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Graphite electrode material and manufacturing process-Carbo Graphite industry

Graphite electrode material and manufacturing process-Carbo Graphite industry

  • 2020-03-10 11:29:12
Graphite electrode material and manufacturing process

Graphite electrode is a kind of high-temperature graphite conductive material produced by a series of processes, such as mixing, molding, roasting, dipping, graphitization and mechanical processing, using petroleum coke and needle coke as aggregate and co

 GRAPHITE ELECTRODE material and manufacturing process

 
   GRAPHITE ELECTRODE is a kind of high-temperature graphite conductive material produced by a series of processes, such as mixing, molding, roasting, dipping, graphitization and mechanical processing, using petroleum coke and needle coke as aggregate and coal asphalt as binder.
 
   GRAPHITE ELECTRODE is an important high temperature conductive material for steelmaking in electric furnace. The electric energy is input into electric furnace through GRAPHITE ELECTRODE, and the high temperature generated by electric arc between the electric extreme part and the charge is used as the heat source to melt the charge for steelmaking.
 
   Some other smelting materials such as yellow phosphorus, industrial silicon, abrasive ore furnace also use GRAPHITE ELECTRODE as conductive material.
   GRAPHITE ELECTRODE has been widely used in other industries for its excellent and special physical and chemical properties.
 
   The materials for producing GRAPHITE ELECTRODEs are petroleum coke, needle coke and coal pitch
 
   Petroleum coke is a combustible solid product of petroleum residue and petroleum pitch after coking.
Black porous, the main element is carbon, ash content is very low, generally less than 0.5%.
Petroleum coke belongs to the category of easy graphitization carbon, petroleum coke has a wide range of USES in the chemical industry, metallurgy and other industries, is the main raw material for the production of artificial graphite products and carbon products for electrolytic aluminum.
 
   According to the heat treatment temperature, petroleum coke can be divided into two types: coke generation and calcined coke.
Most refineries in China only produce coke, and most of the calcining is done in the carbon plant.
 
   Petroleum coke can be divided into high sulfur coke (containing more than 1.5% sulfur), medium sulfur coke (containing 0.5-1.5% sulfur), and low sulfur coke (containing less than 0.5% sulfur). The production of GRAPHITE ELECTRODE and other artificial graphite products generally USES low sulfur coke.
 
   Needle coke is a kind of high-quality coke with obvious fibrous texture, especially low thermal expansion coefficient and easy graphenization. When the coke block breaks, it can split into long and thin strips according to the texture (the aspect ratio is generally above 1.75). Anisotropic fibrous structure can be observed under polarized light microscope, so it is called needle coke.
 
   The physical and mechanical anisotropy of the needle coke is very obvious. It is parallel to the direction of the long axis of the particles and has good conductivity and thermal conductivity. The thermal expansion coefficient is low.
Therefore, needle coke is a key raw material for manufacturing high-power or ultra-high-power GRAPHITE ELECTRODE, which has low resistivity, small thermal expansion coefficient and good thermal shock resistance.
 
 
   Needle coke is divided into oil series needle coke made from petroleum residue and coal series needle coke made from refined coal asphalt.
Coal tar is one of the main products of coal tar processing.
Is a mixture of various hydrocarbons, black high viscosity semi-solid or solid at room temperature, with no fixed melting point, softened by heat and then melted, with a density of 1.25-1.35g/cm3.
According to its softening point, it can be divided into three types: low temperature, medium temperature and high temperature asphalt.
The yield of medium temperature asphalt is 54-56% of that of coal tar.
The composition of coal pitch is very complex, which is related to the properties of coal tar and the content of heteroatom, and is also affected by the coking process and the processing conditions of coal tar.
There are many indexes to characterize the characteristics of coal pitch, such as asphalt softening point, toluene insoluble (TI), quinoline insoluble (QI), coking value and coal pitch rheology.
 
 
   Coal asphalt is used as binder and impregnating agent in the carbon industry.
Binder asphalt is generally used moderate softening point, high coking value, high resin medium temperature or medium temperature modified asphalt, macerate to use low softening point, low QI, good rheological properties of medium temperature asphalt.
 
