Needle coke is a kind of high-quality carbon raw material, which is divided into coal and oil series. Its surface shows obvious stripe pattern. When broken, it is mostly long needle-shaped fragments. Fibrous structure can be observed under a microscope, so it is called needle coke. Needle coke is easily graphitized at high temperatures above 2000 degrees. Graphite electrodes made from needle coke have low resistivity, high bulk density and low coefficient of thermal expansion. They are the necessary raw materials for the production of ultra-high power electrodes and high power electrodes. The price of needle coke is much higher than that of ordinary coke, which is about 5-8 times higher at present.
► Needle coke uses
Needle coke is mainly used to manufacture graphite electrodes for ultra-high power electric arc furnaces, which have high electrical conductivity, high mechanical strength, excellent thermal shock resistance and oxidation resistance.
Graphite electrodes are made of needle coke as the main material and medium-temperature pitch as the binder, which are formed through processes such as molding, roasting, impregnation and graphitization.
The performance of the graphite electrode largely depends on the performance of the aggregate needle coke, which requires that the needle coke must have high anisotropy, easy graphitization, and high purity. Otherwise, the graphite electrode is easy to break during steelmaking in the electric arc furnace, causing losses.
► National Performance Index Standard for Coal Series Needle Coke
The quality of needle coke varies greatly because of the different raw materials and processes. Generally, density, thermal expansion coefficient, strength, resistivity, ash and sulfur content are used as the main performance indicators of needle coke to measure the quality of needle coke.