samples are added, specifically: a special graphite product of the same material as Example 1 is used to make a sample, the sample is a cylinder with a diameter of 60mm and a height of 60mm; two identical samples are coaxial up and down, with a center distance of 96cm (the upper circular surface of the upper sample is in the same plane as the upper surface of the graphite product, and the bottom circular surface of the lower sample is in the same plane as the bottom surface of the graphite product) are placed on a bracket, and placed in an impregnation tank together with the graphite product, and the impregnation operation is carried out together. The remaining operating steps are the same as those of Examples 1-4 and Comparative Examples 1-5.

[0147] All samples obtained from Examples 1-4 and Comparative Examples 1-5 in this experiment were weighed and their weight gain rates were measured. The results are shown in Table 2.

[0148] Table 2 Weight gain rate of samples of the embodiments and comparative examples

[0149]

[0150]

[0151] Table 2 is a table of weight gain rates of samples of the embodiment and the comparative example. It can be seen from Table 2 that (1) when the method of the present invention is used for impregnation, the weight gain rates of the upper sample and the lower sample are unchanged and the same; (2) when the traditional method is used for impregnation, the weight gain rate of the upper sample is high and the weight gain rate of the lower sample is low, and the weight gain rate of the upper sample and the lower sample differ by 0.2-0.4%. This shows that the technical solution of the present invention solves the problem of poor impregnation uniformity.

[0152] Example 6.

[0153] This embodiment belongs to the third dipping operation of the four-baking and three-dipping process, and the specific operation steps are as follows:

[0154] S1 Preheating: Load the special graphite product on the bracket and place it in the impregnation tank for preheating, and preheat it to 150°C at a heating rate of 40°C / h.

[0155] S2 Gas replacement: When the temperature in the impregnation tank is preheated to 150℃, the impregnation tank is evacuated for the first time to a vacuum degree of 200Pa, and argon is filled in to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slight positive pressure of 50Pa, the argon replacement is stopped, and the impregnation tank is evacuated for the second time to a vacuum degree of 100Pa. When the temperature in the impregnation tank rises to 220℃, the constant temperature and pressure are maintained for 1h.

[0156] S3 cleaning and drying: inject 75℃ deionized water into the impregnation tank. When the deionized water submerges the graphite product and the liquid level is 4cm above the top, stop injecting deionized water. Fill the impregnation tank with argon gas and pressurize it to 2.0MPa. The soaking time is 4h. Then, drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 400Pa and maintain constant pressure operation.

[0157] S4 channel unblocking: heat the temperature in the impregnation tank to 150℃ at a heating rate of 30℃ / h, evacuate the tank for the third time to a vacuum degree of 200Pa, maintain the pressure in the impregnation tank unchanged, and wait until the temperature in the impregnation tank rises to the standby temperature of 160℃, and perform constant temperature and pressure drying for 6h.

[0158] S5 impregnation-flash evaporation: inject xylene heated to 155°C into the impregnation tank. When the pressure in the impregnation tank returns to a slightly positive pressure of 40Pa, stop injecting the flash solution.

[0159] S6 impregnation - variable pressure impregnation: After heating the coal tar with a softening point of 60℃ to 155℃, inject it into the impregnation tank, and maintain the micro-positive pressure of 40Pa in the impregnation tank by discharging the gas in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 6cm, stop injecting the liquid coal tar, evacuate the impregnation tank for the fourth time, and evacuate to a vacuum degree of 99.5KPa, stop evacuating, and use a circulating pump to establish the circulation of the liquid coal tar in the impregnation tank, and enter the variable pressure impregnation stage. By filling argon or discharging gas, the pressure in the impregnation tank changes between micro-positive pressures of 100Pa-2.4MPa, and the pressure is changed once every hour. The variable pressure impregnation time is 4h. During this period, the gas in the impregnation tank is cooled when the gas is discharged, and the flash solution is recovered for reuse.

[0160] The pressure change process is as follows: the first time (first hour) the pressure change is from 99.5KPa in the immersion tank to 2.0MPa, in the second hour it is reduced from 2.0MPa to a slight positive pressure of 1000Pa, in the third hour it is increased from a slight positive pressure of 1000Pa to 2.4MPa, and in the fourth hour it is reduced from 2.4MPa to a slight positive pressure of 100Pa.