 
The following figure is the process flow chart of GRAPHITE ELECTRODE production in carbon enterprises
 

Properties

UHP

HP

RP

Φ300-φ500

Φ550-φ800

Φ300-φ800

Φ300-φ800

Resistivity (uΩm max)

Electrode

4.8-5.8

  4.6-5.8

5.8-6.6

7.0-10.0

Nipple

3.5-4.0

3.5-4.0

3.5-4.0

4.0-4.5

Modulus of rupture

(Mpa)

Electrode

10.0-14.0

10.0-14.0

10.0-13.0

8.0-10.0

Nipple

20.0-24.0

22.0-26.0

20.0-23.0

19.0-22.0

Young's modulus(Gpa)

Electrode

9.0-13.0

10.0-14.0

8.0-12.0

7.0-9.3

Nipple

15.0-18.0

16.0-19.0

14.0-16.0

12.0-14.0

Bulk Density (g/cm³)min

Electrode

1.68-1.74

1.70-1.74

1.64-1.68

1.53-1.56

Nipple

1.78-1.82

1.80-1.84

1.75-1.80

1.70-1.74

CTE (100-600℃)max

Electrode

1.1-1.4

1.1-1.4

1.6-1.9

2.2-2.6

Nipple

0.9-1.2

0.9-1.2

1.1-1.4

2.0-2.5

Ash (%)

 

0.3

0.5

 

Current load and current density

Diameter(mm)

RP

HP

UHP

 

Current load(A)

Current density(A/cm3)

Current load(A)

Current density(A/cm3)

Current load(A)

Current density(A/cm3)

200

5000-6900

15-21

5500-9000

18-25

 

 

225

6100-8600

15-21

6500-10000

18-25

 

 

250

7000-10000

14-20

8000-13000

18-25

8100-12200

20-30

300

10000-13000

14-18

13000-17400

17-24

15000-22000

20-30

350

13500-18000

14-18

17400-24000

17-24

20000-30000

20-30

400

18000-23500

14-18

21000-31000

16-24

25000-40000

19-30

450

22000-27000

13-17

25000-40000

15-24

32000-45000

19-27

500

25000-32000

13-16

30000-48000

15-24

38000-55000

18-27

550

32000-40000

13-16

37000-57000

15-23

42000-66000

17-26

600

38000-47000

13-16

44000-67000

15-23

49000-76000

17-26

 

Nipple Size and Nipple Range (4 buckles)

Nominal diameter(mm)

Nipple socket average diameter(mm)

Nipple max diameter(mm)

Nipple length(mm)

Nipple socket depth(mm)

Buckle length(mm)

D4

D1

L1

L2

L3

800

428.64

431.80

635.00

323.50

319.50

750

403.24

406.40

609.60

310.80

306.80

750

403.24

406.40

584.20

298.10

294.10

700

371.49

374.65

558.80

285.40

281.10

700

371.49

374.65

457.20

234.60

230.60

650

352.44

355.60

558.80

285.40

281.40

650

352.44

355.60

457.20

234.60

230.60

600

314.34

317.50

457.20

234.60

230.60

600

314.34

317.50

355.60

183.80

179.80

550

295.29

298.45

457.20

234.60

230.60

550

295.29

298.45

355.60

183.80

179.80

500

266.72

269.88

457.20

234.60

230.60

500

266.72

269.88

355.60

183.80

179.80

450

238.14

241.30

355.60

183.80

179.80

450

238.14

241.30

304.80

158.40

154.40

400

219.09

222.25

355.60

183.80

179.80

400

219.09

222.25

304.80

158.40

154.40

350

200

04

203.20

304.80

158.40

154.40

350

200.04

203.20

254.00

133.00

129.00

300

174.64

177.80

215.90

114.00

110.00

 
Calcining: the process of producing carbonaceous raw materials by heat treatment at a high temperature to discharge the moisture and volatiles contained therein and correspondingly improve the physical and chemical properties of the raw materials is calcining.
Generally, carbonaceous raw materials are calcined with gas and its own volatiles as heat source, and the highest temperature is 1250-1350 ℃.
Calcination causes profound changes in the structure and physical and chemical properties of carbonaceous raw materials, mainly reflected in the improvement of coke's density, mechanical strength and conductivity, and the improvement of coke's chemical stability and antioxidant properties, which lays a foundation for the subsequent process.
 
 
The equipment of calcining mainly includes pot calciner, rotary kiln and electrocalciner.
Calcination quality control index is oil JiaoZhen density of not less than 2.07 g/cm3, resistivity is not more than 550 mu Ω. M, needle coke is not less than 2.12 g/cm3 density, resistivity is not more than 500 mu Ω. M.
 
