阅读说明：本技术 一种φ700mm超高功率石墨电极的制备工艺 (Preparation process of phi 700mm ultrahigh-power graphite electrode ) 是由 李骏 刘雁伟 范志利 符凯凯 于 2020-10-21 设计创作，主要内容包括：一种φ700mm超高功率石墨电极的制备工艺,属于石墨电极制备工艺技术领域,本发明主要解决现有超高功率石墨电极石墨电极抗折强度低、弹性模量高、客户使用效果不佳等技术问题。本发明的技术方案为：一种φ700mm超高功率石墨电极的制备工艺,包括以下工艺步骤：1)配料；2)混捏制糊；3)挤压成型；4)一次焙烧；5)浸渍；6)二次焙烧；7)石墨化处理；8)机加工。本发明具有工艺过程简单易操作、生产效率高、所制得的石墨电极性能高等优点。(The invention discloses a preparation process of a phi 700mm ultrahigh-power graphite electrode, belongs to the technical field of graphite electrode preparation processes, and mainly solves the technical problems of low breaking strength, high elastic modulus, poor customer use effect and the like of the conventional ultrahigh-power graphite electrode. The technical scheme of the invention is as follows: a preparation process of a phi 700mm ultrahigh power graphite electrode comprises the following process steps: 1) preparing materials; 2) kneading to prepare paste; 3) extrusion molding; 4) primary roasting; 5) dipping; 6) secondary roasting; 7) carrying out graphitization treatment; 8) and (6) machining. The invention has the advantages of simple and easy operation of the process, high production efficiency, high performance of the prepared graphite electrode and the like.)

1. A preparation process of a phi 700mm ultrahigh power graphite electrode is characterized by comprising the following steps: the method comprises the following process steps:

1) preparing materials: selecting 16 parts by weight of domestic Jingyang needle coke with the grain diameter of 10-20mm, 12 parts by weight of domestic Jingyang needle coke with the grain diameter of 4-10mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 2-4mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 0-2mm, 3 parts by weight of graphite fragments with the grain diameter of 2-4mm, 6 parts by weight of graphite fragments with the grain diameter of 0.5-2mm, 41 parts by weight of calcined coke powder and 0.5 part by weight of Fe₂O₃As an aggregate;

2) kneading and making paste: adding the aggregate into a kneading pot with the temperature of 178 ℃, dry-mixing for 50 minutes at the speed of 9r/min by a stirring knife until the temperature of the dry material reaches 140 ℃, and then mixing the aggregate: 77.5% of binder: 22.5 percent of binder is added into the kneading pot, a stirring knife is used for wet mixing for 20 minutes at the speed of 9r/0min, stearic acid which is 0.15 percent of the total weight of the materials is added into the kneading pot and then is continuously wet mixed, paste is produced after 15 minutes, and the final paste production temperature reaches 170 ℃; after paste is discharged, the paste material is put into a material airing pot with the pot temperature of 35 ℃ and the stirring knife rotating speed of 9r/min for airing for 23 minutes until the paste material is cooled to 131 ℃;

3) extrusion molding: conveying the aired paste material in the step 2) to a material chamber of a 41MN horizontal extruder by using a belt blanking machine, wherein each pot is used for 12 minutes; the temperature of a material chamber of the press is kept at 138 ℃, the temperature of an initial deformation section is kept at 165 ℃, the temperature of a nozzle is kept at 178 ℃, and the temperature of a nozzle is kept at 170 ℃; after the first pot is fed, vacuumizing a material chamber to remove smoke of the paste, tamping the paste by using a press when the vacuum degree reaches 50Mbar, keeping the tamping pressure at 260Mbar for 2 minutes, continuously filling the dried paste in the second pot, vacuumizing the material chamber after the feeding is finished, prepressing when the vacuum degree reaches 50Mbar, and keeping the prepressing pressure at 300Mbar for 5 minutes; after the pre-pressing is finished, the nozzle baffle can be put down to start the extrusion operation, 3 pieces of materials can be extruded in each cylinder, and the extrusion pressure is respectively 68Mbar, 66Mbar and 65 Mbar; rolling into a cooling water tank at 32 ℃ after each extrusion is finished, cooling for 8 hours, and then fishing out;

