Graphite electrodes are important high-temperature conductive materials for electric furnace steelmaking. Electrical energy is input into the electric furnace through graphite electrodes, and the high temperature generated by the electric arc between the high quality graphite electrode point and the charge is used as the heat source to melt the charge for steelmaking. Some other electric furnaces for smelting materials such as yellow phosphorus, industrial silicon and abrasives also use high quality graphite electrode as conductive materials. By taking advantage of the excellent and unique physical and chemical properties of high purity graphite electrode, they also have extensive applications in other industrial sectors.
Needle coke is a high-quality type of coke with distinct fibrous patterns, an extremely low coefficient of thermal expansion, and is prone to graphitization. When the coke blocks break, they can split into slender strip-like particles along the patterns (the aspect ratio is generally above 1.75). Under a polarizing microscope, anisotropic fibrous structures can be observed, hence the name needle coke.
The anisotropy of the physical and mechanical properties of needle coke is very significant. It has good electrical and thermal conductivity in the direction parallel to the long axis of the particles, with a relatively low coefficient of thermal expansion. During the extrusion molding process, the long axes of most particles are arranged in the extrusion direction. Therefore, needle coke is a key material for making high power graphite electrode or UHP graphite electrode. The graphite electrodes made from it have a low resistivity, a small coefficient of thermal expansion, and good thermal shock resistance.
Needle coke is divided into oil-based needle coke produced with petroleum residue oil as raw material and coal-based needle coke produced with refined coal tar pitch as raw material.
SHP graphite electrodes are the intermediate grade between UHP graphite electrodes and HP graphite electrodes