 
Crushing of raw materials and ingredients
 
 
 
Before mixing, large calcined petroleum coke and needle coke should be crushed, ground and sifted.
Medium crushing is usually about 50mm of material through jaw crusher, hammer crusher, roll crusher and other crushing equipment to further crushing to the required 0.5-20mm of particle size material.
Pulverization is a process in which the carbonaceous raw materials are ground to small powdery particles with particle size below 0.15mm or 0.075mm by means of hanging roller ring mill (ramon mill), ball mill and other equipment.
Screening is a process in which materials with a wide size range after crushing are divided into several particle sizes with a narrow size range through a series of screens with uniform holes. Current electrode production usually requires 4-5 particle sizes and 1-2 powder sizes.
Batching is the production process of calculating, weighing and focusing the aggregate, powder and binder of various particle sizes according to the formula requirements.
The scientific suitability of the formulation and the stability of the operation of the ingredients are one of the most important factors affecting the quality index and performance of the product.
 
The formula shall be determined in 5 aspects:
Select the type of raw materials;
Determine the proportion of different kinds of raw materials;
(3) determine the particle size composition of solid raw materials;
Determine the amount of binder;
 
 
Determine the type and amount of additives.
 
 
Mixing and kneading: the process of kneading into a malleable paste is called mixing and kneading when the quantitative carbonaceous granule and powder are mixed evenly with the quantitative binder at a certain temperature.
Mixing and pinching process: dry mixing (20-35 min) and wet mixing (40-55 min)
 
Mixing and kneading:
(1) dry mixing to make all kinds of raw materials mix evenly, at the same time to make different particle size of the solid carbonaceous materials evenly mixed and filled, improve the density of the mixture;
(2) after the addition of coal asphalt to dry materials and asphalt mixture evenly, liquid asphalt evenly coated and infiltrated particle surface, the formation of a layer of asphalt bond layer, all materials together with each other, and then form a homogeneous plastic paste, conducive to the formation;
(3) part of the coal asphalt soaked to the carbon material inside the void, further improve the paste density and bonding.
 
Molding: the molding of carbon material refers to the plastic deformation of the mixed and pinched carbonaceous paste under the external force exerted by the molding equipment, and the final formation of green (or called raw products) with a certain shape, size, density and strength.
 
 
Molding types, equipment and products:
 
Forming Methods 
Common Equipment
    Main Products                         
  mould pressing
  • Vertical hydraulic press

Electric Carbon
  extrusion 

Horizontal hydraulic extruder

 

Screw extruder 

 

GRAPHITE ELECTRODE
Vibrating forming 
Vibration molding machine
Aluminum with Carbon 
Isostatic press
Isostatic pressure molding machine

Isotropic graphite,

anisotropic graphite


 

Extrusion operation

Cool materials: disk cool materials, cylinder cool materials, mixing pinching type cool materials, etc

Discharge volatiles, reduce to the appropriate temperature (90-120℃) to increase the bonding force, so that the paste lumpiness uniform conducive to molding 20-30 min

(2) loading: press lift baffle - 2-3 times -4-10MPa compaction

(3) preloading: pressure 20-25mpa, time 3-5min, and vacuum at the same time

(4) extrusion: pressure drop baffle -5-15MPa extrusion - shear - into the cooling tank


Extrusion technical parameters: compression ratio, press chamber and nozzle temperature, cooling temperature, prepressing pressure time, extrusion pressure, extrusion speed, cooling water temperature


Inspection of green body: volume density, appearance knock, analysis


Roasting: it is the process of carbonizing coal bitumen in the green carbon products under the protection of filling materials and in a specially designed heating furnace for high temperature heat treatment.

The bituminous coke formed after carbonization of coal pitch consolidated carbonaceous aggregate and powder particles together, and the roasted carbon products had higher mechanical strength, lower resistivity, better thermal stability and chemical stability.


Roasting is one of the main processes in the production of carbon products and an important link in the three heat treatment processes of GRAPHITE ELECTRODE production. The production cycle of roasting is long (22-30 days for the first roasting and 5-20 days for the second roasting), and the energy consumption is high.

The quality of green calcination has a certain influence on the quality of finished products and production cost.

In the process of calcination, the coal pitch inside the green is coked, and about 10% volatiles are discharged. At the same time, the volume shrinks by 2-3% and the quality loss is 8-10%.

Physico-chemical properties of the carbon billet have changed dramatically, due to the porosity increased volume density decreased from 1.70 g/cm3 is 1.60 g/cm3, resistivity, 10000 mu Ω. M or so reduced to 40-50 mu Ω. M, roasting billet mechanical strength is greatly improved.


Secondary calcining is a process in which calciners are impregnated and calcined again to carbonize bitumen in the pores of calciners.

For the production of electrodes with high volume density (all kinds except RP) and the joint blank, second baking is required.