[0161] S7 impregnation - static impregnation: After the variable pressure impregnation is completed, the circulation of liquid coal tar is stopped, argon gas is filled into the impregnation tank and pressurized to 3.5MPa, and the temperature and pressure are maintained at a constant level for 10 hours.

[0162] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 90°C, fill the impregnation tank with argon gas and pressurize it to 4.2MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 35°C, release the pressure to obtain the impregnated product.

[0163] Example 7.

[0164] This embodiment belongs to the second dipping operation of the three-baking and two-dipping process, and the specific operation steps are as follows:

[0165] S1 Preheating: Load the special graphite product on the bracket and place it in the impregnation tank for preheating, and preheat it to 170°C at a heating rate of 50°C / h.

[0166] S2 Gas replacement: When the temperature in the impregnation tank is preheated to 170℃, the impregnation tank is evacuated for the first time to a vacuum degree of 250Pa, and argon is filled in to replace the gas in the impregnation tank. When the pressure in the impregnation tank rises back to a slight positive pressure of 100Pa, the argon replacement is stopped, and the impregnation tank is evacuated for the second time to a vacuum degree of 200Pa. When the temperature in the impregnation tank rises to 240℃, the constant temperature and pressure are maintained for 0.8h.

[0167] S3 cleaning and drying: inject 70℃ deionized water into the impregnation tank. When the deionized water submerges the graphite product and the liquid level is 3cm above the top, stop injecting deionized water. Fill the impregnation tank with argon gas and pressurize it to 2.1MPa. The soaking time is 5h. Then, drain the deionized water. When draining, reduce the pressure to a slight positive pressure of 500Pa and maintain constant pressure operation.

[0168] S4 channel dredging: heat the temperature in the impregnation tank to 170℃ at a heating rate of 50℃ / h, evacuate the tank for the third time to a vacuum degree of 300Pa, maintain the pressure in the impregnation tank unchanged, and wait until the temperature in the impregnation tank rises to the standby temperature of 300℃, and perform constant temperature and pressure drying for 6h.

[0169] S5 impregnation-flash evaporation: Inject the flash solution heated to 295°C (the fraction of coal tar impregnating agent cut at room temperature -280°C) into the impregnation tank. When the pressure in the impregnation tank returns to a slightly positive pressure of 50Pa, stop injecting the flash solution.

[0170] S6 impregnation - variable pressure impregnation: After heating the coal tar with a softening point of 160℃ to 295℃, inject it into the impregnation tank, and maintain the micro-positive pressure of 50Pa in the impregnation tank by discharging the gas in the impregnation tank. When the liquid coal tar submerges the top of the graphite product by 6cm, stop injecting the liquid coal tar, evacuate the impregnation tank for the fourth time, and evacuate to a vacuum degree of 99.2KPa, stop evacuating, and use a circulating pump to establish the circulation of the liquid coal tar in the impregnation tank, and enter the variable pressure impregnation stage. By filling argon or discharging gas, the pressure in the impregnation tank changes between micro-positive pressures of 100Pa-2.4MPa, and the pressure is changed once every hour. The variable pressure impregnation time is 7h. During this period, the gas in the impregnation tank is cooled when the gas is discharged, and the flash solution is recovered for reuse.

[0171] The pressure change process is as follows: the first time (first hour) the pressure change is from the vacuum degree of 99.2KPa in the impregnation tank to 2.4MPa, in the second hour it drops from 2.4MPa to a slight positive pressure of 500Pa, in the third hour it increases from a slight positive pressure of 500Pa to 2.4MPa, in the fourth hour it drops from 2.4MPa to a slight positive pressure of 1.0MPa, in the fifth hour it increases from a slight positive pressure of 1.0M Pa to 2.4MPa, in the sixth hour it drops from 2.4MPa to a slight positive pressure of 100Pa, and in the seventh hour it increases from a slight positive pressure of 100Pa to 2.4MPa.

[0172] S7 impregnation - static impregnation: After the variable pressure impregnation is completed, the circulation of liquid coal tar is stopped, argon is filled into the impregnation tank and pressurized to 3.6MPa, and the temperature and pressure are maintained at a constant level for 11 hours.

