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Graphite Electrode Production Process

Raw materials: In the production of carbon, commonly used raw materials can be divided into two categories: solid carbon raw materials, binders and impregnating agents. Solid carbonaceous materials include petroleum coke, pitch coke, metallurgical coke, anthracite, natural graphite and graphite crushing, and binders and impregnants include coal tar pitch, coal tar, anthracene oil and synthetic resins. In addition, quartz sand, metallurgical coke powder, coke powder and other auxiliary materials are also used in the production. Other special raw materials are used to produce some special carbon and graphite products (such as carbon fiber, activated carbon, pyrolytic carbon and pyrolytic graphite, glassy carbon).

Calcination: The process of heat treating carbon raw materials at high temperature (1200≤1500 ° C) under isolated air is called calcination. Calcination is the first heat treatment process in carbon production. Calcination has caused a series of changes in the structure and physical and chemical properties of various carbon-containing raw materials.

Both anthracite and petroleum coke contain a certain amount of volatile matter and need to be calcined. The coking temperature of asphaltene coke and metallurgical coke is relatively high (above 1000 ℃), which is equivalent to the temperature of the calcination furnace of the carbonization plant. It can no longer be calcined and only needs to be dried. However, if pitch coke and petroleum coke are mixed before calcination, they should be sent to the calciner together with petroleum coke. Natural graphite and carbon black do not require calcination.
Screening:
Kneading: The purpose of kneading is to obtain a uniform paste with good plasticity, but due to changes in certain factors, the kneading quality will be greatly changed, resulting in unstable product quality. It is proved by experiments that the softening point is 80- When the hard asphalt is 90 ℃, the paste temperature should be increased to 168-174 ℃. Within this temperature range, the asphalt has the best wettability and adhesion to the dry material. The resulting paste has good plasticity and extrusion properties. The time is generally 30 minutes for dry mixing and 40 minutes for wet mixing. If the mixing time is too long, large particles will be destroyed and the original particle composition will be destroyed, so that the body density of the product will decrease, the plasticity will deteriorate, and the porosity will increase , Reduced mechanical strength

Molding: molding includes extrusion molding, vibration molding and molding. Our factory uses a 3500t extruder for molding. Before molding, the resulting paste is reduced from 168-174 ° C to 116 ° C in a cooling machine. The cooling time should not exceed 11 minutes and not less than 8 minutes. After 20 minutes of heat preservation on the heat preservation table, the well-preserved paste is loaded into the cylinder of the extruder. The pre-pressing pressure is generally not less than 25MPa for 3-5 minutes. Extruders are generally produced in batches. The production is divided into three stages: in the first stage, when the plunger head starts to pressurize, the paste particles move quickly, and the gap between the large paste particles is separated by the small paste particles Filling, the contact between particles tends to be tight. In the second stage, when the indenter continues to apply pressure, the electrode density gradually increases. After the density reaches a certain value, the pressure continues to increase and the density increases slowly. In the third stage, the pressure reaches the limit and the density tends to be uniform. Then squeeze the electrode from the nozzle

Roasting: Roasting is a heat treatment process in which the green product after molding is heated in a protective medium in a heating furnace under the condition of isolating air at a certain heating rate.

The purpose of roasting is to:

The main research results are as follows: (1) The emission of volatile matter after roasting the product using coal pitch as a binder is about 10%. Therefore, the firing yield is generally less than 90%.

The coking raw materials are calcined according to certain technological conditions, the coking agent cokes, and a coke network is formed between the aggregate particles, so that aggregates of different particle sizes are firmly connected together, and the product has certain physical and chemical properties. Under the same conditions, the higher the scorch rate, the better the product quality. The residual carbon content of medium temperature asphalt is generally about 50%.

(3) During the firing process of green products with fixed geometric forms, softening and binder migration occur. As the temperature rises, a coking network is formed, making the product rigid. Therefore, even if the temperature increases, its shape will not change.

(4) Decrease in resistivity During the roasting process, due to the elimination of volatiles, pitch coking forms a coke grid, the pitch decomposes and polymerizes, and a large hexagonal carbon ring flat network is generated. The resistivity drops significantly. The resistivity of raw products is about 10000 × 10-6Ω〃m, and it is reduced to 40--50 × 10-6Ω〃m after firing, which is called good conductor

(5) The volume shrinks further after roasting. The diameter of the product shrinks by about 1%, the length shrinks by about 2%, and the volume shrinks by 2-3%.

Impregnation: The porosity of the raw product after compression molding is very low. However, after the roasting of the raw product, part of the coal pitch is decomposed into gas during the roasting process, and the other part is coked into pitch coke. The volume of generated pitch coke is much smaller than the volume originally occupied by coal pitch. Although it shrinks slightly during the roasting process, many irregular micropores with irregular pore sizes are still formed inside the product. The existence of a large number of pores will inevitably have a certain impact on the physical and chemical properties of the product. The oxidation rate is accelerated at a certain temperature, the corrosion resistance is also deteriorated, and gases and liquids are more easily penetrated.

Impregnation is a process that reduces product porosity, increases density, increases compressive strength, reduces finished product resistivity, and changes product physical and chemical properties.

Graphitization: Graphitization is to heat the roasted product in the protective medium in the graphitization furnace to a high temperature, so that the hexagonal carbon atom planar grid changes from disordered overlap in two-dimensional space to ordered overlap in three-dimensional space, and has a graphite structure High temperature heat treatment process. the purpose is:
(1) Improve the thermal and electrical conductivity of the product.
(2) Improve the thermal shock resistance and chemical stability of the product.
(3) Improve the lubricity and abrasion resistance of the product.
(4) Eliminate impurities and increase product strength.
Mechanical processing: Why should carbon products be mechanically processed?
(1) The need for shaping, the carbon raw products with a certain size and shape after compression molding, deformed and damaged in varying degrees during the roasting and graphitization process, and at the same time, some fillers are bonded on the surface, if It can not be used without mechanical processing, so the product must be shaped and processed into a specified geometric shape.
(2) The need for use is processed according to the user's use requirements. For example, graphite electrodes for electric furnace steelmaking need to be connected and used, and threaded holes must be made at both ends of the product, and then the two electrodes are connected and used with special threaded joints.
(3) Technological needs, some products are processed into special shapes and specifications according to the technological needs of users, and even require lower surface roughness

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