4) primary roasting: standing the extrusion-molded product in the open air for 2 days, performing initial inspection, standing for 1 day, performing recheck, loading the extrusion-molded product into a ring type roasting furnace with a cover for primary roasting after the extrusion-molded product is qualified, wherein a temperature rise curve is 599 hours, and the temperature rises from room temperature to 350 ℃ for 1 hour; the temperature is raised to 0.7 to 1.1 ℃ per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, and the temperature is raised to 1.2 to 1.6 ℃ per hour at the temperature of 550 ℃ and 1000 ℃ for 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling for 168 hours to prepare a primary roasted product, and inspecting the primary roasted product;

5) dipping: placing the qualified primary roasting piece into a 390 ℃ preheating tank for constant-temperature preheating for 8 hours, then placing the primary roasting piece into an impregnation tank, firstly vacuumizing to-90 kpa and maintaining the vacuum for 90 minutes, then injecting impregnated asphalt to pressurize to 1.83Mpa, maintaining the pressure for 3 hours, finally extracting the asphalt, injecting cooling water for cooling, and taking out of the tank to obtain an impregnated product;

6) secondary roasting: placing the dipped article into an open roasting furnace for secondary roasting, wherein a temperature rise curve is 599 hours and is raised from room temperature to 350 ℃ within 1 hour; the temperature is raised to 0.7 to 1.1 ℃ per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, and the temperature is raised to 1.2 to 1.6 ℃ per hour at the temperature of 550 ℃ and 1000 ℃ for 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling for 168 hours to prepare a secondary roasted product, and inspecting the secondary roasted product;

7) graphitization treatment: placing the qualified secondary roasting piece into an internal heat serial type graphitization furnace for graphitization treatment, wherein at the stage of room temperature-1200 ℃, the temperature rise speed is controlled at 230 ℃/h, and the graphitization treatment is carried out for 5 hours; then in the stage of 1200-1900 ℃, the temperature rise speed is controlled at 110 ℃/h and 100-1900 ℃, and graphitization treatment is carried out for 6 hours; finally, in the stage of 1900-3000 ℃, the temperature rise speed is controlled at 300-310 ℃/h, and graphitization treatment is carried out for 3.5 hours; after power transmission is finished, power is cut off, natural cooling is carried out for 7 days, then the graphite is discharged, and sampling inspection is carried out on the graphite treatment piece after the graphite is discharged;

8) and machining to obtain the phi 700mm ultrahigh-power graphite electrode.

2. The preparation process of the phi 700mm ultrahigh-power graphite electrode according to claim 1, characterized in that: the purity of the domestic Jingyang needle coke with the particle size of 10-20mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 4-10mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 2-4mm is more than or equal to 70%, the purity of the graphite fragments with the particle size of 2-4mm is more than or equal to 70%, the particle size of the calcined coke powder is less than 0.075mm, and the purity is 63 +/-2%.

3. The preparation process of the phi 700mm ultrahigh-power graphite electrode according to claim 1, characterized in that: the binder in the step 2) is medium-temperature modified asphalt.

Technical Field

The invention belongs to the technical field of graphite electrode preparation processes, and particularly relates to a preparation process of a phi 700mm ultrahigh-power graphite electrode.

Background

With the development of the power industry, the continuous improvement of process equipment and the improvement of smelting technology, electric arc furnaces are widely applied, the production capacity and the scale are larger and larger, the proportion and the quantity of large electric arc furnaces for steelmaking are greatly developed in the coming years, and the production capacity of the electric arc furnaces depends on the furnace capacity and the unit input power. At the same unit power level, the capacity increases with increasing capacity.