[0173] S8 Cooling: Turn off the heating and cool. When the temperature in the impregnation tank drops to 180°C, fill the impregnation tank with argon gas and pressurize it to 4.4MPa. Start to discharge and recover the liquid coal tar. When the temperature in the impregnation tank cools to 125°C, release the pressure to obtain the impregnated product.

[0174] The above is only a preferred embodiment of the embodiment of the present invention, and does not impose any form of limitation on the embodiment of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiment based on the technical essence of the embodiment of the present invention are still within the scope of the technical solution of the embodiment of the present invention.

Claims

1. A method for impregnating special graphite, characterized in that: The following steps are involved: S1 preheating: Place the special graphite in an impregnation tank for preheating; S2 Gas replacement: After preheating to 140-180°C, the impregnation tank is vacuumed for the first time to 50-300Pa, and then the protective gas is filled to replace the gas in the impregnation tank to 50-300Pa. The impregnation tank is vacuumed for the second time to 50-300Pa, and the pressure is maintained at 180-300°C for 0.5-1h; S3 cleaning: inject deionized water at 60-80°C into the impregnation tank until the special graphite is submerged, fill with protective gas to 1.8-2.4MPa, soak for 4-6h, then drain the deionized water and reduce the pressure to 300-500Pa; S4 channel dredging: after heating to 140-180°C, the impregnation tank is evacuated for the third time to 50-300Pa, and then maintained at a constant temperature and pressure of 160-300°C for 6-10h; S5: adding a flash solution at 155-295° C. into the impregnation tank until the pressure of the impregnation tank returns to 10-50 Pa; S6: Add an impregnating agent at 155-295° C. to the impregnation tank until the special graphite is submerged, evacuate the tank for the fourth time to 98.6-99.8 KPa, and use a circulating pump to establish a circulation of the liquid impregnating agent to perform variable pressure impregnation treatment, changing the pressure once every hour for 4-8 hours; S7: After the variable pressure impregnation treatment is completed, the circulation of the liquid impregnating agent is stopped, and the impregnation tank is filled with protective gas to 3.0-3.9 MPa, and the temperature and pressure are maintained for 6-12 hours; S8 Cooling: When the temperature in the impregnation tank is cooled to be 20-40°C higher than the softening point of the impregnating agent, the protective gas is filled into the impregnation tank to 4.0-5.0MPa, and after the impregnating agent is discharged and recovered, the pressure is released when the temperature in the impregnation tank is 25-50°C lower than the softening point of the impregnating agent.

2. The impregnation method according to claim 1, characterized in that The protective gas is nitrogen or argon.

3. The impregnation method according to claim 2, characterized in that The protective gas is nitrogen.

4. The impregnation method according to claim 1, characterized in that In the step S1, the heating rate is 30-60°C / h; In the step S3, the injection height of the deionized water is at least 3 cm above the top of the special graphite; In the step S6, the impregnating agent is injected at a height of 5-10 cm above the top of the special graphite.

5. The impregnation method according to claim 1, characterized in that In the step S6, while the impregnating agent is injected, the gas in the impregnation tank is discharged to maintain the pressure at 10-50Pa; The pressure-changing impregnation treatment is carried out by filling in protective gas or exhausting gas, and the pressure is 100Pa-2.4MPa.

6. The impregnation method according to claim 1, characterized in that The temperature difference between the temperature of the impregnation solution and the flash solution when they are added and the standby impregnation temperature does not exceed 5°C.

7. The impregnation method according to claim 1, characterized in that The flash solution is one of toluene, xylene, a fraction of a distilled impregnating agent cut at room temperature -280°C, and methylnaphthalene; The impregnating agent is coal tar pitch with a softening point of 60-160°C.

8. The impregnation method according to claim 7, characterized in that The flash solution is methylnaphthalene; The impregnating agent is coal tar pitch with a softening point of 80-90°C.

9. The impregnation method according to claim 8, characterized in that The preparation temperature is 205-245°C; The addition temperature of the flash solution is 200-240°C; The impregnating agent is added at a temperature of 200-240°C.

10. A special graphite, characterized in that: The product is obtained by impregnation using the impregnation method described in any one of claims 1 to 9.

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