The main raw materials for graphite electrodes include petroleum coke, needle coke, and coal tar pitch. Petroleum coke and needle coke are the primary carbonaceous raw materials for electrode production, while coal tar pitch is mainly used as a binder. Petroleum coke is typically produced from heavy oil generated during petroleum refining through processes such as delayed coking. It has a high carbon content and is commonly used in the production of ordinary power and some high-power graphite electrodes. Needle coke has a low coefficient of thermal expansion, good electrical conductivity, and a high degree of graphitization, and is mainly used in high-power and ultra-high-power graphite electrodes with high performance requirements. Coal tar pitch acts as a binder during production, binding coke particles of different sizes together to give the mixture good molding properties. The quality and proportion of raw materials directly affect the bulk density, resistivity, mechanical strength, and high-temperature performance of the graphite electrode. Therefore, manufacturers typically need to select appropriate raw material combinations based on the electrode's power rating and application.
The production of graphite electrodes may also use auxiliary materials such as impregnated pitch to further improve the material's density and overall performance. During the manufacturing process, petroleum coke or needle coke typically undergoes calcination to reduce volatile matter and moisture, and improve raw material stability. The coke is then crushed, sieved, and mixed with a binder in a specified ratio, followed by kneading, molding, and calcination to produce electrode blanks. For products requiring increased density and strength, impregnation and secondary calcination are also performed to reduce internal porosity and improve material properties. Finally, the electrode blanks undergo high-temperature graphitization to make the carbon atoms more orderly arranged, resulting in better conductivity and high-temperature resistance. The specific processes and number of treatments used by different manufacturers may vary and need to be determined based on product type and technical requirements.
The selection of raw materials is a crucial factor in determining the quality of graphite electrodes. Different raw materials differ in ash content, sulfur content, volatile matter, particle structure, and thermal expansion characteristics. For example, the structural characteristics of needle coke are advantageous for manufacturing high-power electrodes with low resistivity and low coefficient of thermal expansion, while ordinary petroleum coke, after proper processing, can also meet the performance requirements of some conventional industrial electrodes. The softening point, binding capacity, and coking properties of coal tar pitch affect the molding effect of the mixture and the structural quality after calcination. High impurity content in the raw materials, or improper particle size distribution and binder ratio, can lead to increased porosity, decreased strength, or increased resistivity within the electrode. Therefore, graphite electrode production requires not only the selection of suitable raw materials but also strict control over raw material quality, batching ratios, and each processing step to ensure stable performance and a long service life for the final product.