Compared with an electric arc furnace with common power, the electric arc furnace with high capacity and ultrahigh power has higher production efficiency and relatively lower comprehensive cost. When the power of the electric arc furnace is increased, the electric arc furnace also puts higher requirements on the maximum allowable current of the graphite electrode for the electric arc furnace, and the maximum allowable current of the graphite electrode is directly dependent on the diameter of the graphite electrode. Therefore, if the requirement of increasing the power is to be met, a large-size ultrahigh-power graphite electrode is needed, and the requirements of high flexural strength, low elastic modulus, low resistivity, moderate volume density, low thermal expansion coefficient, low ash content and the like are needed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a preparation process of a phi 700mm ultrahigh-power graphite electrode, and solves the technical problems of low rupture strength, high elastic modulus, poor using effect of customers and the like of the conventional ultrahigh-power graphite electrode.

In order to solve the problems, the technical scheme of the invention is as follows: a preparation process of a phi 700mm ultrahigh power graphite electrode comprises the following process steps:

1) preparing materials: selecting 16 parts by weight of domestic Jingyang needle coke with the grain diameter of 10-20mm, 12 parts by weight of domestic Jingyang needle coke with the grain diameter of 4-10mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 2-4mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 0-2mm, 3 parts by weight of graphite fragments with the grain diameter of 2-4mm, 6 parts by weight of graphite fragments with the grain diameter of 0.5-2mm, 41 parts by weight of calcined coke powder and 0.5 part by weight of Fe₂O₃As an aggregate;

2) kneading and making paste: adding the aggregate into a kneading pot with the temperature of 178 ℃, dry-mixing for 50 minutes at the speed of 9r/min by a stirring knife until the temperature of the dry material reaches 140 ℃, and then mixing the aggregate: 77.5% of binder: 22.5 percent of binder is added into the kneading pot, a stirring knife is used for wet mixing for 20 minutes at the speed of 9r/min, stearic acid which is 0.15 percent of the total weight of the materials is added into the kneading pot and then is continuously wet mixed, paste is produced after 15 minutes, and the final paste production temperature reaches 170 ℃; after paste is discharged, the paste material is put into a material airing pot with the pot temperature of 35 ℃ and the stirring knife rotating speed of 9r/min for airing for 23 minutes until the paste material is cooled to 131 ℃;

3) extrusion molding: conveying the aired paste material in the step 2) to a material chamber of a 41MN horizontal extruder by using a belt blanking machine, wherein each pot is used for 12 minutes; the temperature of a material chamber of the press is kept at 138 ℃, the temperature of an initial deformation section is kept at 165 ℃, the temperature of a nozzle is kept at 178 ℃, and the temperature of a nozzle is kept at 170 ℃; after the first pot is fed, vacuumizing a material chamber to remove smoke of the paste, tamping the paste by using a press when the vacuum degree reaches 50Mbar, keeping the tamping pressure at 260Mbar for 2 minutes, continuously filling the dried paste in the second pot, vacuumizing the material chamber after the feeding is finished, prepressing when the vacuum degree reaches 50Mbar, and keeping the prepressing pressure at 300Mbar for 5 minutes; after the pre-pressing is finished, the nozzle baffle can be put down to start the extrusion operation, 3 pieces of materials can be extruded in each cylinder, and the extrusion pressure is respectively 68Mbar, 66Mbar and 65 Mbar; rolling into a cooling water tank at 32 ℃ after each extrusion is finished, cooling for 8 hours, and then fishing out;

4) primary roasting: standing the extrusion-molded product in the open air for 2 days, performing initial inspection, standing for 1 day, performing recheck, loading the extrusion-molded product into a ring type roasting furnace with a cover for primary roasting after the extrusion-molded product is qualified, wherein a temperature rise curve is 599 hours, and the temperature rises from room temperature to 350 ℃ for 1 hour; the temperature is raised to 0.7 to 1.1 ℃ per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, and the temperature is raised to 1.2 to 1.6 ℃ per hour at the temperature of 550 ℃ and 1000 ℃ for 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling for 168 hours to prepare a primary roasted product, and inspecting the primary roasted product;

5) dipping: placing the qualified primary roasting piece into a 390 ℃ preheating tank for constant-temperature preheating for 8 hours, then placing the primary roasting piece into an impregnation tank, firstly vacuumizing to-90 kpa and maintaining the vacuum for 90 minutes, then injecting impregnated asphalt to pressurize to 1.83Mpa, maintaining the pressure for 3 hours, finally extracting the asphalt, injecting cooling water for cooling, and taking out of the tank to obtain an impregnated product;

