Raw material: what are the raw materials used in carbon production?
In the production of carbon, the raw materials usually used can be divided into solid carbon raw materials, binder and impregnant. Solid carbon raw materials include petroleum coke, bituminous coke, metallurgical coke, anthracite, natural graphite and graphite crushing, etc. Binders and impregnating agents include coal bitumen, coal tar, anthracene oil and synthetic resins. In addition, some auxiliary materials are used in production, such as quartz sand, metallurgical coke particles and coke powder. Some special carbon and graphite products (such as carbon fiber, activated carbon, pyrolytic carbon and pyrolytic graphite, glass carbon) are produced by other special raw materials.
Calcination: what is calcination? Which raw materials need to be calcined?
Carbon feedstock heat treatment at high temperature (1200-1500°C) is called calcination. Calcination is the first heat treatment process of carbon production. Calcination changes the structure and physicochemical properties of various carbon materials.
Both anthracite and petroleum coke contain a certain amount of volatile matter and need to be calcined. Asphalt coke and metallurgical coke have higher coking temperature (more than 1000°C), which is equivalent to the temperature of calciner in carbon plant. However, if asphalt coke and petroleum coke are mixed before calcination, they should be sent to calciner together with petroleum coke. Natural graphite and carbon black do not require calcination.
Pressure: what is the principle of extrusion?
The essence of extrusion process is to make the paste pass through a certain shape of die mouth under pressure, and be compacted and plastic deformed to become a hair embryo with a certain shape and size. The extrusion process is mainly the plastic deformation process of paste.
Paste extrusion process is carried out in the material chamber (or paste cylinder) and arc nozzle. The hot paste in the feeding chamber is pushed by the rear main plunger. Force the gas in the paste to be removed, the paste is dense, and the paste moves forward. When the paste moves in the cylinder part of the material chamber, the paste can be regarded as a stable flow, and each granular layer is basically parallel moving. When the paste enters the extrusion nozzle with circular arc deformation, the paste close to the mouth wall is subjected to greater friction resistance, the material layer begins to bend, the inner paste produces different propulsion speed, and the inner paste advances ahead. The internal stress caused by the different velocity of inner and outer layer is produced in the extrusion block. Finally, the paste enters the straight deformation part and is extruded.
Roasting: what is roasting? What is the purpose of roasting?
Roasting is the heat treatment process of pressed raw products in the protective medium of heating furnace, under the condition of isolating air, according to a certain heating rate.
The purpose of roasting is:
(1) Products that exclude volatile matter and use coal pitch as binder are generally discharged about 10% of volatile matter after roasting. Therefore, the roasting yield is generally below 90%.
Binder coking raw products are roasted according to certain technological conditions, so that the binder coking, forming a coke network between aggregate particles, all different particle sizes of aggregate firmly linked together, so that the product has certain physical and chemical properties. Under the same conditions, the higher the coking rate, the better the quality. The coke residue rate of medium temperature asphalt is about 50%.
(3) Fixed geometry Raw products in the roasting process, softening, binder migration phenomenon. With the increase of temperature, the coking network is formed, which makes the products rigid. Therefore, the temperature increases again, its shape also does not change.
(4) Reduction of resistivity In the roasting process, due to the elimination of volatile matter, the coking of asphalt forms coke mesh, the decomposition and polymerization of asphalt, and the formation of large hexagonal carbon ring plane network, the resistivity decreases greatly. The resistivity of raw products is about 10000×10-6Ω·m, and then it is reduced to 40-50×10-6Ω·m, called good conductor
(5) Further contraction of volume After roasting, the diameter of the product shrinks about 1%, the length shrinks about 2%, and the volume shrinks to 2-3%.
Impregnation: why impregnate carbon products?
The porosity of raw products after pressing is very low. However, after roasting, the raw products are decomposed into gas escape and the other part is coking into asphalt coke. The volume of asphalt coke produced is much smaller than that of coal asphalt. Although it shrinks slightly during the roasting process, it still forms many irregular small pores with different pore sizes inside the product. For example, the total porosity of graphitic products is 25-32 and that of carbon products is 16-25. Because the existence of a large number of pores will inevitably have a certain impact on the physical and chemical properties of the product. Generally speaking, the porosity of graphitic products increases, its bulk density decreases, resistivity rises, mechanical strength decreases, oxidation speed increases at a certain temperature, corrosion resistance also deteriorates, gas and liquid permeate more easily.
Impregnation is a process that reduces product porosity, increases density, increases compressive strength, reduces resistivity of finished products, and changes physical and chemical properties of products.
Graphitization: what is graphitization? What is the purpose of graphitization?
graphitization is to heat the roasted products in the protective medium of the graphitic furnace to high temperature, so that the hexagonal carbon atom plane mesh can change from the disordered overlap in two-dimensional space to the ordered overlap in three-dimensional space, and the high temperature heat treatment process with graphite structure.
Its objectives are:
(1) Improving the thermal and electrical conductivity of the product.
(2) Improving the heat-resistant impact and chemical stability of the product.
(3) Improve lubricity and abrasion resistance of products.
Remove impurities and improve product strength.
Machining: why should carbon products be machined?
(1) Plastic needs
Compressed carbon products with a certain size and shape have different degrees of deformation and damage during roasting and graphitization, and at the same time, some fillers are bonded on the surface, which can not be used if they are not machined, so the products must be shaped and processed into specified geometry.
(2) Need for use
According to the user's use requirements for processing. If graphite electrodes for electric furnace steelmaking need to be connected, threaded holes must be made at both ends of the product, and then the two electrodes are connected with special threaded joints.
(3) Process requirements
Some products should be processed into special shapes and specifications according to the process needs of users, and even require lower surface roughness.
