Raw materials: What are the raw materials used for carbon production?

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

Calcination: What is calcination? Which raw materials need to be calcined?

The process of high-temperature (1200-1500°C) heat treatment of carbonaceous raw materials in isolation from air 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 various carbonaceous raw materials.

Both anthracite and petroleum coke contain a certain amount of volatile matter and require calcination. The coking temperature of pitch coke and metallurgical coke is relatively high (above 1000°C), which is equivalent to the temperature of the calcining furnace in the carbon factory. They no longer need to be calcined, and only need to dry the water. However, if pitch coke and petroleum coke are mixed before calcination, they should be sent to the calciner together with petroleum coke for calcination. Natural graphite and carbon black do not require calcination.

Pressing: What is the principle of extrusion molding?

The essence of the extrusion process is that after the paste passes through a die nozzle of a certain shape under pressure, it is compacted and plastically deformed to become a blank with a certain shape and size. The extrusion molding process is mainly the plastic deformation process of the paste.

The paste extrusion process is carried out in the material chamber (or paste cylinder) and the arc-shaped nozzle. The hot paste loaded into the material chamber is pushed by the rear main plunger. The gas in the paste is forced to be continuously eliminated, the paste is continuously dense, and the paste moves forward at the same time. When the paste moves in the cylindrical part of the material chamber, the paste can be regarded as a stable flow, and each particle material layer basically moves in parallel. When the paste enters the extrusion nozzle with arc deformation, the paste close to the mouth wall encounters greater frictional resistance when advancing, the material layer begins to bend, and different advancement speeds are generated inside the paste, and the inner layer of paste The material is advanced ahead of time, resulting in uneven density of the product along the radial direction, resulting in internal stress caused by different flow rates of the inner and outer layers in the extrusion block. Finally, the paste enters the linear deformation part and is extruded.

Roasting: What is roasting? What is the purpose of roasting?

Roasting is a heat treatment process in which the pressed raw products are heated at a certain heating rate in a protective medium in a heating furnace under the condition of isolating air.

The purpose of roasting is to: (1) Eliminate volatile matter. Products using coal pitch as a binder generally discharge about 10% of volatile matter after roasting. Therefore, the roasting yield is generally below 90%.

(2) The binder coking raw products are roasted according to certain process conditions to coke the binder and form a coke network between the aggregate particles to firmly connect all aggregates of different particle sizes. At the same time, the products have certain physical and chemical properties. Under the same conditions, the higher the coking rate, the better the quality. Generally, the coking residual rate of medium-temperature asphalt is about 50%.

(3) Fixed geometric form? During the roasting process, the raw product softens and the binder migrates. As the temperature increases, a coking network is formed, making the product rigid. Therefore, its shape does not change as the temperature increases.

(4) Reduce resistivity? During the roasting process, due to the elimination of volatile matter, the asphalt is coked to form a coke grid, and the asphalt decomposes and polymerizes to form a large hexagonal carbon ring planar network. The resistivity dropped significantly. The resistivity of the raw product is about 10000×10-6Ω·m, and after roasting it is reduced to 40--50×10-6Ω·m, which is called a good conductor

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

Impregnation: Why should carbon products be impregnated?

The porosity of the raw product after compression molding is very low. However, after the raw product is roasted, part of the coal pitch decomposes into gas and escapes during the roasting process, and the other part is coked into pitch coke. The volume of the generated pitch coke is much smaller than the original volume occupied by coal pitch. Although it shrinks slightly during the roasting process, many irregular tiny pores with different pore sizes are still formed inside the product. For example, the total porosity of graphitized products is generally 25-32%, and the total porosity of carbon products is generally 16-25%. The presence of a large number of pores will inevitably have a certain impact on the physical and chemical properties of the product. Generally speaking, as the porosity of graphitized products increases, its volume density decreases, its resistivity increases, its mechanical strength decreases, its oxidation rate accelerates at a certain temperature, its corrosion resistance deteriorates, and gases and liquids are more likely to penetrate.

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

Graphitization: What is graphitization? What is the purpose of graphitization?

Graphitization is to place the baked product in a protective medium in a graphitization furnace and heat it to a high temperature, so that the hexagonal carbon atom plane grid changes from disordered overlapping in two-dimensional space to ordered overlapping in three-dimensional space. And it has a high-temperature heat treatment process with graphite structure.

Its 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 anti-wear properties of the product. (4) Eliminate impurities and improve product strength.

Mechanical processing: Why do carbon products need to be mechanically processed?

(1) The pressed carbon products need to have a certain size and shape for shaping. They will be deformed and damaged to varying degrees during the roasting and graphitization process, and their surfaces will also be bonded. Some fillers cannot be used without mechanical processing, so the product must be shaped and processed into the specified geometric shape. (2) The use needs to be processed according to the user's requirements. If graphite electrodes for electric furnace steelmaking need to be connected for use, threaded holes must be machined at both ends of the product, and then the two electrodes must be connected with special threaded joints. (3) Technical needs: Some products must be processed into special shapes and specifications according to the technical needs of users, and even require lower surface roughness.

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