6) secondary roasting: placing the dipped article into an open roasting furnace for secondary roasting, wherein a temperature rise curve is 599 hours and is raised from room temperature to 350 ℃ within 1 hour; the temperature is raised to 0.7 to 1.1 ℃ per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, and the temperature is raised to 1.2 to 1.6 ℃ per hour at the temperature of 550 ℃ and 1000 ℃ for 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling for 168 hours to prepare a secondary roasted product, and inspecting the secondary roasted product;

7) graphitization treatment: placing the qualified secondary roasting piece into an internal heat serial type graphitization furnace for graphitization treatment, wherein at the stage of room temperature-1200 ℃, the temperature rise speed is controlled at 230 ℃/h, and the graphitization treatment is carried out for 5 hours; then in the stage of 1200-1900 ℃, the temperature rise speed is controlled at 110 ℃/h and 100-1900 ℃, and graphitization treatment is carried out for 6 hours; finally, in the stage of 1900-3000 ℃, the temperature rise speed is controlled at 300-310 ℃/h, and graphitization treatment is carried out for 3.5 hours; after power transmission is finished, power is cut off, natural cooling is carried out for 7 days, then the graphite is discharged, and sampling inspection is carried out on the graphite treatment piece after the graphite is discharged;

8) and machining to obtain the phi 700mm ultrahigh-power graphite electrode.

Further, the purity of the domestic Jingyang needle coke with the particle size of 10-20mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 4-10mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 2-4mm is more than or equal to 70%, the purity of the graphite fragments with the particle size of 2-4mm is more than or equal to 70%, the particle size of the calcined coke powder is less than 0.075mm, and the purity is 63 +/-2%.

Further, the binder in the step 2) is medium-temperature modified asphalt.

The invention takes the domestic Jingyang needle coke, calcined petroleum coke and graphite fragments as aggregates, medium-temperature modified coal pitch with the softening point of 95-105 ℃ and the coking value of more than or equal to 58 percent as a binder, the graphite electrode is formed by kneading and extruding, and the phi 700 ultrahigh-power graphite electrode prepared by optimizing the roasting temperature-rise curve and the graphitization temperature-rise curve has lower cost and physical and chemical performance indexes superior to the national industrial standard, is used for large-scale electric arc furnace steelmaking, reduces the continuous connection times of steel plants due to the large specification of the phi 700 graphite electrode, reduces the labor amount and danger coefficient of operators, and improves the production efficiency. Compared with the prior art, the method has the advantages of simple and easy operation process, high production efficiency, high performance of the prepared graphite electrode and the like.

Detailed Description

The present invention will be described in further detail with reference to examples.

A preparation process of a phi 700mm ultrahigh power graphite electrode comprises the following process steps:

1) preparing materials: selecting 16 parts by weight of domestic Jingyang needle coke with the grain diameter of 10-20mm, 12 parts by weight of domestic Jingyang needle coke with the grain diameter of 4-10mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 2-4mm, 11 parts by weight of domestic Jingyang needle coke with the grain diameter of 0-2mm, 3 parts by weight of graphite fragments with the grain diameter of 2-4mm, 6 parts by weight of graphite fragments with the grain diameter of 0.5-2mm, 41 parts by weight of calcined coke powder and 0.5 part by weight of Fe₂O₃As an aggregate; by the burdening, the aggregate particles are packed more tightly, the packing density reaches 1.33g/ml, and the prepared graphite electrode has moderate volume density, high breaking strength, low elastic modulus and small thermal expansion coefficient. In addition, 0.5% of Fe by weight of the total dry material is added₂O₃The electrode can be effectively prevented from ballooning and cracking caused by volatilization of sulfur in the raw material during graphitization of the product.

