Raw materials: What are the raw materials used for carbon production?
In carbon production, the raw materials usually used can be divided into solid carbon raw materials and binder and impregnating agent.
Solid carbon raw materials include petroleum coke, bituminous coke, metallurgical coke, anthracite, natural graphite and graphite scrap, etc.
Binder and impregnating agent include coal pitch, coal tar, anthracene oil and synthetic resin, etc.
In addition, some auxiliary materials such as quartz sand, metallurgical coke particles and coke powder are also used in production.
Some special carbon and graphite products (such as carbon fiber, activated carbon, pyrolytic carbon and pyrolytic graphite, glass carbon) are produced from other special materials.
Calcination: What is calcination?What raw materials need to be calcined?
The process of heat treatment is called calcination.
Calcination is the first heat treatment process in carbon production. Calcination causes a series of changes in the structure and physical and chemical properties of all kinds of carbonaceous raw materials.
The coke forming temperature of bituminous coke and metallurgical coke is relatively high (above 1000°C), which is equivalent to the temperature of calcining furnace in the carbon plant. It can no longer calcinate and only needs to be dried with moisture.
However, if bituminous coke and petroleum coke are used together before calcining, they shall be sent to the calciner for calcining together with petroleum coke.
Natural graphite and carbon black do not require calcination.
The extrusion molding process is mainly the plastic deformation process of the paste.
The extrusion process of the paste is carried out in the material chamber (or the paste cylinder) and the circular arc nozzle.
The hot paste in the loading chamber is driven by the rear main plunger.
The gas in the paste is forced to be continuously expelled, the paste is continuously compacted and the paste moves forward at the same time.
When the paste moves in the cylinder part of the chamber, the paste can be regarded as stable flow, and the granular layer is basically parallel.
When the paste enters the part of the extrusion nozzle with arc deformation, the paste close to the mouth wall is subject to greater friction resistance in the advance, the material begins to bend, the paste inside produces different advance speed, the inner paste advance in advance, resulting in the product along the radial density is not uniform, so in the extrusion block.
Finally, the paste enters the linear deformation part and is extruded.
Roasting is a heat treatment process in which compressed raw products are heated at a certain rate under the condition of isolating air in the protective medium in the furnace.
In the roasting process, due to the elimination of volatiles, the coking of asphalt forms a coke grid, the decomposition and polymerization of asphalt, and the formation of a large hexagonal carbon ring plane network, etc., the resistivity decreased significantly.About 10000 x 10-6 raw products resistivity Ω “m, after roasting by 40-50 x 10-6 Ω” m, called good conductors.
After roasting, the product shrinks by about 1% in diameter, 2% in length and 2-3% in volume.
However, after roasting the raw products, part of the coal asphalt is decomposed into gas and escapes, and the other part is coking into bituminous coke.
The volume of generated bituminous coke is much smaller than that of coal bitumen. Although it shrinks slightly in the roasting process, many irregular and small pores with different pore sizes still form in the product.
For example, the total porosity of graphitized products is generally up to 25-32%, and that of carbon products is generally 16-25%.
The existence of a large number of pores will inevitably affect the physical and chemical properties of the products.
Generally speaking, graphitized products with increased porosity, decreased volume density, increased resistivity, mechanical strength, at a certain temperature of the oxidation rate is accelerated, corrosion resistance is also deteriorated, gas and liquid more easily permeable.
Impregnation is a process to reduce the porosity, increase the density, increase the compressive strength, reduce the resistivity of the finished product, and change the physical and chemical properties of the product.
Its objectives are:
(1) Improve the thermal and electrical conductivity of the product.
(2) To improve the heat shock resistance and chemical stability of the product.
(3) Improve the lubricity and wear resistance of the product.
(4) Remove impurities and improve product strength.
The compressed carbon products with certain size and shape have different degrees of deformation and collision damage during roasting and graphitization. At the same time, some fillers are bonded on the surface of the compressed carbon products.
It cannot be used without mechanical processing, so the product must be shaped and processed into a specified geometric shape.
(2) The need for use
According to the user’s requirements for processing.
If the graphite electrode of electric furnace steelmaking needs to be connected, it must be made into threaded hole at both ends of the product, and then the two electrodes should be connected to use with special threaded joint.
(3) Technological requirements
Some products need to be processed into special shapes and specifications according to the technological needs of users.
Even lower surface roughness is required.
Post time: Dec-10-2020