Graphite electrode raw materials are divided into solid raw materials and binders. For manufacturers, the production process of graphite electrodes of grades is the same, but the ratio of raw materials used is different. Classified according to the state of matter, it can be divided into solid raw materials (i.e., aggregate) and liquid raw materials (i.e., binder and impregnating agent). Due to the different functions and application ranges of various raw materials, the quality requirements are also other.
Petroleum coke is used as graphite electrode material.
Petroleum coke is a solid product obtained by coking various petroleum residues, petroleum pitches, or heavy oil. The main element is sulfur; the ash content is shallow, generally below 0.5%. Its appearance is a black or dark gray honeycomb structure, and the pores in the coke block are mostly oval through holes. Petroleum coke belongs to the easy graphitization category.
Compared with metallurgical coke, the microcrystals of petroleum coke are relatively neatly stacked between the sheets of the carbon network layer, and the distance between the sheets is relatively tiny. After high-temperature graphitization treatment, the carbon network layer lamellar lattice arrangement is close to that of natural graphite. So their resistivity decreases significantly, and their actual density increases accordingly. Therefore, we can manufacture graphite electrodes with lower resistivity from petroleum coke.
Classification of petroleum coke
Petroleum coke is usually classified by four methods, coking method, heat treatment temperature, sulfur content, structure, and performance. In the production of ordinary petroleum coke in the world, more than 85% of the coking process is delayed coking. Only some refineries in a few countries (such as the United States) use fluid and soft coking.
Pitch coke is a solid product obtained by coking coal tar pitch. It is a high-quality raw material with high carbon content, good mechanical strength, low ash, and low sulfur. It is a graphitizable carbon, but its graphitization properties are worse than petroleum coke’s. Pitch coke is also a low-ash raw material and has good mechanical strength.
Graphite electrode manufacturers mainly used carbon production to improve the mechanical properties of products. For example, when producing ordinary power graphite electrodes, graphite electrode manufacturers generally add 20%-25% pitch coke to the solid raw material. This increases the mechanical strength of the product.
What is needle coke, and what are its characteristics?
Needle coke has significant anisotropy from macroscopic morphology to microscopic structure. Because the particles become fine needles after crushing, we called it needle coke. Needle coke has several advantages: small thermal expansion, low porosity, low sulfur content, low ash content, low metal content, and high electrical conductivity.
Its graphitized products have good chemical stability, corrosion resistance, high thermal conductivity, and mechanical strength at low and high temperatures. Needle coke is a high-quality carbon raw material that people vigorously develop since the 1970s.
What are the uses of needle coke?
It mainly produces UHP, HP graphite electrodes, RP graphite electrodes, and unique carbon products for electric furnace steelmaking. Graphite electrode manufacturers used it to make high-quality carbon brushes, batteries, carbon raisers for steelmaking, and high-temperature refractory furnace materials. Using high-power or ultra-high-power electric furnaces for steelmaking can shorten the smelting time and save electricity. The economic benefits are undeniable.
Binders and impregnants
In production, graphite electrode manufacturers use binders and impregnants. These materials are mainly coal tar pitch and resin. Sometimes we also blend coal tar pitch with a small amount of coal tar and anthracene oil. The source of coal tar pitch is coal tar, a by-product of the coking industry. It is a product of the distillation process of coal tar. It is a black solid at room temperature, without a fixed melting point, and is a complex mixture. In addition, there are many artificial resins; we mainly use them as binders and impregnating agents in carbon production. Commonly used oil phenolic resins, epoxy resins, and furan resins are resistant to strong acids, strong alkalis, and organic solvents and have good heat resistance.