2) Kneading and making paste: adding the aggregate into a kneading pot with the temperature of 178 ℃, dry-mixing for 50 minutes at the speed of 9r/min by a stirring knife until the temperature of the dry material reaches 140 ℃, and then mixing the aggregate: 77.5% of binder: 22.5 percent of binder is added into the kneading pot, a stirring knife is used for wet mixing for 20 minutes at the speed of 9r/min, stearic acid which is 0.15 percent of the total weight of the materials is added into the kneading pot and then is continuously wet mixed, paste is produced after 15 minutes, and the final paste production temperature reaches 170 ℃; after paste is discharged, the paste material is put into a material airing pot with the pot temperature of 35 ℃ and the stirring knife rotating speed of 9r/min for airing for 23 minutes until the paste material is cooled to 131 ℃; the proportion of the aggregate and the binder is 77.5:22.5, so that after the aggregate and the binder are kneaded, the obtained paste is basically not agglomerated or has a few agglomerated, and a formed product with higher volume density is obtained after forming.

3) Extrusion molding: conveying the aired paste material in the step 2) to a material chamber of a 41MN horizontal extruder by using a belt blanking machine, wherein each pot is used for 12 minutes; the temperature of the material chamber of the press is kept at 138 ℃, the temperature of the initial deformation section is kept at 165 ℃, and the temperature of the mouth shape is kept at 178 DEG CThe temperature of the mouth is kept at 170 ℃; after the first pot is fed, vacuumizing a material chamber to remove smoke of the paste, tamping the paste by using a press when the vacuum degree reaches 50Mbar, keeping the tamping pressure at 260Mbar for 2 minutes, continuously filling the dried paste in the second pot, vacuumizing the material chamber after the feeding is finished, prepressing when the vacuum degree reaches 50Mbar, and keeping the prepressing pressure at 300Mbar for 5 minutes; after the pre-pressing is finished, the nozzle baffle can be put down to start the extrusion operation, 3 pieces of materials can be extruded in each cylinder, and the extrusion pressure is respectively 68Mbar, 66Mbar and 65 Mbar; after each extrusion, the mixture is rolled into a cooling water tank at 32 ℃ for cooling for 8 hours and then fished out, and the volume density of the mixture is measured and is 1.76g/cm³. The paste is pre-pressed in the step, so that the yield and the physical property of the formed green body are improved.

4) Primary roasting: standing the extrusion-molded product in the open air for 2 days, performing initial inspection, standing for 1 day, performing recheck, loading the extrusion-molded product into a ring type roasting furnace with a cover for primary roasting after the extrusion-molded product is qualified, wherein a temperature rise curve is 599 hours, and the temperature rises from room temperature to 350 ℃ for 1 hour; the temperature is raised by 0.7 to 1.1 hours per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, the semicoke begins to form at the stage, and the slow temperature rise is beneficial to improving the coke yield of the roasted product, so that the volume density and the strength of the roasted product are improved, and the generation of cracks is avoided; the polycondensation reaction in the roasted product is enhanced at the temperature of 550 ℃ and 1000 ℃, the semicoke begins to be converted into coke, the organization structure is further densified, the influence of the heating rate speed on the coke yield of the roasted product is not great, so the production cost is saved by heating at a higher speed, the temperature is raised by 1.2-1.6 ℃ per hour, and the time is 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling to reduce the cracking of a roasted product, preparing a primary roasted product after 168 hours of cooling, and inspecting the primary roasted product; the test results are as follows: bulk density: 1.69-1.71g/cm³Resistivity: 34-35 mu.omega.m, yield 92.86%, length shrinkage 1.87%, and outer diameter shrinkage 1%.

5) Dipping: placing the qualified primary roasting piece into a 390 ℃ preheating tank for constant-temperature preheating for 8 hours, then placing the primary roasting piece into an impregnation tank, firstly vacuumizing to-90 kpa and maintaining the vacuum for 90 minutes, then injecting impregnated asphalt to pressurize to 1.83Mpa, maintaining the pressure for 3 hours, finally extracting the asphalt, injecting cooling water for cooling, and taking out of the tank to obtain an impregnated product; the weight gain of the obtained impregnation product is more than 12%.