 Main types of roaster:
Continuous operation - ring furnace (with cover, without cover), tunnel kiln
Intermittent operation -- flame kiln, car bottom type calciner, box type calciner
Roasting curve and maximum temperature:
One roasting --320, 360, 422, 480 hours, 1250 ℃
Second roasting --125, 240, 280 hours, 700-800 ℃
Inspection of calcined products: external percussion, resistivity, volume density, compressive strength, internal structure analysis
Impregnation is a process in which the carbon material is placed in a pressure vessel and the liquid impregnating agent asphalt is immersed into the electrode pores of the product under certain temperature and pressure conditions.
The purpose is to reduce the porosity, increase the volume density and mechanical strength of the products, and improve the electrical and thermal conductivity of the products.
Impregnation process and related technical parameters are: calcined billet -- surface cleaning -- preheating (260-380 ℃, 6-10 hours) -- loading into impregnation tank -- vacuuming (8-9kpa, 40-50min) -- asphalt injection (180-200 ℃) -- pressurization (1.2-1.5MPa,3-4 hours) -- asphalt return -- cooling (inside or outside the tank)

Impregnation inspection: impregnation weight gain rate G=(w2-w1)/W1×100%
Weight gain rate of one impregnation ≥14%
Weight gain rate of secondary impregnation ≥9%
Weight gain rate of three impregnations ≥5%

     Graphitization refers to the high temperature heat treatment process in which the carbon products are heated to more than 2300 ℃ in the protection medium of high temperature electric furnace, and the amorphous carbon with random layer structure is transformed into three-dimensional ordered graphite crystal structure.

The purpose and function of graphitization:
(1) improve the carbon material's electric and thermal conductivity (resistivity reduced 4-5 times, thermal conductivity increased about 10 times);
To improve the thermal vibration resistance and chemical stability of carbon materials (linear expansion coefficient reduced by 50-80%);
(3) make the carbon material lubricity and wear resistance;
(4) eliminate impurities, improve the purity of carbon material (product ash content from 0.5-0.8% to 0.3%).

Realization of graphitization process:
      The graphitization of carbon material is carried out at the high temperature of 2300-3000 ℃, so the industry can only be realized through electric heating, that is, the current directly through the heated calcined goods, this fashion into the furnace calcined goods is not only through the current generated by the high temperature of the conductor, is heated to the high temperature of the object.
At present, the widely used types are Acheson graphitization furnace and LWG furnace.
The former has large output, large temperature difference and high power consumption, while the latter has short heating time, low power consumption and uniform resistivity, but it is difficult to install the connector.
The control of graphitization process is controlled by determining the electric power curve corresponding to the temperature rise by measuring the temperature. The electrification time of acheson furnace is 50-80 hours, and that of LWG furnace is 9-15 hours.
 
     The power consumption of graphitization is large, generally ranging from 3200 to 4800KWh, and the process cost accounts for about 20-35% of the entire production cost
Inspection of graphitized products: appearance knock, resistivity test
Machining: the purpose of machining carbon graphite materials is to achieve the required size, shape, precision, etc., by cutting, to make the electrode body and joints in accordance with the requirements of use.
GRAPHITE ELECTRODE processing is divided into two independent processing processes: electrode body and joint.
The body processing includes three working procedures: boring and rough end face, cylindrical and fine end face and milling thread. The processing of conical joint can be divided into six working procedures: cutting off, plain end face, cone surface, milling thread, drilling hole, bolt and grooving.
Connection method of electrode joint: conical joint (1 "3" and 1 "4"), cylindrical joint, concave and convex (male and female)
Machining precision control: thread taper deviation, thread pitch, joint (hole) large diameter deviation, joint hole coaxiality, joint hole verticality, electrode end plane flatness, joint point deviation, etc.
Check with special ring gauge and plate gauge.


Finished electrode inspection: precision, weight, length, diameter, volume density, resistivity, preassembly fit precision, etc.

 

Client Comment

2020-06-20 16:50:00:

Place of Origin: Henan, China
Brand Name: CarboGraphite
Type: Electrode Bolt
Application: Steel Making
Length: 1800-2700mm
Grade: UHP (Ultra High Power)
Resistance (μΩ.m): 5.5
Apparent Density (g/cm³ ): 1.58 - 1.76 G/cc
Thermal Expansion: 1.5.

2020-06-12 15:10:58:

Place of Origin:
Henan, China
Model Number:
UHP 450mm
Application:
Metallurgy Industry, EAF LF
Length:
1800mm
Grade:
UHP (Ultra High Power), UHP HP RP.

2020-03-10 12:52:34:

Quality index of graphite electrode The main indexes reflecting the quality and performance of graphite electrode are: volume density db, resistivity, fl.

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