6) Secondary roasting: placing the dipped product into an open roasting furnace for secondary roasting, further improving the volume density and strength of the roasted product, wherein a temperature rise curve is a 599-hour curve, and the temperature rises from room temperature to 350 ℃ within 1 hour; the temperature is raised to 0.7 to 1.1 ℃ per hour at the temperature of 350 ℃ and 600 ℃ for 278 hours, and the temperature is raised to 1.2 to 1.6 ℃ per hour at the temperature of 550 ℃ and 1000 ℃ for 320 hours; then cooling to 800 ℃ at the rate of 10 +/-5 ℃ per hour, naturally cooling for 168 hours to prepare a secondary roasted product, and inspecting the secondary roasted product; the test results are as follows: bulk density: 1.77-1.78g/cm³Resistivity: 34-35 mu.omega.m, and the actual yield is 92.86%.

The purpose of roasting is to carbonize the binder pitch, form coke grids among the aggregate particles, and firmly bond the aggregates with different granularities into a whole. When a large-size graphite electrode is prepared, the probability of cracks appearing in the subsequent heat treatment process is high, the yield is possibly low, and the invention improves the coking rate of the binder by optimizing and improving factors such as a heating curve, heating duration and the like during roasting, thereby improving the body density and strength of a roasted product.

7) Graphitization treatment: placing the qualified secondary roasting piece into an internal-heating serial-type graphitization furnace for graphitization treatment, wherein the stage of room temperature to 1200 ℃ is a repeated roasting stage, cracks can not be generated even by adopting a higher heating rate, the heating rate is controlled at 230 ℃/h, and the graphitization treatment is carried out for 5 hours; then at the 1900 ℃ stage of 1200-; finally, at the stage of 1900-; after power failure and natural cooling for 7 days after power transmission, discharging, and sampling and detecting the graphitized treated piece after dischargingTesting; the sampling test results are as follows: bulk density: 1.76-1.77g/cm³Resistivity: 4.7-4.9 μ Ω · m, coefficient of thermal expansion: 1.43X 10-6/DEG C, flexural strength of 10.94-11.02MPa, modulus of elasticity: 12.1-12.6Gpa, ash: 0.03 percent.

Compared with the traditional Acheson graphitizing furnace, the internal-heat series-connection type graphitizing furnace has the characteristics of large current density, high heating speed, low unit power consumption, high graphitization temperature and more uniform graphitization degree. In the internal heating series furnace, the roasted product is one after the end surface is flat, the roasted product is connected in series with the end top and arranged along the direction of current, the current directly passes through the electrode blank to generate Joule heat in the electrode blank, and the blank is heated more uniformly. The power transmission time is 14.5 hours, and the final temperature of the product reaches 3000 ℃. In the process of energization, since the end face contact position has a large resistance, the temperature of the contact portion rises, and cracks are likely to occur in the end face contact portion. In contrast, when charging, the flexible graphite gasket with proper thickness is embedded and pressed at the connecting part of the end parts of the two roasted products, thereby preventing the cracks from generating. In the electrifying process, because the heat dissipation of the outer surface of the electrode is large, the temperature of the outer surface is lower than that of the middle part in the same time, the resistance of the graphite electrode is inversely proportional to the temperature, and the higher the temperature is, the lower the resistance is, the more and more current is concentrated on the central part of the electrode, the larger and more radial temperature difference of the product is caused, and finally the product is cracked. In order to prevent the cracking, a shallow groove with proper diameter is bored in the center of the end face of the roasted product, so that current can only pass through the pressing surface at the outer edge of the end face of the roasted product, the temperature difference between the core part of the serial column and the excircle is reduced, the thermal stress in the electrode is reduced, and the electrode is not easy to crack.

8) Machining to obtain a phi 700mm ultrahigh power graphite electrode, wherein the actually measured resistivity is as follows: 4.5-4.7 mu omega.m.

Further, the purity of the domestic Jingyang needle coke with the particle size of 10-20mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 4-10mm is more than or equal to 80%, the purity of the domestic Jingyang needle coke with the particle size of 2-4mm is more than or equal to 70%, the purity of the graphite fragments with the particle size of 2-4mm is more than or equal to 70%, the particle size of the calcined coke powder is less than 0.075mm, and the purity is 63 +/-2%.

Further, the binder in the step 2) is medium-temperature modified asphalt.